NASA Conference Publication 3201 

Workshop: 

Standard Experiments in 

Engineering Materials 

Science and Tech,nology 

Proceedings of a workshop held in 

Oak Ridge, Tennessee 

November 11-13, 1992 

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3 1176 01403 4327 NASA Conference Publication 3201

National Educators'

Workshop: Update 92

Standard Experiments in

Engineering Materials

Science and Technology

Compiled by

James E. Gardner

NASA Langley Research Center

Hampton, Virginia

James A. Jacobs

Norfolk State University

Norfolk, Virginia

Douglas F. Craig

Oak Ridge National Laboratory

Oak Ridge, Tennessee

Proceedings of a workshop sponsored jointly by the

United States Department of Energy, Oak Ridge, Tennessee,

Norfolk State University, Norfolk, Virginia, the National Aeronautics

and Space Administration, Washington, D.C., and the National Institute

of Standards and Technology, Washington, D.C., and held in

Oak Ridge, Tennessee

November 11-13, 1992

National Aeronautics and

Space Administration

Office of Management

Scientific and Technical

Information Program

1993
The opinions expressed in this document are not necessarily approved or endorsed by the

National Aeronautics and Space Administration.
PREFACE

NEW:Update 92 was held during the anniversaries of two of our sponsors: Oak Ridge National Laboratory

(ORNL) celebrating 50 years and NASA Langley Research Center (NASA LaRC) celebrating 75 years. The

workshop was held November 11-13, 1992, at Oak Ridge National Laboratory (ORNL) in Oak Ridge,

Tennessee. As with previous workshops, the theme was strengthening materials education. Participants

witnessed demonstrations of experiments, discussed issues of materials science and engineering (MS&E) with

people from education, industry, government, and technical societies and heard about new MS&E

developments. Faculty in attendance represented community colleges, smaller colleges, and major universities.

Marking the 7th annual NEW:Update, we continue to see an increase in the quantity and quality of

experiments and demonstrations related to materials science through the efforts of the presenters and writers

of the materials enclosed in this notebook. This year we added a set of half day mini workshops utilizing the

facilities and expertise at ORNL.

Through the invaluable coordination of Mr. James Gardner, of NASA, announcements, mailings, and the

production of the this NEW:Update 92 publication are possible. Dr. Linda Horton, with involvement of Mr.

Edward Aebischer and Ms. Bonnie Reesor, provided the key link in making arrangements at ORNL and with

the Department of Energy. Dr. Robert Berrettini, of the Materials Education Council, arranged for a

distinguished review panel to provide peer review of the experiments. At Norfolk State University Ms. Diana

LaClaire, Dr. Heidi Ries and Mr. Todd Winters have kept tile workshop activities on track. We also wish to

recognize all of you for continuing to support these on-going efforts to strengthen materials education. We

received continual praise, input, and requests for the products of the NEW:Update series from around the

nation and world.

As with past NEW:Updates, we developed this year's workshop based on the input from participants of

previous workshops. An extensive peer review process of experiments was followed. After submission of

abstracts, selected authors were notified of their acceptance and given the format for submission of experiments.

Experiments were reviewed by a panel of specialists through the cooperation of the Materials Education

Council. Authors received comments from the panel prior to NEW:Update 92, allowing them to make

necessary adjustments prior to demonstrating their experiments. Participants at NEW:Update 92 also provided

verbal and written comments to authors/presenters. Finally, the NASA LaRC editorial staff provided a quality

check of the documents for grammar, spelling, etc.

NEW:Update 92, as with previous NEW:Updates, resulted from considerable cooperative efforts among

individuals in government, education, and industry. The workshops' goals are to maintain the network of

participants and to continue to collect these ideas and resources to bring them together in a comprehensive

collection of experiments and demonstrations ill materials science, engineering and technology.

The three-stage review process coupled with field testing, promotes useful experiments and demonstrations.

With this publication, we will have produced 139 experiments and demonstrations. For past issues see ordering

information on page v.

With involvement of the Materials Education Council and the Materials Division of the American Society for

Engineering Education, we have begun steps to select experiments and demonstrations from previous

NEW:Updates to produce a new publication for distribution throughout the materials education community.

111
We hope that the material presented in this publication will assist you in teaching about materials science,

engineering and technology. We would like to have your comments on their value and means of improving

them. Please send comments to James A. Jacobs, School of Technology, Norfolk State University, Norfolk,

Virginia 23504.

Without the support of our sponsors, the NEW:Update series would not be possible. The Department of

Energy, National Aeronautics and Space Administration, National Institute of Standards and Technology, and

Norfolk State University have provided the major funding. Joining in the support are ASM International,

American Society for Engineering Education, Battelle Pacific Northwest Laboratories, Martin Marietta Energy

Systems, Inc., Materials Education Council of the United States, and Westinghouse Environmental Management

Company of Ohio, and American Society for Testing and Materials.

NEW:Update 93 is being planned for November 2-5, 1993, at NASA Langley Research Center (LaRC) in

Hampton, Virginia. As with this year, we plan to spend a part of a day with small groups in various labs at

NASA LaRC.

We thank the many people who have been instrumental in the progress of NEW:Update, especially the people

at FMPC and ORNL for their hospitality and hard work this year. We hope the materials in this publication

will enhance your instructional capabilities for materials education.

We express our appreciation to all those who helped to keep this series of workshops viable.

The use of trademarks or manufacturers' names in this publication does not constitute

endorsement, either expressed or implied, by the National Aeronautics and Space

Administration.

Workshop Co-Directors Liaisons

Douglas F. Craig James E. Gardner, NASA-LaRC

Metals and Ceramics Division Roy Bunnell, ASM International

Oak Ridge National Laboratory Robert Berrettini, Materials Education Council

Linda Horton, Oak Ridge National Laboratory

Edward Aebischer, Oak Ridge National Laboratory

James A. Jacobs

Professor of Engineering Technology Director's Assistant

Norfolk State University Diana P. LaClaire

Norfolk State University

Organization Committee Members

Seth Bates, San Jose State University Peggy Weeks, Coming Community College

William Callister, Materials Div., ASEE John W. Patterson, Iowa State Univ.

David Werstler, Materials Div., ASEE Heidi Ries, Norfolk StateUniversity

Jonice Harris, NIST ThomasF. Kilduff, Thomas Nelson CommunityCollege

William Winn, Departmentof Energy F. Xavier Spiegel, Loyola College

Woodrow W. Leake, ASEE Jennifer Taylor, NYS College of Ceramics at Alfred

Robert J. Sullivan, WMCO James Thomas, American Society for Testing & Materials

iv
CONTENTS

PAGE

PREFACE ................................... iii

REVIEWERS OF EXPERIMENTS AND ACKNOWLEDGEMENTS ........... viii

PARTICIPANTS ................................ ix

LISTING OF EXPERIMENTS FROM NEW:UPDATES ................ xiv

ORDERING INFORMATION FOR ADDITIONAL RESOURCES ............ xix

GROUP PICTURE ............................... xxi

NEAR NET SHAPE PROCESSING---A NECESSITY FOR ADVANCED

MATERIALS APPLICATIONS .......................... 1

Howard A. Kuhn - National Center for Excellence

DEVELOPMENT OF AN EXPERIMENTAL METHOD TO DETERMINE THE

AXIAL RIGIDITY OF A STRUT-NODE JOINT ................... 35

W. V. Brewer and Hui-Ru Shih - Jackson State University

MECHANICAL PROPERTIES OF COMPOSITE MATERIALS ............. 43

H. Richard Thomton and L. R. Comwell - Texas A&M University

NEW MATERIALS: FOUNTAINHEAD FOR NEW TECHNOLOGIES AND

NEW SCIENCE ................................ 49

Rustum Roy - The Pennsylvania State University

MICROPIPET MANIPULATION OF LIPID MEMBRANES: DIRECT

MEASUREMENTS OF THE MATERIAL PROPERTIES OF A COHESIVE

STRUCTURE THAT IS ONLY TWO MOLECULES THICK .............. 99

David Needham - Duke University

TOOL GRINDING AND SPARK TESTING ..................... 121

Edward L. Widener - Purdue University

EXPERIMENTS IN CORROSION FOR YOUNGER STUDENTS BY AND FOR

OLDER STUDENTS .............................. 127

James V. Masi - Western New England College

A MINIATURE FATIGUE TEST MACHINE .................... 137

Steven M. Tipton - The University of Tulsa

INTRODUCTION TO I-I_GH PERFORMANCE COMPOSITES ............. 147

Norman J. Johnston - National Aeronautics and Space Administration,

Langley Research Center

V
MATERIALS EDUCATION ACTIVITIES ..................... 193

Heidi R. Ries - Norfolk State University

Jonice Harris - National Institute of Standards and Technology

Woodrow W. Leake - American Society for Engineering Education

L. Roy Bunnell - Battelle-Pacific Northwest Laboratories

Robert Berrettini - Materials Education Council

IMPROVED MEASUREMENT OF THERMAL EFFECTS ON MICROSTRUCTURE 197

Mansur Rastani - North Carolina A&T State University

DIRECT TENSION EXPERIMENTS ON COMPACTED GRANULAR MATERIALS .... 209

Steven W. Perkins - Montana State University

APPLICATION OF HARDNESS TESTING IN FOUNDRY PROCESSING

OPERATIONS: A UNIVERSITY AND INDUSTRY PARTNERSHIP .......... 221

Donald H. Martin - Tri-State University

Bruce Lash - AL-FE Heat Treating,/nc.

LABORATORY EXPERIMENTS IN INTEGRATED CIRCUIT FABRICATION ...... 223

Thomas J. Jenkins - Air Force Institute of Technology

Edward S. Kolesar - Air Force Institute of Technology

A 69 CENT LOOK AT THERMOPLASTIC SOFTENING ............... 273

Linda S. Vanasupa - California Polytechnic State University

SOLVING A PRODUCT SAFETY PROBLEM USING A RECYCLED HIGH

DENSITY POLYETHYLENE CONTAINER ..................... 281

Ping Liu and T. L. Waskom - Eastern Illinois University

TRIBOLOGY: FRICTION, LUBRICATION, AND WEAR TECHNOLOGY ........ 293

Peter J. Blau - Oak Ridge National Laboratory

WALKWAY FRICTION: EXPERIMENT AND ANALYSIS .............. 311

Mark I. Marpet - St. John's University

Robert J. Brungraber - Bucknell University

THERMOFORMING FROM A SYSTEMS VIEWPOINT ............... 329

Jerry L. Wickman - Ball State University

Nikhil Kundu - Purdue University

THE CHARACTERIZATION OF MATERIALS USING X-RAY DIFFRACTION ..... 337

A. F. Sprecher, Jr., Harvey A. West, and A. A. Fahmy

North Carolina State University

FRACTURE OF GLASS ............................. 351

John M. Henshaw - University of Tulsa

PHASE TRANSITION STUDIES IN BARIUM AND STRONTIUM TITANATES

AT MICROWAVE FREQUENCIES ........................ 359

Jai N. Dahiya - Southeast Missouri State University

vi
EXPERIMENTS IN MATERIALS SCIENCE FROM HOUSEHOLD ITEMS ....... 371

F. Xavier Spiegel - Loyola College

AN AUTOMATED DATA COLLECTION SYSTEM FOR A CHARPY IMPACT

TESTER ................................... 377

Bernard J. Weigman and F. Xavier Spiegel - Loyola College

VISUALIZING WELD METAL SOLIDIFICATION USING ORGANIC ANALOGS .... 385

Daniel W. Walsh and Gary Ray Rogers - California Polytechnic

State University

PERFORMANCE OF THERMAL ADHESIVES IN FORCED CONVECTION ....... 393

Nikhil K. Kundu - Purdue University

TAGUCHI METHOD OF EXPERIMENTAL DESIGN IN MATERIALS EDUCATION 403

Martin W. Weiser - University of New Mexico

POWDER METALLURGY: SOLID AND LIQUID PHASE SINTERING OF COPPER 415

Rex Sheldon and Martin W. Weiser - University of New Mexico

HIGH THERMAL CONDUCTIVITY OF DIAMOND ................. 431

Patrick M. Stephan - Norton Diamond Film

TEMPERATURE-DEPENDENT ELECTRICAL CONDUCTIVITY OF SODA-LIME

GLASS .................................... 441

L. Roy Bunnell - Battelle-Pacific Northwest Laboratories

T. H. Vertrees - Kennewick High School

CONSTRUCTION AND TESTING OF SIMPLE AIRFOILS TO DEMONSTRATE

STRUCTURAL DESIGN, MATERIALS CHOICE, AND COMPOSITE CONCEPTS .... 449

L. Roy Bunnell - Battelle-Pacific Northwest Laboratories

Steven W. Piippo - Richland School District

vii
REVIEWERS FOR NEW:Update 92

Nicholas Akinkuoye Thomas Gorman

Assistant Professor Assistant Professor

Dept. of Industrial Education and Department of Forest Products

Technology University of Idaho

Iowa State University

Girish Harshe

Else Breval Postdoctoral Fellow, MRL

Senior Research Associate Pennsylvania State University

Materials Research Laboratory

Pennsylvania State University Sue Hayle

Research Associate

Witold Brostow Materials Research Laboratory

Professor of Materials Science Pennsylvania State University

Center for Materials Characterization

University of North Texas James Provan

Dean of Engineering

Paul Brown University of Victoria

Associate Professor of Ceramic Science British Columbia, Canada

and Engineering

Materials Research Laboratory Jerzy Ruzyllo

Pennsylvania State University Associate Professor of Electrical

Engineering

William D. Callister Pennsylvania State University

Materials Science and Engineering

University of Utah Mary Shaw

Assistant Professor, Engineering

Wenwu Cao Science and Mechanics Department

Research Associate Pennsylvania State University

Materials Research Laboratory

Pennsylvania State University M.S. Wang

Professor of Civil Engineering

James A. Clum Pennsylvania State University

Mechanical & Industrial Engineering

T. J. Watson School of Engineering

State University of N.Y. at Binghamton

Technical notebooks were prepared by

NASA LANGLEY RESEARCH CENTER

Video taping was provided by

WESTINGHOUSE ENVIRONMENTAL MANAGEMENT COMPANY OF OHIO

Announcements of the workshop were printed by

NASA LANGLEY RESEARCH CENTER

viii
PARTICIPANTS

Edward Aebischer L. Roy Bunnell

Manager, University & Educational Programs Battelle

Martin Marietta Energy Systems, Inc. Pacific Northwest Laboratories

Oak Ridge National Laboratory P.O. Box 999 MSIN P8-44

P. O. Box 2008 Richland, WA 99352

Oak Ridge, TN 37831 509-376-2799

615-574-0762

Douglas F. Craig

Abayomi Ajayi-Majebi Director, Metals & Ceramics Division

Central State University Oak Ridge National Laboratory

114-A Jenkins Martin Marietta Energy Systems, Inc.

Wilberforce, OH 45384 P.O. Box 2008

513-376-6525 Oak Ridge, TN 37831-6263

615-574-4065

Robert Berrettini

Materials Education Council Jai N. Dahiya

Materials Research Laboratory Southeast Missouri State University

University Park, PA 16802 One University Plaza

814-865-1643 Cape Girardeau, MO 63701

314-651-2390

Peter J. Blau

Martin Marietta Energy Systems, Inc. C. Ray Diez

Oak Ridge National Laboratory University of North Dakota

P. O. Box 2008 P,O. Box 8057

Oak Ridge, TN 37831-6063 Grand Forks, ND 58202

615-574-5377 701-777-2249 ext. 2198

W. V. Brewer Ravinder Diwan

1031 Voorhees Avenue Southern University

Jackson State University Mechanical Engineering Department

Jackson, MS 39209 Baton Rouge, LA 70813

601-968-2466 504 -771-4705

Robert J. Brungraber Russell Eng

Bucknell University Portland Community College

Lewisburg, PA 17837 12000 SW 49th Avenue

908-879-4174 (home) Portland, OR 97219-0990

503-244-6111 Ext. 4653

ix
William D. Forgeng David Hinaman

California Polytechnic State University Westinghouse Environmental Management

Materials Engineering Department Co. of Ohio

San Luis Obispo, CA 83407 P.O. Box 398704

805-756-1537 Cincinnati, OH 45239-8704

James E. Gardner Linda Horton

NASA Langley Research Center Oak Ridge National Laboratory

11 Langley Boulevard MS-118 Martin Marietta Energy Systems, Inc.

Hampton, VA 23681-0001 P.O. Box 2008

804-864-6003 Oak Ridge, TN 37831-6263

615-574-5081

Robert J. Gray Matthew Hsu

Metals & Ceramics Division Materials Research Center

ORNL, P.O. Box 2008 Northwestern University

Oak Ridge, TN 37831-6139 2145 Sheridan Road

615.-574-4069 Evanston, IL 60208-3116

708-491-3607

George T. Hahn Emil H. Isaacson

Vanderbilt University University of District of Columbia

Box 1593 Sta B 39 Great Pines Court

Nashville, TN 37235 Rockville, MD 20850

615-322-3594 301-762-1277

Ian W. Hall James A. Jacobs

University of Delaware Norfolk State University

Spencer Laboratory 2401 Corprew Avenue

Newark, DE 19716 Norfolk, VA 23504

302-83 l -1295 804-683 -8109

John M. Henshaw, P.E. Thomas J. Jenkins

Dept. of Mechanical Engineering Dept. of Electrical & Computer Engr.

University of Tulsa (AFIT/ENG Bldg. 640 Area B)

Tulsa, OK 74104 Air Force Institute of Technology

918-631-3002 Wright-Patterson Air Force Base

Ohio 45433-6583

Astor Y. Herrell 513-255-3708; 4960; 6027

Winston-Salem State Uni_'ersity

P. O. Box 13236 Norman Johnston

Winston-Salem, NC 27110 NASA Langley Research Center

919-750-2543 MS-226

Hampton, VA 23681-0001

804-864-4260
Lisa Ketron Jed S. Lyons

Hocking Tech. College Dept. of Mechanical Engineering-Sumwalt

3301 Hocking Parkway University of South Carolina

Nelsonville, OH 45764 Columbia, SC 29208

614-753 -3591 803 -777-9552

Thomas F. Kilduff

504 Brafferton Circle Pat L. Mangonon

Hampton, VA 23663-1921 Florida Institute of Technology

804-851-0272 150 W. University Blvd.

Melbourne, FL 32901

Howard A. Kuhn, Program Director 407-768-8000/8068/7560

National Center for Excellence

Metalworking Processing Technology Mark I. Marpet

1450 Scalp Avenue St. John's University

Johnstown, PA 15904 Staten Island Campus

814-269-2426 300 Howard Avenue

Staten Island, NY 10301

Nikhil K. Kundu 718-390-4545

Purdue University

Statewide Technology

2424 California Road

Elkhart, IN 46514 Donald H. Martin

219-264-3111 Tri State University

Manufacturing Technology

Woodrow W. Leake Angola, IN 46703-0307

Deputy Executive Director 219-665-4100

American Society for Engineering Education

Suite 200 Eleven Dupont Circle James V. Masi

Washington, DC 20036 Western New England College

202-293-7080 Dept. of Electrical Engineering

Springfield, MA 01119

Stephen Lin 413-782-1344

Department of Chemistry

North Carolina Central Harvey E. Miller

3116 Annandale Road Oral Roberts University

Durham, NC 27707 7777 S. Lewis Avenue

919-560-6100 Tulsa, OK 74171

918-495-6952

Ping Liu

Eastern Illinois University David Needham

School of Technology Duke University

101 Klehm Hall Department Mechanical Engineering

Charleston, IL 61920 & Materials Science

217-581-6267 Durham, NC 27706

919-660-5329

xi
Thomas Nunnelley Hui-Ru Shih

Tarrant County Junior College Department of Technology

5301 Campus Drive Jackson State University

Fort Worth, TX 76119 1400 J. R. Lynch Street

817-531-4779 Jackson, MS 39217

601-968-2466

Matthew A. Panhans

Milwaukee School of Engineering Ram N. Singh

1025 N. Milwaukee St. Louis Community College

Milwaukee, WI 53202 3400 Pershall Road

414-277-7277 St. Louis, MO 63135-1499

314-595-2311

Edwin J. Prior

NASA-Langley Research Center Alphonso C. Smith

MS' 400 Hampton University

Hampton, VA 23681-0001 Department of Engineering 1F

Hampton, VA 23668

804-727-5292

Mansur Rastani, P.E., CMfgE

Department of Manufacturing Systems Carl Smith

NC A&T State University Kanawha Manufacturing Co.

Greensboro, NC 27411 and WVU at Parkersburg

919-334-7585 1520 Dixie Street

Charleston, WV 25311

Bonnie Reesor 304-342-6127

Oak Ridge National Laboratory

Martin Marietta Energy Systems, Inc. F. Xavier Spiegel

P. O. Box 2008 Department of Engineering

Oak Ridge, TN 37831 Loyola College

615-574-5984 4501 N. Charles Street

Baltimore, MD 21210

Hei di.Ri es 410-617-2515

Norfolk State University

2401 Corprew Avenue A.F. Sprecher

Norfolk, VA 23504 Dept of Materials Science & Engineering

804-683-8020 North Carolina State University

Raleigh, NC 27695-7907

William Ross 919-515-2377

Muskegon Community College

221 S. Quarterline

Muskegon, MI 49442 Patrick M. Stephan

616-777-0367 Norton Diamond Film

Goddard Road

Rustum Roy Northboro, MA 01532-1545

The Materials Research Laboratory 508-351-7600

The Pennsylvania State University

University Park, PA 16802

814-865-9951

xii
Ali Taba-Tabai David Werstler

Don Bosco Technical Institute Western Washington University

1151 San Gabriel Boulevard Technology Department

Rosemead, CA 91770 Bellingham, WA 98225-9086

818-280-0451 206-676 -3447

A. H. Tabrizi Harvey A. West

Evergreen Valley College Dept of Materials Science & Engineering

3095 Yerba Buena Road North Carolina State University

San Jose, CA 95135 Raleigh, NC 27695-7907

408-274-7900 919-515-2377

H. Richard Thornton

Texas A&M University Jerry L. Wickman

Department of Mechanical Engineering Plastics Research and

College Station, TX 77843-3123 Education Center

409-845-6151 Ball State University

College of Applied Sciences and Technology

Steven M. Tipton Department of Industry and Technology

The University of Tulsa Muncie, IN 47306-0255

Mechanical Engineering Department 317-285-5641

600 S. College

Tulsa, OK 74104 Edward L. Widener

918-631-3000 MET Department

Purdue University

Jeffrey Wagner Knoy Hall - Room 119

Westinghouse Environmental Management West Lafayette, IN 47907

Co. of Ohio 317-494-7521

P. O. Box 398704

Cincinnati, OH 45239-8704 Todd A. Winters

513-738-6084 Norfolk State University

2401 Corprew Avenue

Tom Waskom Norfolk, VA 23504

Eastern Illinois University 804-683-8109

School of Technology - Klehm Hall

Charleston, IL 61920

217-581-5762

Martin Weiser

Mechanical Engineering Department and

Center for Micro-Engine6red Ceramics

University of New Mexico

Albuquerque, NM 87131

505-277-2831

,°,

Xlll
LISTING OF EXPERIMENTS FROM NEW:UPDATES

EXPERIMENTS & DEMONSTRATIONS IN TESTING AND EVALUATION

NEW:Update 88 NASA Conference Publication 3060

Sastri, Sankar. "Fluorescent Penetrant Inspection"

Sastri, Sankar. "Magnetic Particle Inspection"

Sastri, Sankar. "Radiographic Inspection"

NEW:Update 89 NASA Conference Publication 3074

Chowdhury, Mostafiz R. and Chowdhury, Farida. "Experimental Determination of Material Damping

Using Vibration Analyzer"

Chung, Wenehiang R. "The Assessment of Metal Fiber Reinforced Polymeric Composites"

Stibolt, Kenneth A. "Tensile and Shear Strength of Adhesives"

NEW:Update 90 NIST Special Publication 822

Azzara, Drew C. "ASTM: The Development and Application of Standards"

Bates, Seth P. "Charpy V-Notch Impact Testing of Hot Rolled 1020 Steel to Explore Temperature Impact

Strength Relationships"

Chowdhury, Mostafiz R. "A Nondestructive Testing Method to Detect Defects in Structural Members"

Cornwell, L. R., Griffin, R. B., and Massarweh, W.A. "Effect of Strain Rate on Tensile Properties of

. Plastics"

Gray, Stephanie L., Kern, Kristen T., Harries, Wynford L., and Long, Sheila Ann T.

"Improved Technique for Measuring Coefficients of Thermal Extension for Polymer Films"

Halperin, Kopl. "Design Project for the Materials Course: To Pick the Best Material for a Cooking Pot"

Kundu, Nikhil. "Environmental Stress Cracking of Recycled Thermoplastics"

Panchula, Larry and Patterson, John W. "Demonstration of a Simple Screening Strategy for Multifactor

Experiments in Engineering"

Taylor, Jenifer A.T. "How Does Change in Temperature Affect Resistance.'?"

Wickman, Jerry L. and Corbin, Scott M. "Determining the Impact of Adjusting Temperature Profiles on

Photodegradability of LDPE/Starch Blown Film"

Widener, Edward L. "It's Hard to Test Hardness"

Widener, Edward L. "Unconventional Impact-Toughness Experiments"

NEW:Update 91 NASA Conference Publication 3151

BunneU, L. Roy. "Tempered Glass and Thermal Shock of Ceramic Materials"

Lundeen, Calvin D. "Impact Testing of Welded Samples"

Gorman, Thomas M. "Designing, Engineering, and Testing Wood Structures"

Strehlow, Richard R. "ASTM - Terminology for Experiments and Testing"

Karplus, Alan K. "Determining Significant Material Properties, A Discovery Approach"

Spiegel, F. Xavier and Weigman, Bernard J. "An Automated System for Creep Testing"

Denton, Nancy L. and Hillsman, Vernon S. "Isotropic Thin-Walled Pressure Vessel Experiment"

Allen, David J. "Stress-Strain Characteristics of Rubber-Like Materials: Experiment and

Analysis"

Dahl, Charles C. "computer Integrated Lab Testing"

Cornwell, L. R. "Mechanical Properties of Brittle Material"

xiv
NEW:Update 92 NASA Conference Publication 3201

Bunnell, L. Roy. "Temperature-Dependent Electrical Conductivity of Soda-Lime Glass and

Construction and Testing of Simple Airfoils to Demonstrate Structural Design, Materials

Choice, and Composite Concepts"

Marpet, Mark I. "Walkway Friction: Experiment and Analysis"

Martin, Donald H. "Application of Hardness Testing in Foundry Processing Operations: A University and

Industry Partnership"

Masi, James V. "Experiments in Corrosion for Younger Students By and For Older Students"

Needham, 'David. "Micropipet Manipulation of Lipid Membranes: Direct Measurement of the

Material Properties of a Cohesive Structure That is Only Two Molecules Thick"

Perkins, Steven W. "Direct Tension Experiments on Compacted Granular Materials"

Shih, Hui-Ru. "Development of an Experimental Method to Determine the Axial Rigidity of a

Strut-Node Joint"

Spiegel, F. Xavier. "An Automated Data Collection System For a Charpy Impact Tester"

Tipton, Steven M. "A Miniature Fatigue Test Machine"

Widener, Edward L. "'Fool Grinding and Spark Testing"

EXPERIMENTS & DEMONSTRATIONS IN METALS

NEW:Update 88 NASA Conference Publication 3060

Nagy, James P. "Sensitization of Stainless Steel"

Neville, J. P. "Crystal Growing"

Pond, Robert B. "A Demonstration of Chill Block Melt Spinning of Metal"

Shull, Robert D. "Low Carbon Steel: Metallurgical Structure vs. Mechanical Properties"

NEW:Update 89 NASA Conference Publication 3074

Balsamel, Richard. "The Magnetization Process - Hysteresis"

Beardmore, Peter. "Future Automotive Materials - Evolution or Revolution"

Bunnell, L. Roy. "Hands-On Thermal Conductivity and Work-Hardening and Annealing in Metals"

Kazem, Sayyed M. "Thermal Conductivity of Metals"

Nagy, James P. "Austempering"

NEW:Update 90 NIST Special Publication 822

Bates, Seth P. "Charpy V-Notch Impact Testing of Hot Rolled 1020 Steel to Explore Temperature Impact

Strength Relationships"

Chung, Wenchiang R. and Morse, Margery L. "Effect of Heat Treatment on a Metal Alloy"

Rastani, Mansur. "Post Heat Treatment in Liquid Phase Sintered Tungsten-Nickel-Iron Alloys"

Spiegel, F. Xavier. "Crystal Models for the Beginning Student"

Yang, Y. Y. and Stang, R. G. "Measurement of Strain Rate Sensitivity in Metals"

NEW:Update 91 NASA Conference Publication 3151

Cowan, Richard L. "Be-Cu Precipitation Hardening Experiment"

Kazem, Sayyed M. "Elementary Metallography"

Krepski, Richard P. "Experiments with the Low Melting Indium-Bismuth Alloy System"

Lundeen, Calvin D. "Impact Testing of Welded Samples"

McCoy, Robert A. "Cu-Zn Binary Phase Diagram and Diffusion Couples"

Patterson, John W. "Demonstration of Magnetic Domain Boundary Movement Using an Easily

Assembled Videocam-Microscope System"

Widener, Edward L. "Heat-Treating of Materials"

xv
NEW:Update 92 NASA Conference Publication 3201

Dahiya, Jai N. "Phase Transition Studies in Barium and Strontium Titanates at Microwave

Frequencies"

Rastani, Mansur. "Improved Measurement of Thermal Effects on Microstructure"

Walsh, Daniel W. "Visualizing Weld Metal Solidification Using Organic Analogs"

EXPERIMENTS & DEMONSTRATIONS IN POLYMERS

NEW:Update 89 NASA Conference Publication 3074

Chung, Wenchiang R, "The Assessment of Metal Fiber Reinforced Polymeric Composites"

Greet, Richard and Cobaugh, Robert. "Rubberlike Elasticity Experiment"

Kern, Kristen T., Harries, Wynford L., and Long, Sheila Ann T. "Dynamic Mechanical Analysis of

Polymeric Materials"

Kundu, Nikhil K. and Kundu, Malay. "Piezoelectric and Pyroelectric Effects of a Crystalline Polymer"

Kundu, Nikhil K. "The Effect of Thermal Damage on the Mechanical Properties of Polymer Regrinds"

Stibolt, Kenneth A. "Tensile and Shear Strength of Adhesives"

Widener, Edward L. "Industrial Plastics Waste: Identification and Segregation"

Widener, Edward L. "Recycling Waste-Paper"

NEW:Update 90 NIST Special Publication 822

Brostow, Witold and Kozak, Michael R. "Instruction in Processing as a Part of a Course in Polymer

Science and Engineering"

Cornwell, L. R., Griffin, R. B., and Massarweh, W.A. "Effect of Strain Rate on Tensile Properties of

Plastics"

Gray, Stephanie L., Kern, Kristen T., Harries, Wynford L., and Long, Sheila Ann T. "Improved Technique

for Measuring Coefficients of Thermal Extension for Polymer Films"

Humble, Jeffrey S. "Biodegradable Plastics: An Informative Laboratory Approach"

Kundu, Nikhil. "Environmental Stress Cracking of Recycled Thermoplastics"

Wickman, Jerry L. and Corbin, Scott M. "Determining the Impact of Adjusting Temperature Profiles on

Photodegradability of LDPE/Starch Blown Film"

NEW:Update 91 NASA Conference Publication 3151

Allen, David J. "Stress-Strain Characteristics of Rubber-Like Materials: Experiment and Analysis"

Chowdhury, Mostafiz R. "An Experiment on the Use of Disposable Plastics as a Reinforcement in

Concrete Beams"

Gorman, Thomas M. "Designing, Engineering, and Testing Wood Structures"

Lloyd, Isabel K., Kolos, Kimberly R., Menegaux, Edmond C., Luo, Huy, McCuen, Richard H., and Regan,

Thomas M. "Structure, Processing and Properties of Potatoes"

McClelland, H. T. "Laboratory Experiments from the Toy Store"

Sorensen, Carl D. "Measuring the Surface Tension of Soap Bubbles"

Wickman, Jerry L. and Plocinski, David. "A Senior Manufacturing Laboratory for Determining Injection

Molding Process Capability"

NEW:Update 92 NASA Conference Publication 3201

Kundu, Nikhil K. "Performance of Thermal Adhesives in Forced Convection"

Liu, Ping. "Solving Product Safety Problem on Recycled High Density Polyethylene Container"

Wickman, Jerry L. "Thermoforming From a Systems Viewpoint"

xvi
EXPERIMENTS & DEMONSTRATIONS IN CERAMICS

NEW:Update 88 NASA Conference Publication 3060

Nelson, James A. "Glasses and Ceramics: Making and Testing Superconductors"

Schull, Robert D. "High Tc Superconductors: Are They Magnetic?"

NEW:Update 89 NASA Conference Publication 3074

Beardmore, Peter. "Future Automotive Materials - Evolution or Revolution"

Bunnell, L. Roy. "Hands-On Thermal Conductivity and Work-Hardening and Annealing in Metals"

Link, Bruce. "ceramic Fibers"

Nagy, James P. "Austempering"

Ries, Heidi R. "Dielectric Determination of the Glass Transition Temperature"

NEW:Update 90 NIST Special Publication 822

Dahiya, J. N. "Dielectric Behavior of Superconductors at Microwave Frequencies"

Jordan, Gall W. "Adapting Archimedes' Method for Determining Densities and Porosities of Small

Ceramic Samples"

Snail, Keith A., Hanssen, Leonard M., Oakes, David B., and Butler, James E. "Diamond Synthesis with

a Commercial Oxygen-Acetylene Torch"

NEW:Update 91 NASA Conference Publication 3151

Bunnell, L. Roy. "Tempered Glass and Thermal Shock of Ceramic Materials"

Craig, Douglas F. "Structural Ceramics"

Dahiya, J.N. "Dielectric Behavior of Semiconductors at Microwave Frequencies"

Weiser, Martin W., Lauben, David N., and Madrid, Philip. "Ceramic Processing: Experimental

Design and Optimization"

NEW:Update 92 NASA Conference Publication 3201

Bunnell, L. Roy. "Temperature-Dependent Electrical Conductivity of Soda-Lime Glass"

Henshaw, John M. "Fracture of Glass"

Stephan, Patrick M. "High Thermal Conductivity of Diamond"

Vanasupa, Linda S. "A $.69 Look at Thermoplastic Softening"

EXPERIMENTS & DEMONSTRATIONS IN COMPOSITES

NEW:Update 88 NASA Conference Publication 3060

Nelson, James A. "Composites: Fiberglass Hand Laminating Process"

NEW:Update 89 NASA Conference Publication 3074

Beardmore, Peter. "Future Automotive Materials - Evolution or Revolution"

Chung, Wenchiang R. "The Assessment of Metal Fiber Reinforced Polymeric Composites"

Coleman, J. Mario. "Using Template/Hotwire Cutting to Demonstrate Moldless Composite Fabrication"

NEW:Update 90 NIST Special Publication 822

Bunnell, L. R. "Simple Stressed-Skin Composites Using Paper Reinforcement"

Schmenk, Myron J. "Fabrication and Evaluation of a Simple Composite Structural Beam"

West, Harvey A. and Sprecher, A.F. "Fiber Reinforced Composite Materials"

xvii
NEW:Update 91 NASA Conference Publication 3151

Greet, Richard J. "Composite Column of Common Materials"

NEW:Update 92 NASA Conference Publication 3201

Thornton, H. Richard. "Mechanical Properties of Composite Materials"

EXPERIMENTS & DEMONSTRATIONS IN ELECTRONIC MATERIALS

NEW:Update 88 NASA Conference Publication 3060

Sastri, Sankar. "Magnetic Particle Inspection"

NEW:Update 89 NASA Conference Publication 3074

Kundu, Nikhil K. and Kundu, Malay. "Piezoelectric and Pyroelectric Effects of a Crystalline Polymer"

Molton, Peter M. and Clarke, Clayton. "Anode Materials for Electrochemical Waste Destruction"

Ries, Heidi R. "Dielectric Determinafon of the Glass Transition Temperature"

NEW:Update 90 NIST Special Publication 822

Dahiya, J.N. "Dielectric Behavior of Superconductors at Microwave Frequencies"

NEW:Update 91 NASA Conference Publication 3151

Dahiya, J. N. "Dielectric Behavior of Semiconductors at Microwave Frequencies"

Patterson, John W. "Demonstration of Magnetic Domain Boundary Movement Using an Easily Assembled

Videocam-Microscope System"

NEW:Update 92 NASA Conference Publication 3201

Bunnell, L. Roy. "Temperature-Dependent Electrical Conductivity of Soda-Lime Glass

Dahiya, Jai N. "Phase Transition Studies in Barium and Strontium Titanates at Microwave

Frequencies"

xviii
ORDERING INFORMATION FOR ADDITIONAL RESOURCES

NATIONAL EDUCATORS' WORKSHOP PUBLICATIONS AVAILABLE FROM:

Dr. James A. Jacobs

Department of Technology

Norfolk State University

2401 Corprew Avenue

Norfolk, VA 23504

Shipping and handling charges

1988 $17.00

1989 $27.00

1990 $31.00

1991 $39.00

1992 $43.00

All of the above $73.00

Any three of the above $55.00

BOB POND'S "FUN IN METALS" TAPE - AVAILABLE FROM:

Johns Hopkins University

Maryland Hall 210

3400 N. Charles Street

Baltimore, Maryland 21218

Cost $30.00

xix
JOURNAL OF MATERIALS EDUCATION SUBSCRIPTIONS:

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Other Materials Education Council Publications available:

Classic Crystals: A Book of Models - Hands-on Morphology. Twenty-Four Common Crystal

models to assemble and study. Aids in learning symmetry and Miller indices. $17.00.

A Set of Four Hardbound Volumes of Wood Modules - The Clark C. Heritage Memorial

Series. Published by MEC in cooperation with the U.S.Forest Products Laboratory, Madison,

Wisconsin. A compilation of nine modules entitled Wood: Its Structure and Properties (I),

edited by Frederick F. Wangaard. A compilation of eight modules especially developed for

architects and civil engineers entitled Wood As A Structural Material (II). Also, Adhesive

Bonding of Wood and Other Structural Materials 011) and Wood: En_ineerin_ Design Concepts

__.__. Each of the first three wood volumes costs $27.00; the fourth volume costs $37.00. The

entire four-volume set is only $115.00 plus $3.50 shipping ($4.50 overseas).

The Crystallography Course - MEC's popular nine-unit course on crystallography. $37.00.

Instructional Modules in Cement Science - Five units prepared for civil engineering and

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Laboratory Experiments in Polymer Synthesis and Characterization - A collection of fifteen

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polycondensation and end-group analysis, interfacial polycondensation, gel permeation

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Metallographic Atlas - Royal Swedish of Technology. $28.00. A brief introduction to the

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Please add $2.00 per book shipping charge.

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XX
NationalEducators'WorkSho

Left to Right, RowsTop (10) to Bottom(1)

Row 10: R. Diez, D, Craig, D. Needham, [3. Forgeng, H. Miller

Row 9: J. Maai, L Hall, D. Warstler, L Ketron,T. Jenkins

Row 8: J. Wickman, H. Shih, E. Isaacson,A. Smith,A. Hen'eU

ROw 7: T. Waskom, H. West, P. Liu, R. Diwan

Row 6: A. Sprecher,M. Hsu, D. Martin, R. Borreffini,1"._lduff

ROw 5: C. Smith, G. Hahn, S. Lyons,A. AjayI-Majebi,A. TabrizJ

Row 4: R. Eng, S. "lipton,J. Gardner, R. Brungraber

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NATIONAL EDUCATORS' WORKSHOP

Update 92: Standard Experiments

in Engineering Materials Science

and Technology

November 11..13, 1992 - Oak Ridge, Tennessee

water reservoir

ery__ selenold/valve

12 V batt 1

loading fixture

(metal)

Imen

metalc

Insulating

Sponsored by

@ 0 '

UnitedStates NationalAeronautics&SpaceAdministration NorfolkState University NationalInstituteof Standards

Departmentof Energy LangleyResearchCenter SchoolofTechnology &Technology,MaterialsScience

FMPCandORNL & EngineeringLaboratories

with the support of American Society for Engineering Education

ASM International

Battelle, Pacific Northwest Laboratory

Martin Marietta Energy Systems, Inc.

Materials Education Council

Westinghouse Environmental Management Company of Ohio

xxiii

NEAR NET SHAPE PROCESSING -

A NECESSITY FOR ADVANCED MATERIALS

APPLICATIONS

Howard A. Kuhn

Program Director

National Center for Excellence

Metalworking Processing Technology

1450 Scalp Avenue

Johnstown, Pennsylvania 15904

Telephone 814-269-2426

1

Near Net Shape Processing

-- A Necessity for Advanced Materials Applications

Howard A. Kuhn, P.E.

Concurrent Technologies Corporation

1450 Scalp Avenue

Johnstown, PA 15904

High quality discrete parts are the backbones for successful operation of equipment

used in transportation, communication, construction, manufacturing and appliances.

Traditional shapemaking for discrete parts is carried out predominantly by machining, or

removing unwanted material to produce the desired shape. As the cost and complexity of

modem materials escalates, coupled with the expense and environmental hazards associated

with handling of scrap, it is increasingly important to develop near net shape processes for

these materials. Such processes involve casting of liquid materials, consolidation of

powder materials or deformation processing of simple solid shapes into the desired shape.

Frequently, several of these operations may be used in sequence to produce a finished part.

The processes for near net shape forming may be applied to any type of material, including

metals, polymers, ceramics and their composites. The ability to produce shapes is the key

to implementation of laboratory developments in maerials science into real world

applications. This seminar presents an overview of near net shapemaking processes, some

application examples, current developments and future research opportunities.

3
Net Shape Processing

--- A Necessity for Advanced Material

Applications--

HowardA. Kuhn

ConcurrentTechnologiesCorporation

Johnstown,PA

_Outline

Overview and Historical Perspective

Taxonomy of Net Shape Forming

Examples of Processes

New Developments

Powder Forging

Powder Injection Molding

Spray Forming

Metal Matrix Composites

Process Modeling and Concurrent Engineering

Challenges

4
Ultimate Goal of Manufacturing

Generation of Wealth Through Production of Components and

Systems

(i.e., Making "things" from "stuff")

Economic viability of the nation requires sharp focus on

generation of wealth, with secondary attention to services and

distribution of wealth.

High Quality

Components and Systems

are the keysto successfulperformanceof equipmentused

in everydayactivities:

Communication Construction

Transportation Manufacturing

Utilities Appliances

Defense Medicine

5
Materials Processing

• Materials in natural state are not useful as

functional implements

(exception: stones for throwing or hammering)

• Production of parts and components involves a

series of transformations of materials from their

natural or recycled state into a useful state

Useful State

• Shape - form, dimensions, tolerances

° Surface - finish, appearance, wear and

corrosion resistance

° Structure - determines properties, e.g.

strength, toughness,

conductivity
Transformations of materials to useful state:

Shapemaking

° Solidification of liquid material

• Forming of solid material

• Consolidation of powder material

• Removal of excess material

Structural Chanaew

• Thermal treatments

• Radiation treatment

Surfacing

• Cladding and plating

• Implantation

• Grinding and polishing

r II Recycled Materials [ Natural Materials ]

I I

{

7
Material removal is most common

process for making parts:

• Stone impacton stonefor spear points,

arrowheads

• Cuttingof bark andtwigs from tree branchto

form club, spear, arrowshaft

• Machiningwith lathe,miller,grinder, plane,saw

• Electrodischargemachining,lasercutting,

waterjetcutting

In modern times material removal has

deleterious side effects:

• Chips and scrap must be recycled or disposed

• Cutting fluids cause pollution

• Airborne pollutants are generated

• Process is costly and time-consuming for

production of complex shapes

$
Net Shape Processes

produce desired shape by solidification of liquid material,

forming of solid material or consolidation of powder

material, rather than material removal

Near-Net Shape Processes

require small amount of material removal to reach target

shape, dimensions and tolerances.

(secondary objectives are net surface and net structure)

Solidification(metals& polymers)

• Cast Ingots _ deformation processing

• Atomization of Powder --_ consolidation

• Casting of Shapes:

Sand Mold

Permanent Mold

Injection Molding

Die Casting

Investment Casting

9
BulkF

Forging Stretching

Rolling Bending

Extrusion Deep Drawing

Drawing

Cold Hot

Die Compaction Hot Pressing

and Sintering

Slip Casting Hot Isostatic Pressing

Powder Forging

10
Cost Comparisons of Forging vs.

Machining

1

Quantity -- Averoll, (:oil per path

400 I_=m/Contrm 60 l_ecl/'l_eme

Faorlcatlng Matet:a_ ; Tooh_ 0_1 Macl_lnl(_ _t'UO Total

Method (Part Cost) Cost Cost Cost Colt Cost

Pressing 1435 663 - 2.50 23.58

M_hrmng 2._0 3.00 - 24.00 0._)0 30.00

I.

'; \ -

i

Quantltv - A_rage COst _ mlr!

4QO Ptuc_/_mr_ 6Q Piec_lRelmee

FaOc'_catlrlg Mscer tal Tooh_ _)_ MacI1rnt,'_ S,t .Up Total

Method IPlrl COSt) COl Colt COlt Colt COlt

Pressln,_ 24.75 1.25 24.30 6.00 2.50 58.80

MJ_mjng 18.00 5.00 48.00 1.00 72.00

b.

Forging

_'-\__ /

Quamltv - Averaoe cos_ tier part

P_brSC_ltn_ Matertal Toohl_ O*lt M_chm,r_l _4et.Up Total

Melt_od Ip_rl COSt) COSt Cost Coil COil COIl

PreSSing 2.40 - 0 05 - 025 2 70

Macl_,mng 0.fi0 0.0_S 5 40 0.06 6,02

]!
Exam.DieSequences

BeverageCans S.DarkPlugs

Aluminum alloy 3004 production Steel 1008 AI203 Copper

Cast Ingot Continuously HIP Continuously

Hot rolled to 0.120 Cast Billet Cast Billet

Cold rolledto 0.011 Hot roll to 1" dia. Hot roll to wire

Blank, deep, reversedraw cup Cutoff slug Cutoff roll thread

Iron wall

Back extrude

Trim & flange

Finish machine

(Body) (Insulator) (Electrode)

AssembleSpark Plug

Semi-Solid Metalworking

• Emerging methodfor the manufacture of near-net shape

discrete components

• Incorporateselements of both casting and forging

• Capable of producing parts essentially free of extensive

porosity

• Components can be heat-treatedto obtain mechanical

properties superior to those achievable by die casting and

permanent mold casting processes.

• Properties equivalent to those of forgings are obtainable at a

significantly lower cost.

12
THE SEMI-SOLID METALWORKING PROCESS

COHVEHIOOHALLY

8SM CAST

_'I'EN _ INDUCIION

13
SCHEMATIC OF THE POWDER

INJECTION MOLDING (PIM)

PROCESS

ll0 [o Ljlo

]4
Criteria for PIM Processing

• size < 300 g or 100 mm (thickness)

• complex shape

° quantity over 10,000

° sinterable powder material

• +/- 0.3%tolerances

15
Pseudo Isostatic Pressing

• Granular or soft material used as the pressure transmission medium in a

conventional trap forging die

• Shorter cycle times than hot isostatic pressing

° Equipment less costly than hot isostatic pressing

Example: Ceracon Process

CERACONPROCESS

COMBINATION OF HEATED

PART WITH HEATED GRAIN

HEATED PREFORM

CONSOL IDAT ION

----I

EJECTION

SEPARATION

PARTS FOR FINI.SHING

GRAIN RECYCLED

16
PowderForging

• Die compaction and sintering of a preform

• Forging of the preform into a fully dense part

• Forging implies large amount of metal flow

(a) Illustrationof a trap diefor powderforging and (b) animpression

die withflashforconventional forging.

;........................... i!_i_tiii_itifiitili!_!i!_iii

(a) (hi

Comparisonof(a)powderepressingend(b)powderforging.

17
Comparison of Powder Forging

and Conventional Forging

(Original Photo Not Available.)

Compadsonofconventionaforging l practiceandthepowderforgingprocess

18
Powder Forging

• Example: Torque converter clutch hub

Torque converterclutch hub, forgingpreform,courtesy ImperialCleviteof

Canada.

• All Ford automobile engine connecting rods

made by powder forging

Torqueconverterclutchhub, Torque converterclutchhub,

forged blank, courtesy Imperial Clevite finish machined, courtesy ImperialCleof Canada vitc of Canada.

(Original Photos Not Available.)

19
Spray Forming

• Thermalsprayof powderto formshapes

• Liquidparticles impactsubstrate,flatten, solidify

valve

plasmagun

powder

filter

manipulator

Typical structure of deposit made at low spray density

2O
Metal MatrixComposites

Continuous fiber

• Forming of shapes by hot isostatic pressing of assembly in

a canister

• Assemblymay be foil/fiber/foilconstruction,or plasma

sprayedfiberfoils

• Variety of shapes,includingtubes,sheet, hat sections

• Applications to aerospace structures, such as NASP

Cross-sectionof consolidatedcompositeshowinggood consolidationat thecentral pan

of the specimen.

21
r--I (,, Initideforma al t,on

ProcessVariables: Temperature.T(t) at contactpoints

Pressure,p(t)

(,, Interlaminarporosityarises

dueto surfaceroughness

¢) IntermetallicMatrix

(e.g. TiaAI)

c5

¢_ Fiber (e.g.SiC. AI203)

Fiber- inducedanisotropy

Fiber- matrixreactions

Stressconcentration

z_ ¢) Internalporosity HIP Cannister

(e.g. Titanium) L_I

Schematic illustration of the HIP processas applied to the consolidation

of plasmasprayedcomposite foils.

22
DIRECTIONAL SOLIDIFICATION OF NiAI EUTECTIC COMPOSITES

Backscattered SEM microstructures of a transverse section of a NiAI10 at % Mo alloy directionally solidified at 0.5 mm/min.

(a) Eutectic colonies consisting of fine Mo filaments in a NiAI matrix.

(b) Uniform distribution of Mo filaments in the NiAI maxtrix.

23

Concurrent Engineering

• Geometric data file serves as starting point

(CAD wireframe or solid model)

• File is shared by Product Design group and

Process Design group

• Experience knowledge bases as well as

computer modeling are used

• Material behavior is measured to provide

input to computer models and assure realistic

predictions

• Environmental considerations are brought to

design stage

Computer Modeling

Focus on:

• Shape and dimension predictions

(Mold or die dimensions plus shrinkage)

• Structure and defect predictions

• Residual stress predictions

Integrates:

• Metallurgical factors

(Structural evolution, void formation,

ductile fracture)

• Continuum mechanics

(Heat transfer, fluid flow, stress analysis)

• Computer graphics

(Solid models, animation)

25
Fbormabilityof hard-to-work a!loys is aided

y the use of formability and workability

diagrams

• Laboratory tests establish combinations of

strains at fracture for a given material.

• These strains are plotted to produce a

formability or workability map for the given

material.

• Strains in actual process are compared with

formability or workability maps.

• Process changes and/or material changes

are determined to avoid defects.

26
Sheet Metal Forming Limit

Diagrams

• Limiting strains at failure are determined through simple

sheet metal tests

.70

•eO FJ

Safe Safe

ZO

Minorstretch

Establishing•safetnuy_ginwithFLDo.(NahonalSteelCorporo_on)

• Strains in a formed part are measured from grid circles and

compared with the forming limitdiagram

RadngformingseveriP/byIoc_on,(HahonolSleetCorpormioa)

27
Application of Forming Limit Concept

F ' '

Form,Lngllmi!

__.ot-_--'\-I_ I._.i,__°- :_

0.0 t5.O 30.0 45.0 60.0 75.0 0.0 15.0 30.0 45.0 60.0 75.0

X--mm X--mm

Proposed design Initial design

Upset Test

28
Fracture Strain Linesfor 2024 Alumlnum Alloy

,. 0.S

2SO*C. _ - S*"

.. o_._ "_

:)2

HomolOeneou| ¢ompre*|ion ._ il.Z 1

_.-_.

o S_r_ght " b. l.I

• TmlNftd '_' ,_.

• Fleeql_ll

%

-O.Y -0.11 -O.S -li.6 -0.) -t1.| -0.1 0

ComtMmNive lilrlin

Upsettlng

_ Material II I

,,,--.% _Li

Coml_rllllVl IIllif_

Material Fracture Strain Limits

29
kLI

Cutaway view of double hub forging. Left figure shows a schematic of the toolingarrangement

and the righttigureshows a cross sectionof a forging containinga crackat the center.

(OriginalPhotosNotAvailable.)

3O
Finite element mesh for simulation of extrusion forging 
3.00 1

e E£_. Btn Rt

]. 2.00 - Object # 2

13= 1.4112

_ A= 0.32138Z-

•---, I_ A= O. O0000EB= O. 17640

. C= 0.35281

1.00 D= 0.52921

E= O.70561

F= O. 88202

G= 1.0584

H= 1.2348

I= 1.4112

O.O0

Object # 3

El= O.O0000E

A = O.O0000E

A= O.O0000F

_t .00 I I I

0.00 1.00 2.00 3.00

Radi us

Contours of effective strain rate in finite element

simulation of extrusion - forging

Net Shape Forming Challenges

• Improve dimensional control

• Improve shape complexity

• Improve structure control

• Improve surfaces

• Reduce tooling costs

• Adapt to small batches

32
Workshop Location

Registration

33
Welcome

Keynote

34
DEVELOPMENT OF AN EXPERIMENTAL METHOD TO

DETERMINE THE AXIAL RIGIDITY OF

A STRUT-NODE JOINT

W. V. Brewer

and

Hui-Ru Shih

Department of Technology

Jackson State University

1400 J. R. Lynch Street

Jackson, Mississippi 39217

Telephone 601-968-2466

35

DEVELOPMENT OF AN EXPERIMENTAL METHOD TO DETERMINE

THE AXIAL RIGIDITY OF A STRUT-NODE JOINT

W. V. Brewer and Hui-Ru Shih

Department of Technology

Jackson State University, Jackson, Mississippi

KEY WORDS: rigidity, torque, strut-node joint.

PREREQUISITE KNOWLEI)GE: The concepts of force, deflection, and rigidity.

OBJECTIVES: To present: (i) the experimental procedure and the results that have been

performed to determine the axial rigidity of the strut-node joint; and (ii) the method for

modifying a simple testing machine to make it capable of performing more accurate tests over a

specific load range and able to accept larger test assemblies.

EQUIPMENT AND SUPPIJES: Vega Universal Testing Machine, dial gage, strut

and strut-node joint assembly, torque wrench, pressure gage, manual needle-stop valve, brake

lines (the last three items were inserted into the hydraulic line of the testing machine).

PROCEDURE: In this experiment, the test specimen was a joint assembly consisting of

a node with a strut half mounted on either side (figure 1). The strut is a hollow aluminum tube

which has a hex-head bolt attacted to its one end by means of a bonded, interference fit

aluminum plug. The node is a hollow steel sphere with eighteen threaded holes for strut

attachment.

A simple "Vega Universal (VU) Testing Machine" was used to provide load in this

experiment. This machine was intended to test small stout material specimens [11,rather than

the bulkier less robust strut-node joint assembly we have. Space in both tensile and

compressive frames was insufficient to accommodate our joint assembly. Lengthened frame

posts of our own manufacture have been installed.

Loads which were applied to the strut-node system in the experimental procedure range

from 0 to 1600 N. Whereas the load gage on the VU testing machine, which ranges from 0 to

89000 N (20000 lb), reads in 445 N (100 lb) increments with very little precision in the range

of interest. In order to measure loads more accurately, a pressure gage of appropriate range has

been inserted into the hydraulic line of the VU testing machine. The corresponding load is the

gage pressure times the cross-sectional area of the hydraulic load piston. Available gages in the

37
range of interest have to be protected from higher pressure capabilities of the testing machine.

To accomplish this, a manual needle-stop valve was used. This valve must be closed if the

testing machine is used at pressures above the upper limit of the pressure gage.

The VU testing machine employs universal jaws with V grips to hold the test specimen.

The end of each strut to be placed in the machine was fitted with a solid plug in order to prevent

the strut from being crushed. Three dial gages were employed to measure the deflection of the

specimen. These dial gages were around the test specimen and mounted between two mounting

plates by using clamps and threaded rods. The deflections of three dial gages were averaged to

compensate for any bending that occurred in the specimen [2].

In order to calibrate the system to ensure the experiment set-up was operating properly, a

segment of a strut having the same length as the joint assembly was tested first to determine its

axial rigidity. The load-deflection curve for the strut is shown in figure 2. From this curve, the

experimentally determined rigidity is 4.449x106 N. This rigidity value is calculated by

multiplying the slope of the load-deflection curve by the test specimen length, 355.6 mm (14.0

in.) [3], i.e.

EA= _PL (1)

8

where E is the Young's modulus, P is the applied load, 8 is the deflection, and A and L are the

cross-sectional area and the length of the test specimen, respectively. The product EA in

equation (1) is known as the axial rigidity. The strut is a hollow aluminum tube, with a material

Young's modulus of 70 GPa and a cross-sectional area of 62.97 mm_-(22.05 mm outer

diameter, 0.95 mm wall thickness). Thus, the predicted axial rigidity is 4.408x106 N. This

represents a difference of only 0.923 percent from the experimentally determined value of

4.449x106 N and thus verifies the test procedure.

After verifying the test procedure, a strut-node joint assembly was loaded to determine its

rigidity and the effect of the attachment bolt torque value on joint rigidity. To accomplish this,

tests using two torque values, 3.39 N-m (30 lb-in.) and 16.95 N-m (150 lb-in.), were

conducted. As shown in figure 3, the rigidity of the strut-node joint assembly increases as the

attachment bolt torque value is increased. A comparison of the rigidity values for strut and

strut-node joint assembly with different torque values is presented in table 1. An examination

of table 1 reveals that the percent increase in rigidity of the strut-node joint assembly over that

of the strut varies from 4.1% for a torque value of 3.39 N-m to 7.8 % for a torque value of

16.95 N-m.

SAMPLE DATE SHEETS: Self-Evident.

INSTRUCTOR NOTES: An experimental method has been developed to determine

the axial rigidity characteristics of a strut-node joint, and to compare that with the rigidity of a

38
similar length of strut without a joint. The experimental results have shown that the strut-node

system is stiffer than the strut and the rigidity of the strut-node joint assembly increases as the

attachment bolt torque value is increased. The structural performance of the strut-node joint

assembly can be improved by increasing the pre-load in the threaded connections between the

node and strut. This experiment was performed with a simple Vega Universal Testing

Machine. Through the specialized modification, this testing machine could be used to test a

strut-node joint or other larger assembly where the required measurable load range is much

smaller.

REFERENCES:

1. Materials Technology Laboratory Manual, VEGA Enterprises Inc., Decatur, Illinois, 1980.

2. McGowan, D. M.; and Lake, M. S.: "Experimental Evaluation of Small-Scale Erectable

Truss Hardware", NASA TM 89068, June 1987.

3. Gere, J. M.; and Timoshenko, S. P.: Mechanics of Materials, third edition, PWS-KENT

Publishing Company, Boston, 1990.

SOURCES OF SUPPLY: The strut and strut-node joint assembly are provided by

NASA langley Research Center. Hardware stores can provide the rest of supplies.

ACKNOWLEDGEMENT: This work was supported by NASA Langley Research

Center under NASA/HBCU Grant.

39
Strut i'-7 Attachment Bolt - I_[

•"1 ...q

Node _ °I O0 q

Bonded Plug _ 1

--J

Strut _

Figure 1. Strut-Node Joint Assembly

050 f

Load (N)

700

350

0 _ • i I i i I i i I _ ,

0.00 0.03 0.06 0.09 0.12

Deflection (mm)

Figure 2. Load-Deflection Curve for Strut

40 •
1400 ' ' , ' ' , ' ' , ' '

1050

Load (N)

7oo

350 / + 16.95 N-m

/

/

0 _ _ I _ _ I _ _ , I

0.00 0.03 0.06 0.09 0.12

Deflection (mm)

Figure 3. Load-Deflection Curves for Strut-Node Joint with 3.39 N-m

and 16.95 N-m Torque values

Table 1. Comparison of the Rigidity of Strut and Strut-Node Assemblies

for a Fixed Length of 355.6 mm (14.0 in)

Rigidity % Difference with

Specimen Strut

(Nx 106 )

Strut 4.449 .....

Strut-Node 1 4.631 4.1

Strut-Node 2 4.798 7.8

Strut-Node 1 is a strut-node joint assembly with 3.39 N-m torque

Strut-Node 2 is a strut-node joint assembly with 16.95 N-m torque

41
Participants

42
MECHANICAL PROPERTIES OF COMPOSITE

MATERIALS

H. Richard Thornton

and

L. R. Cornwell

Department of Mechanical Engineering

Texas A&M University

College Station, Texas 77843-3123

Telephone 409-845-6151

43

MECHANICAL PROPERTIES OF

COMPOSITE MATERIALS

H.R. Thornton and L.R. Cornwell

Department of Mechanical Engineering

Texas A&M University

College Station, Texas 77843-31123

KEY WORDS: fiber reinforced composites, laminate,orthotrooic, longitudinal,

transverse, and shear stress, strain, modulus of elasticity, tensile test, "Laminate" analysis

(computer).

PREREQUISITE KNOWLEDGE: The student should understand orthotropic

characteristics and how off-angle plies are layed-up into fiber reinforced composite

laminates. The understanding of orthotropic elastic properties is basic.

EQUIPMENT AND SUPPLIES: Universal testing machines such as Instron or MTS,

Tabbed 07, 90°, and off-angle composite laminate specimens, "Laminate" computer program

on PC.

INTRODUCTION: A composite material incorporates high strength, high modulus

fibers in a matrix (po]lymer, metal, or ceramic). The fibers may be oriented in a manner to

give varying in-plane properties (longitudinal, transverse-stress, strain, modulus of elasticity).

The lay-up of the composite laminates is such that a center line of symmetry and no

bending moment exist through the thickness. The laminates are tabbed, with either

aluminum or fiberglass, and are ready for tensile testing.

The determination of the tensile properties of resin matrix composites, reinforced

by continuous fibers, is outlined in ASTM standard D 3039, "Tensile Properties of Oriented

Fiber Composites." The tabbed flat tensile coupons are placed into the grips of a tensile

machine and load-deformation curves plotted. The load-deformation data are translated into

stress-strain curves for determination of mechanical properties (ultimate tensile strength and

modulus of elasticity).

PROCEDURE: Composite test coupons (in our case graphite/epoxy) are

fabricated in the following fiber orientations:

1. 0° laminate (all fibers oriented in 0° direction to applied load)

2. 90° laminate (all fibers oriented 90° to applied load)

3. laminates containing off-angle plies.

45
The flat coupons are tabbed on both ends (both sides) to accept the perforations

from the grips on the tensile machine. The tensile coupons are shown in figure 1. The wddth

and thickness are measured and the length is the distance between the tabs. The cross

sectional area and the average ply thickness are calculated for each tensile coupon.

7ram

(12.7 rnmx/ 76ram

25mm

Figure 1. Tensile coupons ,

The tensile coupons are normally 12.7 mm wide and 1.4 mm in thickness. The

thickness is normally 8 plies. The length is appro_mately 76 mm. These dimensions can

vary as long as they adhere to ASTM standard 3039.

The mechanical properties of the 0°and 90° laminates are required for input into the

"Laminate" computer program. The computer program also requires the number of plies

through the thickness and the average ply thickness.

The tensile coupon is placed into the grips of the tensile test apparatus. Align the

coupons and tighten the grips onto the tabbed ends of the specimen. A low strain rate (0.02

mm/mm/minute) is selected for test. Most fiber reinforced composites have limited _

deformation at fracture. The load vs displacement spectrum is recorded and mechanical

property data calculated. 0° coupons provide longitudinal stress and modulus data and

90°coupons provide the transverse properties. "llm fracture surfaces are examined and

failure modes determined. The laminates containing off-angle plies are tensile tested and

data reduced.

COMPOSITE ANALYSIS-"LAMINATE": The theory for composite plate

analysis considers constitutive equations (Jones, 1975). The "Laminate" computer program

calculates mechanical properties of a given laminate considering constitutive [A}

(extensional), [B] (coupling), and [D] (bending) stiffness matrices (Andrews, Killespies,

Ochoa, 1992). Test data from 0° and 90° laminates define the longitudinal (E_)and

transverse (Ez) properties for the composite system. This assumes that the fiber volume

46
percent is the same in all cases.

The program requires the following data:

1. total number of lamina (plies)

2. E l - longitudinal modulus (00)

3. Ez - transverse modulus (90°)

4. Gtz - shear modulus (not determined in test and given by

instructo 0

5. ultimate tensile strength

Sj - longitudinal (00)

S2 - transverse (90 °)

7"12- shear (given by instructor)

6. ply orientation (degrees) of laminates with off-angle plies (i.e.,

+45, --45, 0- - -)

7. ply thickness (mm).

The program will now calculate plate solutions for selected boundary conditions.

Stress-strain valves can be calculated at either the lamina or the laminate level. This

experiment will consider the laminate level as our students are not familiar with orthotropic

materials at this point.

INITIAL EXPERIMENT: The mechanical properties of the 0° and 90 °

laminates and laminates with off-angle plies are determined by test. The initial experiment

would consider the moduli of elasticity. The 0° and 90°laminates are required for analysis,

The moduli of elasticity for the laminates containing off-angle plies are also determined

from test. The input data are fed into the "Laminate" program and the moduli of elasticity

for laminates with off-angle plies are calculated. An analysis can now be made between the

test and analytical moduli of elasticity for laminates with off-angle plies.

This experiment can be used to introduce students to the mechanical properties of

composite materials. Also, values can be compared with other materials with which the students are more familiar.

SECOND EXPERIMENT: More in depth information can be determined from the

"Laminate" program. For students that are familiar with composite materials, stress-strain

relationships can be calculated at the lamina level (ply). The composite plate analysis will

determine "first ply failure" within the laminate. This would require that the student have

a greater knowledge of the mechanics of composite materials. An understanding of the

failure mechanism is required. Also, a failure theory is included in the "Laminate" program

that the student should be aware of. The failure theory (Tsai-Hill, Tsai-Wu) should be

explained to the student.

This experiment can be considered as a second step in the understanding of the

47
tensile properties of composite materials.

REFERENCE:

Jones, R.M., Mechanic's of Composite Materials, McGraw-Hill Book Company,

New York, 1975.

Andrews, S., Killespies, H. and Ochoa, O., TAMULAM- Composite Plate

Ana_sis, Department of Mechanical Engineering Texas A&M University,

College Station, Texas 77843, 1992.

48
NEW MATERIALS: FOUNTAINHEAD FOR NEW

TECHNOLOGIES AND NEW SCIENCE

Rustum Roy

Evan Pugh Professor of the Solid State

Professor of Science, Technology and Society

The Pennsylvania State University

University Park, Pennsylvania 16802

Telephone 814-865-9951

International Science Lecture Series

sponsored by

The U.S. National Academy of Sciences

and

The Office of Naval Research

49

NEW MATERIALS: FOUNTAINHEAD FOR NEW

TECHNOLOGIES AND NEW SCIENCE

Rustum Roy

MaterialsResearch Laboratory

The Pennsylvania State University

Abstract

The role of materials as the benchmark technologies which give epochs of

human history their names continues into the present. The discovery of new

materials has nearly always been the source of new materials science, and frequently

of new technologies.

This paper analyzes the actual processes by which new materials are

synthesized, i.e. whether driven by serendipitous observations, new knowledge

pulled by the market, or integrated into a technological thrust. This analysis focuses

on modern ceramic materials discoveries, since WW II, and uses 45 years experience

in materials synthesis in the author's own laboratory as case studies.

A dozen different families of materials or processes are involved:

hydrothermal reactions; sol-gel processing; clays and zeolites; electroceramics; zero

expansion ceramics; diamond films; radioactive waste host phases. Nanocomposite

concepts introduced by the author a decade ago offer an entire, large, new class of

materials which will dominate synthesis for the next period.

The future of materials research for the next 25 years cannot be extrapolated

from the past 25 years. We are near the asymptote for materials utilization in most

metals. Likewise we are approaching saturation in improvement of many useful

properties. Justifying much further "basic" R/D for incremental improvement in

civilian-oriented industries will not be easy. In materials synthesis the near-term

future is sure to emphasize not "new phases," but tailored micro- and nanocomposites for chemical, electrical, optical and magnetic uses. Unexpected new

discoveries such as the Lanxide process may offer rarer chances for step function

advances.

The new structure of knowledge management will rely less on local research

than on integration of worldwide inputs. Better scientific and technological

opportunities will lie in designing knowledge intensive materials to meet the new

environmental and conservation goals, and the human" needs of the very large

numbers at the bottom of the socio-economic structures of the world.

$1
NEW MATERIALS: FOUNTAINHEAD FOR NEW

tECHNOLOGIES AND NEW SCIENCE

THE ROLE OF MATERIALS IN HUMAN SOCIETY

This rather bold title has been chosen to call attention to the long-neglected pivotal role that the

discovery of a new material or a new process for making--typically new--materials has played in the

progress of humankind and the science of materials.

Figure 1 recalls that historical epochs have been named after materials. Today our post WW II

epoch would be accurately named the silicon era. We will conclude this paper by claiming that the

next era will be that of the nanocomposites. Figure 2 brings together some characteristics of all the

materials that humankind uses. In national and world policy it is important to have a feel for the

volumes of the different materials actually used. Many are surprised to find the rank order of the

tonnages of these materials: wood; ceramics including cement; metals; polymers; and semiconductors.

Another interesting comparison in Figure 3 introduces the importance of the comparative scale in very

old (paleo) /

• STONE AGE

\

new (neo)

• Pottery

• BRONZE AGE

• Cement

• IRON AGE

• Aluminum

• SILICON AGE

• (Nano) Composite

"FIDES SUBSTANTIA RES" Teilhard de Chardin RES SUBSTANTIA SPEI

Figure 1. The "progress" of human history has been marked by (new) materials. It is not an

unreasonable index as the philosopher scientist Chardin observed "Faith is the substance

of things." I have paraphrased the modem situation for many societies on the right,

"Materials give substance to hope."

