United States Department of Commerce

National Institute of Standards and Technology

NATL INST, or STAND & TECH R.I.C.

A111D3

NIST Special Publication 822

National Educators Workshop.

Update '90

Standard Experiments in Engineering

Materials Science and Technology

Proceedings of a workshop held in Gaithersburg, Maryland

November 13-15, 1990

United States Department of Commerce

National Institute of Standards and Technology

U97

Ml

6J

NIST Special Publication 822

National Educators Workshop:

Update '90

Standard Experiments in Engineering

Materials Science and Technology

Editors:

Jonice S. Harris

Materials Science and Engineering Laboratory

National Institute of Standards and Technology

Gaithersburg, MD 20899

James A. Jacobs

School of Technology

Norfolk State University

Norfolk, VA 23504

Issued November 1991

Proceedings of a workshop sponsored jointly by the

National Institute of Standards and Technology,

Gaithersburg, Maryland; the National Aeronautics and

Space Administration, Washington, D.C.; and the

Schools of Technology and Science, Norfolk State

University, Norfolk, Virginia, and held in Gaithersburg,

Maryland, November 13-15, 1990

With the support of ASM International, Battelle

Pacific Northwest Laboratory, Materials Education

Council, Ford Motor Company, and Westinghouse

Materials Company of Ohio

c

U.S. Department of Commerce

Robert A. Mosbacher, Secretary

National Institute of Standards and Technology

John W. Lyons, Director
National Institute of Standards U.S. Government Printing Office

and Technology Washington: 1991

Special Publication 822

Natl. Inst. Stand. Technol.

Spec. Publ. 822

336 pages (Nov. 1991)

CODEN: NSPUE2

For sale by the Superintendent

of Documents

U.S. Government Printing Office

Washington, DC 20402
PREFACE

NEW:Update '90 was held November 13-15, 1990, on the campus of the National Institute of

Standards and Technology (NIST) in Gaithersburg, Maryland. 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; heard about new MS&E developments;

and toured state-of-the-art NIST laboratories. Faculty in attendance represented community

colleges, smaller colleges, and major universities. Some were the only materials educators on their

campus, while others were from well established MS&E programs.

NEWiUpdate '90 marked the fifth annual National Educators Workshop:Update. Seventy-four

participants including first-time attendees and those who attended previous NEW:Updates aided in

evaluating nearly 30 experiments that were presented before the group. Additional updating

information relating to materials science, engineering, and technology was also presented.

Material in this publication can serve as a valuable guide to faculty who are interested in useful

experiments for their students. The material was the result of years of research aimed at better

methods of teaching materials science, engineering, and technology. The experiments were

developed by faculty, scientists, and engineers throughout the United States. There was a blend of

experiments on new materials and traditional materials. Uses of computers in MS&E, experimental

design and an approach to systematic materials selection were among the demonstrations

presented.

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 an intemational panel through the cooperation of the

Materials Education Council. Authors received comments from the panel prior to NEW:Update

90, allowing them to make necessary adjustments prior to demonstrating their experiments.

Participants from the United States and Canada, who attended NEW:Update 90, observed

demonstrations of the experiments and provided critiques for the authors to make further

modifications prior to this publication.

Videotapes were made of the workshop by Westinghouse Materials Company of Ohio. As with

previous NEW:Updates, critiques were made of the workshop to provide continuing improvement

of this activity.

The Materials Education Council of the United States was represented again and will publish

selected experiments in the Journal of Materials Education.

NEWiUpdate '90, and the '86, '87, '88 and '89 workshops are, to our knowledge, the only

national workshops or gatherings for materials educators that have a focus on the full range of

issues on strategies for better teaching about the full complement of materials. Recognizing the

problem of motivating young people to pursue careers in MS&E, we have included exemplary preuniversity activities such as Adventure in Science, ASM Intemational Education Foundation's

Career Outreach Program, and several programs run through high schools.

iii
Through the workshops we have learned about the Materials Science Technology Project at Richland High School (Richland, Washington) that has received support from Battelle Pacific

Northwest Laboratory (PNL). An experiment was presented from the National Science Foundation

and AT&T supported program at Science School in Newark, New Jersey. One high school science

fair experiment, presented by its student author, had value for MS&E education at the college level.

NEW:Update '90, with its diversity of faculty, industry, and government MS&E participants,

served as a forum for both formal and informal issues facing MS&E education that ranged from the

challenges of keeping faculty and students abreast of new technology to ideas to ensure that

materials scientists, engineers, and technicians maintain the proper respect for the environment in

the pursuit of their objectives.

NEWrUpdate '90 resulted from considerable cooperative efforts by individuals in government,

education, and industry. The workshop's goal is to maintain the network of participants and to

continue to collect these ideas and resources to bring together in a comprehensive manual of

standard experiments in materials science, engineering, and technology.

We hope that the experiments 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, VA 23504.

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

Workshop Co-Directors Liaisons

Jonice S. Harris

Materials Science and Engineering Laboratory

National Institute of Standards & Technology

Carol Houk

ASM Intemational

James A. Jacobs

Professor of Engineering Technology

Norfolk State University

Robert Berrettini

Materials Education Council

frene Hays

Battelle PNL

Director's Assistant

Diana LaClaire

Norfolk State University

iv
CONTENTS

PAGE

PREFACE iii

PLANNING COMMITTEE MEMBERS AND REVIEWERS viii

PARTICIPANTS ix

MATERIALS PROCESSING LABORATORY INSTRUCTION: STRUCTUREPROPERTY-PROCESSING RELATIONSHIPS 1 James A. Clum —T. J. Watson School of Engineering

INSTRUCTIONAL SOFTWARE FOR TEACHING POLYMER SCIENCE AND

ENGINEERING 11

Witold Brostow and Michael R. Kozak —University of North Texas

DESIGN PROJECT FOR THE MATERIALS COURSE: TO PICK THE BEST

MATERIAL FOR A COOKING POT 21

Kopl Halperin —The Pennsylvania State University at Erie, The Behrend College

CRYSTAL MODELS FOR THE BEGINNING STUDENT 31

F. Xavier Spiegel —Loyola College

MICROSTRUCTURE ANALYSIS (UNIVERSITY AND INDUSTRY

PARTNERSHIP) 45

Donald H. Martin —Indiana University Purdue University at Fort Wayne and

Gary L. Dawson —Dana Corporation

A NONDESTRUCTIVE TESTING METHOD TO DETECT DEFECTS IN

STEEL PLATES 53

Mostafiz R. Chowdhury —East Carolina University

COOLING FIN MATERIALS AND CONVECTIVE COOLING 67

Richard J. Greet —University of Southern Colorado

FABRICATION AND EVALUATION OF A SIMPLE COMPOSITE

STRUCTURAL BEAM 77

Myron J. Schmenk — Miami University

MEASUREMENT OF STRAIN RATE SENSITIVITY IN METALS 91

Y. Y. Yang and R.G. Stang —University of Washington

POST HEAT TREATMENT IN LIQUID PHASE SINTERED TUNGSTEN

NICKEL-IRON ALLOYS 101

Mansur Rastani — North Carolina A & T State University

IMPROVED TECHNIQUE FOR MEASURING COEFFICIENTS OF

THERMAL EXTENSION FOR POLYMER FILMS 119

Stephanie L. Gray, Kristen T. Kern, Wynford L. Harries — Old Dominion

University and Sheila Ann T. Long —NASA Langley Research Center

V
CHARPY V-NOTCH IMPACT TESTING OF HOT ROLLED 1020 STEEL

TO EXPLORE TEMPERATURE - IMPACT STRENGTH RELATIONSHIPS 129

Seth P. Bates — San Jose State University

FIBER REINFORCED COMPOSITE MATERIALS 137

Harvey A. West and A. F. Sprecher — North Carolina State University

DIELECTRIC BEHAVIOR OF SUPERCONDUCTORS AT MICROWAVE

FREQUENCIES 145

J. N. Dahiya — Southeast Missouri State University

IT'S HARD TO TEST HARDNESS 161

Edward L. Widener —Purdue University

UNCONVENTIONAL IMPACT-TOUGHNESS EXPERIMENTS 169

Edward L. Widener —Purdue University

ADAPTING ARCHIMEDES' METHOD FOR DETERMINING DENSITIES

AND POROSITIES OF SMALL CERAMIC SAMPLES 175

Gail W. Jordan —Hocking Technical College

EFFECT OF HEAT TREATMENT ON MAGNETIC PROPERTIES OF

A METAL ALLOY 183

Wenchiang R. Chung and Margery L. Morse — San Jose State University

ASTM—THE DEVELOPMENT AND APPLICATION OF STANDARDS 187

Drew C. Azzara —Director, Technical Committee Support, ASTM

DETERMINING THE IMPACT OF ADJUSTING TEMPERATURE PROFILES

ON PHOTODEGRADABILITY OF LDPE/STARCH BLOWN FILM 221

Jerry L. Wickman and Scott M. Corbin — Ball State University

DEMONSTRATION OF A SIMPLE SCREENING STRATEGY FOR

MULTIFACTOR EXPERIMENTS IN ENGINEERING 233

Larry Panchula and John W. Patterson — Iowa State University

ENVIRONMENTAL STRESS CRACKING OF RECYCLED THERMOPLASTICS ... 253

Nikhil K. Kundu — Purdue University

HOW DOES CHANGE IN TEMPERATURE AFFECT RESISTANCE? 261

Jenifer A. T. Taylor —New York State College of Ceramics at Alfred University

DEMONSTRATION OF KINETIC RELATIONSHIPS BY PRECIPITATIONHARDENING EXPERIMENTS 265

Phihp J. Guichelaar and Molly W. WilHams —Western Michigan University

SIMPLE STRESSED-SKIN COMPOSITES USING PAPER REINFORCEMENT ... 273

L. R. Bunnell —Battelle Pacific Northwest Laboratories

EFFECT OF STRAIN RATE ON TENSILE PROPERTIES OF PLASTICS 279

L. R. Cornwell, R. B. Griffin, and W. A. Massarweh —Texas A&M University

vi
BIODEGRADABLE PLASTICS: AN INFORMATIVE LABORATORY

APPROACH 291

Jeffrey S. Humble — Shawnee State University

FRESHMAN CHEMISTRY AND MATERIALS SCIENCE: MERGING

THE MICROSCOPIC WITH THE MACROSCOPIC 297

Gary E. Wnek and Peter J. Ficalora — Rensselaer Polytechnic Institute

INTRODUCTORY MATERIALS LAB 305

Sayyed M. Kazem —Purdue University

DIAMOND SYNTHESIS WITH A COMMERCIAL OXYGEN-ACETYLENE

TORCH 309

Keith A. Snail et al. —Naval Research Laboratory

SIMPLE STRATEGIES FOR IMPROVING RETENTION OF WOMEN IN

TECHNICAL STUDIES 333

Jenifer A. T. Taylor — New York State College of Ceramics at Alfred University

vii
PLANNING COMMITTEE MEMBERS

Seth P. Bates — San Jose State University

Peter Beardmore —Ford Motor Company

Robert Berrettini —Materials Education Council

WiUiam Callister —Materials Division, ASEE

Milton Ferguson —Norfolk State University

James Gardner —National Aeronautics & Space Administration

Irene Hays — Battelle, PNL

Alfred McKenney —Norfolk State University

Carl Metzloff —Erie Community College

John W. Patterson — Iowa State University

Heidi Ries —Norfolk State University

REVIEWERS FOR NEW: Update '90

Robert J. Heinsohn

Professor of Mechanical Engineering

The Pennsylvania State University

Stephen H. CanProfessor of Materials Science

Northwestern University

Herbert McKinstry

Associate Professor of Solid State Technology

The Pennsylvania State University

Witold Brostow

Professor of Materials Science

University of North Texas

Irene Furara, Director

Centre Region Solid Waste Authority

State College, PA

Qayton O. Ruud

Professor of Industrial Engineering

The Pennsylvania State University

Amar S. BhaUa

Professor of Solid State Science

The Pennsylvania State University

Srikanth Varanasi

Research Associate, Materials Research Laboratory

The Pennsylvania State University

T. DebRoy

Professor of Metallurgy

The Pennsylvania State University

Else Breval

Senior Research Associate, Materials Research Laboratory

The Pennsylvania State University

Don Strickler

Research Associate, Materials Research Laboratory

The Pennsylvania State University

Wenwu Cao

Research Associate, Materials Research Laboratory

The Pennsylvania State University

Bruce E. Knox

Associate Professor of Materials Science

The Pennsylvania State University

Anil K. Kulhami

Associate Professor of Mechanical Engineering

The Pennsylvania State University

Technical notebooks were prepared by

NASA LANGLEY RESEARCH CENTER

Videotaping was provided by the

WESTINGHOUSE MATERIALS COMPANY OF OHIO

Announcements of the workshop were printed by

ASM INTERNATIONAL

The use of trademarks or manufacturer's names in this publication does not constitute endorsement, either

expressed or implied, by the National Institute of Standards and Technology

viii
I

I

NATIONAL EDUCATORS WORKSHOP.Update 90

National Institute of Standards and Technology

Gaithersburg, MD

November 13-15, 1990

Final Participants List

Norman L. Asper

Trenton State College

Dept. of Engineering

Hillwood Lakes

Trenton, NJ 08650

609-771-2774

Drew C. Azzara

Director, Technical Committee Support

ASTM

Standards for Materials, Products,

Systems, & Services

1916 Race Street

Philadelphia, PA 19103-1187

215-299-5498

Seth P.Bates

Division of Technology

San Jose State University

San Jose, CA 95192-0061

408-924-3227

Robert Berrettini

Pennsylvania State University

110 Materials Research Laboratory

University Park, PA 16802

814-865-1643

L. Roy Bunnell

Battelle-Northwest

Battelle Blvd.

Richland, WA 99352

509-376-2799

Dilip K. Chaudhuri

Tennessee State University

Department of Mechanical Engineering

3500 John Merritt Blvd.

Nashville, TN 37209

615-320-3555

Mostafiz R. Chowdhury

East Carolina University

331 Rawl

Greenville, NC 27858

919-757-4140

Wenchiang R. Chung

Assistant Professor of DOT

San Jose State University

School of Applied Arts and Sciences

Division of Technology

One Washington Square

San Jose, CA 95192-0061

408-924-3226

Chet Blake

Walla Walla College

204 South College Avenue

College Place, WA 99324-1 198

509-527-2712

Witold Brostow

University of North Texas

Center for Materials Characterization

P. O. Box 5308

Denton, TX 76203

817-565-4358

James A. Clum

SUNY-Binghamton

Mech. & Ind. Engr. Dept.

P. O. Box 6000

Binghamton, NY 13902-6000

607-777-4860/4747

Jai N. Dahiya

Physics Department

Southeast Missouri State University

One University Plaza

Cape Giradeau, MO 63701-4799

314-651-2390

ix
John DeFilippo

Hartford State Technical College

401 Flatbush Avenue

Hartford, CT 06106

203-527-4111

C. Ray Diez

University of North Dakota

Box 8057, University Station

Dept. of Industrial Technology

Grand Forks, ND 58202

Wayne L. Elban

Loyola College

4501 N. Charles Street

Dept. of Electrical Eng. & Eng. Science

Baltimore, MD 21210

301-323-1010, ext. 2853

Mehrdad Faezi

Assistant Professor

Central Connecticut State University

New Britain, CT 06050

203-827-7412

William O. Fellers

American River College

4700 College Oak Drive

Engineering Department

Sacramento, CA 95841

916-487-5895

Milton Ferguson

Norfolk State University

Norfolk, VA 23504

804-683-8369

Keith C. Finkral

Trenton State College

Hillwood Lakes CN4700

32 Armstrong Hall

Trenton, NJ 08650-4700

609-771-2780

Michel Fiset

Dept. Metallurgy

Laval University

Quebec, GIK7P4

CANADA

418-656-2156

Stephen G. Fogle

County College of Morris

124 Midvale Road

Mountain Lakes, NJ 07046

201-328-5750

Gregg Geckle

Westinghouse Materials Company of Ohio

P. O. Box 398704

Cincinnati, OH 45239-8704

513-738-6084

Hamid S. A. Ghazanfar

Temple University

12th & Norris Streets

CECSA

Philadelphia, PA 19122

215-787-6422

Richard Greet

University of Southern Colorado

2200 Bonforte Blvd.

Pueblo, CO 81001

719-549-2884

Leonard B. Gulbransen

Washington University in St. Louis

Box 1185

Lindell & Skinker

Box 1185

St. Louis, MO 63130

314-889-6073

Ken Halperin

Behrend College of Pennsylvania State

Station Road

BA3 #3

Erie, PA 16563

814-898-6347

Jerry Harris

Northern Michigan University

Jacobetti Center, Room 122-B

Marquette, MI 49855

906-227-2897

Jonice Harris

Materials Bldg. 223, Room B226

National Institute of Standards & Technology

Gaithersburg, MD 20899

301-975-6007

X
Larry D. Helsel

School of Technology

Eastern Illinois University

Charleston, IL 61920

217-581-3226

Edward E, Hornsey

University of Missouri-Rolla

102 Basic Engineering Building

Rolla, MO 65401

314-341-4591

Emil H. Isaacson

Univ. District of Columbia

39 Great Pines Court

Rockville, MD 20850

202-282-7426

James A. Jacobs

Norfolk State University

2401 Corprew Avenue

Norfolk, VA 23504

804-683-8109

Glenn E. Johnson

Andrews University

Berrien Springs, MI 49104

616-471-3191

Richard W. Jones

Youngstown State University

410 Wick Avenue

Youngstown, OH 44555-0001

216-742-1735

Gail Jordan

Instructor,

Ceramic and Materials Engineering

Technologies

Hocking Technical College

3301 Hocking Parkway

Nelsonville, OH 45765

614-753-3591

Sayyed M. Kazem

Purdue University

MET Dept.