52
Millions of Properties.

Use Started In Tons/Year Resources Needed Products Utilized

I_u 3,000,000 B.C. 1-10,000 renewable, but somewhat building mechanical

ralcomposites) geographically limited

CERAMICS] <10,000 B.C. 1-10,000 SiO2, AI203, CaO, MgO pottery mechanical

Fe203 glass - bulk - optical

universally available cement; refractories; optical

Incl. cemL_t 1,000 no re_urce problem for cutting tools;

any nalion diamonds; turbines electrical

5,000 B.C. iron = 500 viable ores geographically myriad products mechanical

others = <500 very uneven steel, copper,

aluminum alloys electrical

POLYMERS-] 1900 ..100_- petroleum(now) containers, mechanical

furniture, (electrical)

textiles

SEMICONDUCTORS I 1940 <<.001 no n.'sourceissue small electrical electrical

devices

ICOMPOSrrES I 1950 1-10 not important furniture to mechanical

airplanes (electrical)

Figure 2. The Material World.

53
Highway Materials Ceramic Matrix

Factor Asphalt & Concrete Superalloy Microchip Composite

Tons/yr 1,000,000,000 50,000 100 10

Second phase Stone, rebar, pores y' Epitax layer SiC

Size of second FromI upto 1010 103 102 104

phase (nm)

Cost, $/# 0.05 100 23,000 100

U.S. Research 3 x 107(1977) 108 109+ 108

Effort

Figure 3. The enormous range in contemporary materials (after R. Decker), in volume, size, price, and

total research effort which is not related to the business opportunity.

different parameters among different materials. Not only volumes and size and second phase are

significant. One notes that the research effort bears some relation to the cost per pound, but none at all

to the total volume of cost of the class of material. Figure 4 is a summary of the status of our ability

today to design to specification and synthesize materials, by the size of the units involved in composite

or single phases. The larger the size from meters to tens of micrometers, the more advanced our ability.

At the unit cell or "atomic" level our synthesis ability is still very primitive indeed. It is a major

thesis of this paper that the nanocomposite level provides the level of aggregation which will form

the frontier for materials research worldwide in the immediate future.

Macro (cm-m) Excellent Materials for very large structures have been optimized;

e.g. reinforced concrete, airframe alloys.

Micro (ram-gin) Very good Lab scale and small objects (GRP to graphite-epoxy

composites; transparent Luca!ox, composite transducers,

etc.).

Nano (0.1 to 10nm) Primitive but new New materials designed an6 made: intercalates, glassceramics, toughened zirconia, nanocomposite desiccants, etc.

Atomic (0.1 nm) Poor New materials found by serendipity: penicillin, teflon,

magnetic garnets, R.LB., 1:2:3superconductors, etc.

Figure 4. A comparison of our contemporary capacity to prepare new materials or composites

arranged as a hierarchy of size.

$4
THE INNOVATION PROCESS

We turn now to _ question of what the historical record teaches us on how innovation has

occurred in science and technology.

In earlier reviews (1,2) I have referred to the work of J. D. de Solla Price (3), one of the great

historians of science who shows definitively how much advances in all branches of sciences depended

on new instruments. I argued by analogy (4) that "new materials" play exactly the analogous role in

the materials sciences and technologies. The relationship is that shown in Figure 5. This figure makes

several points. First it supports Price's contention (the title <_ his AAAS address) that by and large

(contrary to the totally unsupported maxims of many scientists in academia), science is largely applied

technology. From Galileo, applier of the telescope, to the modern particle accelerators, appliers of

magnet and electronic technology, there is no room for argument that in most cases, as Price puts it, "the

Materials Technology I New Materials I New Science

Other Inputs ,1,

I <

Figure 5. In parallel with de SoUa Price's assigning of the key role to new instruments in advancing

science and then technology, new materials can independently advance both materials science

and materials technology. The science has not led to new materials, except increasingly in

the design of composites.

arrow of causality" is from technology _ science. Certainly particle physics CANNOT help the

materials science of magnets; the latter is essential to the former. Second is the point that a new

material, often discovered serendipitously, leads to new science. The extent to which this is true is

illustrated by the case of new superconducting materials to BCSand other theories of

superconductivity. The latter certainly did not give an iota of guidance on finding new materials. Yet

the discovery by amateur chemistry of 1:2:3oxide superconductors will provide activity and

employment for hundreds of theorists in physics worldwide. Exactly analogous examples may be found

in magnetic or ferroelectric materials. New materials certainly are'the fountainhead for new

materials science.

In the advancement of technology, the story is the same. The new material--tenon,

polyethylene, the magnetic garnets, new zeolites---all lead rather directly to new technologies. The

feedback loop going towards products requires, in addition, the major components of capital, labor,

$$
entrepreneurship, etc. Any contributions from the science often comes later as an add-on in the second

generation of products, new zeolites, magnetic bubbles, etc. Thus materials science often helps in the

fine-tuning and optimization. But the discovery of the new material is the pivotal point. Had zeolite

A not been discovered by Brecket al. (5) an entire industry of catalysts and separation might not exist.

Why then has materials synthesis been so neglected, especially in the U.S.? My analysis of this

issue illustrates the necessity for understanding the human dimensions of scientific research. I attempt

in this paper to interweave the science with the human and societal dimension. By omitting it l

believe we give a false picture of how science really progresses. My studies of why scientists pursue

particular topics show the following factors to he most significant in decreasing order of importance:

Fashion (based on stories in the popular press), availability of money, local access to particular

specialized equipment, the more specialized or exotic, the more powerful the influence. Other factors

such as novelty of idea, significance to science, etc., have a very small impact. Few scientists today

have even thougi_t about their research in those terms. Thus, in the post WWII U.S., it was the agile

and active physics community returning from the Manhattan project that saw the opportunity and took

over the field of materials research. They brought with them the incredibly naive and totally

spurious notion that basic science (the more the better) "leads automatically to technology and thence

to prosperity." [This is a quote from G. A. Keyworth (6), President Reagan's science adviser for seven

years]. This notion was built on similar simplistic, later to be proved totally erroneous (7), aphorisms

such as "The A-bomb l_i to the defeat of Japan." And the greatest swindle of all, since Jacoboutwitted

Esau, that "I'he bomb was a triumph of science," and not of the incredible power of organized American

technology.

Based on these erroneous precepts U.S. national science policy went off on a totally erroneous

track as traced by Shapley and Roy in their book (8). Following the ruling paradigm of the day that

the more "basic" the science the better, materials science was, in the fifties and sixties, equated to

metal physics and solid state physics of idealized alkali halides and similar substances. By the

fortunate coincidence of the discovery of transistor action in a new rnaterialmhighly purified

germaniumman ideal marriage of opportunity and availability appeared in the semiconductor world

and appeared to support the value of such science. Ge, then Si, in the simple diamond structure, became

available in extraordinarily pure and perfect form_thanks to a triumph of materials synthesis. And

this opened up the enormous opportunity for the fantastic new science of semiconductors, and the new

technologies underlying modem electronics.

In the meantime, inacademia and the research-supporting agencies, synthesis of new materials,

whether in metallic alloys, ceramics, or polymers was relegated to second class, or worse, status.

Theory and phenomena ruled the day. In industry the situation was very different. All corporations

remained very active in materials synthesis and processing: Bell Laboratories in Ge, Si, garnets, etc.;

GE in new alloys; Lucalox, polymers; Coming in glass-ceramics, photoceramics, etc.; 3M in sol-gel fibers

$6
and grains; Phtlips in fen'ires, and so on. At Penn State, the Materials Research Laboratory was the

lone exception amon8 major universities with "Materials Preparation" (as the keystone of our clearly

articulated research strategy). This put us closer to the kind of materials research regarded as most

significant by industry. Hence it was no accident that the Laboratory has had for decades the highest

percentage of support from industry among such U.S. laboratories. And for the thirty-year life of the

Laboratory and a dozen years before it was formed, we have had at Penn State a major continuing

research effort--with several striking successes--in materials synthesis. This long and broad track

record was all focussed in the area of ceramic materials. And it is to an examination of the details of

what we can learn from these results that we now turn.

DIFFERENTMODELS FOR DOING MATERIALS (SYNTHESIS) RESEARCH

In a lecture such as this I believe it is not productive merely to review the literature on synthesis,

or to catalogue our own studies, but to conduct a meta-analysis of the latter to extract insights on the

thought processes involved. Our goal here is not to invent new epistemologies, or come up with new

theories of innovation or creativity. Rather it is to try to examine clearly the empirical data on 45

years of researchon synthesis and see if one can find underneath some comn_n patterns among the

successful cases.

We start by making distinctions within the very fuzzy term "science" as it is used in our culture.

At least the following three categories of science, S1,S2 and S3, can be identified and defined below:

S1 = Serendipitous discovery (careful observation by highly trained observer).

S2 = _cience for Iociety (purposive, long-term basic science).

S3 = _,cience for _elf and the institution of _ience.

Next, we turn to determining the relationship of these kinds of science to the motivation or

context for the synthesis research. Here also we define three categories, of which the first two are well

known:

S.P.: Science Push. This is the concept that the pursuit of knowledge in itself leads to (useful)

discoveries.

M.P.: Market Pull. The concept that a need--either in a company or in society--in the

"marketplace" for improving a product or finding a better one leads to the

advancement. S2 science based on such market pulls wouid tend to be narrow in scope

and short term. Much new product development research in industry, today, would

fit into this category.

T.T.: Technology Traction. This is my own term describing the linking of the new research to

a societal need or private market through a specific application or technology.

Such a "traction" from existing or new devices, hardware, etc., provides a feedback

mechanism to the S2 science from the real application. All such research also

57
utilizes all relevant "science on the shelf" which will have accumulated partly

from S3 science. Italso maintains the S2 focus for the longer-term science, and hence

am, in turn,be sustained for longer periods because it is linked to an existing or

definitely needed technology. Much of the longer-term research in industry,

connected to, or directly relatable to a technology, fits into this category. And it is

precisely only this T.T.-S2 research within industry that is by far the most costeffective and productive component of "research" or science. It was this fraction of

the total research spectrum which led to the enormous U.S. technological prowess

up through the seventies. It is not fully realized that it is Japan's clear-sighted

focus on this T-T-S2 research which has brought Japanese industry into a

commanding position in so many technologies. Unfortunately during the fifties and

sixties much of American industry, taking its miscue from U.S. academia, conflated

its S2 and its S3 research. This muddle continues into the present. In the late

eighties it became clear that S3 research supported by industry was simply not

justifiable. Regrettably, however, not only S3 but much T.T.-S2 research has now

been eliminated in U.S. industry demonstration of the ur_ency for clarifying our

terminology, and properly classifying particular research. Figure 6 is a schematic

representation of the T.T. process. In many ways it is the realization of the U.S.

Defense Department's "basic" or "6.1" research. The imminent downsizing of all

industrial research will be followed, in my estimation, by appropriate similar

reduction in S3 academic research. But this will affect all T-T-S2 research also

unless we start making the distinctions very clearly now.

It is clear that these classifications are hardly sharp and watertight, but they are no less

essential for that.

EMPIRICAL ANALYSIS OF LOCAL MATERIALS

SYNTHESIS RESEARCHUSING THESE CATEGORIES

In earlier papers (1,2), I have alluded to the fact that the basic sciences necessary for a scientific

_proach to materials synthesis of inorganic nonmetallics are phase equilibria and crystal chemistry.

In this respect the U.S. is at a substantial disadvantage compared to the U.K., Europe, the former

U.S.S.R., India, etc., since these topics are ignored in chemistry and physics departments and in many

materials departments.

This section of this paper is an attempt to analyze the processes by which successful materials

synthesis research has actually been conducted in this Laboratory. It analyzes retrospectively using

the lens of the categories defined above what actually happened in ten areas where significant

58
innovation in materials synthesis or processes actually took place. Table 1 gives an overview of the ten

subject areas we deal with.

$3

Science J ON SHELF I

(scienc e fo r se if v liii::ii::i::::::::::iliiiiiiiiiiiiiiiiiiiil 'i_

and science) I

Iii,iiiiiii!iiiiiiiiiiiiiiiiiiiiii.i !i!iiiiiiiii!iii!ii!iiiiiii , .............

$1

Serendipity

(= experience and

observation)

Figure 6. Technology traction model of materials science. In many ways this represents the ideal of

what is attempted in the U.S. defense departments 6.1 and 6.2 research.

la. Hydrothermal Processing; lb. Sol-Gel Process

These two processing innovations are dealt with together because in fact the basic advances and

initial "reduction to practice" were completed in one year (July 1948-June 1949). Together they form a

rather clear example of "S.P.," a science-push innovation.

In 1948, hydrothermal techniques had been known for a couple decades as a means of making

hydrous phases. The principal "instrument" was the Morey bomb limited to about 400"-450"C and about

I kbar H20 pressure. The idea of using water pressure to catalyze anhydrous reactions per se or the

hydration of anhydrous phases in the system A1203-SiO2-H20 called for new equipment which could

reach higher temperatures. The design of the "test-tube bomb" and multiplexing of several of them

with one pressure source created almost a perfect example of the kind of "instrument" to which

de Solla Price attributes much of scientific advance. Based on this "instrument," Penn State became the

world HQ for systematic hydrothermal synthesis and phase equilibria work for 2-3 decades. It is

remarkable to note that this design of the hydrothermal "instrument" has not changed for forty years

and the January 26, 1992 issue of Chemical & Engineering News carries on its back cover, a full-page

$9
Table 1. Retrospective analysis of "context" of Roy's ceramic research, 1948-1991.

RESEARCH AREA MOTIVATION STATUS

• Hydrothermal processes S.P. To accelerate reactions Widely adopted worldwide

among oxidesatlow immediately

temperatures

• Sol-gelprocess To make homogeneous On theshelf(O.S.)for

ceramicsforalllab 15-20years

research

• Glass Ceramics

(a)phase diagramfor S.P. Basicstudiesin Utilizedby Coming

Li20-A1203-SiO2 areaknown

(b)metamtableimmiscibility T.T. To beusefulinindustry Pickedup veryslowly

• New zero expansion ceramics T.T. Clear technology- Applications being explored

market pull. Based on wide front after 5-year

on major sciencebase. incubation.

• New methods for fine powders

(a) EDS S.P. Improve options for O.S. 10 years

(b) RESA lab powders Unpredictable

• Clay mineral synthesis S.P. Systematic basic work. Used immediately. Fed

stability. Known tobeuseful into industry.

to oil industry

• Zeolite synthesis T.T.

• BaO-TiO2 phase diagram T.T. Value of basic science Universally utilized rapidly.

to tech. was clear

• Perovskite xl chemistry

• High pressure materials S.P. Opportunity push No application for any results

synthesls/stability (anvils) (based on instrument) from huge worldwide effort.

helped by diamond

tech. pull.

• Design and synthesis of M.P. Apply basic science Strong worldwide impact via

crystalline radioactive waste to obvious societal need regulatory agencies.

Ditto hazardous wastes. T.T.

• Theory and practice of glass S.P. Originally basic Enters general broad stream of

formation In oxides science of above activity.

• Thin films. Si, Ge; diamonds T.T. Pure tech traction Enormous impact on industry

• Concept of SSG-derived T.T. New broad concept in Very rapid entry into science

nanocomposites our area of expertise and technology

6O
advertisementforthesevessels,stillsoldby a localfirm,withtheexactdesignwe optimizedwithina

year or two of ita original development.

The sol-sel process was also bornout of the community's needs in experimental work in oxide

systems at low temperatures. The goal was simple and global: To make atomically homogeneous

ceramic powders of essentially any composition. Without such intimate mixing, in the system being

studied (A1203-SiO2-H20), reaction rates were essentially zero. Necessity was the mother of

invention.

It was clear that mixing via a solution step was the only way in which such atomic scale mixing

could be achieved. This was already in use for precipitating or pyrolyzing to obtain powders, but

gelling ions mixed in solution was the difficult step. To achieve this, I originally used organic

precursors for the first time to mix in SiO2, A1203, TiO2, etc. Later inorganic sois with 20-100 run

particles proved to be equally efficacious. The conceptual advance was the use of a gel step instead c:.:a

glass step (then in common use in high temperature silicate equilibria studies, but limited to glassforming compositions). Here again although it was S.P. research, there was a distinct generic

experimental "need" which was being addressed at the same time. This makes a kind of connection to a

T.T. type research. What is truly remarkable about the sol-gel process is, first, how completely

successful it was. Within a decade our Laboratory files held vials of several thousand compositions in

dozens of simple and complex oxide systems made by several different investigators and described in

dozens of papers. Secondly, it was remarkable how long it took for the sol-gel method to be picked up

by the ceramics community--nearly 15 years in industry and 25 years in academia. This, in spite of the

fact that the large number of papers had been published by the Penn State groups and the world-wide

geoscience community.

2. Glass-Ceramics: This is an Excellent Combination of S.P. and T.T.

My connection to glass ceramic research came about entirely serendipitously because my Ph.D.

thesis was the detailed phase diagram for the system Li20-AI203-SiO2, including the spodumeneeucryptite join. Simultaneously with this study my_olleague, F.A. Hummel, discovered the

extraordinary low and negative thermal expansion of the eucryptite and spodumene phases. Stookey

at Coming, after his doubly serendipitous discovery of the glass ceramic process, of course, utilized

Hummel and Roy's work in making the first commercial glass-ceramics, Comingware.

Thus our S.P. contribution was prior to Corning's discovery of the process, but our further

contributions were strongly pulled by the T.T.process since many other corporations such as Pfaudler

and PPG turned to us for collaboration in their glass-ceramic research. Their goals were met in a very

shorttime.Our subsequentcontribution tounderstandinthe g glass-ceramic processcamefromourphase

equilibria studieson titano-silicate systems.ThusinpureS.P.research,DeVriesRoy , and Osborn(8)

firsttotallyrevisedthephasediagramofthesystemTiO2-SiO2fromsupposedlyhavingzeroliquid

61
immisdbility, to nearly 80% immiscibility. And their work on the CaO-TiO2-SiO2 (9) system outlined

large areas of stable liquid-liquid immiscibility, bordered by large regions where enamel-like glasses

formed. This led me to the key paper (10) on the role of metastable liquid immiscibility as the correct

nucleation step (correcting Stookey's original and sometimes still reported, assignation of the

nucleation step to "ruffle" formation). The two highly relevant phase diagrams are shown in Figure 7.

One of the issues in contemporary synthesis research is the general weakening in the materials

community of the ability to interpret especially more complex phase diagrams and the absence of

classical crystal chemical knowledge.

' " _ 183q, O I • •

• I • _O Ilta_" ,

IIOC • .I • " o1"/00:10 :-- • -_

- • • II "v

o• • • •

Z t71_ •

1700 •

-\ • Rut,_¢_r_dLrquld

tll : .• • • • 0 e • • • •

E 160C an_l • * • *

:'. Liq_ ee 1 50 _"4 • . , II |

Crastob<_htancd Ruble * *

as°_ioi_•o _oJ 3*o ,'o sto 6I0 _oI 0 o_ 9_ T, =

Weight [%]

(I) _. Spectal Structure Liquids

\ (2) =

_Two Liquids', ,-.-..L.

,I _, // ;L --.\ _

I i

I I \\ // :J \\ \

I \ / ,. \

,l L__ \\ // Metoist°ble "'

I_ _._ _.,_-

I Metosfoble Two L0quods i Two Liquids \

Figure 7. Therole of liquid-immiscibility in TiO2-rich silicate melts was hinted at from the phase

diagram for the system TiO2-SiO2 (and CaO-TiO2-SiO2not shown) and metastable mixing

of two liquids explicitly identified as the nucleation step in such glass ceramics.

62
3. Zero-Expansi_ C_ics: A Model T.T.Success in Synthesis

This is one of the clearest examples of a technology traction development. Because of our

involvement with the initial discovery of the major zero expansion materials of commerce, the lithium

aluminosilicates ([.AS, see above), the Air Force Office of Scientific Research approached us to try to

develop a new material with thermal expansions even closer to zero at -100"Cfor space structures. Here

was a clear market pull; well-established technologies existed that could use such materials and while

much new data on new materials had been accumulated in the 40 years since the LAS discovery, no

other crystal structure had even begun to compete. Our approach proceeded sequentially:

I. Modifying, compositionally, a known near-zero a material: cordierite. By using solgel processing we were able to introduce more Ce than hitherto achieved and

obtained some very acceptable 10w a phases (see Ref. II).

2. "Theory" was totally useless in helping locate an inherently anomalous structure. By

serendipitous observation, using our own empirical guidelines (structures articulating

strongly (4+ and 5+ valent cations), bonded polyhedra around large "holes") we

discovered the low-o_ properties of a very well known structural family, the NZP

(NaZr2P3012) or _ (Ca0.sTi2P3012) family (Refs. 12-14). We were able to show

that a dozen different compositions completely bracketed the low+ and low- a range,

with extensive solid solution allowing every value in between (Figure 8).

THERMAL EXPANSION OF [NZP]-FAMILY

+.00._ =.c_j_q._

3. CaZr2TI2P6024

4. NaTI2P3012

S. Na3Cr2P30t 2

+.002 6.

?. N13/2Zr158P3012

|. C8_,4NI 1.2Zr2P3012

I. C,II1,.4NI 1,_TI2P301 |

"4".OOi 10. N13,2Zr3/2Crl/2P3Ot|

_L O0 ,0 L

Z

-.00i 7

-.OO2 6

'4

I I I I I

,50 IOO 150 200 250 300 350 400 450 500

Temperature (°C]

Figure8.

63
Success with this objective led the AFOSR to set another:, eliminate the

anisotropy of a if possible. There appeared to be no rational process to eliminate the

anisotropy of a in the hexagonal phase, since it is by averaging a negative a in "a" or

"c" direction with a positive a in the "c" or "a" direction, that we get zero. But

another serendipitous observation (that in Sr0.sZr2P3012 the "a" and "c" axes were

reversed) led us to the "zero"-a, "zero"-anisotropy Sro.sCao.sZr4P6024 family which

also turned out to have melting points above 1700"C(14).

3. The third objective given to us of making a ferrimagnetic NZP phase to absorb radar

signals (market pull) appeared like a reasonable challenge due to the fact that most

3d and 4f ions can be accommodated in the structure. Yet,in spite of very extensive

experimental substitution, this approach did NOT work. We were unable to

synthesize any ferrimagnetic NZP phase. Instead, we had to design a

microcomposite of two thermodynamically compatible (determined experimentally)

phases, one with a negative a (Na4Zr2Si3012) and a ferrimagnet (YIG) with a

positive c_.

The NZP family of controllable low expansion ceramics is an outstanding

example of systematic T.T. materials synthesis. There are obvious technological

opportunities for,such materials but the actual penetration into established markets

will be decided by many other factors outside science. This example is almost a

textbook case of T.T. practice at its best--which is, of course, NOT universally

successful. Itdemonstrates the value of having access to an "on-the-shelf" science

base--in our very long experience in the field. And it demonstrates that "theory" is

not of much help in designing new materials. And finally, it proves the value of

serendipity based on careful observation by experienced observers who can recognize

anomalies and pick up hints in not directly related literature.

4. Processes for Making Fine Powders (S.P.)

In the early fifties in parallel with the sol-gel processes we had also experimented (15) with

spray pyrolysis of the mixed solutions. By a decade later Ruthner (16) had exploited the same process

and made it into a successful commercial process formaking ferrite and alumina powders. We showed

that the EDS or DMS (decomposition of misted solutions) process had both general and special

applications in powder preparation in the laboratory also (17). However, in spite of the enormous

interest in ceramic powders, few really new methods have appeared in decades. The laser pyrolysis

approach had proved to be very limited in the range of ceramic powders which can be made and very

costly. This "need" in science and technology provided the very diffuse pull for our work. The concept

of the "reactive electrode submerged arc" (RESA) (modified after the classical work of Faraday on

64
makln 8 bold sots) works by striking an arc under water, solutions, organic liquids, silicones, etc. The

apparatus is shown in Figure 9.

The RESA process has proved to be quite general (18) for making pure submicron powders of

oxides, carbides, nitrides, and very recently (unpublished) of new crystalline carbons related to

BuckyhaUs. It represents a successful science push development, not yet linked to a technology, but has

obvious potential for special application. And a recent development, the so-called "combustion

synthesis" developed in India, appears to be another really novel process (19) for making fine powders.

._Gomputw

Interface

|

IPrlntw 1

Figure 9.

In all such S.P. advances that we have made to date an important common characteristic is the

discontinuous break with the past. S.P.advances in synthesis or processingoccurfar from mainstream

activity and therefore are very likely to be missed and ignored for years. This again argues the case for

scouring the literature on the periphery of one's interest to pick up hints or related advances which

may have been already demonstrated in other connections.

5. Clay and Zeolite Synthesis (S.P. + T.T.)

We have noted that the first application of the hydrothermai instrumentation was to the system

AI203-SiO2-H20 for the catalysis of subsolidus equilibria among anhydrous phases, and studies of the

synthesis (and stability) of the hydrated clay minerals (kaolinite and pyrophyllite) in the system.

With that beginning, we launched a ten-year emphasis on the synthesis and stability of all clay

65
minerals first in the system AI203-SiO2-H20 and later with the systematic, step at a time, addition of

alkali (K, Na) and alkaline earth (Ca, Mg) oxides as an additional component.

Figure 10 gives but one example of two dozen of the kind of detailed phase equilibrium "maps"

(this one for the system Na20-AI203-SiO2-H20) which we produced, at enormous personnel cost by

today's standards, as the permanent template to guide all such synthesis efforts. Alongside this S.P.

science, we were able, for the first time, to create entire suites of di-octahedral (Mg) and tri-octahedral

(Al) sets in the 7_, 10A and 14_ mica and clay mineral families. Both expanding and non-expanding

4CO- 525" _25- 580" 5" 00"

_C C C C

Figure 10.

66
10._ minerals of completely controlled charge density were synthesized in various systems including

exotic ones involvin 8 Ni, Ga, Ge, Zn, etc. The demand for this depth of basic work was, of course, due to

a T.T.linkage to the petroleum industry's interest in clay minerals both as stratigraphic markers and as

drilling muds.

Even in the mid-fifties we were able to even control the morphology of micron size powders from

high aspect ratio fibers, to equant hexagonal flakes [see Roy and Roy (20)] by compositional

manipulation (i.e., AlTMand AlVIsubstitution for MgVl and siIV).

Following the systematic clay syntheses, we pursued the same strategy on the known major

zeolite families. Systematic detailed studies of the synthesis and stability of the phillipsite,

analcite and mordenite-wairakite families were carried out in the hydrothermal regime. Even after

the Union Carbide discovery of zeolites A and X, due to the highly proprietary nature of the work, in

spite of our obvious expertise, we were not invited by industry to be involved in the race to create new

zeolites, i.e., there was an insufficient T.T. element to channel our synthesis capabilities into possibly

fruitful directions. Our zeolite syntheses therefore "stayed on the shelf."

6. Perovskite Electroceramics (T.T. and S_P.)

This area constitutes a first-rate example of using all our knowledge base to put materials

synthesis of an important new family of materials on an intellectually sound basis. The U.S. Army

Electronics Command recognized the need (a) to grow single crystals of BaTiO3 and (b) to look for

similar phases whichmight be even more useful. In the early fifties there was enormous research

activity in applications of such phases to capacitors and the technology traction feedback loops were

active and rapid.

For task (a) it was realized that a reliable phase diagram was essential. Figure 11 shows the

phase diagram for the system BaO-TiO2 which was determined by us, the first such detailed high

temperature equilibrium diagram of a titanate system with any degree of reliability. And it was on

the basis of this diagram that Linz et al. at MIT were then able to grow the first reproducible large

single crystals of BaTiO3. Here was S.P.-T.T. coupling across institutions.

For task (b), we worked in the V. M. Goldschmidt tradition of empirically determining the

structures of a large number of rationally engineered (with respect to composition) candidate phases.

From the structural data we were able to provide structure field maps for future materials synthesizers

in search of a particular phase. See the book by Muller and Roy (21) for a compilation of such SFM for

all ternary ceramic stnictures. Our crystal chemical study on the perovskite structure (22), for example,

besides lists of very much-used substitutions, shows the first of the phases Ba3NiTa209 prototypical of

the PMN (Pb3MgNb2Os) or relaxor ferroelectric materials, which have now become possible successors

of BaTiO3 in certain applications.

67
Figure 11. BaO, TiO2.

7. High Pressure Materials Synthesis: Pure S.P. Syntheses with no Spin-off

Although in the mid-1950's we were the leading laboratory in the hydrothen'nal high pressure

regime (up to a maximum of say 10kbars) we had failed to synthesize any of the high pressure minerals

(kyan/te, jadeite, pyrope, and of course diamond) mineralogists had set their sights on. With the work

of Coes at Norton and Hall at GE, two new kinds of apparatus--the piston-cylinder and belt--were

developed which enabled one to reach the P-T regime for synthesis of all minerals occurring on the

surface of the earth. Again, the "instrument" played the key role.

Yet these apparatuses were extremely expensive and time-consuming to operate. Hence we chose

to develop instead Bridgman's simple and compound anvils as a simple "instrument" for use in

materialssynthesis, at very high pressures(-,200kbars)and modest(-500"C) temperatures. Our

68
opposed-anvil apparatus proved to be a very effective and reliable tool in materials synthesis [see

Dachille and Roy (23-2,5)]and also became widely used. Indeed later on the utilization of single

crystal diamond as the anvils by van Valkenburg at the National Bureau of Standards led eventually

to the work of Mao and Bell at the Geophysical Laboratory in reaching megabar pressures at ,-2000"C

temperatures to study in-situ transformations especially those related to the interior of the earth. The

diamond anvils have not produced many new quenchable phases.

Our opposed-anvil apparatus allowed us to synthesize--by 1970--more new high pressure

materials (which could be retained at ambient conditions) than all other laboratories combined. On

the other hand, our own crystal chemical studies on the effects of pressure showed that there was no

scientific reason why high pressure would lead us to new structures with extraordinary properties. The

logic of each of our structure field maps showed that whatever structures could only be achieved with

pressure at a certain composition, could often be created at I armpressure merely by changing the

composition. Hence nothing especially interesting should be expected among high pressure phases with

the single exception of diamond which is the unique extrernum in composition in the middle and top of

the periodic table.

In any event, we were proved correct. No product of any value, no technology, has emerged from

the extensive worldwide high pressure program. This was quintessential S.P. materials research

which led only to "science on the shelf"; in geophysics the results proved to be very stimulating to new

hypotheses about the mantle.

8. Materials for Radioactive Waste Immobilization; Excellent Example of M.P. (T.T.)

This area is an extraordinarily apt example to illustrate the relationship between society's

needs, and universally expressed desires from the world of science and technology, and how the U.S.

system of R/D actually responds.

Reading in the general press about the enormous public anxiety about nuclear waste and the

national plans for the solidification of radioactive waste, it became clear to us before 1970 that modern

ceramic materials research could be brought to bear on the problem. To our astonishment, in spite of the

enormous public and vocal "market pull" in this very visible area, quite literally zero research was

being done on examining alternative solids in which to contain the radionuclides. The design scenario

in 1976 (more or less tacitly adopted by all nations worldwide) was to melt the radionuclide mixture

into a borosilicate glass, fill the molten glass into steel canisters 3m x lm diameter, and dispose of these

in selected rock formations (either salt or shale) with equilibrium centerline temperatures of 500"C (or

more).

In a few months of preliminary work we established two key facts:

I. That the projected glasses would totally decompose in times of about I week if exposed to any

water at the proposed repository temperatures. The one-page paper we published in Nature

69
(26) had probably more technological impact than any single equivalent recent scientific

paper. It forced every nation to redesign their waste form by diluting the radioactive content.

Thus, this multiplied the volume of glass waste 3-4 times, and hence increased the projected

repository area and cost proportionately by billions of dollars.

2. In the second paper [McCarthy et al. (27)] we proved that an ordinary multiphase crystalline

ceramic (as in a porcelain or brick) could be made to incorporate all the radionuclides of

reprocessing waste.

Only after this S.P. demonstration on two fronts was the M.P. strong enough to actually start a

modest national research program on alternative solidification. Yet, and this is enormously significant,

since there was no technology in place, the M.P. could only sustain the program for five years. This

shortlived research effort (worldwide) on novel ceramic waste form synthesis produced notable successes

including Oak Ridge's Fuetap cement, Penn State's first tailored ceramics and Australia's synroc subset of

the tailored ceramics. (See Table 2 for details.) While it lasted, excellent science started to provide the

kind of data the technical community and the public wanted, the scientific data on synthesis stability

and leachability and the related data needed to make a judgment on quality of product and costs with

these alternative forms [Roy (28,29)]. But the Reagan Administration decided--since alternatives would

take time to study--to proceed with the most advanced-in-engineering form--borosilicate glass--in order

to "complete the job" on a totally unrealistic time schedule. A decade later, in an area where the total

costs will run into the hundreds of billions of dollars, no glass technology exists, no alternative waste

forms arebeing studied nor waste form options for commercial waste. And we areno closer to acceptance of

any solution and this materials component of the research is not yet done. So much for the efficacy of M.P.

in the absence of T.T. in sustaining synthesis research.

9. Ceramic Thin Films From Glass Formation to Diamond Films (S.P. to T.T.)

When we started our research on thin films in the 1960's probably few ceramic thin films existed

in technology; the science was non-existent. Sol-gel derived noncrystalline films were starting to

appear as coatings on windows, and MgF2 coated lenses were being modified by other oxide optical

coatings on glass.

Our interest in the thin film form of ceramics derived from the vapor, was that it would offer a

new way to create noncrystalline phases from compositions which could not normally be so rendered. By

(splatting and) sputtering we were in fact able to create a wide range of such new glassy materials. But

then the interest shifted to being able to prepare unique thin film glassy or crystalline ceramics

(including Si, Ge, CdS, etc.) by utilizing RF sputtering onto virtually any substrate. This gave us the

ability to create very interesting new materials such as hyperdense noncrystalline Ge (30-32) which

could be crystallized "explosively" at room temperature by a mechanical or thermal trigger pulse. It

also started the work to determine the processing conditions to yield thin film crystalline perovskites

7O
Table 2. Ceramic radionuclide containment.

Possible Radionuclides

Structure Illustrative and other f.p. incorporated

Type Compositions Total Major Minor

A. "Insoluble" Minerad-Modelled Phases

[Monazite] (Ln, AI3+)PO4 Ln,An

An4+SiO4

(Ca0.5An0_.5)PO4

[Perovskite] (Sr,Ba)(Ti,Zr)O3 Sr Ru,Tc4+ Ti,Cs,An,Ln

[Poilucite] Cs,A1Si2o 6 Cs

[Spinel] (Ni,Fe)(AI,Fe)204 Tc4+ Ru

[Apatite] (Ca,Sr)5(PO4) 3 Sr Ru

[Scheelite] (Sr, Ba)MoO4 Sr Tc6+ Ln,An,Ru,Te

[Feldspar] SrAl2Si208 Sr

[Fluorite] (An, Ln,Zr)O2+x Ln,An Sr

[Zirconolite*] CaZrTi207 Sr Ru

(ordered fluorite)

[Rutile] RuO2 Ru,Te

[Fcc Metal] Pd Pd

[Hollandite*] BaA12Ti6016 Cs

[Nepheline] NaAISiO4 Cs(?)

[Barium-aluminate* Ba(AIFe)2Fe8Ti13038 Cs

iron titanate]

[Magnetoplumbite*] BaFe12019 Sr Cs

B. Tailored Ceramic Assemblages to Accommodate PW-4b Waste Ions

High concentration of (i) + scheelite + fluorite + pollucite + apatite + corundum

fission products (ii) + scheelite + fluorite + pollucite + zircononia + monazite + corundum

(iii) perovskite + fluorite + pollucite + monazite + spinel

Low Concentration of Zirconolite + perovskite + hoUandite

fission products

i i

(33)lespecially high K materials such as BaTiO3. Sputtering also provided an easy route to

synthesize a whole range of crystalline or noncrystalline solutions of ceramics in one run simply by using

two targets or mixed targets (32).

When the synthesis of BaBiPb oxide superconducting perovsl_ite was announced by Sleight et al.,

we began the first systematic study to attempt to raise the Tc by crystalline substitution, The sputtering

process for producing the first crystalline ceramic superconductors was described by Gilbert, Messier and

Roy (33) nearly ten years before Geballe et al. (34) reported on similar sputtered films of the 1:2:3

composition perovskite.

71
Up to this point our substantial thin film effort had been driven mainly by S.P. Some T.T. work

had been incorporated in attempts to apply these techniques to electrochromic films of WO3. But it was

in 1985 that a radical transformation occurred when I personally encountered the successful CVD

diamond film work at NIRIM in Tsukuba, Japan, and at the Institute for Physical Chemistry in Moscow.

After convincing skeptical agenices, and supported by the Office of Naval Research in a T.T. model,

we drove the system into a major effort of understanding the process of making CVD diamond thin films

(35,36) and transferring our knowledge about them effectively. Our diamond film synthesis effort has

been comprehensive, to be able to compare all the methods for diamond film synthesis; and evaluative,

not advocating one or other method or explanation or theory. This stance has allowed us to observe how

slowly indeed real progress is made in materials synthesis. Today after hundreds of person years of

research, the original Derjaguin and Fedoseev discovery (theory) of using atomic H to dissolve

graphite and retain diamond (37) lies at the heart of every process in use (see Review 35). The original

Japanese utilization of microwave plasma (and hot filaments) still is the standard method (38). The

most novel addition has been Hirose's (39) utilization of the oxy-acetylene torch. The extensive

theoretical and modelling research--as in all cases of materials synthesis--has proven to be so far

without any redeeming social or scientific value. Research managers must face the empirical reality

that here, as in 1:2:3superconductors, in ferroelectrics, in new magnets: theory and models have

provided zero guidance to any synthesizer.

Our local research contributions so far include the creation by Badzian et al. of rather perfect

homoepitaxial diamond films which, when diamond was featured as the first "Molecular of the Year"

in 1991 graced the cover of Science, and also some of the first diamond electronic devices (40) based on

such films.

10. Nanocomposites and Their Formation Via the SSG Route (S.P. + T.T.)

Ina series of presentations in 1983 and 1984 1presented (41) an approach to the synthesis of an

entirely new class of materials which I termed nanocomposites. My argument ran as follows. All

traditional materials synthesis and processing techniques--sintering, melting, etc., must allow enough

kT energy to equilibrate the total composition involved on at least the scale of micrometers or tens of

micrometers.

In other words, in known multicomponent-single phase and multiphasic materials (except certain

alloys with post formation heat treatment) the size of the phases are at least on that scale. On these

scales the two phases do not interact with each other with respect to chemical, structural, and most

electrical, optical and magnetic properties. Bulk properties are averages or additions. If we could

reduce the scale of mixing--I argued--to the nanometer dimension, we would be able to create a

hybridization of properties of two phases. Moreover, if one could use low temperature processes to

synthesize such "nanocomposites," radically different phases, very far from equilibrium with one

72
another, could be mixed with one another. This change of direction for SSG research has been described

in context in a review (42). At approximately the same time E. Gleiter at Saarbrucken was reporting

his own work on the very interesting advantages of simply reducing the size of particles of a single

pha,_ to nanometer dimensions (43).

Our earliest attempts to create such nanocomposites were to use two target sputtering, to combine

A1203 with Au, or platinum with teflon or polyimids. These gave rise to interesting combinations of

1-2 nm size metal particles, some with 5-fold symmetry (44) in an insulator matrix. The process,

however, was tedious and the only form which the materials appeared in was as thin films.

It was then in 1983 that I re-entered the world of solution-sol-gel research which worldwide was

now addressing universally the goal I had set for myself in 1948, viz: to make maximally homogeneous

ceramics. My new goal was to create maximally heterogeneous ceramics (i.e. with the maximum

interface area of two or more phases) by the SSG route (see Ref. 42). In the next several years, making

nanocomposites became a major research area in our laboratories (45-47). Our Japanese colleagues held

the first international conference on the topic in 1989 (48) where vet 3) interesting new composites,

created and studied, were reported on. Our original efforts and these results signal that nanocomposites

may well have as substantial an impact on the field of ceramics as did the original sol-gel work.

Our own research in SSG-derived nanocomposites has demonstrated that--by the simple

universally accessible expedient of mixing two sols---one can achieve the entire set of processing

innovations shown in Table 3. Two interacting phenomena explain all these chemical-structural

effects, the effects of chemical heterogeneity and structural heterogeneity (Table 3).

Table 3. Nanocomposites will certainly offer a family of new materials with improved properties in

various applications. Our work has demonstrated such improvements in the chemical/

structural area. The work of others has started to provide examples of real improvements in

other properties.

What can nanoscale mixing achieve? In different properties?

Chemlcal/Structural * Control of phases formed

• Lowers reaction and sintering temperatures Our

• Control of microstructure studies

• Control of morphology

• Via solid state epitaxy

Mechanical • Five-fold increase in strength as size goes from 100-20 nm

• Suprahard (>diamond?) materials

Work

Optical • Ten-fold increase in luminescence of

others

Electrical • Change in fundamental conduction

Magnetic • New super-, para-, and ferri-magnets

73
1. Compositional Heterogeneity

Such composites may make possible exothermic and rapid reactions of two intimately mixed

phases far from equilibrium with each other. For example, one may contrast these classes of mixtures

of, say, A1203+SIO2 at the mullite composition (or ZrO2 + SiO2 at the zircon composition):

(a) Mixed 325 mesh powders of A1203 and amorphous SiO2.

(b) Single homogeneous liquid solution made into an atomic scale homogeneous (one phase) solid

(xerogel) solution.

(c) A composite of 1-10 run size particles of A1203 and SiO2 (d/phasic xerogel).

Mixture (a) heated at, say, 1250"Cfor 1 hr will show no measurable reaction by XRD, and little in TEM

except perhaps in the reaction rim around some of the grains. Mixture (b) would show a high

percentage of formation of mullite but mixture (c) would show the highest percentage of weUcrystallized mullite.

The explanation lies in the fact that the diphasic xerogel has the advantage that the reaction of

A1203 with SiO2 is auto-catalytic because it is exothermic, due to the _Hreaction. In the monophasic

gel, the reaction rate is much slower because the only AG available to drive is the AH of the

noncrystalline --_ crystalline transition. Generically compositionally heterogeneous nanocomposites

utilize the heat of reaction of the metastable _ stable assemblages.

2. Structural Heterogeneity

The idea of seeding gels with desirable structural templates goes back to the very first year

(1948-49) of the discovery of the SSG process and hydrothermal process (49). We used 10-50_ size

crystalline templates as one phase and noncrystalline xerogels as the other. In these early papers we

demonstrated the successful overgrowth on such phases as diaspore, ct-spodumene, benitoite, etc., in

hydrothetmal reactions. Here one could assume the second phase with the "right" crystallography

was serving as an epitaxial substrate for material transported via the liquid phase. Thirty years later

crystallographically seeded xerogel nanocomposites showed remarkable effects on the kinetics even of

solid state reactions completed in minutes or hours.

3. Combined Structural and Compositional Homogeneity

An additional wrinkle in utilizing such composites is to make them tri- or tetraphasic and

combine both the compositional and structural inhomogeneities in the composite.

In the last 8 years we have demonstrated the large effects which can be caused on materials

synthesis by these simple experiments in many systems: alumina; mullite; zircon; thorite; cordierite.

Figure 12 is a schematic summary of the temperatures to achieve equivalent formation of ZrSiO4 from

74
various mono-, di- and triphasic xerogels. The advantage is clearly very substantial: lowerings of

about 250"-300"C.

Solid-State Epltaxy

Finally, in the early diphasic work we unequivocally established the fact that the efficacy of

structural di-phasicity (seeding) was due to crystallographic epitaxy. This was done by using seeds of

different structure and demonstrating that only the one with the structure of the product phase was

effective. The effects could not be associated with just overall heterogeneous nucleates (46,49).

However, another approach provided complete proof of the phenomena of solid state epitaxy. In

recent papers (50) we have grown very highly aligned crystals of the product phase (TiO2, SrTiO3,

A1203, PZT, PMN, etc.) onto large (cm size) single crystal substrates of the same phase. Indeed

utilizing the "solid" state epitaxy principle, it has been possible to crystallize albite (NaAISi308)

from a di-phasic gel made from its own glass with crystalline albite seeds. This is possibly one of the

most difficult glasses in existence to crystallize (51).

We have also shown that by using the appropriate crystallographic template one can drive the

reaction to different products-either metastable or stable assemblages (e.g., ThSiO4 can be

crystallized at 1400"C to either the huttonite or thorite structures. And by controlling the composition

one can control the morphology of the final product phase (52).

Crystallization begins in ZrSiO4 at

Compositionally

o

Homogeneous Nanocomposite

0

O 1350"C 1175"C

ll00"C 1075"C

O

Z

Figure 12. Efficacy of nanocompositing in starting material in lowering reaction temperatures in

various mono- and di-phasic gels. The reaction of crystalline ZrO2 and SiO2 would be very

small at these temperatures.

75
Outside our work on chemical structural effects we can see that compositional and s_ructural

engineering at the nanolevel is certain to become a routine powerful tool in ceramic processing from the

results reported in Ref. 48. No better demonstration can be found than in the dramatic results achieved

by Niihara et al. (53) in all the mechanical properties of engine ceramics (A1203, SiC, sialon) by the

use of nanoscale dispersions of second-hard phases.

NEW MATERIALS SYNTHESIS: FUTURE DIRECTIONS

SOME BLIND ALLEYS: CONTROLLED DESIGN OF NEW MATERIALS

In Figure 4, I summarized the capability we have to create new materials. It is self-evident that

in any mature technology, the combination of two or more materials always will do better than one. It

is well established for all mechanical applications that composites do vastly better than single

phases. The initial success of discrete silicon devices was soon eclipsed by composite structures on a

micrometer scale of the chip technology. Optical fibers are all graded composites.

But what is the potential of synthesizing by design a completely new crystal structure, at the

unit-cell level with desirable optical, magnetic, superconducting properties? Again, however hard it is

for the scientist and the manager to accept, the empirical track record is unassailable. Our capacity is

nearly zero. No better example can be found than the worldwide search for new superconductors. After

the first public announcement by Zhao (54) of high Tc phases in the system Y203-BaO-CuO found by

sheer empirical mixing and measuring, it was a matter of one or two person weeks of work in several

different laboratories in IBM, AT&T and Bangalore to isolate the YBa2Cu30 7 phase. But since then,

after some thousands of person years, with full benefit of theory, with no shortage of equipment or

money, the world's synthesis communities have found exactly zero really new structures outside the

'perovskite + Cu-O layers' family. The recent serendipitous discovery of superconductivity in Rb3C60

and Cs3C60 Buckyball compounds, confirms the total scientific ignorance in our theory of synthesis of

really new phases with desirable properties.

The original serendipitous discovery of the magnetic rare earth garnets in 1954 by Keith and Roy

(55) did not equip us or any of the enormous range of extremely competent magnetic materials groups in

the world to design or even to find, in 40 years, any comparable 3 sub-lattice structural families with

similar ferrimagnetism. The new rare earth iron borides again were.a unique and serendipitous

discovery with little transferability of knowledge, and again, surprisingly, no follow-on success.

In 1992 we must therefore admit that it is not possible to synthesize any new phases with

different crystal structures, with specifically desired properties, based on any theories or models. Even

serendipitously discovered new materials provide but little empirical guidance for tinkering with

neighboring compositions and obvious substitutions.

76
BLIND ALLEYS 11..BIOMIMETICS; BIOGNOSIS

In the last year or two as the publicity surrounding quasi-crystals and cold fusion subsides, a wave

of publicity has been created to suggest that one might make useful new materials by mimicking nature.

The extraordinary gullibility of the present-day scientist community is evidenced in the reception to

this idea since it is never presented based on a single, even modest, achievement. Yet, surprisingly no

synthesis of any material with any extraordinary or useful property has been reported by all those who

advocate the value of this route to new biomimetic materials (56). To the best of our knowledge, only

one single useful material which can by any stretch of the language be called a biomimetic material,

has ever been made. This is the replamine process by E. W. White et al. in this laboratory, who

mimicked a South Sea coral in its key external morphology of a 3:3 connected structure. From this they

made both biomaterials for dental and bone implants, and exactly mimicked the morphology of the

same materials (see Fig. 13) using them as templates for making biological and electroceramic

composites (see 57-59).

The implication in the oft-repeated appeals, that Nature, which optimized its materials for

low temperatures (<50"C) and aqueous environments, would provide some miraculous templates for

mimicking to make materials for airframes, or superconductors, or magnetic or optical materials,

smacks, as Professor Jonathan Black of Clemson (60) remarks, of a return to the philosophy of

"vitalism." The empirical facts are exactly the reverse. Materials science and technology have

Figure 13. Three-dimensional SEM photograph of original coral (var. Porites) made of CaCO3 on the

left, and the exactly copied biomaterial on the right after transformation under

hydrothermal conditions to apatite. This is the only example of a commercialized

biomimetic material known.

'/7
provided enormous help from non-bio-derived materials for the human biological system: Metal,

polymer and ceramic parts for teeth and bones; polymers for skin and other soft tissue, etc., are

ubiquitous and unlikely to be displaced to any large extent by bio-derived solids.

This is not to say that the materials designer and synthesizer may not have much to learn from--

not necessarily to mimick--nature. Ihave termed this process biognosis. Here again one must note that

the extraordinarily detailed studies by the three or four British schools, of Vincent, Currey, Mann,

Birchall, etc., which have described biological hard tissue in great detail over the last 10-20 years

have yet to synthesize their first novel material based on such learning. Ifbiognosis is to offer any

help in synthesizing materials, it is clear from the record that the experts have not found it. Very

recently my colleague, R. E. Newnham (64), has ingeniously learned from the grunts generated in fish

bladders, and the sound receiving systems of bats, to design and prepare successful composite transducers

utilizing the same principles. These are the only biognostic derived "electronic" materials known to us.

Biomimetics as a major design route for useful materials is not likely to be of significance outside of

biomaterials, and excepting for White's work (op. cit.) has yet to record its first success.

SUCCESS STORIES: I. LANXIDE

The history of the development of the directed metal oxidation process by the Lanxide

Corporation is one of the most interesting success stories of innovative materials synthesis. For the first

time in human history a process involving a reaction of Liq + vapor _ solid was used to make useful

materials. The ceramic matrix composites produced were the largest, simplest to make, and had many

unique properties. The degree of innovativeness of the discovery can be judged by the fact that the

corporation has filed nearly 3,000 patents worldwide in about six years and most are issuing with little

or no challenge. Yet more than five years after the public announcements of the process (61-63) it is an

extraordinary phenomenon that no more than one or two other groups in the entire world seem to have

embarked on research in this process. Why? The only sharp difference from other fields such as high

Tc superconductors, cold fusion, quasi-crystals, Buckyballs, is the total absence of deliberate publicity in

the science press or newspapers since the company did not want such.

Table 4 shows the range of compositions of metal, ceramics, and reinforcements which canbe

incorporated into Lanxide composites. Table 5 shows some of the properties attained in some of these

CMC. The second generation development by Lanxide of the metal matrix composites also made by this

method bodes well for directed liquid metal oxidation--one of the most significant single synthesis and

processing discoveries of the post-war era.

78
'Fable 4. Examples of LanxideTM ceramic matrix systems.

Parent Metal Reaction Product

Aluminum Oxide, nitride, boride, titanate

Silicon Nitride, boride, carbide

Titanium Nitride, boride, carbide

Zirconium Nitride, boride, carbide

Hafnium Boride, carbide

Tin Oxide

Lanthanum Boride

Table 5. NicalonTU/Al203 mechanical properties.

Flexural Fracture

Temperature Strength Toughnc_ss

"C MPa MPa_/m

("F) (k.s.i.) (k.s.i. i%F_,)

R.T. 461 + 28 (8) 27.8 _+4.6 (3)

(67) (25.3)

1200 488 + 22 (12) 23.3 + 2.7 (3)

(2192) (71) (21.2)

1300 400 + 12 (4) 19.2 + 2.8 (3)

(2372) (58) (17.5)

1400 340+ 11 (4) 15.6 + 3.7 (3)

(2552) (49) (14.2)

SUCCESS STORIES: ]rl. NANOCOMPOS1TES: A MAJOR FUTURE ROLEIN SYNTHESIS

In the section above I referred to the real success story found in the chemical reactivity of

nanocomposite powders themselves or when used as starting materials. This nanocomposite principle

can be carried to the next hierarchical level of structure.

My argument above has been that we cannot purposively design new phases at the unit cell level.

At the same time we have learned to design a whole world of composite materials. Initially the only

application was for superior mechanical properties. In the 1950-80 period, a strong iterative process.

between technology and society has led to a more or less routinized capability to "synthesize" novel

composites for structural uses.

However, the design of microcomposites for electrical, magnetic and optical properties was

decades behind. While every semiconductor device is today a precisely architected composite, the

different elements of the composite are used for their different properties. They do not interact to

79
enhance one property. In the last decade L. E. Cross and R. E. Newnham have designed from first

principles and created whole families of electroceramic composites. These have been model examples

of very fruitful T.T. research for over 15 years. The properties of such composites, e.g. the pioneering

polymer-PZT transducer, are often orders of magnitude better than the separate components. The paper

by Newnham (64) provides a magisterial overview of the state of this art and gives the theoretical

basis for this new thrust. It shows clearly why the future of synthesis will belong to such micro-nanocomposites in the near-term future. Although no other families of applications have been analyzed

and treated so thoroughly, similar composite materials are now appearing in magnetic powders and

optical intercalates (65).

LOOKING AHEAD IN CERAMIC SYNTHESIS RESEARCH

Some time ago C. F. yon Weizsacker, the physicist-philosopher, made the case (66) that

thermodynamics was not symmetrical with respect to time. We cannot extrapolate from the past into

the future even in fundamental physics. Prognostication must be based on the past record and any known

constraints in the future. I have made the case (67), following Victor Weisskopf of MIT and Gunther

Stent of Caltech, that useful and utilizable overall fundamental "scientific knowledge" is finite and

that humankind is rapidly approaching the asymptote. Recently David Mermin (68) has made a more

radical case that little new fundamental physics has been discovered since quantum mechanics.

What do I foresee in the field of materials synthesis and processing which has suddenly been

singled out for policy attention in the U.S.? First one must exclude the absolutely certain flux of

serendipitous discoveries from any analysis. However, the distribution of the flux, number and

significance of serendipitous events may not be compared to the number and size of meteorites striking

the moon or earth, because scientists are more like beachcombers going over already well-combed

beaches. Moreover, contrary to glib assertions about the great value of new analytical tools and new

computer capabilities, these are of little use and almost certainly will prove to be of negative value in

really new syntheses. The major recent "discoveries": 1:2:3 superconductors, the diamond films,

Lanxide, Buckyballs, putative cold-fusion, required only the most modest apparatus available in most

laboratories a century ago. Large instruments have historically proved to be idea-sinks, not idea

sources. Of course, second generation materials engineering by, say, MBE machines, will be valuable.

The two spectacular successes in materials synthesis of the postwar era were the introduction of

two active classes of materials: semiconductors and polymers. These step functions can never be

repeated in scientific or technological significance. There are no more classes of materials left. The

next set of discoveries will involve replacements of existing materials by others with superior

performance. In the field of ceramics, since WW II, we have had entire industries such as the magnetic

ceramic materials from the spinels to the garnets to SmCO5 and the NdFe borides; the BaTiO3 and PZT

80
capacitor and transducers, the various phosphors, the zeolite and other catalysts, and the optical

fibers as the volume and dollar leaders. The field is much more crowded now, so that entirely new

materials for new fuz_tions are doubly unlikely, and replacing an existing material is technologically

very difficult indeed.

Hence in looking ahead one has to be very careful to analyze the impact of the new data one

prese-' ,.s. In this connection, I will contrast two documents on the past and future of materials

technology. The U.S. National Academies produced, after four years of committee work, the Materials

Science and Engineering Report (69). In this report, we find a set of graphs depicting the enormous

program which has been made in the improvement of the desirable properties of materials by

serendipitous discovery or science-based engineering. Figure 14 shows four examples from

superconductors, magnetic materials, etc. But a study of these figures forces one to a very important

conclusion about future materials synthesis research: It has a very short life expectancy. In 1979 in my

book, Experimenting with Truth (67), I first made the case that these "exploding exponentials"

guaranteed a very major change in a very short time (<25 years). Obviously if research on high Tc

superconductors continues to increase the Tc at the same rate as in the past we will be above the melting

point of all materials soon. Similarly the BxH product in magnets will be infinite, etc. The optimistic

upbeat suggestion of the great advances we have made in this report, is therefore totally unjustified in

their future scenario which would be roughly: If we keep going at this pace there will be nothing left to

discover in 20 years.

Turning to the other document (70) from the U.K., Professor A. Kelly looks at the utilization of

bulk materials. Figure 15 reproduces some of his figures. Here are plotted the total world usage figures

for all the major metals and a per-capita usage of steel. These data present a very different tone for

any planner. They tell us that humankind is reaching a new and unexpected asymptote in the total

consumption of materials. That with more and more producers the battle for "market share" will

increase. Part of the slowdown is due to conservation and an understanding of the finltude of resources.

This "sustainability" argument has in fact slowly come to dominate technological decisions. Agriculture

research dominated for nearly 100 years by growth scenarios and the research and technologies

derivative of those (supported unquestioningly by all university and agriculture colleges) now finds

itself radically re-directed towards low-input sustainable agriculture. Moreover it is instructive to

note that this revolution did not come from a university or major industry. Instead it was championed

by a few individuals such as Robert Rodale, the CEO of the Rodale.Press, and Lester Brown, President

of Worldwatch Institute. Another societal impact example is the fact that in spite of the

exaggerations both by the activists, and the apple industry, Alar is off the market and the apple

industry is healthy--but again it was not done by the traditional research groups. What is instructive

from those snapshots on current R/D trends is that societal and environmental concerns have totally

reshaped the research directions and agenda of agriculture research.

81
IGURE 1.1 Progress in matcr1al5 ~trenpth-to-density rarlo as a function of tlrnr., shou 11rg 

SO-fold increase in the strcngrh of loday's advanced rnatertals compared lo that of 

rlrnlllve mater~als. 

10 

8 

6 

4 

2 

0 ' 

YEAR 

- 

- 

- 

- 

- 

&onl. Cu 

Con 

FIGURE 1.4 Progress of cntlcal temperature of the ks~'supcrconductin~ rnvtcnal n a 

t'unut~on of time, 

FIGURE 1.3 Progress in the 

flux-mgmttzation pruduct (a 

measure of the strength of a per. 

rnancnt magnet In mepagauss 

oersteds) of magncttc matcr~als 

over II~. Nolc: RE. rare euh. YEAR 

Figure 14. Curves from MSE study by U.S. N.R.C. suggest that in a very short time we will have 

reached physical limits in property improvement. 
80O

7O0 o

300 a

m

2_ " ! '" ! " ! i I I

1.930 4O 50 60 7O 80 1990

20 •

16 I • # • # • • • ALVM_IN}Vn

o

II

}J2

10 " )m,._)

6 n _ _ O _ n _

4

2 I I I i

19_5 1970 I 975 1900 190,5 1990

I0o

700 AA A A 'iiA ...A dm.AA

_ A &A 600

5_

4_

3OO

2OO

I00 .-- o | ! i ! i ! i I

1945 t9 ¢'a'O 19,55 1960 196S 1970 197,5 IgO0 1985 1990

vEA/_

Figure 15. The future (1975-90) was obviously not predictable from the past (1950-75). World usage of

all major classes of metals has plateaued after 1975. Per capita use is declining (after

A. Kelly).

83
It is certain that analogous societal pressures--whether they are scientifically "correct," or

justifiable--will shape the future macro directions of materials research. Itbehooves the science

community to anticipate such changes and start to reshape the directions of our research to match

society's new priorities. In "looking ahead" I see a radical change from the situation in the last 25

years. In the past whatever was discovered by the science community's research set the directions for

development and technology and thence the agenda for society. There was no countervailing force.

That force has now appeared in the shape of the environmental demands of citizens translated into

regulation by legislatures. It has appeared in the form of safety and "hypersafety" demands by the

public. Hence the future research directions will be the resultant vector of one arising from societal

constraints and the other from scientific discovery. I will end by treating each of these in turn.

Some Likely Directions for Discovery-Led Materials Synthesis Research

One cannot conceive of any materials developments which will come close to the enormous impact

which the discovery and exploitation of semiconductors and of polymers has had on the materials

industry. The functions which these new materials opened up in the communications and computer

industries are now being fulfilled by third and fourth generation optimizations. Any new material will

either be a drop-in improvement over the established ones---such as diamond over GaAs--or it will

have a very hard time getting into the field. New functions for known materials based on new

synthesis or processing will also have to compete against the existing technologies which are also

constantly being improved. Twenty years ago the hope for ceramic turbines was very high. After

enormous research expenditures the total role of ceramics in the engine area is now seen as being more

modest.

On the other hand, the electroceramic area which was not much publicized has grown into a

major industry. The high band gap and narrow gap materials are getting closer because of two advances

in synthesis/processing. Firstis the ability to make, say, diamonds and/or ferroelectrics, as thin films to

mate with traditional semiconductor processing. Second, the switching from electronics to optonics

involves a whole new range of electro-optical materials most of which are transparent, and this will

make the way for more ceramic involvement in the communications technologies.

Table 6 lists the families of "bulk" and thin film materials in which I believe the successful

research drive will generate some new opportunities. The family of "chemically bonded ceramics", as I

named cement and its cogeners, will offer continuing opportunities because these materials are needed

worldwide for highways, buildings, waste disposal, i.e., for the entire population, and because these

resources are geographically relatively uniformly distributed.

I have separated out the thin film form of ceramics as a special case because there is so far very

little usage in this form, and hence specially attractive opportunities may present themselves. Just as

metals have been widely used as a plated (or evaporated) thin film for electrical or chemical

84
applications, there appears to be no reason why ceramic phases and functionally graded materials may

not make a major contribution here. The fact that ferroelectrics in thin film form are different from the

bulk, and in fact one can modify the surface to change its properties, points to the kind of direction where

there will be many opportunities for research.

Table 6. New ceramic materials.

(a) New (Bulk) Ceramics (via New Processes)

• Functionally gradient materials

• Lanxide as prototype of CMC

• Chemically bonded ceramics (cements, clays, zeolites and other low temperature reaction

products)

• Nano-micro composites as substitutes in many fields

(b) Ceramics in Thin Film Form

• Ultrahard and/or conducting coatings

- diamond, cBN, DLC, ceramic metals

• Ferroic materials

- active surface modified

- passive: key properties different from bulk

• Functionally gradient materials

Societal Constraints on the Future of Materials Synthesis Research

The basic societal trends are not difficult to summarize and I have attempted to do this in tabular

form in Table 7.

Table 7. The future: Asymptotes and limits of low input materials-inventive

technology. (LIMITis analogous to LISA in agriculture.)

• Minimize energy and materials usage.

• Minimize depredations on environment.

• Cope with absolute physical limits.

• Atomic scale inventions will continue to be serendipitous.

• Nanocomposites is the major opportunity for new materials.

• U.S. role in materials research will diminish rapidly.

• New high volume materials will be driven by needs of less industrialized countries.

In the developed world, energy and materials conservation and environmental issues will

dominate R&D directions more than property improvements. Many of these improvements--as

indicated earlier--are coming up against absolute physical limits in any case. This is similar to the

communications industry where transmission speed and "useful" information (for the masses) have

saturated.

85
Really new materials will appear from time to time as a result of serendipitous discovery, but the

commercial significance of such discoveries will inexorably diminish because existing materials are not

going to disappear. No new laws of physics can appear to explain most of what humans do and

experience (i.e. of any significance to other sciences or society) for the simple reason that the laws of

motion, of electromagnetism, of quantum mechanics, etc., are so completely verified and adequate. So

also the major classes of materials are established and they have been optimized for a myriad

applications. Of course, each application driven by the commercial and social factors will seek to

improve on the present materials, in a technology traction mode. It is in these applications where I see

the emphasis on tailored micro and nanocomposites as playing the central role in materials synthesis in

the decades ahead. Furthermore, as the U.S. role in materials research and in most science diminishes

the science-push model will be displaced--indeed it already has been as witness the existence of the

thrust towards synthesis and processing---by the technology traction model which is central to Japanese

R/D management. The extent to which this has occurred is evident from Fig. 16, after Roy and Silsbee,

TC}T£LSo.,.

_llcoa NIIr_

NO.PUBLIC_ TIONS

1/_._ :',:_',:'.',:I_',: ',........

...............

J I II I I 11 I I iJ.I I 1 I ********

1965 1970 1975 1980 1985 1990

GERI'4,_IY 0 61 162 98 193 206

PRC 0 O I 36 140 279

USSR 4 687 876 1028 738 719

J,_,_ 3 4g 496 1124 1941 2758

UK 0 0 0 21 220 228

USA 12 144 476 781 945 1422

PUBLICATIONYEAR

USA _ UK l:m:lJAPAN

LISSR I_ PRC. !==1GERHANY

Figure 16.

86
(unpublished) which shows the dominance of Japanin published American research. The emergence of

second and third tier countries as substantial research centers will also slowly move the center of

gravity of materials research towards the basic needs of the vast majority of humankind in shelter,

transportation, etc.

Changing Role of Research in Knowledge Management

A major change has occurred--unnoticed by most policy makers--in the value of locally carried

out research in the total management of knowledge. Figure 17, taken from my presentation (71) at a

conference on comparison of U.S. and Japanese research practice, makes the following key points:

1. No local laboratory---even of the biggest industries---can produce more than a minuscule

fraction of the total S3 and S1discoveries being produced.

2. It is more cost effective by orders of magnitude to college knowledge (by carefully sifting

through the literature, by visits to key laboratories, etc.) than to generate it.

3. That only experienced personnel in the S2-T.T.mode canfind the most usable knowledge

available and both put it to work directly and typically use it to guide the S2 research.

What this implies is revolutionary in its implication for the training of scientists (that breadth

of training and critical thinking are much more important than specialization). It is also revolutionary

for research in third tier countries. Instead of investing in large specialized instruments they should

invest in all major literature data bases and train managers to collect and sift new knowledge rather than

generate it.

Goals for Materials Research in the 21st Century

Most humanists and social scientists have not accepted the classical model of "disinterested" (S3)

science. Moreover, the support of S3 science, increasingly accurately perceived as a luxury

"consumption good," is certain to dwindle. The public will continue todemand more S2 science. But can

lofty goals be set for aspiring scientists in apartly globalized economy which on the one hand are

sensitive to the new societal demands, and on the other encourage the inventiveness of the community?

A recent Japanese document offers one such.

The Science and Technology Agency in Japan, in its February 1991 report to Prime Minister Kaifu,

set as Japan's R/D policy goal: "Harmony among science and technology, humankind and society." In

Fig. 18 I have combined this kind of universal goal for scientific research with.the S.P., T.T., and M.P.

motifs for research, expressing the clear change in the vector by which society will now drive and pull

its needed technology and in turn its science (see Ref. 72).

87
KNOWLEDGE MANAGEMENT

oeeeteo*I**eeatI**oo Jloet aeeoot*eeelt**oeooeoo •

: : comrmu

EDUCATION & TRAINING • SYSTEMATICALLY

m_.'.RCH • _ _ ....

• RECOGNITION

OF

DATA i ANOMALY

= DISCOVERY

INFORMATION ......

INVISIBLE

{FAX)

KNOWLEDGE

(WISDOM)

LAB VISITS _ i

SET 1_ ' Disseminate Limit Seczet

[ Gl_p

LI'I_RKMIRE

especially om periphery

Figure 17. A new role for local research which radically diminishes significance is seen when it is

placed in the context of the total flux of knowledge which universities or other agencies

must learn to manage.

88
CONCEPT H_trmony

/Lt/U_" AS GOAL

FOR A/.L "PU/_L"VECTORS.

THE RF_AC_ONS

HAVE SET/IV.

GENERATF_ (ecospherel PRO_ HERE

1

BECOME TECHNOLOGY HAD Technology I INCREASINGLY

AUTONOMOUS_PANDUSHY.

Figure 18.

Acknowledgements

The research described herein has been supported by three main agencies: Office of Naval

Research, Air Force Office of Scientific Research, and National Science Foundation.

89
REFERENCES

1. (a) R. Roy, Synthesizing New Materials to Specification, Solid State Ionics 32/33:3-22 (1989).

(b) R. Roy, "Rational and Irrational Strategies for the Synthesis of New Materials,"

Microelectronic Systems, Am. Ceram. Soc., Washington, DC (1990), pp. 3-10.

2. R. Roy, in Ceramics and Civilization, Vol. 11, High technology ceramics--past, present and future,

Ed. W. D. Kingery, Am. Ceram. Soc., Washington, DC, pp. 351-370 (1987).

3. D. de Solla Price, "Sealing Wax and String: A Philosophy of the Experimenter's Craft and Its

Role in the Genesis of High Technology," Sarton Lecture, AAAS Meeting (May 1983).

4. R. Roy, "HTSC: Restoring Scientific and Policy Perspective," Proc. World Superconductivity

Congress, World Scientific, Singapore, p. 27 (1988).

5. D.W. Brock,W. G. Eversole, R. M. Milton, T. B. Reed and T. L. Thomas, J. Am. Ceram. Soc. 78:5963

(1956).

6. G.A. Keyworth, quoted in Physics Today (April 1985).

7. G. Alperovitz, Technology Review (Aug/Sep 1990), p. 23 ft.

8. DeVries, R.C., Rustum Roy and E.F. Osborn. The System TiO2-SiO2, Trans. Brit. Ceram. Soc.

53:525-540 (1954).

9. R.C. DeVries, R. Roy and E. F. Osborn, "Phase Equilibria in the System CaO-TiO2-SiO2," J. Am.

Ceram. Soc. 48:158-171 (1955).

10. R. Roy, "Metastable Liquid Immiscibility and Subsolidus Nucleation," J. Am. Ceram. Soc. 43:670-

671 (1960).

11. D.K. Agrawal, V. S. Stubican and Y. Mehrotra, "Germanium-modified Cordierite Ceramics with

Low Thermal Expansion," J. Am. Ceram. Soc. 67:847-51 (1986).

12. R. Roy, D. K. Agrawal, J. Alamo and R. A. Roy, "[CTP]: A New Structural Family of Near-Zero

Expansion Ceramics. Mat. Res. Bull. 19:471-477 (1984).

13. Alamo, James and Rustum Roy, "Ultralow-Expansion Ceramics in the System Na20-O2-P20 5-

SiO2," Communications of the American Ceramic Society, C-78-80 (May 1984).

14. S.Y. Limaye, D. K. Agrawal and Y. Mehrotra, "Synthesis, Sintering and Thermal Expansion of

Cal-xSrxZr4P6024--An Ultra Low Thermal Expansion Material," J.Mat. Sci. 26:93-98 (1991).

15. A.J. Majumdar and Rustum Roy, "The System CaO-Ai203-H20, "J_ Am. Ceram. Soc._4:434-442

(1956); R. Roy, Proc. Conf. on the Silicate Industry, Budapest, pp. 1005-1017 (1973); reprinted in

Powder Metal. Intl. 6:25 (1974); Keramische Z. 26:386 (1974).

16. M.J. Ruthner, Third Roundtable Meeting, Internat. Team on Sintering, Herceg-Novi, Yugoslavia

(September 1973).

17. T.P. O'Holleran, R. Roy and D. M. Roy, "Amorphous Powder and Sintered Nab-Al20 3 by DMS

Process," Powder Metallurgy International 17(3):134-136 (1985).

9O
18. (a) Amitabh Kumar and Rustum Roy, "Reactive-Electrode Submerged-Arc Process for Producing

Fine Non-Oxide Powders," J. Am. Ceram. Soc. 72(2):354-356 (1989).

(b) Amitabh Kumar and Rustum Roy, "RESA--A Wholly New Process for Fine Oxide Powder

Preparation," J. Mater. Res. 3(6):1373-1377 (1988).

19. J.L. Kingsley and K. C. Patti, Mat. Lett. 6:427 (1988).

20. Della M. Roy and Rustum Roy, "An Experimental Study of the Formation and Properties of

Synthetic Serpentines and Related Layer Silicate Minerals," Am. Mineralogist 39:957-975 (1954).

21. O. Muller and R. Roy, The Major Ternary Structural Families, Springer-Verlag, Heidelberg (1974).

22. R. Roy, "Multiple Ion Substitution in the Perovskite Lattice,'; J. Am. Ceram. Soc. 37:581-588 (1954).

23. Frank DachiUe and Rustum Roy, "The Spinel-Olivine Inversion in Mg2GeO4," Nature 183:1257

(1959).

24. Frank Dachille and Rustum Roy," High Pressure Region of the Silica Is, types," Zeits. fiir Krist.

3:451-461 (1959).

25. Mark Myers, Frank Dachille and Rustum Roy, "Contribution to Calibration of High Pressure

Systems from Studies in Opposed-Anvil Apparatus," High Pressure Measuremen, Giardini and

Lloyd, pp. 17-33 (1963).

26. G.J. McCarthy, W. B. White, R. Roy, B. E.Scheetz, S. Komarneni, D. K. Smith and D. M. Roy,

"Interactions Between Nuclear Waste and Surrounding Rock," Nature 273:216-217 (1978).

27. G. McCarthy and M. T. Davids, n, Bull. Am. Ceram. Soc. 54:782 (1975).

28. Roy, Rustum, Radioactive Waste Disposal, Volume 1: The Waste Package, Pergamon Press, New

York, 1982. 232 pp.

29. Roy, Rustum, "Science Underlying Radioactive Waste Management: Staths and Needs," Scientific

Basis for Nuclear Waste Management, Vol. 1, pp. 1-20. Ed. G.J. McCarthy, Plenum Publishing

Corp., New York (1979).

30. T. Takamori, R. Messier and Rustum Roy, "New Non-Cxystalline Germanium which Crystallizes

'Explosively' at Room Temperature," Appl. Phys. Lett. 20:201-203 l(1972).

31. Russell Messier and Rustum Roy, "Thermal Behavior of Noncrystalline Sputtered Films in the

System Ge-Te," Mat. Res. Bull. 6:749-758 (1971).

32. Russell Messier, A.K. Sarkar and Rustum Roy, "New Metal-Rich Germanide and Carbide NonCrystalline Solids," Mat. Res. Bull. 9:157-166 (1974).

33. L.R. Gilbert, R. Messier and R. Roy, "Superconducting BaPbl.xBixO 3 Ceramic Films Prepared by

R.F. Sputtering," Thin Solid Films 54:129-136 (1978).

34. K. Char, A. D. Kent, A. Kapitulnik, M. R. Beasley and T. H. Geballe, "Reactive Magnetron

Sputtering of Thin-Film Superconductor Yttrium Barium Copper Oxide (YBa2Cu3OT.x)," Appl.

Phys. Lett. 51(17):1370-1372 (1987).

35. A.R. Badzian and R. C. DeVries, Mat. Res. Bull. 23:385 (1988).

91
36. R. Roy, "CVD Diamond Science and Technology: One of Three Materials Revolutions," Proc. 41st

Annual National Conference on the Advancement of Research, September 27-30, 1987, Tech'nomic

Publishing Company (1988).

37. B.V. Derjaguin and D. V. Fedoseev, "Growth of Diamond and Graphite from the Gas Phase," lzd.

Nauka, Moscow (1977).

38. S. Matsumoto and N. Setaka, Carbon 17:485 (1979); Carbon 19:232 (1981).

39. Y. Matsui, A. Yuuki, M. Sahara and Y. Hirose, Jpn. J. Appl. Phys. 28(29):1718 (1989).

40. G. Gildenblatt, S. Grott and A. R. Badzian, "Electrical Properties and Device Applications of

Homoepitaxial and Polycrystalline Diamonds," Proc. IEEE 79:647 (1991).

41. (a) R. Roy, "New Hybrid Materials Made by Sol-Gel Technique, " Bull. Am. Ceram. Soc. 61:374

(1982).

(b) R. Roy, "Ceramics from Solutions: Retrospect and Prospect," MRS Annual Meeting Abstracts,

p. 370 (1982).

(c) R. Roy, "New Metal-Ceramic Hybrid Xerogels," MRS Annual Meeting Abstracts, p. 377 (1982).

42. R. Roy, "Ceramics by the Solution Sol-Gel Route," Science 238:1664 (1987).

43. H. Gleiter, Mat. Sci. & Engr. 52:92(1982); review in Nanostructured Mat. 1:1-19 (1992).

44. R.A. Roy, R. Messier and J. M. Cowley, "Fine Structure of Gold Particles in Thin Films Prepared by

Metal-Insulator Co-Sputtering," Thin Solid Films 79(3):207-215 (1981).

45. David Hoffman Rustum Roy and S. Komameni, "Diphasic Ceramic Composites via a Sol-Gel

Method," Mat. Lett. 2(3):245-247 (1984).

46. R. Roy, S. Komarneni and D. M. Roy, "Multi-phasic Ceramic Composites Made by Sol-Gel

Technique," Better Ceramics Through Chemistry, Proc., Mat. Res. Soc. Symp., Vol. 32. Ed.

C. J.Brinker, D. E. Clark and D. R. Ulrich, Elsevier Science Publishing Co., Inc., NY. pp. 347-359

(1984).

47. R. Roy, S. Komameni and W. Yarbrough, "Some New Advances with SSG-Derived

Nanocomposites," Chapter 42, Ultrastructure Processing of Advanced Ceramics, John MacKenzie

and Don Ulrich (eds.), Wiley Interscience, pp. 571-588 (1988).

48. Proc. Seventh Seminar on Frontier Technology m Nano-Hybridization and Creation of New

Functions, Feb. 7-10 (1989), Oiso, Japan.

49. G. Ervin, thesis, Pennsylvania State College, University Park, PA (1949); E. F. Osborn, J. Geol.

59:381 (1951); V. G. Hill, R. Roy and E. F. Osborn, J. Am. Ceram. Soc. 35:135 (1952); R. Roy,

D. M. Roy and E. F. Osbom, ibid (1950).

50. (a) U. Selvaraj, A. V. Prasadarao, S. Komarneni and R. Roy, "sol-Gel Fabrication of Epitaxial

and Oriented TiO2 Thin Films," J. Am. Ceram. Soc. (in press).

(b) U. Selvaraj, A. V. Prasadarao, S. Komarneni and R. Roy, "Epitaxial SrTiO3 Thin Films by

Sol-Gel Processing," J. Mat. Res. (in press).

92
51. U. Selvaraj, C. LoLiu, S. Komarneni and R. Roy, "Epitaxial Crystallization of Seeded Albite

Glass," J. Am. Ceram. Soc. 74:1378-1381 (1991).

52. G. Vilmin, S. Komarneni and R. Roy, "Crystallization of ThSiO4 from Structurally or

Compositionally Di-phasic Gels," J. Mat. Res. 2:489 (1987).

53. K. Niihara and A. Nakahira, "Structural Ceramic Nanocomposites," Ceramics: Towards the 21st

Century, Ceramic Society of Japan, Tokyo (1991), p. 404 ft.

54. Z. Zhao, "Chinese Scientists Success in Highest Tc Superconductor," PeoplesDaily, Beijing,

February 25, 1987.

55. M.L. Keith and R. Roy, "Structural Relations Among Double Oxides of the Trivalent Elements,"

Am. Min. 39:1-23 (1954).

56. (a) A. HI Heuer, "Biological and Biomimetric Ceramics: A New Frontier," Orton Lecture, 93rd

Ann. Mtg. of the American Ceramic Society, April 28-May 2, 1991, Cincinnati, OH, p. 338.

(b) I. Aksay, quoted by R. Eisner, The Scientist, July 8, 1991, p. 14.

(c) A. V. Srinivasan, G. Haritos and F. Hedberg, "Biomimetics: Naturally Evolved Systems as

Paradigms for Advanced Aerospace Materials and Systems," Air Force Office of Scientific

Research, Washington, DC (1990).

57. J. N. Weber, E. W. White and J. Liebiedzik, "New Porous Biomaterials by Replication of

Echinoderm Skeletal Microstructure," Nature 233:337-339 (1971).

58. R. A. White, J. N. Weber and E. W. White, "Replamineform: A New Process for Preparing

Ceramics, Metal, and Polymer Prosthetic Materials," Science 176:922-924 (1972).

59. E.W. White, J. N. Weber, D. M. Roy, E. L. Owen, R. T. Chiroff and R. A. White, "Replamineform

Porous Biomaterials for Hard Tissue Implant Applications," J. Biomed. Mat. Res. Symp. 6:23-27

(1975).

60. Jonathan Black, personal communication.

61. M. Newkirk et al., J. Mat. Res. 1:81 (1986).

62. A.S. Fareed, B.Sonuparlak, C. T. Lee, A. J. Fortini and G. H. Schiroky, "Mechanical Properties of

2-D Nicalon TM Fiber Reinforced LANXIDETM Aluminum Oxide and Aluminum Nitride Matrix

Composites," Ceram. Eng. Sci. Proc 1117-8]:782-794(1990).

63. C.A. Andersson, P. Barron-Antolin, A. S. Fareed and G. H. Schiroky, "Properties of Fiberreinforced Lanxide TM Alumina Matrix Composites," ASM Proc. hit. Conf. Whisker- and Fibertoughened Ceram., pp. 209-215 (1988).

64. R.E. Newnham and G. Ruschau, "Smart Electroceramics," J.Am. Ceram. Soc. 74:463 (1991).

65. N. Tsuya, Y. Saito, H. Nakamura, S. Hayano, A. Furugohri, K. Ohta, Y. Takui and T.Tokushima,

"A Perpendicular Magnetic Recording Medium by Aluminte," J. Mag.. Mat. 54-57:1681-1682 (1986);

T. Endo, T. Sato and M. Shimada, "Fluorescence Properties of the Dye-intercalated Smectite," J.

93
Phys. Chem. Sol. 47(8):1423-1428 (1988); R. E. Newnham and S. E. Trolier-McKinstry, "StructureProperty Relationships in Ferroic Nanocomposites," Ceramic Trans. 8:235-252 (1990).

66. C.F. yon Weiz,_cker, The Unity of Natur_ Farrar, Strauss and Giroux (1980).

67. R. Roy, Experimenting With Truth, Pergamon Press, NY (1973).

68. D. Mermin, Physics Today (November 1990), p. 9 ft.

69. Materials Science and Engineering for the 1990's, U.S. National Research Council, Washington,

DC (1989).

70. A. Kelly, "The Future of Metals," Min. Ind. Intnl. Bull. 996:5-10 (1990).

71. Rustum Roy, "The Management of Knowledge and the Role of Culture in the R/D Enterprise,"

Japanese/American Technolgical Innovation, Elsevier Science Publishing Co., Inc., 253-257 (1991).

72. R. Roy, "Achieving Harmony Between Science and Technology and Humankind and Society,"

presented at The Kanagawa Academy of Science and Technology (May 29, 1991).

94
MATE!RIALS SYNTHESIS TODAY

ACHIEVEMENTS IN CERAMICS POST WW II

• Magnetic Materials: ferrites, garnets, SmCOs,R.B.I.'s

• Glass Ceramic Process: Materials: Process: Understanding

• Low Expansion Ceramics: Cordierites, L-A-S, CZP

• Synthetic Diamonds, CBN.

• Sol-Gel Process: Maximizing homogeneity; now heterogeneity

• Float glass

• Strong Polycrystalline Ceramics: LAS--b.SiC--_. sialon

• Toughened Ceramics: Fibers, transition (ZrO _; Lanxide

• Fine, Pure Powders: Solution, EDS, hydrothermal, RESA

• New Cements

LANDMARK MATERIALS SYNTHESES POSTWWII

METALS

1.Ni-based superalloys

2.Basicoxygenprocess

3,Aircraft engineall0ys-directi0al solidification singlecrystalurbineblades

4.Amorphous metals(allied: 100millionIbscapacity)

5.Permanent magnets: SmC0_, NdFeb0rides

95
The Historians of Science Have Shown the Critical Role

of Instruments in Advancing Science

Material• Techn.ology-.-)lNew Materials _-_New Science

-%.

Inexactly analogous ways"NewMaterials" coming outof"Technology" advance materials science

96
High Risk

Possibilil_es owned up by new

"cuttingedge" S I,S 2 science.

S

Consumer-driven

commercial technologie,

Materials

Research and

Development

System Technologies

Private Public

Sector Sector

Human Needs

Public Sector

What drives technology?

WHAT DRIVES EFFECTIVE SYNTHESIS RESEARCH?

S.P. = SCIENCE PUSH

M.P. = MARKET PULL

NEW--> T.T. = "TECHNOLOGY TRACTION"

CONNECTION OF SCIENCE TO A

TECHNOLOGICAL GOAL (DETERMINED BY

PUBLIC OR PRIVATE SECTOR NEEDS)

THREE KINDS OF "SCIENCE"

S = SERENDIPITOUS DISCOVERY

(CAREFUL OBSERVATION BY HIGHLY TRAINED

OBSERVER)

S 2 = SCIENCE FOR SOCIETY (PURPOSIVE, LONG-TERM BASIC

SCIENCE)

S 3 = SCIENCE FOR SELF AND THE INSTITUTION OF SCIENCE

97
A. FURNACE

Raw

materials

are melted --//--o 7 _ ,._ -,.,, _ B. MOLTEN M ETAL

--_---F_°/_'_,J --_T_Moltrooen,eaSy ts, ,o_e, ,ve,,,

= .-_1 I_{ (_-"_ _{{_E_'''_ _ Molten metal under pressure

(_-{ __J'= is sprayed Irorn nozzle

F. MANIPULATOR Positions _ f

amorphous metal ribbon , ...... _ / _,.J --'_ t '¢")

I I I _ N [ I E. COOLING BOX Keeps

temperature o{ belt near oo,,

D. HIGH SPEED ROTATING COPPER BELT temperature

Molten metal sprayed on cooled copper belt

iorms amorphous metal ribbon

A REAL WINNER OF NEW MATERIALS SYNTHESIS

GLASSY METALS.

(S.P. & T.T)

98
MICROPIPET MANIPULATION OF LIPID MEMBRANES:

DIRECT MEASUREMENT OF THE MATERIAL

PROPERTIES OF A COHESIVE STRUCTURE THAT

IS ONLY TWO MOLECULES THICK

David Needham

Department Mechanical Engineering & Materials Science

Duke University

Durham, North Carolina 27708-0300

Telephone 919-660-5329

99

MICROPIPET MANIPULATION OF LIPID MEMBRANES: DIRECT MEASUREMENT

OF THE MATERIAL PROPERTIES OF A COHESIVE STRUCTURE THAT IS ONLY

TWO MOLECULES THICK

David Needham

Department of Mechanical Engineering and Materials Science,

Duke University, Durham, NC 27708-0300

Key Words: lipid bilayer, stress, strain, elasticity, failure, biological cells.

Prerequisite Knowledge:

To appreciate this demonstration, students should have some understanding of the

concepts of stress and strain, elasticity, tensile strength, strain energy and composites. A

rudimentary familiarity with the chemical composition of surfactant-like molecules, in

particular phospholipids, is also required.

Objectives:

The objectives are to demonstrate how we can make direct measurements of the

mechanical properties of a special structure in biology, namely the lipid bilayer membrane,

using a micromanipulation technique; and how these properties compare and contrast with

"more traditional" technological/engineering materials. Given that the investment in

equipment and expertise to carry out these experiments is probably beyond the scope of

most teaching labs, the described experiment is not intended as one that can actually be

demonstrated in a student laboratory class. The intention behind presenting this work is to

begin to raise awareness in the Material Science community about the material properties of

biological material that form a new (to us) category of soft engineering materials that have

dimensions on the nanoscale.

Introduction:

Nature has chosen a specific state of matter and some exceptional materials with

which to construct the biological world. She colonized the colloidal state of matter

(material in the size range 10/_ to 101.tm) and has used the solvent, water, to great

advantage in forming and maintaining the integrity of structures that have both hydrophilic

and hydrophobic components. From a materials design perspective, 109 years of evolution

have gone into Nature's design methodology; materials have been selected based on their

availability, compatibility with a given system, and their ultimate performance in service.

The systems that have survived, and that give good service performance, provide lessons

101
for scientists and engineers regarding materials selection and properties, especially for

those concerned with designing artificial systems that must interface with biology's own

materials.

Nature's materials are different to our usual notion of engineering materials, in that

they and their interfaces are soft. The softness derives from the fact that, in water, the

separation of polar and non-polar phases relies on entropy rather than enthalpy; the, so

called, hydrophobic effect [1] excludes oil-like, non-polar material from the water phase.

These separate, non-polar phases are not strongly bonded (attractive forces are weak van

der Waals forces) and, consequently, biological material is soft and often liquid-like. The

lipid bilayer membrane is a "classic" material that includes both hydrophilic and

hydrophobic regions in a structure that is only 5nm thick.

The importance of the simple lipid bilayer is underscored when we realize that it is

the structure thatsurrounds every cell on our planet.

Figure 1. Scanning electron micrograph of a neutrophil (top) and an erythrocyte

[2]. The erythrocyte has an excess of surface area compared to a sphere of the same

volume and its smooth membrane is supported by a viscoelastic cytoskeleton. In contrast,

the neutrophil is spherical and its 100% excessmembrane area is supported in microvillious

structures.

102
In addition to its many important functions of a chemical and biochemical nature,

the lipid bilayer provides a mechanical, chemical and electrical barrier that isolates the

cellular interior. It is also the structural matrix of the composite cell membrane to which,

and in which, all the other, more "exotic", protein and carbohydrate molecules are located.

This membrane defines the interface and site of communication between the cell and its

surrounding medium. To give two common examples consider the electron micrograph in

Figure 1. We see two different cells, a white blood cell and a red blood cell.

The red blood cell, or erythrocyte, is characterized by a smooth membrane and a

discoid shape. The white blood cell, in this case a neutrophil, has a highly microvilliated

surface. In addition to the lipid membrane experiments described here, we have used the

micropipet method and devised experiments (large deformation and recovery after large

deformation) that allow us to make measurements of the viscous and elastic properties of

whole cells [2, 3, 4, 5, 6, 7].

When we look inside the neutrophil, as shown in Figure 2, we see that it is

composed of a highly complex arrangement of microfilaments and granules.

Figure 2 Scanning electron micrographs of an osmotically lysed and a detergent

solubilized neutrophil.* By bursting a hole in the plasma membrane using osmotic stress

or by dissolving away the whole membrane with gentle detergentthe complex

filamentous and particulate nature of the cytoplasm isrevealed.

*Hochmuth, R. M., H. P. Ting-Beall, B. Beaty. D. Needham. R. Tran-Son-Tay, "'The Viscosity of Passive

Human Neutrophils Undergoing Small Deformations." Biophys. J.. in press.

103
Having introduced the lipid membrane as a biological structure, let us now consider

some basic material features of the lipid bilayer membrane and, through this discussion,

demonstrate a special technique that allows us to make micromechanical measurements on

these colloidal-sized, soft materials.

As a class of material, the lipid membrane is an association colloid made up of

surfactant-like, phospholipid molecules that have both hydrophilic and hydrophobic parts.

These molecules associate in aqueous media due to the operation of the hydrophobic effect

and, to varying extent, to secondary attraction forces (van der Waals dispersion forces).

Figure 3. Schematic of bilayer arrangement of phospholipid molecules showing transverse

section through the bimolecular lipid layer. The circles represent the polar phospholipid

headgroups (e.g. phosphocholine) oriented towards the water interface, and the squiggles

represent the long hydrocarbon chains (e.g., 18 carbons per chain; 2 chains per molecule)

that form the hydrophobic interior of the bilayer.

The membrane is formed by the packing of molecules into a bilayer configuration

with the hydrophobic acyl chains forming the core of the layer and the hydrophilic

headgroups forming the interface with the aqueous phase, as shown in the schematic in

Figure 3. The bilayer interior is essentially a liquid-like hydrocarbon and, in the plane of

the membrane, molecules move about in a liquid-like manner, without significant shear

rigidity.

In our micromechanical studies we have been and continue to be concerned with

composition-structure-property relations in lipid bilayer membranes [8, 9, 10, 11]. We

have found that the material properties of lipid bilayer membranes depend on the chemical

structure of the constituent lipid molecules and the interaction of the lipids with cholesterol

and other lipid-membrane-soluble components. We have used micropipet manipulation

methods to measure the response of this membrane to several modes of deformation

(bending, in-plane shear for solid bilayers and isotropic area dilation I81). Here we will

focus on area expansion, the elastic area expansion modulus and, the failure parameters,

tensile strength, critical areal strain and strain energy.

104
Procedures:

Experimental Methods and Equipment

The preparation of lipid vesicles from lipid solutions and the procedures for

carrying out thermomechanical studies on a range of lipid and mixed lipid systems are

documented in several recent publications concerning the micromanipulation of such

structures[8, 9, 12,13, 14,15]. Inorder toprepare lipid bilayer vesicles, that are suitable for

micromanipulation using optical microscopy, an aqueous solution is added to dry the lipid

(Avanti Polar Lipids Pelham, AL; Sigma, St. Louis, MO) and the lipid spontaneously

hydrates to form spherical capsules, called lipid vesicles or liposomes. Depending on the

level of _mposed agitation during or after this hydration step these lipid vesicles can be

made to vary in size from 250Ain diameter (e.g., by sonication), to 'Giant' liposomes of

20 _M to 50 [tM in diameter, (formed by the gentlest of convective procedures).

Preparation procedures can give varying degrees of multil.amellarity to these lipid bilayer

structures that can range from single membrane capsules, to multiwalled "onion-skin"

liposomes, to unusable gobs of partially hydrated material. In our micropipet experiments

we select single walled liposomes from the largely multilamellar population. (Note: other

techniques that complement our mechanical measurements, such as x-ray methods, require

detcctable repeat periods of multiwalled liposomes and can yield information about the

bilayer geometry, phase behavior and colloidal interaction between membranes [10, 16]).

The lipid vesicle solution is diluted into a glucose solution and placed in a simple glass

microchamber on a microscope stage.

With regard to the experimental set-up and equipment, details have also been fully

documented in recent publications [15, 17, 18, 19]. The micromanipulation system is

centered around an inverted microscope that has micromanipulators mounted directly on the

microscope stage. Control over micropipet suction pressure is in the range of

microatmospheres to tenths of atmospheres (1 dyn/cm 2 to 100,000 dyn/cm 2) and is

achieved by a micrometer-driven manometer and recorded by in-line pressure transducers

(Validyne). An essential part of the manipulation system is a glass micropipet of desired

internal diameter (-8-10 _m) and flat tip that is used to apply the force to the aspirated

vesicle during the vesicle deformation tests. Micropipets are made from 0.75 mm internal

diameter glass capillary tubing (A-M Systems, Inc., Everett, WA), formed into

microneedles by a heated pipet puller.

105
a

O-ring

\

chucknut

sidearm

b

Figure 4. The chuck and micropipet arrangement, a) individual pieces; b) assembled

chuck and micropipet. (Courtesy of Research Instruments Inc., Durham, NC)

lateral coarse adjust

verticalcoarseadjust

\

chuck locking thumbscrew

/

'i axial coarse adjust

vortical motion

receiver chassis

lateral motion

axial motion

Figure 5. The manipulator (Courtesy of Research Instruments Inc., Durham, NC)

106
The flat pipet tips of desired diameter (1 gm to 15gm) are broken by quick fracture

on a microforge. The pipets are filled with a NaC1solution that matches the osmolarity of

the solution that the liposome properties are measured in. The measuring micropipet is

inserted into a metal chuck (Research Instruments Inc., Durham, NC), as shown in Figure

4, that connects the pipet to the water-filled manometer system. The chuck with side-arm

access, allows any suitable micro-tool to be rapidly sealed to the chuck with an "O"-ring

compression seal.

Figure 6. "Aerial" view of manipulator with micropipet mounted on the microscope stage

connected to the joy stick that allows fine pneumatic control of micropipet position.

(Courtesy of Research Instruments Inc., Durham, NC)

The pipet-chuck assembly is then mounted into a de Fonbrune-type

micromanipulator, Figure 5, (Research Instruments Inc., Durham, NC) The manipulator

has three course positioning knobs for making preliminary adjustments of the micropipet in

107
the axial, lateral and vertical directions. Fine adjustments are made by the transduction of

three separate and variable air pressures provided by the joy stick via flexible transmission

tubes. The whole assembly is then mounted on the microscope stage as shown in the

"aerial" view in Figure 6 so that the pipet enters the microchamber horizontally

(microchamber not shown). The small micromanipulators are pneumatically controlled by

hand operated joy sticks that allow smooth motion in all three axes (axial, lateral and

vertical), zero drift and control of position on the micron scale.

Figure 7. Videomicrographs of a giant lipid bilayer vesicle (30 l.tmdiameter) aspirated

by micropipet (8 _tmdiameter), a) lipid vesicle with the same solution inside and out. b)

lipid vesicle in an external medium that has a different refractive index than the internal

solution for ease of visibility and capture.

108
This micropipet manipulation system together with video interference microscopy

then allows us to manipulate individual cell-sized lipid vesicles. Figure 7a shows a

videomicrograph of a lipid vesicle that is being manipulated by a suction micropipet. Time

and pipet pressures are multiplexed onto the video screen, as shown in the top of each

micrograph. Pressurization of the liposome by the suction pipet induces an isotropic

tension in the membrane and a corresponding expansion in lipid vesicle area. The pipet

therefore acts as a means to manipulate individual vesicles, to apply suction pressure, and,

by measuring changes in the length of the vesicle projection in the pipet, it also provides a

sensitive measure of small changes in membrane area that may be as small as ~1-5%. The

applied pipet suction pressure together with the pipet and vesicle geometry are used to

calculate the induced isotropic membrane tension. The pipet diameter is 8 I.tm and the

vesicle diameter is 30 _m. The lipid vesicle in Figure 7a contains the same medium inside

and out and it is "seen" by virtue of its diffraction pattern in the interference contrast

microscope (Leitz, inverted microscope equipped with Hoffman Modulation Optics). It is

more usual for us to load the liposomes with a solution (e.g. 160 mM sucrose) that is more

dense and has a different refractive index than the subsequent suspending solution (e.g.,

equiosmotic glucose or NaC1) so that the liposomes collect on the bottom of the microscope

chamber and observation is easier, as shown in Figure 7b. Experiments are recorded on

videotape and information such as time and pipet suction pressure are multiplexed directly

onto the video using video multiplexing (Vista Electronics, 8226 Vista Dr. La Mesa CA).

A series of experiments can then be carded out and recorded su'ch that geometrical analyses

(vesicle and pipet dimensions) can be made subsequent to the experiment using a video

caliper system (Vista Electronics, CA).

Stress Strain Plot

In each experiment, area changes are derived from the projection length of the lipid

vesicle in the micropipet as a function of membrane tension at constant temperature.

Membrane tension (x) is uniform over the entire vesicle surface and is given by the pipet

suction pressure (P) and the pipet/vesicle geometry [12]:

= PRp/(2 - 2Rp/Ro) (1)

where Rp is the pipet radius and Ro is the radius of the outer spherical segment of the

vesicle. Changes in vesicle membrane projection length (AL) inside the pipet are a direct

measure of the fractional change in total vesicle membrane area (AA):

AA = 2PRp(1 - Rp/Ro)AL (2)

109
This relationship is valid only if the volume of the vesicle is constant. Changes in

volume (due to filtration of water by pipet suction) are in fact found to be negligible when a

vesicle is held under maximum suction for periods well in excess of the duration of the

experiment. Since the number of molecules in the membrane is fixed (due to extremely low

lipid solubility in aqueous media), changes in vesicle area represent changes in surface area

per lipid molecule. The mode of deformation that we examine in this micropipet

experiment is area dilation and a simple relation between membrane tension and area change

which characterizes the area elasticity in terms of an expansion modulus K. If Ao is the

reference area of the vesicle in the pipet at a low (.--0.5dyn/cm) initial membrane tension,

then cx,the relative, fractional change in vesicle membrane area (AA/Ao) in response to

a change in membrane tension at constant temperature, yields the compressibility modulus,

K, from the constitutive relation,

K = Ax/Ao_ (3)

In the experiment we sequentially load and unload the membrane by increasing and

decreasing the pipet suction pressure, and finally increase the suction pressure to a level

that produces failure, as shown in Figure 8. The deformation is elastic (the motions of

molecules are on the order of microseconds for this liquid-like membrane, so we don't see

any viscous effects); there is no ductility and the failure is that of a liquid membrane.

By using this micropipet method then we can characterize lipid membranes in terms

of several common material parameters:

1) Membrane area compressibility represents the resistance of the membrane to

isotropic area dilation and is characterized by an elastic area compressibility (or

expansion) modulus K;

2) tensile strength is given by the membrane tension at failure "Is;

3) critical areal strain is the fractional increase in membrane area at failure O_c;

4) membrane strain energy (or toughness) Es represents the work done on the

membrane up to failure and is given by the area under the stress strain plot

K(Ct¢)2/2.

These parameters were measured for several lipid and lipid/cholesterol mixtures, in

particular for Stearoyloleoylphosphatidylcholine (SOPC) (18:0/18:1) alone and in

combination with cholesterol. SOPC is a "standard lipid", equivalent to the average acyl

chain composition of natural lipid membranes, and cholesterol is an almost ubiquitous

110
component that is present in natural cell membranes; for example, it is present at 40 mol%

in red blood cell membranes.

20 /

vesicle -"

15 ("--"- Ts _E

dyn/cm K

5 EnergyEs

/ - I " I " I " I " i°"

0.00 0.01 0.02 0.03 0.04 0.05 0.06

(X

Figure 8. Stress vs strain plot for micropipet pressurization of a lipid vesicle. Vesicle

membrane tension 1; resulting from the applied micropipet suction pressure is plotted

against the areal strain 0_(i.e., the observed increase in vesicle membrane area AA relative

to an initial low stressed state Ao). The slope of the 1: vs _ plot is the elastic area

compressibility modulus K. The star symbol represents the point of membrane failure at

the critical areal strain O_cand tensile strength l:s. The area under the plot represents the

strain energy at membrane failure Es.

Results:

Elastic Area Compressibility (Expansion) Modulus

The results for the SOPC/CHOL mixtures are shown in Figure 9. As the amount of

cholesterol in the lipid bilayer is increased, the elastic modulus shows little change initially

but then increases rapidly. At -60mo1% or slightly less the property saturates and reflects

the chemical saturation of cholesterol in the bilayer phase. At greater stoichiometries, any

excess cholesterol is present in aqueous suspension as cholesterol crystalites.

111
1400

12oo

1000

80O

K

dyn/em 600

400 2001

0 ! i a !

0 20 40 60 80 100

Nominal mol%CHOL

Figure 9. Area expansion modulus K versus Nominal Mol% Cholesterol in SOPC lipid

bilayers. Also shown is the molecular composite model (solid line).

By analogy with common macroscopic composite theory for fiber- or particulatereinforced materials (in which a matrix material is stiffened by the incorporation of particles

of a higher modulus material), a simple 2 dimensional (isostress) molecular composite

model was used to fit the data for the SOPC/CHOL system. Briefly, the simple equation

for the composite bilayer is,

KL/Cl (4)

in which the area compressibility modulus of the membrane Km is a linear combination of

the moduli of the two components, namely, free lipid KL and a lipid/cholesterol molecular

complex KL/C scaled by their area fractions aL and aL/C.

The area fractions of the two components (uncomplexed lipid aL and

lipid/cholesterol complex aL/C) were calculated from experimental measures of the

molecular areas of the free lipid 65/_2, the limiting value of 48/_,2 for lipid in a cholesterol

saturated bilayer, and for cholesterol, from experiments involving spread monolayers

112
leading to a limiting area per molecule of 37,/_2. (i.e., AL = 65/_2 and AL/C= 93/_2). The

theoretical value for the modulus thus obtained for the simple composite membrane as a

function of mol%CHOL in the bilayer phase is also plotted in Figure 9 and matches the

increase in bilayer area expansion modulus with increasing mol%CHOL.

Thus, when the mol% of cholesterol in the bilayer is increased, a simple property

averaging theory can account for the non-linear increase in area modulus that is observed.

In the model, no assumptions were made regarding size or shape of component domains.

Whether homogeneously mixed or separated into component-rich domains the correlation

with a macroscopic composite theory indicates that each molecular component brings to the

bilayer phase its "characteristic modulus" and reflects its average interactions with its

neighbors.

Membrane Failure: Critical Areal Strain, Tensile Strength and Failure

Energy

Figures 10 a, b and c show the changes in critical areal strain O_c,membrane

tension at vesicle lysis '_s and energy per unit area at failure K(ac)2/2 plotted vs nominal

mol%CHOL for the SOPC/CHOL system. If we look at these parameters, what do we

learn about the failure mechanism?

0.07

0.05 t

0.04

0.01

0.00 - • , •

0 2'0 40 6'0 8'0 1O0

Nominal mol%CHOL

Figure 10 a Critical areal strain _c

113
40

30 tt

dynlcm

lo {_

0 2'0 4'0 6'0 80 100

Nominal mol%CHOL

Figure 10 b Membrane tension at vesicle lysis 1;s

0.7'

0.6

20, t. K(_ c ) /2

erg/cm 2 0.3

0.2 t

0.1

°0 ! | • • •

o 20 4'0 6'0 8'0 loo

Nominal moI%CHOL

Figure 10 e Energy per unit area at failure K(ac)2/2, stored in the bilayer membrane due

to elastic deformation.

114
The fact that the critical areal strain increases then decreases (Figure 10a)

demonstrates that bilayer failure per se (at least for two components) cannot be linked to an

area criterion and a single value for critical strain, i.e a critical percent expansion in area per

molecule. We have recently measured much stiffer membranes and the trend is for stiffer

membranes to expand the least, sometimes as little as 1% at failure.

The increase in critical tension (Figure 10b) shows that the addition of cholesterol

increases the strength of the bilayer, and points to an increase in cohesion that cannot be

just due to the hydrophobic effect; cholesterol must increase the strength of the molecular

interactions and create a more bonded material. The peak in critical areal strain and the

steadily increasing tensile strength are combined in Figure 10c as K(otc)2/2 to show that the

lipid membrane is essentially "toughened" by the addition of cholesterol, but only up to a

certain point, around 40 mol%CHOL.

If we are designing for "toughness" and not strength, then intermediate cholesterol

concentrations give the best membranes. This may be coincidence, but it is interesting to

note that the natural RBC membrane also contains ~40mol%CHOL. Red blood cells flow

almost interminably (120 days) in the blood stream and must survive the rigors of

fluctuating hydrodynamic forces. Were the membranes "designed/selected" for toughness

and not strength? As with the modulus measurements, all these properties showed

constancy above ~58 mol%CHOL, which again indicated a constant bilayer composition

for nominal cholesterol concentrations above 58 mol%CHOL.

Our analysis can be taken a step further by converting the failure energy per unit

area K(ac)2/2 into an energy per mole of lipid by multiplying by Avogadro's number and

the appropriate area per molecule. Interestingly, the amount of energy that is stored in the

SOPC/CHOL membrane when it breaks ranges from 35 J/mol for the single component

SOPC membrane to 130 J/mol for the 40 mol%CHOL membrane. When compared to RT

(2400 J/mol), the thermal energy per mol, we see that a relatively small amount of energy is

required to cause irreversible failure by applied tensile stresses. The energy stored in the

membrane up to failure is only a small fraction of the available thermal energy per mole.

This might be taken to imply that failure results from a defect that comprises many (~50-

100) molecules. We are currently investigating defect formation and failure during electric

field-induced breakdown of lipid bilayers and the formation of a pore-like defect made up

of many molecules seems to be at the heart of bilayer failure [20, 21].

115
Finally, a simple thermodynamic interpretation along the lines of Whol, [22] can be

made if we recognize that an increase in bilayer strain energy represents an increase in

stability and may be correlated with a decrease in the overall free energy of the bilayer. A

decrease in the excess Gibbs energy of the bilayer due to mixing the two membrane

components, namely, uncomplexed lipid and the lipid/cholesterol complex, would make a

stabilizing contribution to the overall free energy. This simple analysis indicates a

maximum in overall stability of the bilayer structure for bilayer cholesterol concentrations

around 35mol%CHOL. The experimental membrane strain energy shows approximately

the same form as the excess mixing free energy and gives some credence to the hypothesis

that simply mixing the two (postulated) bilayer components confers stability on the

structure. The enhanced stability then, would appear to come from an increase in internal

energy, i.e., an increase in the cohesive energy density of the material due to the mixing.

Concluding Remarks and Perspectives

The bulk elastic modulus of the lipid bilayer is ~109 Nm -2, in the range found for

normal incompressible fluids and high density polyethylene. However, because the

membrane is a highly anisotropic structure the surface area compressibility at constant

bilayer volume is expected to contrast markedly with the bulk elasticity. From our

micromechanical measurements, the in-plane, elastic area compressibility modulus for

normal phospholipids is found to be ~10 -1 Nm -1 and when this is converted to an

equivalent bulk modulus by dividing by the membrane thickness of ~5 nm, we see that the

surface compressibility is -107 Nm-2, i.e., in the surface plane, the structure has a

compressibility somewhere between that of an ordinary liquid and a gas! This defines the

softness of this nevertheless cohesive material. We can therefore view the membrane as a 2

dimensional cohesive liquid that (in-plane) can be about 100 times more compressible than

its embedding, aqueous fluid.

Some of our more recent, as yet unpublished, results also show that this area

elasticity can range over two orders of magnitude (50 - 4000 dyn/cm) depending on the

lipid composition and alloying with cholesterol. Compare this behavior with that of metals,

where the Young's elastic modulus for lead and tungsten varies by not quite 20 times, and

for ceramics, where ice to diamond ranges by about two orders of magnitude. Thus, the

lipid bilayer shows a very wide range of elasticity for any single type of material because

it starts from a state of weakly bonded softness.

Before these measurements were made it was generally accepted that the cohesion

in lipid membranes is approximated by twice the interfacial tension between hydrocarbon

116
and water, giving K ~ 100 dyn/cm; i.e., surface pressure is opposed by the hydrophobic

effect between the lipid hydrocarbon chains and the bathing water at the membrane

interface. Whilst the hydrophobic effect can be responsible for getting the lipids to

assemble in aqueous media and sets the lower cohesive limit, the higher moduli for

cholesterol-rich bilayers indicates that there are additional bonding forces responsible for

bilayer integrity, and points to a specific interaction between phospholipids and cholesterol.

These high modulus membranes are now showing expansion behavior like more traditional

solid and liquid materials where the repulsive (thermal) forces between molecules are

counteracted by the attractive, in this case van der Waals, forces between the hydrocarbon

chains.

The phospholipid bilayer, then, presents to the Material Scientist a very accessible,

versatile and simple liquid (or solid) structure with which to test models for elasticity,

cohesion, and failure, including mixing relations. There are not many alternatives for

energy storage and dissipation in this kind of structure and agreement between experimental

data and simple theories is likely to be good.

Finally, these kinds of materials engineering studies are important to both

fundamental and technological endeavors. They provide a basis for understanding the

material properties of natural cell membranes and in formulating mechanisms of membrane

breakdown and cell damage caused by.disease or environmental insult. For example, in

cancer, abnormalities in the biosynthetic regulation of cholesterol constitute early events in

tumorigenesis and underlie many of the phenotypic hallmarks of cancer cells [23]. Altered

cholesterol levels, particularly in membranes, lead to the development of a host of altered

metabolic patterns within the affected tissue, since the normal function of integral

membrane proteins often requires a specific lipid environment. Thus, membrane

expansivity appears to be a very important regulator of cellular events. Our measurements

of the material properties and colloidal interactions of lipid-based systems also provide

much needed engineering design parameters for medical and other technologies that use

lipid bilayers and similar organic thin films in, for example, encapsulated drug delivery,

optics, tribology and biosensors. This is a new area of nanoengineering that uses selfassembling systems to form well ordered 2D arrays of molecules at surfaces. We are

currently involved in the engineering of nanocarrier delivery systems (Stealth@ liposome

drug delivery [24]). These drug-carrying lipid capsules, upon intravenous injection, have

the ability to evade the body's defenses and shift the distribution of toxic anti-cancer drug

away from healthy organs and tissues and more towards the tumor [25, 26].

117
Acknowledgements:

This work was supported by grant GM 40162 from the National Institutes of

Health. I would like to thank Dr. H. P. Ting-Beall for her electron micrographs of cells,

and Mr. R. F. Overaker (of Research Instruments Inc., Durham, NC) for the technical

information regarding micromanipulators andjoy sticks. David Needham is grateful to the

Alfred M. Hunt Fund for the Hunt Faculty Scholarship Award.

References:

1. Tanford, C. 1980. "The Hydrophobic Effect: Formation of Micelles and Biological

Membranes." John Wiley and Sons, Inc.

2. Needham, D., H. P. Ting-Beall and R. Tran-Son-Tay, 1991. A physical

characterization of GAP A3 hybridoma cells: morphology, geometry and mechanical

properties. Biotech. and Bioeng. 38, 838-852.

3. Needham, D., M. Armstrong, D. L. Hatchell and R. S. Nunn, 1989. Rapid

deformation of "passive" polymorphonuclear leukocytes: the effects of pentoxifylline.

J. Cell. Physiol. 140, 549-557.

4. Hochmuth, R. M. and D. Needham, 1990. Viscosity of neutrophils and their transit

times through small pores. Biorheology. 27, 817-828.

5. Needham, D. and R. M. Hochmuth, 1990. Rapid flow of passive neutrophils into a

4gm pipet and measurement of cytoplasmic viscosity. J. Biomech. Eng. 112, 269-

276.

6. Tran-Son-Tay, R., D. Needham, A. Yeung and R. M. Hochmuth, 1991. Time

dependent recovery of passive neutrophils after large deformation. Biophys. J. 60,

856-866.

7. Needham, D. and R. M. Hochmuth, 1992. A sensitive measure of surface stress in

the resting neutrophil. Biophys. J. 61, 1664-1670.

8. Evans, E. and D. Needham, i987. Physical properties of surfactant bilayer

membranes: thermal transitions, elasticity, rigidity, cohesion, and colloidal

interactions. J. Phys. Chem. 91, 4219-4228.

9. Needham, D. and R. S. Nunn, 1990. Elastic deformation and failure of lipid bilayer

membranes containing cholesterol. Biophys. J. 58, 997-1009.

10. Mclntosh, T. J., S. A. Simon, D. Needham and C.-h. Huang, 1992. Structure and

Cohesive Properties of Sphingomyelin:Cholesterol Bilayers. Biochemistry. 31, 2012-

2020.

118
11. Simon, S. A., T. J. McIntosh, A. D. Magid and D. Needham, 1992. Modulation of

interbilayer hydration pressure by the addition of dipoles at the hydrocarbon-water

interface. Biophys. J. 61, 786-799.

12. Kwok, R. and E. Evans, 1981. Thermoelasticity of large lecithin bilayer vesicles.

Biophys. J. 35, 637-652.

13. Needham, D. and E. Evans, 1988. Structure and mechanical properties of giant lipid

(DMPC) vesicle bilayers from 20 C below to 10 C above the liquid crystal-crystalline

phase transition at 24 C. Biochem. 27, 8261-8269.

14. Needham, D., T. J. McIntosh and E. Evans, 1988. Thermomechanical and transition

properties of dimyristoylphosphatidylcholine/cholesterol bilayers. Biochem. 27,

4668-4673.

15. Needham, D., 1992. "Measurement of interbilayer adhesion energy." Membrane

Fusion Techniques. Diizgtines ed. Academic Press. in press

16. McIntosh, T. J. and S. A. Simon, 1986. Hydration force and bilayer deformation: a

reevaluation. Biochem. 25, 4058-4066.

17. Evans, E., 1988. "Mechanics of cell deformation and cell-surface adhesion." Physical

Basis of CeU-CeU Adhesion. Bongrand ed. CRC Press, Inc. Boca Raton, Fla.

18. Evans, E., 1988. "Micromethods for measurement of deformability and adhesivity

properties of blood cells and synthetic membrane vesicles." Physical Basis of Cell-Cell

Adhesion. Bongrand ed. CRC Press, Inc. Boca Raton, Fla.

19. Evans, E., 1989. "Structure and Deformation Properties of Red Blood Cells."

Methods in Enzymology. Academic Press.

20. Needham, D. and R. M. Hochmuth, 1989. Electro-mechanical permeabilization of

lipid vesicles: role of membrane tension and compressibility. Biophys. J. 55, 1001-

1009.

21. Zhelev, D. and D. Needham, 1992. Long-lived reversible pores in giant vesicle:

determination of pore size and edge energy. Biochim. Biophys. Acta. submitted for

publication.

22. Wohl, K., 1946. Thermodynamic Evaluation of Binary and Ternary Liquid Systems.

AIChE. 42, 215-249.

23. Coleman, P. S. and B. B. Lavietes, 1981. Membrane cholesterol, tumorigenesis, and

the biochemical phenotype of neoplasia. CRC Crit. Rev. Biochem. 341-393.

24. Stealth®, "Stealth" is a registered trademark of Liposome Technology Inc.

25. Needham, D., T. J. McIntosh and D. D. Lasic., 1992. Repulsive interactions and

mechanical stability of polymer-grafted lipid membranes. Biochim. Biophys. Acta.

1108, 40.-48.

119
26. Needham, D., K. Hristova, T. J. Mclntosh, M. Dewhirst, N. Wu and D. D. Lasic,

1992. Polymer-grafted liposomes: physical basis for the "stealth" property. J.

Liposome Res., Vol. 2, p. 411-430.

120
TOOL GRINDING AND SPARK TESTING

Edward L. Widener

MET Department

Purdue University

Knoy Hall - Room 119

West Lafayette, Indiana 47907

Telephone 317-494-7521

121

TOOL GRINDING AND SPARK TESTING

Edward L.Widener,PE

Mechanical Engineering Technology Dept.

Purdue University, West Lafayette, IN 47907-1252

KEY WORDS: sparking, non-sparking, grinding, testing, recycling.

PREREQUISITE KNOWLEDGE: Students should be familiar with the

Standard Symbols to identify chemical elements (say Fe, C, Mn, Cr,

Si); and with Standard Systems to identify metal alloys (say AISI 4340

low alloy steel; AISI 316 stainless steel; AISI/SAE M34 tool steel,

i.e. UNS TI1334; ASTM A242, HSLA steel; AA 6061-T6 aged aluminum; and

CDA 122, i.e. UNS C12200). These letters designate the American Iron

and Steel Institute; the Society of Automotive Engineers; the Unified

Numbering System; the American Society for Testing and Materials; High

Strength-Low Alloy; the Aluminum Association; and the Copper

Development Association.

OBJECTIVES: To revive the neglected art of metal-sparking. To

promote quality-assurance in the workplace. To avoid spark-ignited

explosions of dusts or volatiles. To facilitate the salvage of scrapmetals. To summarize important references.

EQUIPMENT & SUPPLIES: (i) Grinding wheel, bench or portable

type; e.g., the common "Dremel Moto-Tool Kit," keyless model 395, with

5-speeds, plus Si-carbide disk (#85422,grey) or Al-oxide disk

(#8215,brown) is satisfactory and readily available at hardware

stores. (2) Eye protection, safety glasses or goggles. (3) Samples

of lo-alloy steels, with lo/med/hi-carbon contents. (4) Stainlesssteels, including iron-crystal types of ferritic/martensitic/austenitic.

(5) Cast-irons, including gray/white/malleable/ductile/wrought grades.

(6) Tool-steels, including types with W/O/A/D heat-treatments. (7)

Light-metals(Li,Mg,Ai,Ti). (8) Copper and its brass/bronze alloys.

(9) Classic sparkers, like Zirconium and Cerium. (10) Optional camera,

instant-color preferred, to freeze motions and record observations.

BACKGROUND: After discovering fire, primitive peoples apparently

learned to kindle flames from tinder and sparks, possibly with rocks

struck by metal ores. Later on, hunters and soldiers of the 16th or

17th centuries replaced fire-locks (ignited by matches) with flintlocks (striking steel-steel) pistols or rifles. Today, we have

cigarette- lighters and gas-igniters (using sparks from cerium,

scratched by steel). Pouring molten steel or cutting structural steel

can produce cascades of twinkling, scintillating sparkles. Driving

behind a gasoline--truck, especially at night, we see sparks from a

chain which discharges static-electricity to the pavement. Also,

plastics and ceramics, although insulators, can collect static charges

and may arc if grounded. Surely, the study of sparking materials is

important for identifying metals, discerning alloy contents, and

averting explosions.

123
PROCEDURE: Students must have proper eye-protection! They should

not test non-ferrous metal-samples on a shop-grinder, normally used by

the iron-workers; soft-metals may clog the wheel, requiring

maintenance to re-dress the wheel and reduce its life.

Samples are then hand-held against the bench-mounted grinder; or

a portable tool with attached grind-wheel can bear against the clamped

sample. Students can stand back to observe sparkles and compare

specimens, before grinding their own. Obviously, bearing-pressures and

spark-arcs can vary, so consistent procedure is recommended for metal

comparisons or contrasts. Although hand-held samples do not exceed 140

Fahrenheit ( threshold of pain for bare skin), there is risk of injury

to ungloved fingers; using tongs brings risks of over-hot samples or

flying pieces; so be careful!

Materials may be identified or classified, referring to standard

charts or tables. However, consult an experienced machinist to save

time and improve diagnoses.

RESULTS: For plain steels, sparking has greater length/frequency/

complexity, as carbon content increases. The characteristic color is

orange. Low-carbon/high-alloy steels, like stainless or magnet grades,

may not spark much.

Grey cast-iron, with much higher carbon-content than

steel,nevertheless has virtually no sparks. The graphite flakes in

iron are soft and not dissolved in a matrix of iron atoms. However,

wrought-iron pipe being cut by torch, may shower sparks profusely

(although carbon is negligible in alpha-ferrite). White iron (chilled

to transform graphite to cementite) sparks well.

Tool steels are traditionally characterized by their distinctive

sparking. However, this is a dying art, practiced mainly by expert

machinists.

Titanium is a real surprise, with its blue-white glow. In dull

contrast, the light-weight aluminum and magnesium alloys produce no

sparks at all! Similarly, copper and its alloys of brass or bronze

have no sparks.

However, zirconium does give that amazing blue-white glow.

Moreover, cerium literally sputters and smokes, if you merely strike

it with a steel bar; it is ideal for cigarette-lighters.

CONCLUSIONS: This is a cheap & quick way to identify tools,

predict carbon-content of steel, select non-sparking equipment, and

salvage valuable metals. However, for unsophisticated eyes and

unskilled hands, the subtle differences in alloy-compositions of tools

and stocks are probably undetectable. Variations of hand-pressure and

spark-flight are troublesome. Moreover, published tables and charts

(by makers of abrasives and welders) tend to be inconsistent and

contradictory.

For scrap dealers or maintenance workers, a set of standard

samples may be collected or purchased; these are controls (benchmarks)

for comparing (gaging) sparks. Another technique is to make or buy

color-photos or dynamic video-tapes of major metals.

For large lots of costly metals, the modern techniques of DTA

(Differential Thermal Analysis) or APS (Arc Plasma Spectrometer) are

often more reliable. These could be used to train novices in spark124
grinding or to verify the preliminary assessments by veteran sparkers,

as insurance against the day when hi-tech units are unavailable or

unaffordable.

RECOMMENDATION: A lab experiment is enhanced by a written report.

Students should explore why materials do or don't spark. Why do

sparks differ in appearance and behavior? What is the size and shape

of grinder dust? How does grinder-wheel composition affect the sparks

and dusts? Apparently, the material hardness and grinder speed

contribute to frictional heating; a material's oxidizing rate or

melting temperature may be involved; consider oxygen concentration or

static electricity. What causes sparks to twinkle or scintillate?

Perhaps particles have blowouts, as the crust is solidified and/or the

heat of fusion is released. Possibly the particles tumble, as they fly

off the grinder, depending on shape variations. Use the references;

search the literature; consult with mechanics; and find the experts

may disagree. This could spark some research and development activity!

ACKNOWLEDGEMENTS: Prof. F.Xavier Spiegel, EE & ES Dept of Loyola

College in Baltimore, MD, provided most of my references and exhibits.

Like Newton, he claims only to stand on the shoulders of giants in the

spark-testing field. Messrs.E.Bishop and EoPitois may indeed be gurus,

but to me Spiegel is special.

Prof.Marvin L.Sarapin, Dept.of Technology, Kean College of

Union,NJ, introduced spark-tests while directing ten summer seminars

to train welders and pipefitters of the United Association. The late

W.Fred Stone conducted sparking demonstrations for the"Ed & Fred Sho_ °

in our lab sessions.

The late Prof.Sayyed M.Kazem, MET Dept, Purdue University, has

been an important resource for team-teaching the metals lab these past

22-semesters.

Prof. David Werstler, Eng.Tech. Dept., MS 9086, W.Washington

University, Bellingham,WA, sent the "Metal I.D." pages from an Allen &

Mortensen lab manual.

Dr. L.Roy Bunnell, Materials Science Dept, Battelle Pacific

Northwest Labs, Richland,WA, sent data and information sheets from the

"Welding Engineer" files.

REFERENCES:

i) Bishop,Edsel E., "The Art of Spark Testing", Wyckoff Steel Co.,

Pittsburgh,PA, 1954.

2) Pitois,E., "Sparking of Steel", transl.by J.D.Gat, Chem. Publ.Co.,

Easton,PA, 1929.

3) Spiegel,F.X.et al, "Scrap-Metal Bibliography", U.S.Bureau of

Mines, Avondale,MD, 1984.

4) Spiegel,F.X.et al, "Scrap-Metal Identification Based on Particles

Generated During Spark-Testing", U.S.Bureau of Mines, Avondale,MD,

1984.

5) Palmer,F.R., "Tool-Steel Simplified", Carpenter Steel

Co.,Reading,PA, 1937.

6) Aston,J. and Story,E.B., "Wrought Iron", A.M.Byers

Co.,Pittsburgh,PA, 1944, p79.

125
7) Hildorf,W.G.and McCollam_C.H., "Metal Pellets, Produced by Spark

Tests, to Identify Alloy Steels", The Iron Age, New York,NY; voi.126,

no.l, pl.

8) Sarapin,M.L., "Properties & Characteristics of Metals", UL#38

Instructor Training Notebook, Purdue University, W.Lafayette,IN, 1988.

9) AIIen,D.K. and Mortensen,K.S., "Materials Science Lab Manual",

Am.Tech. Soc., Chicago,IL, 1992 , p59.

I0) Norton Co., Spark Chart & Table, "Grits and Grinds", June 1940.

EDWARD L. WIDENER

Has taught mechanical engineering technology

at Purdue University (since 1978), concentrating on statics, fluid.mechanics,

materials, labs and technlcal

writing...Member ASME, ASEE, ASM, TAPPI.

Registered P.E. in New York and

Indiana...ABET visitor in 1983-921...B.S.

M.E. from Purdue University and M.S.E.M.

from the University of Kansas...Taught

evenings at IUPU Indianapolis and

Danville, IL. Worked as Mechanical

Development Engineer for "Coria" collagen

casing with Teepak Co., Continental Group

(1976-78). Process Group Leader for

mechanical contractor, Baker-McHenryWelch, Indianapolis (1974-76). Project

Leader for creped-waddlng and secondaryfibers with Kimberly Clark Co., Memphis,

TN (1968-74). Process Engineer for

"Nomex" nylon with E.I. DuPont Co.,

Richmond, VA (1963-68). Associate

Engineer for electro-furnace alloys with

Union carbide Co., Niagara Falls, NY

(1952-60). Fuel Englneer with U.S. Steel

Co., Gary IN,(1951-52).

126
EXPERIMENTS IN CORROSION FOR YOUNGER

STUDENTS BY AND FOR OLDER STUDENTS

James V. Masi

Western New England College

Department of Electrical Engineering

Springfield, Massachusetts 01119

Telephone 413-782-1344

127

EXPERIMENTS IN CORROSION FOR YOUNGER STUDENTS

BY AND FOR OLDER STUDENTS

James V. Masi, PhD

Western New England College

Dept. of Electrical Engineering

Springfield, MA 01119

THE COLLEGE EXPERIMENT

KEY WORDS: corrosion, batteries, electromotive force

series, anode, cathode, plating.

PREREQUISITE KNOWLEDGE: The college student should

understand the concepts of electrochemical potential through a

basic chemistry course and a concurrent materials science course

(usually third year level). The colle_e student is first given

his or her classroom lecture on corroslon, is shown the

"Corrosion in Action" video from LaQue Center for Corrosion

Technology, Inc. (Wrightsville Beach, NC), and performs a

laboratory experiment. This allows the college student to be a

mentor to the junior high school student. The junior high school

student should have had a general science course and be in the

upper half of his or her class.

OBJECTIVES: To illustrate the electrochemical nature of

corrosion and to observe the location of anodes and cathodes

(arising from differences in composition and cold work) of metals

immersed in electrolyte solutions. The magnitudes of voltages

and current densities on corroding couples is obtained.

EQUIPMENT AND SUPPLIES: College: Iron nails, three Petri

dishes, 400 ml beaker, 3% NaCl electrolyte, agar gel, copper

displacement plating cell, zinc electroplating cell, two high

impedance multimeters, phenolphthalein in alcohol solution,

potassium ferricyanide, deformed nails, zinc plated nails, and

copper wlres and sheets. Junior High: Two multimeters, small

d.c. power supply with clip leads, 10X microscope, large and

small area electrodes of zinc, platinum, calomel, graphite,

aluminum, copper, 1018 steel, 300 series stainless steel,

mercury/silver amalgams, lemons and potatoes, and nails of iron,

copper, and aluminum.

PROCEDURE: The work is to be done by pairs of students.

Each pair will observe three different, previously prepared

corrosion specimens in Petri or glass dishes. Prepare one

similar specimen, and observe two different specimens freshly

prepared by other groups in the class. Also, each group will

measure emf and corrosion current density for the following cells

(all of which use the 3% NaCl solution as the electrolyte): iron

vs cold worked iron, iron vs zinc, iron vs copper wire and

subsequently vs copper sheet of much larger area.

i. Observe the corrosion couples prepared at least six hours in

advance. The advance preparation allows for the indicator

129
reactions to develop fully. The cells are prepared using the

following recipe. To make 250 ml, adequate to cover nails in

three Petri dishes, dissolve 5 grams of agar in 250 ml of 3% NaCl

solution. Place one nail in each Petri dish. Pour agar solution

evenly into three Petri dishes. The first dish should contain an

ordinary iron nail. The second should contain a nail dipped half

its length for two minutes into the copper sulfate displacement

solution (200 g/L H20). The third should contain a nail

electroplated for ten minutes over the tip half with zinc (200

g/L potassium chloride, 32g/L zinc chloride, galvanized nail

anode, and current density of 1 A/dm2). Check these specimens

occasionally to observe any changes. Record.the observations.

Other small objects of interest to the indivldual student may be

placed into the solution not in contact with the nail.

2. Fill a 400 ml beaker approximately half full with 3% NaCl

solution (NOTE: This is about the concentration as in seawater

and about three times more concentrated than in blood.). Clip

multimeter leads to the selected pairs of electrodes and dip the

electrodes (but not the clips) into the NaCl electrolyte.

Measure the voltage and current, noting the polarities. Prior to

immersion, estimate the approximate areas of each electrode

so that current densities can be calculated. Describe any

visible effects in the solution while the electrodes are

immersed. Note any changes in the surface of the electrode after

they are removed from the electrolyte and washed. The electrode

pairs are: (a) iron nail vs deformed iron nail; (b) iron nail vs

copper wire and copper sheet; and iron nail vs a zinc coated

nail.

3. Questions: Answer the following questions in the report.

(a) In what order of electrochemical activity should

iron, copper, and zinc be placed? Illustrate by the

quantitative emf differences recorded in your

measurements.

(b) How does the magnitude of the emf generated by the

difference in cold work compare with the emf of the

galvanic couples?

(c) What is the cathodic reaction and why does it cause

phenolphthalein to turn red only in those regions?

(d) For each of the cells in the beakers, calculate the

approximate current densities for cathodes and anodes.

In which case is the most rapid corrosion taking place?

Why? What is the effect of the ratio of cathode to anode

area and why is there an effect?

(e) Would you use zinc-coated roofing nails on aluminum

flashing?

(f) How could you eliminate the emf between the shank of

the nail and its head or tip?

DISCUSSION: Corrosion in aqueous electrolytes arises

because of electrochemical differences of conducting solids that

are coupled through an electronically conducting external

circuit. Dissolution of metallic ions (or oxidation) takes place

130
at the anode while reduction (of 02, hydrogen, metal ions,

cations) occurs at the cathode in a galvanic cell.

The experiments illustrate the contributions of differences

in the amount of cold work and chemical composition differences

to the establishment of electromotive forces that cause corrosion

to take place. Reactive indicators locate anodes and cathodes by

color changes. The deep blue-black color of the ferroferricyanide ion identifies the anode where iron dissolves. A

less distinct white color is formed by zinc ferrocyanide. In

either case, the increasing alkalinity or pH at the cathodic

areas causes phenolphthalein to turn red.

Using the same basic materials dipped into a sodium chloride

solution in a beaker, the emf difference and the total corrosion

current can be measured approximately with a high impedance

multimeter. A "zero-resistance" ammeter is used by the corrosion

engineer, since a normal ammeter has appreciable resistance,

which could limit the current flow appreciably. For instance,

the difference between the "true" short circuit current and the

one actually read by the multimeter can be as much as 20%,

depending on the quality and method of current measurement

employed in the multimeter. The recording of the polarity is

equally important and indicates the anodes and cathodes. An

uncoated iron nail should be measured against a copper nail and

copper sheet and against a zinc-plated nail. Also, an undeformed

iron nail should be measured against a heavily deformed nail. In

each case, both voltage and current should be recorded. Using

the sizes of the immersed areas of anodes and cathodes allows the

experimenter to estimate current densities. Verify that the

ratio of cathode to anode area is important for the measurements

of the iron nail vs a smaller copper wire or nail and against a

larger area copper sheet. Keep the clip contacts out of the

electrolyte at all times.

THE JUNIOR HIGH SCHOOL EXPERIMENT

Under the auspices of a National Science Foundation Grant

for teaching junior high school students math and science, the

Electrical Engineering Department at Western New England College

has developed a set of three experiments taught at two different

levels. These experiments are developed by E.E. professors to be

taught to the junior high school students by assigned, mentor

junior level electrical engineers at the College, during the

summer and after school during the regular year. Some of the

experiments are also performed by the college junior class in

their Materials Science course during the regular school year in

a different context and at a higher level. The experience has

proven to demonstrate corrosion, qualitatively and quantitatively

to younger, potential engineers and to provide learning

experiences for the student-teacher as well as the college

students at a higher level.

131
The three experiments chosen were: I. POTATOES, LEMONS,

NAILS, AND MONEY; 2. CORROSION IN EVERYDAY LIFE: ANODES AND

CATHODES; and 3. CORROSION PREVENTION: MINDING YOUR A's AND C's.

The first of these experiments is included in the following

section.

BATTERIES:

POTATOES, LEMONS, NAILS, AND MONEY

Name Date

INTRODUCTION

Often, many people think that there are two kinds of

electricity - static electricity and current (or moving)

electricity. Actually, they are really the same. The difference

is that the electrons (negative charges), ions (negative or

positive), or positive charges are not moving in static

electricity, while current electricity is made up of moving

charges. When electrons move and produce an electrical current,

they develop a magnetic field. To understand electricity, it is

necessary to know something about the relationship of electricity

and magnetism. The two subjects are closely related.

Electricity can produce magnetism and magnetism can produce

electricity. This understanding has led us to many useful

devices such as motors, generators, pacemakers, automobiles,

batteries, electroplating, etc.

Electrochemical energy works for us and against us. It

works against us when we have corrosion, such as the rust on a

car or the rotting of gutters with nails of different materials

than the gutter. It works for us when we see the action of a

battery or an electroplating bath (like when we chromium plate a

bumper on a car).

EXPERIMENT OBJECTIVES

As a result of this experiment you should be able to:

i. Predict when things will corrode;

2. Understand the electromotive series;

3. Make and measure the voltage of batteries using

different materials;

4. Predict what voltage a particular battery will have

MATERIALS AND EQUIPMENT

1-POTATO 1-STEEL NAIL

1-LEMON SOME PAPER TOWELS

1-VOLTMETER TEN PENNIES

1-AMMETER TEN DIMES OR NICKELS

1-COPPER NAIL A SMALL LIGHT BULB

1-GALVANIZED NAIL

1-PIECE OF ALUMINUM FOIL

1-PIECE OF COPPER FOIL

SOME VINEGAR OR LEMON JUICE

132
PROCEDURE

Insert one end of the steel nail into one end of the potato

and stick one end of the copper nail into the other end of the

potato as shown. Connect the negative probe of the meter to the

copper nail. The meter should read about 1/2 volt d.c. A lemon

can be substituted for the potato. Try moving the nails closer

together to see if the voltage changes. Do the same with all the

combinations of materials you have available. Now measure the

current produced by these materials, noting the changes with the

size of the material used. Fill out the tabular chart below to

see what the results are for various pairs of materials tested.

What did you notice about the voltage change with distance?

What did you notice about the voltage change with electrolyte?

What did you notice about the current change with size of the

materials?

Now use lemon juice or mix a tablespoon of vinegar with a

_lass of water. Then soak a paper towel in the solution. Tear

It into coin-sized pieces. Place a penny on the table and lay a

wet piece of paper towel on top as shown in the next figure.

Place a dime on top of that and then another piece of paper

towel. You want a stack of alternating pennies and dimes, with

each coin separated by a wet paper towel. Start the stack with a

penny and end with a dime. Connect a voltmeter to the bottom

penny and the other lead to the dime. What is the voltage?

What is the current?

What can you conclude from some test you can perform on this

setup as to how the voltage and current vary with the number of

penny/dime pairs?

Multimeter with lemon battery

NAILS

133
TABULAR CHART

NAIL COPPER NAIL STEEL NAIL GALVANIZED AL_INUM NAIL/FOIL

COPPER

NAIL

STEEL

NAIL

GALVANIZED

NAIL

ALUMINUM

NAIL/FOIL

How many penny/dime pairs do you need to light the bulb supplied

with the setup?

What kind of results would you get if you did the same thing with

alternating layers of copper and aluminum?

What could you make with this setup?

Stack of coins as a battery

PAPER

TOWEL

COIN8

IIII

r ) /

©

I +3.812 /

/

134
REFERENCES

1. Fontana, M. G., Corrosion Engineering, McGraw-Hill Book Co.,

New York, NY. 1986.

2. Barrett, C. R,, Nix, W. D., Tetelman, A. S., The Principles

of Engineering Materials, Prentice-Hall, Inc., New Jersey.

1973.

3. Wood, R. W., Physics for Kids, Tab Books, New Jersey. 1990.

I_e_cmu_m Force Series

Standard Potent_lt

Electrode Reaction _°(in volts) at 2YC

Au "_- + 3e- = Au 1.50

Ptz" + 2e- = Pt ca. 1.2

Pd:" + 2e-= Pd 0.987

Hg2" + 2e- = Hg 0.854

Ag" + e- = Ag 0.800

Hg_,'" + 2e- = 2Hg 0.789

Cu" + e- ffi Cu 0.521

Cuz" + 2e- ffi Cu 0.337

2H ° + 2e- = H., 0.000

Pbz_ + 2e- = Pb -0.126

Snz" + 2e- = Sn -0.136

Mo3" + 3e- = Mo ca. -0.2

Ni:" + 2e- = Ni -0._0

Co2° + 2e- = Co -0.277

TI* + e- =TI -0.336

In3" + 3e- ffiIn -0.342

Cd2" + 2e- = Cd -0.403

Fe z- + 2e- ffi Fe -0.440

Ga 3- + 3e- ffi Ga -0.53

Crz- + 3e- = Cr -0.74

Cr_ + 2e- = Cr -0.91

Zn-'" + 2e- = Zn -0.763

Nb _" + 3e- = Nb ca.-I.I

Mn 2. + 2e- ffiMn -1.18

Zr" + 4e- = Zr -1.53

Ti2. + 2e- = Ti -1.63

AP ° + 3e- ffiAI -1.66

Hf4. + 4e- = Hf -1.70

Us° + 3e- = U -!.80

B¢2"'+ 2e- = Be --1.85

Mg2. + 2e- = Mg -2.37

Na* + e- = Na -_71

Ca2" + 2e- = Ca -2.87

K" + e- ffi K -!.93

l.i* + e- = Li -3.05

135
Participants

136
A MINIATURE FATIGUE TEST MACHINE

Steven M. Tipton

Mechanical Engineering Department

The University of Tulsa

600 S. College

Tulsa, Oklahoma 74104

Telephone 918-631-2994

137

A Miniature Fatigue Test Machine

Steven M. Tipton

Mechanical Engineering Department

The University of Tulsa, Tulsa, Oklahoma

KEY WORDS: Fatigue, wire, strain-life, fatigue data reduction, statistics

PREREQUISITE KNOWLEDGE: This experiment requires a basic knowledge of strength-of-materials bending stress-strain relations and basic fatigue concepts (S-N or e-N). Also, an introduction

to physical metallurgy and material microstructures is helpful.