Knoy Hall

West Lafayette, IN 47907

317-494-7528

Kristen T. Kern

NASA Langley Res. Center

MS229

Hampton, VA 23665-5225

804-864-4278

Michael Kozak

University of North Texas

P. O. Box 131

Denton, TX 76203

Jerry Kroll

College of Lake County

Graylake, IL 60030

708-223-6601

Nikhil K. Kundu

Purdue University

Statewide Technology

2424 California Road

Elkhart, IN 46514

219-264-3111

Francis Lai

University of Lowell

One University Avenue

Lowell, MA 01854

508-934-3434

Calvin Lundeen

University of the Pacific

3601 Pacific Avenue

Mechanical Engineering

Stockton, CA 95211

209-946-3084

Donald H. Martin

Indiana University-Purdue University

at Fort Wayne

2101 Coliseum Blvd. East

Neff 360

Fort Wayne, IN 46805 , 219-481-6390

W. Massarweh

Texas A&M University

College Station, TX 77843-3123

409-845-1251

xi
John C. Mauer

Pellissippi State Technical Community College

P. O. Box 22990, B-125

Knoxville, TN 37933-0990

615-694-6512

Don Miotto

Delta College

Delta at Mackinaw

S-267

University Center, MI 48710

517-686-9293

Lars J. Norrby

Dept. Chem. & Chem. Eng.

Royal Military College of Canada (RMC)

Kingston, Ontario K7K5LO

CANADA

613-541-6384

Martin (Larry) Panchula

Iowa State University

110 Engineering Annex

Ames,IA 50011

515-294-7562

Patrick Pandolfi

Pasadena City College

355 South Maringo Avenue

Pasadena, CA 91109

818-795-6841

John W. Patterson

Professor, Department of MSE

Iowa State University

1 10 Engineering Annex

Ames,IA 50011

515-294-7562

John Petrewski

Broome Community College

P. O. Box 1017

MET Dept.

Binghamton, NY 13902

607-771-5129

Mansur Rastani

NC A&T State University

Dept. of Manufacturing Systems

111 Price Hall

Greensboro, NC 27411

919-334-7585

Heidi Ries

Norfolk State University

Norfolk, VA 23504

804-683-8020

William A. Ross

Muskegon Community College

221 S. Quarterline Road

Muskegon, MI 49442

616-773-9131

Myron J. Schmenk

Miami University

140 Kreger Hall

Oxford, OH 45056

513-529-1453

Lyle Schwartz, Director

Materials Science and Engineering Laboratory

National Institute of Standards & Technology

Gaithersburg, MD 20899

Ram N. Singh

St. Louis Community College

Engineering Dept.

3400 Pershall Road

St. Louis, MO 63135

314-595-2311

Keith Snail

Naval Research Laboratory

4555 Overlook Avenue, SW

Washington, DC 20375-5000

202-404-7308

F. Xavier Spiegel

Loyola College

4501 N. Charles Street

Donnelly Science 221

Baltimore, MD 21210-2699

301-323-1010 ext. 2515

Robert G. Stang

Dept. of Materials Science & Engineering

University of Washington

FB-10

Seattle, WA 98195

206-543-2623

xii
David Stienstra

Rose-Hulman Institute of Technology

5500 Wabash Avenue

Box 160

Terre Haute, IN 47803-3999

812-877-8207

Jenifer A. T. Taylor

New York State College of Ceramics

at Alfred University

Alfred, NY 14802

607-871-2190

Mori Toosi

School of Technology

Eastern Illinois University

Charleston, IL 61920

217-581-3226

Emmanuel O. Uwejeyan

7 Welcome Court

Portsmouth, VA 23701-3150

804-465-3890

Jeff Wagner

Westinghouse Materials Company of Ohio

P. O. Box 398704

Cincinnati, OH 45239-8704

513-738-6314

Martin W. Weiser

University of New Mexico

Mech. Engineering Dept.

Albuquerque, NM 87131

505-277-2831

Harvey A, West

North Carolina State University

College of Engineering

Department of Materials Science and

Engineering

Box 7907

Raleigh, NC 27695-7907

919-737-2377

Edward L. Widener

Purdue University - MET. Dept.

Knoy Hall - Room 119

West Lafayette, IN 47907

317-494-7521

Molly W. WilUams

Western Michigan University

College of Engineering

Kalamazoo, MI 49008-5062

616-387-4017

Gary Wnek

Rensselaer Polytechnic Institute

Dept. of Chemistry

Troy, NY 12180

518-276-2885

xiii

MATERIALS PROCESSING LABORATORY INSTRUCTION:

STRUCTURE-PROPERTY-PROCESSING RELATIONSHIPS

James A. Glum, Professor

Mechanical & Industrial Engineering

T. J. Watson School of Engineering

State University of New York at Binghamton

P.O. Box 6000, Binghamton, NY 13902-6000

KEY WORDS: Solder Alloys; Solidification Rate; Creep/Stress-Relaxation; Recovery

and Recrystallization

PREREQUISITE KNOWLEDGE REQUIRED: Ability to analyze simple phase

diagrams; Ability to use reflected light microscope and determine ASTM grain size.

OBJECTIVES: - Prepare metallographic samples;

- Determine thermal process conditions from phase diagrams;

- Distinguish differences in cast microstructures due to

variations in freezing range and solidification rate;

- Determine effects of thermomechanical treatments on

microstructure and properties;

a. Recognize creep and stress relaxation behavior in

stressed materials;

b. Determine recrystallization conditions at various T/T„;

- Measure hardness and microhardness;

- Perform quantitative image analysis microstructures to

determine grain size and phase fractions;

EQUIPMENT: a. Two Thermolyne muffle furnaces (maximum temperature of

1000C with microprocessor programmable operating control);

b. One Olympus SZ-TR Stereo Zoom Microscope with

magnification range of 7X to 40X;

c. Two Olympus BHM reflected light microscopes with

magnification ranges of SOX to 500X;

d. One LECO hardness tester (Rockwell scales);

e. One LECO microhardness tester (Vickers indenter);

f. One Nikon Epiphot inverted metallographic microscope with

magnification range of SOX to 1 0OOX in bright field and

differential interference contrast and attachments for:

i. closed circuit television viewing of images;

ii. photographic image recording with automatic

exposure control (35mm and Polaroid film);

iii. Nikon MircoPlan II image analysis system

includes: digitizing tablet with preprogrammed

image measurement/analysis menu; an alphanumeric printer; a multi-function cross-hair cursor.

1
g. One Lab Sciences Universal Materials Testing Machine

operated in compression mode.

MATERIALS: Series of solder alloys: 1) 75Pb-25ln; 2) 60Pb-40ln; 3) 50Pb50iN; 4. 40Pb-60ln; or,

1) 70Pb-30Sn; 2) 60Pb-40Sn; 3) 50Pb-50ln; 4) 40Pb-60Sn;

5) 37Pb-63Sn.

PROCEDURE: 1. Organize into working groups (one group assigned to

study a given alloy):

The following tasks are to be completed by each group:

2. Melting and solidification of each alloy to show the effect of

freezing range and cooling rate on as-cast microstructure and

hardness:

a. melt approximately 25 grams of each alloy in porcelain

crucibles at constant superheat (to be determined by Group*);

b. solidify each alloy in two ways:

i. slow cool by casting into heated plaster molds;

ii. cast into a "chill" mold (an aluminium block at room

temperature.

(Molds are either, plaster of paris, or aluminum blocks which measure

approximately 5 cm x 5 cm x 5 cm, with four holes of 1 cm diam. x 1 cm deep spaced uniformly on one face. Plaster molds must be

thoroughly dry and are heated in the furnace with crucible during the

melting of the charge. Measurement of cooling rates can be

approximated bv determining the time from pouring until no liquid

motion is seen on the casting surface.)

3. Measurement of microstructure (grain size; phase fraction and

phase distribution), hardness and microhardness of the as-received

and as-cast samples of each alloy which will include:

a. metallographic specimen preparation;

b. photographic recording of microstructure (magnification

determined by Group*);

c. image analysis of microstructure.

NOTE: Each member of each group must carry out the full range of processing

specimen preparation and analysis for at least one set of the group's specimens.

The results obtained by the individual are to be noted in the final report.

2
4. Heat treatment of as-cast and as-received alloy samples

(temperatures and times of heat treatments to be determined by

Group*).

5. Repeat Step 3 after doing heat treatments.

6. Compression deform each alloy (samples from each of the as-cast

and as-received conditions) to at least two levels of % height

reduction, e.g., 25% and 50%. During deformation use the dial gauge

in contact with the sample grip fixture to follow deformation vs. time at

fixed load and use the pressure gauge to follow the load drop vs. time after load increase. (NOTE: Loads are not to exceed 900

pounds.)

7. Measure microstructure, hardness and microhardness of each

cold-worked sample as in Step 3.

8. Carry out a Recrystallization heat treatment of each sample from

Step 6 attempting to obtain the minimum as-recrystallized grain size

(choice of Recrystallization Temperature must be justified).

9. Repeat Task 7.

1 0. Submit all raw data to the Central Data File (Room A3) as soon

as it is acquired (including prints of photographs).

**1 1. Each Group is to submit a typed Summary Report (addressed

to, Supervisor, Materials Laboratory) in the following format:

a. using SV2" x 1 1" paper with one inch margins.

b. text report is not to exceed 1 0 pages, exclusive of data

tables, figures and references.

c. all data from all Groups is to be included in the report of

each Group and to be discussed in the Discussion of Results

section.

(NOTE: A typical report includes the following sections:

Introduction

Experimental Plan/Procedures

Results (Data, Tables, Figures)

Discussion of Results (theory vs. experiment)

Summary/Conclusions

References

Further details are given in DEPARTIVIENTAL STANDARDS FOR FORIVIAL

WRITTEN REPORTS.

3
12. Each individual is to keep a LABORATORY NOTEBOOK as a

permanent, up-to-date record of their activities. (Laboratory

Notebook requirements and procedures are described in

DEPARTMENTAL STANDARDS FOR LABORATORY

NOTEBOOKS). (NOTE: The notebool<s may be collected for

inspection at any time upon request by the Instructor. Keep them

available.)

SUPPLEI\/IENTAL INFORI\/IATION: 1. No use of furnaces, microscopes

polishing equipment or testing equipment is permitted

without permission of Instructor.

2. Safety goggles are required at all times.

3. Use of breathing masks and gloves is required during

melting, metallographic specimen preparation, heat

treating and deformation processing operations.

SAI\/IPLE DATA: Attached are examples of: 1. a sample preparation flow sheet;

2. microhardness measurements; 3. grain size measurements;

There are no "standard" data sheets used. Each group constructs

their own form of data presentation. As noted, however, the Final

group reports must include the data from the other groups.

INSTRUCTOR NOTES: This Experiment is one of only two conducted in our

Junior year Materials Processing Lab. (See attached ME 395B . Materials Lab, course handout.) It occupies about 80% of the semester long laboratory. The first

Experiment is an individually performed and reported procedure in which each

student learns to observe, record and analyze the microstructure of a set of

stainless steel samples. It serves as an important preliminary experiment to the

lengthy group Experiment II described here.

This Lab course is closely tied to a lecture course on materials and

manufacturing processing (M/MP). The two courses incorporate, uniquely, we

believe, a pedagogical feature which we call peer assisted learning (pal). In gal

we involve the more proficient students in a tutorial role to provide assistance to

their less proficient peers. This use of students teaching students, or cooperative

learning, or peer assisted learning is necessitated in both the lecture and the

laboratory course.

In the lecture course we need the assistance of those students who have had a

previous materials engineering/science course to help us carry out a series of

extraordinary make-up tutorials. Those sessions are required because of the fact

that approximately 67% of incoming Junior transfer students have not had the

prerequisite introductory Materials course. To overcome this deficiency we: 1)

conduct a materials engineering/science diagnostic survey at the start of the

lecture course to identify the extent of the deficiencies; 2) conduct a set of 30

minute tutorial lectures, on an optional attendance basis, prior to the regularly

scheduled class period; 3) use the ga! groups to provide supplementary help to

4
the students with deficiency. In the lab course the gal process is used to leverage

our instruction in the performance of experimental procedures. That is, in each lab

group one person is identified as the "lead experimentalist" for each separate

procedure, e.g., melting, deformation processing, hardness testing, microscopy,

image analysis and metallographic specimen preparation. That person then serves

as the instructor for others in her/his group as each one of them goes through that

part of the Experiment. (NOTE: Each person in each group must do at least one

completely cycle of the entire Experiment from melting to image analysis.) The use

of gal in the lab course frees the official Instructors to supen/ise critical operations

for safety and to assist with such operations as interpretation of microstructural

observations, etc..

There have been several useful outcomes from this intensive group Experiment.

One has been the success of the paj process. It has made for more efficient use

of the lab facilities since essentially no time is lost in waiting for the Instructor to

provide operating information. Additionally, the "lead experimentalists" develop an

apparent pride in their role and become quite proactive as instructors.

An equally important outcome from these Experiment II labs has been the

compilation of the results into summary reports which have been published and/or

presented at technical society meetings, e.g., "Observations of the Effect of Alloy

Composition and Processing on Ambient Recrystallization Behavior of Solders",

2nd Electronic Materials and Processing Conference. ASM International, Phila., PA,

1989. A second summary presentation of work on the Pb-ln alloys is scheduled

for the 4th Electronic Materials and Processing conference to be held in Montreal

in August, 1991.

The development of student observational and reporting skills is another

feature of this course which we emphasize. Of particular interest to us is that the

students become proficient in keeping a laboratory notebook. As noted in the

Experiment II descripiton their notebooks must conform to a specific format and

they are collected for evaluation at least four times during the semester. That

evaluation includes a critique on both content and presentation. Report writing

also gets attention through the individual reports for Experiment I as well as the

g'roup report from Experiment II. In fact in the case of the individual reports each

of those is read and edited by two classmates before being graded by the

Instructor. The student editors are frequently harsher critics than the Instructor.

Perhaps of greatest value has been the recognition on the part of many of the

students of the relation between structure and properties of materials. Especially

notable from the work with the solder alloys is the demonstration of the dynamic

nature of materials microstructure and the relation to property changes. Additional

recognition of the effect of composition on both microstructure and properties is

gained when the groups compare data between groups for the final reports.

Significant differences in sample preparation, observed phase fractions and phase

distributions, e.g., primary vs. eutectic Pb in Pb-Sn alloys, and microhardness are

noted and remarked on by the groups.

The metallographic sample preparation technique for these soft alloys

deserves some special mention. In general higher Pb content alloys are somewhat

easier to prepare than higher Sn or higher In alloys. In all cases, however, the

5
emphasis is on using the minimum amount of time with each abrasive step and

using the minimum amount of pressure. Such variations of technique as "single

hand, one direction" vs. "two hands, both directions" have been reported to be

successful. We recommend the former technique for each novice and we also

encourage them to actually keep count of the number of strokes on each paper,

and the number of revolutions of each wheel in the polishing steps. Since each

student's self-adjusting pressure application, or feel, cannot be duplicated in

another student we only can use such data as guidelines. Nevertheless, the true

novice finds such guidelines helpful; along with frequent trips to the stereo-zoom

microscope as grinding and polishing proceeds.

SOURCES OF SUPPLIES: The most expensive items in this Experiment II are the

diamond pastes used in the metallographic specimen preparation. We use a

procedure which uses 9, 3, and 1 micron pastes for polishing. Each alloy group

has separate wheels and cloths (also a potentially large expense, but separate

cloths are really all that is necessary). The Pb-Sn solder alloys are quite

inexpensive and can be purchased from many industrial suppply houses. The

indium bearing alloys are more expensive and we have relied on alloy

manufacturers for donations. A final obvious cost item is the photographic

expenses. We use a combination of 35 mm and Polaroid film. As the proportion

of the latter increases so do the costs. Mounting of the samples for metallographic

preparation requires epoxy mounting materials which do not have a high curing

temperature. We have used a resin and hardener combination manufactured by

the Hysol Corporation for use in the microelectronics industry. The resin is #RE2038 and the hardener is #HD-3416. We have used a ratio of R:H = 10:1, by

weight with success. However, the system is very sensitive to moisture and in

humid weather a vacuum bell jar is recommended to extract dissolved gasses from

the mix.

FIGURES: 1. Copy of Evaluation Sheet used for Lab Notebook Inspection.

2. Copy of Processing Flow Sheet for One Set of Samples/One Alloy.

3. Copy of "Table 1

." and "Table 2." from Publication of Summary of

Lab Experiments on Pb-Sn Allovs.fASM 2nd EM&P Conf. 1989).

4. Copy of a Summary Table from a Group Rpt on Pb-ln Alloys.

5. a. (upper left) 70Pb-30Sn, Slow Cool/50% Def./Rm. Temp..

Note beginning recrystallization in lighter areas. 400X.

b. (upper right) 70Pb-30Sn, Slow Cool/50% Def./Annealed (O.GT^),

30 min. Note recrystallization in two-phase regions. 400X.

c. (lower left) 75Pb-25ln, Slow Cool/50% Def./Rm. Temp. 200X.

Note recrystallization colonies at deformed grain boundaries.

d. (lower right) 75Pb-25ln, Slow Cool/50% Def./Annealed (0.75TJ,

30 min. 200X. Note grain growth of recrystallized regions.

6. Copy of Course Syllabus, ME 395B.

6
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7

COURSE: ME 395B

Materials Lab

WHEN:

INSTRUCTOR:

TEXT:

SUPPLEMENTAL:

COURSE DESCRIPTION:

COURSE SCHEDULE:

Spring 1 990

T,R, 1:15-4:15

J. A. Glum, M&IE Department

Office: EB S-18, Pfione 777-4860

"The Role of IVIicrostructure in Metals", A. R.

Bailey, Metallurgical Services Lab. Ltd., 1982

Metals Handbook, ASM International

8th Ed. V. 7 "Atlas of Microstructures"

V. 8 "Metallography, Structures and Phase

Diagrams"

9th Ed. V. 9 "Metallography and Microstructures

A laboratory course designed to introduce students to the methods of

materials characterization (microstructures and properties).

Experiments involve specimen preparation and microscopic structure

examination. The specimens are chosen to illustrate the role of

materials processing and history on microstructure and properties.

Materials processing includes: casting, mechanical deformation and

heat treating of metal alloys.

I. Introduction to laboratory facilities, notebook use and laboratory

safety procedures and regulations.

II. Safety Review and Experiment I (individual assignment using

metallurgical microscopes).

III. Experiment II (group project on materials processing and

microstructure/properties measurement)

COURSE GRADING:

NOTE:

Topic

Safety Quiz

Experiment I Report

Experiment II Report

Lab Notebook*

% of grade

5

25

35

35

100

*Lab Notebooks are to be available for collection and examination at all times.

All entries should be permanent and up-to-date. (See Dept. Stds. for Lab

Notebooks.)

Each student should bring to lab

1. A notebook; permanently bound, 10 1/8x7 1/8 inch,

5x5 quad ruled pages.

2. A pair of safety glasses with side shields or safety

goggles.

9

1990/09/19

Paper for the 4th Annual National Educators' Workshop on Standard

Ex periments in Engineerin g Materials . Science 8< Technolog y. November

13-15, National Institute of Standards &^ Technology, Gaithersburg, MD

INSTRUCTIONAL SOFTWARE FOR TEACHING

POLYMER SCIENCE AND ENGINEERING

Witold Brostow

Center for Materials Characterization

University of North Texas

Denton, TX 76203-5308

and Michael R. Kozak

Department of Industrial Technology

University of North Texas

Denton, TX 76203

1. Formulation of the problem

Teaching a comprehensive course in polymer science and engineering (PSE)

is a complex task. Let us consider teaching processing as an example. The

student has to acquire, at least to some extent, skills of a processing machine operator. Moreover, he has to be able to modify the process parameters

in function of the nature of the material and property specifications imposed

upon the product. Further, contemporary processing machines have computerized decision-making units where process parameters are changed automatically. However, one cannot trust blindly those decision units; they work

according to certain universal algorithms - not necessarily best suited to a

specific resin or a specific product. Other constituting elements of PSE

such as synthesis, characterization, mechanical testing or viscoelasticity

pose similar problems in teaching.

2. Ap proach taken i

We have solved the above complex problem by using a variety of concomitant tools and approaches to teach PSE: a) lectures; b) video presentations; c) computer software for personal computers with schemes, computations and animations - used by the students individually on their own time;

and d) hands-on experience with processing equipment (computer-controlled

closed loop; injection molder; temperature controller and liquid chiller;

pneumatic loader and dryer; robot). At the University of North Texas we

are working on a project called CIMSE , or Computer Instruction in Materials

11
Science and Engineering. The software we are developing for instruction in

polynners forms a part of CIMSE. Already in 1981 a distinguished national

panel ' has concluded that there is a "... need for progranns and actions that

will augnnent the present representation of polynner studies in the universities and enhance their quaHty. The intellectual challenges and practical dividends ... and the relevance of polynners to national needs ... warrant attention by the academic community and interest on the part of funding agencies."

We believe that our CIMSE effort related to polymers at least one possible

response to the call of that national panel.

3. Software developed

Previously ^ we have adapted a utility called TKiSolver for solving numerical problems in materials science and engineering. Now we have amplified

the TK.'Solver software (and also converted it from black/white to color). We

have taken advantage of capabilities of Hyper Card Stacks and more recently of Super Card with color capabilities.

During the workshop we shall show our instruction scheme and demonstrate the software we have developed for Macintosh computers. We hope to

develop analogous software for IBM PCs at a later time. Since "One picture

is worth a thousand words" we show some of the screens that the student

can call from a disc - to study from and work with. The following pages of

this paper are black/white copies made from color screens/printouts.

References

1 . Polymer Science and Engineering , Report of a Panel of the National Academy of Sciences and National Academy of Engineering, C.6. Overberger and

R. Pariser, co-chairmen, National Academy Press, Washington, DC 1981

2. W. Brostow and P.P. Turner. J. Mater. Educ . 1988,10,119.

3. D.Goodman, HyperCard Developer's Guide . Bantam, New York 1988.

4. D.Goodman, The Complete HyperCard Handbook . Bantam, New York 1988.

Acknowledgments

We would like to acknowledge: participation of Mr. Miguel A. Bilbao, Mr.

Slawomir Blonski, Mr . Miroslaw Latka, Dr. Nikolai Medvedev, MissM.-H.Tai

and Mr, David P. Turner in software development; CIMSE use and evaluation by

our students in various courses; partial financial support of the E.l. du Pont

de Nemours & Co., Wilimington, DE, and the University of North Texas; and

also guidance from Mr. John T. Lund and his Committee on Educational Aid of

du Pont. 12
13
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19

DESIGN PROJECT FOR THE MATERIALS COURSE:

TO PICK THE BEST MATERIAL FOR A COOKING POT

(Including two laboratory experiments and an oral presentation)

Kopl Halperin

Division of Science, Engineering, and Technology

The Pennsylvania State University at Erie

The Behrend College

SUMMARY

We have developed a sequence of laboratories and an oral presentation which

comprise a design project in materials. We have chosen a common household object, a saucepan. The first laboratory of the term concerns itself with non-steady-state

heat conduction through the pan; the last laboratory of the term tests corrosion of

the pan. The students are then asked to make a presentation as if they were

competing for the job of materials supplier to a firm considering making saucepans.

Each lab group picks the material it feels to be the best, based on the measured

properties of thermal diffusivity and corrosion potential, as well as on everything

else they have learned during the term and during library research into other

properties which may be important. The students are graded on how well they defend

their choice of material. The feedback from the students has been good; they seem

to have learned something and enjoyed doing so.

INTRODUCTION

Many engineering students take a single course in the properties of materials,

which typically Includes a lab. This course is a good place to teach some of the

fundamentals of design, as the choice of a material is one of the main components of

any design project. Typically there is more than one material under consideration

for any project. The designer, or the student designer, must trade-off among the

better properties of each when attempting to find the optimal material.

We have chosen a simple household object, a saucepan, to illustrate the design

process. Saucepans are available made from a variety of materials; this effectively

proves that no one material is best for all of the relevant materials properties.

The material which is optimal for one property or one application of saucepans may

not be appropriate for another property or application. The manufacturer must

decide what to market, and the consumer must decide what to buy, and in the case of

saucepans, both are design decisions. Table 1 shows the available saucepan

materials. Instructors will note that the materials span the range of polymers,

ferrous and non-ferrous metals, glasses, and ceramics, and that most of the pots on

the market are composites.

We have turned the choice of material for a saucepan into a design project for

the students in our Properties of Materials course. At the end of the term, the

21
students, working in groups of two or three, must choose the best material for a saucepan based on everything they have learned in the course, and must defend that

choice to their classmates. The class gets a chance to rate how well they feel each

choice was defended.

LABORATORY WORK

The students performed two laboratory experiments relevant to this design

project. In these, they measured non-steady-state heat transfer and non-steadystate corrosion potential. These two experiments illustrate two of the most

important properties of cooking pots; their ability to rapidly and efficiently heat

what is in them, and their ability to withstand corrosive environments such as the

foods being cooked in them. This latter property is one of the important ones for

determining how long the pot will last, and it is important for ease of cleaning,

and for toxicity. Both experiments are non-destructive.

The two experiments have been described elsewhere (1,2). Briefly, in both of

them each student brings in a small saucepan. The instructor at this point owns a fairly impressive array of pots, and generally also contributes one or two to the

experiment. In the heat transfer experiment it is important to rule out the effects

of the geometry of the cooking surface, and so pots of similar geometries are

compared to one another. It turns out that material dominates geometry (1).

In the heat transfer experiment, 500 ml of water is poured into the pot and the

pot is placed on a pre-heated electric burner or over a flame. We have found the

flame to work better; the electric burner makes uneven contact with some of the

pots. Of course, ability to work on an electric burner is a criterion in the design

of a saucepan. The temperature of the water is monitored constantly and recorded

every 15 seconds. The experiment is terminated when boiling is reached or when a couple of minutes of constant temperature readings occur. The experiment is

repeated with each of the other pots. The results are compared to tabulated thermal

conductivities and dif f usivities , and it is generally obvious that the material with

the highest heat transfer coefficients heats water the fastest, as expected.

The heat transfer experiment is performed first in the term as a simple way to

introduce the students to what is expected of them on a lab report, and in order to

introduce the concepts of design early on. In addition, the students have already

had an introduction to heat transfer, and are thus familiar with the properties

involved. We have found this to work out well.

Figure 1 shows a student plot of data from the heat transfer experiment.

The corrosion experiment is performed at the end of the term. Corrosion is a property studied in the properties of a materials course, and thus is familiar to

them by the end of the term. And since this experiment is once again one involving

design, it comes at the end as a wrap-up, and a way to lead into the final oral

presentation, the design project.

In the corrosion experiment, 500 ml of 3 wt % table salt solution or of vinegar

is placed in each pot. A reference electrode is inserted into the solution, and

another lead attached to the pot wall. The potential is measured on a multimeter.

The property measured is non-steady-state corrosion potential of the pot. Non22
steady-state is, of course, the way saucepans find use. We have had the students

heat the pot with the corrosive solution in it. This is particularly useful with

stainless steel, which is attacked by boiling organic acids such as vinegar, but not

by room temperature ones (3) .

The results are plotted as corrosion potential against time. The results are

compared to published corrosion rates, and follow as expected. The only pot

material in which surprising results are gotten is stainless steel; for stainless,

the non-steady state corrosion we measure may not be the same as the steady state

corrosion tabulated in corrosion rates tables, as the protective oxide layer

apparently needs time to form.

Figure 2 shows a student plot of data from the corrosion experiment.

THE DESIGN PROJECT

The students give two short oral presentations on lab work during the course of

the semester. At the end of the term, they are asked to give a more major

presentation, a design project involving their data from the two saucepan

experiments described above.

Each student group is asked to pick the material they prefer of the ones

saucepans are made from. Table 1 lists the options. They then are asked to present

a talk as if they were trying to convince a manufacturing firm to buy their material

to use for making saucepans.

Each group has to list the important properties that a saucepan should have.

Some of these properties are shown in Table 2. The students must do library

research on at least one property that they did not test. In their presentations,

they show data from their two experiments and from their library research to back up

their argument as to why their material has the optimal combination of properties.

There is no right or wrong optimal material for making a saucepan. The grading

is on the effectiveness of the presentation, the depth of the research, and on

whether the group made a convincing case for their material as the best one for the

job. The students get a chance to evaluate the effectiveness of their peers, in

writing.

r CONCLUSIONS

The range of pots that different groups have chosen for their design was great.

Some chose aluminum, because of its heat transfer advantage, some chose stainless,

because of a combination of middling heat transfer, good corrosion resistance, and

good mechanical properties. Some chose vitreous enamel on steel because of its

next-to-top heat transfer properties and excellent corrosion resistance. Some chose

cast iron, because of its good thermal conductivity and its nutritional advantages

(4). We have learned that students will enjoy and do well at a design project which

involves materials which are familiar to the students, and which they can relate to

their own lives.

23
REFERENCES

1. Negrin, Barry; Landry, Adam; Halperin, K. : Heat Conduction in Pots and

Pans. J. Mater. Educ, vol. 11, 1989, pp. 397-406.

2. Meehan, Kevin; Halperin, K. : Corrosion Potential of Common Cooking Pots

Under Conditions of Simulated Use. J. Mater. Educ, vol. 11, 1989, pp.

407-415.

3. Schweitzer, P. A.: Corrosion Resistance Tables: Metals, Plastics,

Nonmetallics , and Rubbers. 2nd ed.. Marcel Dekker, Inc., New York and

Basel, 1986.

4. Brittin, Helen C; Nussaman, Cheryl: Iron Content of Food Cooked in Iron

Utensils. Journal of the American Dietetic Association, vol. 86, 1986,

pp. 897-901.

TABLE 1. SAUCEPAN MATERIALS AVAILABLE TO THE CONSUMER

IN THE UNITED STATES, FALL 1990.

Simple Materials

Material

Stamped aluminum alloy

Anodized aluminum alloy

Cast iron

Borosilicate glass

White ceramic

Class

Non-ferrous metal

Non-ferrous metal

Ferrous metal

Glassy ceramic

Polycrystalline ceramic

II. Composites

Materials

Cast aluminum alloy, PTFE lined

Wrought aluminum alloy, PTFE lined

Anodized aluminum alloy, PTFE lined

Cast iron, PTFE lined

Vitreous enamel on mild steel

Stainless steel, aluminum core

Stainless steel, copper core

Stainless steel, aluminum bottom

Stainless steel, copper bottom

Copper alloy, tin lined

Copper alloy, nickel lined

Classes

Non-ferrous metal, thermoplastic

Non-ferrous metal, thermoplastic

Non-ferrous metal, thermoplastic

Ferrous metal, thermoplastic

Glassy ceramic, ferrous metal

Ferrous metal, non-ferrous metal

Ferrous metal, non-ferrous metal

Ferrous metal, non-ferrous metal

Ferrous metal, non-ferrous metal

Two non-ferrous metals

Two non-ferrous metals

24
TABLE 2. SOME IMPORTANT CRITERIA OF MATERIALS FOR SAUCEPANS

I. Criteria Measured by the Students in the Lab

Criterion Physical Property

Fast-heating

Non-corrosible

Thermal conductivity and diffusivity

Corrosion potential

II. Other Criteria

Criterion Physical Property

Non-breakable

Non-dentable

Non-meltable

Non-stick

Non-abrasible

Microwavable

Inexpensive

Nutritious

Non-toxic

Toughness

Strength, ductility

Melting point and softening point

Friction coefficients

Abrasion resistance

Electrical conductivity

Extraction and forming costs, marketing

Bio-chemical properties

25
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27
Appendix 1: Lab handout on heat transfer experiment.

Heat Transfer through Common Pots

Object: To determine the heat transfer behavior of various common pot

and pan materials under simulated cooking conditions. To compare

those non-equilibrium conditions to the tabulated values of relevant

materials properties: thermal conductivity k, or thermal diffusivity.

To determine which pot heats water the fastest, and decide if that

result is based more on materials properties or on pot geometry.

Specimens: Various pots and pans, depending on what is brought in by

different students in different sections. Possibly including:

American-made stainless steel. Far Eastern stainless steel, ceramic

coated steel, aluminum, PTFE-lined aluminum, cast iron, and glass or

ceramic, with some more exotic materials possible.

Special apparatus: Gas burners, thermometer, watch with second hand.

Or possibly computer A-to-D board with thermocouples.

Procedure

1. Light the burners.

2. Choose a pot.

3. Pour 500 ml of water into the pot,

4. Take a reading of the initial water temperature.

5. Place the pot on the burner and simultaneously lower the

thermometer into the pot.

6. Take a temperature reading immediately, and again every 15

seconds

7. Continue taking readings until the water temperature reaches

boiling (100 degrees Celsius) or until the temperature levels off,

meaning the reading is the same for four consecutive times.

8. Dump out the water and allow the pot to cool, run cold water over

the thermometer.

9. Select another pot, and repeat.

Plot: temperature versus time for four to six pots on the same plot.

Be sure to label the overall plot, the x-axis including units, the yaxis including units. Make sure all data plotted together is from

the same burner. Make a second plot for data from the other burner.

Report: The report will be a formal written report, following the

standard format I have given you. Discuss the correlation of the

data with published values of k. Discuss what you feel is the best

pot material for heat transfer.

Note to NEW90 participants: sometimes I have given the students a

heat transfer equation to fool with, and sometimes not. Sometimes I have given them a calculation of energy wasted by using the slowest

pot, and sometimes not. I own a number of the cheaper pots

available; it is an inexpensive lab to run.

28
I

Appendix 2: Lab Handout on Corrosion experiment and final project.

Corrosion of Common Pots

Object: To determine the corrosion behavior of various common pot

and pan materials under simulated cooking conditions. To compare

those non-equilibrium conditions to the conditions of more typical

corrosion results. To compare the corrosion results obtained on the

pot and pan experiments to the more typical galvanic series, as in

Table 21.1 from M.F. Ashby and D.R.H. Jones, Engineering Materials,

Pergamon Press, Oxford, 1980. To combine the corrosion data with

other data on pots and pans, to pick the best possible pot material.