OBJECTIVES: To enable the student to generate statistically sound fatigue data sets on wire specimens

of varying diameter, microstructure or material. The student can then assess the effect of these parameters of fatigue resistancel The student can also be exposed to ASTM techniques for fatigue data reduction and presentation. Experiments involving variable amplitude block loading are also easily conducted.

EQUIPMENT AND SUPPLIES: A miniature fatigue testing apparatus and wire ranging in size from

14 to 22 gauge.

PROCEDURE: This experiment represents a refinement of the "paper clip demonstration" many professors use to demonstrate the concept of fatigue. Numerous mechanisms could be used to obtain deflection controlled bending. An example experimental set up is illustrated in Fig. 1. A wire specimen is

mounted in a cantilevered support. The other end of the wire is oscillated transverse to its undeformed

axis. When a wire of a particular diameter, d, material and microstructure, is displaced a constant distance, H, above and below the support centerline, the severity of bending is dependent only on the distance, L, from the fixed end of the wire to the moving end.

wire carrier shut- off switch base

specimen _ _'/ shut-off _-- assembly _ plate

_, ./---- d trigger

_ f._ 1 2 3 4 5 6 7 8 I '_- 14 16 18

H ooooooooc(o)oooooo )

__ _._ v0 / cantilever 0 support"

-- ZL_ //

specimen set screw /

carrier pivot point "

digital counter

Figure 1. Experimental set up.

139
The carrier moves in an arcuate path, since it is fixed to the end of a pivoting member that oscillates

underneath the support plate about a pivot point as shown in Fig. 1. An AC motor drives the pivoting member via a scotch yoke mechanism. The motor operates at 1550 RPM, but the speed of the carrier is reduced to about 600 RPM using a timing belt and pulleys. This reduction is necessary to reduce

inertial effects.

When a wke is mounted in the cantilever support, a trigger is depressed and held in place by the wire

specimen. The trigger holds closed a switch that completes a circuit to the motor, and serves as an automatic shut- off. Since the specimen always fails at the grip, the trigger is released upon specimen failure,

cutting power to the motor.

Since specimen deformation and damage are confined to the grip area, the design of the grip fixture

can significantly influence results. However, as long as a consistent gripping configuration is used from

test to test, this effect is less important in comparing data sets. In the apparatus presented here, cylindrical brass inserts were fabricated with holes bored through their center corresponding to a clearance fit

for wires of a particular gauge. A transverse set screw hole was drilled radially at the center of each

insert to secure the specimen. Contact stresses between the specimen and insert at the failure site could

be diminished if a tough polymeric material (e.g., nylon or polycarbonate) were used instead of brass.

Figure 2 illustrates the specimen support and shut-off switch configuration.

specimen set scrc

brass insert _ O

O

O shut- off switch O

shut-off trigger assembly

Figure 2. Specimen support and shut-off switch configuration.

A digital counter is used to record cycles. This electronic counter is battery operated and triggered by

a magnetic reed switch. A magnet on the pivoting member closes the reed switch to record one count

each cycle. A pushbutton reset is located on the front of the counter.

In order to correlate data from different diameter wires, a consistent damage parameter is required.

For instance, in a conventional axial fatigue test or rotating-bending fatigue test, the stress amplitude

is usually plotted versus fatigue life. However, deformations associated with conventional fatigue experiments are much smaller. Forces are controlled and therefore stresses are straightforwardly calcu140
lated. For the wire samples tested in this experiment, a more involved analysis is required to develop

a stress or strain relation. This, in itself can provide an interesting aspect to the experiment for undergraduate or graduate level students.

INSTRUCTOR NOTES:

Fatigue is a complex subject. To convey fatigue concepts in the classroom, the subject is often oversimplified to the point where the methodology grasped by a student is too simple to be applicable to any

serious fatigue problems. Experience is the best teacher when it comes to fatigue and a good way to

gain experience is to conduct fatigue testing. However, the cost and time involved in generating meaningful, statistically sound fatigue data is usually prohibitive in a student laboratory setting. Rotatingbending tests make it possible to rack up cycles quickly, but even then specimens are not inexpensive

or easy to obtain. Students usuallygenerate one or a few points each, then blame scatter on the dubious

nature of their lab partners. The majority of undergraduate students never gain the experience of generating and reducing their very own fatigue data set.

To make up for this, many students have been required to bend paper clips back and forth, by hand,

controlling the degree of bending as closely as possible. In this way, crude but useful lessons can be

learned about very low cycle fatigue. The experimental apparatus demonstrated in this experiment represents a refinement of the paper clip exercise.

The main difficulty with the apparatus is the complexity in characterizing the exact state of stress and

strain at the failure site. However, this is overcome by the consistency between tests, by the repeatability

of the data and by the extreme ease of "specimen preparation."

The embodiment of the miniature fatigue testing apparatus can take on any number of forms. With such

an apparatus, a student can gain first-hand experience in fatigue testing and data reduction. A machine that is simple and safe to operate can be used for a wide range of experiments, from extremely

simple in concept for underclassmen, to quite refined for graduate students.

SAMPLE DATA SHEETS:

A summary of potential experiments that could be undertaken with this apparatus is listed below:

• Fatigue Damage Correlation Parameters: As a wire is displaced back and forth

in fully-reversed deflection, the state of stress-strain at the failure site fluctuates. It is possible to investigate several potential damage parameters to find the

most suitable. For instance, for a given wire diameter, d, horizontal displacement,

H and lateral position, L, approximate expressions can be derived for the stress

amplitude, Sa, or strain amplitude, ea. Both of these have been used extensively

to correlate fully reversed fatigue data. However the derivation of these expresSions can be a formidable task. A simple approach is to plot elastically calculated

stress amplitude,

3HdE

se= 2 L 2

(where E = the elastic modulus) versus life. Even though the value of this parameter usually greatly exceeds the yield stress of the material, the parameter is likely

141
to provide a relative measure of the bending strain amplitude at the failure site.

To refine the analysis, data from tests conducted on wire of identical material, but

varying diameter would be extremely useful. Some factors that could be considered are: Plastic Hinging (larger diameter wire or higher amplitude deflections

can result in the formation of a plastic hinge at the grip),DynamicEffects (the inertia of the moving wire can add to the stress-strain at the support point), Contact

Stresses (these could be reduced if a tough polymeric material were used for the

specimen mounting insert) and OverallMachine Geometry (such as the carrier arc

radius and the width of the opening in the carrier).

• Effect of Microstructure on Fatigue Life: Wire samples could be prepared by applying varying heat treatments to initially identical material. Figure 3 depicts data

for 1090 steel musicwire in three heat treat conditions. These data are correlated

using elastically calculated bending stresses (just discussed). (The data were generated by a.freshman student in one afternoon.)

_, 13 Gauge 1090 Steel Music Wire

"4

lOOOm +q-AA X

• annealed

r,.) + -i-Ak- _, )

× cold drawn

• F,,,,I

................... i i ! I I r I

10 100 1000 10000

Cyclesto Failure

Figure 3. Data from 1090 steel wire in three different heat treat conditions. These datawere generated using a hand powered prototype in one

afternoon by a freshman student.

Another example would be to quench sets of steel wire samples, then temper at

varying times or temperatures to produce a range of microstructures/hardnesses.

For comparison, an additional set could be austempered. Microhardness tests

could be used to find the hardness of each set. The question could then be addressed: Do the data from austempered samples correlate with the data from

tempered martensite samples at similar hardness?

142
• Relative Fatigue Behavior of Different Materials: Wire made from several materials (stcel, aluminum, copper and brass) can be obtained from any hardware

store. Music wire also is readily available.

° Cumulative Damage in Variable Amplitude Block Loading: A small set of constant amplitude baseline fatigue data could be generated, for instance, by testing

several samples each at two different bending deflections (corresponding to two

different hole settings in Fig. 1). The most severe deflection would cause samples

to fail at a mean life of N1, while the less severe setting would result in a longer

mean life of N2. Variable amplitude block loading could then be generated at follows: at the most severe deflection, use the machine to apply _1/2 cycles to a new

specimen. Next, change to the less severe hole setting and run until failure. Miner's rule would predict the wire to break in NJ2 cycles, but how well does the rule

work for this high-low block loading sequence? The procedure should be repeated several times, then reversed by applying the less severe bending first, followed by the more scvere loading (a low-high block loading sequence). It has

been demonstrated that high-low block loading has been found to be more severe than low-high load blocks [1,2]. To demonstrate this experiment, consider

the baseline data for dark annealed wire (purchased at a hardware store) as presented in Fig. 4.

19 Gauge Dark Annealed Steel Wire

_IK _ Level 1

m 1000.

m

X>O¢_------ Level 2

>IKX._----- Level 3

¢3

Level 4 _ ×X

_a 10{3 ..................

100 1000 10000

Cycles to Failure

Figure 4. Data from 19 gauge dark annealed wire. There are

four data points per load level.

In addition to this baseline data, additional block loading tests were run as summarized in table 1 on the next page:

143
Table 1 - Block Loading Test Data

19 Gauge Dark Annealed Steel Wire

Level 2 Mean Life, N 2 = 1,080 cycles (N2/2=540 cycles)

Level 4 Mean Life, N4 = 10,945 cycles (N4/2=5472 cycles)

HIGH-LOW BLOCK: LOW-HIGH BLOCK:

Apply 540 cycles at Level 2 Apply 5472 cycles at Level 4

Next: Apply loading at Level 4 Next: Apply loading at Level 2

Leads to failure in: 3640 cycles Leads to failure in: 422 cycles

3942 cycles 389 cycles

3394 cycles 252 cycles

In the high-low tests, the mean number of less severe (level 4) cycles following

the 540 applications of level 2 loading is 3658 cycles. This represents a cycle fraction of 0.336, considerably less than the 0.5 cycle fraction predicted by Miner's

rule (which corresponds to a predicted remaining life of 5472 cycles). A similar

result is demonstrated by the low-high blocks. Loading at level 2 following 5472

cycles of level 4 loading, the mean life was 357 cycles (a cycle fraction of .328).

This test could be repeated with different cycle ratios and between different load

levels to demonstrate sequence effects on cumulative fatigue damage.

Any of the assignments just presented could be supplemented with the following tasks or

follow- up experiments:

• Correlation of Fatigue Strength with Tensile Strength: Wire could be tested in

an axial testing machine. Strength, ductility and microhardness could be compared with a material's fatigue behavior.

• Fractography: Fracture surfaces from an entire set of specimens can be mounted

on a single stage for examination under a light microscope or a scanning electron

microscope.

• Statistical Reduction of Fatigue Data: The ASTM Book of Standards, Volume

03.01 (Metals Test Methods and Analytical Procedures) contains several standard

practices pertaining to the analysis and presentation of fatigue data. Among these

are:

E 468- 90, "Presentation of Constant Amplitude Fatigue Test Results for Metallic

Materials" and

E 739-91, "Statistical Analysis of Linear or Linearized Stress-Life (S-N) and

Strain Life (e-N) Fatigue Data."

Students could gain valuable, first hand experience in the applications of these

standards.

144
REFERENCES:

1. Fuchs, H.O. and Stephens, R.I., Metal Fatigue in Engineering, John Wiley and Sons, New York, N.Y.,

1980.

2. Mitchell, M.R., "Fundamentals of Modern Fatigue Analysis for Design," Fatigue andMicrostructure,

Society of Automotive Engineers, 1977, pp. 385-437.

SOURCES OF SUPPLY:

An experimental set up like the one depicted in this paper can require a considerable amount of development time. For instance, safety must bc considered since the carrier can do damage if cncountcred

by the operator. Electrical switches and wiring must be isolated and well grounded. For a fully enclosed

apparatus, the heat generated by an electric motor must be accounted for, since the machine can conceivably run for long periods of time. The development of such an apparatus could make an excellent

student design project.

Thc earlicst vcrsion of this machinc to bc investigated by the author was powered by a hand-cranked

fishing reel. Thiswas followed by a prototype similar tothe one presented in this paper, powered by an

electric motor. Although the results wcrc useful, the prototype revealed two main difficulties that must

bc addressed. First, the AC motor (1/25 hp) used for the device develops a great deal of heat and would

not bc suitable for long term testing in an enclosed device. Second, the scotch yoke mechanism utilized

to oscillate the carrier moves more quickly one direction than the other. This leads to uneven inertial

loading on specimens. How to achieve fully harmonic oscillation, with minimal inertial loading on the

motor, is not as trivial a design problem as it first appears.

A refined, more portable version is currently being designed and is depicted in Fig. 5. The new machine

is to be mounted in a can3,ing case with a transparent lid. A fan is included for cooling the motor and

a new mcchanism is incorporated to provide uniform, harmonic oscillation. Thc mcchanism is a cam

that drives a follower mounted to the wire cantilever support. This oscillates the wire support while

fixing the frcc end of the wire bctwecn two ground and hardened pins (as opposed to moving the free

end, as in Fig. 1). The harmonic oscillation ensures that inertial loading on specimens is the same in

both directions. The new mechanism further reduces dynamic effects on sample loading by decreasing

the overall motion of the wire samples. Furthermore, vibration of the machine itself is reduced since

the moving parts are smaller and oscillate over a much smaller amplitude. For safety sake, the closing

of the lid activates a switch that sets the machine into operation. The machine is inexpensive enough

that a number of them could be obtained for considerably less than the cost of a single rotating-bending

machine. Students can utilize the machine in a laboratory or could check the machines out for use in

their rooms.

145
slot in support plate cam (under support plate)

•....,..../" .I, . .cam center, of rotation

, \ .-- , / , pivotmgspecimen

i'' jX,",_. ° .-- ',7 ,,. ,, support hardened pins

..:: .,

,,, , © 0

I

15"'" ,,..

O

pivot free end support

point (moves to control

specimen set screw bending deflection)

insert

_._....2. ! !- _lr_ I pOlymeric I

Figure 5. Revised experimental set up.. (Shut-off switch not shown for clarity.)

146
INTRODUCTION TO HIGH

PERFORMANCE COMPOSITES

Norman J. Johnston

National Aeronautics & Space Administration

Langley Research Center

MA-226

Hampton, Virginia

Telephone 804-864-4260

147

INTRODUCTION TO HIGH PERFORMANCE COMPOSITES

Norman J. Johnston

NASA Langley Research Center

Mail Stop 226

Hampton, V'trginia 23681

ABSTRACT

THE TALK WILL ADDRESS THE FOLLOWING QUESTIONS:

• WHAT ARE HIGH PERFORMANCE COMPOSITES?

° HOW ARE THEY USED TODAY? (i.e., WHY ARE

THEY IMPORTANT TO YOU AS USERS AND AS

TEACHERS?)

• WHAT ARE THEIR PROPERTIES?

° HOW DO YOU MAKE THEM?

• WHAT ARE THE FUTURE TECHNOLOGY NEEDS FOR

COMPOSITES? (i.e., WHY SHOULD YOU TEACH

STUDENTS THIS TECHNOLOGY?)

IN ADDTION, SAMPLES OF COMPOSITE

REINFORCEMENTS SUCH AS GLASS, CARBON AND

KEVLAR FIBERS, MATRIX MATERIALS AND

FABRICATED COMPOSITE PARTS WILL BE

DEMONSTRATED AND MADE AVAILABLE.

149
STRUCTURAL BUILDING

MATERIALS

HISTORICAL PERSPECTIVE

WOOD

STONE

ICE

CLAY/CERAMIC

METAL

SYNTHETIC POLYMERS

COMPOSITES

NOMINAL RELATIVE PROPERTIES OF

THERMOPLASTIC MATERIALS

-'-' Unreinforced

Short-fiberreinforced

Lonq-fiber reinforced

(0° _rientation)

Tensile strength

Flexural

strength J

Modulus !

Heat dist. _

temp.

Impact -

strength

I I I I I I

0 5 10 15 20 25 30

Relativevalue

150
POLYMERICCOMPOSITEMATERIALS

Reinforcement

Glass _ Pre-impregnated tape Laminatedstructure

Boron

Graphite

Kevlar

Matrix

Epoxy Fiber _ _

Bismaleimidepolyimide } Matrix --f

ii ;iiii ̧

151
ROLE OF FIBER

• CARRIES IN-PLANE LOADS: PROVIDES STIFFNESS AND

STRENGTH

• REDUCES THERMAL COEFFICIENT OF EXPANSION

ROLE OF MATRIX

• BONDS AND HOLDS FILAMENTS IN PLACE

• PROTECTS FILAMENTS

• PROVIDES TRANSVERSE STRENGTH

• ACTS AS A LOAD TRANSFER MEDIUM

• PROVIDES INTERLAMINAR TOUGHNESS

• PROVIDES DURABILITY

SOME DIFFERENT STRUCTURAL LEVELS FOR COMPOSITES

GLOBALLEVEL

•SUBCOMPONENLEVEL T

"*" LAMINATELEVEL

-,-... ,,,...

SUBLAMINATELEVEL

MICROMECHANI CSLEVEL

FIBER

MATRIX

152
POTENTIAL BENEFITS OF COMPOSITES

SUPERIOR TO METALS

DESIGN FLEXIBILITY

CORROSION RESISTANCE

HIGH SPECIFIC STRENGTH/STIFFNESS

LOW THERMAL EXPANSION

HIGH FATIGUE RESISTANCE

UNPROVEN POTENTIAL

LOWER COMPONENT COSTS

o FABRICATION COSTS

o QUALITY ASSURANCE COSTS

o BUY-TO-FLY RATIO

DAMAGE TOLERANCE

o COMPRESSION AFI'ER IMPACT

o OPEN HOLE STRENGTH

o FRACTURE TOUGHNESS

REPAIR/MAINTENANCE

RELIABILITY

OUTLINE

• WHAT ARE HIGH PERFORMANCE COMPOSITES?

• HOW ARE THEY USED TODAY? (i.e., WHY ARE THEY

IMPORTANT TO YOU AS USERS AND AS TEACHERS?)

• WHAT ARE THEIR PROPERTIES?

• HOW DO YOU MAKE THEM?

• WHAT ARE THE FUTURE TECHNOLOGY NEEDS FOR

COMPOSITES? (i.e., WHY SHOULD YOU TEACH

STUDENTS THIS TECHNOLOGY?)

153
APPLICATIONS FOR CARBON FIBER

REINFORCED COMPOSITES

Airframe Components

• Lightly-LoadedStructure

• ControlSurfaces • Empennaqe(Horizontaland Vertical

• Fairings Stabi[izers)

• Doors • Floor Panels

• Heavily-LoadedStructure

Wing • HelicopterBlades Fuselage

• EngineComponents

Missiles

• Fins,Tubes

SportingGoods

TennisFishing RacketsR°ds andBoxes • GolfClubShafts

RecreationalBoats

• Hulls • Masts

APPLICATIONS FOR CARBON FIBER

REINFORCED COMPOSITES

Automotive

• Drive Shafts • Small Engine Components (pistons rods, etc.)

• Frames • Leaf Springs

Industrial

• Pressure Vessels • Offshore Drilling Platforms and Cables

• Housings, Covers • Downhole Drilling Equipment

• Piping and Ducting Components

Submarines

• Hulls • Dry Deck Sheiter

Ordnance

• Shelters • Personnel and Vehicle Armor

• Weapons • Bridging and Portable Structures

154

Composite Components

737

Elevator

150-1b weight savings per. airplane

(26% weight savings) _,_

Stabilizer (NASA)

116-1b weight savings per airplane

727 (22% weight savings)

AIRCRAFT ENERGY EFFICIENCY

(ACES)

COMPOSITE PRIMARY AIRCRAFT

STRUCTURES

I TRANSPORT SECONDARY COMPONENTS I

26.4% WEIGHT SAVED 23.6% WEIGHT SAVED 24.6% WEIGHT SAVED

12 UNITS IN FLIGHT SERVICE 8 UNITS IN FLIGHT SERVICE 10 UNITS IN FLIGHT SERVICE

SIZE'. 3.2' x 13.2' SIZE: 4.2' × 7.7' SIZE: 3.4' x 17.4'

WEIGHT: 67# WEIGHT: 107# WEIGHT: 98 #

156
AIRCRAFT ENERGY EFFICIENCY

(ACEE)

COMPOSITE PRIMARY AIRCRAFT

STRUCTURES

[TRANSPORT MEDIUM PRIMARY COMPONENTS I

. --'4- " :_ '-'.,r_ _,

I

_- _._. . '_... _ ._'. . '_':'_,,,I I

SIZE: T' X 23' SIZE: 9' X 25' SIZE: 4' X 17'

WEIGHT: 78G_* WEIGHT: 620_* WEIGHT: 204-

WEIGHT SAVED: 22.6% WEIGHT SAVED: 28,4% WEIGHT SAVED: 22.1%

157
158
Advanced Composite Structural

Applications Are ,_

Continually Expanding

ATF

40% of Structure

• Fuselage Substructure

• Inlet Structure

• Integral Tankage

• Bulkheads

2% oi Structure

• Secondary Structure

• Empennage Applications

• Full Depth Honeycomb

• Co-Cured Assembly AV.8B

27% of Structure

F.18 • Wing Substructure

10% of Structure • Fuselage Apphcahons

• Primary Structure • Integral Shffeners

• Wing Applications • Strakes

• Monollth_c Laminates

• Bolted Assembhes

• Sandwich Panel Skins

159
A GLIMPSE OF THE FUTURE 

- F-22 STEALTH FIGHTER - ..------ * .- *-.7--;-T--- --- -7.F.- ... . . ., .; ,:*: + , 3, .. d.<3 , ?s:g:2g:..?c . . . . . . . . .' , , ..; ..'. .! .I .... ... . . . .' . . . - . ., :- . .. ,,#: +.- .- -.- .. :- " -,. . . . :' . .... ...... ,;::. 

' : .a .. ,* ,.-.- .. . ..... ... 
Douglas Mach 2.4 Baseline Design

Titanium sandwich

Composite sandwich

Composite stiffened sheet

Other

COMPOSITE STRUCTURE WEIGHT SAVING POTENTIAL

38"/o WEIGHT

5%i SAVINGS

0%7- PER BASELINE CENT

STRUCTURAl.

WEIGHT

4%

33%

14%

161
PERCENT WEIGHT SAVINGS IN TRANSPORT WINGS

BY 1990-1995

1980

2nd generationcomposite

__ 32%

1

1stgenerationcomposite [

Advanced - =

metals A 10%equals25Mgallons fuel per year*

10% '_Assume200airplane fleet,

200passengersper airplane,

1000N.mi. flights

I I I I

0 10 20 30 40

Weightsavings, %

SUBSONIC TRANSPORTS

-COMPOSITES RATIONALE-

• 1990's Subsonic Commercial and Military Aircraft

World Market is Projected to be > $200 Billion.

• Subsonic Aircraft Sector Contributes to U. S.

Industrial Technology and National Security Base

Comprising Over 15,000 Industrial Firms.

• Subsonic Aircraft Industry is Important to U. S.

Economy, Accounting for Largest Positive Contribution

of Any Manufactured Goods to Our Balance of Trade.

• U. S. Dominance Has Declined Dramatically in Recent

Years.

• New Technology Can Triple the Fuel Economy of

Today's Best Aircraft and Provide Substantially More

Cost Effective Operation.

162
TRANSPORTAIRCRAFTCOMPOSITE

WING STRUCTURES

McDONNELL DOUGLAS

AV-8B

DOUGLAS DG-IO

POTENTIAL WEIGHT SAVINGS TREND FOR FUTURE

STRUCTURAL MATERIALS

50

40 Thermoplastics-'__

._,adva ,._\\\\\\"_ ncedepoxies_ "'_"Met I a Potential Advancedfiber/&\\_ matrix

structural 30 .,_ modifiedepoxy___composites

_\\\\\ ' '

_SPF

wsaveight ing, __'_A_F'_iPOm_da_:__

10 _.2321

0 I I I •

1970 1980 1990 2000 2010

163
SCHEMATIC REPRESENTATION OF

,iii:ii:i:i::i::!::i:i::i:::i:i:i:ii iCiUTiiBOA Ai:iPiRI!NT RDiiE:ii:i:i_iiiii::i:iiii_iiiii:ii_:iiiiDiii!iCiIR 

I

_;; RESIN/

REINFORCEMENT

TOP VIEW CROSS SECTION

164
ADVANCED POLYMER COMPOSITES

- Kline Report,1988-

Education/

* I Aerospace: Research Recreational

Commercial Universities 1.0M Ib,$61M

Industry/NASA Industry

*1 U.S.

Aerospace:

Military National Industrial

Composites 3.2M lb,$215i

DoD/NASA Program Industry

(* Aerospace"_ 11 M Ib'_ 1987 \ 5.5M Ib,$586M) $950 M J

* l Space Automotive

Structures 0.3M Ib,$15M

Other Industry DoD/Industry/ 1.2M Ib,$72M

NASA DoD/Industry

165
HIGH PERFORMANCE COMPOSITES

KEY GROWTH SEGMENTS FOR THE U.S.*

Market Value Annual Growth Rate

Market 1988 1993 1988-1993

Aerospace $810,000,000 $1,560,000,000 14%

Recreation 40,000,000 50,000,000 5

Industrial 100,000,000 180,000,000 12

Automotive 10,000,000 15,000,000 8

Military 20,000,000 110,000,000 30

Other 40,000,000 55,000,000 5

Average $1,020,000,000 $1,970,000,000 14

* P.W. Kopf,PolyimideSymposium,San Diego,CA,January22-25, 1990.

SOME REASONS FOR ADVANCED COMPOSITES'

SLOW PENETRATION OF THE OVERALL

AEROSPACE MARKET*

• The extreme consequences of failure and the resulting

conservativeness with respect to introducing new materials and

technology.

• The need to develop new design technology specifically for

composites.

• Labor-intensive and expensive methods of fabrication.

* P.W. Kopf, Polyimide Symposium, San Diego, CA, January 22-25, 1990.

166
INTRODUCTION OF NEW MATERIALS

The introduction of new materials is usually

an evolutionary rather than revolutionary process.

-- 10 to 15 years required to develop data base and

assess potential and risk prior to committing.

to production

-- new materials for extensive application about

the year 21300are in the laboratory today

OUTLINE

• WHAT ARE HIGH PERFORMANCE COMPOSITES?

• HOW ARE THEY USED TODAY? (i.e., WHY ARE THEY

IMPORTANT TO YOU AS USERS AND AS TEACHERS?)

• WHAT ARE THEIR PROPERTIES?

• HOW DO YOU MAKE THEM?

• WHAT ARE THE FUTURE TECHNOLOGY NEEDS FOR

COMPOSITES? (i.e., WHY SHOULD YOU TEACH

STUDENTS THIS TECHNOLOGY?)

167
Stress - Strain Curve

_ooo- 0

I

/

I

I

I

I

I

/.__I3 E (modulus)

/

/

Stress, (_ t

ksi 500 - /0

/ 500,000 psi / E = = 50,000,000 psi

/ 0.01 or /

/ 50 msi

/

/

/

/

/

/

/

,'(' J i

0 1 2

Strain, e

%

COMPOSITE MECHANICAL PROPERTY TESTS

(Strength, Modulus, Elongation)

O

LAMINA PROPERTIES (0°. 90°) _ t2

TENSION _i

COMPRESSION

FLEXURE ,04 _a

SHEAR LONGITUDINAL (0°) TRANSVERSE (90")

SHORT BEAM SHEAR STRENGTH TENSION TENSION

TENSION _

COMPRESSION

FSHLEXEARURE O_ O_

COMPRESSION

FRACTURE TOUGHNESS PROPERTIES SHEAR

• 2,

DOUBLE CANTILEVER BEAM (DCB) - MODE I ,3 ENNOT B FCLHEXU(ENREF)- MODII E _L,

CRACKED LAPSHEAR(CLS- )MIXEDMODE

EDfiEDELAMINATION(EDT) - MIXED MODE FLEXURE

OPEN HOLE TENSION

OPEN HOLE COMPRESSION

COMPRESSIONAFTER IMPACT

168
TYPICAL PROPERTIES OF THE CONSTITUENTS

OF CONTINUOUS CARBON FIBER REINFORCED

COMPOSITE MATERIALS VERSUS METALS

REINFORCEMENT

Tensile Tensile Tensile

Strength, Modulus, Strain, Density,

Fiber Ksi Msi % _l/CC

Carbon 600 34 1.6 1.8

Carbon 800 44 1.8 1.8

(Intermediate Modulus)

S Glass 665 13 5.4 2.5

ARAMID 550 19 - - 1.5

Boron 510 60 0.8 2.5

PE 435 25 2.7 0.97

MATRIX

Organic Polymers 15-20 0.4-0.6 1-60 1.2-1.4

METALS

Steel 70-150 30 - - 7.8

Titanium 125 16 - - 4.5

Aluminum 70 11 - - 2.7

RULE OF MIXTURES

FOR

MODULUS CALCULATIONS

Tensile Volume Theoretical

Modulus Fraction Value

Fiber 34.00 Msi 0.60 20.40 Msi

Resin 0.45 Msi 0.40 0.18 Msi

Total 20.58 Msi

169
TYPICAL PROPERTIES OF CONTINUOUS

CARBON FIBER REINFORCED COMPOSITES

Property Unidirectional Quasi-isotropic

0° Tensile Strength, Ksi 250-300 110

0° Tensile Modulus, Msi 16-20 5-7

0° Tensile Strain, % 1.2-1.5 1.0

90° Tensile Strength, Ksi 7-12 - -

90° Tensile Modulus, Msi 1.0-1.5 - -

90° Tensile Strain, % 1-15 - -

0° Compression Strength, Ksi 150-250 100-120

SPECIFIC PROPERTIES OF MATERIALS

[--1SPECIFICSTRENGTH

[-] SPECIFIC MODULUS

_ UNIDIRECTIONAL

UNIDIRECTIONAL CROSS-PLY(01901

RELATIVE FABRIC

SPECIFIC

STRENGTH

AND

SPECIFIC

MODULUS

ALUMINUM STEEL TITANIUM[E-GLASS BORON KEVLAR GRAPHITEJ (7000) (4_0) (6AI-4V) EPOXY MATRIX

170
LAMINATEDAMAGERESULTINGFROMPROJECTILEIMPACT

171
FRACTURE INTERFACE

DELAMINATION INTRAPLY

METHODSFOR TOUGHENINGTHERMOSET

MATRICES

(1) ADDITION OF A SECOND PHASE

CTBN OR ATBN REACTIVE RUBBERS

UNREACTIVE RUBBER

CHOPPED FIBER OR FIBRILS

THERMOPLASTICS/ SEMI-INTERPENETRATING

NETWORKS (IPN'S)

(2) INTERLEAFING

(3) INCREASE LENGTH BETWEEN CROSS-LINKS

(4) NOVEL CURING AGENTS

(5) 3D-STITCHING, -WEAVING, -BRAIDING, -KNITTING

(6) COMBINATIONS OF THE ABOVE

172
IMPORTANT TESTS

° RESIN FRACTURE TOUGHNESS

• COMPOSITE INTERLAMINAR FRACTURE TOUGHNESS

• COMPRESSION STRENGTH AFTER IMPACT (CAI)

• RESIN MODULUS

HIGH PERFORMANCE COMPOSITES

Interleaf conceptsfor impactresistance

Graphite

composite

prepreg

0

Release

paper Graphitefibers in

matrix resinwith

hot-wetstrength

Discretelayerof

highstrain resin

for "toughness"

173
TOUGHENED EPOXY COMPOSITE PROPERTIES

RT RT

RESIN/FIBER COMPRESSIVE COMPRESSIVE GIc,

STRENGTH, STRENGTH AFTER IN.LB/IN 2

KSI IMPACT, KSI

BMS-8-276 200 45 NO

SPEC.

TORAY 3900-2/ 245 53 1.6

T800H

ICI 977/IM7 216 50 4.1

HERCULES 8551-7/ 252 53 2.9

IM7

THERMOPLASTIC COMPOSITE PROPERTIES

RT RT

RESIN/FIBER COMPRESSIVE COMPRESSIVE GIc,

STRENGTH, STRENGTH AFTER IN.LB/IN2

KSI IMPACT, KSI

BMS-8-276 200 45 NO

SPEC.

ICI APC-2/AS-4 160 45 8.5

DUPONT AVIMID K/IM-6 144 38 8.1

PHILLIPS RYTON PPS/ 130 26 3.9/5.1

AS-4

AMOCO RADEL C! 159 45 ....

T650-42

AMOCO TORLON 230 45 7.5

AIX-159/T650-42

174
Damage-Tolerant StiffenedPanelConcept

Basic 9-Ply subelement _ Stiffener

AS4 Uniweave .,•_" L

+45°

0° _

Skin Stiffenedpanel //_

"z"_/+CL--/--/- _lf _/' ,..

/ /_ / / / I W/! s J,,

/..- 7-- -,, -- _ -- ,L --L -_F

/-'-," -/--/--/--H

Six 9-ply segments Stringer flanges stitched to skin

STITCHING CAN SIGNIFICANTLY IMPROVE

DAMAGE TOLERANCE OF COMPOSITES

Detailsof_ phlbl_l

Stitching _ _ hlltll_lCt

spaced at 1 /

/8 in. --.-_/.- 100 F" A = Unstitched AS4/3501-6

•'';""' ','," ;' ' "?'*',',"""" / . _C B == Toug Stitched henedAS4matrix /3501-6composites

•" " ".;.'/;,',,',,':,." Stitching 80 _

/;.;;.'.'.','.'.'.'."IT pitch / \\ L:.: :,'.','.',','.','l / 8 per in.

*'e*eq • w •_ e

*ooo _oo e e ,o

........... 60

........... Comp.

:""" '": " " '" stress,

ksi

/Load direction 40 _-value- _ B'_ _"

48 ply stitched laminate "....

[+45/0/-45/90] 6s 20 A ...... -

AS4 carbon fabric

3501-6 epoxy resin 0 i I I i ,, 1

S-2 glass stitching thread 0 20 40 60 80

Resin transfer molding Impact energy, ft-lb

175
THROUGH THE THICKNESS REINFORCED

TEXTILE FORMS

Stilched/woven fabric Layer-to-layerinterlockweave

3-D braid

TEXTILE MATERIALS BEING EVALUATED

+ ' +N

Multlaxlal warp knit 2-D trlaxlal braid

(stitched & unstitched) (stitched & unstitched)

3-D braid 3-O Interlock weave

176
SOME DESIRED PROPERTIES OF POLYMER

MATRICES AND THEIR COMPOSITES

Resin ProDerty at RT Composite

450 Ksi 0° tensile & compressive moduli 20 Msi

200 Ksi shear modulus 1.0 Msi (G12)

16 Ksi 0° tensile strength 300 Ksi

16 Ksi 0° compressive strength 200 Ksi

16 Ksi shear strength 16 Ksi (1;12)

8% strain-to-failure >1.5%

>4 in-lb/in2 GIc >4 in.lb/in2

(700 J/m2) (700 J/m2)

>50% retention of RT properties at elevated temp >50%

wet

-- compressive strength after 1500 in-lb/in 50 ksi

impact on quasi-isotropic panel (0.6% strain)

OUTLINE

• WHAT ARE HIGH PERFORMANCE COMPOSITES?

• HOW ARE THEY USED TODAY? (i.e., WHY ARE THEY

IMPORTANT TO YOU AS USERS AND AS TEACHERS?)

• WHAT ARE THEIR PROPERTIES?

• HOW DO YOU MAKE THEM?

• WHAT ARE THE FUTURE TECHNOLOGY NEEDS FOR

COMPOSITES? (i.e., WHY SHOULD YOU TEACH

STUDENTS THIS TECHNOLOGY?)

177
POLYMER MATRIX COMPOSITES TECHNOLOGY

SYNTHETIC APPROACHES

e TOUGHENED THERMOSETS

EPOXIES,BISMALEIMIDES+THERMOPLASTIC ADDITIVES

_ eLIGHTLY CROSSLINKEDTHERMOPLASTICS

POLYSULFONES,POLYIMIDES+ CROSSLINKERS

CRYSTALLINE THERMOPLASTICS POLYESTERS,POLYARYLETHERS(PEEK,ETC.,)

e LINEARTHERMOPLASTICS

POLYIMIDESULFONE,TPI

178
RTM RESINSFOR AEROSTRUCTURES

Current Desired Pro )erties

• Liquid epoxies/room temperature • Low viscosity liquid

• Solid epoxies/elevated temperature • Cure without evolution of volatiles

• Solid BMIs at room or elevated temperatures

• Acceptable hot/wet

mechanical properties

• Acceptable thermal performance

New Approaches

• Ring opening of low molecular weight cyclics:

A

Cyclic High molecular weight polymer

• Addition polymerization of monomeric reactants:

METHODS TO COMBINE RESINS AND FIBER

• SOLUTION: Standard for woven prepreg

Organic solvents undesirable

• HOT=MELT: Standard for epoxies

Difficult for thermoplastics

• RTM AND RIM: Mainly for preform technology

• INTERMINGLED

FILAMENTS: Costly fiber spinning

Difficult for large parts

• SLURRY: Versatile: insoluble powders, carrier liquids,

binders, soluble polymers, blends

• POWDER: Solventless process in research stage

Yields boardy, tackless prepreg

• ELECTROPOLYM.,

VAPOR POLYM.

& DEPOSITION: In research stage, needs ideas

179
PolymerPowderResearch

Drypowder prepreg equipment Powderprepreg

Woven powder towpreg Composite properties

300

20 250

Flexure 200

Short 15 strength,

beam ksi t 50

shear 10

strength, 1O0

ksi 5 50

o__lr 0__It

Solution Powder Solution Film Powder

prepreg prepreg prepreg prepreg prepreg

COMPOSITE PROCESSING TECHNOLOGIES

• RESIN TRANSFER MOLDING INTO TEXTILE PREFORMS

• PULTRUSION

• ROBOTIC PLACEMENT (FILAMENT WINDING,

ADVANCED TOW AND TAPE PLACEMENT)

• THERMOFORME_G

• HAND LAY-UP OF UNITAPE AND FABRIC PREPREG

All require molds (or dies), temperature and pressure during the

processing cycle

180
AUTOMATED COMPOSITE FABRICATION PROCESSES

Weaving/braiding MaterialPlacement

Pultrusion FilamentWinding

MILACRON'S THERMOPLASTIC/CARBON FIBER

TAPE LAYER

181
PROCESSING TECHNIQUES

PRESSURE:

• PRESS

• AUTOCLAVE

• VACUUM BAG

• INFLATABLE MANDREL

• EXPANDABLE TRAPPED RUBBER

TEMPERATURE:

• ELECTRICAL RESISTANCE

• HOT GAS

• MICROWAVE

• INDUCTION

OUTLINE

• WHAT ARE HIGH PERFORMANCE COMPOSITES?

• HOW ARE THEY USED TODAY? (i.e., WHY ARE THEY

IMPORTANT TO YOU AS USERS AND AS TEACHERS?)

• WHAT ARE THEIR PROPERTIES?

• HOW DO YOU MAKE THEM?

• WHAT ARE THE FUTURE TECHNOLOGY NEEDS FOR

COMPOSITES? (i.e., WHY SHOULD YOU TEACH

STUDENTS THIS TECHNOLOGY?)

182
RESIN MATRICES

-Future Needs -

• Conformational Chemistry

• Predict Bulk Polymer PropertiesFrom Polymer Chemistry

• .ImprovedProcessability

• Let's Get Rid of the Autoclave: Oven Cure Only

• Thermoplastics That Cure Like Epoxies

• Ring-Opening and Addition PolymerizationsWithout Volatiles

• .LonqLife Durability of Hiqh Temperature Matrices

• 60,000 Hours at 350°F Under Cycle Load

• Volatile and Microcracking Issues

• .T.ouqheninqTechnoloqy

Interleaving and Second Phase Morphology

versus

Stitching and Textile Technology

• Preceramics

• Cost Consciousness

183
TRANSPORT PRIMARY STRUCTURES

i

KEY BARRIER TO APPLICATION

COST

TO DEVELOP

TO PRODUCE

COST COMPARISON OF GRAPHITE FIBERS

AND FABRICATED STRUCTURES

[" I

Graphite $20/Ib fibers

Prepregs I $40/Ib

Fabricated !' $200-500/Ib structures

184
Factors That Influence Cost of

CompositeStructures

• Costof Materials

-Fiber

-Resin

-Prepreg

-Preforms

• CostofFabrication

-Tooling

-Labor

• Costof Assembly

-Equipment

-Labor

• Costof Design

MULTI-AXIS RBER PLACEMENT MACHINE

I

Pitch

Roll

Head elevation

Yaw

Longitudinal ........

185
AUTOMATED FIBER PLACEMENT

Cincinnati Milacron Automates Fabrication of ATF Duct

ROBOTICS

- Future Needs-

• Laydownto Net Shape

• Rapid (Pounds Per Hour)

• Versatile

• Quality Construction

• Application on the Factory Floor

186
Artist's Conceptof

AFP Factoryof the Future

Multineedle Stitching Station

(Textile Rivets)

Single Needle Stitching Robot

de Interchangeable Thermoplastic Ribbon or

Powder Coated Tow Welding Heads

Multiple Interchangeable Staggered

Tacky Epoxy Tow Placement Heads

CURRENTOUTLOOK: CONCORDE ANDHSCT

CONCORDE 'HIGH-SPEED ClVIL'rRANSPORT.

30(]0 RANGE(n.mL) 5000-6500

100 PAYLOAD(passengers) 250-300

400_000 WEIGHT(lb.) 750_000

EXEMPT COMMUNITYNOISESTANDARD FAR 36 - STAGE Ul

PREMIUM FARELEVELS STANDARD

187
HSR AIRFRAME MATERIALS TECHNOLOGY

Key Issue

Nolong-term,high-temperature

materialsdata basefor HSCTairframes

(60,000-hrdesignlife,120,000-hrfatiguelife)

Key technology needs

• Life prediction methodology

Goalsfor HSR • Accelerated test procedures

• Long-term flight

simulation durability

Service NC

life | • Demonstrated 300 °- 500°F

1000,hrs polymer matrices, adhesives and

MU sealants for _>60,000-hr lifetimes

• Demonstrated 300°- 600°F

lightweight metals and

o 200 4o0 eoo metal matrix composites

Temperature for >_60,000-hr lifetimes

MAJOR HIGH TEMPERATURE STRUCTURAL

RESIN REQUIREMENTS

• Acceptable Handlability (non-toxic, drape, etc.)

• Processable

• Volatileless or low volatile systems

• High Mechanical Properties (durable, damage tolerant, etc.) over

temperature range-65° to 350°F, 60000 hours

• Environmental stability (moisture,fuel, etc.)

• Long sheiflife

• Acceptable cost (final component)

• Amenable to different fabrication methods (automatedtape laying,

RTM, filament winding, etc.)

188
Candidatei Resins i for HSCT

° Bisrnaleimides including toughened versions

° PMR-15includingmodifiedversions

o Polyimides(thermoplastics, semi-crystailineTP)

o Poly(aryleneether)s

° Emergingsystems(e.g. benzocyclebutenes)

The Future

Decades To Go Possible Composite Applications

1 Commercialaircraftwings and fuselage elements

Dry deck shelter

Space station

Surface ships

ICost parity with equivalent metal structure I

2 Wide body commercial aircraft wings and fuselage

High Speed Civil Transport

Submarine elements

Moon/Mars space vehicles/structures

Composites industrialization

• Mil handbook/Alloy database

• Factories established

• Warehouse composite building block forms

189
COMPOSITES FOR INFRASTRUCTURE RENEWAL

• BRIDGES

• Use of >150,000 filament carbon fiber tow (small

rope)

• Use of low cost, environmentally durable and safe

resin matrices

• Use of very rapid, low cost fabrication techniques

(such as pultrusion of large I-beams)

• TRANSPORT VEHICLES

• Composite Railroad Freight Cars

• Composite High Speed Passenger Railroad Cars

• Composite Vans for 18-Wheelers

• Composite Truck, Van and Passenger Car Bodies,

Leaf Springs, Drive Shafts

NOMENCLATURE

B-STAGE: AN INTERMEDIATECURE STAGE.

STRAND (TOW): A BUNDLE OF CONTINUOUSFILAMENTSCOMBINEDINTO A SINGLE COMPACTUNIT WITHOUT

TWIST, E.G., 6000 FILAMENTSTRAND. A TOW IS GENERALLY10,000 OR MORE

FILAMENTS.

YARN: FORMED BY COMBININGll¢OOR MORE CONTINUOUSFILAMENTSINTO AN ASSEMBLAGEOF

TWISTED STRAHDS_GENERALLYFEWERTHAN 10,000 FILAMENTS.

ROVING: A COLLECTIONOF BUNDLESOF CONTINUOUSFILAMENTSEITHERAS UNTWISTEDSTRANDS OR

TWISTED YARNSWOVEN FABRICS: THOSE PRODUCEDBY INTERLACINGSTRANDSAT MORE OR LESS RIGHT ANGLESWARP: IN A WOVEN FABRIC, YARN RUNNINGLENGTHWISE.

FILL (WEFT): IN A WOVEN FABRIC, YARN RUNNINGFROM SELVAGETO SELVAGE (CROSSWISE)AT RIGHT

ANGLES TO THE WARP.

SIZE: A SUBSTANCEAPPLIED TO A YARN OR FIBERDURING ITS FORMATIONTO PROTECT ITS

SURFACE AND AID HANDLINGAND FABRICATION. STARCH, _INCUREDEPOXY,WAX, 01L.

COUPLING AGENT: PROMOTES A STRONG BOND BETWEEN FIBERAND MATRIX.

(FINISH)

SURFACE TREATMENT: CHEMICAL TREATMENT(IISUALLYOXIDATIVEON CARBONFIBER) PRIORTO APPLICATIONnF

A SIZE OR FINISH.

DENIER: WEIGHT IN GRAMS OF 9,000METERSOF YARN OR FILAMENT.

TENACITY: DENOTES BREAKING STRENGTHOF A YARN OR FILAMENTIN G/DENIER (PULLEDAT A RATE

OF 12 INCHESPER MINUTE).

PREPREG: WOVEN OR CONTINUOUSFIBERTAPE SHEETSIMPREGNATEDWITH RESIN AND READY TO

ROLDj RESIN CAN BE UNCUREDOR PARTIALLYCURED.

190
NOMENCLATIIR(CEONTINUED)

FIBER AREALWEIGHT: IN A PREPRE6ORCOMPOSITEW, EIGHTOF FIBER PERUNIT AREA;USIIALLYCITED IN

(FAW) filmzPLY: ONELAYERIN A COMPOSITE.

UNIDIRECTIONAL ONEWHICHHASALL FIBERSORIENTEDIN THESAMEDIRECTION,

LAMINATE(O)x:

CROSSPLIEDLAMINATE: ONE WHICH HAS FIBERSORIENTEDIN VARIOUS DIRECTIONSIN THE PLANEOF THE

LAMINATE. ,SIIALLYHAS BALANCEDCONSTRUCTIONABOUTTHE CENTERLINE OF THE

THICKNESSOF THE LAMINATE.

STACKINGSEQUENCE: ORDER OF PLY ORIENTATIONIN A LAMINATE

(O/±q5/90)S = Ol+qSl-q5190190/-q51+qs/o

(_301±301901_0)s= +301-301+301-301901901901-301+301-301+30

ISOTROPICLAMINATE: ONE IN WHICH THE STRENGTHPROPERTIESARE EQUAL IN ALL DIRECTIONS.

ANISOTROPICLAMINATE: ONE IN WHICH THE STRENGTHPROPERTIESARE DIFFERENTIN DIFFERENTDIRECTIONS;

E.G., UNIDIRECTIONALLAMINATE.

FABRIC DESIGNATIONS

FABRICSARE GENERALLYDESCRIBEDACCORDINGTO THE TYPE OF

WEAVE AND THE NUMBEROF,YARNSPER INCH,FIRST IN THE WARP

DIRECTION(PARALLELTO THE LENGTH OF THE FABRIC),THEN IN

THE FILL DIRECTION(PERPENDICULARTO THE WARP). FOR

EXAMPLE,A "20 X 18" FABRIC HAS 20 YARNS/IN.IN THE WARP

DIRECTIONAND 18 YARNS/IN.IN THE FILL DIRECTION.

•w_rp

_lin Weave_ln this consfrucllon,

one warp end is woven over _veral

succelJuve fill yitn$, ll_,en under

one hliylrn. A configuration hiving

one wlrp and passing over four ind

under one fill ylrn is tilted i

We4we-_n this construction, five-hamel, l _llin weave. $imilihy,

one warp end is repelilively woven in in e_ght-hMness elfin te I>r_c. one

o_r one fill ylm and under the wirp end pisses over seven fill

ylrnl, fhen under one fill yarn. The

consfruction, which provides for utln wiDive is more plilble thin the

pomelty and minimum IlippaOe, plain weive, If conforrnl mldily to

Strengfh is uniform in bolh compound curves, end can he

woven to i very high density. Sihn

wemvee ere loll open fhan other

weaves; strength ll high in both

dlrectmnL FIVE-HARNESS SAT_NWEAVE PU_N WEAVE

SHEPLER,TOWN AND SAYLOR,MACHINE

DESIGN,MAY 24, 1979.

191
REFERENCES

0 HANDDOOKOF COMPOSITES,G. LUNIW, ED., VANNOSTRANDCO., 1982

0 ASTHSTPs

0 VENDORDATA SHEETS

0 JOURNALS

• COHPOSITES

• J. COHPOS]TEHATERIALS

• SAHPEJ.j QUART., PREPRINTS

• J. HATERIALSSCIENCE

• INTERNAT. J. ADHESIONAND ADHESIVES

• Jo ADHESIVES

• J* REINFORCEDPLASTICS

• A[AA JOURNAL

• J. COMPOSITESTECHNOLOGYAND RESEARCH

• COMPOSITESSCIENCE AND TECHNOLOGY

• COHPOSITESTRUCTURES

0 GOVT. PUBLICATIONS

• NASA: CR, TR, TH, CP, RP

• AFWAL: TR, CR

• ADVANCEDCOHPQS[TE$DESIGN GUIDE

0 HODERNCOHPOSITEMATERIALS, Lo J. BRAUTHANAND R. Ho KROCE,ED.,

ADD[SION-WESLEYPU8. CO., 1967

0 ASME, AIAA, SEN, ASC, AHS, ETC. AND PREPRINTSOF MEETINGS

0 EXPERIMENTALCHARACTERIZATIONOF ADVANCEDCOMPOSITEMATERIALS, L. Ao

CARLSSONAND R. B° PIPES, PRENTICE-HALL, [NC., 1987

0 EXPERIMENTALMECHANICSOF FIBER REINFORCEDCOHPOSITEMATERIALS, 3o H°

WH[THEY, [. H. DANIEL, AND R. B. PIPES, PRENTICE-HALL, I_C. AND THE SOCIETY

FOR EXPERIHEHTALSTRESSANALYSIS, MONOGRAPNHO. q, 1982

0 INTERNATIONALSAMPETECHNICALCONFERENCESERIES (FALL)

0 _CIENCE OF ADVANCED I_IATERIALSAND .PROCESS_NGINEER[NG SERIES (SPRING)

192
MATERIALS EDUCATION ACTIVITIES

Heidi R. Ries, Moderator, Norfolk State University

Jonice Harris, National Institute of Standards and Technology

Woodrow W. Leake, American Society for Engineering Education

L. Roy Bunnell, Battelle-Pacific Northwest Laboratories

Robert Berrettini, Materials Education Council

193

INTEGRATING MANUFACTURING AND ENGINEERING EXAMPLES INTO

SCIENCE TEACIIING

Ileidi R. Ries

Department of Chemistry and Physics

Norfolk State University

Last year, at NEW: Update '91, a panel discussion was held to address tile unique

difficulties of "Attracting and Retaining Minorities and Women in Technical Studies"

Unfortunately, retention in technical majors is a problem of varying proportions for the

entire student population [1], and must be improved in order to maintain the strength ofthe

nation's industrial base.

To investigate the cause of student attrition in technical majors, in-depth interviews

of both current and former (non-graduating) engineering students at four colleges and

universities in Colorado were conducted by Hewitt and Seymour [2]. They found that there

was no significant difference in tile level of high school preparation and undergraduate

academic performance in these two groups, despite the prevailing faculty perception that

most students who switch from technical to nontechnical majors were "underprepared".

The majority of engineering students who changed majors reported that they were "turned

off by science", while one-third complained of poor teaching.

Since most of these students transferred to other majors during the first two years in

college, this suggests the need to examine the content of tile introductory curriculum. The

first year of a technical program generally includes basic mathematics and science courses,

with little or no exposure to engineering or manufacturing applications. The abstract nature

of these initial courses and the lack of instructor interest in "real world" examples may

contribute to the loss of student interest in technical careers.

The Industrial and Management Systems Engineering Department at Penn State

University, University Park Campus, elected to imp_-ove instruction in introductory

mathematics and science courses by providing faculty members who teach these courses

with experiences and materials which will enable them to incorporate appropriate

manufacturing and engineering examples into their teaching. With National Science

Foundation funding, a "Teaching Enhancement Program on Applications of Science and

Mathematics to Manufacturing for Undergraduate Faculty" was offered during the summer

of 1992. Over 50 mathematics and science instructors from various colleges attended, and

enthusiastically participated in the metal casting, circuit board manufacturing, and

machining modules, which included both lecture and laboratory experiences. A summary of

concepts demonstrated in the modules was made, and implementation ideas were developed and

discussed. The Teaching Enhancement Program will be repeated in the summer of 1993

[3].

At Morgan State University, a more direct approach is being used to address the

entry-level curriculum, through the use of a "Phenonaena-Driven Engineering Curriculum"

(ECSEL program). In this effort, engineering problems (such as designing an electric

vehicle or a bridge) are introduced in the first year of the program. This problem then

195
becomes the unifying theme in all courses, including introductory physics, chemistry,

mathematics, and English. Since this program was initiated in Fall, 1991, the full impact on

retention is not yet clear.

Norfolk State University is also pursuing integration of the topics in the technical

curricula. Currently, chemistry, engineering, physics, and mathematics majors are enrolled

together in a one semester hour orientation/seminar class. Faculty members from all

programs present general information about careers and research in the various fields. A

more expanded course is being developed which will emphasize interdisciplinary topics,

"real world" problem solving, and visitations to research and/or industrial facilities. It is

anticipated that students will gain a better understanding of the relevance of their

introductory coursework to their ultimate career goals.

1. "A Profile of Undergraduates in the Sciences" Kenneth C. Green American Scientist

77 (475) 1989

2. "A Long, Discouraging Climb" Nancy M. Hewitt and Elaine Seymour ASEE Prism

February 1992, p. 24

3. For further information and application materials, contact:

Dr. Clayton Ruud

Dept. of Industrial and Management Systems Engineering

The Pennsylvania State University

207 Hammond Building

University Park, PA 16802-1401

196
IMPROVED MEASUREMENT OF THERMAL EFFECTS

ON MICROSTRUCTURE

Mansur Rastani

Department of Manufacturing Systems

NC A&T State University

Greensboro, North Carolina 27411

Telephone 919-334-7585

197

Improved Measurement of Thermal Effects on Microstructure

Mansur Rastani, P.E., C.Mfg.E.

Department of Manufacturing Systems

NC A&T State University, Greensboro, NC

Key Words: partially and fully recrystallized microstructure,

unrecrystallized microstructure, spring elongation number, elastic recovery

factor, ohmic-resistance heat treatment.

Prerequisite Knowledge: elementary knowledge of material elasticity,

metal structure, heat treating, and some quantitative metallographic

measurements on microstructure.

Objectives: To introduce a simple methodology which could be used to

replace the time-consuming and expensive conventional methods of metallographic and quantitative analysis of thermal treatment effect on microstructure.

Equipment & Supplies: The experiment itself needs ten standard 60

or 75 or 100 W light bulbs, a lamp holder and stand hooked up to an electric

wire, a chronometer, a scale for measuring distance and two tweezers.

However, in order to compare the results of this method with the ones of

metallographic analysis, specimen preparation station, a fast curing epoxy

mounting, and an optical metallurgical microscope are required.

Introduction: Metallurgical analysis continually calls for the

evaluation of thermal treatment effects on microstructure. This commonly

demands metallographic sample preparation and microscopic examination,

which are time absorbing and costly. These drawbacks are burdensome when

large numbers of samples must be levied fast. Mechanical testing can

sometimes be substituted, but sample size and shape frequently make these

methods impractical. The experiment described here is ideal for the

microstructural evaluation of lamp filaments and other wire samples such as

copper wire which can be conveniently coiled.

Procedure: In this experiment, a common coiled incandescent lamp

filament is used. The coil body was about 12.5 mm long, and it was made

from standard grade tungsten lamp wire. The samples were heat treated by

ohmic resistance; simply each light bulb is placed in an electric current

circuit and is lighted for a fraction or a multiple of seconds. The treatment

took place in steps of 0.8 seconds duration at temperatures which were

expected to span the recrystallization range. Ten samples were treated so

199
that each was removed from this process at a progressively higher step, table

1.

,Spc:: :irrm1 ! ;_ } 4 5 6 7 8 9 I0

H.T[)(i_Jin (se_) ('.k] 1.6 '?..4 ,].2 4,0 4.,.B '; 6 6.4 7.2

Table 1. Ohmic-resistance heat treatment on ten specimens at time

duration steps which are expected to span the

recrystallization temperature range.

The recrystallization temperature of the tungsten filament is around

2000 °C. When the lamp is lighted for the first time, filament temperature

rises quickly to about 2500 oC. At this temperature, the tungsten filament

readily recrystallizes and the fibrous grain structure of the filament, figure 1,

is replaced by recrystallized grains. Figures 2 and 3 show the fracture

surfaces of the cross sections of the filaments with no heat treatment and

with heat treatment respectively.

After treatment, the samples were evaluated in the elastic recovery

test. Using a scale and tweezers each sample was carefully stretched to a coil

length of 40 mm and then allowed to return to a relaxed length. Then, the

deflection recovered (e) was measured. The recovered portion of the deflection

(e)is

e=L-l'

where L is the stretched length, 40 mm, and 1qis the length after elastic

recovery, as indicated in figure 4.

]

L =_4

-,

Figure 4. The recovered portion of the deflection (e) is shown

in an elastic recovery test on a filament

200
Figure 1. SEM micrograph of the fibrous microstructure of an

unrecrystallized filament, 1000X.

Figure 2. SEM micrograph of the fracture surface of an uncrystallized

filament, 1000X.

201
Figure 3. SEM micrograph of the fracture surface of a crystallized filament,

IO00X.

202
The normalized elastic recovery factor (erf) is defined in terms of deflections

as:

err = (e-emi n )/(emax-emi n) (1)

where e is the deflection of a specimen of unknown degree of recrystallization,

emi n is the minimum value of recovered deflection presumably for the fully

recrystallized material and em_x is the maximum deflection value for the

totally unrecrystallized structure. In the following, the results on three

specimens illustrate how computations are made.

Results: In the elastic recovery test, amount of stretch was 40 mm, the

calculated erf for three specimens are listed in table 2.

t

e

.,in,,_l_-,n f' (,rnrii) (_'Uy,m_, _'II (r,_nl')

F'crl<l7 7<_<:. 20 e ---;70 50Z

f-uilyR+:'<.. '""

._C> ehnin=14 0.%

t.h_ie<ryr.;t 1.4 emcl×._-vg ,n ....

• - i,,.,07<)

Table 2. Results of elastic recovery test on three specimens.

In order to evaluate the amount of crystallized and uncrystalIized

portion in different filaments by the conventional metallography method, the

specimens are metallographically prepared. The samples were carefully

placed in a mounting cup and encapsulated in EPO-KWICK fast curing

epoxy. Each sample was then ground and polished with care. The polished

samples were etched with Murakami's* etch to reveal the microstructure of

the wire cross-section. Figures 5, 6, show the optical micrographs of

filaments' cross sections with partial recrystallization which illustrate some

of the problems associated with quantitative measurement of the partially

recrystallized microstructures. A full recrystallized filament is shown in

figure 7. The microstructure of the region of the wire which remained

unrecrystallized, consists of long, thin fibers having longitudinal axes

parallel to the axis of the wire. Corresponding sections of the recrystallized

portions of the wire usually show no grain boundaries. Along the length of

M okomi'setchcon'3irslsof I091ofpolqsiumIroncy<!nideondI0 grof potosiumhydroxidein100ccwoter

203
Figure 5. Optical micrograph of partially-crystallized filament section, 1 sec

heat treated, murakami's etch, 1000X.

Figure 6. Optical micrograph of partially-crystallized filament sections, 5 sec

heat treated, murakami's etch, 1000X.

204
Figure 7. Optical micrograph of fully-crystallized filament section, 7.2 sec

heat treated, murakami's etch, 1000X.

205
the coiled wire there may be variations in relative proportions of

recrystallised and unrecrystallized structures. The elastic recovery factor

and the fraction of uncrystallized material determined metallographically

are both plotted as a function of the heat treating duration on the same

diagram, figure 8. Altogether, five comparisons were made, and the

correspondence was always good.

_ 0"8 !l'O_''l''''l'''ll'O_O 0.8 _

m

0.6 0.6

0.4

0.4_ o_r _

1 2 3 4 5 6

Specimen #

Figure 8. Elastic recovery factor (ERF) and fraction of unrecrystallized

material, determined metallographically (MET), as a

function of heat treatment duration.

The elastic recovery factor versus the fraction of unrecrystallized

material is plotted in figure 9 for five different heat treated filaments which had

different recrystallisation behavior. The fraction of unrecrystallized

materials as determined metallographically appears to be consistently lower

than would be predicted from the elastic recovery factor data.

1.0 _r

0.8

_, o.4

0.2

0 8o oo o

Fraction Unrecrystallized

Figure 9. Elastic recovery factor vs fraction recrystallised

material as determined metallographically.

206
Conclusion: Experimentally it has been shown that elastic recovery factor

depends on the degree of recrystallization, i.e.; those sections of the filament

where most recrystallization had taken place showed the most coil

deformation. Theoretically, the reason for this is perhaps obvious. As yield

strength is diminished by the progress of recrystallization, since the elastic

modulus is not affected much by the heat treatment, it can be concluded that

the extent of recovery after deflection, e, is also proportionally diminished.

Because the elastic recovery method examines the whole filament rather

than just one section through the filament, as in the metallographical method, it

more accurately measures the degree of recrystallization. The method also

takes a considerably shorter time and cost compared to the conventional

method. The elastic recove/,y method may be applied to other metals and

alloys which could be formed into coil so that after heat treatment they could

be stretched to obtain measurable plastic elongation and elastic recovery.

Analogous Tests: The Following People Used a "Spring Elongation

Number" Test on Copper Wire For Different Purposes as Follows:

R. Nilsson (J. Inst. Metals, 1960) :

To Differentiate Between Grain Sizes.

S. Harper (J. Inst Metals, 1965):

To Differentiate Cooling Rates.

S. Carlen (J Inst Metals, 1960):

To Measure the Effect of Finish Temperature.

A. Smith (Inst of Min & Metall. Trans., 1966):

To Demonstrate Variation in Drawing [_ractice.

References: 1. S. Harper and A. Goreham, Factors Affecting the

Springiness of Copper Wire, J of the Inst. of Metals, 1965, Vol. 93, pp. 409-

17.

2. F. Schuckher and R. Nilsson, A Method for Assessing the Suitability of

Copper Wire for Enamelling, J of the Inst. of Metals, 1960, Vol. 88, pp. 7-14.

3. K. MacKay and G. Smith, Quality Control of Electrolytic Tough Pitch

Copper, Inst. of Min. & Mer. Trans., 1966, Vol 75, PP. 269-85.

207

DIRECT TENSION EXPERIMENTS ON COMPACTED

GRANULAR MATERIALS

Steven W. Perkins

Assistant Professor of Civil Engineering

College of Engineering

Montana State University

Bozeman, Montana 59717-0007

Telephone 406-994-2111

209

DIRECT TENSION EXPERIMENTS ON

COMPACTED GRANULAR MATERIALS

Steven W. Perkins

Department of Civil and Agricultural Engineering

Montana State University, Bozeman, Montana

KEY WORDS: granular materials, tensile strength, low mean stress, material modeling.

PREREQUISITE KNOWLEDGE: The student should have an understanding of soil

mechanics, concepts of stress and strain, and the formulation of ideally elastic stress-strain behavior in

loading and unloading.

OBJECTIVES: The objective of this experiment is to determine the level of tensile strength of

uncemented, dry, granular materials. The experimental apparatus does not lend itself to a direct

measurement of the material's tensile strength, but must be analyzed as a stress field problem in order to

arrive at a tensile strength value. The experiment, and subsequent analysis, serve to instruct the student

on the influence of gravitationally induced stresses in frictional granular materials, the importance and

difficulty of accurately describing the entire failure envelope for granular materials in the low mean stress

range, and the fundamental principles of material modeling.

BACKGROUND AND THEORY: Granular materials, such as highly angular dry sands and

silts, are known to contain a small but significant level of cohesive strength. It has been shown that a dry,

silty, highly angular sand, prepared to near 100% relative density, possesses a cohesion of approximately 2.5

kPa (1). Cohesive strengths in these materials are believed to arise mainly from interlocking of highly

angular particles.

By virtue of the continuous nature of a material's failure envelope, materials containing a cohesive

strength must contain a small, but finite, level of tensile strength. This is illustrated schematically in Figure

1, where the tensile strength is represented by the symbol "T" and the cohesion by "c", where compression

is taken as positive and tension as negative. This tensile strength is typically much smaller than the

corresponding cohesive shear strength, which implies a high degree of non-linearity in the failure envelope

in this low range of mean stress. In the absence of tensile strength information it has been common practice

to extrapolate the failure envelope back to the intersection with the tensile mean stress axis. This fails to

account for the dramatic curvature of the failure surface in the region of low mean stress. In addition, the

tensile strength of a material is often times overestimated by this technique. To avoid these problems it is

necessary to deternfine the material's tensile strength, no matter how small this strength may be.

Problems of low mean stress confinement have received considerable attention in conjunction with

plans for developing facilities on the surface of the moon. The low gravity level on the moon, coupled with

the light weight of proposed structures, requires that the properties of lunar soil be examined in the low

mean stress regime. The study of the mechanics of granular materials at low mean stress levels also has

terrestrial applications in the study of liquefaction problems and the performance of roadway bases.

Engineering problems associated with this low mean stress range are significantly impacted by the

assumptions made with regard to the level of tensile strength of the material. For example, the soil behind

a retaining wall of conventional height, erected in a low gravity environment such as that on the moon, will

experience relatively low levels of mean stress confinement. A condition of active failure will produce stress

paths in the various soil elements which progress towards tensile states of stress. An accurate description of

the tensile strength of the material is necessary to evaluate the active earth pressure acting on the wall.

This problem is more significant in a low gravity environment where a greater proportion of the material

experiences lower levels of mean stress confinement. Overestimation of the tensile strength by extrapolation

techniques can result in an overprediction of the capacity of structures with loadings in the low mean stress

211
r (p_)

T a (Pro

Figure 1: Schematic Failure Envelope

range.

In addition to conventional geotechnical engineering solutions, modern constitutive models often

rely on the assessment of the isotropic tensile strength as an input parameter. The proper identification of

this parameter is essential when using the material model in conjunction with finite element codes to

determine the response of complex loadings involving initially low levels of mean stress confinement. The

problem then lies in developing an appropriate experimental device to determine the tensile strength of a

weakly cohesive material.

EXPERIMENTAL PROCEDURE: A new apparatus has been designed and built for

measuring the tensile strength of uncemented silty sands (1). This device is shown schematically in Figure

2. The device consists of a mounting plate (not shown), loading system (consisting of a motor support

block, motor, load cell and screw mechanism), horizontal travel rails and ball bearing blocks, split specimen

box, and horizontal restraint rails (vertical guide rails). The device is designed to contain a 17.8 cm

cuboidal specimen in a box split along a vertical plane. The box is split to form two equal halves. The

front half of the box is mounted to two lateral guide rails by roller bearing (pillow) blocks attached to its

underside. The rear half of the box rests on two aluminum blocks to position it to the same vertical height

as the front. The rear half of the box is restrained from horizontal movement by two vertical guide rails. It

is noted that these guide rails may serve to translate the rear half of the box upwards. This can allow the

box to be modified to impose a shearing force on the plane of failure.

With the soil specimen in place, the front half of the box is pulled in a direction perpendicular to

the vertical plane of split by a motor as shown in Figure 2. The load required to split the sample is

measured with a load cell attached to the front of the box. This load cell has a range of 0-222 N and a

resolution of +/- 0.0555N. Lateral displacement is measured with LVDT's having a linear range of+/- 1.27

mm (not shown). The force required to overcome rolling resistance between the pillow blocks and the guide

rails is estimated by placing a weight inside the front box and operating the motor at the same speed used

for the experiments. This force is negligible compared to the resistance of the material itself.

Specimens of silty sand were prepared by closing the two boxes together and attaching the

loading system so that no gap existed between the two boxes. This required driving the motor and screw

mechanism in reverse until the boxes mated. Known masses of material were then placed in the box in

212
Back Half of Split Box

Front Half of Spill Box Ver j tical Guide Rails

F--_ )

I

Load Cell

Motor

!

Motor Support Block I LateralPillowBlocks

Vertical Pillow Blod_s

LateralGuide Rails

Figure 2: Direct Tension Device (Perkins, 1991)

several lifts and compacted with a small (4cm x 5.5cm) fiat metal plate attached to a commercial metal

etcher. The metal etcher served to vibrate the plate to provide compaction to the underlying material.

Packings approaching 100% relative density have been achieved using this technique. Specimen uniformity

is obtained by employing the method of "undercompaction" (2). The lateral earth pressure induced in the

sample during preparation was monitored by recording the voltage output from the attached load cell. The

specimen is "gripped" by the sides and bottom of the box by lining the inside of the box with coarse sand

paper and relying on shear stresses developed between the sand paper and the sand specimen.