Specimens: Various pots and pans, depending on what is brought in by

different students in different sections. Possibly including:

American-made stainless steel. Far Eastern stainless steel, ceramic

coated steel, aluminum, PTFE-lined aluminum, cast iron, and glass or

ceramic, with some more exotic materials possible.

Special apparatus: Reference electrode, voltmeter or computer A-to-D.

Or one can use a strip of low-potential material for the reference

electrode, for example copper.

Procedure

1. Make a solution of salt water. Our solution will be 10 g NaCl in

one liter water. You must calculate what that is by weight % and by

mole %.

lA. Make an acidic solution of 1/2 vinegar and 1/2 water. The

acidity of this is nominally 2.5%.

2. Choose a pot, pour 500 ml of the salt solution into the pot.

3. Lower the reference electrode into the salt water. Attach one

lead to the reference electrode, the other to the wall of the pot.

The two leads go to a voltmeter.

4. Measure the initial voltage, and the voltage subsequently at 15

second intervals, until 5 minutes. In most pots, these voltages will

be negative.

5. Vigorously scrape the bottom of the pot (unless it is Teflon lined

aluminum) with a glass rod. Glass is chosen so that it adds nothing

to the water, being harder and more inert than pot materials. A

steel spoon might give spurious readings by corroding itself.

6. Then make the same measurements as in the previous step.

7. Repeat the above steps with the remaining pots, and with acidic

solution.

Plot: voltage (remember it is usually negative) versus time for each

pot, scratched and unscratched, separately for salt solution and

acidic solution.

Report: I'll want the following plots: One for each pot, scratched

and unscratched on the same plot. Plot one for all the pots

unscratched, on the same plot. In your discussion, compare this kind

of experiment to the equilibrium data of the charts you have. And

discuss what the scratching does. Discuss what you feel is the best

pot material for corrosion, and then discuss the best pot material in

general, taking into account your pot heat transfer data.

The report will be the last oral presentation, and will include the

results from this lab and from the heat transfer one at the

beginning. Taking into account corrosion, heat transfer, and any

other variables you feel are important (with bonuses given for good

discussion of extra variables), answer the question (and defend your

answer) What is the best cooking pot material? 8 minutes per group.

29

CRYSTAL MODELS FOR THE BEGINNING STUDENT

F. Xavier Spiegel

Loyola College

Department of Electrical Engineering

and Engineering Science

4501 N. Charles Street

Baltimore, MD 21210

SUMMARY

A set of hard sphere models for the B.C.C., F.C.C., Hexagonal, and H.C.P. crystal

structures has been produced to help materials science students to understand the relationships

of the atom positions in these and related structures. The models consist of sets of arrayed

vertical rods and uniform size spheres containing oversized diametral holes for easy placement

onto the rods. Many unit cells result that can easily be assembled and disassembled one

sphere (atom) at a time. The crystal models are constructed so that nearest neighbors touch

and the important planar as well as directional linear arrays are easily visualized and identified. The effect of stacking sequences, vacancies, and impurity atoms can also be shown

quite dramatically.

INTRODUCTION

Ball and stick models of the crystal systems have been available for quite some time^

Experience has shown that these models have been very useful but do not show many unit

cells, and consequently can be misleading as to nearest neighbors, size and position of

interstices. Models which are glued together invariably show only certain planes and relationships and consequently can also be misunderstood because important crystallographic information is rendered either partially or totally invisible. Ruoff pictured some very interesting

models which seem to alleviate many of these difficulties^. These models represented many

unit cells and were constructed in such a way that the nearest neighbors touched and the

individual atoms could be removed one at a time to show various planes, interstitial sites etc.. Models for B.C.C., F.C.C., and the hexagonal system were designed and constructed based on

Ruoffs pictures.

DESIGN

The calculations for the spacings and placement of atoms in most crystal systems are

straightforward once the size of the atom is known. Hard wooden spheres, nominally one inch

(2.54 cm) in diameter, with a 1/8 inch (0.3175 cm) diametral hole were selected based on the

desired size of the models and ease of visualization. Various colors were selected for ease of

demonstrating ordered structures and stacking sequences. The spheres were each measured

31
for uniformity of size and placement of the diametral hole. Upon inspection only a few

spheres were rejected, none for size, although since the spheres were painted the diameter

was 1.025 inches (2.604 cm). The spheres which were rejected had holes which were off

center. The eccentricity was checked by placing the sphere on a 3/32 inch (0.238 cm) rod and

rotating the sphere. Visual observation was sufficient to determine eccentricity.

The number of unit cells to be shown for each crystal system to allow for clarity of

observation was determined to be at least twenty seven unit cells. Twenty seven might seem

to be a large number of unit cells but experience with smaller models met with mixed success. With the above restrictions, the design concluded with the selection of 3/32 inch diameter

Type 303 stainless steel for the rods and Micarta for the base material. The Type 303

stainless steel was selected for durability and rigidity, while Micarta was selected because there

was a scrap supply made available. Any hard wood will probably work as well. The base

layout patterns for the three models are shown in Figures 1-3. These patterns show the

placement of the stainless steel rods. The holes are 1/2 inch (1.27 cm) deep and the rods

extend approximately six inches (15.24 cm) above the base. Note that in the case of the

hexagonal system (Figure 3) there are no rods to support all of the possible stacking sequences. Placement of such rods would not allow the spheres to stack at all. Merely dropping a sphere into the system once the first layer is placed will give one of the other two stacking

sequences and the third sequence can be demonstrated by dropping spheres on the second

layer. Photographs A-E show some of these models assembled to demonstrate the B.C.C.,

ordered B.C.C, disordered B.C.C., the (111) plane of the F.C.C., and the ABC stacking of

closest packed planes (F.C.C.). Table 1 lists the supplies and cost information.

THE EXPERIMENT

The student is given the bases with rods imbedded and a supply of spheres, and

instructed to place the spheres on the appropriate rods or interstices to construct the basic

models. The bases are not labeled in any way in order that the student put some thought

into the lattice position of each layer and the appropriate placement of subsequent layers.

Once the model is constructed with identical spheres, the student is advised to find various

planes, directions and interstices by disassembling the model. The effect of a vacancy,

impurity, or interstitial can also be investigated by merely leaving a position vacant or

introducing a smaller or larger sphere at a regular lattice site or at an interstitial site.

Stacking sequences can readily be studied using the hexagonal model and the relationship

between the F.C.C. and hexagonal structures is dramatically seen. Ordered structures can be

demonstrated by using different colored spheres in the appropriate positions. Disordered

structures can be demonstrated by randomly selecting different colored spheres and dropping

them in place. The relationship between primitive and conventional unit cells can also be

demonstrated.

32
EXPERIENCE

The students have received these models with enthusiasm. Quite often the students

refer to these models in subsequent laboratory sessions to better understand a particular

feature of a crystal or to explain a concept to a classmate. Colleagues have frequently used

these models and remarked how useful and straightforward the models are. These models

have been used for over 500 hours and have shown no appreciable wear or damage.

CONCLUSIONS

For a modest investment, a set of crystal models for three of the most important

crystal systems can be constructed. These models can be assembled, disassembled, and

modified to show the fundamental relationships between atoms, directions, planes, and

interstices as well as vacancies, impurities, interstitials and stacking sequences. Ordered and

disordered structures can be easily demonstrated. More detailed drawings suitable for

machining are available upon request.

ACKNOWLEDGEMENTS

The author wishes to express his gratitude to Mr. John Ross, friend and Research

Associate at The Johns Hopkins University, for his continued encouragement and advice on

this project, and to Mr. Walter Krug and Mr. Michael F. Franckowiak for their assistance and

the machining of the bases, I also wish to thank my daughter, Stephanie, for typing this

manuscript. A special thanks to Mr. Howard Moore, Technical Assistant, Loyola College

Physics Department, for his speedy production of the photographs.

33
REFERENCES

1. Klinger Educational Products Corp. 112-19 14th Road, College Point, New York 11356.

2. Ruoff, Arthur L. : Introduction To Materials Science. Prentice Hall, 1972, pp. 249-250.

34
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Photograph B

An Ordered Body Centered Cubic Structure

41
Photograph C

A Disordered Body Centered Cubic Structure

42
Photograph D

The Face Centered Cubic Structure with the Closest

Packed Plane (111) clearly visible

43
Photograph E

ABCA Stacking of Closest Packed Planes Demonstrating

the Face Centered Cubic Structure

44
MICROSTRUCTURE ANALYSIS

(UNIVERSITY AND INDUSTRY PARTNERSHIP)

by Donald H. Martin - Assistant Professor IPFW

and

Gary L, Dawson - Metallurgical Analyst Dana Corporation

SUMMARY:

This paper describes a laboratory experiment using an industrial

partnership, utilizing the University and Industry strengths. In Phase

I the student will tour the Plant Research and Product Development

Laboratories. He will follow all the necessary steps to prepare a

material sample and analyze the nodule count and roundness measurements

in ductile iron, using the Leco 2001 Image Analysis System. In Phase II

the student will be given a known sample and will be required to develop

a written laboratory report which will include: title, objectives,

procedures, library research, conclusion, and bibliography.

INTRODUCTION

:

Industries today are forming partnerships with each other and utilizing

each others particular strengths to form the strong, long lasting

business directions that are necessary to survive. Education needs to

be a part of that long term partnership. Purdue (IPFW) and Dana

Corporation are working together to provide the needed real world

working exposure to students when it comes to material testing and

analysis

.

OBJECTIVES:

1. To understand the methods of preparing and evaluating

metallographic specimens, and to familiarize the student with the

fundamentals of metallography.

2. To visit an Industrial Metallography Laboratory and follow the

process of obtaining, preparing, examining, interpreting, and

photographing representative metallic specimens.

3. To provide for the identification and evaluation of known material

samples (material analysis and reporting) including lab report &

research.

EQUIPMENT

:

Dana Corporation

1. Abrasive wheel cut-off saw (12")

2. Sample Mounting Press

3. Roll Grinder Sample Polisher . 4. Hardness Testers

5. Image Analysis System (Leco 2001)

45
Purdue

6 . Set of Knovm Material Samples

7. Specimen Mounting Equipment

8. Polishing Equipment (250, 400 & 600 grit)

9. Acid Etch (2% NITAL)

10. Metallurgical Microscope

11. Camera for Photomicrography

PROCEDURE

PHASE I: DANA CORPORATION LIGHT AXLE DIVISION TOUR

Dana Corporation - Spicer Light Axle Division, Materials Engineering,

Fort Wayne, Indiana recently developed a Laboratory Manual for their

complete operation. Included in the Manual is the following analysis

flow chart.

MATERIALS ENGINEERING LAB

ftNALVSIS FLOU CHART

SAMPLE FOR EUALUATIOH

LOG-IH PROCEDURES

OBTAIN MATERIAL SPECS

ft RELATED IHFORtlATION

SAMPLE PREPARATION

{ i I

PHVSICAL

TESTINQ

CHEMICAL

AHALVSIS

PHVSICAL

AHALVSIS

URIIE REPORT CHANGES on CLAHIFICflllOHS

REPORT APPROVAL

REPORT DISTRIBUTION

This pictorially shows all the necessary steps used to process a sample

through their Materials Engineering Laboratory.

This is the actual sequence that is followed for testing and reporting

material samples in the Dana Corporation - Materials Engineering

Laboratory.

46
During the tour of the Dana Corporation - World Axle Development Center

students will observe the following:

1. Axle Design and Development

2. Axle Testing (Machine Endurance Testing/Fatigue Testing)

, 3 . Metal Sample Preparation

4. Metal Sample Testing

5. Leco 2001 Image Analysis System Operation

6. Analysis and Reporting of Data

The Leco 2001 Image Analysis System is a powerful, fast, flexible tool

that is used to perform very detailed examination of metal samples. The

system is easy to operate and does not require in depth knowledge of

computer operating systems (it is menu driven). The operator is able to

measure the grain size in steel, nodule count and roundness measurements

in ductile iron, length and width measurements of inclusions in steel

and particle size distribution of carbides in tool steel. Simply

prepare the sample , place it under the microscope and use the Image

Analysis System to evaluate the sample for necessary characteristics.

Student response sheet must be turned in the following class period.

(Attached)

PHASE II: LABORATORY AT INDIANA-PURDUE UNIVERSITY

MATERIAL: Two (2) mounted and prepared known samples.

DISCUSSION: This lab provides a brief introduction into the topics of

metallography and metallic microstructures . Metallography

can be defined as the study of the structure and physical

properties of metals and alloys, especially by the use of

the microscope and X-rays (taken from Webster's New World

Dictionary) . Microstructures can be thought of as the

structure of a metal or alloy as seen under a microscope.

PROCEDURE: (The following is a brief procedure for preparing a sample

for microscopic examination)

.

1. If the specimen is smaller than 1/2 inch in diameter

or in length, it must be mounted in bakelite in order

to provide a sample large enough to be easily handled.

2. The specimen should be ground down to a flat surface

on a belt sander.

3. The coarse scratches are removed by using

progressively finer grades of emery paper. The

direction of sanding should be 90° or perpendicular to

the direction of the scratches . As the different

grades of emery paper are used, the specimen will be

rotated 90°.

4. When changing emery paper grades, i.e. going to a

finer grade, the specimen should be thoroughly washed

and dried to remove any remaining course grains of

emery which could accidentally scratch the surface as

sanding and polishing continues

.

47
5. When a highly polished surface is achieved, free of

any scratches, the specimen should be washed in an

alcohol bath and dried in a warm air blast to prevent

oxidation of the polished surface.

6. Normally a specimen would be etched. Etching removes

parts of the polished surface, causing the

microstructure to stand out or develop more clearly.

The etching solution to be used depends upon the type

of specimen and the test results sought.

(Since the samples were already mounted and polished,

experiment began with Step #7.)

7. Finish polish the metal specimen if necessary to

remove any heavy scratches

8. Examine each specimen using a metallurgical microscope

at high power. Sketch the general outline or shape of

the sample as well as the observed microstructure,

noting any significant features.

9. Make a Rockwell hardness reading of each sample,

recording the reading and the cross-referenced Brinell

hardness reading.

10. Look up the microstructure of each sample, and using

the hardness data, attempt to identify each structure

or sample

11. Write Laboratory Report following the format and

instructions for laboratory reports (must include

research and references)

48
LABORATORY REPORT FORMAT AND INSTRUCTIONS

TITLE

:

OBJECTIVES

;

State name of experiment. If possible, briefly state

primary and overall- -range- -objectives

.

List step -by- step sequence of making experiments, if

possible to predict.

EQUIPMENT AND ACCESSORIES: Name and sketch; describe operating principles of

equipment. Itemize any standard accessories to adapt

equipment for test.

TOOLS AND SUPPLIES: Hand tools- -standard or special, expendable items,

handbooks or tables, special grips, clamps, scales, gauges,

measuring devices or others, sandpaper, crayons or special

marking devices, clay, magnets, mirrors, rags, towels, drip

pans

.

SKETCHES

;

DATA:

GRAPHS

:

Block diagrams, flow charts, system diagrams, pictorial,

cross section, assembly, detail, mechanism, plumbing,

electrical, structural, method sketches to illustrate

complete operation details. (Frequently, a complete

knowledge of small details will point out errors or

fallacies in experimental methods and erroneous results that

lead to wrong conclusions.)

Take standard type data over wide enough range to include

any pertinent changes , or change in trends

.

Record all variables that could have slightest effect on the

test. Re-evaluate later during analysis and write-up for

further check on their effect. List data to be taken

including initial, periodic, and final readings.

List requirements with x/y/z coordinate titles and units.

List required graphs based on both direct readings and

calculated data.

WRITE-UP: Include graphs, sketches, drawings, applicable equations

with sources and units, calculated results, comparisons with

data of other researchers (including other teams and library

references), reasons for variances between tests. Discuss

improvements you might make in a repeated experiment , such

as sample selection, method, technique, equipment change,

etc. In your write-up include description of any special or

new skills or techniques you learned and include sequence of

making the test or experiment.

CONCLUSIONS: Summarize knowledge that has been verified or expanded and

give possible utilization in industry. Briefly list any

possible directions or goals to expand knowledge for more

efficient or better usage or processes or materials.

REFERENCES: List complete bibliography.

49
DANA CORPORATION LIGHT AXLE DIVISION TOUR

STUDENT RESPONSE

The following are three questions that will be answered during your tour at

Dana. The three areas you will be touring are the Engineering Test Lab, MET

Lab, and Technical Service Department. You may find it interesting how all

three areas are related. Please answer the questions and return to your

instructor per his instruction.

1.) What is the importance of a wet cut vs. a dry cut as far as a

metallurgical analysis and how does each effect the physical properties?

Answer: Dry - It can heat the part and cause microstructural transformation

and alter hardness values

2. ) Using an lA (Image Analysis) system, how can you ascertain the density of

PM (Powder Metal) components?

Answer: (100% - % porosity) x density of steel

3. ) Name two types of actuators that are used in fatigue testing and why are

both types required?

Answer: To simulate road or running conditions, the component must be exposed

to the same type of loading experienced in the field. (E.I. axle shafts =

rotary: Spindles = linear)

50
NOTES FOR THE LABORATORY INSTRUCTOR

AT IPFW

MACROGRAPHIC (Qualitative) - Samples evaluated by eye, or by magnifier (to 30

X ). Sample preparation is simpler, inspected areas are larger, and

interpretation is generally descriptive. Some specimens may be smoothed

and etched, but unprocessed pieces may be adequate. For example, a

tensile or bending sample exhibits ductile necking and cup-cone

fracture, whereas another sample shows a brittle glassy- smooth fracture

and no necking.

MICROGRAPHIC (Quantitative) - Samples evaluated by metallurgical microscope

(reflected light, 30 x to 2000 x) . Sample preparation is much more

critical, smaller areas inspected and measured, with statistical

interpretation of data. Therefore, specimens are carefully polished

(with aluminum- oxide abrasive or diamond paste) and then lightly etched

(with acids or bases)

.

SAMPLE PREPARATION:

MACROSCOPIC - Sample cutout by torch or hacksaw. Specimen sectioned by

"Abrasimet" water-cooled cutter. Burrs ground off. Surface planed by

belt-sander and smoothed on table -grinders (water-cooled) . Polishing by

No. 00 or 000 (size) emery paper may suffice. Avoid frictional heating,

structural distortion, and obliteration of features. Then, sample is

alcohol-wiped (degreased) , water-dipped (heated) , and completely wetted

by reagent (etched) . A 10% solution of nitric acid (HN03) is used for

steel structures; forged- steel flowlines and heat-treating quench cracks

are revealed by 50% water solution, of hydrochloric acid (HCl) or 25%

solution of nitric. After deep-etching is complete, the sample is

scrubbed in hot water, dipped in benzene or acetone, and dried in warm

air-blast. When a dry surface is coated with printer's ink, an

impression may be transferred to art-paper. Also, a simple macrograph

may be obtained by pencil -rubbing or photography.

MICROSCOPIC - Samples are obtained and smoothed as before. Howeverflame -cutting and frictional over -heating should be avoided, because all

surface and sub -surface distortion must be removed by fine polishing and

light etching. Then, a thin section is cutoff (water-cooled) and

mounted in thermoset plastic (Bakelite or Lucite ) . Remove plastic

"flash", lightly round edges (top and bottom), carefully flatten the

sample surface (by wet-belt sander) and leave only parallel scratches.

After thorough washing (hands and sample) in soap and water, start the

complex process of Grinding and Polishing. (Instructions posted at the

machines). Examine polished samples by microscope to detect defects,

which require repolishing. Ideally, a mirror- surface (scratch- free at

1000 x) is achieved before etching. Handbooks are used to

selectreagents , strengths, and applications. For high magnifications

(above 100 x) only a lightly -etched surface is wanted. Additional

etching is easy - over etching requires considerable repolishing.

Finally, rinse etchant off (warm, running water), flush with alcohol,

and dry with warm air-blast. The sample is ready for final microscopic

study.

51
REFERENCES

"Mlnimet Polisher/Grinder", Buehler Metal Digest, Vol. 20, No. 1, 1981.

"Metallographic Sample Preparation, Fine Grinding- Polishing" , Buehler Metal

Digest, Vol. 20, No. 3, 1981.

"Isomet Low Speed Sectioning of Materials", Buehler Metal Digest, Vol. 22, No.

1, 1982.

"Metallographic Test Specimens", Buehler, No. 81-1800 General, 1980.

"The Art of Grinding", Lee Dillinger, Leco Met-Tips No. 11, 1984.

"Sectioning", Lee Dillinger, Leco Met-Tips No. 12, 1986.

"Polishing", Lee Dillinger, Leco Met-Tips No. 13, 1985.

"Tricks-of-the-Trade" , Lee Dillinger, Leco Met-Tips No. 14, 1985.

"Etching", Lee Dillinger, Leco Met-Tips No. 18, 1984.

"Metallographic Sample Preparation", Cornelius A. Johnson, Leco Corp., 1977.

"Metals Reference Book", Shithells, Fourth Edition, Volume 1, pp. 315-351.

"Simplified Metalloscope" , Catalog No. 31-21-39, Bausch & Lomb Incorporated.

"Leco 2001 Image Analysis System", Form No. 203-731-001, Leco Corp., 1989.

52
A NONDESTRUCTIVE TESTING METHOD TO DETECT

DEFECTS IN STEEL PLATES

BY

Mostafiz R. Chowdhury

Department of Construction Management

East Carolina University

Greenville, North Carolina

KEY WORDS: Nondestructive Testing, Modal Analysis, Frequency Response Measurement

ABSTRACT

The vibrational response of a structural system to random excitation contains a unique

characteristic signal for that structure. Using proper signal analysis techniques, this signal can

be retrieved from the random response. A study of this characteristic signal, which contains

information of system behavior, can be used to diagnose system performance. This study

examines the dynamic response of two similar metal plates and evaluates the changes in

dynamic properties due to changes in mass, stiffness and damping. This dynamic response

method will use frequency and modal domain analysis for identifying the dynamic parameters

of the system. The test objects will be tested before and after introducing simulated defects. A

metal rod will be tested similarly to determine the stiffness co-efficient of the material.

OBJECTIVES

The objectives of this experiment are as follows:

i) To relate changes in stiffness, mass, and damping to dynamic parameters of a structure.

ii) To compute the stiffness of a steel rod by evaluating the dynamic response function.

THEORY

A structure when vibrating freely, no external load acting upon the system, tends to assume a

vibrational pattern which is a function of the material and the boundary conditions of the

structure. A freely vibrating system contains information which is unique to its type and can be

studied for extracting the structural behavior of the system. Dynamic information of such

vibration can be measured and expressed by different parameters such as frequency, damping,

and modes of vibration. Experimentally these parameters can be measured by using a dynamic

analyzer. An analysis of the dynamic properties obtained from such a nondestructive testing

procedure can then be used to identify the structural strength, integrity or possible defects.

An experimentally measured dynamic response function can also be used to compute the

stiffness of a structural member. For a known value of fundamental frequency (cOn), the

stiffness coefficient, E, of a structural member can be determined from the standard equations

for natural frequencies, as found in the literature [1]. For a free-free rod the formula for

determining the stiffness coefficient E, equation (2), is obtained from the standard equations

for natural frequencies of a free beam as shown in equation (1).

53
= c

EI

CO n n (1)

where cOn is the natural frequency for the nth mode,

Cn is a constant,

E is the modulus of elasticity,

I is the moment of inertia,

m is the mass per unit length,

and L is the length of the rod.

The dynamic properties of a structure are functions of its mass, stiffness and damping. A

change of these properties, which may result due to many reasons, such as degradation, or

material fatigue, will have a direct influence on the dynamic behavior of the structure.

Conversely, therefore, changes in the dynamic properties can be used to study the changes in

the structural behavior of a system. The trend of such variation in the dynamic behavior will be

used to diagnose the structural performance as well.

MATERIAL SET-UP AND EQUIPMENT

A steel rod of length 25.35" (64.4 cm.) and mass 1.416 lbs (642.3 gm) was used to collect the

data for the stiffness measurement. The diameter of the rod ((])) is 0.50394" (1.28 cm). To

determine the dynamic response of the rod for a near ideal free-free condition, the rod was

suspended at both ends by rubber bands. The lower natural frequencies of the rubber band do

not affect the frequencies of the steel rod, and so this method was taken as being a very close

approximate to the free-free condition. The rod was divided into 10 equal segments consisting

of 1 1 nodal points. The rubber bands were placed at nodal points 3 and 9.

Two metal plates, designated as "A" and "B", are used to collect the data for the structural

performance experiment. Both plates are same in size and shape, except that the plate B has a

three-eighth inch tapped hole in it (see Figure 2). Plate A is tested for two conditions, with and

without a cut. This test is performed to examine the variation in the dynamic properties between

the defective and undefective cases, due to a change in the stiffness about the stronger axis (a

cut perpendicular to the longitudinal axis). A stiffness change is simulated by a one and threefourth inch cut (a one sixteenth inch band saw blade is used to cut the plate) into its side.

Figure 1 shows the location and dimension of the cut in the plate A.

Two experiments are performed on Plate B. One test is conducted to determine the effects of an

external mass to the dynamic behavior of the plate. In this case a steel block (2"x2.75"xr') is

mounted on the plate with a threaded bolt. Figure 2 shows the mounting location of the extra

mass on plate B. In the last test two weatherstripping dampers are added to plate B, as shown

in Figure 3, to observe their influence. The self adhesive on the back of the weatherstrip is

used to bond the damper to the plate.

Both of the carbon tool steel plates tested have the dimensions of 9"xl2"x5/8". Plate A weighs

19.18 lbs. and Plate B weighs 18.82 lbs. The weight of the additional block is 1.54 lbs. A

neoprene sponge rubber (3/16"x3/8"x 9") made by Maico Inc, Cleveland, Ohio is used for

.•.E = (2)

54
adding dampers on plate B. Each plate is divided into a grid with 25 excitation points as shown

as in Figures 1-3. For all test cases, the plates are simply supported over one and a half inch

wide plastic foams. These supports are placed along nodal Unes 6-10 and 16-20.

A mid-size impact hammer (PCB model no. 086B03), a 0-500 Ibf range, with a steel tip (hard

tip) and a mini-size impact hammer (PCB model no. 086C80, 0-50 Ibf), with a plastic tip are used to excite the plates and rod respectively. An accelerometer PCB model 303A03 is used

for all experiments.

Data Acquisition

A portable Compaq HI computer is used for collecting and quantifying the dynamic information

of the plates and rod. In the experiment the test objects are struck by a known input force (by

the use of the hammer) and the response of the objects are collected by an accelerometer. It has

also been demonstrated by the author that a microphone instead of an accelerometer can be used

to collect the output response for the test object [2]. A Fast Fourier Transform (FFT) dual

channel analyzer (WAVEPAK) is used to digitize the analog responses (the input force and

output acceleration) of the test object. This digitized information is processed in the computer

by the use of a STARSTRUCT program (a modal analysis program) in order to obtain the

basic dynamic information of the plates. This software package also extracts modal information

of the test objects.

A maximum cutoff frequency of 8000 Hz for the plates is used to collect the data. This

corresponds to a 5 to 10 Hz frequency resolution. A cut-off frequency of 4000 Hz was used

for the steel rod.The resolution was adjusted depending upon the range of the well-defined

peaks found in the FRF functions.

PROCEDURE

The response of a test object, under any of the above conditions, due to an excitation such as a hammer, when measured by a response measuring device such as an accelerometer, can

provide the dynamic information of the system. The following procedure shows the basic

technique used to collect the data for all cases.

i) The plate (or rod) is excited at each of the nodal points~the intersections of the grid Unes that

divide the surface area of the plates into a number of segments—and corresponding response

noted. Figures 1-3 show the grid pattem for the plates.

ii) For a fixed response point (keeping the output point constant) the input and output data for

the system are collected by exciting the structure at different points one at a time.

iii) An average of at least three hammer strikes are made at each point. The hammer spectrum

and coherence plots are monitored for each strike. This ensures a reliable frequency response

function (FRF).

iv) The transfer function of the system measured as a frequency response function (FRF) is

obtained by simultaneously measuring the input impulsive force and the output response

acceleration of the system. The FRF function is the ratio of the fourier transform of the

response signal to the fourier transform of the known transient input force, and is computed by

the Fast-Fourier Transform (FFT) analyzer.

v) Once the data are collected for all grid points, the saved data are used by the STARSTRUCT

program to compute and isolate the mode shapes of the structure. These mode shapes provide

55
the corresponding modal information of the system. The modal analysis program also provides

dynamic information such as resonant frequency, damping, and mode shapes for the test

object. A mode shape is a well defined shape (waveform) assumed by a vibrating system in

which the motion of every particle is simple harmonic with the same frequency. A few of the

mode shapes for a plate are shown in Figure 4.

In the modal domain measurement, the deflection pattern of the system, the mode shape,

corresponding to each resonant frequency is clearly identified. This information reflects the

effects of the actual boundary conditions the structure is experiencing. By applying a curvefitting technique, modal parameters are derived from the measured transfer function matrix. A

complete detailed description of this method of analysis can be found in literature [3].

vi) The modal parameters (resonant frequency, damping, and associated mode shape) are used

to determine the stiffness of the steel rod as described in the theory portion of this paper. The

information can also be used to diagnose the performance of the plates.

RESULTS AND FINDINGS

Stiffness Effects

The plate A is tested for two conditions, with and without a cut, as shown in Figure 1, to

determine the effects of stiffness change. The frequency and damping for these two conditions

are compared in Figures 5a,b. In these figures, the dynamic parameters, such as frequency, are plotted for each of the corresponding modes of vibration. Only frequencies of the comparable

modes (found in both cases) are plotted and compared. From this plot, it is found that except

for the modes whose vibration patterns remain unaffected by the cut, such as longitudinal

bending (2L in Figure 5b), and 1st torsion (IT), the remaining modes show a lower frequency

for the plate with a cut. This suggests that the dynamic behavior clearly reflects the condition of

the structure. The longitudinal bending resistance (bending about the longitudinal axis) of the

plate is not decreased by the cut as it is perpendicular to this axis of vibration, and therefore no

variation of the dynamic frequency along this axis of bending.

A frequency change due to a change in the stiffness of the plate, however, does not indicate the

location of defects since frequency is the global property of a system. Mannan and Richardson

[4] have used the mode shape information to compute the system matrices, to locate the faults

in an aluminum plate. Modal damping obtained from such a test is not the actual damping of the

system. The damping variations are shown in Figure 5a.

Mass Effects

Plate B is tested with and without the addition of a weight attached at node point 24. The

damping variation for these two cases are compared in Figure 6. In both cases damping

increases with the addition of the mass. The modal frequency for the plate without the added

mass is found to be greater than that of the plate with an attached mass. This means that

frequency decreases with the addition of a mass to the system.

Damping Effects

Figure 7 shows the variation of damping and frequency for each mode of vibration for plate B

with and without a damper. An increase in the modal damping is observed for the plate when

the damper is added to the plate. However, except for the 2nd anti-torsional mode (AT2), no

change is found between the corresponding modal frequencies.

56
Estimarion of Member Stiffness

An estimation of the member stiffness can be determined from the measured modal frequency

(co) as presented in equation (1). Equation (2) is obtained by keeping all other variables, such

as area, length, mass, constant. The FRF for the rod is collected using the above mentioned

procedure. Figure 8 shows the frequency response function of the steel rod when the

accelerometer was placed at the fourth node, and tiie rod was excited at the seventh node by the

hammer.

The peaks in the graph correspond to each of the modes of vibration, first mode, second mode,

etc.. As shown in figure 8, the first bending mode has a frequency of 140 Hz. This mode

shape was confirmed by observing the mode shapes as computed by the STARSTRUCT

program. The appropriate values are substituted into the Equation (2) and E is calculated for the

first bending mode. Cn (equation (2)), for the first bending, has the constant value of 22.3733.

E was found to equal 29.145x10^ psi which closely agrees with the standard value of modulus

of elasticity for steel.

CONCLUSIONS

The experimental results presented here show the application of a nondestructive testing

procedure for system diagnosis. A measurement of the dynamic behavior and their variations

with different structural and boundary conditions can demonstrate the capability of this method

in identifying the performance of a structural system. The study shows a noticeable shifting in

the frequency as a function of the mass and stiffness changes of steel plates. This technique can

easily be used in the classroom to calculate the stiffness of a structural member.

REFERENCES

[1] Paz, Mario, (1985), "Structural Dynamics", Second Edition, Van Nostrand Reinhold

Company, New York.

[2] Bissinger, G., and Chowdhury, M. R., (1990), "Comparison of Modal Analysis

Measurements with Microphone and Accelerometer on Hammer-Impacted Structures,"

The Eighth International Modal Analysis Conference, Orlando, FL, Jan. 29 - Feb. 1.

[3] "Practical Aspects of Modal Analysis" (1988), reference materials. Structural

Measurement Systems, Inc. San Jose, CA.

[4] Mannan, M. A., and Richardson, M.H., (1990), "Detection and Location of Structural

Cracks using FRF Measurements", Proceedings of the Eighth Intemational Modal

Analysis Conference & Exhibit, v. 1, pp. 652-7.

ACKNOWLEDGEMENTS

The author is grateful to the North Carolina Board of Science and Technology for its partial

support in funding the purchase of Modal Analysis System,

57
Figure 1 : Plate A with and without a cut

58
Figure 2 : Plate B with and without an added Mass

59
Figure 3 : Plate B with and without Dampers

60
Figure 4: Mode Shapes of a Plate.

61
Data from "stiffness data"

0 08

O.OG-i

C3Z

Q.<

0.04 -

0.02 -

0.00 4J

I Damping-nc

0 Damp-Cut

IT 2TY 3T AT 2L 3TY AT2 RB

Mode

Figure 5a.: MODE VS. DAMPING FOR PLATE WITH AND WITHOUT CUT

Data from "stiffness data" 8000

6000 -

^ 4000

z

z>2

u. 2000 -

0 4- ^mmmmmm

B No-Cut

0 With-Cut

IT 2TY 3T AT 2L STY AT2 FB

Mode

Figure 5b.: r^DE vs. FREQUENCY FOR PLATE WITH AND WITHOUT CUT

62
0.8

0.6

0,4

0.2

0.0

Data from "mass data"

Ml

111

B Damping-NM

0 Damping-WM

Figure 6a . : Mode vs. Damping for Plate With and Without Mass

6000

5000 -

4000 -

3000

2000 -

1000 -

0 -y

Data from "mass data"

IT 1B 1LB 2T AT2 3T AT 3B 2BY 3TY

Mode

Figure 6b : Mode vs. Frequency of Plate With and Without Mass

No-Mass

0 With-Mass

63
0.08

Data from "damping cata"

CD

Q.