Experimental results are expressed as the average stress on the vertical plane of failure versus the

displacement of the front box. The average stress on the vertical plane of failure is computed by dividing

the measured load from the load cell by the cross sectional area of the plane of split. Results from three

experiments on a dense silty sand are shown in Figure 3. The average horizontal stress on the plane of

split is compressive at the beginning of the tests due to the lateral earth pressure within the soil mass. As

the test proceeds, the average stress tends to decrease towards zero. For materials containing an

appreciable tensile strength, it would be expected that the average stress would reach negative values.

The initial state of stress in the specimen depends on the depth within the sample as well as the

level of compaction, which determines whether the horizontal stress is less or greater than the vertical

stress. Therefore, the initial state of stress is far from uniform. When a uniform tensile load is applied, the

soil in the upper portion of the box will experience tensile failure long before the bottom elements. This

process is discussed and illustrated in the following section. It will be evident that the peak response from

the experimental results is not necessarily the corresponding tensile strength of the material. Furthermore,

it is clear that to determine this value one must analyze this experiment while taking into account the

influence of the gravitationally induced material stresses and the progressive nature of the tensile failure.

DISCUSSION AND ANALYSIS OF RESULTS: The design of the apparatus and the

method of sample preparation allow for the lateral earth pressure (all) in the direction normal to the plane

213
4.5

i i

i j

4.0 ..................... ,_..................... L...........................................

; , l *

3.5 ..................... •..................... -..................................

.'*'-_

3.0 .......... i-.......... _-........................................... ,........... ,........... r,¢3

o 2.5

......... _.......... w .......... _ .......... _ .......... ,........... L .......... _ ..........

2.0 ......... _....... _.......... _.......... _.......... _.......... _.....................

- ', : .... ',

0_ , , ', : : ',

i

,, ,, .... ', 1.5 .......................................................................

,'....

,, DTI0 i i " ; : DTI.I ',

_ 1.0 F-V_7...... r----..... / F.......... ;.................................... //...... :-........

i i * i i _ i

0.5 ............................................................................... ,, ,, , ', ,,

"_ * t * J i i

0.0 ......"-I • I ' -L-- i i i ; -- " .......

-0.5

0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00

Lateral Displacement (mm)

Figure 3: Direct Tension Results (Perkins, 1991)

of split, to be monitored during sample preparation. This was accomplished by using the loading frame

assembly to hold the front box against the rear box. As soil was deposited in the box and compacted by

vibration, the lateral stress in the direction of travel of the front box was resisted by the loading frame.

The load necessary to resist any movement was monitored by the load cell. The coefficient of lateral earth

pressure (Ko = an/av) could be calculated assuming a linear distribution of vertical and lateral stress with

depth. The load cell reading at the end of sample preparation could be converted to lateral stress by using

the vertical cross-sectional dimensions of the box along with the assumption of a linear distribution of

stress with depth. This is illustrated in Figure 4. The variation of vertical stress with depth is given by:

av = pgh (1)

where p is the mass unit weight of the soil, g is the acceleration of gravity and h is the depth below the

surface of the soil. The vertical stress in the soil at the bottom of the box is given by:

av = pgH (2)

where H is the depth of the box. The average lateral stress perpendicular to the plane of split is given by:

P

= (3)

where P is the load on the front half of the box and A is the cross sectional area of the plane of split. The

distribution of aH with depth is then:

2P h

O'H- A H (4)

so that at the bottom of the box o"H is given by:

2P

= T (5)

214
h h

H

av = pgH Ko = aV

Figure 4: Assumed Distribution of Vertical and LaterM Stress With Depth In The Direct Tension Device

The laterM earth pressure coefficient is then calculated from:

Ko = a___H= 2P/A (6)

av pgH

From the above discussion it has been shown that the initial state of stress (immediately following

sample preparation) in the direct tension specimen mass is one where one of the principal stresses is

directed in the vertical direction (due to the material self-weight) while the other two principal stresses lie

in the horizontal plane and are equal and due to the lateral earth pressure condition. If Ko is greater than

one then the two lateral principal stresses will be the major and intermediate principal stresses while the

vertical stress will be the minor principal stress. If Ko is less than one then the two lateral principal stresses

will be the minor and intermediate principal stresses while the vertical stress will be the major principal

stress. These conditions are shown in Figure 5 for an element of soil adjacent to the plane of split.

As the load applied to the front of the box is reduced the assumption is made that this reduction in

load is applied uniformly to the plane of split. This process is illustrated in Figure 6. In order for this

assumption to hold there must be a no-slip condition between the sides of the box and the soil. The sand

paper lining on the interior of the box should ensure this condition. This condition would also create

shearing stresses in the" soil at the soil-wall interface so that the directions of the principal stresses

discussed above would apply only to elements sufficiently far from the box walls.

From Figure 6 it is immediately noticed that the upper portion of the specimen will be subjected

to tensile stresses long before elements located at the bottom of the box. This suggests that failure in the

specimen will progress from the top of the plane of split down to the bottom. This concept is further

illustrated in Figure 7 where possible stress paths for various points along a vertical line along the plane of

split are sketched on a p - q diagram, where p is defined as the average mean stress [p = (al + a2 + a3)/3]

and q is defined as the principal stress difference (q = al - a3). The principal stresses are taken as shown in

the upper right portion of Figure 7 (i.e. Ko > 1). Since the two horizontal stresses (al and or3) are equal at

the beginning of the test, q is zero for all points along a vertical line, denoted by varying levels of h. As a

uniform load is applied to the plane of split, through the front box, q begins to increase by the same

215
Ko > 1 Ko < 1

Figure 5: Initial State of Stress in the Direct Tension Specimen

Distribution of a// Perpendicular To The

Plane Of Split For Increasing Reductions In The

Load Applied To The Front Box

<

Initial Distribution Of trH

Perpendicular To The

Plane Of Split

Tensile Stress Compressive Stress

Figure 6: Mechanism of Load Application ToThe Plane of Split

216
al

2 F a2 15.0 ,.,e //

12.5

,,.o.o% 1

,-- Q--7,,-- =o

",. ",,I \./",, ",

[-- ,. .,3=1⁄2,.,

', \ ', ',, ,, 2.5 ;I _, \ ",. '\

\ \, "\ \

' T , , _ $, I ,

-z.s I 2.s s.o z.s _o.o

p(kV_)

Figure 7: Stress Paths for Direct Tension Loading

amount for all points along a vertical line so that the load steps can be portrayed as horizontal lines on

Figure 7. Superimposed on this diagram is a possible failure envelope. This failure envelope was derived

from conventional triaxial compression experiments conducted within this range of mean stress. The initial

levels of al and 0"3in Figure 7 were derived from actual test results. The loading sequence again illustrates

that the top elements reach the failure envelope far before elements at the bottom of the box.

A simplistic, mechanistic approach is used to describe the loading and failure conditions present

during the direct tension test. The soil specimen is treated as a number of layers whose material properties

are identical but whose initial state of stress is governed by the relative vertical position in the soil mass. A

simple material model is used to describe the soil's stress-strain characteristics. This model describes the

relationship between the stress and strain perpendicular to the plane of split by the elastic modulus in

compression and tension (assumed to be equal) and a softening elastic modulus applicable beyond the

tensile strength of the material as demonstrated in Figure 8. It is assumed that the material can be

described in terms of these elastic parameters for the range of loads considered. Clearly this is an

idealization of the true non-linear, elastic-plastic nature of the material, but nevertheless is useful in

describing the mechanisms associated with this experiment.

It is assumed that this material model applies to each layer in the divided soil mass. The upper

most infinitesimal layer has an initial stress acting perpendicular to the plane of split equal to zero and is

denoted as the point at h = 0 in Figure 8. Successively deeper layers are treated as elastically preloaded

elements and are denoted on Figure 8 as points along the stress-strain curve at successively higher levels of

stress and strain. As a uniform displacement is applied to the box, each of these points moves downward in

equal increments along the stress-strain curve until the maximum tensile strength (o"t) is reached, after

which the element in the layer softens until the stress perpendicular to the plane of split is zero.

This process can be illustrated by an analogy given by a simple set of springs in parallel where each

217
Z/ J

4. _ Or

1.

0. _.._ h = 0

Eu 'E = 0.025 0.050 0.075 0.100 0.125 0.150 0.175 0.200 (_3

-2. "'

V qLOr,

Figure 8: Idealized Stress-Strain Behavior of Soil in Compression-Tension

spring represents a layer of soil, as shown in Figure 9a. Each spring is preloaded by a compressive load, Pi,

as shown in Figure 9b. Each spring, having the same spring constant, is then uniformly unloaded by an

equal displacement, A j, until each spring reaches its maximum tensile carrying capacity, Pt, after which

the spring relaxes according to the spring constant K_ until the spring carries no load. It is seen that this

is a progressive process with the upper most springs reaching "failure" before the lower springs.

In Figure 8, if we assume that a_ remains constant and that there exists a condition of plane strain

in the direction of al, then the stress and strain in the direction of 6r3 are related by:

E

AO'3 -- Ae3 u1-'------ - _ (7)

Assuming values for E, u, E_, and at, it is possible to predict the response of direct tension

experiments using the density of the soil from these tests to determine initial distributions of a3. The

response is strain-driven by applying equal increments of strain to each soil layer. As each soil layer reaches

the assumed level of at the soil softens along the unloading branch until the stress in the element is zero.

A program was written to perform this analysis where the number of soil layers was included as a

variable. The soil mass was divided into 10, 100 and 500 layers. The response appeared more smooth when

the number of layers was increased to 100 but little difference was observed by increasing this number

further. The initial conditions from an experiment were first used to perform this analysis. An elastic

modulus of E = 6000 kPa and u = 0.25 were found to produce results which matched experimental results

during the initial part of loading. A tensile strength value of at = -0.1 kPa was selected at first. The

analysis was performed for five values of the unloading modulus, namely E_, = -E/100, Eu = -E,

Eu = -E * 100, E_ = -E * 1000 and E_ = -E * 100,000, corresponding to increasingly brittle behavior.

By increasing the absolute value of the modulus E_ the observed effect is to increase the brittleness of the

material so that a net negative stress on the plane of failure is never observed. The difference between the

response curves for the various values of E_ was insignificant, due primarily to the small level of at.

Additional analyses demonstrated greater differences in the softening behavior for larger levels of at. In

either case, the behavior was virtually unchanged above levels of E_ = -E • 100.

218
layer 1 /

P,

/

- °

layer 2

F ¢_ _----"_ P2

/

/

laver 3 /

KI .°P3

V,,I

Figure 9: Elastic Spring Model for Layered Soil in Tension

4.5

4.0 ..................................................................................

3.5 ...................................................................................................

_, 3.0 ..................................................................................................

r_

"_ 2.5 .................................................................................................

o

_, 2.0 .............

........ '............ F........................ F........... !....... F...........

1.5 .............

rZ Pm,'diction, Tensile S,ength = p :; ::

o ,.o........... :ZIIII ............. _ 0.5 k- i/ :: _perimeni_DT12 1 ....... [

<

0.0 ...........

_ Prediction, Tensile Strength =-j.0 ,,

-0.5 , I , I , I , I , I , I ,

0.00 0.25 0.50 0.75 1.00 1.25 1,50 1.75 2.00

Lateral Displacement (mm)

Figure 10: Predictions of Direct Tension Tests for Varying Levels of c_

219
Figure 10 shows predictions for different assumed levels of a_ for E_, = -E • 100. For at = -1.0

kPa a noticeable peak in the response is observed. Little difference is observed between the results for

at = -0.1 kPa and at = 0. In these cases the materiM begins to soften as it approaches the zero average

stress level on the plane of split with no peak response being observed. The initial load-displacement curve

is matched reasonably well by the predictions as is the finM state at large displacements. The softening

behavior, however, is not matched very well for this material model. For low levels of tensile strength the

response curve approaches the zero stress line rather abruptly. The predictions tend to show far more

, brittle behavior than the experiments.

CONCLUSION: The above direct tension experiment and analysis approach serves to illustrate

important fundamental material behavior of frictional granular materials. The material model proposed for

the analysis of the experiment relies on simple linear elasticity principles. In addition to this material

model, the student can try other models, some of which might include a parabolic shaped stress-strain

curve in compression and tension, or elastic moduli that vary from each material layer.

REFERENCES:

(1) Perkins, S.W. (1991)"Modeling of Regolith Structure Interaction in Extraterrestrial

Constructed Facilities", Ph.D. Thesis, University of Colorado at Boulder, 324 p.

(2) Ladd R.S. (1978), "Preparing Test Specimens Using Undercompaction", Geotechnical

Testing Journal, GTJODJ, V.1, No.l, pp.16-23.

220
APPLICATION OF HARDNESS TESTING IN FOUNDRY

PROCESSING OPERATIONS:

A UNIVERSITY AND INDUSTRY PARTNERSHIP

Donald H. Martin

School of Manufacturing Technology

Tri-State University

300 South Darling

Angola, Indiana 46703

Telephone 219-665-4265

and

Bruce Lash

Q. A. Manager

AL-FE Heat Treating, Inc.

Columbia City, Indiana 46725

221

APPLICATION OF HARDNESS TESTING IN FOUNDRY

PROCESSING OPERATIONS:

A UNIVERSITY AND INDUSTRY PARTNERSHIP

Donald H. Martin, Associate Professor

School of Manufacturing Technology

Tri-State University, Angola, IN 46703

and

Bruce Lash - Q.A. Manager

AL-FE Heat Treating, Inc.

Columbia City, IN 46725

KEY WORDS: Partnership, Brinell Hardness, Hardness, ASTM

Standards, Brinell Scope, Hardness Equation, Hardness Conversion Scales, Tensile Strength.

PREREQUISITE KNOWLEDGE: The student should understand the

concept of tensile strength of materials either previously or

concurrently presented with the experiment.

OBJECTIVES:

i. Plant tour of local manufacturing facility to observe hardness •testing methods used and how they support the manufacturing process today.

2. To learn the operation of Brinell Hardness Testing,

equipment set up with samples of accessory equipment for

testing of various materials.

3. Use of Brinell _ (hand magnifier) to measure the diameter of the test indentation (in millimeters).

4. Use of the hardness equation to determine the spherical area

of the indentation and the calculation of the Brinell Hardness Number.

5. Use of standard charts for ASTM standard size indenters to

find the hardness number.

6. Method of conversion of the Brinell number to other hardness

scales, their common usage, and also to convert the hardness

number to the approximate %en$ile $%reng%h,

EQUIPMENT AND SUPPLIES: Selection of metal test samples;

Brinell hardness tester; hand held magnifier (Brinell Scope);

ASTM reference hardness charts.

223
PROCEDURE:

PHASE_

Tour of Foundry or Foundry Support Manufacturing Facility:

Tour of AL-FE Heat Treating, Inc., Columbia City.

i. RECEIVING

When material is received at the Columbia City division, it

is held at the dock until the following is accomplished:

Identified

a. by alloy

b. by quantity

c. by any damage

d. by parts matching Bills of Lading

e. by serialized work order identification tag:

1 AI-Fe Heat Treating, Columbia City

2 customer name

3 packing slip number if any

4 customer ID #

5 work order number for each container

6 part number

7 date received

8 container 1 of 1

9 quantity

2. STORAGE

The material is then placed in the as-cast area. There are

two divisions of as-cast materials, i. regular process and

2. special process.

3. HEAT TREAT CONTAINER LOADING

All material is loaded into heat treat containers using the

following criteria:

a. alloy specific

b. process temp.

c. process time

d. specific quench requirements

e. damage prevention

f. weight limitations

4. SOLUTION TREATING

To take advantage of the precipitation hardening reaction,

it is necessary first to produce a supersaturated solid

224
solution. The process by which this is accomplished is called

solution treating. It consists of soaking the alloy at a

temperature sufficiently high to achieve a nearly homogeneous

solid solution and then quenching fast enough to retain the

solute in solution. The temperature is kept low enough so

that eutectic melting does not occur.

5. QUENCHING li.e. controlled cooling)

The quench portion of the process can be accomplished by

either room air cooling, forced air cooling, water, or polymer. To avoid the type of precipitation detrimental to mechanical properties or corrosion resistance, the solid solution formed during solution treating must be rapidly cooled to

produce a supersaturated solution at room temperature, the

optimum condition for subsequent precipitation and hardening.

This is usually accomplished by immersing the parts in cold

water.

6. R_9_QMAGE

Room age is part of the process that is time dependent as

specified by the customer and this specification then becomes

part of our process. The length of time can be 15 min.

minimum to any number of days.

7. ARTIFICIAL AGE

This part of the process, which is an accelerated age cycle,

is dependent on time and temperature. Through this process we

achieve the customer's required specific hardness.

8. HARDNESS __HECKING

In our Heat Treating process, we'll use the following hardness testing methods: Brinell, Rockwell, and Impression.

9. SHIPMENT

All material is packaged to prevent damage in transit, and

the material is identified with an "OK-TO-SHIP" tag providing

the batch number, inspector name, and date of inspection.

Material is CERTIFIED, per customer request, stating the

process performed.

PHASE II

i. After the professor has demonstrated the hardness test,

measured the specimen, calculated the hardness number, and

225
made an equivalent chart determination, all class members

will take turns repeating the measurement.

2. Before testing each specimen, measure the thickness and

record on _ data sheet; then insert the specimen in the tester

and build up to the specified pressure shown on Chart i. Hold

pressure the specified time and release.

3. Remove specimen from tester, and with magnifier, (Brinell

Scope) measure the indenter diameter in millimeters.

4. Calculate the Brinell Hardness Number and record on the data

sheet. Check this number with the thickness in the Chart

II, to see if an anvilling error exists, ie: If the hardness

number is less than that of the table, you are "testing the

hardness of the anvil" instead of the specimen (must use a

thicker material for a valid reading).

5. Utilizing the wall chart and additional conversion charts,

fill in the remaining columns of the data sheet.

6. The far right hand column is reserved for comments if difficulty is experienced. If specimen is too thin and reading

is INVALID, write ANVILLING in this space.

This table shows that a singie Examples of use of ASTM

Brinell Number represents a E-10 Table:

specific hardness. (Thus, LOAD

using different loads on the Spec.

same indntations, material but gives gives different the BHN I 3000 1500 I 500 I No.

same Brinell Number for the 341 3 30 2 35 1

one material!) 302 3 50 2 50 2

262 3 75 2 70 3

223 4 05 2 90 4

159 4 75 3 40 2.00 5

128 5 25 3 80 2.20 6

i01 5 85 4 25 2.50 7

81 6 45 4 70 2.77 8

Diameter is shown in millimeter_

Load is in Kgf

HARDNESS CONVERSIONS

FOR CONVERSIONS TO TENSILE STRENGTH AND TO OTHER HARDNESS SCALES,

USE APPROXIMATE CONVERSION CHART ON NEXT PAGE.

226
From a Brinell hardness reading, read from the scale at the

top, go down to the Brinell "curve" and then horizontal to the

left for the approximate ultimate tensile strength.

From this horizontal line, intersecting other curves, go to

the respective scale to read the approximate hardness conversion to that scale.

RULES FOR ESTIMATING TENSILE

STRENGTH FROM BRINELL HARDNESS:

(For steel)

Under 175 HB:

HB x 515 = Tensile (psi

Over 175 HB:

HB x 495 = Tensile (psi

PSI = Pounds per square inch

227
BRINELL loo 200 inn 400 500 600 700 VICKERS 

ROCKWELL B 

ROCKWELL C 

'SCLEROSCOPE 

GRAPH SHOWING APPROXIMATE CONVERSIONS OF DIFFERENT HARDNESS SCALES 
,, H,m i

BRINELL HARDNESS EQUATION:

. -- i i i . .i J i ,

HB = _ . p Where: P = Load in kilograms Kg F

"[I-D (D -_D _ - d 2) D = Ball diameter (10 mm ±.005 m m)

d = Indentation (mean diameter

in mm)

....

HB = Hardness Brinell in Kgf/mm _

INDENTERS: Steel ball (Vickers hardness 850) for use under

450 HB of specimen. Hultgren ball for use in

specimens with hardness less than 500 HB Carbide

ball for use with specimens of hardness less than

630 HB. (Impression diameter must be 2.50 to 6.00

mm and 25-60% of ball dia.) (Load duration shall

be between 10-15 seconds, at full load).

HARDNESS SPECIFICATION: Example: 63 HB 10/3000/12 means

63 Brinell hardness measured using a 10mm ball and

a load of 3000 kg_ for 12 seconds (If the load

is not specified,-3000 kg F shall be assumed.)

INDENTATION READING TOLERANCE (per ASTM): diameter to

0.i mm and estimate to .02 mm.

SPACING OF INDENTATIONS: Spacing of two adjacent readings

or spacing to a corner shall be a minimum of two

and one half times the diameter of the indentation (2 1/2 d).

,, i ,, , i ,H, , , J l , ..... • .......

229
CHART ZI

LOAD APPLICATION AND ANVILLING EFFECTS (ASTM Standard and

Scott modification)

BRINELL HARDNESS RANGE: 96 to 600 HB 48 to 300 HB 16 to i00 HB

(Overlapping ranges )

2.00 mm d to 6.99 mm d

Kg (F) 3000 Kgf 1500 Kgf 500 Kgf

Pound (Equiv.) 6613.85 # 3306.93 # 1102.31 #

Scott Pressure Gauge (17,779. psi) 8.890. psi _ psi

(Compr. Spec.)

w/ .372 in 2 Area Beyond Range

(.6882 did RAM) of Scott

Best Load Relation to ball did. of _D 2: 30 %2 = 15 %-2- 5

(or P = 30D 2)

Best Ball Did. i0 ram i0 mm 5 mm

ANVILLING EFFECTS: Minimum HB for thickness of specimen to

Min. Thickness prevent mushrooming far side.

Metal Sample

Reqd. 1/16 inches 602 301 i00

Reqd. 1/8 inches 301 150 50

Reqd. 3/16 inches 201 i00 33

Reqd. i/4 inches 150 75 25

Reqd. 5/16 inches 120 60 20

Reqd. 3/8 inches i00 50 17

(Anv_iTing gives_'incorrect data by reading'partial hardness'of anvil,

instead of specimen.)

Softer loads of 250, 125 and i00 Kg F are standard and are occasionally

used.

230
DATA LOG TABLE Date:

MATERIAL SKETCH" THICK- Dia. BRIN- Vickers Mohs ,TENSILE COMMENTS

LOAD NESS D ELL STRENGTH (Evidence

mm. HB p:i of

Anvilling

INSTRUCTOR NOTES: "Hardness" is a term that has different

meanings to different people. It is resistance to penetration

to a metallurgist, resistance to _ to a lubrication engineer, a measure of flow-stress to a design engineer, resistance to scratching to a mineralogist, and resistance to cutto a machinist. Although these' several actions appear to

differ greatly in character, they are all related to the

plastic flow-stress of the material.

To avoid misapplication of Brinell hardness testing, the

fundamentals and limitations of the test procedure must be

clearly understood. _ Further, to avoid inaccuracies some

general rules should be followed:

i. Indentations should not be made on a curved surface having a

radius of less than 1 inch.

2. Spacing of indentations should be correct, as outlined in

the ASTM section, "Spacing of Indentations."

231
3. The load should be applied steadily to avoid overloading

caused by hand-inertia on the weights.

4. The load should be applied in such a way that the direction

of loading'and the test surface are perpendicular to each

other within a 2 ° angle.

5. The thickness of the workpiece being tested should be such

that no bulge or mark showing the effect of the load appears

on the side of the workpiece opposite the indentation. Very

soft samples are unsuitable.

6. The surface finish of the workpiece being tested should be

smooth, so the indentation diameter is clearly outlined.

REFERENCES:

ASM, "Hardness Testing", Materials Park, OH, 1987.

ASM, "Metals Handbook, Desk Edition", 1985 - Metals Park,

OH; Boyer, H.E. & Gall, T.L., editors, pp. 35-4.

American Society For Testing and Materials (A.S.T.M.),

Standards E 6, E i0, A 370, E ii0.

Budinski; "Engineering Materials; Properties and Selection",

3rd ed.; Prentice-Hall, Englewood Cliffs, N.J., 1989.

Jacobs, J.A. & Kilduff, T.F. "Engineering Materials

Technology", Prentice-Hall, Englewood Cliffs, N.J., 1985.

Van Vlack, L.H., "A Textbook of Materials Technology",

Addison-Wesley, Reading, MA 1973.

232
LABORATORY EXPERIMENTS IN INTEGRATED

CIRCUIT FABRICATION

Thomas J. Jenkins

and

Edward S. Kolesar

Professor of Electrical Engineering

Department of Electrical and Computer Engineering

(AFIT/ENG Bldg. 640 Area B)

Air Force Institute of Technology

Wright-Patterson Air Force Base

Ohio 45433-6583

Telephone 513-255-3708; 4960; 6027

233

LABORATORY EXPERIMENTS IN INTEGRATED CIRCUIT FABRICATION

Thomas J. Jenkins, Capt, USAF

Edward S. Kolesar, PhD, P.E., Lt Col, USAF

Air Force Institute of Technology

Department of Electrical and Computer Engineering

(AFIT/ENG, Bldg 640, Area B)

Wright-Patterson Air Force Base, Dayton, OH 45433-6583

KEY WORDS: cross-bridge test structure, diffusion, integrated circuit (IC), metallization, metal-oxide-semiconductor (MOS) capacitor, metal-oxide-semiconductor field-effect

transistor (MOSFET), oxidation, photolithography, pn-junction diode, semiconductor, silicon,

transfer length method (TLM) test structure.

PREREQUISITE KNOWLEDGE: The student should understand the concepts

associated with silicon integrated circuit (IC) fabrication, such as oxidation, photolithography,

diffusion, and metallization. Also, the student should understand the theory of operation of

metal-oxide-semiconductor (MOS) devices and pn-junctions. The fabrication concepts can be

presented in advance of, or concurrently with, the experiment. However, the theory of operation of the devices must be mastered prior to implementing the laboratory experiments.

OBJECTIVES: The objectives of the experiment are fourfold: 1) to provide practical

experience implementing the fundamental processes and technology associated with the science and art of IC fabrication, 2) to afford the opportunity for the student to apply the theory

associated with IC fabrication and semiconductor device operation, 3) to motivate the student

to exercise engineering decisions associated with fabricating integrated circuits, and 4) to

complement the theory of n-channel MOS and diffused devices that are presented in the

classroom by actually fabricating and testing them. Therefore, a balance between theory and

practice can be realized in the education of young engineers, whose education is often criticized as lacking sufficient design and practical content 1.

EQUIPMENT AND SUPPLIES: The equipment required to implement this laboratory experiment is listed in Table I. The equipment list is partitioned into two principal categories. The first category is associated with the fabrication process. The second category is

related to process characterization and testing the fabricated devices.

235
Table I. Laboratory Materials and Equipment

Fabrication Process:

Convection Ovens

Model Imperial IV, Lab-Line Instruments, Inc., Melrose Park, IL

Crystal Thickness Monitor

Model TM-100R, Maxtek, Inc., Torrance, CA

Diffusion/Oxidation Furnace

Model 4100, Thermco Products Corp., Orange, CA

Mask Aligner

Model MJB3, Karl Suss America, Inc., Waterbury Center, VT

Metallization System

Model DV602, Denton Vacuum, Cherry Hill, NJ

Process Characterization and Device Test:

Ellipsometer

Model L117, Gaertner Scientific Corp., Chicago, IL

Four-Point Probe

Model AP-150, Veeco Instruments Inc., Plainview, NY

Low-Frequency Impedance Analyzer

Model HP 4192 A, Hewlett Packard, Palo Alto, CA

Micromanipulators and Probe Station

Model 6200, Micromanipulator Co., Inc., Carson City, NV

Multimeter

Model HP 3478 A, Hewlett Packard, Palo Alto, CA

Optical Microscope Interferometer

Model 255574, Wild Heerbrugg Ltd., Heerbrugg, Switzerland

Photoresist Spinner

Model 1-PM101D-R790, Headway Research Inc., Garland, TX

Profilometer

Model Dektak _A, Sloan Technology Corp., Santa Barbara, CA

Semiconductor Parameter Analyzer

Model HP 4145 B, Hewlett Packard, Palo Alto, CA

236
PROCEDURE: For a typical ten-week academic quarter, the student accomplishes

five distinct, two-week fabrication and testing exercises: oxidation, photolithography, diffusion, metallization, and test. While some of the exercises are obviously repeated throughout

the laboratory, such as photolithography, the student's introduction to a distinct process is

emphasized during each of the two-week exercises. For example, oxidation is initially introduced during the first meeting of the laboratory. In the next exercise, the student explores

photolithography and the conditions required for optimal exposure and development of the

photoresist. However, during subsequent exercises, the results of both the initial oxidation

and photolithography exercises are reinforced and utilized, but the emphasis shifts toward

exploring other process control variables, such as optimal etch times and etch rates.

To implement the laboratory experiments, the student uses a four-level photomask

set, which is illustrated in Figures 1 - 6. Successful implementation of the individual exercises in this laboratory experiment yields pn-junction diodes, cross-bridge test structures,

transfer length method (TLM) test structures, metal-oxide-semiconductor field-effect

transistors (MOSFETs), and MOS capacitors.

1. Initial Oxidation Exercise.

The first laboratory exercise provides the students' orientation with the IC fabrication facilities, as well as a closely supervised oxidation experiment. During the orientation,

the students receive specialized instructions concerning the proper operation of the laboratory

equipment. The instructions also include specific safety concerns appropriate for the equipment or process. After the students have demonstrated their proficiency with the laboratory

equipment or a specific process, only minimal supervision is required. This situation affords

the student the opportunity to exercise engineering design and decision skills. This general

administrative process is repeated during the later exercises, as required.

Each student is furnished with one copy of the photomask set and ten silicon wafers at

I

the beginning of the laboratory experiment. The silicon wafers are prime grade, (100)-

oriented, p-type (boron doped) with a nominal resistivity of 6- 18 _.cm. Before transferring

the wafers to the students, they are thermally oxidized at 1100°C for 485 minutes with dry

oxygen by the students (in conjunction with close supervision by a laboratory technician)

during the first meeting of the laboratory. Since these oxidized wafers will serve as the

starting material for the subsequent phosphorus diffusion exercise, the oxide thickness needs

to be approximately 450 nm.

Before initiating the photolithography exercise, the student estimates the oxide thickness on a representative wafer using an oxide color chart and measures it with an ellipsometer. With this information, the student can correlate the measured oxide thickness with the

237
II 11

[] [] V1OUIZEI

[][]O00[I] _+

Figure 1. Composite view of the four-level photomask reticle.

III I

I mml

__._x:.

ununnnm

+++ r

mmmmmmm

mmmmmmm

Figure 2. Level-one photomask reticle used during the diffusion exerctse.

238
l Ill

i

i

• n Inl..

un i

II

+ F

Rim

Figure 3. Level-two photomask reticle used during the gate-oxidation exercise.

Figure 4. Level-three photomask reticle used to define the semiconductor-metal

contacts.

239
I

Figure 5. Level-four photomask reticle used during the metallization exercise.

In II

PN Junction

_

MOS Capacitor(100 x75)

Figure 6. Relative location of the fabricated devices within the photomask reticles.

240
processing conditions actually utilized during the initial oxidation exercise and the predicted

results obtained by simulating it with the TSUPREM-4 (Technology Modeling Associates,

Inc., Palo Alto, CA) software 2. In a supplemental appendix to the student's laboratory handout, an introductory guide to using TSUPREM-4 is provided. The results of the simulated

oxidation process are depicted in Figure 7a.

2. Photolithography Exercise.

In this exercise, the student prints the Level-One Diffusion Photomask pattern on the

pre-oxidized silicon wafers. This pattern will subsequently be etched through the oxide. The

etched oxide is used to provide a mask for the subsequent diffusion of the n-type (phosphorus) dopant. The reticle of this photomask is depicted in Figure 2.

Having previously characterized the thickness of the oxide, the student is directed to

complete the following steps:

(1) The pre-oxidized wafers have been stored in a photoresist post-bake oven to prevent moisture absorption; therefore, the N2 gas supply is turned-off before the wafers are

removed. To prepare the wafers for the first negative photoresist printing, they must be

cleansed of organic surface contaminants. To accomplish this task, either,

(a) Immerse each wafer into a beaker of acetone and mechanically agitate it

for 30 seconds and follow this step with an immersion into a methyl alcohol ultrasonic bath for

1 minute, or,

(b) Immerse the wafers into a modified piranha solution composed of H2SO 4 :

H20 2 (3:2), whereby the exothermic reaction makes it self-heating. For safety reasons, this

solution must be prepared by adding the H20 2 to the H2SO 4. The wafers should be cleaned

for 20 minutes.

(c) After accomplishing either step (a) or (b), the wafers should be rinsed in

deionized (DI) water, blown dry with N2, and pre-baked at 2000C for 45 minutes to remove

surface moisture.

(2) After the wafers cool to room temperature, the HR200 negative photoresist,

manufactured by Waycoat, Inc., is deposited on the wafers using a photoresist spinner. To

implement this step, the student should flood the center of the wafer with the photoresist

which is dispensed from an eyedropper. There should be a two-inch diameter puddle of photoresist in the center of the wafer. The wafer should be spun at 5000 rpm for 15 seconds to

uniformly distribute the photoresist.

(3) The wafers should then be pre-baked in the photoresist oven at 65°C for 15 minutes to evaporate the solvents from the photoresist and harden its surface.

241
Etched Diffusion Mask

Ltl

l

C

o ivI

o II I

_ ' I'I I 'I

, , / o /s'.l I. P' • , , I" • • /e/ / / f _ #/ / /, # /

_},x,,,,.//,,.. .".S'_,'. ,.', ",/.', .',, , ,,'/', ,/,/'.'/, ,,/.'." "/, , .'/,,;

-" t-,'/,.'."/.'./x ,'/',,', " ', .'/ G;,;" .'/, /,","/,'/.'/,'/.'/ ,-'_/.',//i. ' ". ,', "//,'/ ""/;"/; "-

L_ IP',, --s f /'// ," , t ,' _ /p" / / w _*, +" P / o'/ , _ "P'_ I / _" " _ *' wt/_t/'/ / S' "_--/-- ¢i /p " _i' /

T.// _,, / i//, ,','1"// , ,/,'/,_ "," -//', / "/ /, z./,./..,./,.i,///, "/'-." "/1"," , /. /I //

1;',',',/"/,'.',',',,',. ",.'/." "/', .,'//',',,.',;', _,'._, "/,, /,"/,'/.'.'/._': ,'/ ", ",/',",;

11, _, / i/,. ". ill / "/.'/,".'_-.'//I /", I,' ".'1,"/.','// /.//, . // ," , %'_,', "/..-I, //

•I_,"/.','"/',//, ,/'/.,',",'/,"x//.,.','/,'/:,._/,,/ // .'_/,'../, /l/_ _.'/'1,,',/,I, ".,,"'i /

19,00 19,50 20.00 20.50 21.00 21 50 22.00 22.5@ 23,0@

Distance (m_.crons)

Figure 7. Samples of the simulation results using the TSUPREM-4 software.

a) Diffusion-mask oxide thickness, b) Junction depth resulting from the diffusion and

the gate-oxidation processes, c) Gate-oxide thickness, d) "Small-Gate" MOSFET

cross-section.

242
(4) Each photoresist-coated wafer should be printed using a mask aligner and the

level-one Diffusion Mask reticle that is depicted in Figure 2. The photomask and photoresist

coated wafer "sandwich" should be exposed to the UV light source for 10-30 seconds. Due

to the number of variables involved, the student will have to determine the optimum exposure

duration experimentally. However, due to the geometries of the devices, the negative photoresist can be overexposed without seriously jeopardizing the chances that the student can

realize functional devices.

(5) The exposed photoresist covered wafers should be developed by implementing

the following procedure: a wafer is positioned on the vacuum chuck of the photoresist spinner

configured for developing, and while being spun at 500 rpm, xylene is sprayed onto it from a

squeeze bottle for 30 seconds; next, butyl acetate is sprayed for 30 seconds: and finally, the

wafer is blown dry with an N2 purge for 30 seconds.

(6) The printed wafers should then be inspected under an optical microscope to confirm proper image alignment and pattern definition. However, since the level-one Diffusion

Photomask is the first photomask, proper image alignment is only a concern for those photomasks which follow the level-one Diffusion Photomask. If the photoresist is underdeveloped, step (5) should be repeated. If the image features are misaligned, the remaining photoresist should be stripped using the plasma asher, cleaned, pre-baked, and the process

should be repeated beginning with step (2). An example of an acceptable image alignment of

the "L-shaped" alignment mark is depicted in Figure 8.

(7) The satisfactorily processed wafers should be transferred to a post-bake oven set

at 135°C for 15 minutes to further harden and promote the adherence of the patterned photoresist. The photoresist product literature and a stylus profilometer can be utilized to

determine the final thickness of the photoresist on a representative control sample wafer.

(8) The wafers should be inspected with an optical microscope (dark-field mode). If

the photoresist has pinholes, it must be stripped, and the process should be restarted with

step (2).

(9) The wafer's oxide that is exposed through the open photoresist windows should

be etched using a buffered HF (NH4F : HF, 4:1) solution.

(a) Fresh etchant should be mixed sufficiently early to let it stabilize (2 hours)

before it is used. Nevertheless, it must also be used within 6 hours after mixing.

(b) The wafers should be individually etched. The introduction of bubbles into

the etchant should be avoided.

(c) Periodically (30 second intervals), each wafer should be removed from the

etchant, rinsed thoroughly in deionized (DI) water, blown dry with N2, and inspected for etch

243
Figure 8. Example of an acceptable image alignmentusing the "L-shaped" alignment

feature.

244
completion. The open photoresist windows will appear light-gray, and the wafer's surface

will become hydrophobic when the silicon dioxide (SiO2) has been completely etched away.

(d) Etching should be continued as necessary. From the total etch time, the

etch rate should be calculated. The student should anticipate an etch rate of 110-150

nm/minute.

(10) After this etching process, the student should remove the remaining photoresist

in the plasma asher (approximately 15 minutes, or until all traces of the photoresist are

removed). At this point, the student should verify the thickness of the oxide mask, which

was previously measured with the ellipsometer and calculated using the TSUPREM-4 software for the process variables implemented during the initial oxidation exercise. The thickness of the oxide between two adjacent windows on one of the control wafers should be measured using a mechanical stylus profilometer.

(11) Finally, the student should inspect the wafers with the optical microscope in the

dark-field illumination mode to verify that all of the photoresist has been completely removed.

3. Diffusion Exercise.

In this exercise, the student will perform a two-step dopant diffusion process. The

student will also evaluate the resultant diffusion profile. To accomplish the evaluation, two

control wafers (not patterned and not oxidized) are required. These control wafers are supplied by the instructor during this exercise. To begin, the student should measure the resistivity of the control wafers with a four-point probe to determine the initial conditions prior to

diffusion. To implement the diffusion process, the following steps should be accomplished:

(1) Cleaning:

Since undetectable traces of contaminants can be catastrophic to both the wafer and

the diffusion furnace, proper cleaning is essential before exposing the wafers to the elevated

temperatures in the diffusion furnace.

(a) The wafers should be immersed in the modified piranha solution (H2SO 4 :

H202, 3:2). The wafers should be cleaned for 20 minutes and rinsed thoroughly with DI

water.

(b) After mixing a DI H20 : HF (10:1) deglaze solution; the wafers should be

dipped in this bath for 30 seconds, rinsed with DI water (to a 10 M_-cm standard), and

blown dry with N2.

(c) The wafers should then be transported to the diffusion furnace in a covered

carrier.

245
(2) Predeposition:

(a) The dopant source boat should be loaded with the polished wafer surface

facing the PhosPlus TP360-7130 phosphorus-dopant source wafers, manufactured by OI-NEG

TV Products, Inc.

(b) A furnace setting of 900°C, and a gas flow of one lpm of N2 should be verified.

(c) The wafer boat should then be slowly pushed into the furnace's hot zone

(1 inch per minute), diffused for one hour; and then slowly withdrawn (1 inch per minute).

(3) Deglaze:

To terminate the introduction of impurities, the phosphosilicate glass phase formed

during the predeposition step must be removed. This procedure also prevents contaminating

the diffusion furnace's drive-in tube with impurities which could make subsequent diffusions

unpredictable.

(a) The wafers should be immersed for 30 seconds in the DI H20 : HF (10:1)

bath, rinsed with DI water (10 Mf_.cm standard), and blown dry with N2. A control wafer's

sheet resistance should be measured using a four-point probe instrument.

(4) Drive-in:

(a) The wafers should be transported to the diffusion furnace in a covered container. The drive-in boat should be loaded with the wafers; a furnace setting of 1100°C and an

02 gas flow of one lpm should be verified. In addition, the steam bubbler should be verified to

be operating with a setting of at least 95°C.

(b) The boat should be slowly pushed (1 inch per minute) into the furnace's

drive-in tube. After 30 minutes in dry oxygen, the steam atmosphere should be switched into

the furnace for 30 minutes, and then the nitrogen atmosphere should be switched into the furnace for 60 minutes to anneal the silicon/silicon dioxide interface and complete the diffusion

process. Then, the boat should be slowly withdrawn (1 inch per minute).

(c) After the wafers cool, the student should store them in the post-bake oven.

(5) Evaluation:

Using a control wafer processed along with the working device wafers, the student

should measure the resulting sheet resistance and junction depth. In addition, the student

should calculate the diffusion profile using conventional Irvin curves 3 and the TSUPREM-4

software.

(a) Using the four-point probe instrument, the student should measure the

sheet resistance, Ps; it can be assumed that the phosphorus concentration at the silicon

wafer's surface is solid solubility limited.

246
(b) After carefully scribing a small piece of silicon from a control wafer, it

should be attached with hot wax to a grinding chuck, and a bevel should be polished approximately 1 mm wide. The beveled sample should be stained with several drops of a HNO 3 :

HF : CH3COOH (3:1:10) solution under strong illumination to delineate the junction. An

optical microscope interferometer should be used to measure the junction's depth.

(c) Using the wafer's initial resistivity (before diffusion), the student should

select the proper curve from Irvin's data, assume a Gaussian diffusion profile, and calculate

No, and plot lOgl0 of N(x) with respect to the junction's depth (x), where N(x) is the spatial

distribution of the dopant's concentration.

(d) Using the TSUPREM-4 software and the process parameters employed,

the student should calculate and plot the spatial distribution of the dopant's concentration. A

representative result is depicted in Figure 7b.

(e) From the processing schedule and the oxide's color, the student should

determine the net silicon dioxide thickness.

(f) Using the TSUPREM-4 software and the process parameters employed,

the student should calculate the results of the oxidation process implemented during the

drive-in process.

4. Gate Oxide Exercise.

In order to realize the MOS capacitors and the gate oxide region in the MOSFETs,

the student employs the level-two Gate Oxide Mask that is depicted in Figure 3. In order to

realize an electrically-functional thin gate oxide (for this exercise, a nominal thickness of 600

o

A), the student must oxidize the wafers to minimize pin-holes. Therefore, the student will

accomplish the thermal oxidation process in a dry oxygen environment. The student is

required to establish the conditions necessary to realize the required gate oxide. Their solution for the process variables becomes part of the "recipe". The required oxidation conditions

can be estimated using the reference material provided to the student in the laboratory handout and verified with the TSUPREM-4 software.

(1) To ensure success with the subsequent exercises in this laboratory experiment, the student is also required to select one or more of the wafers from the group that has

been successfully processed with the diffusion's "drive-in" step. However, because of the

critical nature of this particular process, the student should not initially implement the Gate

Oxide Exercise with the wafers that have just been selected. Rather, the student should only

process these selected wafers after the gate oxidation process has been practiced and experimentally verified. If time permits, the effect of a variable gate oxide thickness can be investigated using those wafers that were set aside.

247
Dopant Concentration hollowing Drive-in 

2 phosphorus 

Results of The Gate Oxidation 
Smal l -Gate MOSFET 

t 

-20.00 20 .OO 

Distance l'n~cronsl 
(2) Using negative photoresist, the student should implement the photolithographic steps utilized earlier (Photolithography Exercise).

(3) The student should properly clean the wafers before using the oxidation/drive-in furnace. Two hours in a dry oxygen atmosphere with a furnace setting of 900°C

and gas flow of one lpm should be sufficient.

(4) As before, the student should verify the thickness of the resulting gate

oxide. A control wafer is useful for this measurement.

(5) Using an ellipsometer, the student should measure the final oxide thickness of the field oxide on one of the wafers.

5. Metallization Exercise.

Thermal evaporation and sputtering are two simple processes employed to coat substrates with thin films (especially nonrefractory metals). Patterning the metallization can be

accomplished using a metal-etch process or a metal lift-off process. In this exercise, the student thermally evaporates aluminum (A1) onto those wafers which have been processed with

a patterned positive photoresist, followed by a "recipe" to implement a metal lift-off process.

The student is also encouraged to explore the option of a direct metal-etch process. The

industrious student will realize that this simple alternative procedure, which utilizes the

same photomask that was used for the lift-off process, can be accomplished using negative

photoresist applied to an A1 coated wafer to pattern the metal film. A simple A1etch solution

comprised of phosphoric acid is commonly used for this purpose. This alternative metallization process affords the student the opportunity to exercise engineering decisions and to

explore alternatives within a structured environment.

Whichever process the student implements, the objectives of the metallization exercise are twofold: 1) the locations of the metal-semiconductor contacts are photolithographically defined and etched, and 2) _imetal film is deposited and defined using either a lift-off or a

conventional wet chemical etch process.

To implement the metallization exercise, the student is provided the following process

description:

(1) Bake the wafers at 200°C for 45 minutes to remove surface moisture after they

have been cleaned.

(2) Using the level-three Contact Mask that is depicted in Figure 4, etch windows in

the wafer's surface oxide so that ohmic metal contacts and vias can be t'ealized. The photolithography steps (Photolithography Exercise, steps 1-8 inclusive) are repeated using negative photoresist.

250
(3) Etch the wafer's oxide that has been exposed through the open photoresist windows using a buffered HF (NH4F : HF, 4il) solution. Verify that all the windows are clear of

oxide before proceeding.

(4) After etching, remove the photoresist in the plasma asher; verify that all traces of

the photoresist have been removed before proceeding.

(5) Clean the wafers by immersing them in acetone, rinse them in a methyl alcohol

ultrasonic bath, rinse with DI water, and blow dry with N2. Before continuing, bake the

wafers at 200°C for 45 minutes to remove surface moisture.

(6) A positive photoresist and the lift-off technique can also be used to pattern the

aluminum metallization. To optimize the yield of the positive photoresist process, an adhesion promoter, hexamethyl disilazane (HMDS), should be spin-coated onto the wafers at

4000 rp_n for 30 seconds to realize a homogeneous thin film. Next, the S135OJ positive photoresist, manufactured by Shipley, Inc., is liberally applied to the wafer and spun at 5000 rpm

for 30 seconds.

(7) Then, the wafers are placed in a pre-bake oven at 70°C for 20 minutes.

(8) The level-four Metallization Mask that is depicted in Figure 5 is printed.

Exposure to a UV light source for a duration of 30 to 70 seconds should be adequate (The

student will need to establish the optimum exposure duration experimentally, similar to the

process practiced in the initial Photolithography Exercise). The exposed wafers are

immersed in a bath of chlorobenzene for 2 minutes and then soft baked at 90°C for 15 minutes

to prepare them for development.

(9) Develop the exposed wafers with the Shipley Microposit 351 developer (DI H20:

developer solution, 3:1). Development times on the order of 45 seconds to one minute are

typical. After development, rinse the wafer with DI water and blow-dry with nitrogen.

Examine the wafers under an optical microscope to verify the quality of the procedure.

(10) Post-bake the printed wafers at 90°C for 15 minutes to harden the remaining photoresist.

(11) Before metallizing the wafers, etch them in a DI H20 : HF (10:1) solution to

remove any remaining oxide within the previously patterned metal-semiconductor contact

regions. A 3 to 5 second etch should be sufficient. Follow with a brief rinse in DI water and

blow dry with N2.

(12) Mount the photoresist coated wafers in the vacuum deposition system.

(13) Evacuate the chamber (typically, 10-6 ton" pressure) and deposit the A1 film.

Use the piezoelectric quartz crystal thickness monitor to determine the A1 film's thickness.

(A thickness of at least 7000 ,_ is required for subsequent wire bonding and probing).

(14) Vent the chamber and remove the wafers.

251
(15) Using an acetone filled ultrasonic bath, the lift-off procedure is completed when

the undesired metal and photoresist float away from the wafer. The process can be assisted

by periodically removing the wafer from the bath, and blowing high pressure N2 across the

wafer' s surface.

(16) Finally, sinter the A1metallization at 450°C for 30 minutes in a nitrogen atmosphere to realize ohmic quality contacts.

6. Final Testing and Analysis.

Upon completion of the Metallization Exercise, the student can begin probing the

semiconductor devices. The variety of fabricated devices permits the student to accomplish a

wide range of electrical characterizations. The particular electrical tests can be tailored to the

previous theoretical courses that the student has completed. The student conducts the electrical tests by probing the diffused resistor test structures, MOS capacitors, a pn-junction

diode and several MOSFETs. Having recorded the characteristics of the devices, the student

comments on the results. To assist with the analysis, the student may utilize TSUPREM-4,

PISCES-2B (Technology Modeling Associates, Inc., Palo Alto, CA), and HSPICE H9007

(Meta-Software, Inc., Campbell, CA), as well other theoretical techniques from prerequisite

knowledge.

The student initiates the electrical characterization phase by examining the transfer

length method (TLM) test structure. This structure, which is depicted in Figure 9, is examined first to establish the quality of the ohmic contacts, and then to determine the actual contact resistance. If the TLM exhibits a nonlinear current versus voltage characteristic, the

student should sinter the wafer for an additional 15 minutes at 500°C (not to exceed the Al/Si

eutectic point) and then re-examine the contact quality.

Contact resistance (Rc) can be estimated by fitting a linear least-squares line to the

measured resistance values with respect to the contact spacing 6, as depicted in Figure 9. As

depicted in Figure 9, the measured resistance between pads 4 and 5 can be approximated as

the sum of the Rc associated with pad 4, the length-dependent resistance (proportional to the

spacing d45 ), and the Rc associated with pad 5. That is, in general:

R = 2Rc + (Rsh)"d ( 1)

where R is the measured resistance, Rc is the contact resistance, Rsh is the sheet resistance

normalized to the effective width of the contact, and d is the spacing between contacts. The

function described in (1) is a simple linear function of the dependent variable R and the inde252
T €--20

125 J l

_:3, 4o-71 ,2,

r_° J !

l "-_± 75

475

100 " "t 125

125 _ 1®- _ 12s--4,-

1 ,

Figure 9. a) Transfer Length Method (TLM) contact resistance test structure (dimensions in

microns).

Figure 9. b) Photograph of a fabricated TLM contact resistance test structure.

253
,_, 50- _

_ 30 8 + 0.298 x R2= 0.993

20 , , , , ,

0 20 40 60 80 100

Spacing Be tween Contacts (microns)

Figure 9. d) Sample of the measured results for the TLM contact resistance test structure.

254
pendent variable d. Hence, the R-axis intercept is equal to 2Rc. The measurements can be 

accomplished by sequentially connecting a semiconductor parameter analyzer (model HP 

4145 B, Hewlett Packard, Palo Alto, CA) between each pair of the pads (1-2, 2-3, 3-4, and 4- 

5 as depicted in Figure 9c) in the TLM structure. As depicted in Figure 9d, the contact resistance (Rc) is 12.9 Q. 

The specific contact resistance (pc) can be approximated using the relation: 

where LT is the transfer length of the electrical contact, and W is the width of the contact. LT 

can be determined from the linear least-squares line described in (1) as one-half of the horizontal d-axis intercept. That is, L/r is the distance over which the electrical potential arising 

from the current flowing from the semiconductor to the metal has been attenuated to Me of its 

maximum value. For the data illustrated in Figure 9d, the calculated specific contact resistance is 4 x lo^ Q-cm2. 

The student accomplishes sheet resistance and line-width measurements using the 

cross-bridge sheet resistance test structure7. This structure is illustrated in Figure 10. The 

sheet resistance (ps) can be measured by applying a current of In between pads Il and 12, 

and then measuring the voltage potential V12 which is produced between pads Vl and V2. 

This measurement can be accomplished using a semiconductor parameter analyzer as the current source and the voltage detector. The sheet resistance can be calculated as: 

Using the cross-bridge sheet resistance test structure, ps has been calculated to be 23.5 

Qlsquare. 

Having determined the sheet resistance, the line-width W can be determined with 

additional electrical measurements using the semiconductor parameter analyzer, as depicted 

in Figure 10. By applying a current of In between pads Il and 13, and measuring the induced 

potential of v23 between pads V2 and V3, the line width W is simply 
Figure 10. a) Cross-bridge sheet resistance and line-width control test structure (dimensions in

microns).

_L!III =

Figure 10. b) Photograph of the cross region of a fabricated cross-bridge test structure.

256
Figure 10. c) Test configuration using the cross-bridge test structure. 
where L is the center-to-center spacing between pads V 2 and V 3. Since L is physically very

large, errors associated with its estimate are relatively small. Thus, by using electrical measurements, the width W can be measured relatively accurately. For example, a width of 25.7

microns has been calculated from the experimental data which employed a mask whose feature width was 25 microns.

A variety of measurements can be accomplished by the student using the pn-junction

diode s (which is depicted in Figure 11), MOS capacitors 9 (which are illustrated in Figures 12

and 13), and the MOSFETs 1° (which are depicted in Figures 14 and 15). For example, in the

case of the pn-junction diode, the student may measure the reverse-bias depletion capacitance with respect to the applied voltage. This measurement can be accomplished with a

low-frequency impedance analyzer (model HP 4192 A, Hewlett Packard, Palo Alto, CA).

Using the impedance analyzer, a variable dc voltage bias can be applied while simultaneously

biasing the junction with a 1 MHz, 50 mV (peak amplitude) ac signal. Also, the student can

measure the current-voltage (I-V) characteristics of the diode with a semiconductor parameter analyzer. For the MOS capacitors, the student may characterize the silicon dioxide

dielectric properties using a low-frequency impedance analyzer. Finally, the student can

implement a nearly endless ensemble of electrical tests devoted to the MOSFETs l_ with a

semiconductor parameter analyzer and low-frequency impedance analyzer, as depicted in

Figure 15c. For example, the gate capacitance of the MOSFET can be estimated with the

impedance analyzer by probing the device with a series connection from the gate electrode to

the shunted combination of the source, drain, and substrate electrodes.

SAMPLE DATA SHEETS: Self-Evident.

INSTRUCTOR NOTES: The laboratory experiment is readily partitioned into four

distinct exercises, that consist of oxidation, photolithography, diffusion, and metallization.

Therefore, the laboratory experiment, or portions thereof, can readily be incolporated concurrently with a silicon IC fabrication theory course. In addition, the series of distinct exercises

can each begin with a pre-processed wafer supplied by the instructor: thus, the cumulative

effect of student errors can be avoided.

The experiment affords the student an opportunity to experiment and explore within a

structured environment. Therefore, the student should be encouraged to experiment with

alternative solutions to the challenges presented in the laboratory. Upon completion of the

laboratory experiment, the student should be able to assess the compatibility of their laboratory skills with the requirements associated with an experimentally-based senior project or

graduate thesis topic.

258
Figure 11. a) PN-junction diode structure (dimensions in microns).

Figure 11. b) Photograph of a fabricated pn-junction diode structure.

259
............... +""_'"_" ........... i

t...... i

............... .+..._.:._ ............

Figure 11. c) Test configuration for the pn-junction diode structure.

30"

x:3

I.-t

[] 8 []

20 []

•_ []

r,.

°

) 15 I" , ' ' ''' ' ' ' " ' ' ' ' ' '

-10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 1

Applied Voltage (volts)

Figure 11. d) Sample of the measured results for the reverse-bias capacitance.

260
r_ 100

60 []

_ []

_ u

_ 40 []

20 []

[]

[]

,_ 0 [] " [] [] []"_

O

-2o -. , , . , • , • , , ....

-10 -8 -6 -4 -2 0 2 4 6 8 10

Applied Voltage (volts)

Figure 11. e) Sample of the current-voltage characteristics for a pn-junction diode structure.

300 f--50 = 25

25"-_

2s--_

400 165 140

= 250 -

110

210

tO0

= 200 =

Figure i2. "Large" MOS capacitor structure (dimensions in microns).

261
I._----ls0

175

Figure 13. a) "Small" MOS capacitor structure (dimensions in microns).

Figure 13. b) Photograph of a fabricated "Small" MOS capacitor structure.

262
.............. +t Mos

i............................ 7...._ c_p,_.o,

Figure 13. c) Test configuration for the MOS capacitor structure.

"-" 20

m

16 [] [] [] [] [] [] []

0 14

.,_ [] Large MOS Capacitor

g:_ 12

10 o "SmaU" MO S Capacitor

8

0 0 0 0 0 0 0

"" 6

"c;

4

0 0 ' " ' ' '

-40 -20 0 20 40

Applied Voltage (volts)

Figure 13. d) Sample of the capacitance measurements for "Large" and "Small" MOS capacitor

structures.

263
370 r

175 20

175 115 19S

__[- =

T _ 22.5_ 75 1

Figure 14. "Large-Gate" Metal-Oxide-Semiconductor Field-Effect Transistor

(MOSFET) structure (dimensions in microns).

I" 345 -"

l T

-. i

 _c-Jll

i •, 27S ,1q 212

Figure 15. a) "Small-Gate" Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET)

structure (dimensions in microns).

264
Figure 15. b) Photograph of a fabricated "Small-Gate" MOSFET and a substrate contact.

265
_dm m m mmm m m mmmn m | m m | | | m mmm | | ml,mmm m | m m mm mp m mmmm m m || m m| | mmm mmu| mmmm| m m mmlm

• =_ .

m

Drain

GI_--] Substrate :

nmimmmlm mnlllmmm m

Gate Capacitance ." al m i m m m m m m m mmlm u m i_ n m _

Test Configuration Source

Substrate

.

l

; In m m m ii ii m Im iI m m m Ii ii m ii Ii m m Ii u n n m m m m N i m m m l m m l

Source

Current-Voltage

Test Configuration

Figure 15. c) Test configuration for measuring the MOSFET characteristics.

266
Vds (volts)

Figure 15. d) Sample of the measured results for the current-voltage characteristics of a "SmallGate" MOSFET where Vds is the drain-to-source potential and Vgs is the gate-to-source

potential.

"O

•_ 0 FI 0 FI 0 O D D

_-_ 6

S

_ 5

"_ 4

3 O D O D

2

0 -4o -2o o 20 4o

Applied Voltage (volts)

Figure 15. e) Sample of the gate capacitance measurement for a "Small-Gate" MOSFET.

267
In addition, the student should be required to complete a written report that reflects

their laboratory experiences. The written report will reinforce the need to effectively communicate within a technical community. The suggested format of the report is flexible, but should

include the following: 1) summary of the theory underlying the physical or chemical process

being employed, and how it is monitored and controlled, 2) critical parameters associated

with the structure, pattern, or process which facilitates the desired outcome of the fabrication

step, 3) steps implemented in the fabrication process and evaluation scheme, and 4) results,

problems encountered, and related discussion; including experimental data, measurements,

and their analysis.

To ensure the timely completion of the experiment, a suggested milestone schedule is

provided in Table II. This schedule has worked successfully during a ten-week academic quarter. The laboratory time has been scheduled using four-hour periods, and it has

been accomplished by individual students, as well as with teams composed of two or three

students. However, since the prerequisite knowledge was presented during the previous

academic quarter, the student could focus on the practical implementation of fabrication with

the benefit of having already mastered the theoretical concepts.

REFERENCES:

1. Donald Christiansen: New Curricula. IEEE Spectrum, vol. 29, no. 7, July 1992, p. 25.

2. User's Manual: TMA TSUPREM-4 Two-Dimensional Process Analysis Program,

Version 9035. Technology Modeling Associates, Inc., 300 Hamilton Avenue, Third

Floor, Palo Alto, California 94301, September 1990.

3. John C. Irvin: Resistivity of Bulk Silicon and of Diffused Layers in Silicon. Bell

System Tech. J., vol. 41, no. 2, March 1962, pp. 387-410.

4. User's Manual: TMA PISCES-2B Two-Dimensional Process Analysis Program,

Version 9033. Technology Modeling Associates, Inc., 300 Hamilton Avenue, Third

Floor, Palo Alto, California 94301, November 1990.

5. User's Manual: HSPICE, Version H9007. Meta-Software, Inc., 1300 White Oaks

Road, Campbell, California 95008, 1991.

268
6. Dieter Schroder: Semiconductor Material and Device Characterization, John Wiley &

Sons, New York, 1990, pp. 119-121.

7. Dieter Schroder: Semiconductor Material and Device Characterization, John Wiley &

Sons, New York, 1990, pp. 12-14.

8. Dieter Schroder: Semiconductor Material and Device Characterization, John Wiley &

Sons, New York, 1990, pp. 147-151.

9. Simon Sze: Semiconductor Devices Physics and Technology, John Wiley & Sons,

New York, 1985, p. 471.

10. Dieter Schroder: Semiconductor Material and Device Characterization, John Wiley &

Sons, New York, 1990, pp. 169-180.

11. Simon Sze: Semiconductor Devices Physics and Technology, John Wiley & Sons,

New York, 1985, pp. 200-219.

SOURCES OF SUPPLY: All laboratory chemicals required for this experiment are

available from Mallinckrodt, Inc., Science Products Division, Paris, Kentucky. The phosphorus diffusion sources can be obtained from OI-NEG TV Products, Inc., Toledo, Ohio, and the

silicon wafers are available from Ziti, Inc., 14755 Preston Road, Suite 421, Dallas, Texas.

269
Table II. Laboratory Milestone Schedule

Week Activity

1 Lab staff demonstrates the bulk oxidation of silicon

wafers. Laboratory and safety orientation.

2 Photolithography:

Negative photoresist: apply, pre-bake, expose,

develop, rinse, and post-bake.

3 Diffusion:

Etch diffusion mask, remove photoresist, clean, and predeposition.

4 Strip pre-deposition, clean and drive. Four-point probe.

Bevel and stain.

5 Photolithography:

Negative photoresist, etch gate oxide region.

6 Oxidation:

Grow the gate oxide. Four-point probe. Bevel and

stain.

7 Photolithography:

Negative photoresist, pattern contacts, etch, and clean.

8 Metallization:

Positive photoresist. Deposit metal, lift-off, and sinter.

9 Test:

Probe wafer and test functional devices.

10 Complete laboratory report.

270
Participants

271
272
A 69 CENT LOOK AT THERMOPLASTIC SOFTENING

Linda S. Vanasupa

Materials Engineering Department

California Polytechnic State University

San Luis Obispo, California 93407

Telephone 805-756-1537

273

A 69 CENT LOOK AT THERMOPLASTIC SOFTENING

Linda S. Vanasupa

Materials Engineering Department

California Polytechnic State University

San Luis Obispo, California 93407

KEY WORDS: thermoplastic, glass transition temperature, brittle,

ductile, polyethylene, stiffness, van der Waals bonding, covalent bonding

PREREQUISITE KNOWLEDGE: The student should be familiar with

the microstructure of a thermoplastic. He or she should know that

thermoplastics consist of long polymeric chains (molecules) which are held to

one another by physical bonds. The student should also understand the

concept of heat energy.

OBJECTIVES: To demonstrate the change in mechanical properties of a

thermoplastic polymer when the polymer is heated above the glass transition

temperature.

EQUIPMENT AND SUPPLIES: (1) transparent toothbrush (colored or clear)

(2) hot plate (3) 250 ml pyrex beaker or Erlenmeyer flask (4) washcloth or rag

PROCEDURE: The instructor or student can perform this demonstration.

In preparation for the demonstration, fill the flask or beaker 3/4 full with

water and bring the water to a boil.

First observe the initial stiffness of the toothbrush by slightly flexing it. Note

that it is fairly stiff and retains its initial shape when the forces are removed.

If you were to apply enough force, the toothbrush would break in a somewhat

brittle fashion. Now place the toothbrush in the boiling water for 2 minutes.

After the 2 minutes are up, remove the toothbrush from the boiling water

with the washcloth. At this time you will be able to bend the toothbrush

easily. When it cools it will retain this bent shape. You've just demonstrated

heating the polymer above the glass transition temperature, demonstrating

thermoplastic softening.

INSTRUCTORS NOTES:

The mechanical properties of thermoplastics...

Thermoplastic polymers consist of long chains of a repeating chemical unit

called a mer. 1 Figure 1 below illustrates polyethylene, the polymer made

from the repeating mer, ethylene. The central element of the mer is usually

carbon. The carbon-based units are bonded to one another through strong

275
covalent bonds. These long chains, the polymer molecules, are bonded to one

another by weak physical bonds, such as van der Waals bonds.

H H H H H H H H H H

i I I l l ( I | _

-C-C-C-C-C-C-C .....C C=C

! I { I I I I i _ I

H H H H H H H H H H

polyethylene ethylene

Figure 1. Schematic illustration of polyethylene.

The stiffness of the molecule is due, in the case of polyethylene, to a

combination of the covalent bonding along the backbone of the polymers and

the van der Waals bonding. The long molecules are essentially tangled with

one another. The force that you apply is not large enough to overcome the

"friction" of the molecules against one another. A typical transparent

toothbrush is made of a.polymer similar to polyethylene. Figure 2 shows the

infrared spectrum for your everyday toothbrush.

1.000

0.00.

25OO

_oo.o WAVENUHBERS 600.0

Figure 2. The infrared spectrum for a transparent toothbrush.

(Toothbrush spectrum is the thicker, jagged curve. The other curve is

the reference spectrum for poly(vinyl propionate: acrylate).

276
A note about infrared spectroscopy...

Infrared spectroscopy is a technique that can be used to identify polymers. In

this technique, a beam of infrared light of varying wavelengths is passed

through the sample. The beam emerging from the sample is analyzed to see

which wavelengths passed through and which were absorbed by the sample.

The results are then plotted, showing the relative beam intensity of the

emerging beam for each wavelength of light that was incident on the

specimen. An alternate way of plotting the information is by showing the

absorbance as it varies with wavenumber ("wavenumber" is 1/wavelength)

as shown in Figure 2.

It turns out that the wavenumber range of infrared light is the same energy

range within which covalent bonds vibrate. The wavenumbers that are

absorbed correspond to a particular covalent bond, for example, the C-H bond

has a particular wavenumber which is different from that of the C=O bond.

The wavenumber depends on the strength of the bond and the mass of the

atoms involved in the bond. So, the infrared spectrum serves as a

"fingerprint" for polymers, giving us an indication of the covalent bonds that

exist.

Back to the toothbrush...

If you apply a large enough force to the toothbrush, it will fracture, rather

than deform. By putting the toothbrush in boiling water, you are supplying

enough energy from the water to allow the molecules to slide past one

another when the same force is applied.

The glass transition temperature,Tg, in the polymer is the temperature below

which the polymer is rigid, a "frozen liquid." Above Tg, the polymer is first

rubbery and then becomes a viscous liquid as it nears the melting

temperature. (A more complete explanation can be found in any

introductory materials engineering text2., 3 ) This demonstration shows the

change in mechanical properties for a polymer when it is heated above Tg.

ACKNOWLEDGEMENTS: Partial support for this work was provided by

the National Science Foundation's Instrumentation and Laboratory

Improvement Program through Grant #USE-9152078.

REFERENCES

1Callister, W.D. Jr., Materials Scienceand Engineering:An Introduction,2nd Ed. , John Wiley

andSons, 1991.

2Shackelford, J.F.,Introduction to MaterialsScienceFor Engineers,3rd Ed. , Macmillan

PublishingCo, 1992.

3Smith, W.F., Principles of Materials Science and Engineering, 2nd Ed., McGraw Hill, 1990.

277
Participants

278
__,_i_i_,_ii il_ii ,!_iii iii_iii_ii i_i_!ii_, i_iii_iii_i !i,_ii_i _iii ,_iili_ii_,i!_, il,ii ,ii,_!_i _i i!i _ilii _i!_i ii,_ii!i,iii i!__iii_ i i_! i!i ii _i ii__iiiii_ _'

.............................. _!i!_iiiiii_iiiii_iiii!,iiiiiiiiiii!i_,_!!iiiiiiiii_i!!!!_iiiii

279

SOLVING A PRODUCT SAFETY PROBLEM USING

A RECYCLED HIGH DENSITY POLYETHYLENE

CONTAINER

Ping Liu

and

T. L. Waskom

School of Technology

Eastern Illinois University

101 Klehm Hall

Charleston, Illinois 61920

Telephone 217-581-6267/3226

281

SOLVING A PRODUCT SAFETY PROBLEM USING A RECYCLED HIGH

DENSITY POLYETHYLENE CONTAINER

P. Liu and T. L. Waskom

School of Technology

Eastern Illinois University

Charleston, IL 61920

KEY WORDS: high density polyethylene (HDPE), milk jug, safety

evaluation, stress, safety factor, material strength, permissible stress

PREREQUISITE KNOWLEDGE: The student should understand the

concepts of load, stress, material strength, safety factors and basic engineering design

as well as material testing techniques.

OBJECTIVES: To introduce basic problem-solving techniques fi)r product

safety including problem identification, definition, solution criteria, test process and

design, and data analysis.

EQUIPMENT AND SUPPLIES: (1) recycled one gallon milk jug; (2) utility

knife; (3) tensile test machine.

PROCEDURE: The students are given a recycled milk jug made of high

density polyethylene (HDPE) by blow molding. Their objectives are to design and

perfi_rm proper material test(s) so they can evaluate the product safety if the milk.jug is

used in any of the following working conditions:

(a) Holding a gallon of water;

(b) Holding a gallon of mercury.

It is assumed that the above media do not have any significant chemical effect on the

mechanical behavior of the plastics and no stress corrosion cracking is expected.

The following steps are used to approach the problem:

1. Find the density of the two liquids and calculate the weight of one gaUon of

each liquid;

II. Calculate the expected maximum stress exerted by either water or mercury

on the milk .jug;

There are two ways of calculating the maximum expected stress on the milk .jug.

a. Stress exerted by the weight of liquid:

When the container holding one of the liquids is lifted, the maximum stress

exerted by the liquid weight is the total weight of the liquid divided by the smallest

cross section areas of the container, as in Figure 1.