E

03 Q

0.04 -

0.02 -

0.00

i 4

i I

I

II

IT IB 1LB 2T AT2 3T AT 3B 2BY 3TY

Damping-ND

0 Damping-WD

Mode

X

>

o

z

UJo

Figure 7a. • Mode vs. Damping for Plate With and Without Damper

6000

5000 -

4000 -

3000 -

2000

1000 -

Data from "damping data"

i

II

in

1

i

11

ISI

No-Damper

0 Wittn-Damper

IT IB 1LB AT2 3T AT 3B 2LB 3TY

Mode

Fi gure 7b . : MODE VS. FREQUENCY FOR PLATE WITH AND WITHOUT DAMPER

64
Project : STEELKOp ^ Fr«q Respons* (Block 1) 4Z/ 7Z

Low«r X cursor : 140.000 ^t.. Upp«r X cursor : 140.000

Tracs A v*lu« : 4.027 Trsc* A value : 4.027

40.00

Lot Na«>

-40 .-OO

Figure 8: A Frequency Response Function for the Steelrod

(output response at node 4 and input force at node 7)

65

COOLING FIN MATERIALS

and

CONVECTIVE COOLING

Richard J. Greet

University of Southern Colorado

Pueblo, Colorado 81001

KEY WORDS

Thermal Conductivity, Convective Heat Transfer

PREREQUISITE KNOWLEDGE

The effect of the choice of material for use as a cooling

fin, and the contrast between free and forced convection can

be demonstrated without prerequisite knowledge. A knowledge

of heat transfer theory is needed to derive the equations

used for numerical analysis.

OBJECTIVES

Depending on the level of the class, any of the following

may be stated as experimental objectives:

Demonstrate that the thermal conductivity of a metal is an

important property in determining the metal's effectiveness

as a cooling fin.

Demonstrate the enhanced cooling obtainable with forced, as

opposed to free, convection.

Numerically determine the convective heat transfer coefficient for free and forced convection.

Determine the thermal conductivity of an unknown metal,

using known metals as standards.

EQUIPMENT

Test Fixture: Six rods of common engineering metals, 3/8

inch in diameter and 5.0 inches in length, were mounted

vertically by pressing them into holes drilled into a 3/16

inch thick aluminum baseplate. The materials selected were

1020 cold rolled steel, 308 stainless steel, commercially

pure copper, 70-30 cartridge brass, 1024 aluminum, and a

titanium alloy of unknown composition. Chrome1-Alumel

thermocouples were epoxied to the free ends, and three

thermocouples were mounted to the baseplate.

67
Thermocouple Measuring Device: We are currently using a

computer controlled automated data taker. This is desirable

as there are several pieces of data to collect (nine temperature readings plus the time of observation) , and also the

experiment requires up to an hour to insure that thermal

equilibrium has been obtained.

Laboratory Hotplate

Small fan: A muffin fan mounted to stand for positioning

works well.

PROCEDURE

Before turning on the fan or the hotplate, record all

temperatures

Place the test fixture on the hotplate and adjust the

hotplate setting to approximately half power.

Record temperatures every five minutes until thermal

equilibrium is obtained. For free convection, this will be

typically thirty to sixty minutes.

Turn on the fan and again record temperatures every five

minutes until the new theriual equilibrium is obtained. For

forced convection, this will be typically twenty to forty

minutes

Note: With an automated data taker, students can start the

experiment, go off to attend other things, and return later

to inspect the data to judge if thermal equilibrium has been

achieved.

ANALYSIS OF DATA

The initial temperature readings are averaged together and

taken as the ambient room temperature. This temperature is

then subtracted from the equilibrium free end temperatures

for both the free and forced convection experiments. Typical numerical results are shown in Table 1. The effect of

the choice of material, as well as the enhanced cooling

obtained with forced convection can be demonstrated by

constructing Figure (1).

68
The equilibrium end temperatures correlate with the thermal

conductivities of the metals. The values used here for

subsequent analysis, in SI units (watts/meter-kelvin) are:

Copper 400

Aluminum 240

70-30 Brass 140

1020 Steel 50

Stainless Steel 25

Another illustration of the effect of material choice on

cooling fin performance is obtained by calculating the total

power dissipated by each rod. This is determined from the

relationship:

{h/-KX) cosh (AL) +sinh (XL)

(/z/kA,) sinh (A.L) +cosh(A.L) ©0 (1)

with h -- Convective Heat Transfer Coefficient

K -- Thermal Conductivity

D -- Rod Diameter

L -- Rod Length

and

= (r--rj (2)

The subscript A refers to the ambient temperature, and the

subscript zero refers the baseplate temperature difference.

For a round cooling rod:

X = 2 (3)

For a class in which the materials are emphasized, students

are given typical values for the convective heat transfer

coefficient, for example, h=20 watts/meter ^-kelvin for free

convection and h=100 watts/meter ^-kelvin for forced convection, and instructed to compute Equation (1) for their temperature data and the values of thermal conductivity given

above. Since the calculation involves several steps, computer spreadsheets or programmable calculators are recommended. The results of the data of Table 1 with the values

of h determined below are shown graphically in Figure (2).

69
For a class in which heat transfer is emphasized, the

calculated free end temperature difference is derived to be:

The subscript L refers to the free end of the cooling rod.

This is a standard solution found in heat transfer textbooks

and assumes that heat flow through the rod in by one dimensional thermal conduction. The heated end is taken to be at

constant temperature, and all other surfaces are considered

to lose heat by convection. The experimental value of the

convective heat transfer coefficient is determined by plotting Equation (4) with thermal conductivity as the independent variable and the convective heat transfer coefficient

as an adjustable parameter. Figure (3) shows the experimental data and two computed curves for the values of h indicated. This curve fitting is most easily done using an

electronic spreadsheet.

As a final piece of experimental information, the thermal

conductivity of the unknown titanium alloy can now be determined. Using the value of h=15 watts/meter ^-kelvin for free

convection, Equation (4) computes the thermal conductivity

of the titanium alloy to be 18 watts/meter-kelvin to agree

with the measured equilibrium temperature difference. In

general , the thermal conductivities of poor conductors can

be determined in this manner. Since the computed curves of

Figure (3) flatten out with increasing thermal conductivity,

highly conductive unknown materials can be measured less

accurately.

The manufacturer of the data taking device states an accuracy of ±0.15% on voltage measurements. From the

variation of temperature readings at the beginning of the

experiment, when all thermocouples should read the same, an

accuracy of ±0.5% is assigned to temperature readings. From

the curve fitting sensitivity to test parameters, an accuracy of ±10% is assigned to the measured values of convection heat transfer coefficient and power dissipation.

A detailed derivation of the heat transfer formulae can be

found in J. P. Holman, Heat Transfer (McGraw-Hill, 1990),

7th edition.

(4)

REFERENCES

70
NOTES ON EQUIPMENT

Common shop metals were used for the test fixture construction. The apparatus is not sensitive to dimensions, so long

as the rods are long and thin.

Omega Engineering, Inc., P.O. Box 4047, Stamford, CT 06907-

0047 (1-800-826-6342) is an excellent source of thermocouple

supplies, as well as many other instrumentation transducers

and measuring devices.

Our automated Data Taker was purchased from Zi-Tech

Instrument Corporation, P.O. Box 391567, Mountain View, CA

94039 (1-415-966-8484). It accepts 23 channels of input,

which can be configured as analog or digital signals. It

has an internal battery with storage for approximately

11,000 data points so that it can be programmed from a PC,

disconnected and transported to a laboratory setting, and

subsequently uploaded to a PC for data analysis.

71

t
Table 1

FREE END TEMPERATURE

MINUS AMBIENT TEMPERATURE

Free

Convection

(deg C)

Forced

Convection

(deg C)

Copper 37.5 13.3

Aluminum 34.3 9.9

70-30 Brass 29.2 6.3

1020 Steel 22.1 2.6

Stainless Steel 11.6 0.6

Titanium 7.9 0.4

72
Free End minus Ambient Temperature

40

O 35-

m

oS 304t

8

c

0

(D

G

25

20-tl

E

»2

Cu

1

k (1 w )

Al BRASS 1020

Material

SS Ti

Free Convection Forced Convection

Figure (1): Experimentally Measured temperature differences.

73
Total Power Dissipated

4.5-ri

4

3.5

3

S 2.5

^ 2

1.5

1

0.5

0

!

!

Cu

I

i

I

i

I i

Al BRASS 1020

Material

SS Ti

Free Convection Forced Convection

Figure (2): Computed power dissipation of each material with

free and forced convection.

74
Convection Coefficient Fit

It

0~^^ 1 1 1 1 1 1 1 1 1 1 1 1 » 1 1 1 1 1 r 25 75 125 175 225 275 325 375 425 475

Thermal Conductivity (W/m-K)

Figure (3): Comparison of experimentally measured data (points)

and theoretically computed values (smooth lines).

75

FABRICATION AND EVALUATION OF A

SIMPLE COMPOSITE STRUCTURAL BEAM

Myron J. Schmenk

Department of Manufacturing Engineering

Miami University

OVERVIEW

This experiment involves the team design, fabrication, and

evaluation of composite structural materials. These composite

materials, in the form of small structural beams, are fabricated

from organic fibers or particles selected by the student team and

bonded with an adhesive system also chosen by the team.

This experiment was created in response to a national call

for more hands-on, open-ended design experiences for engineering

students. The experiment has been repeated over a period of

three years at Miami University. The first time the experiment

was run, the results suggested that viable, cost competitive

substitutes for lumber and reinforced concrete might be developed

using cellulose as a primary ingredient. Subsequent iterations

of the experiment have been directed towards the use of recycled

cellulose and polymers in the development of innovative, costeffective building materials.

PREREQUISITE KNOWLEDGE REQUIRED

This experiment is part of the laboratory work done in

introductory material science course for bachelor-level

engineering students. Some knowledge of physics and chemistry is

desirable but extensive knowledge regarding the mechanical

properties of materials is not required. At Miami, the students

are expected to pursue the project to some depth, utilize library

resources, make industrial contacts, and to utilize a systematic

engineering approach to problem solving.

OBJECTIVES

The overall objective is to create an artificial wood

composite to compete with real lumber for home construction

applications such as framing and flooring. Specifically, the

assigned objectives are as follow:

1. To design a composite structural material using organic

fibers or particles that are bonded with one type of

adhesive. The particulate material has to be an

77
agricultural product or by-product. Chopped or pulped

recycled paper would, by this requirement, be very

acceptable. No particle can exceed 0.02 cc in volume

before bonding. Materials selected need to be safe for

student use, reasonable in cost, and available to

complete the experiment on time.

2. To devise a beam fabrication scheme capable of yielding

at least one test beam per student per team. The

fabrication method selected has to be inherently safe,

cannot require painstaking labor, and should likely

employ fabrication resources close at hand.

3. To iteratively refine the material choices and beam

fabrication method experimentally. In particular, the

students are urged to investigate adhesive wetting and

bonding reactions and to fabricate and break prototype

beams

.

4. To produce a final set of composite beams and evaluate

these composites vis-a-vis real lumber. This evaluation

includes consideration of a number of factors including

bending strength, stiffness, cost, and more qualitative

factors such as potential environmental impact.

EQUIPMENT AND SUPPLIES

Some of the adhesives employed, to be considered, include

the following:

- two-part epoxies and polyesters.

- polyvinyl acetates.

- starch and related adhesives.

- lignin-based adhesives.

- urea-formaldehyde.

- phenol-formaldehyde.

- Portland and other inorganic cements.

- protein-based glues such as casein.

- flour pastes.

Some of the particulates, that can be used for composite

fabrication, include the following:

- softwood and hardwood paper pulp.

- Jute, cotton, and other commercial organic fibers.

- recycled paper, cardboard, and polymers.

- sawdust and shredded bark.

- wheat straw and other plant stalk materials.

- husk materials such as peanut and walnut shells.

78
Examples of successful composite beams include the

following:

- melamine laminated paper.

- paper pulp bonded with wood glue.

- strips of grocery bags bonded with resorcinol-type resin.

PROCEDURE: BEAM FABRICATION

The nominal dimensions for a bend test beam are 15 X 30 X

250 mm. The beams can be cut from larger sheets or bars or they

can be fabricated one beam at a time. Fabrication methods that

pose safety and environmental hazards, require tedious labor, or

require the use of highly-specialized pressing and curing

apparatus should be avoided.

Consider simple fabrication schemes such as those

illustrated in Figure 1. As shown in Figure lA, one popular

approach is to bend up a sheet metal tray, fill the tray with the

freshly mixed composite, and press the mix under dead weight

until the adhesive cures. Figure IB illustrates an approach

often favored by paper science students. As in paper-making, the

composite is prepared as a water-based slurry or mix which is

subsequently de-watered by pressing on a screen and air drying.

After drying, the thick sheet of composite is oven cured to set

the adhesive. Both of the fabrication methods described above

usually result in relatively weak composites with high void

fractions unless an effort is made to minimize bubbles in the

adhesive.

A three-step approach to fabrication can produce superior

products. In the first step, prepare thin, prepreg sheets of

uncured composite. In the second step, as shown in Figure IC,

laminate 50 to 100 of these sheets in a stack or coil. In the

third step, set the adhesive by heat curing.

Attempts to manufacture test beams with structurally

efficient cross-sections (e.g., I-beam, corrugated box, and

honeycomb) usually fail. The added complexity of such section

configurations typically results in serious problems with beam

quality and missed deadlines.

PROCEDURE: BEAM TESTING

The simple test apparatus illustrated in Figure 2 is used to

provide tensile strength and stiffness data. This apparatus can

be fabricated using building block components from a Model 9014

Materials Testing Kit produced by the Engineering Science

Division of Scott Aviation Corporation and an Ono Sokki

electronic linear gage sensor with digital readout.

79
Basically, the tester Is a three-point bending rig where the

beam Is simply supported at each end and loaded In the center

using an hand-pumped hydraulic cylinder acting through a yoke

which fits around the beam. Displacement of the yoke, and hence

the beam, is monitored using the linear gage sensor. Load

applied to the center of the beam is obtained by monitoring a

gage indicating the applied hydraulic pressure. Before using the

rig to test fabricated composite beams, it is a good idea to use

the rig to slowly bend and break wood practice beams. This helps

develop a feel for the proper use of the rig and to establish a

consistent data-taking routine.

Wearing of safety glasses is mandatory. Fracture of both

wood and composite materials is usually gradual with the fracture

propagating slowly from the region of highest stress.

Nonetheless, it is wise to anticipate the possibility of sudden

fracture and the risk of flying debris.

As may be seen in Figure 3, plotting the beam deflection

versus applied load reveals the elastic-plastic nature of the

beam prior to failure. The slope of this curve in the elastic

region, the stiffness, is subsequently used to determine the

modulus of elasticity. As may also be seen in Figure 3, pressure

gage readings are converted to units of applied force using a

calibration procedure. The calibration procedure requires the

use of a force gage to obtain a relationship between pressure

gage readings and units of applied force.

The actual cross-sectional dimensions of the test beams can

be determined using a micrometer or vernier caliper. The section

measurements are needed plus the distance between the beam

supports for the subsequent calculation of bending strength and

elastic modulus. Both calculations are based on elastic beam

theory. Use of elastic beam theory for estimating bending

strength is reasonable when the beams fail by fracture without

significant plastic deformation.

The estimation of bending strength (the maximum tensile

stress in the outer fibers at fracture) is Illustrated in Figure

4. The calculation of the modulus of elasticity is illustrated

in Figure 5. Basically, the calculation of the bending strength

and the modulus of elasticity, is done to normalize test results

to facilitate the fair comparison of beams of different

dimensions. Often the beams produced will vary considerably in

cross-section from beam-to-beam and from team-to-team.

Measurement of beam weight permits the calculation of the

strength and elastic modulus on a specific basis (per unit

density). Determination of these properties on a specific basis

emphasizes the Importance of using low density materials in most

structural applications.

80
Another test requirement is the examination of the resulting

fracture surfaces. Almost always, the fracture will be seen to

initiate in a poorly bonded region in the most highly stressed

portion of the beam, of the beam.

PROCEDURE: EVALUATION OF RESULTS

Since this is a multi-objective experiment, the weighted

ranking scheme illustrated in Figure 6 can be employed in the

evaluation of results. In this scheme, there are several

performance categories. Based on test results, calculations,

and/or engineering judgement, the performance of each composite

beam in each category is ranked from 0 to 10 relative to an

arbitrary performance rating of 5 for a standard wood beam. For

example, if a composite beam outperformed the wood standard in a

specified category, it would receive a rating (category rank)

from 6 up to 10 depending upon its relative superiority to wood.

Vice versa, for example, if the cost of materials to make the

composite beam exceeded the cost of an equivalent wood beam, the

ranking for the composite would be less than the arbitrary rank

of 5 for wood.

Assuming that the beams are ranked relative to wood in each

category, it is also necessary to weight each category with a

numerical value representing the relative importance of that

particular category in the overall expectations of composite beam

performance. The rank within each category is then multiplied by

the assigned category weight and the resulting weighted products

for each beam are summed for an overall performance rating.