By water:

Smax. 1 = Wwate r/(A 1 + A2) (1)

By mercury:

Smax. 2 = Wmercury / (A 1 + A2) (2)

283
b. 'l"hin-wall pressure vessel model I11:

When the milk .jug holds the liquid statically (not lilted), the fluid pressure

causes stress on the container according to the thin-wall pressure vessel model as

indicated in Figure 2

Hoop Stress, Shoop = Pmax r/t (3)

where r is radius of the container and t its thickness. Pmax is the maximum hydraulic

pressure of the fluid, governed by

Pmax = pghmax (4)

g = 9.80 m/s2 (gravity constant)

where hma x is the maximum depth and p is the density of water or mercury.

P water = 1.00 X 103 kg/m 3

= 13.6 X 103 kg/m 3 ]2] P mercury

111.Determine necessary test(s) to ensure the product safety; note that the

strength of any material should be greater than the expected stress in relation to the

safety factor.

Alter the analysis of working conditions, it is believed that tension stress is a

potential problem tbr the product safety. Theretbre, it is necessary to determine the

tensile strength of the plastics by pertbrming a tension test.

IV. Design a material test and determine the specimen dimensions according to

ASTM standards;

ASTM standards on plastics testing 131were consulted to set up the tensile test

and to prepare specimens from the milk jug.

The specimen dimensions are shown in Figure 3.

V. Prepare the specimens and pertbrm the designed test(s);

VI. Analyze the test results and compare the material strength with the

permissible stress on the milk jug in relation to the safety factor.

It is recommended that for continuous loading no more than 10% of the material

strength be used for plastic product design criteria 141. That is, the expected stress

should not be higher than 10% of the plastic strength to ensure the product safety.

Vl. Draw a conclusion on product safety.

284
SAMPLE II)ATA SHEETS:

A. Density and weight of 1 gallon of water or mercury:

Th,,edensity of water is 1.00 X l03 kg/m 3 and that of mercury (Hg) is 13.6 X

l03 kg/m-' 121.

1 gal. z 3.79 L _- 3.79 X 10-3 m3

The weight of l gallon water is:

Wwate r _---3.79 X l0 -3 X 1.00 X l03 - 3.79 kg

1 kg -- 9.8N

or Wwate r -- 3.79 X 9.8 - 37.1 N

I kg _ 2.20 lb.

or Wwate r -_ 3.79 X 2.20 -_8.3 lb.

The weight of 1 gallon mercury is:

Wmercury = 3.79 X 10-3 X 13.6 X 103 = 51.54 kg

or Wmercury = 51.54 X 9.8 = 505.1 N

or Wmercury = 51.54 X 2.20 = 113.4 lb.

B. Expected stress on the container:

1. By weight:

The measured results for A I and A2 are:

Wall thickness t = 0.015 in

A 1 = (0.75 in. + 0.875 in.) X 2 X 0.015 in.

-- 0.049 in2

--_3.16 X 10-5 m2

A2 = (0.75 in. + 1 in.) X0.015 in.

----0.053 in 2

----3.42 X 10-5 m2

Maximum stress by water per equation (1)

Smax. 1 = Wwate r/(AI + A2)

= 37.1 /(3.16 X 10-5 + 3.42 X 10-5)

285
=0.56X 106Pa

= 0.56 MP a

Maximum stress by mercury, per equation (2):

Smax. 2 = Wmercury / (A 1 + A2)

-- 505.1 /(3.16 X 10-5 + 3.42 X 10-5 )

= 7.7 X 106 Pa

= 7.7 MPa

2. Pressure vessel model"

The average milk.jug height:

hmax. = 8.5 in. = 0.22 m

The average radius of a milk .jug:

r = 2.5 in. = 0.0635 m

Wall thickness:

t = 0.015 in. = 3.81 X 10-4 m

Maximum pressure of water per equation (4)

Pmax.l =pghmax = 1.0X103X9.8m/s 2X0.22

= 2.16X 103Pa

= 2.16 X 10-3 MPa

Maximum hoop stress by water per equation (3)

Shoop, 1 = Pmax r/t

-- 2.16 X 10-3 X 0.0635/(3.81 X 10-4)

-_ 0.36 MPa

Maximum pressure of mercury per equation (4)

Pmax.2 =pghmax -- 13.6X103X9.8m/s 2X0.22

= 2.93X 104Pa

-- 2.93 X 10-2 MP a

Maximum hoop stress by mercury per equation (3)

286
Shoop,2 = Pmax r/t

--- 2.93 X 10-2 X 0.0635/(3.81 X 10-4)

= 4.88 MP a

3. The maximum expected stresses on the milk.jug are the larger values on the

above two situations, thus;

By water:

Maximum Stress, Swater = 0.56 MP a

By mercury"

Maximum Stress, Smercury- 7.7 MP a

C. Average tensile strength of a high density polyethylene (HDPE) specimen cut

from the milk jug is 2200 psi, i.e.

Material strength, SHDPE = 2200 psi = 15.2 MP a

D. Comparison of material strength with maximum expected stress on the milk

jug in relation to the safety factor (10). The permissible stress 151Spof high density

.polyethylene is the material strength divided by the safety factor or multiplied by 10% 141

m this case:

Sp ----10% SHDPE -- 10% X 15.2 -- 1.52 MP a

Swa_r =0.56MP a < Sp= 1.52MP a < Smercu_ =7.7MP a

All the necessa_ dma and calculated results used _)r the sa_ evaluation am

lis_d in Table !.

Table I. Data for Safety Evaluation of a Milk Jug

Water Mercury

Density, kg/m 3 1.0 X 103 13.6 X 103

Weight per gallon, 37.1 505.1

N (8.3 lb.) (113.4 lb.)

Expected maximum 0.56 7.7

stress, MP a (81.2 psi) (1116.8 psi)

Material strength 15.2 15.2

(S), MP a (2200 psi) (2200 psi)

Permissible stress 1.52 1.52

(Sp), MP a (220.5 psi) (220.5 psi)

287
E. Conclusion:

Since the permissible stress of the high density polyethylene (HDPE) is higher

than the expected stress by water but lower than that by mercury, it is concluded that

the milk jug is sate to hold 1 gallon of water but unsafe to hold 1 gallon of mercury.

INSTRUCTOR NOTES: (1) The experiment gives students comprehensive

practice in materials testing theory and methods as well as the application of material

testing to product design and evaluation. (2) The engineering design approach needs to be

introduced in the beginning of the materials testing course. (3) There are different methods

of solving product safety problems and students should be encouraged to seek various

ways to tackle the problem. For example, some students approached the problem by

pressure-testing the container and comparing the results with the expected pressure on

the container exerted by different liquids. Be aware that pressure tests should be

performed in an approved safety chamber. (4) For those students not having enough

background in mechanics, the instructor should encourage them to estimate the stress

based on common sense and a basic definition of stress.

REFERENCES:

1. Gere, J. M.; and Timoshenko, S. P.: Mechanics of Materials, third ed.,

PWS-KENT Publishing, Boston, 1990, pp 411 - 413.

2. Serway, R. A.: Physics l'br Scientists and Engineers, second ed., Saunders

College Publishing, Philadelphia, 1986, pp 316.

3. Standard Test Method for Tensile Properties of Plastics (Metric), Annual

Book of ASTM Standards, ASTM, Philadelphia, vol. 08.01, 1989, pp 168 - 176.

4. Wendle, B. C.: What Eve_. Engineer ShouM Know About Developing

Plastics Products, Marcel Dekker, inc. New York, 1991, pp 26 -27.

5. Shigley, J. E.; and Mitchell, L. D.: Mechanical Engineering Design, fourth

ed., McGraw-Hill Book Co. New York, 1983, pp 226.

SOURCE OF SUPPLY: The milk .jugs were recycled by faculty at no cost.

This type of recycling reduces the amount of solid waste going to landfills.

ACKNOWLEDGMENT: The idea fi_r this experiment originated from the

authors' research project on mechanical properties of recycled high density

polyethylene. Financial support from the Council for Faculty Resi_arch and Office of

Research and Grants at Eastern Illinois University is greatly appreciated.

288
AI

A2

/

J

Figure 1. Schematic of milk jug subjected to weight loading when it is lifted by the

handle. A 1 and A 2, are the two smallest cross section areas.

S long.

Sh°@ _ -

Slong.

pit

S hoop - t

pr

S long. 2t

p =intemal pressure

r = radius of the container

t = wall thickness

Figure 2. Stresses on thin-wall pressure vessel, caused by internal pressure.

289
m m

SIJ _33mm_l-'_ _,

l I_" 80 mm fl [ [

.( ,,_I-I

115mm .._

Thickness - 0.381 mm

Figure 3. Dimensions of the tensile test specimen for high density polyethylene.

290
Participants

291
292
TRIBOLOGY: FRICTION, LUBRICATION,

AND WEAR TECHNOLOGY

Peter J. Blau

Metals and Ceramics Division

Martin Marietta Energy Systems, Inc.

Oak Ridge National Laboratory

P. O. Box 2008

Oak Ridge, Tennessee 37831-6063

Telephone 615-574-5377

293

FRICTION, LUBRICATION, AND WEAR |

J

TECHNOLOGY

Peter J. Blau

Metals and Ceramics Division

Oak Ridge National Laboratory

Preparedfor the

National Educators' Workshop

Oak Ridge, Tennessee

November 11-13, 1992

<<< Lecture Outline >>>

1.0 Introduction and Definitions of Terms

2.0 Friction Concepts

2.1 Fundamental Causes

2.2 Test Methods and Standards

3.0 Lubrication Technology Concepts

3.1 Types of Lubricants

3.2 Regimes of Lubrication

4.0 Wear Technology:Concepts

4.1 Classification of Wear Modes

4.2 Measurement and Control of Wear Behavior

5.0 Tribologicai Transitions

6.0 Summary

295
<<< 1.0 Introduction and Definitions >>>

|

Friction, lubrication, and wear problems are extremely common in

everyday life.

Many other technologies depend strongly on solving friction,

lubrication, and/or wear problems. (e.g., transportation, utilities,

computers, material processing, construction, and many others)

Despite the importance of friction, lubrication, and wear, the education of

engineers on the classical aspects of these subjects is rarely attempted

in U.S. colleges and universities. (Problem-driven, on-the-job training

and short courses are the main sources of such information.)

Friction, lubrication, and wear, and their principles and applications, are

all part of a multi-disciplinary field which we will call "tribology."

<<< 2.0 Friction Concepts >>>

Most students' exposure to friction problems is from physics or

mechanics courses which stress problems like sliding boxes up inclines,

looping ropes around pulleys, and deciding when a ladder will slip down

a wall.

Mechanics-type approaches generally do not address the root causes for

friction since they begin with an assumed value(s) for the friction

coefficient(s). Little or no attention is given to the proper use of

friction coefficients or to understanding of the origins of friction on real

surfaces. (These are "beyond the usual scope of the course.")

Knowing how friction behaves in a wide range of circumstances will

avoid costly errors in design and help analyze machinery problems.

Friction is not exclusively a property of the two contacting materials!

296
l /

CONTRIBUTIONS TO THE TOTAL FRICTION LOSS

IN ENGINES VARY WITH ENGINE RPM

I

.°x. SYSTEMS

(be,s, etc)Lu.., I:52000 -q)mI

CONNECTING ROD

SYSTEM

CRANKSHAFT

SYSTEM

VALVE

TRAIN

PISTON

SYSTEM

0 10 20 30 40 50 60

ENGINE FRICTION LOSS (% OF TOTAL)

Reference: M. Hoshi, Tribotogy International (1984), Vol. 17(4), p. 185

Data: Subant 4 cyl, OHV engine, SAE 10W-30 oil, 80o C, motored

Classical DeFinitions of the Friction Coefficient

and Some Misunderstandings About Them

F FV

Us = [Jk "-

N N

Static (impending motion) Kinetic (while moving)

THE ABOVE DEFINITIONS ARE NOT UNIVERSAL LAWS OF

SOLID FRICTION

FRmCTION IS NOT INDEPENDENT OF VELOCITY, NORMAL

FORCE, TEMPERATURE, ETC., AS THE EQUATIONS MIGHT

OTHERWISE IMPLY

THE STATIC FRICTION IS NOT ALWAYS GREATER THAN THE

KINETIC FRICTION

FRICTION IS NOT EXCLUSIVELY A "MATERIALS PROPERTY"

FRICTION IS FAIRLY EASY TO MEASURE, BUT NOT EASY TO

PREDICT FROM BASIC PRINCIPLES.

297
BLOCK-on-RING SLIDING FRICTION

(Tests in Ar Gas at 5.0 cm/s)

70 .... I .... j .... I ....

• OFHC Cu

O 60 [] Cu-3.2 AI •

• Cu-7.5 AI /

/t

"o 50 [] Ni /

/

LU • Cu-5 Ni / • •

O) • Cu-20 Ni .-

_: 40

rn_ []

W

n- 30 * [] []re

I-- j[]

LIJ n- 20 _eee"

IX. O /

uJ 10 j_, I--

0 50 100 150 200

FRICTION FORCE (N)

FRICTION EXPERIMENTS HAVE BEEN

CONDUCTED FOR OVER 500 YEARS

Leonard da Vinci, applied mechanics studies (1493-1497)

_7 AdaptedfromD.Dowson,The History of Tribologyi1977)

DOE, OTM, TRIBOLOGY- BY- DESIGN

298
TIME (s)

O tO 20 30

4.5 I I I I

.n_9- _4.00-- _

"_ 0.5O- ba_!!i --

O tO 20 30

REVOLUTIONS

Pin-on-Disk Tests of Two Ceramics Show That

"A Sliding on B" _ "B Sliding on A"

0.4 1

0.4 . N

0,3 0.3 I

o o.2 o.2

U'_ 0.| ALUMINA SPHERE 0.1 [ ALUMINA DISK SILICON CARBIDE DISK

0.0 I 0.0 I

0,0 40. 80. 0.0 40. 80.

TIME (s) 11ME (s)

299
A SURVEY OF FRICTION COEFFICIENT COMPILATIONS 1

Ref. Source(s) Descriptionof Numberof COF Values

# of Data Test Conditions Static Kinetic

1 Rankin (1858) not given 14 19

2 Rankin (1858) not given 31 31

3 not given partial (incomplete) 233 34

4 23 references not given in table

"dry" 29 34

"greasy" 26 44

5 Marks (sametable asin Ref.4, above)

6 2 references not given 16 0

References:

1) Mininf, Engineers ltandbnok, 3rd Ed., Vol. 11 John Wiley (1952) p. 36-42

2) Handbook of Chemistrv and Physics, 351h Ed., CRC Press (1953) p. 1972

3) 11andbook nfChemlslry lind Phvsi_, 51st Ed., CRC Press (1971) p. F-15

4) Marks Slandard Ilandbook for Mechanical En_ineer_, 9lh Ed., McGraw llill

(1987), p. 3-26.

5) Handbook of Lubrleafig[h VoL II, Ed. Booscr, CRC Press (1984), p. 46.

6) SME TOOl and Manufaclurln? Engineers llandbook. 3rd Ed.0McGraw-Ilill

(1976), p. 41-12.

-- DOE, OTM, TRIBOLOGY- BY- DESIGN

['Evolving Concepts of "Sur.face" Strongly Influenced]

[ the Development of Friction and Wear Model s,, J

A G T a _

_'i._",';. __E

Belidor (i 737) Coulomb (1875) Goodman (1886)

AnneahngTwins Annealed Grains

__ Subgra,ns

__ Sharp

_o _ _ Boundaries

-._._'.'_x "_';" /

Abbott and Firestone (1933) Samuels (1982) Nano-probe instruments (1981)

300
SENSIBLE FRICTION

_I II Ill

---.1

HIERARCHY OF INTERACTION LEVELS

! - INTERFACIAL MEDIA

LUBRICATION THEORIES

TRIBOCHEMICAL FILMS

TRIBOPARTICULATES

I[- BOUNDING SOLIDS

DEFORMATION AND FRACTURE

FATIGUE

MATERIAIJENVIRONMENT INTERACTION

WHITE.LAYERS AND TRANSFER

il! - MACHINE AND ITS ENVIRONS

DYNAMICS OF THE CONTAINMENT

<<< 3.0 Lubrication Technology Concepts >>>

i

Functions of Lubricants

1. Reduce sliding friction

2. Support and distribute the contact load

3. Protect surfaces for excessive wear or seizure

4. Cool sliding surfaces

5. Carry away wear particles (debris)

Types of Lubricants

1. Liquid lubricants

2. Greases

3. Solid lubricants (graphite, teflon, soft metals, chaicogenides)

4. Gases (air bearings)

301
REGIMES OF LUBRICATION: THE STRIBECK CURVE

= viscosity

v = velocity

|.O - z HYDRODYNAMIC P = pressure

o.IJ _

_jv

0.00!

P P

Ref:J.A.Schey,Tribologyin Metalworking(1983)

FILMTHICKNESSRATIO,(_,)= [ h/ ( _12+ <_22) 1/2]

SOME COMMON SOLID LUBRICANTS

PTFE(TeflonTM)

graphite (powderand foil)

molybdenum disulphide

talc

Pb,Sn, Ag

SOME LESS-COMMON SOLID LUBRICANTS

barium fluoride / calcium fluoride

boric acid

tungsten diselenide

tungsten disulphide

titanium oxide

ornl tribology --

302
SOLID LUBRICATION:

Simple models for frictional behavior

It is generally assumed that the frictional behavior of a solid

lubricant is proportional to its shear strength.

F=I:A

F = friction force, t = shear strength of the solid, and

A = area of interfacial contact

But, the shear strength of [Bridgeman] solids can be affected by

the pressure on them, and x is modified as follows:

x=x+ c_e

o

= shear strength at ambient pressure, _ = a constant, and

o P = contact pressure

ornl trlbology -

SOLID LUBRICANT FILM PROPERTIES:

Pressure Dependence of the Shear Strength

"_=%+ o_P

Test conditions: glass hemispherical slider, glass

substrate, 0.24 mm/s sliding speed, 1-300 mN load,

40-150 MPa mean contact pressure q] o , (MPa) (Z

molybdenum disulphide: commercial grade 2.0 0.15

molybdenum disulphide: research grade 2.0 0.17

oleophilic, high-purity graphite 4.0 0.09

high-density polythene 2.5 0.10

low-density polythene 6.0 0.14

[Ref.: B. J. Briscoe and A. C. Smith, ASLE Transactions (1981)]

ornl trlbology -

303
SELF-LUBRICATING COATINGS:

Current Applications and Technology Needs

(1) ceramic engine parts - valve guides, piston ring grooves, etc.

(2) dieselturbocharger bearings- high-temperatures

(3) seals for non-CFC-containing refrigerationsystems

(4) bearing element retainers(spacers between balls and rollers)

(5) cryogenic bearings (Space Shuttleturbopump, etc.)

(6) moving parts in advanced gasturbine engines (seals and bearings)

(7) gimbals and pointing control systemsin orbital guidance systems

(8) dry-lubricated bearingsfor cruise missileengines (elevated temp.)

(9) machinetool spindles (grinders, high-speed drills, honing machines)

(10) moving parts in hard-to-lubricatelocations in industrial machinery

(11) small parts in computer magneticstoragesystems

(12) mechanical parts in office copiers andother business machines

(13) small parts in motorized cameras

(14) aircraft auxilliary power units (APU's)

ornl tribology m

<<< 4.0 Wear Technology Concepts >>>

i

Wear Modes (c.f. wear mechanisms)

There are numerous ways to classify wear. Here is one scheme that

depends on the relative motion and the geometry of contact:

1. Abrasive wear (2- and 3-body)

2. Erosive wear (impinging particles; solid or liquid)

3. Cavitation erosion

4. Impact wear

5. Fretting wear (fretting fatigue; fretting corrosion)

6. Sliding wear ("adhesive wear")

7. Rolling contact wear (rolling contact fatigue; fatigue wear)

[Note: Galling and scuffing are not strictly forms of wear since they do

not always involve progressive loss of material. ]

..................................................................................

304
THERE IS NO UNIVERSAL, "STANDARD"

WEAR TEST

WEAR TESTS ARE DESIGNEDOR SELECTED FOR THE

FOLLOWINGREASONS

(1) TO SIMULATE A SPECIFICSET OF CONDITIONS IN AN

APPLICATION

(2)TO ISOLATEA PARTICULARTYPE OF WEAR PROCESS

(ABRASION,SLIDING,ETC.) FOR RESEARCHPURPOSES

(3) TO SCREEN MATERIALSASTO THEIR RELATIVE WEAR

RESISTANCEUNDERSPECIFIED CONDITIONS.

Tabelle 2. Kategorien der VerschleiF_priJfung bei einem Nutzkraftwa en-Getriebe

Kategorien Art des Versuches Symbol

Betriebs- bzw. _ _,-/x,;

betriebs_hnliche

II Versuche Pr(Jfstandsversuch

,/////////,

Pr_fstBndsversuch mit Aggr egat _'_ _'G _'_1 F_

III oder Baugruppe

v//)////_,v._////.c _1z/],'/////,'//////,

_---- Versuch mit unver:_ndertem

IV Bauteil oder verkleinertem _ ,)_]'-_

Aggregat

Beanspruchungs_hnlicher _

V Versuche mit Versuch mit Probek6rpern

Modellsystem

& eF-- Modellversuch mit einIachen (_VI Probek6rpern

305
FRICTION AND WEAR DEVICES

Second Edition

1976

Revised and Enlarged Reoor%

of

SubconTnitte on Wear

Lubri cati on Fundamental s Co_m,itree

American Society of Lubrication Engineers

Authors

R. Benzing

i. Goldblatt

V. HoDki ns

W. Jami son

K. Mecklenburg

H, l%terson

Printed in the United States of America

American Society of Lubrication Engtneers

838 Busse Highway, Park Ric_ge, III. 6006B

A list of 234 different testing machines

THERE IS NO UNIVERSAL UNIT FOR WEAR

UNITS FOR WEAR DEPEND ON THE REASON FOR TESTING:

(1) DIMENSIONAL CHANGE (increase inclearance in a bearing or

seal)

(2) WEIGHT CHANGE (generation of contaminating debris)

(3) DISTANCE (guarantees on automobile tires)

(4) MANY OTHER UNITS (volume, volume loss per unit time,

weight loss per unit distance slid, relative wear, etc., etc., etc ....

306
[ "10-15% _16-30% _31-50%

_51-75% _76-I00%

Topology of wear of a shoe. Between 76 and 100% of the shoes

examined showed wear of the edge of the heel. (James, D. I. (Ed,)

(1967). "Abrasion of Rubber", Rubber and Plastics Research

Association of Great Britain, London.)

<<< 5.0 Tribological Transitions >>>

ii

Definition

tribological transition, n. - a change in friction or wear behavior

produced by either an external change in the operation of a tribosystem,

or by the aging of materials or components during use.

Some Examples and Manifestations

1. running in a new set of brakes

2. a bearing suddenly begins to smoke and rattle

3. a valve begins to leak after operating satisfactorily for a year

4. your engine starts to burn oil

5. increasing the sliding speed during a test causes friction to drop

Controlling friction or wear transitions can be vitally important to the

effective design and long-term operation of machines of all kinds.

307
To model friction or wear, a comprehensive

definition of the tribosystem is needed.

All relevant variables must be specified.

Load-related variables: direction, magnitude, distribution (pressure),

history, vibration, contact stiffness

Contact geometry-related variables: size of the nominal contact, surface

roughness, macro-geometry (Hertz arguments)

Materials variables: composition, surface micromechanical properties,

processing history

Thermal variables: ambient temperature, frictional heating contribution

Chemical variables: reactivity of the environment, tribo-chemistry

r_ Cleanliness and effects of particles: initial surface cleanliness, wear

debris, contaminating particles

State of lubrication: boundary, dry, mixed, hydrodynamic, intermittent

<<< 6.0 Summary >>>

Friction, lubrication, and wear technology impacts everyday life.

Friction and wear are properties of the system, not just tile contacting

materials.

Friction is not easy to predict, despite deceptively simple definitions Ibr

the friction coefficient given in introductory texts on physics and

mechanics of materials. Measuring friction is usually easy, but

understanding it is not.

Lubrication technology is the key to transportation, manufacturing, utilities,

defense, and many other sectors.

Tile regimes of lubrication can be controlled to alter the effectiveness of

friction reduction.

(continued)

308
(Summary - continued)

Solids, liquids, and gases can all lubricate. Lubricant formulation is

both a science and an art.

There are various ways to classify and measure wear. Methods of wear

measurement should suit the desired application.

Tribological transitions can be affected by intentional changes in

operating parameters or by aging of the tribosystem.

Friction, lubrication, and wear technology should be a part of the

academic training of every undergraduate mechanical engineer, industrial

engineer, and materials engineer because tribology is an enabling

technology.

309
*** BIBLIOGRAPHY ***

Books:

D. Dowson, History of Tribology, Longman Pub. (1979).

ASME Wear Control Handbook, ed. W. O. Winer and M. B. Peterson,

ASME, New York (1980).

Friction, Lubrication, and Wear Technology, ASM Handbook, 10th Ed.,

Vol. 18 (1992).

E. Rabinowicz, Friction and Wear of Materials, John Wiley (1965).

Handbook of Lubrication, Vol. I (Applications and Maintenance) and II

(Theory and Practice of Tribology), ed. R. Booser, CRC Press (1984).

F. P. Bowden and D. Tabor, The Friction and Lubrication of Solids,

Clarendon Press, Oxford (1986).

K. C. Budinski, Surface Engineering for Wear Resistance, Prentice Hall

(1988).

P. J. Blau, Friction and Wear Transitions of Materials, Noyes Pub. (1989).

Journals:

Journal of Tribology, ASME (formerly J. of Lubrication Technology)

Wear, Elsevier Sequoia Pub.

Tribology International, Butterworth-Heineman

Lubrication Engineering, STLE

Tribology Transactions, STLE

310
WALKWAY FRICTION: EXPERIMENT AND ANALYSIS

Mark I. Marpet

Associate Professor of Quantitative Analysis

St. John's University

Staten Island Campus

300 Howard Avenue

Staten Island, New York 10301

Telephone 718-390-4545

and

Robert J. Brungraber

Bucknell University

Lewisburg, Pennsylvania

311

WALKWAY FRICTION: EXPERIMENT AND ANALYSIS

Mark I. Marpet, Ph.D., P.E.

St. John's University, New York City, New York

and

Robert J. Brungraber, Ph.D., P.E.

Bucknell University, Lewisburg, Pennsylvania

KEY WORDS: friction, walkway safety, tdbology, articulated strut.

PREREQUISITE KNOWLEDGE: The student should either be familiar with the classical (Amontons-Coulomb) friction model or, alternatively, this model should be

presented concurrently with the experiment.

OBJECTIVES: To explore the utility and the limitations of the Amontons-Coulomb

friction model. To explore Design of Experiments issues which underlie competent testing.

EQUIPMENT AND SUPPLIES:

(1) Two test devices: a drag sled tester and an articulated strut tester must be

fabricated. If friction versus test foot I velocity is to be tested, obtain a suitable

small, variable-speed gear-motor.

(2) Walkway surrogates (test surfaces). Test surfaces can include steel, wood, vinyl

tile, ceramic tile, and carpet (glued to a substrate).

(3) Foot-bottom surrogates can include various leather and synthetic shoe bottoms

(taken from old shoes), standard leather, neolite, steel, and silicone elastomer.

(4) A calibrated dynamometer (or a pull scale) is used to weigh and pull the drag sled.

(5) Double-sided carpet tape is needed to affix a test surface to the table for the drag

sled tests.

(6) A stopwatch may be used to time the residence time 2 for the drag sled tester.

(7) 400 grit wet/dry sandpaper is needed to prepare the test feet.

(8) An engineering calculator is needed to convert the articulated strut readings to

friction coefficients. Alternatively, a computer program can be written to automate

the conversions; this is an excellent student project.

(9) A commercial statistical analysis program will be needed to perform Multivariate general linear hypothesis 3 tests. We use MyStat. It retails for under $20

(DOS or Macintosh).

(10) A computer to run the software is needed.

1 Frictionis an interfaceproperty.It is normallyconsideredto be a propertyrelatingto two surfacesin

contact,perhapswithlubricantsor contaminantsat theinterface.Walkwayfrictionhas a naturalorientation

whichis notpresentwhenonetalksin generalaboutfriction:the pedestrian'sfootcontactsthewalkway

surface,andnotthe otherwayaround.Walkwayfrictionconcernsincludewhatkindof footsurrogatescan

be usedto test walkwaysurfaces,whattypesof floorsurrogatescanbe used to testshoeor footbottoms,

and whatsuitesof interfaceconditionsare relevanttoreal-lifepedestrianwalking.In orderto avoid

ambiguity,wewillin thispaperdenotethatmaterialthatstandsin forwhateveris on thebottomof the foot

asthe testfoot or thefoot-bottomsurrogate(orjustfoot surrogate)and whateverstandsin forthewalkway

surfaceas thetestsurfaceor walkwaysurrogate.We willdenoteanyinterfacelubricants(e.g.,water)or

contaminantssimplyas contaminants.

2The timebetweenthe applicationof the normalforceand theinitiationofslip

3A techniquewhichcombinesregressionanalysis(curvefitting)andanalysisof variance(multi-family

testsof hypotheses)

313
BACKGROUND: Pedestrian accidents have been shown to be the leading cause of direct and morbidity accident costs in the United States. Thus, the analysis and prevention

of pedestrian slips is a high priority if fall-induced injury costs are to be minimized.

Many of the walkway friction testing methodologies used today are based upon

the 'classical friction model,' that is, upon the Amontons-Coulomb friction axioms: that

friction is independent of pressure, temperature, humidity, velocity, and residence time.

In fact, these assumptions are not, in general, strictly correct. More to the point, these

axioms are unjustified in many walkway situations, especially if the friction interface is

wet or contaminated, as is often the case.

The purpose of this experiment is to discuss design of experiments issues in an

information-gathering experiment, to investigate the variation in friction with respect to

the above parameters, and to explore the envelope of the Amontons-Coulomb friction

model. The tests illustrate how using inappropriate tests will obtain anomalous results (for

example, drag sled tests of wet leather against wet tile often exhibit higher friction results

than do tests of dry leather against the same (dry) tile) and m in contrast m show that if

appropriate methods are employed, one obtains results consistent with common sense.

PROCEDURE:

Introduction: The two friction testers can be fabricated according to the designs

given in this paper. Both testers have been designed to use the same test foot mounting

scheme. If the drag-sled is to be motorized, the dynamometer can be rigidly mounted to

the sled (as low as possible) and the pull wire fastened between the motor pulley and the

dynamometer. The pull wire should be 'axially stiff'. A strain gauge apparatus with appropriate instrumentation may be substituted for the dynamometer. Students may design

their own testers. In the case of the articulated strut tester, this is a non-trivial exercise.

Before the equipment can be utilized for testing, an experimental design must be

developed and the test sensor set must be prepared.

Experimental Design: The test plan, or experimental design, is formulated in advance so as to explicitly consider and effect reasonable compromises in the number of

tests, the amount of information gathered, and the amount of test replication. Replication

helps ensure reliability of results, but only at the price of a substantially increased number

of tests. And the number of tests can mount factorially if too much is attempted. For

example, if one wanted to conduct a complete test suite: the two test devices with steel,

leather, neolite, and silicone test feet against steel, wood, vinyl tile, and carpet test

surfaces at two contact pressures, two velocities, and wet and dry, one would need to

conduct

2machines " 4sensors " 4surfaces " 2pressures " 2velocities "2wet&dry = 256 tests (1)

without any replication. Four replications are often conducted for each set of test conditions. Each replication is conducted in a different compass point orientation, i.e., the test

surface (or the tester) is rotated 90° between each test. That implies that the test design

would require 256 • 4 = 1024 tests! 4

The first element in the test design is to estimate how many tests can reasonably

be run by dividing how long each test will take (time tests conducted on each machine to

get an estimate of the time needed) into a realistic estimate of how many hours can be

4 Now you know why the mathematical symbol for the factorial operation is '!'.

314
devoted to testing. Once that number of tests is determined, the compromises needed to

fit the experiment into the real world should become clear.

The general linear model should be used for the analysis of the significance of

test results. Essentially, one starts with a set of baseline conditions, e.g., articulated strut

tester, neolite test surface, vinyl tile, low contact pressure, low velocity. Each

modification to the baseline is accounted for, first, by a linear categorical constant attached to a dummy variable and, if desired, by compound (non-linear) terms which

quantize the factor interaction effects:

Its = bo+ btxl + b2x2 + " "+ bixi +"" + bnxn + bl2xlx2 +"" + bijxixj +"" (2)

where

Ps = static coefficient of friction

bo = the static friction coefficient under baseline conditions

b i = the marginal friction increase or decrease for condition i

xi = a dummy variable, xi = 0; 1; ifif condition condition isis absent present

bij= the marginal increase in friction when both

conditions i and j are present

Similarly, bijkand higher-order interactions can be defined, bijk,for

example, is the marginal friction factor when i, j, and k are all present. Higherlevel interactions will likely overpower all but the most powerful statistical

analysis programs.

The data should be collected in tabular form.

Machine j_ or 0 I Sensor . Surface I Wet/Dry

Strut 32° Neolite Steel Dry

Strut 75° Neolite Steel Wet

Figure 1. A sampledata collection format.

Test Sensor Preparation: An adequate number (this can be determined by reference to the experimental design) of steel test-foot brackets must be fabricated. Test feet

from old shoe soles can be prepared by cutting a 3-inch square (or smaller, as the

experimental design dictates) from the heel or sole of the shoe, and trimming and sanding

the back of the sole or heel until it is smooth and level. Small heels, as those found on

high-heeled shoes, may be used in pairs (or in groups of three) for stability. Each foot

bottom surrogate is glued to a test-foot bracket.

Before each test, the sensor is prepared for use by sanding it lightly -- four times

in each of two orthogonal directions -- with 400 grit wet-or-dry sandpaper.

The Drag Sled Tester: The drag sled tester is utilized by mounting a test surface to

the table using double-sided carpet tape. A test foot is held to the weight bottom by the

magnetic tape adhered to the bottom of the weight. The drag sled/test-foot assembly is

weighed; the weight, fn, is recorded. The drag sled/test-foot assembly is placed on the test

surface. If residence time is to be monitored, a stopwatch is started when the weight is placed

upon the test surface. An increasing horizontal force is then applied to the sled, either manually or through a motor arrangement. When the sled moves (breaks away), the lateral force,

315
jS, is recorded. If residence time is monitored, the stopwatch is stopped when the sled first

moves. It is essential to keep the pull wire horizontal. The motor or the dynamometer can be

shimmed with wood or another material to ensure this. The static friction coefficient,/_s, is

computed as the ratio of the lateral to the weight force:

h

/4 (3)

The articulated strut tester: It is easy to see that, if the static friction coefficient

is defined as the ratio of the lateral and normal forces, it is equivalently characterized by

the tangent of the angle at which slip occurs:

tail O WS in O f l

-- WCos0 - fn (4)

WCosO f, is, by reference to the diagram on the left, the ratio of

the lateral force to the normal force. That ratio is the

definition of the static friction coefficient.

WfiinO

wi

Figures 2 and 3. Idealized and actual free body diagrams of an articulated strut tester.

The tester described in the sequel has a somewhat more

complex mathematical model because the strut is

cantilevered to the weight/transport assembly, and not

hinged, as in the more complex commercial articulated

strut devices. Noting that, at slip, there is no weight on

the forward wheel, that the reaction at the rear wheel is

perpendicular to the strut axis, and that the line of action

of the strut passes, by construction, through the center of

gravity, we can determine the formula for the static

_ W_ \_,_[.___ friction coefficient by summing moments about the

center of gravity:

__ 4.1,_n _F ---, _ and d2sn_Fn=d2cos_Ft+dlFr (5)

d2sinCFn d l Fr

d2cosOFt - 1 + d2cosOFt (6)

It follows that

]Is1F-n Ft - tan¢l + d2cosOdlFrFt tanO- m-_+ 1 d2cos2 di _an¢- tan¢ 1( 1+ d2c-_s2¢ dl I (7)

( co:, )

a2,c cos+oass)-+

Itis clear that, to minimize the correction factor, dl should be made as small as possible

by moving the back wheels close to the center of gravity of the strut assembly.

316
The articulated strut tester is operated by clamping the test surface onto the

baseboard, setting the angle board at a specific angle: the ramp angle measured from the

vertical, dropping the weight, and seeing if the articulated strut assembly 'breaks away.'

For the tester design described here, breakaway detection is visually obvious.

Figure 4. Side views of the articulated strut tester, depicting how breakaway is detected.

If there is no breakaway, the coefficient of friction is greater than the adjusted

tangent of ¢, the ramp angle. The test foot does not need to be re-sanded. The angle board

is then adjusted with the wing nuts to a larger ramp angle, the weight is raised, and the

strut assembly is again released.

If the articulated strut breaks away, the friction coefficient is less than the adjusted

tangent of ¢, the ramp angle. The test foot is re-sanded, the ramp angle is reduced, and the

test sequence is repeated.

Repeated tests home in upon the breakaway angle. Using the articulated strut

tester, it is customary to record the full sequence of test angles for each test set, circling

those angles which result in sensor breakaway, e.g., in the simulated results below,

25 °, 30 °, 35 °, 40°, 4_, 41°,42°,@

the slip angle lies between 42° and 43°. The tangent of that breakaway angle is the

desired friction coefficient. In this simulated example, 0 = 42°-43 ° corresponds to /zs =

0.46--0.47. (Use the formula above, with d/d2 = .525, for our tester.)

Data Analysis: The use of computerized statistical analysis is essential. (This

example uses MyStat.) The example below is based upon real data obtained in walkway

friction testing. The following factors were accounted for in the experimental design:

• LATFORCE (These results are from drag sled tests; lateral force is more convenient

to work with than the friction coefficient derived directly from it.)

• WETDRY (1 = dry, 2 = wet)

• SENSOR [i.e., the test foot] (1 = neolite, 2 = leather, 3 = rubber)

• TILE [i.e., the test surface] (1 = 'brand A' tile, 2= 'brand X' tile, 3 = 'brand Z' tile)

• DIRECTIO[n] (1 = 'North', 2 = 'East', 3 = 'South', and 4 = 'West')

. 317
The analysis is started by inputting the data into the data editor, which appears to

be a spreadsheet, but is not. (In the example below, only 12 of the 72 cases are shown.)

!LRTFORCE ! I,IETDRV L SENSOR L TILE ]OlRECTIO ".................. i........... _ ................ V.656i.............. V.6"66......... i '"'T"66'6"_ ............... i'".666

:................... ";j'..........! A,_ nnn ."................._-'_'_'_"r .............. _-;_'_'a-r" ............. i""a'_................. 'a ":_'-'_'a;_

........ --... [ .... ..=...'/".r.%" .'f...... i "..;""" I.... ,.v,,v I ..... i .....

...................... i............................ _......................... , ....................... i........................... i...............................

........................................................................................................ 3 i 38. 000 i I. 000 •t........................... I. 000 •I-............................ 1.000, I............................ 3,000

4 i 40. 000 i I. 000 i I. 000 i I. 000 i 4. 000

................... "5.......... " I.................. ";i"i":'60"6"I ................. ]-"6"56"[ .............. ]-.6"6"0"I" ...........'2:6"0"6"! ................. ]'"'60"0

6 I 43. 000 1 I. 000 1 I. 000 1 2. 000 1 2. 000

................. I.............. ............. .............. ........... ............

............... '/..... i I.............. _6"2i5"6"[ ............. V.55"6"_ .............. i-5"66T..........."_".'655"! .............',i'7665

•.................. _.......... !.................. _Z_66i................. T;666I.................. T._66[............. §"."6................... 66i i".66a

............... I.o......._...............43.,o..o.o.. t.............1_oot.............. o LogO............ t. ?.-.9..go.I............ 2-0o0

......................11 I=.................... 392......... oooi=............... _..%"....................... oool _._"........................ oooI 3 " .........

O001,.......................... 3 000

% % I I I

12 ., 43.000 ! I. 000 t 1.000 : 3.000 _ 4 000

Figure 5. h computer screen 'snapshot' of the MyStat (Macintosh) data editor. The

factor namesare first enteredinto the top row. The data are then entered, one

caseat a time, row by row. The numbersin the left-hand column are the 'case'

numbers,andare notenteredby the experimenter.By way of example,test4 had

a lateral force of 40 lbs.,and wasconducteddry, with a neolite sensoron abrand

A tile in the 'West' direction. The triple-digit accuracyis a software artifact;

ignore it.

After all the data were entered into the editor, they were saved, and the regression

tool was selected. In regression, T.ATFORCE was first selected as the independent

variable. The rest of the variables were specified to be categorical; all were utilized as

dependent variables. No interactions were examined. The fact that all the dependent

variables are categorical implies that MyStat will use analysis of variance (ANOVA).

Analysis of Variance

Dependent variable: LATFORCE N: 72

Multiple R: 0.499 Squared Multiple R: 0.249

Source Sum-Squares DF Mean-Souare F-Ratio P-Value

WETDRY 6. 125 1 6. 125 0. 345 0. 559

SENSOR 241. 750 2 120. 875 6. 815 0. 002

TILE 95. 083 2 47. 542 2. 680 0. 076

28.486 3 9.495 0.535 0.660

Error 1117. 431 63 17. 737 i

Figure 6. These results of the ANOVA are slightly rearranged for clarity.The dependent

variable and the number of cases analyzed (72) are presented first. Multiple R is

the overall correlation coefficient. Squared multiple-R is the proportion of

experimental variation explained by the ANOVA. (This ANOVA explained 25%

of the variation, a rather poor stlowing.) The remainder of the results is the

ANOVA table, shown in canonical form.

The first and last columns of the ANOVA table are of interest to the experimenter.

The first column lists the factors (WETDRY, SENSOR, ...)controlled in the experimental

design. The last table column gives, for each line, the P- value of the factor in that line.

The P- value is the probability that one will be wrong if one ascribes significance, i.e.,

causality, to that factor. (The opposite of significance is, of course, non-significance: that

any effects which can be attributed to a given factor are, in fact, due to chance.)

318
For example, if one asserted that WETDRY-- whether the tile floor surface was

wet or dry -- was a significant factor, one would be wrong over half of the time. Clearly,

if you accept these experimental results, any observed effect of water on the tile surface is

due to chance! In other words, no confidence can be placed in the assertion that WETDRY

is a significant factor. (The notion that wet tile surfaces are neither more nor less slippery

than dry tile surfaces should fly in the face of your experience. That's because these tests

were conducted with a drag sled, which is completely unsuitable for testing in the wet because of sensor/test surface adhesion effects: the test foot literally suction-cups itself to

the test surface.)

Similarly, if you asserted that the sensor material was a significant factor in the

lateral force, you would be wrong only 0.2% of the time. Great confidence can be placed

in the hypothesis that the sensor material was a significant determinant of lateral force

and in the corresponding static friction coefficient.

In the United States, it is customary to ascribe significance to P-values at or below 5%, and non-significance to P-values above 5%. In the given example, only the

SENSOR material was a significant determinant of friction. WETDRY, DIRECTIO[N], and

TILE would not be considered statistically significant.

Other Considerations:

Average contact pressure: While average, i.e., bulk contact pressure, can be varied by

changing the weight, it is simpler to vary the size of the sensor. For example, changing from the

standard 3 inch-square sensor to a l_x3 inch sensor cet. par., doubles the average contact

pressure.

Velocity: If velocity is used as a factor in the experimental design, the sled (or the

strut assembly) should be driven by a variable-speed motor. If velocity is not used as a

factor in the experimental design, operators should practice with the equipment, endeavoring to operate the testers at a uniform velocity so as to eliminate velocity as a factor in

the experimental results. Better yet, motorize the instruments.

REFERENCES & BIBLIOGRAPHY:

Hale, Robert L., MYSTAT Statistical Applications, Available in Macintosh and DOS

Editions], Course Technology, Inc., 1990.

Adler & Pierman, A History of Walkway Slip-Resistance Research at the National Bureau of

Standards (NBS Special Publication 565), U. S. Department of Commerce, 1979.

Anderson & Senne, ed., Walkway Surfaces: Measurement of Slip Resistance (ASTM STP

649), American Society for Testing and Materials, 1978.

Brungraber, Robert J., The Measurement of Slip-Resistance and the Setting of Standards,

Educational Workshop on Building Safety, Georgia Inst. of Tech., April, 1992.

Brungraber, Robert J., An Overview of Floor Slip-Resistance Research With Annotated

Bibliography (NBS Technical Note 895), U. S. Department of Commerce, 1976.

Brungraber & Templar, Controlled Slip Resistance in Progressive Architecture, March, 1991.

Ekkebus & Killey, M_asurcment of Safe Walkway Surfaces in Soap/Cosmetics/Chemical

Specialties, February, 1973.

James, D. I., A Broader Look at Pedestrian Friction. in Rubber Reviews: Rubber Chemistry & Technology, 1980.

Marpet, Mark I., Gait Dynamics and Walkway Safety. Educational Workshop on

Building Safety, Georgia Inst. of Tech., April, 1992.

Irvine, Charles, A New Slipmeter for Evaluating W_dkway Slipperiness in Materials Research and Standards, December, 1967.

319
Guide WirePulley

Guide Wire

Figure 7. Articulate_ 5tru_

slot_ Bar Tester (5icle view).

WingNut & Washer

le Board

Arr,lculated Strut Assembly

Protractor- Ensure that the

Wing Nut & Washer protractor center Is aligned with the

Angle Board Hinge Pivot Center

Test Foot Suppor_Struts

Test Foot Assembl Test Surface

Stationary Stop

AngleBoard HingePivot Center

Angle Board Hinge /- MoveableStop Assembly

Baseboard. Placeon horlzontal surface.

Protractor Index Mark. PlaceIndexmark

on Angle Board. Ensure that indexmark

is radial with respect to the hlngepivot and

that It reads correctly.

Weight

Figure 8. Drag-Type

Teeter.

Axially-Stiff PullWire:Keephorizontal

Dynamometer: Pull horizontally

_st Foot Glued to Test Foot Bracket

Steel L-shapedTest Foot Bracket L Block to keepdynamometer horizontal

320
Moveable 5_op Assembly

ThreadedStop Bolt (round headcorners) Sllp fit pln with head

_._uide wire Moveablestop block

1/2" Radius

Articulatecl Strut Assembl

Baseboard

L Holeson 1"centers

Figure 9. Articulated

Strut Tester Detaile.

fit both

pport Struts

Into welght.

nthe holesin the two struts

Weight so the Sensor Support Base does not bind.

\

/-Test Foot Support Pivot Shaft

Sensor Assembly \ /

\

Vari-speed Motor

//_///_t """'""'' "":""'" :" ;" "_;'"v";'";" ;'";'";""'" ;'";;';;":" _;°_;'_;"_;"t

_-Test Foot Gluedto Sensor Bracket

Motor Installation Detail /// L Steel L-shapedTest Foot Bracket

/ L_3" sq.adhesiveMagnetic 'Tape'

/-- Sensor Support base

321
ii i

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Walkway Friction:

Experiment & Analysis

\

IIIIllmF" - [I I I

I'

• Robert Brungraber, Ph.D., P.E.

• Buck,nell University, Lewlsburg, Pennsylvania

• Mark Marpet, Ph.D., P.E.

• Saint John's University, New York City, New Yolk

i

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i

i

WalkwayFriction?

So What?

(Why explore walkway friction?)

• The high $$ losses fromwalkway accidents

• Interesting Real-World deviation from t_e

classical (Amontons-Coulomb)friction model

• Interesting designof experiments issues

i

ii

322
i •

Walkway Friction

¥,

Amontons-Coulomb Friction

•Anomalous results vis _ vis Amontons-Coulomb

• Resilientv. non-resilientsurfaces

• Violationsof the assumptionsof independenceof

frictionwith respect to:

• Contact pressure

• Temperature

• Humidity

• Velocity

• Residence time

Walkway Friction Testing

Instruments

• Drag sled

• Inclined plane

• Pendulum

• Articulated strut

• Inclinedstrut

I

323
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m. u i| i |l i i

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The Design of Experiments:

An exploration of the minefield

between the rock and the hard place

• THE ROCK--A linear increase in the factors requires a

geometric increase in the number of tests

• THE HARD PLACE--If the test design is not complete,

confounding (aliasing) of results can occur

• STEP WITH CAREw

• explicitly consider the goals of the testing

• expliciUy consider the testing 'budget'

• explicitly consider confounding

•A horrorstorl

, , , , ,, ii i

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Hal I "' I I

ii =|, i i

The General Linear Model

(It's not really linear, but it sure is

general)

• ll•,,bo+br_+bz_+...+b _ +...+bx

+ blzxlx2 +... + b_x 1+... + H.O.T.

,,The first line of the equation is linear

• Without replication,the number of experiments in the

full model grows with the product of the factorlevels.

• Replication

• Canned software

• General math engines: MathCAD, Mathematica

• Statistical software: MyStat, MiniTab, SPSS, ...

,, J , i

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324
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Setting up the data for analysis

• Designa formtorecordyourdata iii i

l_achine fl or O Sensor' Surface Wet/Dry

5 lr,ru¢ 32 ° N_wllCe Vinyl T|le D_

S_ru_ 75" " Noo._ Vl.yl hi= W_

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•Enter the data intothe program

I I .ii_lhi'- i,O_l I °_.1 ' c_-J.-------L.°_- •

i I oi oooJ__.__L..=RL____.L..o_.J___._Lo'..'t_L____Lo_..

7 I....,_o_.,F___..L_..I__._L._'_J___.-I_.tw_.-L..----..L.._

,I 1 , i "_ R_'I-_,I_T----_. _ lm. _

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(ll_ _r_r _rv, Continued)

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*D,epcmdr$c:klnlrvaJc_aJDJ.el [_kTFOI_C]_ Ni ?=

_l"_plo itm 0.499 S_,md )¢u_t_p_e Rm 0.249

WE'rDR¥ " I 6.'J. 2S l I /_.lis o.)p o.sst I

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Tx,, I,S.o,_ 21 i,7-= :,.,;.p 0.07,I

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325
Participants

326
327

THERMOFORMING FROM A SYSTEMS VIEWPOINT

Jerry L. Wickman

Director Plastics Research and Education Center

College of Applied Sciences and Technology

Department of Industry and Technology

Ball State University

Muncie, Indiana 47306-0255

Telephone 317-285-5648

and

Nikhil Kundu

Purdue University

329

THERMOFORMING FROM A SYSTEMS VIEWPOINT

J.L. Wickman Ph.D.

Ball State University

Nikhil Kundu

Purdue University

KEY WORDS: thermoforming, statistical process control,

metrology, fixture design, gage R&R, processing variability

PREREQUISITE KNOWLEDGE: The student should understand the

concepts ofthermoforming, statistical process control, metrology,

and be familiar with ASTM standards as related to manufacturing.

OBJECTIVES: To be able to select and manipulate control charts

to adequately reflect processing characteristics and variation.

Understand how a manufacturing process can be broken down into its

basic components and subsequently analyzed. Understand how

statistics, standards, and metrology are critical to manufacturing.

EQUIPMENT AND SUPPLIES: Standard tooling and gages available

to the students should include but not be limited to a(n):

infrared thermometer portable contact thermocouple

calipers height gages

dial indicators micrometers

surface plates DataMyte data collection units

stop watches melt index unit

ASTM standards

universal test equipment (Instron model 1011)

statistics package for process control

AAA model MB-5 thermoforming unit with 24" x 24" capacity

INTRODUCTION:

Thermoforming can be one of the processes that meets the objectives

and allows for an in depth manufacturing study. This type of

experiment has the potential to involve/combine any or all of the

following topical areas:

Quality control

Heat transfer

Parts handling

Materials testing

Materials design

Data collection

Data analysis

Statistics

Materials processing

Standards

Fixture design

Metrology

Gage R&R (repeatability & reproducibility)

Material selection

331
Berins (1991) indicates that thermoforming is the process of

heating a plastic material in sheet form to its particular

processing temperature and forming the hot and flexible material

against the contours of a mold by mechanical or pneumatic means.

When held to the shape of the mold and allowed to cool, the plastic

retains the shape and detail of the mold. Thermoforming of plastic

sheet stock has been used extensively to produce inexpensive

disposable containers. Recent developments have focused on

sophisticated material and processing developments that meet microwaveable, ovenable, barrier type packaging demands. Thermoforming

as a system has come into its own and is beginning to produce

engineered products that effectively compete with other more

expensive plastics processing techniques.

The students will be working in groups of 3 in order to complete

the project in the approximate time interval of 5 to 7 weeks.

Cooperation by all members is critical. The students will be asked

to quantify and to provide all documentation necessary to identify

all possible sources of variability; this includes incoming

material, all components of the process, operator caused variation,

and operational methods. They are then requested to select and use

appropriate tools to begin to control variation. The use of ASTM E

178-Standard Practice for Dealing With Outlying Observations is

encouraged. A log book will be essential to each laboratory report

submitted. Appropriate written operating, setup, gaging, data

collection, data analysis policies and procedures will be required

for the entire operational sequence.

Input, process, and output represent a logical breakdown of the

process into critical components. Additional divisions may be

necessary as the project continues. It is safe to assume the

students have had some contact with all of the issues. This is the

first time that a manufacturing system of this type is being

addressed.

Flowcharts of the process must be developed. Flowcharts display the

various stages in the process and, through the use of different

types of symbols, demonstrate the flow of a product or service

over time. Extensive detailing will be required of the flowchart

before the project is allowed to begin. Mistakes will occur on

paper and should be minimized in the experiment.

Cause-and-effect diagrams (Ishikawa diagrams) will also be

required. Juran and Gryna (1980) indicate that this will force

organization of all known causes into general categories such as

methods, materials, machine, and human, illustrating the common

relationships. Its impact on the students comes from the graphic

representation of the relationships between problems and their

sources.

Documentation and traceability are critical to this project.

Everything that is used or input into or out of the process should

be measured and evaluated as per the appropriate ASTM standard. If

no standard exists then an appropriate mutually acceptable, logical

332
procedure should be documented and followed as closely as possible.

INPUT:

Incoming material to be thermoformed should have a particular

molecular orientation as a result of the former extrusion process.

It is important that the molecular orientation for all sheets be

kept as a constant, all being placed in the machine in the same

direction.

ASTM D 1898, Recommended Practice for Sampling of Plastics, will be

used to select appropriate samples for additional testing.

ASTM D638, Standard Test Method for Tensile Properties of Plastics,

will be used to evaluate tensile properties in the extruded

direction and perpendicular to the extruded direction of the sheet.

Test number, sample number, and material type will be documented.

All data collection forms for all documentation will be developed

prior to running the experiment.

ASTM D 1238, Standard Test Method for Flow Rates of Thermoplastics

by Extrusion Plastometer, will be used to determine flow rates. Flow

rate is an empirically defined parameter critically influenced by

the physical properties and molecular structure of the polymer and

the conditions of measurement. Melt flow is one of the most often

used tests of this nature. This measurement may later be correlated

with processing problems that may occur within or between lots.

A sampling procedure and fixture must be developed to evaluate the

thickness of incoming material. It is assumed that incoming

material will have a particular target dimension but it is the

students'obligation to determine how much variation exists in the

incoming product. Six data points will be measured per sheet, 1

data point per cavity. The number of data points required per sheet

is a function of the shape and number of cavities of the

thermoforming tool being used. Appropriate statistics and control

charts as selected, and defended by the student, should be used to

indicate sheet thickness and variation. Control charts can be

developed from attribute or variable data. Although attribute

control charts are easier to use, variable control charts will

provide more insight into the process under consideration. Hayes

and Romig (1982) have developed one of the more complete sources

for applications with and without standards. The fixture or gage

used to measure sheet thickness should take gage R&R (repeatability

and reproducibility) and their implications intoconsideration. The

DataMyte Handbook (1989) references the formulas for gage R&R. It

is the opinion of the authors that the issue of gage R&R needs to

be addressed in this experiment but actual calculations might be a

more appropriate topic if taken as a separate study. Documented

procedures should at least exist relative to the design and use of

the fixture to minimize operator error.

333
PROCESS:

Thermoforming is a process whereby the sheet material is loaded

into a frame and moved into a heated enclosed box and subjected to

elevated temperatures to soak for a predetermined amount of time.

Heat sources are located above and below the sheet material in an

effort to uniformly bring the plastic to temperature. Time and

temperature are the critical processing variables. For a particular

processing tool, processing standards will be developed along with

documented procedures. It will be the students' obligation to

develop statistics and control charts with documentation to reflect

processing characteristics over a production run of 60 good parts.

Subgroup size if used, will also be determined by the student.

Procedures developed by the students will document all necessary

information so that a person familiar with the process could

reproduce the experiment. It can not be over emphasized that tools,

gages, times, locations, machine settings, and other items must be

documented. Part removal from the thermoformer and placement on a

cooling fixture needs documentation and standards to minimize the

introduction of operator error.

OUTPUT:

The resultant product that is to be evaluated is a function of the

thermoforming tool being used. The tool being used in this

experiment is a 6 cavity tool that allows the students to consider

within cavity and between cavity variation.

Kennedy et al. (1987) contend that the metrology fixture is also a

function of the tool being used. The most desirable tool would have

1 cavity, but with 6 cavities the student can concentrate on several

or all cavities. Documentation, time invested, and number of

measurements required increase considerably with multiple cavity

tools. If the student wants to capture 6 data points from each part

in a 6 cavity tool, there is a total of 2160 data points for the 60

part run. That's a dilemma that the students will have to resolve.

It is also their responsibility to determine where to take

measurements, how many measurements per part, how to take

measurements (fixture design), control charting procedure, and

other items, but the process they develop must represent the

critical characteristics of the part and process. Once again gage

R&R is an important factor. Given the limitations of the gaging,

the measurement process can be destructive of the part.

SYNTHESIS:

Webster defines synthesis as the putting together of parts or

elements so as to form a whole. The individual components of the

project need to be assembled into a cohesive unit that best

describes where variation may be taking place, how to minimize

variation and how to hold to the new levels of productivity.

Material input, material testing, process control, fixtures and

fixture design, gaging, statistics, operators, documentation,

standards, output, variations of all those articles mentioned

above and others need to be assembled to form a whole that best

represents typical manufacturing. A statistically quantifiable

334
relationship exists and must be shown between input, process,

operators, and output.

SUMMARY:

Using the thermoforming unit gives us the flexibility to develop a

complete manufacturing process. The manufacturing students,

cooperating within a group, should be able to look at a process and

break it down into critical components that can be easily

understood and manipulated. The student should be able to take the

processing components and use whatever statistics, gaging,

recognized standards, and other tools that are available to analyze

the components as they relate to the whole, reduce variability and

improve upon the process. The manufacturing student must be able to

identify the various sources of variability and how they might

impact the system.

Modern manufacturing will not exist without the use of statistics.

We must improve the students' understanding and appreciation for

statistics and the use of statistics. The use of statistics

should become second nature as should the use and familiarity with

the science of measurement (metrology) and all associated standards

(ASTM/ANSI/ASQC/ISO/Others).

REFERENCES:

Berins, M.L., Editor, Plastics Engineering Handbook,

Fifth Edition, 1991,Van Nostrand Reinhold, New York

Annual Book of ASTM Standards, 1986, American Society For

Testing and Materials, Philadelphia

Juran, J.M., and F.M. Gryna Jr., Quality Planning and

Analysis, Second Edition, 1980, McGraw Hill, Inc.,

New York

Hayes, G.E., and H.G. Romig, Modern Quality Control,

Revised Edition, Glencoe Publishing Co., Inc. California

DataMyte Handbook, Fourth Edition, 1989, DataMyte

Corporation, Minnesota

Kennedy, C.W., et al., Inspection and Gaging, Sixth

Edition, 1987, Industrial Press., New York

Neufeldt, Victoria. Editor, Webster's New World

Dictionary, Third Edition, 1988, Simon Shuster, Inc. Ohio

335

THE CHARACTERIZATION OF MATERIALS

USING X-RAY DIFFRACTION

A.F. Sprecher, Jr.

Harvey A. West

and

A. A. Fahmy

Department of Materials Science & Engineering

North Carolina State University

Raleigh, North Carolina 27695-7907

Telephone 919-515-2377

337

THE CHARACTERIZATION OF MATERIALS USING

X-RAY DIFFRACTION

A. F. Sprecher, Jr., H. A. West, and A. A. Fahmy

Department of Materials Science and Engineering

North Carolina State University

Raleigh, NC 27695-7907

Telephone: (919) 515-2377

FAX: (919) 515-7724

Key Words

X-ray, diffraction, Debye-Scherrer, crystallography, Miller indices, Bragg's law

Prerequisite Knowledge

This laboratory requires a general knowledge of crystal structure and wave diffraction

phenomena.

Objectives

1. Familiarize the studentwith X-ray techniques for diffraction patterngeneration.

2. Show the student how to utilize X-ray diffraction data for crystal structure

determination.

3. Illustrate systematic and random errors associated with experimental data.

Background

Crystalline materials, by definition, are composed of atoms arranged in a periodic array; such

a configuration can also be viewed as regularly spaced planes of atoms. The properties of the

plane, such as atoms per unit area or interplanar distance, depend upon the crystal structure

as well as the angles the plane makes with the axes of the unit cell. The orientation of a plane

is given by its Miller Indices (hkl) which are the reciprocals of the axial intercepts of the

plane. For a cubic system the interplanar distance dhk l is given by:

dhkl - a

_/h2+k2+12 (1)

where a is the length of the side of the cubic unit cell.

When X-rays of wavelength _, are reflected off of these parallel planes of atoms, a

measurable signal will only be produced when constructive interference of the reflected

339
waves takes place. By geometry, this condition will result if the path difference (depicted in

Figure 1) is equal to an integral number of wavelengths. This condition for X-ray

diffraction can be expressed by Bragg's Law:

nl, = 2dta,lsin 0 (2)

where 0 is the angle that the incident X-rays make with the Planes and n is the integral

number of wavelengths difference in the diffracted X-rays. When 0 is such that this

equation is first satisfied (n=l), a strong X-ray signal will be emitted from the specimen

at a similar angle 0, In practice, the signals diffracted for n=l are the strongest, which is

primarily due to absorption of X-rays in the material. By measuring the intensity of

X-rays as a function of 0, a pattern of diffraction peaks will be produced which yields

information about the material's atomic structure.

Incident )_-Ra _, J.iffc d.Rays

4'

## O#

0_110, O4'

dsintJ •

Figure 1 - Diffraction of X-Rays from Atomic Planes

Substitution of equation (1) into equation (2) yields:

_,- 2a sinO (3)

_h2+k2+2l

340
By squaring both sides and substituting Q2 for h2+k2+/2, equation 3 becomes:

sin20 = ___ (Q2) (4)

4a2

This relationship shows that for a given crystal rotated in a columnated beam of

monochromatic X-rays (constant wavelength), diffracted radiationwill occur at certain values

of 0, the sine squares of which are directly proportional to the Q2 value for the reflecting

plane. So how does this render information about the placement of atoms in the unit cell?

Not all crystal planes will produce a diffracted beam, even if Bragg's Law is satisfied. For

instance, assume that Figure 1 represents a set of (100) planes in a body-centered cubic

material. The "body center" atoms make another set of planes (200) exactly half way

between the (100) planes. More importantly, these intermediate planes will have the same

number of atoms per unit area (planar density) as the (100) planes. Therefore, the beam

reflected off of the (200) planes will be of equal intensity and exactly 212 out of phase with

the beam reflected off of the (100) planes and no net signal will be detected. Hence, there

will not be a diffraction peak at that angle. However, at a higher value of 0, there will be a

primary (n=l) diffraction corresponding to the distance between (200) planes as there does

not exist a set of populated (400) planes to cancel these reflections. (Note: The diamond cubic

structure does have such a set of planes and, consequently, diffraction does not occur here

either.) This condition, known as "systematic extinction", exists for different sets of planes

for each type of crystal structure, and, if it can be determined exactly which planes are

producing the primary diffracted beams, the structure of the crystal can be determined. The

rules for the existence of diffraction peaks for any plane (hkl) in the common crystal

structures are given in Table I.

Table I - Conditions of Diffraction for Various Crystal Structures

Crystal Structure Conditions for Diffraction

Simple Cubic all planes

FCC h,k,l are all even or odd (zero is considered even)

BCC h + k + l = even number

HCP (h + 2k) _ 3n (n is an integer) and l is even

341
From the information in Table I, it is possible to predict the increasing values of Q2

corresponding to diffraction peaks as 0 is varied from 0 ° to 180°. Furthermore, the values

of sin20 obtained from actual diffraction data should follow the same proportional scheme

as the Q2 values. In other words, dividing the sin20 of the first observed peak by the first

possible Q2, and the second peak by the second Q2, etc., should all result in a constant

number if the proper crystal structure is chosen. By employing equation 4, this constant

number can be used to calculate the lattice parameter a for the particular material.

The Production of Diffraction Patterns

One of the most common methods of obtaining X-ray diffraction data is the Debye-Scherrer

"powder method". As shown in Figure 2, a polycrystalline sample, usually a powder of the

material covering a glass fiber, is exposed to an incident beam of monochromatic radiation

(for instance CuK a radiation, _.=1.5418A). The random orientation of the planes in the

sample coupled with physical rotation of the sample, gives rise to diffraction from every

possible set of planes in the specimen. The "cones" of diffracted radiation will expose the

film and cause a pattern of concentric arcs to be formed. As will be discussed in the

proceeding section, the location of these arcs gives the value of 2 0 for each set of planes

causing diffraction.

Incident

Collimator cs Diffracted

X-rays

Sample _ Film

21

Figure 2 - Debye-Scherrer Diffraction Geometry

342
Other methods of obtaining X-ray diffraction information are:

Diffractometer - a polycrystalline specimen is placed at the center of a circle and exposed

to monochromatic radiation. A detector is swept around the perimeter of the circle and

intensity vs. angle is recorded.

Laue method - a single crystal is exposed to polychromatic radiation and the diffracted

beams produce spots on a flat piece of film located behind (transmission) or in front

(back-reflection) of the specimen.

Errors Associated with the Debye Technique

Several sources of error exist when using the Debye-Scherrer powder technique. These lead

to inaccuracies in determining the lattice parameter. Aside from the obvious random errors

in measuring the locations on the film, four sources of systematic error in the diffraction

angle 0 are as follows:

1. Film shrinkage

2. Incorrect camera radius

3. Off-centering of specimen

4. X-ray absorption of specimen

These errors act to systematically shift the observed diffraction angles on the film. They are

experimental effects and not true variations of the diffraction angles found in the Bragg

equation. Rather, the geometry inherent in the Debye-Scherrer technique acts to shift the

measured angles. It can be shown that the shift in line distance on the film is given by."

Ad/d = Kcos20 (5)

where Ad/d is the relative line shift and K is the constant of proportionality due to all

sources of error. This relation of accumulated errors is known as the Nelson-Riley function.

It follows that:

Ad/d = Aa/a = (a - ao)/ao = Kcos20 (6)

upon rearranging:

a = ao + aoKcos20 (7)

343
It can be seen that in order to get the true lattice parameter ao, equation 7 can be used. Each

angle 0 measured corresponds to a unique set of (hkl). By using equation 4, a value for a

can be calculated. This is not the true lattice parameter a o, but includes all the

aforementioned errors associated with this technique. By plotting equation 7, a versus

cos20, the value ao can be obtained. Referring to Figures 3-6, the intercept represents

aowhile the slope is equal to aoK. This known as a back extrapolation technique and is

common in many experimental situations where measurements are subject to real,

unavoidable errors.

Experimental Procedure

Debye-Scherrer diffraction patterns for five unknown materials are provided (Figure 7).

These materials are elements (rather than compounds) and their crystal structures are

restricted to one of the following systems: SC, BCC, FCC, or HCP. The overall goal of the

experiment is to identify each material from its pattern. In order to accomplish this goal, the

following steps are performed on each pattern.

1. Measure all 2 0 diffraction lines from the patterns presented in Figure 7. Place the

diffraction pattern with the tab situated in the upper right hand corner. Begining with the

hole on the left side, set the ruler on the first ring to the left side of the hole. Then

measure all the diffraction tings to the tight in millimeters ( one millimeter = one degree).

Stop measuring when the opposite hole is reached. The angle 0 is determined through

the formula:

On (°) = Diff. Linen - ( Diff. Linel + Diff. Line2)/2 (8)

2. Generate tables for sin20 and take ratios of these values. Compare them to the ratios for

the values of Q2, as described in the previous section, for all the possible crystal

structures. By matching the two sets of ratios, a crystal structure determination can be

made.

3. Once the crystal structure has been identified, calculate the lattice parameter a for each

plane using Bragg's law.

4. Employ the back extrapolation technique in order to determine the true lattice parameter ao

for each pattern. This is done by plotting a versus cos 20 and extrapolating the value of

ao at cos20 -- O.

5. Once ao and the crystal structure are known, a material identification can be made by

comparing these values with those tabulated for the elements listed in the reference given

at the bottom of Table II.

344
Instructor notes

The pattern for the HCP material requires a slightly different approach and is usually not a

required pattern but is given for potential extra credit in order to stimulate the more

imaginative or motivated student.

The problem with the HCP pattern is that it has two independent lattice parameters, a and c,

making it impossible to take ratios of sin20 as with the other crystal structures. The

problem can be circumvented in the following manner.

1. Measure all diffraction lines and generate values of 20.

2. Assume the pattern is HCP. This can be done by inspection since the students have

identified the other crystal systems and know what they look like.

3. Prove the pattern is HCP. Taking the first two 0 values, 01 and 02, and using Bragg's

law and equation 9 below, generate two equations with two unknowns, a and c. Solve

both equations simultaneously to obtain values for the two lattice parameters. Using these

values of a and c, check the rest of the pattern. Do the calculated values of 0 from

Bragg's law match those that are measured directly from the diffraction pattern? They of

course will match, thereby making the crystal structure and lattice parameters

determination.

dhklh_. = a (9)

Table II summarizes the data obtained from the diffraction patterns and Figures 3- 6 represent

values of ao attained from the data.

345
Table II - Data Summary for Diffraction Patterns

Pattern # 1 2 3 4 5

Material Ni W Cu Nb Zn

Crystal

Structure FCC BCC FCC BCC HCP

Lattice

Parameter, ao*

(/_) 3.5239 3.1653 3.6148 3.3067 ao = 2.6650

co = 4.9470

Diffraction

Angles, 0 22.15 20.05 22.00 19.55 18.30

26.00 29.40 25.45 27.95 19.80

38.20 36.95 37.15 35.05 21.75

46.60 43.85 45.10 41.45 27.35

49.30 50.55 47.65 47.70 35.45

61.20 57.85 58.45 54.05 38.60

72.15 65.95 68.10 60.95 41.35

77.80 77.40 72.30 69.05 43.30

45.45

47.65

54.70

58.20

62.30

63.75

69.55

* Cullity, B.D. Elements of X-Ray Diffraction, Addison-Wesley, 1978.

346
3.57

,-, 3.56

o<

3.55

_ 3.54

3.53

•,_ 3.52

,.a 3.51 ao = 3.5200 A

3.50 , I , I , I , I ,

0.0 0.2 0.4 0.6 0.8 1.0

COS20

Figure 3 - Back Extrapolation for Nickel Data

3.19

_ 3.18

_ 3.17

3.16

0.0 0.2 0.4 0.6 0.8 1.0

COS20

Figure 4 - Back Extrapolation for Tungsten Data

347
3.70 , , , ,

Copper

°_,_ 3.65 '

_ 3.60

_ 3.55

3.50

0.0 0.2 0.4 0.6 0.8 1.0

COS20

Figure 5 - Back Extrapolation for Copper Data

3.40 , , , ,

Niobium

°< 3.35

_ 3.25_ 3.20

0.0 0.2 0.4 0.6 0.8 1.0

cos20

Figure 6 - Back Extrapolation for Niobium Data

348
1

2

3

4

5

Figure 7 - Debye-Scherrer Patterns

349

FRACTURE OF GLASS

John M. Henshaw

Assistant Professor

Department of Mechanical Engineering

University of Tulsa

Tulsa, Oklahoma 74104

Telephone 918-631-3002

351

Fracture of Glass

John M. Henshaw

Department of Mechanical Engineering

University of Tulsa, Tulsa, Oklahoma 74104

KEY WORDS: glass, fracture, bending, stress/strain, static fatigue, delayed fracture,

fracture mechanics, residual stress.

PREREQUISITE KNOWLEDGE: The student should understand the fundamentals of

beam bending - as would normally be obtained in an introductory mechanics of materials course.

Some understanding of elementary statistical concepts, such as mean and standard deviation, is

also helpful. Some elementary concepts of fracture mechanics are introduced in this lab,

although no previous knowledge of this subject is required.

OBJECTIVES: To observe and understand the fracture behavior of a brittle material.

To quantify the effects of various treatments on that material designed to modify its strength.

EQUIPMENT AND SUPPLIES:

(1) Glass microscope slides (1" by 3" - approx. 12 per student)

(2) Three-point bending loading fixture (see attached drawing)

(Note: Item (2) is not intended to be constructed by the student)

(3) Continuous loading mechanism: Small solenoid valve and 12V battery, two 2-liter plastic

water reservoirs and fixture, misc. lengths of tubing and wiring, tap water (see attached drawing)

(4) Calibrated weights (1000, 500, 200, 100g)

(5) Anhydrous HF acid (not to be handled by students)

(6) Bench-top metallurgical heat treating oven

(7) Mass balance (4 kg capacity)

(8) Micrometer (preferably) or dial calipers

(9) Diamond-point scribe

(10) Straight edge

(11) Computer spreadsheet (preferably) or hand calculator

INTRODUCTION: Common plate glass, such as is used to make laboratory

microscope slides, is a very brittle material. Such materials exhibit large variations in fracture

stress. These variations can be due to very small surface defects (to which brittle materials are

highly sensitive), or to residual stresses in the material.

Beam Bending: To understand the role of the surface in determining the fracture

strength, it is necessary to examine the state of stress within the glass slide as it is loaded in

three-point bending. The equations below should be familiar from your background in

mechanics of materials. The deflection at the center of a simply supported beam with a single

concentrated load at mid span (i.e., a beam in three-point bending) is

F13

Y- 48EI (1)

where y is deflection, F is the load, 1 is the distance between the outer supports, i is the moment

of inertia (= wh3/12 for a beam of rectangular cross-section, where w is the width of the beam

and h is the thickness), and E is the modulus of elasticity of the material. Since glass is a

homogeneous isotropic material, there is a linear distribution of stresses through the specimen

thickness, with compression at the top surface, zero stress at the mid plane, and tension at the

bottom surface, as illustrated in Figure 1.

353
i© lt ©J

'°p

(-) (+)

boll

Figure 1. Distribution of tensile (+) and compressive (-) stresses through the thickness of beam

in bending.

The maximum normal stress occurs at the top (compressive) and bottom (tensile) surfaces

of the slide and equals

3F1

Smax- 2wh2 (2)

Fracture Mechanics: .Since the maximum stress of a beam in bending is at the surface

(tensile at the bottom and compressive at the top), and since glass is a brittle material, we would

expect the bending strength of glass to be very sensitive to surface flaws.

The science of fracture mechanics tells us that the more brittle a material is, the more

sensitive it will be to smaller and smaller flaws - even flaws that may be too small to see with the

unaided eye. This relationship is quantified through a quantity called "stress intensity" (K) as

follows:

K = o _3_a (3)

where o is the applied stress and a is the length of a crack oriented perpendicular to the applied

stress. When the stress intensity reaches a critical value, fracture mechanics theory predicts that

the material will fracture. This critical stress intensity value varies for different materials and is

known as the "fracture toughness" (KI¢), a material property. Very tough materials such as some

steels have high KIc values (say, 75-100 MPa(m)l/2), whereas brittle materials like glass have

extremely small values of KIc (say, 0.5-1.5 MPa(m)l/2).

The exact form of equation (3) will vary with the shape of the specimen, the location of

the crack, and the type of loading, but what doesn't change is this: if the material property KIc is

very low, then the critical combination of stress and crack length necessary to cause fracture is

also very low. For materials like glass, even if the stress is not very great, a "crack" in the form

of an "invisible" surface scratch can induce fracture.

Investigating the Influence of Surface Flaws: The influence of surface condition on

the fracture stress of glass may be investigated by testing specimens whose surfaces have been

altered. One simple way to alter the surface is by introducing a sharp scratch with a glass-cutting

instrument. The scratch thus produced is clearly much deeper than any.of the slight imperfections

that might have pro-existed on the surface. Equation (3) predicts that since the crack length a has

increased, the stress necessary to reach the critical stress intensity (KIc) will decrease. This

prediction can be easily verified experimentally. We can also investigate the influence of crack

location, by testing specimens with the crack oriented down (crack in tension) or up (crack in

compression).

354
Another way to alter the surface of the glass is by chemically removing the surface layer

(along with any scratches that might be on the surface). This can be accomplished by immersing

the glass in HF acid, which readily attacks glass. NOTE: HF acid is an extremely dangerous

chemical. Thus, all HF acid etching will be done ahead of time by the lab assistant. After the

acid has been allowed to remove the surface layer, the specimens are thoroughly rinsed and

dried. The acid-treated specimens may then be tested, and the fracture strengths obtained should

allow conclusions to be drawn about the presence or absence of surface flaws on the "as

received" (straight out of the box) glass specimens.

Residual Stresses: Another factor that can influence the fracture properties of a material

is the presence of residual or "locked-in" stresses. The beam theory stress distribution shown

above assumes that the material is in the unstressed state prior to application of the bending load.

This may or may not be true. Glass can be processed so as to induce compressive residual

stresses at the surfaces - this process is known as "tempering" (and is quite different from the

tempering of steel!). Tempered glass is much stronger than untempered. This is because extra

force is required to overcome the compressive residual surface stresses. The stresses due to

external loading are added to any residual stresses present. Conversely, glass, if it is improperly

processed, could end up with harmful residual tensile stresses at the surfaces. These stresses,

when added to the stresses due to external loading, should result in an observed reduction in

strength.

By annealing glass (heating it hot enough to relieve the residual stresses, then cooling it

very slowly to ensure that no new residual stresses are created) and then testing its strength, we

should be able to draw conclusions regarding the state of residual stress in the as-received

specimens. Since the annealing treatment is somewhat time-consuming, the annealed specimens

will be prepared ahead of time by the lab assistant.

Static Fatigue: One factor that complicates the strength testing of glass is a phenomenon

known as "static fatigue". Static fatigue, or delayed fracture, is the tendency exhibited by many

glasses to withstand a given static load for a short period of time, say 30 seconds, before

suddenly fracturing without warning. In order to ensure that static fatigue is not adversely

affecting our results, it is important to apply load to the specimens slowly, and to repeat the same

loading procedure for each specimen (see below). In addition, we can investigate the influence

of static fatigue on strength by carefully varying the loading rate (N/min.).

PROCEDURE:

Safety considerations:

1. Be very careful around the glass loading fixture, especially when the glass is under

load! The broken glass fragments will of course be very sharp.

2. Protective eye wear is mandatory for all those in the lab area.

3. Please clean up all glass fragments after each specimen fractures, and before you test

the next specimen.

Specimen Preparation: Each student will test 12 glass specimens:

Specimen Condition # Specimens to be tested

by each student 4

"as received" 4

annealed 1 2

acid-etched 2 2

scratch UP 3 2

scratch DOWN 3 2

TOTAL 12

1. Heat treated at 600°C for 10 minutes and slow cooled (inside furnace) to room

temperature.

2. Soaked in 5% HF acid for 20 minutes to remove surface layer.

355
3. The glass specimens will be scratched by the students. The scratch should be centered

across the width of the specimen (i.e. a one-inch wide scratch!) Try to be as consistent as

possible from one scratch to the next! (Obviously, this is a potential source of error.)

Use the diamond point scribe and straight edge to scratch your specimens.

4. As described below, ALL data generated by all the students in your lab should be

averaged in order to obtain accurate strengths for the various specimen conditions.

The heat treated and acid-soaked specimens will be prepared ahead of time by the lab

assistant. This is in the interest of saving time (in the case of the heat treating) and safety (in the

case of the HF acid, which is very dangerous).

Measure and record the thickness and width of your specimens. Because of the

importance of the thickness in calculating the maximum stress, at least three measurements of the

critical thickness dimension should be taken and averaged. The thickness should be around 1

mm, or approximately 0.040 in. (Thickness should be reduced for the acid-etched specimens.)

Specimen testing: There are two ways to accomplish the loading of the glass specimens

in this lab. The first loading method involves continuous loading of the specimens, while in the

second method the specimens are loaded manually in discrete stages.

In the continuous loading method, Figure 2, the glass specimens are loaded by draining

tap water from a reservoir suspended above the loading fixture, through a solenoid valve, and

into a second container positioned on the three-point bending fixture. As the level of water in the

second container goes up, the load on the specimen increases. When the specimen breaks, the

upper arm of the loading fixture drops down, making contact with the base of the machine, and

closing a circuit through which the solenoid valve is automatically shut. The water in the

container on the fixture is then weighed and added to the (predetermined) weights of the

container and arm of the fixture to determine the load at fracture of the glass. The fracture stress

is then calculated using equation (2).

In the manual loading method, the glass specimens are loaded by placing calibrated

masses on the loading pan one-by-one. Weights should be placed on the pan at 30 second

intervals. (This is done to reduce the influence of static fatigue - see Introduction.) When the

specimen breaks, the fracture load is determined by adding the weight of the masses on the pan

to the weight of the loading arm. The fracture stress is then calculated using equation (2).

Statistical Treatment of Data: All the students in your lab should share all the fracture

data generated. One way to do this easily is to enter all the data directly onto a computer

spreadsheet during the lab period. At the end of the period, each student can copy the data file

onto a floppy disk for analysis and report writing. The mean fracture strength for each specimen

condition is determined by summing all the individual data points, Smax,for that condition, and

dividing by the number of data points, n:

_m.,= _sm"'' (4)

n

The standarddeviation for eachcondition is determined as follows:

std. dev. = Y n - 1 (5)

356
waterreservoir

12Vbatte_ _ solenoid/valve u m

I

loading fixture

(metal)_ II

/ test specimen

/ metalc,)ntact'4'v ll , _ . '

L insulating p°st_: _

Figure 2. Schematic of glass fracture test fixture showing the continuous loading method

SAMPLE DATA SHEETS: Each student should complete by hand a data table similar

to the one shown below. If a computer spreadsheet is being employed, this data should also be

entered into the spreadsheet.

Specimen Condition max. load I w h Smax

(N) (m) (m) (m) (MPa)

as received

as received

as received

as received

annealed

annealed

acid-etched

acid-etched

scratch UP

scratch UP

scratch DOWN

scratch DOWN

357
INSTRUCTOR NOTES:

1. Extreme care should be taken during the HF acid etching of the glass. Eye protection

and elbow length gloves should be worn at all times - of a type designed for use with HF. One

drop of this material on your skin will give you a burnyou will not soon forget! Observe proper

disposal procedures for this material.

2. One of the most important lessons the students can get from this lab relates to the

"significance" of the results. Students have been known to write long paragraphs explaining why

"condition A", with a mean strength of 70 MPa and lots of scatter, was "stronger" than "condition

B" with a mean strength of 69 MPa! Depending on the background of the students in statistics,

one can introduce the subject of significance tests as a means of determining which of the

conditions are significantly different from each other. Otherwise, students can simply be asked

to use their best "engineering judgment" to determine the significance of the results.

3. Because of the large statistical variation in the strength of a brittle material like glass,

it is very important in this lab for all the students in the lab to share their data. An added benefit

of this is thatit requires a fair amount of cooperation among the students.

4. The influence of static fatigue on the strength of the glass can be investigated using

the continuous loading (water) setup. By using a set of valves with varying flow rates, and

testing a sufficient number of specimens with each, the influence of loading rate on strength can

be determined.

5. It is a simple matter in this lab to determine the modulus of elasticity (E) of the glass.

This can be done by measuring deflections using a dial indicator and then calculating E from

equation (1). Or, E can be determined directly if a strain gage is centered on the bottom surface

of a glass specimen. Stress/strain data are then gathered, from which E is determined. It can be

an interesting addition to the experiment to allow the students to investigate the influence of the

various glass treatments on modulus.

REFERENCES:

1. Hertzberg, R.W., Deformation and Fracture Mechanics of Engineering Materials, 2d

ed., John Wiley and Sons, 1983.

2. Kingery, W.D., Bowen, H.K., and Uhlmann, D.R., Introduction to Ceramics, 2d ed.,

John Wiley and Sons, 1976.

SOURCES OF SUPPLY: Glass microscope slides may be obtained from the Biology

department of most schools or from a biological supply store. The solenoid valves and batteries

may be purchased at most industrial/commercial equipment and supply stores. Most of the rest

of the equipment is easily obtained at a hardware store.

358
PHASE TRANSITION STUDIES IN BARIUM AND

STRONTIUM TITANATES AT MICROWAVE

FREQUENCIES

Jai N. Dahiya

Southeast Missouri State University

One University Plaza

Cape Girardeau, Missouri 63701

Telephone 314-651-2390

359

PHASE TRANSITION STUDIES IN BARIUM AND STRONTIUM

TITANATESAT MICROWAVE FREQUENCIES

J. N. Dahiya

Physics Department

SoutheastMissouri State University

KEY WORDS

Phase transition,crystal lattice,simple cubic,

dielectric behavior,frequencyshift, Q-change

OBJECTIVES

1. To understand the phase transformationsin barium and

strontium titanatesas the crystals go from one temperatureto

the other.

2. To study the dielectric behaviorof barium and strontium

titanate crystals at a microwave frequencyof 9.12 GHz and as

a function of temperature.

SUMMARY

Phase transition studies in barium and strontiumtitanate are

conducted using a cylindricalmicrowave resonant cavity as a

probe. The cavity techniqueis quite successful in establishing

the phase changes in these crystals. It appears that dipole

relaxation plays an importantrole in the behaviorof the

dielectric response of the medium loading the cavity as phase

change takes place within the sample. The method of a loaded

resonantmicrowave cavity as applied in this work has proven to

be sensitiveenough to monitor small phase changes of the cavity

medium.

INTRODUCTION

The dielectric constant of single crystalsof barium titanate has

been measured at different frequencies(Ref. 1 and 2). In this

investigationa microwave resonant cavity is used to study the

dielectric behavior of barium and strontiumtitanate ceramics at

a microwave frequencyof 9.12 GHz. The cavity techniqueused is

very successful in monitoring the phase changes in a fine crystal

of barium titanate as it goes from the paraelectriccubic phase

to the ferroelectrictetragonalphase, to the orthorhombicphase,

and to the rhombohedralphase successively. The heating and the

361
cooling methods involved are very effectivein maintaining a

certain temperatureof the sample under investigationfor some

time. The details of the microwavespectrometerused for this

study along with the heating and coolingmethods are given

elsewhere (Ref. 3-7). This technique is also applied to study

the dielectric propertiesof a sample of a mixture of 75 percent

barium titanate and 25 percent strontiumtitanate.

EQUIPMENT,THEORY AND PROCEDURE

A microwave spectrometeroperatingin the x-band of frequencies

was used to study the dielectricpropertiesof barium and

strontium titanate at a fixed frequencyof about 9.12 GHz. The

spectrometerinvolved has a tunable klystronwith a frequency

range of 8.4 to 11.0 GHz. The block diagram of the microwave

spectrometeris shown in Figure 1 and the details of its components and operation are given in other papers (Ref. 5 and 6).

In ferroelectricsubstances,the static dielectric constant

varies with temperatureas follows.

_s = B + C for T > Tc (i) T - To

In Eq.(1), B and C are constantsthat do not depend on

temperature,C is the Curie constant and Tc is known as the Curie

temperature. As shown in Eq.(1), the behavior of the dielectric

constant is valid for temperaturesthat are more than the Curie

temperature. At temperaturesless than the Curie temperature,

the ferroelectricmaterial develops a spontaneouselectric

polarization. As the material is brought to this temperature

(To),there is a phase transition from the paraelectriccubic

phase to the ferroelectrictetragonalphase. There is a very

strong field produced in the material because of the interaction

of dipoles below this temperatureand because of this there is a

perfect alignmentof the dipoles and the material exhibits a very

strong polarization. The polarizationis related to the electric

field as shown below.

P = _E (2)

where a is the polarizability. The total polarizabilityhas

contributionsfrom dipolar, ionic and electronic

polarizabilities. The contributionsto the polarizabilitiesare

functionsof the frequencyof the applied field. At microwave

362
frequenciesthe dipolar contributionsto the total polarizability

are very weak and the complex permittivityhas contributionsfrom

ionic and electronic polarizations.

The strong polarizationeffects in ferroelectricsubstances like

barium titanate below the Curie temperatureare responsiblefor a

very high value of the dielectricconstant of the material.

Ferroelectricmaterials also exhibit piezoelectricity. According

to the piezoelectriceffect, a pressure applied to the ends of a

crystal of barium titanate for example will produce a very large

potentialdifference between the ends of the crystal. This is

mainly because of the coupling between the polarizationand the

shape of the sample. The stress will change the shape of the

sample, which induces the change of polarizationand produces a

very strong charge density at the ends of the crystal. On the

other hand, if a potentialdifference is applied between the ends

of the same crystal, the crystal will have mechanical

oscillationsbecause of this electro-mechanicalcoupling.

Above temperatureTc (120°C),barium titanate has a perfect cubic

structure as shown in Figure 2. The barium ions occupy the

corners of the cube, the oxygen ions are on the faces and the

titanium ion at the body center of the cube. In other words,

above the Curie temperature,also called the critical temperature,

barium titanate has a body center, face center cubic structure.

Below this temperatureTc there is a small shift of about 0.15A°

in the ions. The titanium ions at the center of the cubic

structureshift about 0.006 nm with respect to the barium ions

that are at the corners of the cube. The shift for the oxygen

ions is in the opposite direction. The net shift in these ions

produces a very strong polarizationin the material as it goes

through the critical temperatureof 120°C.

At microwave frequencies,the dielectric constant e becomes a

complex quantity c* = c' - jc" where _' and c" are the real and

imaginaryparts of the complex dielectricconstant. According to

the Slater's perturbationequationsthe real and imaginaryparts

of the complex permittivityare related to the frequencyshift

and the Q-changes of the signal as shown below (Ref. 4).

Af c/-1 I g,"

dv

- (3)

fo 2 fg'E,_ dV

j _

and

363
1 fEs "E, dv

A (-_)= ,H (4)

where _s, E_and E_ are the field of the sample, the unperturbed

cavity and the microwave field as applied to the cavity

respectively,and v is the volume of the sample with V being the

volume of the cavity.

Also

(--> I = FAw (s)

Q fo

where AW is the width of the signal at half power points and fo

is the resonant frequencyof the system.

According to Debye's theory, the relaxation time i:is related

to e' and e" as shown below.

= _)_ (6)

8//

where _ = 2Xfoand cs is the static permittivityof the material.

The fine crystallinesamples of barium and strontium titanate are

placed in capillarytubes. The capillarytube is then placed in

the microwave field of the resonant cavity. This causes a

perturbationin the microwave field of the cavity and the

correspondingperturbationsin the signal are recorded in terms

of the frequencyshift and width change of the signal. This

becomes the initial reading of the measurementof dielectric

constant. The sample under investigationis then allowed to go

through a temperaturechange from lower to higher temperatures

and the correspondingvalues of frequencyshifts and width

changes are recorded. Slater's perturbationequations (3 and 4)

are used to calculate the real and imaginaryparts of the complex

dielectric constant of the material.

364
EXPERIMENTALRESULTS AND CONCLUSION

Figures 3 and 4 show the behaviorof the dielectric constant of

barium titanate as determined in this investigation. The

frequency shifts (Af/fo)and the Q-changes [A(1/Q] are plotted as

a function of temperature. From Eqs. 3 and 4 these correspond to

the real and imaginary parts of the complex dielectric constant.

As the temperature is reduced below the critical value of 120°C,

barium titanate changes from the paraelectriccubic phase to the

ferroelectrictetragonal phase. This change is very dramatic and

is visible with a very high value of the dielectric constant

around 120°C. As the temperatureis further lowered to

approximately0-10°C, this material changes from tetragonal to

the orthorhombicphase and finally around -100°C it goes from

orthorhombicto rhombohedralphase.

Figures 5 and 6 show the dielectric relaxation in a sample

containing 75 percent barium titanate and 25 percent strontium

titanate. The frequency shifts and Q-changes are plotted as a

function of temperature at a microwave frequency of 9.12 GHz. As

can be seen from Figure 5, Af/fo that corresponds to c' increases

dramatically around 34°C and then it lowers to a value between

70-110°C. The corresponding curve for &(I/Q) or constant e" also

exhibits a similar behavior except it has a higher value around

-40°C. As we know that the Curie temperature for a pure crystal

of barium titanate is 120°C, in comparison the Curie temperature

for a composition of 75 percent barium titanate and 25 percent

strontium titanate changes dramatically.

The microwave resonant cavity technique as applied in this

investigationwas very successful in monitoring the phase changes

in barium titanate as it goes from paraelectriccubic phase to

the ferroelectrictetragonalphase, to the ferroelectric

orthorhombicphase, and to the ferroelectricrhombohedralphase

respectively. The heating and the coolingmethods involved in

this techniquewere very effective in maintaining a certain

temperature. Data was taken at a microwave resonant frequencyof

9.12 GHz and the experimentwas repeated several times to observe

the dielectric behavior of barium titanate and also a mixture of

75 percent barium titanate and 25 percent strontiumtitanate.

365
The reason that barium titanate has a high dielectric constant is

because of the Ba2.ion that is so large as compared to the very

small Ti4.ion that is sitting in the middle of the crystal

structure. The oxygen and barium ions are so large, they push

each other apart, leaving the titanium ion in an octahedral hole

where it can rattle around. Therefore,when an electric field is

applied to a crystal of barium titanate, the titanium ions are

repelled by this field and are drawn over to one side of their

octahedral hole. Because of this very strong displacementof

titanium ions, the crystal of barium titanate becomes highly

polar in nature and the total polarizationof the material

increasesdramaticallyaround 120°C. As shown in Figures 5 and

6, an addition of 25 percent strontiumtitanate to 75 percent

barium titanate changes the Curie point dramaticallyand there is

also a change in the dielectric behaviorof the crystal.

ACKNOWLEDGEMENTS

The author wants to thank Mark Wetzler, an undergraduatephysics

major, for his contributionto this work. I also wish to thank

Ms. Theresa Buttry for typing this manuscript and Mrs. Betty

Black for preparingthe figures.

366
REFERENCES

1. Lurio, A., and Stern, E.: Measurementsof the Dielectric

Constant of BaTiO3 Single Crystals in the ParaelectricRegion

at X'band. J. Appl. Phys., 31, 1960, p. 1805.

2. Arlt, G., Hennings,D., and de With, G.: Dielectric

Properties of Fine-grainedBarium TitanateCeramics. J. Appl.

Phys., 58 (4), 15 August 1985, p. 1619.

3. Dahiya, J. N., and Freeman, R. W.: Computer Interfacingof

Microwave ResonantCavity for TemperatureMeasurementsDuring

Dielectric Relaxation. Computersin Physics,July/Aug. 1989,

p. 49.

4. Dahiya, J. N., Jani, S. K. and Roberts, J. A.: Phase

Transition Studies in Polar and Non-Polar Liquids at Microwave

Frequencies. J. Chem. Phys. 74___4_C6_ 1981,, p. 3609.

5. Dahiya, J. N.: DielectricBehavior of Superconductorsat

Microwave Frequencies. NIST Special Publication822, 1990, p.

145.

6. Dahiya, J. N.: Dielectric Propertiesof Germanium and Silicon

as Determined in the Microwave Field. J. Mater. Educ., 13,

1991, p. 367.

7. Hong, K. H., and Roberts,J. A.: Microwave Propertiesof

Liquids and Solids Using a ResonantMicrowaveCavity as

Probe. J. Appl. Phys., 45__5_5_5_5_5_5_5_(6_ 1974, p. 2452.,

367
I POWER I

SUPPLY

I

F H RESONANT F[ MICRO"

KLYSTRON ATTENTUATOR DIRECTIONA COUPLER L WAVEMETER CAVITY COMPUTER

INTERFACE I

MIXER ..... COUNTER I

| DETECTOR PRINTER

I I

EXTERNAL MODULATED GENERATOR AMPLIFIER I

MODULATION SIGNAL [ OSCILLOSCOPE

I I r

I

I. Block diagram of the microwave spectrometer used in this

investigation.

2. Structure of barium titanate above Tc.

368
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is _ _

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, , , , , , , , , , , , o o,- , , , , , , , , , , , 

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= _ sl!unl_e_l!q_eot / tV sl!un/iJeJl!q_e(_r)V 4 
10"-

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c-'_ 8" • • I • I Bi n

_ 7 LI i n

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3 n H m U

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0 I I I I I I I I I

-40 -20 0 20 40 60 80 1O0 120 140

Temperature(°C)

5. Microwave loss A(1/Q) as a function of temperature for a

sample containing 75 percent barium titanate and 25 percent

strontiumtitanate.

I0"

oo 9 "

m m

(-- 8 • []

"_ 7 •

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,,__ []

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5 m .

}=_ [] •

o 3 m []

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-40 -20 0 20 40 60 80 100 120 140

Temperature(°C)

6. Frequencyshift Af/fo as a function of temperaturefor a

sample containing 75 percent barium titanateand 25 percent

strontiumtitanate.

370
EXPERIMENTS IN MATERIALS SCIENCE FROM

HOUSEHOLD ITEMS

F. Xavier Spiegel

Department of Engineering

Loyola College

4501 N. Charles Street

Baltimore, Maryland 21210

Telephone 410-617-2515

371

EXPERIMENTS IN MATERIALS SCIENCE FROM HOUSEHOLD ITEMS

F. Xavier Spiegel

Department of Electrical Engineering & Engineering Science

Loyola College, Baltimore, Maryland

ABSTRACT: Everyday household items are used to demonstrate some

unique properties of materials. A coat hanger, rubber band, balloon,

and corn starch have typical properties which we often take for

granted but can be truly amazing.

KEY WORDS: Polymer, Coat Hanger, Rubber band, Balloon, Corn

Starch.

PREREQUISITE KNOWLEDGE: Curiosity.

OBJECTIVES: The purpose of these demonstrations is to illustrate

some interesting properties of household items. The following

demonstrations have been performed by the author for many years and

have been received enthusiastically by audiences of all ages. 1,2

EQUIPMENT AND SUPPLIES:

1) Metal Coat Hanger

2) String

3) Rubber Band

4) Balloon

5) Corn Starch

THE COAT HANGER: A metal coat hanger can be used to demonstrate

the ability of string to transmit sound better than air. Sound

travels more efficiently in a more dense medium than a rarefied

medium. If a metal coat hanger is inverted and a piece of string

approximately three feet long is tied to each end of the coat hanger,

and then it is moved to strike a wall or some other solid, a rather

dull thud will be heard. However, if the ends of the strings are

placed close to the ears (by holding the strings against each ear with

a finger) and then the experiment is repeated, a resounding tone will

373
be heard that is much more beautiful than the dull thud. Different

types of string, twine or monofilament will produce different qualities

of the sound.

THE RUBBER BAND: A rubber band is a polymer which consists of

long bulky chain molecules. These molecules are tangled and not

strongly bound to each other, similar to a bowl of spaghetti noodles.

When the rubber band is stretched, the long chain molecules rearrange

to line up along the direction of the stretching and the rubber band

becomes warm. This warming is caused by internal friction as the

molecules slide over one another and can be readily observed by

touching the stretched rubber band to the lower portion of the upper

lip (a very sensitive temperature sensor of the body). 3

THE BALLOON: A balloon is also a polymer and can be used to show

the different behavior of a stretched polymer as opposed to an

unstretched polymer. If a balloon is inflated and touched by a sharp

object such as a skewer it will burst. However, if the skewer is

inserted carefully from the bottom of the balloon and then into the

top from the inside the balloon will stay inflated for some time. The

reason the balloon bursts in the first instance is that the molecules

have been stretched apart and cannot inhibit the burst. In the latter

case the molecules are relatively unstretched and hence, as jumbled

molecules, "grab" the skewer and prevent air from escaping. A

variation on the above is to skewer the balloon before inflation and

show that the balloon can still be inflated. 1,2,3

CORN STARCH: Corn starch is used in cooking for thickening

gravies. However, if corn starch is mixed with water to about the

consistency of pancake batter, it will be noticed that if it is moved

slowly, for instance by pouring or trying to slowly stir the corn

starch "batter", it will behave normally as most fluids do. However, if

you try to stir the "batter" rapidly or drop something into it the

"batter" will behave more like a solid. The "batter" is known as a

non-Newtonian fluid. Variations of the above can be tried by mixing

the "batter", freely pouring from one glass to another, and then

374
suddenly trying to throw the "batter" from the glass by a jerk of the

wrist. Please note, experiment with your mixes before trying this

towards an unsuspecting audience. Unfortunately the "batter" has a

very limited shelf life.

CONCLUSIONS: The author has had enthusiastic response from

audiences of all ages. With each of these demonstrations, quantitative

results can be measured and each can be expanded and/or altered. You

are only limited by your imagination and curiosity.

REFERENCES:

1. Fellers, William O.: Materials Science, Testing and

Properties for Technicians, Prentice-Hall 1990.

2. Jacobs, James A. and Kilduff, Thomas F.: Engineering

Materials Technology, Prentice-Hall 1985.

3. Spiegel, F. Xavier: Five Experiments in Materials

Science for Less than $10.00, NASA Conference

Publication 3151 November 1991 263-265.

ACKNOWLEDGEMENT: The author wishes to thank Mary L. Spiegel for

typing this manuscript.

375

AN AUTOMATED DATA COLLECTION SYSTEM

FOR A CHARPY IMPACT TESTER

Bernard J. Weigman

and

F. Xavier Spiegel

Department of Engineering

Loyola College

4501 N. Charles Street

Baltimore, Maryland 21210

Telephone 410- 617 -2515

377

AN AUTOMATED DATA COLLECTION SYSTEM

FOR A CHARPY IMPACT TESTER

Bernard J. Weigman and F. Xavier Spiegel

Department of Electrical Engineering and Engineering Science

Loyola College, Baltimore, Maryland

ABSTRACT: A method for automated data collection has been

developed for a Charpy impact tester. A potentiometer is connected to

the pivot point of the hammer and measures the angular displacement of

the hammer. This data is collected with a computer and through

appropriate software accurately records the energy absorbed by the

specimen. The device can be easily calibrated with minimal effort.

KEY WORDS: impact, Charpy, potentiometer, fracture energy,

potential energy, computer, analog to digital converter.

PREREQUISITE KNOWLEDGE: Thestudent should understand the

concepts of fracture and the use of a computer for automatic data

collection.

OBJECTIVES: This experiment is intended to familiarize the

student with the technique of automated data collection using a Charpy

Impact Tester, a potentiometer, and a computer. 1'2,3,4,5

EQUIPMENT AND SUPPLIES: (i) Charpy impact tester; (2)

Potentiometer; (3) Computer; (4) Analog to Digital Converter; (5)

Samples as desired.

EXPERIMENTAL PROCEDURE: A i0 Kfi potentiometer was fastened to

the rotating arm of the Charpy impact tester so that as the arm of the

tester rotated, the resistance of the potentiometer increased linearly

with the angle (Figure 1). The voltage at the wiper arm of the

potentiometer then also varies linearly with the angle of the tester

arm. In the experiment, the tester arm is released from a known

height which corresponds to a known angle which in turn corresponds to

379
a known voltage, V I. The tester arm then breaks a piece of material,

in this experiment wood, and keeps swinging until it reaches its final

height, which corresponds to its final voltage, V F. The difference in

height from the initial position of the pendulum to the final position

corresponds to a loss in potential energy. This loss in potential

energy is equal to the energy used to break the piece of wood. The

Charpy impact tester is calibrated, not in angle, but in inch-pounds

of energy used to break the material placed at the bottom of the

pendulum's swing. 6

When the experiment is done without the use of a computer, an

observer visually determines how high the hammer swings after it

breaks the sample and relates this to the loss of potential energy in

inch-pounds. When the computer is used in the experiment, the voltage

output from the potentiometer, Vout, is measured by the computer by

reading the output of an Analog to Digital Converter (ADC) every

fiftieth of a second for the duration of the swing of the pendulum.

The program then picks out the maximum voltage, which corresponds to

V F and calculates the loss of energy due to breaking the sample in

inch-pounds. 7

It is necessary to calibrate the Charpy impact tester before the

experiment and sometimes during the experiment. This is done by

measuring the voltage, Vl, at the beginning position, the voltage, V2,

at the bottom of the swing (the point of lowest potential energy), the

voltage, V3, when the arm makes a 90 ° angle with the vertical and the

voltage, V4, when the pendulum swings to its largest height with no

sample present. The wiring of the potentiometer is set up so that

VI<V2<V3<V4 . Once the differences between the four voltages are known,

they will not change, even if all of the voltages rise or fall due to

a twisting of the potentiometer shaft because of the sharp impact each

time a sample is broken. Thus to re-calibrate, all we need to do is

measure the voltage, Vl, when the pendulum is at rest.

380
THEORY:

AE=Mg(H-h) (i)

When h = 0 then AE = 50 in-lb

Therefore, MgH = 50 in-lb

Vout:Ke+_ ,(2)

v3:_:--_+v_ (3) 2

2

,c= -- (V3' V2) (4)

O- v°'_t-v2 (5)

K

O- _ V°_t-v" (6)

2 v3-v,.

h : L(ILCOS0) (7)

AE: Mg(H- L+ LCOS0) (8)

h = H when You t = V 1 and O = 01

H: L(I-cosO I) (9)

0 is a function of You t

0 = 0 (You t) (10)

and

O_=0(v_) (11)

Then

381
r _ 1 (12)

H 1 - COS01

L

AE= MgH(I - _ (l-cosS)) (13)

AE = MgH COS0 - COS01 (14 )

1 -cos81

Finally,

&E= 50 cosS-cosS_ (15)

1 - cos01

INSTRUCTOR'S NOTES: In this experiment, wooden samples of pine

were fractured with and against the grain. The automated experiment

provides much more consistent results than visual observation.

Variations on the fracture of wood can be performed such as the

fracture energy of wood as a function of water content, the effects of

knots and/or notches, and the relative strengths of various types of

glue by gluing the fractured pieces and repeating the experiment. Not

to be overlooked is the appearance of the fracture surfaces.

REFERENCES:

I. Eggebrecht, L. C.: Interfacing to the IBM Personal Computer,

Howard W. Sams & Co.

2. Thompson & Kuckes: IBM-PC in the laboratory, Cambridge

University Press.

3. Krutz, Ronald L.: Interfacing Techniques in Digital Design,

Wiley.

4. Stone, Harold S.: Microcomputer Interfacing, Addison Wesley.

382
5. Cripps, Martin: Computer Interfacing - Connection to the

Real World, Edward Arnold Publisher, a division of Hodder &

Stoughton.

6. Spiegel, F. Xavier; and Weigman, Bernard J.: "An Automated

System for Creep Testing," NASA CP-3151, 1991.

7. Fellers, William O.: Materials Science, Testing and

Properties for Technicians, Prentice Hall, 1990.

ACKNOWLEDGEMENT: The authors wish to thank Stephanie M. Spiegel

for typing this manuscript.

383
power supply

computer

Figure 1

Cherpy Imlsec-t Tester

384
VISUALIZING WELD METAL SOLIDIFICATION USING

ORGANIC ANALOGS

Daniel W. Walsh

and

Gary Ray Rogers

Materials Engineering Department

School of Engineering

California Polytechnic State University

San Luis Obispo, California 93407

Telephone 805-756-2131

385

VISUAL][ZING WELD METAL SOLIDIFICATION USING ORGANIC

ANALOGS

Daniel W. Walsh and Gary Ray Rogers

Materials Engineering Department

California Polytechnic State University

San Luis Obispo, CA

KEY WORDS: solidification, weld metal, solidification modes,

equiaxed, columnar, cellular, dendritic, planar

PREREQUISITE KNOWLEDGE: The student should

understand basic solidification theory and be familiar with the

different types of solidification modes.

OBJECTIVES: To allow the student to observe the

solidification of a low melting temperature transparent crystalline

organic compound that exhibits behavior similar to that of weld

metal.

EQUIPMENT AND SUPPLIES: (1) Cell assembly 2.00-in. x

6.00-in. brass plate with a 0.75-in. x 2.00-in. slot milled out of the

geometrical center of the plate. (2) Two glass slides rest in this slot,

serving to encapsulate the organic compound. The movable platform

upon which the cell is mounted, (3) a 12.00-in. x 8.00-in. x 0.5-in.

aluminum plate has a 2.00-in. x 6.00-in. slot milled out for insertion

of the cell assembly. The movable platform is mounted on (4) four

linear motion pillow block bearings which support the load. The

pillow blocks run along (5) two 15.00-in. long AISI 1060 casehardened and ground steel rails. The rails are in turn supported by

(6) four malleable iron support blocks, and the entire assembly is

mounted on a (7) 28.00-in. x 22.00-in. x 1.00-in. aluminum base

plate to provide dimensional stability. (8) A Dayton 1/15

horsepower, variable speed electric motor is mounted on the base

plate and drives the platform via a 1/2-20 UNF feed screw/nut

assembly consisting of a (9) 1/2-20 UNF feed screw and (10) two

387
1/2-20 UNF nuts welded to the movable platform. The feed screw is

connected to the motor through a (11) small flexible coupling. Below

the cell a variable intensity light source is mounted to provide the

necessary back light illumination for microscopic observation. This

consists of (12) a sewing machine lamp with a bayonet-type 15 W

bulb connected to a (13) standard dimmer switch. The filament

assembly consists of a (14) 0.004-in. diameter AISI 304 stainless

steel filament wire connected to (15) two quick release terminals on

(16) 16 gage wire connected to a (17) 2-12 volt, 0-5 amp rated DC

power supply. The filament assembly simulates the welding arc.

The organic compound chosen for use in the apparatus is (18)

Succinonitrile; a few grams will suffice. To view the solidification

event a (19) low power stereomicroscope will be needed. This can be

mounted directly to the base plate.

PROCEDURE: It is assumed that a student or technician has

constructed the Organic Weld Solidification Analog (OWSA), as the

experiment described here is intended to further the understanding

of the organic simulator, not the .construction of it.

The study of solidification often lacks immediacy. Akin to the

paleontologist, researchers in materials scan the "fossil" remains of

long past solidified pools to gain clues to the nature of the

solidification event. This experiment provides a method to improve

students' understanding of solidification by exposing them to in-situ

solidification. The organic weld solidification simulator is a device

that allows the observation of solidification at low temperature. The

device takes advantage of the transparency and low melting

temperature of several crystalline organic compounds. This system

provides the students with visual reinforcement to concepts

discussed in lectures, and is exciting and fun to use.

Direct observation of the solid liquid interface in metals is

difficult; metals are not transparent and the temperatures associated

with the interface prohibit simple visualization systems. The

interface is a critical region, as much of the structure resulting from

solidification depends on the interface morphology. The OWSA

allows students access to this event.

388
Solidification processes depend upon the roughness, on an

atomic scale, of the solid-liquid interface. Materials can be classified

in terms of their freezing behavior according to their entropy of

melting. Certain organic compounds exhibit entropies of melting that

are very similar to those of metals. The availability of transparent

materials for metallic analogs presents an opportunity to directly

observe the phenomena that determine the structure of cast metals

and fusion welds.

This device has been used to view many of the features

associated with welds in metals. Direct observations of epitaxial

nucleation, competitive growth, morphological changes and defect

formation have been accomplished in the laboratory. Students

experimentally verify the relations shown below.

lASt LIOUIO_ " "/ I__

OENORITIC _ sucotsstve t \

/ _ - t_ 2 t .tX*OO.AL I

. / o_No.,_,c/ 1_',"i_! _,,'°,V.;,W'°"" _ .... , ...... ,

o .... '_. ,h'tf/

o _ ttLLULAR OROWTHMOOtOF SOL!_IFICA11ON

I / / / CELLULAR i I=I.' ...... mT[RFAOE__ Ne...... PtANAn _: I•

SOt.IOIFICATION PARAME;TER

I_ 0VSION zo_t _ . ._

_sc u__'At._

..... r_ ,);7,>,,.'/i:.

¢_os$- stc_o_

SOC_O._ S.ow._* =.e[*.A.C[ 0_" ___--'C S-e-' SCHEMATIC SHOWING THf ._C_u_IOf(_'_¢¢ ¢u_l_6 _ ( ¢( ¢* ApprARANCE OF ,Hit

C(_.kUI._*O(NO_IT*¢ MOOt ¢_0_** _o.,_,¢ .ODt SOLID-LIDUID INT[RFAC(

i _ o' _O_m-,¢itiO_ FOR AN iSOLATED [OUIAX[O

: ! ',*,,'t. DEA NDRI LIOUIO TE GROWING M(TAL IN

......, t

389
These drawings depict the relationships among solidification

substructures, the process parameters (G/¢I_-, where G is the thermal

gradient and R is the rate of motion of the solidification front) and

the production parameter (Co), the nominal composition. One may

view the diagram as providing limits for the breakdown of a planar

solidification front based on the time necessary to redistribute

matter by diffusion or heat by conduction.

As the student uses these diagrams, it should become apparent

there is a basic philosophical conundrum involved with the

microstructures thus generated. There is solid growth proceeding

from the pool edge, where it is relatively cool, toward the pool

center, where it is hot. How can this be? Why should bits of solids

form as cells, or dendrites, and jut ahead of the planar interface?

Solidification should proceed in a planar fashion, that is, as the liquid

cools, the planar surface should move uniformly forward.

Once again, reality is more complex and beautiful than it is

obvious. Neither solids nor liquids are homogeneous isotropic

continua. This experiment demonstrates graphically that a

solidification front engenders a solute gradient in the liquid ahead of

that front.

We can derive an expression for the effective liquidus

temperature as a function of distance from the solidification

interface. We know

EQN 1 C1 = Co[1 + {(1-k)/k} exp(-R/D1)x']

and

EQN 2 dTe/dx' = (dC1/dx') (dTe/dC1)

Thus

EQN 3 (dC1/dx') = -(CoR/D1) {(1-k)/k} @ x'= 0

and

EQN 4 dTe/dC1 = ml

Thus

EQN 5 Gc = -(RCo)/D1 {ml[1-k]/k}

where Gc denotes the effective thermal gradient induced

by compositional variance.

390
If Gt, the thermal gradient, is greater than Gc solidification will

proceed on planar fronts. If Gt is equal to or less than Gc, the planar

front will become unstable. Depending on the magnitude of the

difference between the two, any of the following substructures can

occur: cellular, cellular dendritic, columnar dendritic or equiaxed

dendritic growth. In effect, by altering the composition ahead of the

interface, we have created a chemical supercooling. The physical

thermal gradient (Gt), though positive, may be less severe than the

chemical gradient (Gc), leading to virtual supercooling.

SAMPLE QUESTIONS:

1. Discuss the solidification of the succinonitrile analog in the context

of weld solidification in general.

2. Discuss the macroscopic bead shape as affected by process

parameters.

3. Relate macroscopic process parameters to resultant

microstructures.

4. Relate microstructures to resultant properties.

5. Certain process parameters will give rise to centerline cracks and

cracks at the edge of the pool. Discuss the changes in process and

production parameters which cause the formation of these cracks.

6. How does the dynamic character of solidification change the

composition and the phase distribution in an engineering material

vis-a-vis its hypothetical equilibrium counterpoint?

7. Verify the relationships between the microstucture and the

process and production parameters using the diagrams enclosed.

8. What ramifications does solidification have for corrosion

properties, mechanical properties, and for magnetic behavior in

ferromagnetic metals?

9. Develop a relationship between the velocity of the moving heat

source and the velocity of the pool interface. What limits the

stability of pool shape? Relate this to question 5.

SAFETY NOTE: The organic compound most suitable for this

type of study is succinonitrile. This is readily available from most

chemistry departments. This is a relatively safe compound at

391
temperatures below its boiling point. Nonetheless, basic chemistry

lab rules should be followed. The Material Safety Data Sheet for

succinonitrile should be available for all students to read as should

the MSDS for all lab chemicals in the lab.

REFERENCES:

(1) Savage, W.F., Nippes, E.F., and Miller, T.W.,

"Microsegregation in 70Cu-30Ni Weld Metal", Welding Journal

Research Supplement, Vol 55, No. 6, June 1976, pp. 165s-173s.

(2) Chalmers, B. Principles of Solidification, John Wiley and

Sons, Inc., New York, 1967.

(3) Savage, W. F., Lundin, C. D. and Chace, T. F. "Technical Note:

Direct Observation of Microstructural Changes Associated with Fusion

Welding." Welding Journal Research Supplement, Vol. 47, No. 11,

November 1968, pp. 527s -528s.

(4) Jackson, K. A. and Hunt, J. D. "Transparent Compounds That

Freeze Like Metals." Acta Metallurgica, Vol. 13, 1965, pp. 1212 -

1215.

(5) Savage, W. F. and Hrubec, R. J. "Synthesis of Weld

Solidification Using Crystalline Organic Materials." Welding Journal

Research Supplement, Vol. 51, No. 5, May 1972, pp. 260s - 271s.

392
PERFORMANCE OF THERMAL ADHESIVES IN

FORCED CONVECTION

Nikhil K. Kundu

Statewide Technology

Purdue University

2424 California Road

Elkhart, Indiana 46514

Telephone .219-264-3111

393

PERFORMANCE OF THERMAL ADHESIVES

IN FORCED CONVECTION

NikhiI K. Kundu

Purdue University

Elkhart, Indiana

ABSTRACT:

Cooling is critical for the life and performance of electronic equipment. In

most cases cooling may be achieved by natural convection but forced convection

may be necessary for high wattage applications. Use of conventional type heat

sinks may not be feasible from the viewpoint of specific applications and the

costs involved. In a heat sink, fins can be attached to the well by ultrasonic

welding, by soldering, or with a number of industrially available thermal

adhesives. In this paper the author investigates the heat transfer characteristics

of several adhesives and compares them with ultrasonic welding and

theoretically calculated values. This experiment was conducted in an air flow

chamber. Heat was generated by using heaters mounted on the well. Thermstrate

foil, Uniset A401, and Aremco 571 adhesives were tested along with an

ultrasonically welded sample. Ultrasonic welding performed far better than the

adhesives and Thermstrate foil.

This type of experiment can be adapted for a laboratory exercise in an

upper level heat transfer course. It gives students an exposure to industrial

applications that help them appreciate the importance of the course material.

KEY WORDS:

heat transfer, thermal conductivity, thermal interface, heat sink, ultrasonic

welding

PREREQUISITE KNOWLEDGE:

The students should understand the concept of heat transfer by

conduction and convection.

OBJECTIVe:

Cooling is critical for the life and performance of electronic equipment.

Conventional heat sinks for high wattage applications consist of a well with fins

attached with thermally conductive interface materials or ultrasonic welding.

Any interface increases thermal resistance of the system. The objective of this

experiment is to investigate the thermal effectiveness of a number of selected

interface adhesives and ultrasonic welding.

INTRODUCTION:

Cooling devices for electronic equipment are generally rated by their

thermal resistance. It is expressed by the temperature rise per unit of heat

395
transfer or power dissipated. The major goal of any cooling system is to lower

thermal resistance of the heat sink. The heat sink is composed of a well, a thermal

adhesive interface between heat source and well and between well and fins so the

heatsinkhas threemajorlocationsofthermalimpedance.

The aluminum well makes up approximately 25 % to 30%, the adhesive

makes up between 15 to 20%, and the fin convection resistance makes up

between 50% to 60% of the total thermal resistance (fig 1).

The adhesives are often called thermal interface due to their conductive

nature. A desirable adhesive interface should possess a high thermal

conductivity and must be installed with uniform pressure yielding minimum

film thickness. The area of contact is dictated by the fin geometry and the

semiconductor device. The film thickness again depends on the viscosity and

surface tension of the adhesive at installation temperature. Trapped air bubbles

may cause significantly higher thermal resistance. Thermal conductivity is not a

sufficient measure of the suitability of an adhesive. Adhesives have thermally

conductive filler materials. High conductivity materials with large particles may

be found to be thermally poor for bonding high conductivity materials as they

gap the surfaces excessively.

Thermal resistance is given by R = L/kA (1)

where L is the interface thickness, k is the thermal conductivity of the adhesive,

and A is the contact area.

The convection resistance Rc is a function of the air flow rate, fin

configuration and geometry. Temperature drop across the fins increases with

decreasing fin thickness.

TEST EQUIPMENT

An air flow chamber (fig 2) with fan and adjustable nozzles;

heat sink well with four sets of fins, two sets attached with thermal adhesives,

(Uniset A401 and Aremco- 571) one set with thermstrate foil, and one set with

ultrasonic welding; two 300 watt heaters, and a power supply.

PROCEDURE:

The sampleheatsinkconsistedofa 3"x 1"aluminum channelwith2" high

and .010' thick fins; two 300 watt heaters were mounted on the channel with

thermally conductive grease between the heater and the channel. The heaters

were securely held with C clamps. Thermocouples were soldered at eight

locations. Two thermocouples were used for each sample interface, one on the

heater side and the other on a fin (fig. 3).

The heat sink assembly was installed at the exit gate of an air flow

chamber with a shroud (fig. 4). The tests were run at varying power levels and air

flow. All tosh_ wore run at a well tomporatxLrO of 130 _.

396
Table I:

Thermal conductivities of selected adhesives and their curing temperature and

time.

,, Btu/hr. ft.°F curing time(hr) curing temp(°C)

Thermstrate Foil K= 2.395 - -

Uniset A 401 Kffi0.417 1/2 150

Silicon Grease 540 K= 0.430 24 25

Aremco 571 Kffi18.082 - -

Table II:

Temperature difference between well and fins at varying air flow.

air velocity AT air velocity AT

(fpm) between (fpm) between

well and well and

fins _oc) fins _°C)

Thermstrate 1300 77.5 Uniset 1300 70.0

Foil A401

i800 61.0 1800 60.2

2200 60.3 2200 ..... 57.8

3000 51.8 3000 53.0

3200 50.6

Aremco 571 1300 64.9 Ultrasonic 1500 53.5

Welding

1800 56.5 1600 53.5

2300 57.8 2100 52.0

3000 53.5 2500 45.0

3200 54.0 2600 45.0

RF_SULTSAND DISCUSSION:

Two sample adhesives tested were Uniset A401 and Aremco 571. These

were compared against samples with thermstrate foils and ultrasonic welding.

The temperature difference between the well and the fins at varying air flow

was recorded for evaluation.

The curves in figure 5 for temperature differential between well and fins

versus air flow demonstrate the heat transfer capability of the interface materials.

Out of four samples ultrasonic welding performs the best. Ultrasonic welding

maintains a temperature difference of approximately 10°C with other samples

throughout the testing range. Thermstrate foil is least effective in heat transfer

because of non uniform contact area between well and fins. The temperature

differential between well and fins decreases with increased air flow for all four

interfaces. All four curves tend to level off around an air velocity of 300 feet per

minute.

397
The temperaturedifferentialforsAremco and Unisetadhesivesarenot

representativofetheirthermalconductivitieArs.emco 571was expectedtobe far

betterthanUnisetA401,buttheylieverydose toeachother.Thisexplainsthe

fact hatthereareotherfactorrsesponsiblfeorheattransferthroughinterface

suchasviscosity,surfacetensionfil , mthicknessa,ppliedpressure,particlsiz e es

offilermaterials,and chemistryofadhesives.The performanceofinterface

materialsalsogreatlydepends on thecleanlinessand roughnessofbothsurfaces.

RECOMMENDATION:

Ideallthy ereshouldbe verylittleorno temperaturedifferencebetween

welland finswhich would be thecaseofa unibodyheatsinkdesign(fig6)In. a

_mibodyheatsink,welland finsaremachined fromone blockofmetal.The

number offinsina unibodyheatsinkislessdue tothickerfinsand

manufacturinglimitations.Thismay notbe economicallyattractivbe,utmany

timesthedesignofcoolingsystemsisdictatedby thesizeor compactnessofthe

electroniequ c ipment.

REFERENCe:

1. Scott, A.W., "Cooling of Electronic Equipment n,Wiley Interscience

Publishing.

2. Thermalloy Inc., Engineering Information Releases on Thermal Interfaces.

3. Technical Data Sheet from Power Devices Inc., Masterbond Inc., Aremco

Products, and Thermalloy Inc.

SOURCES OF SUPPLY:

ThermstrateAdhesive Thermal Grease

Power DevicesInc. ThermaIloyInc.

Thermal Interface Products Group P.O.Box 810839

27071 Cabot Road Dallas, TX 75381-0839

Laguna Hills 114 phone: (214) 245-4521

phone: (714) 582-6712

Aremco 571 Adhesive Uniset A-401 Adhesive

Aremco Products Amicon Corporation

P.O.Box 429 Polymer Products Division

Ossining, NY 10562-0429 25 Hartwell Avenue

phone: (914) 762-0685 Lexington, _MA 02173

ACKNOWLEDGMENTS:

This research was conducted in the laboratory of Crown International in

Elkhart, Indiana. The author wants to express his deep appreciation to Joe

McGuire and Ross Brady of Crown International for their guidance and support.

398
R&

Rs Conductive Sink Resistance

) [ Ra Adhesive Resistance

_.__. _[[ Rc Convective Resistance

Rs R_ Rc

T case T ambient

V /

T adhesive T fins

Figure I: Heat sink thermal resistance

Figure 2: Air flow chamber

399
Thermstrate Uniset Aremco Ultrasonic welding

/ / / _ Fins

Well

Heater

Thermocouple

Interface

Figure 3: Heat sink assemblyAir

Heaters_

. /_--_ _nter_ac _ _

well __ ----___ .

/

Shroud j Air flow chamber

Figure 4: Test set up at air chamber

400
- 70

60

50

40 -

THERMAL INTERFACE

30 -

--_Thermstrate foil

--_'Uniset A-401

m 20 -

-4_-Aremco 571

-(_Ultrasonic welding

10

I I I ,I I i .

500 1000 1500 2000 2500 3000

Air velocity (fpm)

Figure 5: Temperature differential

between well and fins vs. air velocity

Air

/

/ / / /f Transistor

guuuuuuuuuuuF/

RFIRRRFrHNRUNnF/

/ /

Figure 6: Unibody heat sink

401

TAGUCHI METHOD OF EXPERIMENTAL DESIGN

IN MATERIALS EDUCATION

Martin W. Weiser

Mechanical Engineering Department and

Center for Micro-Engineered Ceramics

University of New Mexico

Albuquerque, New Mexico 87131

Telephone 505-277-2831

403

Taguchi Method of Experimental Design in Materials Education

Martin W. Weiser

Mechanical Engineering Department and

UNM/NSF Center for Micro-Engineered Ceramics

University of New Mexico, Albuquerque, NM 87131

Abstract

Some of the advantages and disadvantages of the Taguchi Method of experimental design as

applied to Materials Science will be discussed. This is a fractional factorial method that

employs the minimum number of experimental trials for the information obtained. The

analysis is also very simple to use and teach, which is quite advantageous in the classroom. In

addition, the Taguchi loss function can be easily incorporated to emphasize that improvements

in reproducibility are often at least as important as optimization of the response. The

disadvantages of the Taguchi Method include the fact that factor interactions are normally not

accounted for, there are zero degrees of freedom if all of the possible factors are used, and

randomization is normally not used to prevent environmental biasing. In spite of these

disadvantages it is felt that the Taguchi Method is extremely useful for both teaching

experimental design and as a research tool, as will be shown with a number of brief examples.

Introduction

The Taguchi Method of experimental design is a

methodology that performs the minimum number of

experiments necessary to determine the effects of three to

as many as 63 independent variables on a response. It is ...... _ j ......

a very efficient method that is well suited to use in

Materials Science since it is conceptually quite simple ,._ l_Tolerance_2

andcanbeadaptedtospecificapplications. Inaddition, _" _ Limits /-

the method meshes very well with Taguchi's loss

function shown in Figure 1, which associates a cost with

the response being away from the optimal value

regardless of whether the error is due to the process \Tar.;et/Target

being out of specification or the process being variable \ I /

or noisy. However, as with all highly efficient methods, _ k ,_/ there are a number of problems with this technique that

can result in erroneous results, particularly if a high Response, y

degree of precision is required. Figure 1 The Taguchi loss function.

Funded in part by a grant from the UNM Teaching Allocation Subcommittee. The author would like to

thank P.G. Madrid, D.N. Lauben, K.B. Fong, and R. Sheldon for assisting with performance and analysis

of the experiments used as examples.

405
Some of the advantages and disadvantages of the Taguchi Method are listed in Table I and are discussed

in more detail below. Later, brief summaries of a number of examples where the Taguchi Method has

proven very beneficial in Materials Science are presented. In addition, a number of comments on how the

Taguchi Method can be employed in the typical Undergraduate Materials Laboratory and how it might be

used to lead into other highly efficient methods of experimental design are offered.

Table I Advantages and Disadvantages of the Taguchi Method

High efficiency requires a minimum number of experimental trials

Error analysis is normally not exact

Can handle both continuous and discrete factors

ls conceptually very simple

Is computationally very simple

Easily incorporates the concepts involved in robust design

Does not handle factor interactions very well

Randomization is not commonly employed

Only a limited number of orthogonal arrays exist

High Efficiency

The Taguchi Method is very efficient in that it can be used to find as many factor effects as the number of

trials that are performed, particularly the main factor effects. Use of carefully designed orthogonal arrays

insures that the factor space is covered as uniformly as possible using the minimum number of trials. In

addition, the arrays are at least pairwise orthogonal (the combination of levels AI and B_occurs as often as

A2 and B2, etc.) so that any one factor interaction will not dominate the results.

This minimal number of trials results in a dramatic reduction in the amount of effort needed to obtain

information about the system. For example, use of the L9 array, which examines four factors at three

levels each, reduces the number of experimental trials from 81 for the full factorial design to nine for the

Taguchi design. A consequence of this is that there are zero degrees of freedom in the system of

equations that is used to calculate the main factor effects. This state is often referred to as "a statistician's

bad dream*" because the response surface is required to pass through all of the data points. As such there

are no degrees of freedom remaining for error variance analysis. This problem can be overcome by using

one or more of the factors as a dummy variable to introduce additional degrees of freedom or to repeat

the different trials. Repetition of the trials is particularly beneficial because it allows some examination of

noise factors that cannot be controlled

Error Variance Analysis

Saturated orthogonal arrays with no degrees of freedom directly available for error variance analysis are

normally used in the Taguchi Method. Error is therefore analyzed by assigning the factors that have the

smallest effects on the response(s) to a pool. This can be done by simplistic Pareto analysis where the

absolute magnitude of the effects is examined or by performance of the more detailed Analysis of Variance

(ANOVA) which involves calculating the sum of squares of the effects due to each factor and then ranking

* A negative number of degrees of freedom is known as "a statistician's nightmare" for very good

reason.

406
them. Both of these methods of analysis are performed for the fired density in the powder metallurgy

experiment presented elsewhere in this volume, tSj These results are displayed in Figure 2 (Pareto

Analysis) and Table II (ANOVA) where it is readily seen that the consolidation pressure is the most

significant factor, followed by the particle size, while the firing temperature and time were found to be

relatively insignificant.

1.6

1,4

_" 1.2

1.0

0.8

0

'_ 0.6

0.4 _//_/-//_/

0.2

o.0

B A D C

Factor

Figure 2 Pareto Diagram for the P/M experiment.

Table II ANOVA for the P/M Experiment

Factor DOF* Sum of Mean F§ % of

Squares Square Variation

B. Pressure 2 1.354 0.677 30.30 78.88%

A. Size 2 0.273 0.137 6.11 15.92%

D. Time 2 0.079 0.039 4.60%

C. Temperature 2 0.010 0.005 0.61%

Total 8 1.717

Pooled Error 4 0.089 0.022

The pooled factors are assumed to have effects that are comparable to the noise in the system. The use of

one or more dummy factors will further improve the error variance analysis by including degrees of

freedom that are devoted entirely to error analysis. In either case, a larger number of trials are required

* The degree of freedom is one less than the number of levels since the effects must sum to zero.

Mean square divided by pooled mean square error. Values greater than 1 indicate significance.

Technically the F test cannot be applied unless the trials are fully randomized. This problem is

handled in an unrandomized Taguchi experiment by stating that values of F between 1 and 2 are

probably significant rather than definitely significant.

407
for most other experimental schemes to achieve the same level of error variance for each of the factors.

For the L9 array, the process of progressively finding the best level for each of the four factors would

require a total of 27 trials as opposed to the nine using the orthogonal array to achieve the same level of

error variance. In addition, the true optimum might be missed since this approach is not pairwise

orthogonal andan important factor interaction might be missed: The predictions from the Taguchi Method

will not include the interaction, but it will show up as a discrepancy between the predicted optimum and

the confirming trial result. The reader is referred to chapter 3 of Phadket21for a more complete discussion

of this topic and how it can be related to Fourier analysis where the weaker harmonics are frequently

classified as noise.

Continuous and Discrete Factors

The Taguchi Method is designed so that each of the factors is broken down into a small number of

discrete levels and information is obtained about the factor effects only at these levels. This is very

beneficial when one or more factors can only have discrete values such as a switch which can only be on

or off. However, the discrete nature of the factor levels is not a problem when the factor is continuously

variable, particularly if care is taken to systematically map the actual values of the factor to the factor

levels.

The different factor effects from the Taguchi analysis are normally plotted versus the factor levels as

shown by the filled circles in Figure 3 for a single four level factor. A solid line is traditionally used to

connect the data points for a given factor to guide the eye. This line is not intended to present any

information about the effect of the factor at any level between the experimental levels. In fact this line has

absolutely no meaning if the factor can only have discrete values that correspond to the experimental

levels. However, if the factor is continuous and systematic mapping has been done between the values of

the factors and the levels, there must be factor effects corresponding to factor levels between those that

were tested. The problem lies in determining what these factor effects are.

6

4

3 ,x

1 _ Linear

o "","N,\ T

-1 Cu \_

Cubic \ x Quadratic .-"- "

-2

-3

-4 I ,, I I i I i I

1 2 3 4

Factor Level

Figure 3 Different Fittings of the Factor Effects

for a Four Level Factor

408
It is proposed that the solid lines, which are normally drawn to guide the eye, are actually a rather poor

estimate of the intermediate factor effects since most systems respond to a continuous change in a factor

with a continuous change in response rather than to the discontinuous response represented by the solid line.

The most obvious solution to this problem is to use a continuous function that passes through all of the

data points. This has been done using a cubic equation in Figure 3. The problem with this approach is

that increasing the number of levels normally results in worse prediction of the factor effects at

intermediate levels when noise is present in the experimental results since the curve must pass through all

of the data points. This is contrary to the expectation that increasing the number of levels should improve

prediction of the factor effects at intermediate levels.

Instead it is proposed that regression analysis should be used to fit a curve with fewer adjustable factors to

the factor effects. This has been done using the least squares technique for both linear and quadratic

functions in Figure 3. The quadratic function represents the experimental factor effects and the type of

behavior that is expected by most systems fairly well, particularly when the error bars are considered.

This method is quite similar to the approach employed in the various surface response techniques.

However, it should be pointed out that this method of analysis should not be used for making predictions

of the system response. Rather it should be used to gain additional information that will help guide further

experimental exploration of the system. For example, if the goal is to minimize the response, a confirming

trial with this factor set to level 2 would be required. However, the quadratic regression analysis indicates

that the true minimum lies closer to a level of 2.9, so either additional confirming trials should be

performed in this range or an another array experiment should be performed which covers a smaller range

of factor values that are close to the indicated optimum.

Concept and Computation

The basic premise of the Taguchi Method is that a minimum number of trials are used to determine how a

set of factors at a number of levels affect one or more responses. This is accomplished by arranging the

levels of the factors in an array so that each level of a factor appears the same number of times and is

paired with each of the levels of the other factors the same number of times. This array is a small subset

of the full factorial experimental array in which all of the possible combinations of the factor levels are

used. The result is an experimental array that is quite small and easily examined by the users.

The computations involved in the Taguchi Method are very simple and quite transparent to the

practitioner. Determination of the effect of a factor at a given level is done by finding the mean response

when the factor has this level and then subtracting the overall mean response. The optimal response is

found by adding the effect for the most beneficial level of each factor to the overall mean response. This

simplicity is extremely beneficial to students and instructors since it is not necessary to use complicated

calculations or proprietary algorithms.

The conceptual and computational simplicity of the Taguchi Method allows students to quickly master the

fundamentals of the analysis technique and then proceed to more complex issues in experimental

design. This is of particular benefit in Materials Science where the underlying science is often quite

complicated. The simplicity of the analysis makes it possible for the student to quickly begin to apply

statistical methods of error variance analysis (particularly ANOVA) without having an extensive statistics

background. The meaning of the statistics can be easily seen by comparing the results to those shown in a

Pareto chart such as was described earlier.

409
The minimal number of experiments used in the Taguchi Method makes it feasible to use the first

experiment to develop additional experiments to gain more insight into the process that is being

investigated. The need to perform confirming trials at factor levels that are close tO the predicted optimum

is a first step in this development. The extreme simplicity of the technique makes it possible for the

student to make modifications to the basic technique that make it better suited to studying their system.

An example of this is the use of regression to fit the factor effects which is a simple surface response

technique.

Robust Design

Robust design involves development of processes that are tolerant of perturbations in the controlled factors

or the environment. This topic is of great interest from an industrial standpoint, but is often neglected in

engineering education as science is currently deemed to be far more important in most programs. The

Taguchi Method directly incorporates a number of aspects of robust design. Since only a small number of

trials must be investigated to examine a system, it is possible to conduct each trial a number of times to

examine the statistical nature of the process. Optimization of one of the Taguchi signal-to-noise functions,

rather than the actual response, reinforces the concept that reproducibility is often as important as achieving

the optimal response in an industrial setting. The quick determination of the near optimal factor settings

via the Taguchi technique makes it possible to examine other aspects of robust design. This can include

examination of how non-linear factor effects can be exploited to deal with inherently noisy factors.

Factor Interactions

One of the biggest problems that arises in the Taguchi Method is that of factor interactions. The technique

relies upon the additivity of the main factor effects for both its efficiency and computational simplicity.

Since there is at least a small amount of factor interaction in most real processes it is necessary to conduct

confirming trials that involve the near optimal factor settings to make sure that the optimal settings are

found. However, even strong factor interactions are not necessarily fatal to the successful application of

the Taguchi technique.

Factor interactions are generally classified as synergistic and antisynergisfic as shown in Figure 4.

Synergistic interactions are such that the response varies in a consistent manner so that the Taguchi

Method finds the optimal factor levels but does not predict the proper response sinci_the interaction

violates the additivity rule. Antisynergistic interactions result in inconsistent factor effects which can result

in not finding the optimal factor levels.

The basic Taguchi Method cannot handle antisynergistic interactions since they violate the additivity rule.

However, it is possible to modify the technique to account for the' interactions by using one or more of the

columns in the orthogonal array to incorporate a new factor based upon the type of factor interaction that

is to be investigated, just as dummy factors can be used to improve error variance analysis. This technique

is not as elegant as that used in some of the surface response techniques, but it is simply a modification of

a technique that the students already understand rather than a brand new technique.

Randomization

Another major complaint about the Taguchi Method is that lack of randomization can lead to

systematic errors. The method does not use randomization so that fewer errors are caused by constantly

410
Re'sponse B3 Response B_

B_ B2

_B_ B3

A_ A2 A3 Al A2 A3

Figure 4 Synergistic (left) and antisynergistic (right) parameter effects

for a two parameter system. After Phadke. TM

setting and resetting the factor levels. The orthogonal arrays used in the Taguchi Method are designed so

that the first factor is changed quite infrequently so a difficult to change factor can be associated with it.

An example of this type of factor is a process temperature that requires a long time to stabilize.

Constantly changing the process temperature will either result in inaccurate temperatures or a very long

experimental procedure as the temperature is allowed to equilibrate.

Randomization can be employed in the Taguchi Method, particularly if none of the factors are difficult to

change or control. The first type of randomization involves randomly assigning the factor letters and level

numbers to the actual factors and levels. This procedure would allow a large series of experiments to be

conducted using the same orthogonal array and factor levels without repeating any one experiment, which is

very useful in a classroom setting. This type of randomization will not disrupt the mapping from the

factor setting to the factor level since the levels can be rearranged for plotting. For example, if

randomization yielded BI = 125°C, B2 = 150°C, and B3 = 100°C, the effects would be plotted in the

order B3, BI, Bz to more clearly show the relationships. The second type of randomization involves

conducting the trials in a random order. This technique will help eliminate systematic biases due to

instrument drift. However, it may cause problems with reproducibility since instrument drift is one of the

factors that must be accounted for when developing a stable process.