A final project report is required. This report should

include the final test results but must also include a clearly

written description of the systematic, iterative approach

employed in designing, fabricating, and evaluating the specific

composite material that was developed.

INSTRUCTOR NOTES

The weighted ranking scheme is relatively easy to understand

and it is a systematic approach for combining both quantitative

and qualitative performance data. Often young engineers are

prone to dismiss qualitative factors such as environmental

concerns as unimportant when they cannot find appropriate

definitions and equations for such factors in their engineering

references

.

Typically students respond enthusiastically to the openended challenge to select their own component materials and to

develop a safe and cost-effective method of beam fabrication.

81
Carefully steering student choices, however, will Improve results

and reduce potential hazards. For example, when students were

encouraged to consider the use of water-base adheslves, the

consistency of the results improved with a corresponding decrease

in beam fabrication difficulties.

The Manufacturing Engineering Department at Miami University

has a well-equipped model shop for student use. In addition,

there are materials science and paper science laboratory

facilities suited to the safe production of simple composites.

Facilities include mixing areas under exhaust hoods, basic mixing

machinery, hand-operated presses, ovens, and a full complement of

safety gear. Student efforts are carefully monitored. One-onone instruction is provided for students involved with unfamiliar

tools and procedures.

The first time the experiment was assigned, there was

probably too much emphasis placed on designing a minimal cost

composite and on the development of a novel fabrication method.

Lately, emphasis has been placed having the students choose their

adhesive intelligently to promote wetting and facilitate

component mixing. In the future, the use of fire retardant

adhesives will be promoted and emphasis will be placed on

discovering simple methods to reduce void formation to improve

composite integrity. To maintain the open-ended nature of the

experiment, bonus points are usually awarded for to students who

elect to pursue lines of investigation that are deemed, a priori,

to be desirable.

REFERENCES

This experiment was inspired by several stories regarding

interesting structural engineering and architecture projects

where the students were expected to design, build, and test loadbearing structures based on ordinary materials such string,

cardboard and toothpicks. This experiment is quite similar

except that the students are now encouraged to work with recycled

waste materials, renewable-resource agricultural materials, and

today's rapidly advancing adhesives technology.

Two references that the students should find valuable are:

- Vance Setterholm, "Recycling Wood Fiber in Municipal Solid

Waste: Opportunity for Government-Industry Partnership",

TAPPI Proceedings, 1990 Pulping Conference, pp2-5. (Note:

Mr. Setterholm is Assistant Director, USDA Forest

Service, Forest Products Laboratory, Madison Wisconsin.)

- J.E. Gordon, The New Science of Strong Materials or Why

You Don't Fall Through the Floor , Second Edition, 1984,

Princeton University Press, Princeton, New Jersey.

82
SOURCES OF SUPPLY

Initially, most of the composite component materials were

obtained from local suppliers such as hardware stores and

lumber yards. When emphasis was directed towards finding more

effective adhesives, the students focus shifted towards adhesives

and coatings in common use in the forest products industry. Many

suppliers to the forest products (paper and wood furniture)

industries are listed in the Thomas Register and maintain offices

in Georgia, Ohio, and Wisconsin.

Material expenses for a team of four students are estimated

to be less than $20.00 or $5.00 per student if all materials were

purchased. The most costly component material is typically the

adhesive which usually comprises 10 to 20% of a test beam by

volume. In seeking information on adhesives by contacting

industrial suppliers, many students have received generous

technical assistance including free samples of adhesives.

83
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89

MEASUREMENT OF STRAIN RATE SENSITIVITY IN METALS

Y.Y. Yang and R.G. Stang

Department of Materials Science and Engineering FB-10

University of Washington

Seattle, WA 98195

Prerequisites:

1. Knowledge of the use of a universal testing machine for tensile testing.

2. The ability to reduce load-elongation data to produce engineering stress-strain curves.

3. Familiarity with the true stress-strain concept and conversion of engineering stress-strain data

to true stress-strain data.

Equipment and Supplies:

1 . Tensile testing machine with crosshead speed control over several orders of magnitude.

2. 500Kg full scale load cell.

3. Grip assembly for wire or rope samples.

4. Measuring equipment for gauge length and diameter measurement.

5. 1/8 inch diameter 60wt% Sn-40wt% Pb solid solder.

The Department of Materials Science and Engineering at The University of Washington is fortunate to have an Instron 4505 Universal Testing Machine to use for work of this type. This machine is a computer controlled testing machine with a computer system for data acquisition. Figure 1 shows the

complete testing machine setup and figure 2 the grip assemply used in this work. These experiments

could also be performed using an analog system and a micro computer or hand calculator for data

reduction.

Objective:

This experiment demonstrates the high temperature stress-strain behavior of metallic materials.

Eutectic lead-tin solder melts at 183°C, thus room temperature deformation represents deformation at 0.63Tj^, where T^^ is the melting temperature in degrees kelvin. Under these conditions the shape of the

stress-strain curve is very dependent on the applied strain rate. Thus the flow stress, defined as the stress

to produce plastic flow at a given strain, is also sensitive to the strain rate imposed on the material under

these conditions.

Experimental:

60wt%Sn-40wt%Pb solder was purchased locally in coiled form. Samples were carefully

straightened and fit in the wire grips. The grips were positioned so that the gage length was 75 mm. The

sample was allowed to relax before the test was started.

Results:

The data reported here was collected using a computer controlled universal testing machine

equipped with an IBM-PC to record the data. This data was then imported to a spread sheet which was

programmed to calculate engineering stress and strain and true stress and strain. These data were then

used to plot the engineering and true stress strain curves in figures 3,4 and 5. The duration of the tests reported here varies from a few minutes to one week.

The flow stress-strain rate relationship can be expressed through the strain rate sensitivity

equation:

where

cy=flow stress K=constant

e= strain rate

m= Strain rate sensitivity coefficient, which is constant

91
The strain rate sensitivity coefficient can be determined by plotting log flow stress vs strain rate,

fitting the data to a straight line. The strain rate sensitivity is equal to the slope of this line. The true

stress-strain data should be used in making this plot. In this case the curves shown in figure 5 were used

to determine the flow stresses. The results are shown in figure 6.

Eutectic lead tin solder exhibits superplastic behavior under some conditions of strain rate and

temperature. This can be illustrated by plotting fracture strain vs strain rate. This data is shown in figure

7. At the lowest strain rates, superplastic behavior is being approached.

Acknowledgment:

The authors wish to thank Mr. D.F. Lii for help in setting up the Instron Machine, Drs Wendell

Jones and John Stevens, Sandia National Laboratory, Albuquerque, NM and the attendees at the NEW-90

UPDATE Conference who supplied helpful comments.

References:

1. George E. Dieter, Mechanical Metallurgy, 3rd ed, McGraw-Hill, New York

(1986) pp. 295-300.

2. Thomas H. Courtney, Mechanical Behavior of Materials, McGraw-Hill,

New York (1990) pp295-309.

3. M. A. Meyers and K. K. Chawla, Mechanical Metallurgy, Principles and Applications,

Prentice-Hall, Englewood Cliffs, N.J. (1984) pp559-574.

STUDENT HANDOUT

MEASUREMENT OF STRAIN RATE SENSITIVITY

IN 60-40 SN-PB SOLDER

Objective: The objective of this experiment is to examine the effect of strain rate on the stress strain

behavior of 60-40 Sn-Pb solder.

Procedure:

1. Five samples, each with the same gauge length, are to be pulled at five different crosshead

speeds. There should be at least one order of magnitude difference between the crosshead speeds.

2. Set up the testing machine to pull each sample at the correct crosshead speed. Record the

sample diameter, gauge length and test temperature before initiating the test. After fracturing the

sample convert the raw data to engineering stress-engineering strain and true stress-true strain data.

3. Plot the engineering stress-engineering strain curves on the same axes. Label the strain rate for

each curve. Repeat for true stress-true strain data.

4. Determine the flow stress for several selected strains for each strain rate used. Plot the log flow

stress vs log strain rate. Fit the data to a straight line for each selected strain and determine the

strain rate sensitivity coefficient.

5. Examine the effect of strain rate on the strain to fracture. Do any correlations exist? Explain.

92
Figure 1. A view of The Universal Testing Machine used in this study, showing the

crosshead with grips holding a sample, the machine control tower, and a PC to

communicate with the tower and to acquire data.

93
Figure 2. A close-up view of the sample and grip assembly.

94
60-40 Sn-Pb Solder

Engr. Stress vs. Engr. Strain

64. Or

0.0 0.6 1.2 1.8 2.4 3.0 3.6 4.2 4.8 5.4 6.0

Strain (mnn/nnnn) voo-Ying Yang s/i 0/90

Figure 3. Engineering stress-engineering strain curves for 60-40 Sn-Pb solder deformed to failure.

95
60-40 Sn-Pb Solder

True Stress vs. True Strain

Strain (mm/mm) vao-Ying Yang 8/10/90

Figure 4. True stress-true strain curves for 60-40 Sn-Pb solder deformed to failure.

96
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60-40 Sn-Pb Solder

True Stress vs. True Strain

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Strain (mm/mnn) Yao-Ying vong 8/10/90

Figure 5. True stress-true strain curves for 60-40 Sn-Pb showing the low strain region. These

curves were used to prepare figure 6.

97
60-40 Sn-Pb Solder

strain Rate Sensitivity Detemninction at 20— 22 deg C

7

stress

6

5

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Strain Rote Sensitivity Coefficients . O nn = 0.229; e=0.0225

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Figure 6. Log flow stress vs log strain rate for 60-40 Sn-Pb. The strain rate sensitivity

coefficients are determined by measuring the slopes of the straight lines shown.

98
60-40 Sn-Pb Solder

Log Strain Rate vs. Log Strain at Fracture

1 00 ^

Figure 7. Log strain rate vs log fracture strain.

1

99

POST HEAT TREATMENT IN UQUID PHASE SINTERED

TUNGSTEN-NICKEI^mON ALLOYS ( '

)

Mansur Rastani

Dept. of Manufacturing Systems

NC A&T State University

SUMMARY

At sintering temperature, the tungsten-nickel-iron alloy undergo grain growth and pore

coarsening which degrade mechanicEd properties. An attempt was made to show that a post

heat treatment can control the grain boundary condition toward promotion of mechanical

properties of the alloy. Upon a scanning electron microscopy examination of such a heattreated specimen, a formation of precipitation reactions at tungsten-tungsten grain boundsiry

was traced £ind the type of the morphology was characterized. Energy dispersive x-ray

analysis was performed to determine the composition of the precipitate and a quantitative

analysis was used to measure the rate of the precipitation reaction. Also a transmission

electron microscopy examination was made to determine the crystal structure of the

precipitate, using the electron diffraction analysis. An instrumented Charpy test was

demonstrated to show the effect of the interfacial precipitation reaction on mechanical

properties of the alloy.

Key Words: Tungsten heavy alloys, liquid phase sintered W-Ni-Fe, post heat treatment in

tungsten alloys, precipitation at W/W interfacial grain boundary, SEM fracture surface

analysis of tungsten heavy alloys.

INTRODUCTION

The tungsten heavy Eilloys can find application wherever a high density material is

needed. In some applications not only adequate hardness but eJso high strength coupled

with fracture toughness are desirable. Typical application include: 1) static and dynamic

balances and counterbaleinces, 2) rotating inertia members and gyroscopes, 3) penetration

mechanics and projectiles, and 4) Radiation shielding. Cobgilt as the binder metal in these

alloys has escalated in cost by many times in last years. Nickel has been used as a substitute

for cobalt and interestingly, klc veJues for nickel bonded materials can exceed those for

cobalt alloys (ref. 1).

Tungsten (W)-nickel (Ni)-u*on (Fe) Eilloys are manufactured using the standard powder

metEdlurgical technique of hydrostatically cold pressing elemental powders followed by a

liquid phase sintering. During the sintering process, the liquid phase of nickel and iron

dissolve some of the tungsten, while very effectively wetting the remaining solid tungsten. At

the sintering temperature, most materials undergo graiin growth and pore coarsening, which

degrade mechanical properties (ref. 2). Property improvements are related to processing

variables such as heat treatment after sintering to control grain boundary conditions. The

primary outcome being higher mechaniced properties and a better combination of properties

such as strength, toughness and hardness. This paper investigates a post heat treatment

leading to possible formation of £in interfacial precipitation reaction in a commercially

produced tungsten heavy eilloy (90W-7Ni-3Fe). An attempt is made to show that this

precipitation reaction, resulting in changes to the microstructure, can possibly enhance the

mechanicsJ properties of the alloy.

(1) The work has been done under o contract with Battelle columbus

101
EQUIPMENT AND SUPPLIES

90W-7Ni-3Fe alloy specimens, vacuvim furnace, instrimiented Charpy tester, scanning

electron microscope, energy dispersive x-ray system, transmission electron microscope,

specimen preparation stations for optical and transmission electron microscopes, optical

microscope with camera.

EXPERIMENTAL TECHNIQUES & PROCEDURES

Material Processing of Conunercial Alloys

The production of tungsten-nickel-iron (90W-7Ni-3Fe) begins by mixing controlled

amounts of the appropriate elemental powders [90 weight% (wt%), 7 wt% nickel, 3 wt% iron]

and then hydrostatically compacting the blend to produce a green billet. The sintering

process starts by heating the billet to 900 °C for 2 hours in hydrogen atmosphere. The

temperature is then raised to 1310 °C with an 80 °C/hr heating rate and then held for 1 hr.

This is followed by a temperature increase to 16 °C above liquid phase temperature with a

40 °C/hr heating rate and holding at that temperature for 1 hour. At the end of this hold

time the temperature is reduced to 1200 °C. Then hydrogen is switched to helitim and

further cooling proceeds to ambient temperature. During the sintering process, the liquid

phase of nickel and iron dissolve some of the tungsten, while very effectively wetting the

remaining solid tungsten. Figure 1 shows the resulting microstructure in an optical

microscope from the polished surface of the produced as-sintered billet . Spheroidal

tungsten-rich grains are embedded in a Ni-Fe-W matrix. The bulk chemical analysis results

for the produced as-sintered billet is presented in table 1.

Fracture Surface of the As-Sintered Specimen

Many sub-size notched specimens were cut from the as-sintered billets (commercieil 90W7Ni-3Fe), for the study of fracture surface by scEinning electron microscopy (SEM). These

specimens were broken with a sheirp blow to create fracture surfaces. Photomicrographs

were teiken on various areas of a fracture surface by SEM. Figure 2 shows such a fracture

surface with cleavage failure of the tungsten eind ductile dimple failure of the matrix. An

important common feature in these micrographs is the presence of the many smooth

separation facets at the w-w greiin boundaries, while a few facets with precipitation were

observed. It will be subsequently shown that the microstructure of this interface region can

be gJtered by appropriate heat treatments. A counting aneilysis was made on different shots

to measure the average percentage of occurrence of the precipitation formation at the

tungstep/tungsten interface. The percentage of precipitation occurrence (P.P.O) is defined as

follows:

P.P.O = (Nppt/Ntotal)x 100

where, Npp^ referred to the number of facets with precipitation and N^^gj^ is the total

number of w-w interfacieil facets. To establish a comparison basis for the P.P.O veJues from

different micrographs, all the shots are taken with the same magnification. Figure 3

illustrates the w-w smooth and precipitated separation facets from the resulting micrograph

in a shot. The P.P.O for this shot is calculated as follows:

Ntotal = 41, Nppt=15

102
P.P.O = (15/41) X 100 = 37 %

Similarly, the P.P.O. values for different shots (all at X400 mag.) from the micrographs of

the as-sintered specimen were calculated and listed in table 2. The weighted P.P.O for as- sintered specimen is 49 %, as indicated in the table.

Practiure Surface of the Post Heat-Treated Specimen

A range of different post heat treatments, see table 3, on many as-sintered specimens

were performed to locate the optimal heat-treatment process for producing the precipitation

reaction at w-w greiin boundary. All these heat treatments were done in vacuvmi furnace. The

rates of heating £tnd cooling were 50 °C/min. The post heat-treated specimens were broken

by a sharp blow to create fracture surfaces. SEM examination of these fracture surfaces

showed that a precipitation reaction occurs at the interfacied w-w gredn boundary. However,

a significant rate of formation of this precipitation is related to the post heat treatments

numbers 1, 2, 10, 11, and 15 from table 3. SEM photomicrographs for different shots (all at

X400 mag.) of these fracture surfaces are taken. The P.P.O values from the micrographs

related to the post heat treatments with significant rate of precipitation formation are listed

in table 2. The weighted values of these P.P.O's for different post heat treatments are

illustrated in figure 4. From figure 4, the optimal post heat treatment is concluded to be

heat treating process number 10 (solution treatment at 1000 °C for 4 hrs) which has an

average P.P.O of 88 %. Figure 5 shows the SEM photomicrograph of the fracture surface of

such a post heat-treated specimen with many precipitated facets. The type and identification

of these precipitates will be considered in a latter section.

Energy Dispersive Spectroscopy

The SEM photomicrograph of the polished surface of the optimal post heat treated

specimen (solution treatment at 1000 °C for 4 hrs) is shown in figure 6. Three points A, B,

and C are marked on this micrograph, as shown in the figure, for chemicEd analysis purpose.