Limited Number of Arrays

There are only a limited number of arrays that are pairwise orthogonal and suitable for use with the

• Taguchi Method. Phadke I21lists 19 different orthogonal arrays involving four (four factors at two levels

each) to 81 (40 factors at three levels each) trials. However, many of these involve a large number of

factors so they are not particularly suitable to classroom use. Some of the smaller arrays that the author

has found useful in an academic setting are listed in Table Ill. First examination of this table indicates that

the possible number of factors and levels is quite limited. However, one or more of the factors can be

used as a dummy factor to decrease the number of factors and improve the error analysis in any of the

arrays. For example, if the last column of the L'16 array is a dummy, the experiment will examine four

factors at four levels each. In addition, two columns can be combined in some of the arrays to yield a

column with a larger number of levels. For example, the first and second columns of the L18 array can

be combined to create a column with six levels.

411
Table III Nomenclature of Orthogonal Arrays

Name Factors Levels Combinations Conditions

L4 3 2 8 4

L8 7 2 128 8

L9 4 3 81 9

L12 11 2 2,048 12

L16 15 2 32,768 16

L'16 5 4 1,024 16

L18 6, 1 3, 2 1,458 18

L25 6 5 15,625 25

Examples

The Taguchi Method using an L9 array has been used for the past two years to study the processing of a

semi-vitreous ceramic in the Mechanical Engineering Materials Science Laboratory Course at UNM as

described elsewhere, t41 The experiment serves as a very good introduction to both designed experiments

and ceramics processing. The students are told that the optimal product has both maximum strength and

minimum density, which also introduces them to the idea that compromises in product requirements are

often necessary. A total of seven different factors have been used during the four semesters so that the

same experiment is never done two consecutive semesters. The ranges for the factors are selected so that

they all have about the same effect on the response, which prevents the students from simply discarding a

factor as unimportant.

During the fall 1992 semester exactly the same variable factors and settings were used as during the

spring 1992 semester except that their assignment to the factor labels and levels were rearranged. This

resulted in examination of the same factor space using two different L9 array experiments. The results

from the two experiments were similar as shown in Figure 5. The differences between the results are

primarily due to interactions between the factors that are not accounted for by the Taguchi method.

7.50

,_ 5.00

2.50

0.00

_ 2.50

-5.00

-7.50

60 80 100 6 8 10 0 3 8 3 6 12

Composition (%) Solution pH Time (hrs) Rate (°C/rain)

Figure 5 Both the spring and fall 1992 factor effects on the strength of the semivitreous clay

bars where the composition is the percent of goldart clay used.

412
Confirming trials were run during both semesters to find the optimal processing conditions to maximize the

strength of the ceramic. The results of these experiments are shown in Table IV where the labels list the

semester, and if the trial was predicted, to give the first or second highest strength of the actual

maximum. It is seen that the agreement between the measured and predicted values is fairly good

particularly when the normal standard deviation of the strengths (--2-3 MPa) is taken into account. In

addition, the results were used to extend the factor space during the fall semester to longer times and

lower fractions of goldart clay. This resulted in some dramatically higher strengths as shown but the

results were much more variable.

Table IV Results of the Confirming Trials

Experimental Response (MPa) r/ (dB)

Conditions Measured Predicted Measured Predicted

Sp 1st 60 6 3 3 21.93 26.88 25.57 29.50

Sp 2"d 60 6 8 3 24.24 26.59 27.88 29.00

Sp Max 80 6 2 12 26.42 28.21

Fa 1st 60 6 8 3 27.73 25.90 28.77 28.81

Fa 2"d 60 6 51 3 21.22 24.90 26.43 27.62

Fa Max 45 6 8 3 34.44 N/A 29.92 N/A

A powder metallurgy experiment which also uses an L9 array has recently been developed** and will

be alternated with the ceramics experiment. It appears that this experiment will also serve as an excellent

introduction to both designed experiments and the sintering of materials. The copper based system used is

thermodynamically simpler than the semi-vitreous ceramic system so it will be possible to emphasize the

sintering process more in this experiment.

Conclusions and Recommendations

The Taguchi Method of experimental design and analysis is strongly recommended as both an excellent

tool to teach fractional factorial experimental design and as a research tool in Materials Science. The

simplicity of the technique allows the students to concentrate on the concepts behind fractional factorial

experiments and explanation of the experimental results rather than on the experimental design and

analysis. The computational simplicity also insures that the students do not have to use complex or

proprietary computer codes to design and analyze the results as is necessary with many other fractional

factorial experimental designs. The simplicity of the method also makes it possible for the practitioner to

use ANOVA to examine the quality of their results and to modify the method to adapt it to their particular

application.

The Taguchi Method is not the best experimental design method for all applications. However, it is a very

good method that is excellent for screening experimental factors to determine which ones merit further

investigation. It suffers from a number of disadvantagessuch as limited number of experimental arrays,

poor handling of factor interactions, and lack of explicit randomization that limit its utility. However,

many of the competing fractional factorial experimental design methods suffer from some of the same

Not one of the factor levels conducted in the L9 experiment. This effect was interpolated.

** Described elsewhere in this volume, tsl

413
limitations or are less efficient or significantly more complex. The ability to use the experimental design

system that is best suited to the investigation is a skill that must be taught to today's students. The

Taguchi Method is a good start in this process. We are in the process of expanding our use of statistical

design of experiments beyond the Taguchi Method to suit a variety of different applications.

References

1 Taguchi, G., Elsayed, E.A., and Hsiang, T.C.: Quality Engineering in Production Systems,

McGraw-Hill, New York, NY 1989

2 Phadke, M.S.: Quality Engineering Using Robust Design, Prentice Hall, Englewood Cliffs, NJ 1989

3 Ross, P.J.: Taguchi Techniques for Quality Engineering, McGraw-Hill, New York, NY 1988

4 Weiser, M.W., Lauben, D.N., and Madrid, P.G.: Ceramics Processing: Experimental Design and

Optimization, Gardner, J.E., Jacobs, J.A., and Stiegler, J.O., eds.: National Educators' Workshop:

Update 91, NASA, Washington, DC 1992, pp. 67-95

5 Sheldon, R., and Weiser, M.W.: Powder Metallurgy: Solid and Liquid Phase Sintering of Copper,

Craig, D.F. and Jacobs, J.A., eds.: NationalEducators" Workshop Update 92, NASA CP- , 1993

6 Weiser, M.W., Lauben, D.N., Madrid, P.G., and Fong, K.B.: Ceramic Processing Using Designed

Partial Factorial Experiments, to appear in Ceram. Engr. Sci. Proc., Am. Ceram. Soc., Columbus,

OH

7 Weiser, M.W. and Fong, K.B., Ceramics Processing Using Designed Fractional Factorial

Experiments, to appear in Am. Ceram. Soc. Bull., vol. 72, no 3, 1993

414
POWDER METALLURGY: SOLID AND LIQUID

PHASE SINTERING OF COPPER

Rex Sheldon

and

Martin W. Weiser

Mechanical Engineering Department and

Center for Micro-Engineered Ceramics

University of New Mexico

Albuquerque, New Mexico 87131

Telephone 505-277-2831

415

Powder Metallurgy: Solid and Liquid Phase Sintering of Copper

Rex Sheldon* and Martin W. Weiser*

Mechanical Engineering Department

University of New Mexico, Albuquerque, NM 87131

Abstract

Basic powder metallurgy (P/M) principles and techniques are presented in this laboratory

experiment. A copper based system is used since it is relatively easy to work with and is

commercially important. In addition to standard solid state sintering, small quantities of low

melting metals such as tin, zinc, lead, and aluminum can be added to demonstrate liquid phase

sintering and alloy formation. The Taguchi Method of experimental design was used to study

the effect of particle size, pressing force, sintering temperature, and sintering time. These

parameters can be easily changed to incorporate liquid phase sintering effects and some

guidelines for such substitutions are presented. The experiment is typically carried out over a

period of three weeks.

Key Words: Powder Metallurgy, Density, Copper, Solid State Sintering, Liquid Phase Sintering,

Uniaxial Pressing, Hardness

Prerequisite Knowledge: The student should have some basic background knowledge of diffusion in

solids and the microstructure of metals.

Objectives: The experiment demonstrates the fundamentals of powder metallurgy including the effect of

many of the possible process variables. These effects are:

a. effect of consolidation pressure on the density of the green compact,

b. effect of sintering time on the sintered density,

c. effect of sintering temperature on the sintered density,

c. effect of liquid phase additions on densification.

The Taguchi Method of Experimental Design is used to demonstrate a simple, high efficiency experimental

scheme. This allows both the experimental response and its reproducibility to be optimized concurrently.

Equipment and Supplies:

1. 8 to 15 mm diameter punch and die for compacting the powders °

2. Press capable of exerting enough force to yield a compaction pressure of 800 MPa (63 KN or

14,200 lbe for a 10 mm punch and die)

3. Programmable furnace capable of 1000°C with an inert atmosphere retort

4. Sieves to fractionate the copper powder. #325, (45 p.m), #200 (75 p.m), #100 (150 gm), #50 (300

p.m) and #30 (600/zm) work quite well.

This work was funded in part by a grant from the UNM Teaching Allocations Subcommittee.

* Now with the Department of Energy, Idaho Falls, ID

* Also affiliated with the UNM/NSF Center for Micro-Engineered Ceramics.

Plans for a relatively low cost punch and die set are presented in the Appendix.

417
5. Scale capable of measuring up to 20 g with an accuracy of 0.01 g (0.001 preferred).

6. Vernier caliper accurate to 0.1 mm or better.

7. Standard metallographic equipment and supplies for mounting, grinding, and polishing non-ferrous

specimens.

8. One kilogram of copper powder.

9. One hundred grams of lead, tin, zinc, or aluminum powders.

10. 100 cm2 copper foil

11. Cylinder of forming gas (2 to 4% H, in N2 which is non-flammable) and an appropriate regulator.

12. Lubricants and dispersants if desired (stearic acid, metal stearates, light machine oil, carbon powder,

ethyl alcohol, etc.).

Introduction and Background

Powder Metallurgy (P/M) is an important production technique for a wide variety of products including

inexpensive bronze bushings, W/Co cutting tools, and very expensive TiAI turbine blades. The P/M

process is used to create these parts for a number of different reasons, including the ability to create a

porous product that can contain a lubricant, a lower cost due to less waste material when creating complex

shapes, and difficulty in melting the metal due to either a high melting temperature or incongruent melting.

P/M techniques are very similar to the processes used to create many ceramic products since the ceramics

frequently have quite high melting temperatures.

The understanding of powder metallurgy has expanded greatly during the past forty years after

Kuczynski's pioneering study of the sintering of copper, cu Not only have P/M techniques undergone a

great deal of refinement, but new materials formed by P/M processes have been introduced. Metals that

are difficult or impossible to alloy by casting, such as certain superalloys, can be successfully alloyed via

P/M. tzl Cermets and cemented carbides, which are ceramics bonded together with a metal, are P/M

products. Tool steels and specialty steels which depend on a fine dispersion of a second phase constituent

can also be produced by P/M. Filtering mediums, self lubricating bearings, and friction materials depend

upon P/M technology to create unique products.

Materials processed via P/M techniques offer several advantages compared to materials cast from the melt.

Homogeneity and microstructural control are often superior for P/M processes compared to casting.

Energy, time, and material use are frequently more efficient in P/M since parts are produced "near net

shape". Scrap reduction and minimal finishing are particularly beneficial if the item is being manufactured

from expensive stock or difficult to machine materials. P/M parts can be forged, extruded, heat treated,

and machined like cast parts to achieve particular properties, but the operations are normally significantly

faster and more economical for the P/M part.

The largest P/M segment by volume is for ferrous alloys, although there are other important materials that

incorporate P/M in their processing. Since many of the basic considerations and parameters in P/M are

quite Similar for different alloys, a good grasp of the basics can be achieved by demonstrations with simple

systems. Iron, aluminum, zinc, tin and copper powders, for instance, are relatively cheap, available, safe

and easy to use. Insight into the fundamentals of P/M can be gained by using these metals.

Copper is a typical P/M system with wide application, t3J A wide range of physical properties become

available through the proper use of P/M technology and copper powders. The list of copper based P/M

applications is too extensive to list except for a couple of examples. Copper sintered with iron and steel

powders produces a strong, corrosion resistant material with good machining qualities. Copper and tin are

418
used to produce porous bronze bushings. The pores are then impregnated with a lubricant to create a self

lubricating bearing. The biggest advantages of copper based P/M from the standpoint of this experiment

are that the processing is quite simple and a number of different alloying elements can be used to produce

different products with different properties.

The Powder Metallurgy Process

The powder metallurgy process consists of four primary steps" powder preparatj.'on, consolidation,

sintering, and finishing. A number of quite sophisticated powder preparation techniques are currently used

to manufacture metal powders of very specific chemistry and morphology. However, these are beyond the

scope of this experiment so commercial powders will be used. Compaction involves production of a

preform from the loose powders by mechanically pressing them at high pressure. Sintering consists of a

high temperature heat treatment to allow diffusion so that the particles can fuse together. The final step is

finishing of the part by standard metal fabrication techniques to produce the desired final dimensions or

surface finish. Limited details of the production, consolidation and sintering steps are given below with

further information on all of the steps available in references 4 through 7.

Powdered metals can be produced in a variety of ways. Atomization, electrolysis, hydrometallurgy, solid

state reduction and mechanical milling are the most important methods, t41 Each method results in a powder

with different characteristics. Cleanliness, range of particle sizes, particle shapes, internal particle

porosity, and surface oxides are functions of powder production and have a profound influence on the final

product. Consequently, the desired properties of the final product will determine the method of powder

production.

Powder consolidation can be done via a number of different techniques. In all cases the goal is to create a

preform known as a green compact which has the proper shape, a reasonable level of porosity, and enough

mechanical strength so that it can be handled. In all cases the powder is placed in a mold with the proper

shape and then pressurized to push the particles closer together and eliminate the porosity. The most

common consolidation techniques are uniaxial and isostatic pressing. The mold for uniaxial pressing is a

rigid cavity of constant cross section known as the die. The pressure is then applied by a pair of punches

which can have either smooth or contoured inner surfaces that just fit into the cavity. Either one or both

of the punches can move during the pressing operation. A single action punch and die results when only

one punch moves while a double action system involves movement of both punches.

The mold for isostatic pressing is a flexible bag in which the powder is placed. This bag of powder is

then compacted by placing it in a chamber and applying the pressure via a fluid such as nitrogen, water, or

oil. A lubricant such as a metal stearate can be used to reduce friction between the particles and tool wear

in both techniques but this normally results in a loss of "green" strength for the compact. There are

advantages and disadvantages to each technique. Uniaxial pressing is inexpensive and fast but it is limited

to relatively simple shapes that are no taller than they are wide unless inhomogeneities in the powder

packing can be tolerated. Isostatic pressing normally gives very homogeneous parts that can have quite

complicated shapes, but it is expensive and slow.

Sintering is a diffusional process that fuses the particles together. The strength of the part is almost

always increased dramatically (sometimes by 3 to 5 orders of magnitude) and the porosity of the part is

frequently reduced. Sintering can be either a solid state process where none of the components melt or a

liquid phase process where small portions of the powder melt. In either case the diffusion is driven by a

reduction in the total surface energy of the system, which is normally accomplished by replacement of

419
solid/vapor surface by grain boundaries. The advantage of liquid phase sintering is that diffusion is

normally a couple of orders of magnitude faster in a liquid than it is in the solid. However, there are a

number of rules involving the relative melting points and solubilities of the different components along

with the wetting behavior of the system that must be followed for the system to sinter well.tsl

In addition to enhancing the diffusion of the system, the liquid phase additive can dramatically enhance the

properties of the powder compact after sintering. Solid solution and precipitation strengthening are

common phenomena in metallic systems depending upon the solubility of the liquid phase in the solid

phase. In cermets such as WC/Co the metallic liquid phase dramatically increases the ductility of the

composite. Liquid phases that oxidize easily can leave fine oxide particles behind that both result in

precipitation strengthening and help control grain growth. The melting points and the effects of some of

the possible liquid phase additives for copper P/M are listed in Table I.

Table I Liquid Phase Additives for Copper P/M

Additive Tm(°C) Effects

Zinc 420 brass solid solutions and some intermetallics

Tin 232 bronze intermetallics

Aluminum 660 fine AI_O3particles to control grain growth and intermetallics

Lead 328 lubrication only, very limited solubility and reactivity, toxic

Sn/Pb alloys 183 both long term lubrication and intermetallic strengthening

The sintering rate increases exponentially with temperature for both solid sate and liquid phase since

diffusion is thermally activated. However, the rate of grain growth is also thermally activated (normally

with a different activation energy) so it will also increase as the temperature increases. This gives rise to

larger grains and potentially abnormal grain growth which can trap pores inside the grains. In nearly all

P/M systems there is an optimal combination of time and temperature which results in best properties for

the part. While theoretical considerations are useful for estimating the optimal time and temperature, tglthe

P/M process is quite complicated and empirical techniques are needed to determine the true optimum.

Experimental Design

This experiment uses the Taguchi Method of Experimental Design to examine how a variety of factors

affect the measured responses. This technique is used because it is very efficient and quite simple while

incorporating the concept that improvements in the reproducibility of a process are often as important as

improvements in the response. The largest disadvantages of the Taguchi Method are that randomization is

not employed and can introduce systematic errors and that interactions between the parameters are

ignored. However, the extreme simplicity more than compensates for these disadvantages, particularly

with regard to performing screening experiments and teaching the fundamentals of experimental design.

A Taguchi array experiment involves conducting a number of experimental trials (called trials from here

on) that each measure one or more responses for a given experimental condition (a particular combination

of factor levels). This experiment is presented using an L9 orthogonal array which investigates the effects

of four factors at three levels, each using a total of nine experimental trials rather than the 3`) = 81 trials

needed for a traditional full factorial experiment. This smaller number of trials allows the different trials

to be repeated to obtain information about the reproducibility of the process. Other orthogonal arrays such

as the L'16 (16 trials using 5 factors at 4 levels each) and the L4 (4 trials involving 3 factors at 2 levels

each) are also quite suitable to investigate the P/M process in either more or less detail respectively. In

420
any case, it will probably be necessary for the instructor and/or the student to consult additional references

on the Taguchi Method. The authors would like to recommend Appendix A of reference 10 as a fairly

simple treatment of the topic while reference 11 is much more detailed.

The L9 orthogonal array used in this experiment employs four factors at three levels each as shown in

Table II where the factors are listed as A, B, C, and D and the levels are assigned values of 1, 2, and 3.

The response or responses that will be measured and optimized will depend upon the nature of the

experiment being performed and will always be some form of the mean of the results for all of the

repetitions of each trial. One of the best responses to optimize is the Taguchi Signal-to-Noise function, -ii,

which strives to maximize the reproducibility of a property while achieving the "best" value of the

property. One of the most common cases is known as the more-is-better criteria where it is desirable to

maximize the property. In this case the response to optimize is given by

rl_tn = _101Oglo (1 ,=,____:) (1)

where there are n repetitions of the trial each yielding an individual response Yi- A consequence of the

formulation of Taguchi signal-to-noise function is that it is always desirable to maximize the value of )/.

Table II The L90rthogonal Array

Trial A B C D Response

1 1 1 1 1 Yt

2 I 2 2 2 Y2

3 1 3 3 3 Y3

4 2 1 2 3 Y4

5 2 2 3 1 Ys

6 2 3 1 2 Y6

7 3 1 3 2 Y7

8 3 2 1 3 Y8

9 3 3 2 1 Y9

Overall

Regardless of whether the actual response, y, or the Taguchi signal-to-noise ratio, r/, is to be optimized, the

effect of each parameter at each level is found by subtracting the average overall response, y" or

respectively, from the average response for the trials where the factor has been set to the level of interest.

This is illustrated for the case of factor C at level 3 which is known as effect c3. Factor C is set to level 3

in trials 3, 5, and 7 so the overall mean response is subtracted from mean response of these three trials as

shown in Equation 2.

Y3 -Y5 -)'7 (2)

c3- 3 Y"

The predicted response for any combination of factor levels can be found by adding the effects of each of

the factors at the desired h'.velto the mean response. Selecting the smallest effect for each parameter will

predict a minimum response, while selecting the largest effect will attempt to maximize the response. A

421
more accurate prediction is obtained when only the most significant factor effects are included in this

calculation as illustrated in the example at the end of this paper.

In all cases it is necessary to perform one or more confirming trials to determine if the predicted optimal

response is really the optimal response. The authors suggest that confirming trials be performed for the

best two or three sets of experimental conditions to help insure that minor interactions between the factors

do not result in a response that is less than optimal. Major interactions between the factors cannot be

handled by the Taguchi Method without modification and will show themselves as predictions of

impossible response values (negative strengths for example) and very poor correlation between the

predicted and actual responses once the confirming trials are performed.

Experimental Procedure

i. Determine which orthogonal array will be used, which factors will be constants, and which ones

will be varied. The factors that the authors have identified along with suggested ranges of values are

listed in Table III. Determine the settings for the constant factors and the levels.of the variable

factors.

Table III Experimental Variables and Potential Values

Copper Particle Size 45 - 1000/zm

Sintering Time 0 - 12 hrs

Solid State Sintering Temperature 700 - 1050°C

Heating and Cooling Rates 1 - 200°C/min

Liquid Phase Additives Ai, Zn, Sn, Pb

Liquid Phase Fraction 0 - 20 vol% (solids basis)

Liquid Phase Sintering Temperature T_ + 100°C

Consolidation Pressure 50 - 850 MPa

Consolidation Time 0 - 60 s

Lubricant Stearic Acid, Metal Stearates, or Light Oil

Lubricant Fraction 0- 1 vol% (solids basis)

2. Assign each of the variable factors a letter from those listed for the orthogonal array that is to be

used. This can either be done by randomly selecting the letter for each factor or by using A for the

most difficult factor to vary and so on. The former approach is favored when there are apt to be

systematic errors, but _the latter is favored when changing some of the factor levels is difficult or

subject to error.

3. Determine the theoretical density of the solids in the green compact for each composition to be tested

using the rule-of-mixtures. For example the density of solids in a compact composed of 90 vol% Cu

(p = 8.96 g/cm 3) and 10 vol% Zn (7.13 g/cm 3) would be 0.9 x 8.96 + 0.1 x 7.13 = 8.78 g/cm 3.

422
4. Determine how much powder is needed for each pellet and then how much powder is needed for

each trial based upon the number of repetitions to be performed (5 to 10 are recommended). If a

cylindrical punch and die are used, the mass of each pellet will be

0.60 p .nd2h (3)

mp = 4

where p is the density of the metal powder in g/cm3, d is the diameter of the pellet, h is the

estimated height of the pellet which should be approximately equal to the pellet diameter, and the

green density of the pellet is assumed to be roughly 60% of the theoretical density of the metal.

Approximately 10 to 20% should be allowed for waste when the total powder mass is calculated.

5. Sieve the metal powders into the different size fractions desired. This is done by making a stack of

sieves ranging from the smallest opening (largest size number) at the bottom to the largest opening at

the top. A pan is placed at the bottom of the stack and one or two sieves that are larger than the

size of the largest desired sieve are placed on the very top of the stack. The powder is then added

to the top of the stack and the stack is shaken and tapped for a period of time to allow the finer

particles to reach the bottom of the stack. The exact amount of time required depends upon the

powder and the size of the smallest sieves. For metal powders that are larger than 45 #m a couple

of minutes should suffice.

Powders that have been classified by sieving are labeled as +(the smaller sieve) -(the larger sieve)

to indicate that they passed through the larger sieve but did not pass through the smaller sieve. A

powder sample that passed through a 200 mesh sieve and remained above a 325 mesh sieve would

be labeled +325 -200 mesh. This can be stated as +45 -75 ,u.mwhich yields more information

about the actual size of the particle but it is not as precise since the listed size of a sieve is an

average with a coefficient of variation of approximately 10%.

6. Mix the different metal powders together and disperse the lubricant around the particles. Dispersion

of the lubricant is best accomplished by dissolving it in an appropriate solvent (typically an alcohol),

mixing this solution with the metal powder, and drying the mixture.

7. Make tubes with one closed end out of copper foil to contain the powder if any low consolidation

pressures (< 300 MPa) are to be used. These tubes are best made by wrapping a rectangle of

copper foil that is 5 x diameter by 4 x height around the end of a mandrel that is slightly smaller

(-- 10 x the foil thickness) than the punch and then carefully folding the end of the tube over to

close it. Do not be tempted to substitute aluminum foil for the copper foil as this will result in

liquid phase sintering of the outer surface and constrained sintering of the interior of the pellet and

will give erroneous results as the authors found out experimentally.

8. Place the bottom punch in the die and insert the copper tube with the open end up if it is being used.

Use the mandrel to push the tube out against the inside of the die, pour in the proper mass of

powder, and use a pointed rod to fold over the top of the tube. Insert the upper punch, place the

punch and die set on the press, and load it to the appropriate force based upon the desired pressure

and die size. Holding the pressure for roughly 15seconds allows the powder particles to rearrange

and results in more uniform pellets, but this is a factor that can be varied.

9. Eject the pellet from the punch and die by placing it on either a pair of blocks or a short piece of

pipe and loading it to push the bottom punch and the pellet from the die. After the pellet has been

423
ejected the interior of the die and exterior of the punches must be cleaned to prevent the build up of

film from the powder being pressed and will eventually result in seizure of the punch in the die.

10. Measure the green density of the pellets by either measuring the mass and outside dimensions of the

pellets with vernier calipers or via Archimedes' method_12Jif the copper tubes were not used.

Archimedes' method is slightly more accurate but slower and can result in the pellets falling apart,

particularly if a lubricant or lower consolidation pressures were used.

11. Fire the pellets in an inert atmosphere retort with a small flow of forming gas (2 - 4% I-I2in N2).

Heating and cooling rates of roughly 5 to 10°C/min can be maintained by most systems and result in

experiments requiring a reasonable length of time. Rates of greater than 50°C/min almost always

involve moving the pellets in and out of a preheated furnace which is slightly more difficult as

copper will oxidize rather badly at temperatures above 400°C in air.

12. Measure the fired density of the pellets as in step #8. Archimedes' method is facilitated by grinding

off at least a portion of the copper containment tube if it was used.

13. Grind off one end of the pellet to expose a surface that is more representative of the bulk of the

pellet rather than the as fired surface of the pellet. This is particularly important if the pellets were

encapsulated in copper foil.

14. Measure the hardness of the fired pellets to get an idea of their strength. The Rockwell A scale test

is the best for this application since the indentor is big enough to measure the bulk hardness rather

than the local hardness which depends upon whether the material under the indentor is in copper,

alloy, alloying agent (AI, Zn, Sn, or Pb), or void. In addition, the load is low enough to avoid

crushing the pellet. Three to ten measurements should be taken on each pellet to obtain a

representative value. Measurement of the Vickers or Knoop hardness can be done to determine the

relative hardness of the different phases that are present.

15. Mount, grind, and polish one of the ends of the pellet to obtain a surface that is representative of the

bulk of the pellet. Mount the pellet with the ground end exposed in epoxy via vacuum impregnation

to fill the pores with epoxy. The sample is then fine ground and polished using light pressure and

adequate lubrication to avoid smearing the soft metal. Ultrasonic cleaning between the grinding and

polishing steps helps to remove metal that has been smeared and better reveals the microstructure.

16. Calculate the factor effects from the responses for the different trials. The authors strongly suggest

computation of the effects for both the actual response and the appropriate Taguchi signal-to-noise

function to allow comparison of the effect of the different factors on these related responses.

17. Determine the combination of factors that results in the optimal response or responses and the

second and third best responses. Remember that the Taguchi signal-to-noise function should always

be maximized.

18. If the predicted optimal combinations of factors were not one of the initial trials (they rarely are)

perform the confirming trials corresponding to these experimental conditions.

19. Compare the results for the confirming trials to the predicted results. If the values are fairly close

the system can be assumed to abide by the additivity constraint impose by the Taguchi method. If

424
the results do not agree, there are probably strong factor interactions and further investigation will

be necessary to determine the true optimal combination of factors. However, these results will be

very useful in designing the additional experiments necessary to find the true optimum.

Preliminary Experimental Results

Mr. Rex Sheldon developed this experiment and performed it using an L9 orthogonal array during the fall

1991 semester. The factors that he varied and his experimental results are presented below to illustrate the

type of results that might be obtained and a few aspects of the Taguchi analysis. It must be pointed out

that the use of different variable factors and/or different factor levels may yield dramatically different

results. This has the advantage of providing a different experiment each academic term so thata standard

laboratory report cannot be developed but it can present some problems to the instructor who must

explain results that occasionally make little or no sense, particularly if strong factor interactions occur.

The factors and the levels used in this version of the experiment are presented in Table IV where the four

variable factors are labeled A, B, C, and D. The raw experimental results are presented in Table V while

the Taguchi analysis is presented in Table VI and graphed in Figure 1. Only the density is presented in

Figure 1 since the _ effects are very similar. It is seen that the finest particles densify the best as

predicted by theory and that higher compaction pressures result in higher densities as predicted. Heat

treating at 850°C gives the best densification, which is probably a result of the competition between

densification and grain growth. Maximum densification after just one hour heat treatment is somewhat

surprising since longer heat treatment normally results in better densification at these moderate

temperatures, t_ This effect may be the result of factor interactions that will have to be investigated in

more detail.

Table IV Experimental Factors and Levels

A - Particle Size (p.m) 25 - 74, 149 - 250, 600 - 833

B - Consolidation Pressure (MPa) 113, 226, 252

C - Sintering Temperature (°C) 750, 850, 950

D - Sintering Time (hrs) 1, 2, 4

Liquid Phase Additive None

Lubricant 0.1 vol % light machine oil

Consolidation Time (s) 15

425
Table V Experimental Data for the Fired Density of the Copper Compacts

Levels Replications

Trial A B C D 1 2 3 4 5 6 Mean 7/Mn

(g/cm3) (dB)

1 1 1 1 1 6.919 6.882 6.862 6.971 6.919 6.911 16.790

2 1 2 2 2 7.564 7.589 7.630 7.556 7.550 7.606 7.583 17.596

3 1 3 3 3 8.410 8.385 8.375 8.347 8.31'8 8.123 8.326 18.407

4 2 1 2 3 6,116 6.120 6.070 6.131 6.085 6.276 6.133 15.752

5 2 2 3 1 7.186 7.079 7.082 7.125 7.083 7.223 7.130 17.061

6 2 3 1 2 7.541 7,445 7.385 7.512 7.364 7.449 17,441

7 3 1 3 2 5.606 5.977 5.924 5.801 5.883 6.231 5.904 15.409

8 3 2 1 3 7.374 7.031 7.075 7.252 7.168 7,180 17.119

9 3 3 2 1 8.213 8.150 8.027 7.986 8.071 8.022 8.078 18.145

Overall Means 7.188 17.080

Table VI Taguchi Analysis of the Fired Density of the Copper Compacts

Factor Fired Density (g/cm 3) r),_ (dB)

1 2 3 1 2 3

A 0.418 -0.284 -0.134 0.518 -0.329 -0.189

B -0.872 0.109 0.763 -1.096 0.178 0.918

C -0.008 0.076 -0.068 0.037 0.084 -0.121

D 0.185 -0.210 0.025 0.252 -0.264 0.013

426
,.., 1.00

,_ 0.75

>, 0.50

= 0.25

©

"_o 0.00 _,_ -

•" -0.25

=o-o.5o

o -0.75

-1.00 - I i I _ I r I _ r I I I I _ f T I I t ' I

50 200 717 113 226 552 750 850 950 1 2 4

Size _m) Press (MPa) Temp (oC) Time (hrs)

Figure 1 The factor effects on the fired density of copper powder.

Examination of the data in Table VI and Figure 1 shows that the consolidation pressure and particle size

are the most significant factors in this experiment. The relative significance of the factors is a function of

the range of levels used for each factor so the relative significance can be changed by changing the range

of levels. The maximum density and value of _7,_mwere predicted based upon this data using the overall

mean and the maximum effect for factors A and B. The maximum effects for factors C and D were not

used in this prediction even though these factors will be set to their best level for the confirming trial.

Experimental condition alb3c2dtwas predicted to give the largest values of both the density (8.369 g/cm 3)

and r/_m(18.516 dB).

This optimal experimental condition had not been investigated as one of the original nine trials so a

confirming trial was required. Unfortunately, this trial was not performed due to time constraints.

However, a series of three experiments examining the density as a function of particle size were

performed. The results for these experimental conditions and the predicted density for each are presented

in Table VII. It is seen that the predicted and experimental densities do not directly correspond.

However, the lowest experimental and predicted densities both occur for condition a,_b3c3d3which is

promising. This is a result of the moderate sized particles neither packing well in the green state due to

their small size, or sintering well due to their large size.

Table VII Predicted and Experimental Density as a Function of Particle Size

Condition Particle Size Predicted Density Experimental Density

(/zm) (g/cm3) (g/cm 3)

atb3%d3 25 - 74 8.369 7.39

a2b3c3d3 149 - 250 7.667 7.27

a3b3c3d3 600 - 833 7.817 7.91

427
Conclusions

An experiment which explores many of the issues involved in powder metallurgy (P/M) has been

presented. It utilizes the Taguchi Method of Experimental Design to allow both experimental repetition

and a larger number of variables to be explored at one time than is possible using traditional full factorial

experiments. The experimental results do not directly follow from theoretical considerations, which points

out the complexity of the P/M process. Information on possible liquid phase additions to the copper

system used is also included since liquid phase sintering is a very important issue in P/M.

References

1 Kuczynski, G.C.; Self Diffusion in Sintering of Metallic Particles, Met. Trans., vol. 185, 1949, pp.

169-78

2 Lherbier, L.W. and Kent, W.B.; P/M Superalloys: Technical and Economic Considerations, Int. J.

Powd. Metall., vol. 26, no, 2, 1990, pp. 131-37

3 Everhart, J.L.: Copper and Copper Alloy Powder Metallurgy Properties and Applications, Technical

Report: Copper/Brass/Bronze, Copper Development Assn. Inc., NY

4 Bradbury, S., ed.: Sourcebook On Powder Metallurgy, American Society for Metals, 1979

5 Hausner, H.H.: Handbook of Powder Metallurgy, Chemical Publishing Co., New York, NY, 1973

6 Kiar, E.: Powder Metallurgy - Applications, Advantages and Limitations, American Society_for

Metals, 1983

7 Yarton, D. and Argyle, M. : A Practical Course in Powder Metallurgy, Cassel & Company, Ltd.,

London, 1962

8 German, R.M.: Liquid Phase Sintering, Plenum Press, New York, NY, 1985

9 Ashby, M.F.: A First Report on Sintering Diagrams, Acta Metal., vol. 22, 1974, pp. 275-89

10 Weiser, M.W., Lauben, D.N., and Madrid, P.G.: Ceramics Processing: Experimental Design and

Optimization, Gardner, J.E., Jacobs, J.A., and Stiegler, J.O., eds.: National Educators' Workshop:

Update 91, NASA, Washington, DC 1992, pp. 67-95

11 Phadke, M.S.: Quality Engineering Using Robust Design, Prentice Hall, Englewood Cliffs-, NJ 1989

12 Jordan, G.W.: Adapting Archimedes' Method for Determining Densities and Porosities of Small

Ceramic Samples, Harris, J.S. and Jacobs, J.A., eds: National Educators' Workshop: Update 90,

NIST, Washington, DC 1991, pp 175-82

428
Appendix Punch and Die

The design of the simple single acting punch and die set used in the Powder Metallurgy Experiment is

presented here. This punch and die set is designed to be inexpensive and easily refurbished while

maintaining tight tolerances using hardened steel for the wear surfaces. This is accomplished by making

both top and bottom punches from drill rod and the die liner fi'om a drill bushing while the support block

and cap are machined from a medium carbon steel such as AISI 1040. The punch and die set are designed

to yield a pellet that is nearly 1 cm in diameter. However, the dimensions can be changed to produce sets

covering a wide range of pellet diameters.

There are five parts used to make the punch and die set that are described below. It is strongly

recommended that the drill rod and drill bushing be obtained before the rest of the parts are machined so

that the dimensions can be modified to account for different sized parts. In addition, the drill rod and

bushing must be stored in a dry environment such as in a desiccator since the# corrode quite easily.

I

Top Punch

0.375 ---> 1"_-=--

2 -

"---'1 _ Support Block

• _ Bottom Punch

< 2.00 >[

Figure A.1 The punch and die described in this Appendix and used in the experiment.

1. Top Punch 0.375" diameter x 2.5" long polished drill rod with both ends polished perpendicular

to the axis of rotation. In addition, a fiat should be ground on one end so that the cap can be affixed

with a set screw.

2. Bottom Punch 0.375" diameter x 0.5" long polished drill rod with both ends polished

perpendicular to the axis of rotation.

3. Die Liner 0.375" ID drill bushing (ours is 2.125" long) which is made from hardened steel with a

polished interior surface. It is important that the drill bushing have a smooth interior rather than a

stepped interior which is used to assist in chip clearance during drilling.

4. Support Block 2.0" diameter × 2.125" long low to medium carbon steel block. This should have

a hole bored along its axis of rotation to press fit the drill bushing. Our drill bushing has an OD of

429
0.751" so the hole was bored 0.750". The precise amount of interference depends upon the

diameter and can be found in most machining handbooks.

5. Cap 1.0" diameter x 0.5" long medium carbon steel with a 0.375" diameter x 0.25" deep hole in

one face and a set screw (not shown in the figure) into this hole from the side. The cap should be

hardened to prevent deformation by the upper punch at higher loads. The cap should be machined

in an annealed or normalized state including chasing the threads for the set screw. The cap can then

be hardened by heat treating at = 900°C (orange-red) and quenching in oil. The cap can be made

from any scrap of steel that can be hardened with the heat treatment temperature depending upon the

material.

The punch and die must be kept clean to prevent contamination and galling even though they are made of

hardened steel. Galling can be a major problem when hard powders such as ceramics are being pressed.

One of the greatest advantages of the method of punch and die construction presented here is that it is

relatively simple to replace the punches and the die liner when they become worn or galled. Replacement

of the die liner is accomplished by pressing the old liner out of the support block and pressing in a new

liner. Since the liners only cost a few dollars each this allows replacement when wear makes the punch

and die difficult to use rather than having to try to get a few more pellets from the system. However, with

care and cleaning the punch and die should last quite some time. Ours has been used to press in excess of

1000 pellets including many from hard ceramics.

430
HIGH THERMAL CONDUCTIVITY OF DIAMOND

Patrick M. Stephan

Business Development Manager

Norton Diamond Film

Goddard Road

Northboro, Massachusetts 01532-1545

Telephone 508-351-7600

431

HIGH THERMAL CONDUCTIVITY OF DIAMOND:

DEMONSTRATION AND COMPARATIVE ANALYSIS

Patrick M. Stephan

Norton Diamond Film

Northborough, Massachusetts

KEY WORDS: diamond, copper, thermal conductivity, thermal

diffusivity

PREREQUISITE KNOWLEDGE: The student should understand

the principles of heat flow and thermal conductivity of materials,

either previously learned or learned concurrently with the experiments.

OBJECTIVES: To demonstrate the high rate of heat flow from

a synthetic diamond coupon and to compare it to a commonly used

thermal conductor, such as copper. The principles of heat transfer

by conduction and convection may also be demonstrated.

EQUIPMENT AND SUPPLIES: (1) Coupons of synthetic

(chemical vapor deposited, or CVD) diamond and pure copper,

approximately 12-25 mm long, 12 mm wide and 0.3-0.5 mm thick;

(2) Voltmeter with digital readout and data collection and storage

capability; (3) Low thermal input cable with bare wires on one end

and voltmeter converter connection; (4) Two Type T thermocouples

(copper-constantan) with 0.005 in. or 0.010 in. diameter, 12 in. long

wires (apply teflon insulation to bare wires); (5) Temperature

conversion table for Type T thermocouples; (6) Silver epoxy (having

high thermal conductivity) for attaching thermocouples to coupons;

(7) Beaker or cup of icewater; (8) Stand with clip to hold coupons

during experiment; (9) Regular and two-cycle semi-log graph paper.

PROCEDURE: Some preparation is required prior to conducting

the experiments. The thermocouples must be firmly attached to the

diamond and copper coupons using the silver epoxy. The tip of the

thermocouple should be placed against the coupon surface and should

be 3 - 5 mm from either end of the coupon. The beaker of icewater

should be prepared and its temperature should be stabilized.

433
The apparatus for the experiments may be arranged as shown

in Figure 1. Note that the reference thermocouple junction must be

immersed in the icewater. The copper thermocouple wires must be

attached to the copper leads from the voltmeter cable and the

reference thermocouple must be connected to achieve the correct

polarity (this will be obvious from the voltmeter readout).

Voltmeter

,_- .Thermocouple

Sample

Coupon

Reference

Thermocouple

iliiiiii!i Icewaler iiii_i!iii!

:::::.._iiii::Bath ! _i!i_ ........... ._ii!:.!:

Figure 1. Experiment Setup

The sample coupon is held in a stand with an arm having vertical

movement capability. The coupon should not be held above the beaker of

icewater prior to data collection. The voltmeter should be set up for the

diamond experiment to take data at 0.1 second intervals for at least 30

seconds after immersion of the coupon into the icewater. For copper,

data may be collected for 60 seconds at 0.2 second intervals.

When the voltmeter is set up and ready to trigger for data

collection, the sample coupon is rapidly positioned for immersion of one

end, allowing a distance of 5-15 mm between the water and the

thermocouple tip when immersed. The vottmeter is triggered for data

collection, allowing no more than two seconds before the coupon is

immersed 2-5 mm into the water. At the end of the data collection

period, the sample is removed from the water and the data can be

retrieved. The experiment can be enhanced for the students if they can

434
"feel" the coupon before and after the experiment and watch the digital

readout change values during and after the experiment.

Data can be retrieved manually or digitally, if convenient. Data for

the diamond and copper experiments may appear as shown in Figure 2

when plotted on regular graph paper or as in Figure 3, when plotted on

two-cycle semi-log paper.

o.9 _

o.e T _" " Diamond

0.7 t _.

0.6 +,o _ ., " Copper

o.oT'-. • .

-

- , ,,,,,,,. , ; I I

0 10 20 30 ,40

Time, _econds

Figure 2, Thermocouple Oulpul Versus Time for

Sample Coupons Immersed In Ioewater

I 2_ a

II ?1_11 • • •

.°!, uu

"6 .- mZ

._ L._ •

E o., ._ m • Diamond

.," g. •

E • Copper

0

II

II

O.OI I I I I I , I • I ,I

0 5 I0 15 20 25 30 35 40

Time, seconds

Figure 3. Themxx_ouple Output Versus Time IceSample

Coupons Immersed In Icewater

This first experiment (diamond and copper coupons) demonstrates

heat flow by conduction(I) according to the second law of thermodynamics and Fourier's simplified law of conduction:

435
q =kA (T2- T1)/L (1)

Where q = heat transfer rate (in J sec-1)

k = thermal conductivity (in Watts cm-1 K-l)

A = cross-sectional area (in cm2)

T -- temperature (in degrees K)

L = path length of heat flow (in cm)

This equation assumes a steady-state condition where the material

is surrounded by a perfect insulator except at two faces. Temperature

T2 is higher than T_ at different locations along the heat flow path due

to a thermal gradient. Since this is a steady state condition, there is no

external thermal input to the material and there is no internal source of

energy. It is also assumed that the material is isotropic, although the

CVD diamond is anisotropic due to the directional nature of crystal

growth during deposition.

Other simple experiments may be conducted to demonstrate the

principles of heat transfer. Students should note their observations

while conducting the following experiments.

Repeat the first experiment, while decreasing by one-half the

distance from the water to the thermocouple tip. Plot the graphs and

compare them to the graphs from the first experiment. Place an end of

the diamond sample into the icewater and move the sample up and down

in the water while observing the mfllivolt readings on the voltmeter.

Data collection is not necessary.

Place a finger at various locations on the sample and notice the

change and rate of change of temperature in the coupon, as determined

from the voltmeter readings.

Convection of heat may be illustrated by simply blowing warm air

(or breathing) onto the diamond coupon and observing the voltmeter

readings. Also, by placing the diamond sample immediately above, but

not touching the icewater bath, a change in temperature of the diamond

may be observed due to convection.

DATA ANALYSIS: The data plots shown in Figures 2 and 3 indicate

a substantial difference in the rate of temperature change for the

436
diamond coupon compared to that for a copper coupon of nearly the same

size and with the same thermocouple location relative to the ice bath.

One might assume that this observation is due to a fundamental

difference in thermal properties for the two materials. In fact,

equation (1) shows the relationship of thermal conductivity to heat

flow and temperature gradient. While it is not the intent of this

experiment to calculate the value of thermal conductivity for the

diamond, based on the data collected, it is mathematically possible to do

so from the data generated in this experiment.

From the literature and in-house measurements (2,3), Table 1 can be

constructed for the thermal properties of diamond and copper. Thermal

conductivity is often derived from thermal diffusivity data measured by

laser flash techniques. Thermal conductivity is related to thermal

diffusivity by the following equation:

o_= k/(p Cp) (2)

where

o_--- thermal diffusivity

k = thermal conductivity

p = specific gravity

Cp --- specific heat

Table 1. Thermal Properties of Diamond and Copper

Material SpecificHeat Bulk Density Thermal Diffusivity Thermal Conductivity

j g-1K-I gcm_ crn2sec-1 Wcm-1K-1

CVD Diamond 0.50 3.51 5.70 10.00

Pure Copper 0.38 8.92 1.10 3.88

The slope of the data curve for diamond in Figure 3 is nearly a

straight line, indicating that the rate of temperature change is fairly

constant according to an exponential equation. The slope for the copper

data is not constant, perhaps indicating that factors such as convection

of heat around the copper was significant compared to the the heat loss

to the ice bath through conduction. Also note that the temperature

registered by the thermocouple attached to the diamond approached the

temperature of the icewater, while the asymptotic temperature for the

43'7
copper was nearly 5 degrees higher. This illustrates the rapid thermal

transfer and "heat spreading" capability of diamond compared to another

material more commonly used for heat transfer engineering solutions.

SAMPLE DATA SHEETS: In the case of manual data retrieval from

the voltmeter, data sheets ca.n be arranged with headings for data point

number, seconds elapsed, millivolt readings and corresponding

temperature (read from the conversion chart). The graphs are selfevident, being plots of millivolt readings versus time. It might be noted

that data does not need to be written on the sheets for every data point

in the register. Sufficient data is taken to plot a smooth curve by hand

or computer. Programs such as Lotus 123 or Excel can be used to

organize and plot data.

INSTRUCTOR NOTES: This experiment is simple enough to

demonstrate the principles of heat transfer and thermal conductivity

for materials having reasonably high thermal conductivity values. It

should be obvious that the experiment would yield practically no data

for materials having much lower thermal conductivity. Using another

common material for the experiment, such as a glass microscope slide,

would further illustrate the significant difference in thermal

conductivity among engineering materials.

Many textbook cases(I,3) analyze the case of heat transfer or thermal

conductivity for flat planes or slabs of materials through the thickness,

rather than along a plane perpendicular to the thickness plane as

considered in these experiments, although the approach and solutions

are similar. Many different methods are used to measure thermal

conductivity (or diffusivity) for materials having a wide range of

thermal characteristics. Anisotropic materials, such as CVD diamond,

are difficult to measure with consistency by different methods.

Touching the samples during the experiments and observing the

sensitivity of the diamond to slight temperature changes is an

important part of the experiment. While natural diamond is

prohibitively expensive in large sizes, high purity synthetic diamond

made by chemical vapor deposition having thermal, mechanical and

optical properties similar to natural diamond is available in sizes up to

10 cm diameter and up to 2 mm thick. This is expected to revolutionize

many industries, particularly the electronics industry, where thermal

438
management is critical to advancement of computing systems operating

at higher power levels in smaller packages. A working knowledge of

thermal characteristics of materials is used by many scientific and

engineering disciplines, as well in everyday life f

REFERENCES:

(1) Sucec, J., Heat Transfer, Wm. C. Brown publishers,

Dubuque, Iowa, 1985

(2) Weast, R.C., ed., CRC Handbook of Chemistry and Physics,

CRC Press, Boca Raton, Florida, 1988

(3) Lu, G. and Swann, W.T., Measurement of Thermal Diffusivity

of Polycrystalline Diamond Film By the Converging Thermal

Wave Technique, Applied Physics Letters, 59 (13), Sept. 23,

1991, pp 1556-1558

SOURCES OF SUPPLY:

The diamond wafers were made by a DC Arc Jet Plasma CVD process

by Norton Diamond Film in Northboro, Massachusetts.

The digital voltmeter (model 182) and cable used in these

experiments were made by Keithley Instruments of Cleveland, Ohio. The

thermocouples and wire insulation used were made by Omega

Engineering of Stamford, Connecticut. The silver epoxy (DY 325) was

made by Zymet in East Hanover, New Jersey.

The other materials are commonly available from supply houses.

439

TEMPERATURE-DEPENDENT ELECTRICAL

CONDUCTIVITY OF SODA-LIME GLASS

L. Roy Bunnell

Battelle

Pacific Northwest Laboratories

P. O. Box 999 MSIN P8-44

Richland, Washington 99352

and

T.H. Vertrees

Kennewick High School

Kennewick, Washington

441

TEMPERATURE-DEPENDENT ELECTRICAL CONDUCTIVITY

OF SODA-LIME GLASS

L. Roy Bunnell

Pacific Northwest Laboratory, 1 Richland, WA

T. H. Vertrees

Kennewick High School, Kennewick, WA

KEY WORDS: glass, ceramics, silicon carbide, electrical conductivity

PREREQUISITE KNOWLEDGE: This material is suitable as a

demonstration for typical students of chemistry, physics or materials science

at the high school level or above. Additional depth could be provided by

comparisons of temperature-conductivity behavior with typical metals and

other ceramics, or by using a DC power supply to observe polarization

effects as described below.

OBJECTIVE: To demonstrate the difference between the electrical

conductivity of metals and ceramics.

EQUIPMENT AND SUPPLIES: Listed below are the materials required

to conduct the project.

• strips of ordinary window glass, either single or double strength,

approx. 1 x 5 cm

• 10 to 12-gauge copper wire

• 75- or l O0-watt light bulb

• socket mounted on wooden block

• wood screws to mount contact wires

• electrical cord and plug

• propane torch to heat glass

PROCEDURE: Begin by reviewing the principles of current conduction

through water when ions are present. Next, discuss the difference between

electrical conduction in a metal (free or delocalized electrons) and a glass or

ceramic (in glass, ions; in other ceramics, either ions or electrons). Figure 1

or its equivalent should be used to clarify the great difference in the

temperature dependence of electrical resistivity (the reciprocal of electrical

conductivity) of metals and ceramics, resulting from these different

_Pacific Northwest Laboratory is operated by Battelle Memorial Institute for the

U.S. Department of Energy under Contract DE-AC06-76RLO 1830.

443
O = Sods-Llme-Alumlnoslllcate Glass

• : CaO-Stabilized ZrO2

It = Iro.

12

11 Temperature, °C

250 SO0 1000 2000

lo I I ....I I I I

-3 O

4 _ _

-5 I 1

20 10 0

1/1",K'lxl04

FIGURE 1.

444
mechanisms. Note the log scale on the resistivity axis, necessary to show

the large change in the electrical resistivity of the glass or zirconium dioxide

ceramic. The electrical resistivity of the metal increases by a factor of about

13 over the temperature range, although it is not obvious because of the log

axis. This increase is caused when electrons are impeded by vibrating iron

atoms; these vibrations increase with temperature. The current carriers

present in ceramic materials are bonded too strongly to conduct much

electricity at low temperature, but at higher energy (temperature) they

become increasingly mobile and able to carry more current.

The instructor or students should build the simple apparatus shown in Figure

2. The light bulb, which is in the series circuit with the specimen, provides

a visual indication that the resistance of the specimen has dropped enough

that the current passing through the bulb filament is about 1 ampere. The

bulb also provides a current limiter.

Insert the glass specimen into the wire contacts as shown in Figure 2, so

that 1 to 2 cm of glass is between the contacts. Plug the tester into a 110-

V outlet, and observe that the light bulb does not glow. Depending on the

students' background, it may be useful to insert an AC ammeter into the

circuit to provide another indication of current flow. The current through the

light bulb is very low, because most of the voltage drop is across the glass

specimen. Next, the instructor ignites the torch and carefully heats the

glass, keeping the flame moving to avoid breaking the glass by thermal

shock. The entire length of glass between the contacts should be heated,

especially the contact areas. At about the time the glass begins to glow,

the bulb will light. Increased heating will brighten the bulb, indicating that

the glass is a better conductor as the temperature increases. If torch

heating is discontinued, the bulb will continue to glow for a few minutes,

indicating that the glass is being heated to some extent by its own electrical

resistance to the current passing through it. The glass will finally cool to the

point that it will no longer conduct sufficiently to light the bulb. As the

glass cools, it may be possible to observe what appear to be tiny sparks

inside the glass; these can be quite beautiful and are probably caused by

plasma discharges across bubbles or cracks in the glass.

Ordinary window glass is a "soft" glass that contains a relatively large

percentage of ions, such as sodium, that conduct current when the glass is

heated. Other glasses have different temperature dependence of electrical

conductivity; a borosilicate glass such as Pyrex, for instance, may be

difficult to heat sufficiently to light the bulb. Fused silica contains no added

fluxing agents, and so is a thousand times less conductive at 1000 Kelvins

than the soda-lime aluminosilicate glass shown in Figure 1.

The temperature dependence of electrical conductivity in other ceramics can

be demonstrated using the same apparatus as for the glass. A 0.3-cm rod

445
Circuit Schematic

Specimen

Nichrome or

Copper

Mounting Board

Pictorial

F,IGURE 2.

446
of zirconium oxide, if carefully heated, will conduct sufficiently to light the

bulb. The conduction mechanism in this case is the movement of oxygen

ions between oxygen vacancies in the structure. Alternatively, a piece of

silicon carbide heating element or furnace igniter can be used; in this case

the conduction is by means of electrons that become able to move because

of thermal energy supplied by heating. For another comparison, a steel nail

of approximately 0.3-cm diameter will conduct over the entire temperature

range, and the bulb will not dim perceptibly when the nail is heated.

If the AC electricity is replaced by a DC power supply capable of 110 V,

2 A, some interesting effects occur in the window glass. After the current

flows for a few minutes, the glowing bulb will dim and will not conduct well

even if the glass is heated strongly. The glass will now show a dark stripe

at the negative contact and may show bubbles at the positive end. The

bubbles are oxygen, and the dark stripe is caused by silicon ions in the glass

that have been reduced to the metallic state. These effects occur because

the glass is being electrolyzed by the current, just as a bath of water would

be. If the glass is placed back in the contacts with its ends reversed (dark

end is now connected to the positive contact) and heated, current will

immediately flow upon heating because the polarized ends are now

connected to oppositely charged contacts. Current will flow until

polarization again occurs in the other direction.

SAMPLE DATA SHEETS: Not strictly applicable, though the demo

would be good source material for students' journals.

INSTRUCTOR NOTES: Supervise the students closely while they are

around live electrical circuits with bare wires. Always be certain that the

apparatus is unplugged when working around the wires. If the copper wire

contacts oxidize to the extent that contact resistance is too high for the bulb

to light, the oxide can be reduced simply by heating the wire, the inner blue

cone of the torch. The instructor may want to add this to the

demonstration.

REFERENCES: Vertrees, T. H., "Ceramics Conductivity," Technology

Focus, Fall/Winter 1991.

Touloukian, Y. S., ed., Thermophysical Properties of High-Temperature Solid

Materials, Vol. 1 and Vol. 4. MacMillan, New York, 1967.

SOURCES OF SUPPLIES: Most items mentioned here should be

available in a good hardware store.

Zirconium Oxide: One good source of the partially stabilized zirconium oxide

tubing or rod that is most resistant to thermal shock is:

447
Advanced Ceramics Technology

990F Enterprise St.

Orange, CA 92667

(714) 538-2524

(Order several pieces, 0.64 cm (1/4") diameter x 10 cm long, cost unknown

but likely less than $100 total).

Silicon Carbide: The most convenient and reasonable source of silicon

carbide, except for pieces of discarded SiC heating elements, is furnace

igniters made from the material. These are sized to operate on 110 volts,

and include a suitable base and connector wires. Connect the two lead

wires across the position normally occupied by the specimen in the test

apparatus and heat the SiC with the torch to start current flowing. Igniters

may be obtained for $25 or less from:

Igniter Systems, Inc.

12600 Clarence Center Rd.

Akron, NY 14001

(716) 542-5511

448
CONSTRUCTION AND TESTING OF SIMPLE

AIRFOILS TO DEMONSTRATE STRUCTURAL

DESIGN, MATERIALS CHOICE, AND

COMPOSITE CONCEPTS

L. Roy Bunneli

Battelle

Pacific Norhtwest Laboratories

P. O. Box 999 MSIN P8-44

Richland, Washington 99352

and

Steven W. Piippo

Richland School District

Richland, Washington 99352

449

A DEMONSTRATION OF SIMPLE AIRFOILS: STRUCTURAL DESIGN

AND MATERIALS CHOICES

L. Roy Bunnell

Pacific Northwest Laboratory, (a) Richland, Washington

Steven W. Piippo, Teacher

Richland School District, Richland, Washington

KEY WORDS: airfoils, composites, strength/weight ratio, structural testing

PREREQUISITE KNOWLEDGE: This unit is appropriate for a high school

materials science class or lower-division college courses in structural engineering, materials science, or aeronautical engineering. Prepare for the project by

explaining the following: the way that an airfoil shape generates lift (Bernoulli

effect), the importance of airfoil shape regarding lift/drag ratio, and the structural requirements of a wing.

OBJECTIVE: Students will build and evaluate simple wing structures, and

in so doing will learn about materials choices and lightweight construction

methods.

EQUIPMENT AND SUPPLIES: Listed below are the materials required to

conduct the project. The suggested quantities (see Table 1) should be sufficient material to construct three each of the six airfoil variations listed in Table 2,

TABLE 1. Materials for Building 18 Wings (including 50% excess)

Quantity,

Each Description(a)

36 Balsa sheet 1/16" x 3"x 36"

18 Balsa leading edge 3/8" x 5/16"x 36"

16 Balsa trailing edge 1/8" x 3/4" x 36"

12 Balsa 1/8" x 1/4" x 36"

9 Spruce 1/8" x 1.4"x 36"

(a) Wood is typically measured in English units.

(a) Pacific Northwest Laboratory is operated by Battelle Memorial Institute for

the U.S. Department of Energy under Contract DE-AC06-76RLO 1830.

451
TABLE 2. Wing Structural Variations

Variation Description Wt, g(a)

BW Ribs 6 cm apart, balsa spars 38.9

BN Ribs 3 cm apart, balsa spars 55.4

BWS Ribs 6 cm apart, balsa spars, shear webs 53.0

SW Ribs 6 cm apart, spruce spars 52.1

SN Ribs 3 cm apart, spruce spars 56.9

SWS Ribs 6 cm apart, spruce spars, shear webs 55.4

(a) Weights are those of the set built for this presentation, included

here for reference. These were the weights used for the

stiffness/weight and strength/weight ratios calculated below,

including 50% allowance for waste and mistakes. All required supplies can

be purchased at any good hobby shop for under $200 (1991 prices).

• a piece of fibrous ceiling tile about 60 x 120 cm, with a flat finish.

Use back side if no flat tiles are available. (Before applying adhesive,

the parts of the airfoil are pinned to the ceiling tile to ensure proper

alignment; reference lines are used to control component orientation

and spacing.)

• cyanoacrylate adhesive for model building; common brands are Zap

or Hot Stuff

• bicarbonate of soda

• T-head pins, medium size

• transparent polyester covering material, Monokote (or equivalent)

brand

• special iron designed for use in model construction

• special high-temperature heat gun designed for use in model

construction

• steel templates, approximately 3 mm thick (cut to Clark Y airfoil

shape, with notches for spars).

X-Acto or equivalent hobby knives, with straight pointed blades

PROCEDURE: The various parts of a wing are illustrated and labeled for

orientation in Figure 1. Figure 2 illustrates the actual airfoil size, which may be

scaled larger or smaller using a photocopier. [Note that the two notches are

placed to fit spars sized 0.64 cm by 0.32 cm (1/4 in. by 1/8 in.).] The six construction versions, all using the Clark Y airfoil, are listed in Table 2. The Clark Y

was chosen for construction ease, since it is nearly flat-bottomed. These six

versions are identical in cross section, but differ in the amount and placement

452
Shear Web - Vertical Grain Balsa

Section B-B' (without covering)

Section A-A'

B__ B'

Trailing Edge

Leading Edge _ Rib

A I_ Rib Spacing A'

Shear Web

Spar

Top View of Wing Structure

39208111,1

FIGURE 1. Construction Details of a Model Airplane Wing

453
ii

39210034.1

FIGURE 2. Clark Y Airfoil, Actual Size Used in This Project

of internal reinforcements and in the use of either balsa or spruce as spar material. Assign each team of two or three students the task of constructing one of

the six airfoils.

Construction: To make the ribs, the students will need to cut rectangles

slightly larger than the templates from 1.6 mm (1/16-in.) sheets of balsa. Since

the balsa rectangles will be clamped between the templates, oversized holes

should be drilled in the balsa rectangles to match those in the templates. Next,

carve and sand the ribs to the shape of the templates (avoid sanding the templates themselves). To make the notches for the spars, glue a 10-cm strip of

150-grit sandpaper to the 1/4-in. face of some scrap spruce spar wood. Sand

the spar notches in the ribs, using care to avoid enlarging the notches in the

templates.

Cover the building board (ceiling tile) with wax paper to prevent bonding

the wing to the board. Pin the bottom spar in place on the building board.

Pour bicarbonate of soda into a long narrow tray and dip each rib into the soda

before placing it onto the bottom spar. The tiny amount of soda that clings to

the rib accelerates the reaction rate of the cyanoacrylate and strengthens the

bond. Hold each rib perpendicular to the building board, taking care that each

closely follows its reference lines. Apply the cyanoacrylate; the bond will be

complete in 2 to 3 seconds. (Use the cyanoacrylate in a well-ventilated area

and avoid breathing the fumes.) Set the top spar securely into the notches,

and apply cyanoacrylate to the joints. Pin leading and trailing edges in place

using a 3-mm (1/8 in) shim under the leading edge, since the airfoil is not quite

flat; then bond with cyanoacrylate.

If shear webs are to be attached to the spars, cut the webs so the grain is

perpendicular to the building board, then bond to the front and back surfaces

of the top spar with cyanoacrylate. The wing may now be removed from the

building board and the shear webs bonded to the bottom spars. Glue a

doubler of scrap spar material to the outer ribs at either end; this will prevent

warpage as the covering material shrinks. Carefully sand the structure as necessary, and use a vacuum cleaner with brush to remove balsa dust. At this

point, prepare the covering material by cutting it approximately 3 cm larger on

454
ClampOver

Topof Airfoil _ ' Q_-- O .L_

MeterStick,

Verticalto

Floor :_ii_I .: . ,

BenchTop

39210034.2

FIGURE 3. Arrangements to Test Stiffness and Strength of Airfoil Sections

' 455,
all sides than the wing. Follow manufacturer's instructions for applying the cov-

" ering, first tacking it in place using the iron, then using the heat gun to shrink

the film.

Testing: Record the weight of each airfoil before testing for strength and

stiffness. Then, using a clamp that fits the shape of the airfoil's top profile,

fasten the airfoil to the edge of the workbench, allowing approx. 35 cm of the

airfoil to hang free, like a cantilever. Since deflection under load is a cube function of length, the free length should be carefully controlled. Attach a plastic or

cloth bag or small plastic pail to the top spar using strong string and duct tape.

See Figure 3 for details. Using a meter stick fixed to a base, measure the distance to the nearest millimeter from the lower wing surface to the floor.

To measure the relative stiffness of the airfoil, apply weights (used wheel

weights from a tire store will do) until a deflection of 1 cm is attained; weigh the

container and weights, and record this weighL Continue to load the airfoil until

failure occurs; record the failure weight and the approximate deflection at failure.

Be careful to avoid destroying the wing when failure occurs by suspending

the weight container within 5 cm of the floor. When the airfoil fails, the distance

the weight must drop to the floor is limited. After failure, examine the structure

to locate the failure site, taking this information into consideration along with

observations made during testing.

Discussion: in discussing cause for failure, students should speculate on

what could have been done differently during construction. For instance,

because all of our test structures failed in compression at the interface between

the wing and the clamping fixture, a buttress at this point would be appropriate.

If time permits, have students build and test a second airfoil (same cross section as the first) using their proposed remedies for increasing strength and stiffness and for minimizing weight. Alternatively, students may wish to simply

duplicate their first airfoil,being more careful withrWOOdselection and construction. Allow interested students to construct original designs, as long as their

airfoils remain within the initial parameters of dimension, shape and material.

An example of an original construction would be an airfoil cut from polystyrene

insulation foam, using electrically heated wire and templates on each end. This

airfoil could be covered with balsa sheeting bonded with epoxy. In spite of the

weight penalty for such an airfoil, the improvements in strength and stiffness are

impressive.

Plot the class's test results, using a simple bar graph like Figures 4 and 5.

On the x-axis plot structure type; on the y-axis, plot either the weight to cause

1-cm deflection divided by the wing weight or failure weight divided by the wing

weight. Observe and discuss scatter and trends. (Instructor should save

results to use for comparison with subsequent classes.)

456
Based on tests conducted to prepare this presentation, Figure 4 shows

the weight required to cause 1-cm deflection divided by the airfoil weight, which

is proportional to the stiffness/weight of the various wing variations. On the

strength of this single data set, the stiffness of wings built with either spar material appears to be substantially improved when shear webs are used. This is

logical, because the combination of shear web and spar forms a box beam.

The lightest structure, BW, shows stiffness/weight superior to airfoils built with

spruce spars, except where shear webs were used. Finally, the airfoil with

spruce spars had the highest stiffness/weight ratio, but only when shear webs

were provided. Figure 5 shows the weight required to cause structural failure

divided by the wing weight, for each of the six versions. The structures made

with balsa spars and shear webs performed impressively for their weight,

better than spruce-spar wings without shear webs. Although the shearwebbed wing made with spruce spars had the highest strength/weight, the difference was less than 10% more than the shear-webbed wing made with balsa

39210034.3

FIGURE 4. Stiffness/Weight Ratio of Six Structural Version of Same Airfoil

457
FIGURE 5. Failure Weight/Structure Weight Ratio for Six Structural

Versions of Same Airfoil

spars. Of course, in an actual airplane wing design, the strength and stiffness

would be critical factors in themselves and would only be divided by weight for

purposes of comparison, as in this project.

INSTRUCTOR'S NOTES: The model airplane hobby offers students an

excellent introduction to the basic techniques of producing the light, strong

structures that make flight possible. Based on the principles of aircraft

modeling, this project requires students to build an airfoil of constant cross

section and to compare severa_ variations of structural design and materials.

Simple tests of the resulting airfoils enable comparisons of performance as a

function of structural weight. Students should discuss whether the more

elaborate construction methods are justified on the basis of added weight.

Using modern materials and methods, airfoil construction and testing can be

accomplished within the time and economic constraints of the classroom without requiring advanced craftsmanship of the students.

Note that the materials and construction techniques used to construct

model airplanes may be unfamiliar to the average student. However, one or

two students in many classes may have had experience in this particular hobby.

458
These students will be a valuable resource to the class, especially during the

first round of airfoil construction; make use of such students.

SAFETY: Avoid breathing the fumes of reacting cyanoacrylate. In addition, take care not to bond fingers together with the cyanoacrylate, which

adheres quickly and tenaciously to skin. If this should happen, use the

debonding chemical available at hobby shops, or wait ten minutes before

slowly _ the bonded surfaces apart. Do not pull fingers directly apart or

use sharp blades to cut skin surfaces apart. Take extra care to avoid getting

glue into eyes.

*U.S. GOVERNMENT PRINTING OFFICE: 1993-728-150/60051

459
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'. AGENCY USE ONLY(Leaveb'an_)I2. REPO JuneRT199 DATE3 I 3. RConference EPORT TYPEPublication AND DATES COVERED

4. TITLE AND SUBTITLE 5. FUNDING NUMBERS

National Educators' Workshop: Update 92

Standard Experiments in Engineering Materials 505-63-50-01

Science and Technolo _

6. AUTHOR(S)

Compilers: James E. Gardner-NASA Langley Research Center,

Hampton, VA; James A. Jacobs-Norfolk State Univ., Norfolk

VA; Douglas F. Craig-Oak Ridge Nat. Lab._ Oak Ridge 1TN

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATION

NASA Langley Research Center REPORTNUMBER

Hampton, VA 23681-0001 I._17236

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) I0. SPONSORING/MONITORING

National Aeronautics and Space Administration AGENCYREPORTNUMBER

Washington, DC 20546-0001; Norfolk State University, Norfolk, NASA CP-3201

VA 23504; National Institute of Standards and Technology,

Galthcrsburg, MD 20899; United States Department of

Energy, Oak Ridge, TN 37831-6132

i

11. SUPPLEMENTARY NOTES

Supporting Organizations: American Society for Engineering Education, ASM International, Battelle Pacific Northwest

Laboratories, Martin Marietta Energy Systems, Inc., Materials Education Council of the United States, Westinghouse

EnvlzonmentalManagementCompany of Ohio, and AmericanSocietyfor Testingand Materials.

12a.DISTRIBUTION/AVAILABILITY STATEMENT 12b.DISTRIBUTIONCODE

Unclassified - Unlimited

Subject Category 23

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13. ABSTRACT (Maximum 200 words)

This document contains a collection of experiments presented and demonstrated at the National Educators'

Workshop: Update 92 held at the Oak Ridge National Laboratory on November 11-13, 1992, in Oak Ridge,

Tennessee. The experiments related to the nature and properties of engineering materials and provided

information to assist in teaching about materials in the education community.

i

14. SUBJECT TERMS 15. NUMBER OF PAGES

Materials; Experiments; Education 486

16. PRICe CODE

A21

17. SECURITY CLASSIFICATION 18. SECURITY CLASSIFICATIOI_ 19. SECURITY CLASSIFICATION 20. LIMITATION

OF REPORT OF THIS PAGE OF ABSTRACT OF ABSTRACT

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