These three points correspond to tungsten grain, Ni-Fe-W matrix, and W-W grsdn boundary

in the alloy microstructure. The energy dispersive spectroscopy (EDS) are performed to

determine the chemical composition of the alloy at these points. The results are reflected in

figures 7,8, and 9. This analysis is discussed later.

Charpy Test

Charpy V-notched specimens were machined from commerciedly produced alloy to the

dimensions shown in figure 10. Instrumented impact tests on both, as-sintered, and the

optimal post heat-treated specimen (solution treatment at 1000 °C for 4 hrs) were conducted

and compared. The results of these instrumented impact tests are shown in figure 11. These

results are discussed in a latter section.

Transmission Electron Microscopy (TEM)

The precipitate structure was analyzed by TEM, Specimen sections were taken from the

Charpy test specimens at locations near and far from the fracture surface. Thin sections of

approximately 300 microns thick were sliced using a slow speed diamond saw. These sections

were then thinned on a Minimet grinder/polisher. Further thinning to 50 microns was

103
accomplished by using a dimple grinder after which ion milling was used to thin the

specimen to final electron transparency. The TEM micrograph of the precipitate phase at the

w-w grain boundary and the diffraction pattern corresponding to the selected area are shown

in figures 12 and 13 respectively. The results are discussed later.

DISCUSSION OF RESULTS

It was shown that the as-sintered commercial alloys (90W-7Ni-3Fe) has a low weighted

P.P.O. An examination of the SEM micrographs of the fracture surfaces of the as-sintered

specimens compared to the post heat-treated ones shows that the rate of the precipitation

formation in these alloys increases for successive post heat treatments. The average

percentage of precipitation formation at the w-w interfaces reaches to a maximum of 88 %

corresponding to the solution treatment at 1000 °C for 4 hours. At post heat treatments

above 1000 °C temperature, the precipitation appear to be much coarser and less

homogenous and have a lower P.P.O.

The EDS compositional analysis of the tungsten grain and of the matrix as well as of the

grain boundary in a microstructure of the post heat-treated specimen were shown in figures

7, 8, emd 9. As indicated in these figures, the elemental analysis for the matrix is as follows:

Element Weight %

W 16.70

Fe 23.96

Ni 59.33

Also from these figures, the presence of large nickel and iron concentrations in the

precipitates at the w-w grain boundary was verified. Possible electron beam spreading could

have allowed the surrounding tungsten grain to contribute to the tungsten peaks.

The precipitations morphologies are of different tjrpes, noduleir and lamellar, on the same

specimen. Secondary and Backscattered modes are used to show the nodular type

morphology as shown in SEM photomicrograph of the fracture surface, figure 14.

Charpy tests utilized notched specimens to determine the fracture toughness and impact

strength. A comparison of the computer results, figure 11, shows a shght improvement in

toughness £m.d impact strength, calculated as follows:

% Increase in Impact Strength = [(39833-37489) psi/ 39822 psi] x 100 = 6 %

% Increase in toughness = [(7-6) ft.lb/ 7 ft.lb] x 100 = 14 %

TEM micrograph for the thin foil shows the precipitate phase at the w-w grain boundary,

figure 12. Diffraction pattern corresponding to the selected area of figure 12, obtained at 240

Kev, is shown in figure 13. By applying the Bragg's Law formula and using the wavelength of

the incident electron beam (0.033 A°), the interplanar spacing could be calculated. Having

the interplanar spacing, the lattice parameter of the diffracted spots may be determined.

Such a simple calculation shows that all diffraction spots from many different precipitate

have a lattice parameter of 3.60 A° consistent with a fee structure, equivalent to the fee

matrix phase. Higher accelerating voltage (1 Mev) is required to obtain a more complete

pattern to determine the crysteillographic orientation relationship between the fee precipitate

and the adjacent bee tungsten greiin, (ref. 3).

MECHANISM OF PRECIPITATION

Different theories has been proposed to expledn the mechanism of precipitation

enrichment at the tungsten grain boundaries. The following theory, as put forth by Posthill,

(ref.4), is considered here. Posthill concluded that a grain boundary having rational

104
orientation relationships with both adjacent greiins would be expected to minimize the

surface free energy, thus facilitating nucleation by lowering the critical free energy. This

would also increase the probability of precipitate nucleation on that boundary. He tentatively

concluded that precipitation on w-w grain boundaries is due to nickel and iron coming out of

supersaturated w-phase solution. WMle grain boundary diffusion is obviously essential for

the nucleation and growth of the precipitation, it also leads to some transport of nickel and

iron to the matrix region. Figvire 15 illustrates this mechanism.

CONCLUSION

The present examination of the post heat-treated 90W-7Ni-3Fe alloy confirms that a

precipitation of matrix phase type does occur at the tungsten-tungsten interfacial grain

boundary. The post heat treatment at 1000 °C temperature for 4 hrs showed the maximum

percentage of precipitation occurrence at the w-w grain boundary. The types of morphologies

are identified as nodular as well as lamellar with a fee structure. In this study it is believed

that this reactions occurs by precipitation of nickel and iron from the supersaturated

tungsten grains to the boundaries. These reactions are expected to promote the impact

resistance and toughness of the heavy alloy since they improve the cohesion at interfacial

grain boundaries (ref. 5). However, the Charpy tests results showed that the fracture

toughness aind the impact strength of the optimal post heat-treated specimen have improved

slightly. One reason that might account for this, could be the irregular formation of harmful

precipitation hardening in w-phase and matrix region of the heavy alloy. This kind of

precipitation is expected to increase the brittleness of the alloy since they reduce the

interphase boundeiry cohesion (ref. 6). Research should be conducted toward locating a post

heat treatment that accelerates the precipitation occurrence at the w-w interface boundary

and at the same time lowers the harmful precipitation formation in the microstructure of the

tungsten heavy alloy.

105
TABLE I. BULK CHEMICAL ANALYSIS RESULTS (WT%)

FOR THE COMMERCIAL ALLOY 90W-7NI-3FE

AG < lK-4

CR < 4E-I

MG. < 2E-4

SB < 0.002

V. < 0.001

AL. 5E-t

BI < 0.001

MN. < 4EA

CU < 2EA

MO < 0.002

N. 5E^

0 < 0.0071

W 90.74

TH < 0.01

CA. < 0.001

NA. < 0.002

PB < 0.001

SI 5E^

B < E^

SN. < 4E-4

ZR 0.002

CO < 6E^

U. < 0.01

H <0.0091

NI 6.08

FE 2.68

106
TABLE II. CALCULATED P.P.O AT W WGRAIN BOUNDARY

IN COMMERCIAL ALLOY 90W-7NI-3FE FOR AS SINTERED

AND POST HFEAT-TRF^TED SPECIMENS

H.T. shot* ^PPt P.P.O

as-Rintered 1.2. 3,4 23. 18. 20,23 44, 47, 35,38 52, 38, 57,61

#1 1, 9. 23, 20 41, 37 OD, 54

#2 1.2 43.31 63,48 68.65

#1,0 1,2,3 56,44, 46 62.49, 55 90,90, 84

#11 1,2 31.20 46,31 67,65

#15 1,2 26,22 40.34 65, 65

TABLE III. POST HEAT TREATMENTS OF 90W-7Ni-3Fe ALLOY

H.T. # lsth.t. (OQ) Time (hrs) 2nd h.t.(C) Time (hrs)

1 700 1

2 800 1 3 900 1 4 1000 1

1100 1 6 1200 1

7 700 4

8 800 4

9 900 4

10 1000 4

11 1100 4

12 1200 4

13 1000 1 500 2

14 1000 1 600 2

15 1000 1 700 2

107
^'ig^e 1. Optical xnicro^a^h

as-sinterea SOW-TNi-SPeta^^-Jj^aoe of the
Figure 3. Separated and precipitated facets in the microstructvire of the

fracture surface for the as-sintered 90W-7Ni-3Fe heavy alloy

PP.O @ W/W

heat treatment

Figure 4. Percentage of precipitation occurrence at W-W grain boundary

for as-sintered and post heat-treated 90W-7Ni-3Fe heavy alloys.

109
Figvire 5. SEM micrograph of the fracture surface of the commercial tungsten

90W-7Ni-3Fe heavy alloys, post heat treated at lOOO^C for 4 hrs.
S9 TUNGSTEN PARTICLE.. SPOT A A U S / O N

S3

1 0 0 0 0 F S

CUR 0 . 0

FE LL

0 C N T S

1 0 0!

POST HT=10 0 0C .. 4HRS

NOSTD: STAH0ARDLESS ANALYSIS OF BULK SAHPLE

SPECTRUM: 9 ELEHENT

FE

NI TOTAL

16-AL18-89

0 . 0

FE

f'-'''"~' 4.0 6.0

ENERGY <: KEU >

TUNGSTEW PARTI CLE, SPOT fi RELATIVE f;

0.-9936

i^T 7. 99.65

0.35

17:22:85

10.0

Figure 7. Tungsten alloy (90W-7Ni-3Fe), post heat treated at lOOOOC for 4 hrs.

EDS chemical analysis at spot A of the microstructure shown in figure 8.

Ill
SB 9 0 W - 7 H I - 3 F E M A T R I K .. S P O T B A U S . ' OFF

S8

3 0 0 0 F

CUR : 0 . 0

FE LL

0 C H T S

1 0 01

POST H T = 1 0 0 0 C .. 4 H R S

k: . 0

NOSTD; STftNDARDLESS ANALYSIS OF BULK SAhPLE

SPECTRUli: 8 98M-7NI-3FE HATRIX,8P0T B ELEMENT RELATIVE K «T I

N 0,1264 16.70

FE 8.2693 23.96

NI 8.5932 59.33

TOTAL 180.68

4 . 0

E N E R G Y

S 0 10.0

K E U >

1 b - A U "3 = 43

Figure 8. Tungsten alloy (90W-7Ni-3Fe), post heat treated at 1000°C for 4 hrs.

EDS chemical Einalysis at spot B of the microstructure shown in figure 8.

112
Figure 9. EDS spectra of the w-w boundary precipitate, showing subst£inti£il

nickel and. iron, post heat-treated tungsten 90W-7Ni-3Fe alloy.

V

notch angle=45

Figure 10. As-sintered Charpy V-notched specimen

113
i.'.i rvi

I I

U..I

•ci: nj

< 1 1.

( standard

)

r I

.'1 I

i" '

•'

'fi :'"';,.'ri 6,

' fi

— f

I a- t

)::r

1.0 iTi

... u

.

^- '-J-l

Gj

l_j u. JL 1 ij

U-NI-FE HEAVY i-iLLDY

(Post Heat Treated, 1000 oC

)

1 1 1-

fhif

/

L 0 TTo

Figiire 11. Graphical presentation of the instrumented impact results

for the V-notched specimen, tungsten 90W-7Ni-3Fe heavy alloys.

114
Figure 12. TEM micrograph, showing precipitation at w-w grain boundary in

tungsten90W-7Ni-3Fe heavy alloy, post heat treated at 1000°C for 4 hrs.

115
Figure 13. Electron diffraction pattern corresponding to the TEM

micrograph shown in fig 11.

116
Figure 14. SEM secondary and backscattered electron imaging of nodular

morphology of precipitation at w-w grain boundary in 90W-7Ni-3Fe eilloy.

tungsten

tungsten

Figure 15. Mechanism of precipitation enrichment at w-w grain

boundary in tungsten 90W-7Ni-3Fe heavy alloy.

117
REFERENCES

1. Penrice, T. W. : Developments in Materials for use as Kinetic Energy Penetrators.

Powder Met. in Defense Technology, V5, pp. 11-12, 1980.

2. German, R. M. : Sintering Atmosphere Effects on the Ductility of W-Ni-Fe. Met.

Trans., V 15, pp. 747-754, Apr. 1984

3. Posthill, J. B. : Precipitation at Tungsten-Tungsten Interfaces in W-Ni-Fe Heavy

Alloys. Powder Met., V 29 No. 1, pp. 45-51, 1986.

4. Posthill, J. B. : Precipitation Reactions in the Tungsten-Nickel-Iron Heavy Alloy

System. A thesis submitted for the degree of Ph.D. at the university of Oxford, 1983.

5. Edmonds D. V. : Interfacial Embrittlement in Liquid-Phase Sintered Tungsten Alloy.

Met. Trans., V lOA, March 1979.

6. Muddle B.C. : Interphase Boundary Precipitation in Liquid Phase Sintered W-Ni-Fe

Alloys. Met. Trans., V 15 A, pp. 1089-1098, 1984.

118
IMPROVED TECHNIQUE FOR MEASURING

COEFFICIENTS OF THERMAL EXTENSION FOR POLYMER FILMS

Stephanie L. Gray and Kristen T. Kern

Department of Physics

Old Dominion University

Norfolk, Virginia 23529

and

Sheila Ann T. Long

NASA Langley Research Center

Hampton, Virginia 23665

and

Wynford L. Harries

Department of Physics

Old Dominion University

Norfolk, Virginia 23529

•k denotes presenter of paper,

SUMMARY

The coefficient of thermal extension (CTE) is an important material property

that describes the change in length of a material as a function of the change

in temperature. More specifically, a = (1/L^)[(L^ - L.)/(T^ - T^) ]

where a is the CTE of the material, L^ is the length ot the specimen at room

temperature, and L. and L^ are the lengths of the material at temperatures

T. and T^, respectively. CTE values can be determined through the use of

t^iermomechanical analysis (TMA) . A commercial TMA system has been modified to

improve the accuracy of the measv^rement by increasing the length of the

specimen. CTE values for Teflon unexposed and exposed to thermal extremes

have been determined using the modified TMA system.

INTRODUCTION

Thermal expansion and contraction take place in materials due to changes in

temperature. The way a material expands is dependent upon its chemical

structure. When a material expands upon heating, the free space between atoms

expands. A rise in temperature causes atoms to vibrate at higher frequencies;

and, in turn, the average separation between atoms increases. Therefore,

materials with chemical structures that have strong covalent bonds will have

lower CTE values than those of chemical structures that have weak interatomic

bonds. Because of their weak interchain bonds, polymers have relatively high

CTE values. Quartz (Si02) , on the other hand, has very strong molecular

bonds and, therefore, has a low expansion coefficient. CTE values of some

common materials (as found in References 1, 2, and 3) are given in Table 1.

119
The coefficient of thermal extension Is determined by measuring the change In

length of a specimen through a predetermined temperature range. The equation

used for calculating CTE values is

a = (1/L^)[(L^ - L.)/(T^ - T.)] (1)

where a is the CTE of the material, is the length of the specimen at room

temperature, and L. and are the lengths of the specimen at temperatures

T^ and T^, respectively. When the length of the specimen is plotted as a

function of the temperature, it can be seen that the CTE is proportional to

the slope of the extension curve.

TECHNIQUE

Thermomechanical analysis (TMA) was the method used to measure CTE values for

this discussion. TMA is a technique in which changes in specimen length due

to a controlled rate of temperature change are electronically recorded. The

TMA system used was a DuPont 940 (Reference 4) . It consisted of a specimen

holder, probe, linear variable differential transformer (LVDT) , thermocouple,

heating unit, and a DuPont 1090 Thermal Analyzer (Figure 1).

The specimen is clamped on both ends (Figure 2) . The upper clamp is held by a

stationary support, while the lower clamp is hooked to and supports the probe.

As heat is applied to the sample region, the dimensions of the sample, sample

holder, probe, and clamps change. The LVDT, positioned outside the heater

cavity, sends an electrical signal to the analyzer which corresponds to the

net movement of the probe. The quartz specimen holder and probe and the steel

clamps have CTE values much smaller than most samples, and thus, do not

contribute significantly to the signal.

Originally, the TMA system was designed for specimens with length 0.2 inches

(5 mm) and width 0.1 inches (2.54 mm). The quartz probe has been lengthened so

that specimens now have a length of approximately 1.5 inches (38 mm) and a

width of 0.1 inches (2.54 mm). The increased specimen length greatly improves

the accuracy of the thermal extension measurement. As given in Reference 1,

the precision of the test can be determined using the equation,

5a/a = ±(5AL/AL + 5L/L + 5 AT/AT) (2)

where

AL = the change in length of the material, mm,

SAL = the imprecision in measuring AL, mm,

L = the length of the material at room temperature, mm,

5L = the imprecision in measuring the length of the material, mm,

AT = the temperature range of the test^ C,

SAT = the imprecision in measuring AT, C,

a = the coefficient of thermal extension of the material, / C, and

Sa = the imprecision in the measurement of a, / C.

It is noted in Reference 1 that CTE measurements should be made under

conditions such that the imprecision in measuring the length, 5L, 1^ ±0.025

mm; the imprecision in measuring the change in length, SAL, is ±10 mm; and

120
the imprecision in measuring the change in temperature of the test, SAT, is

±0.5°C.

As L becomes larger, the percent error, 5L/L, becomes smaller. A larger

initial length of the specimen also causes a larger change in length over the

same temperature region, causing 5AL/AL to become smaller as well. The

smaller percent errors in measurement of L and AL cause the percent error in

calculating a to decrease. For example, the percent error in calculating a

for aluminum wi^h^initial length 5 mm, and a AL of 11.5 /zm^ (calculated from

a^, = 2 . 3 X 10 / C over a temperature range of 0 C to 100 C) was

calculated to be approximately ±9.7%. The error in calculation with an

initial length of 38 mm and a AL of 84.7 /xm, was approximately ±1.7%.

EXPERIMENTAL

Before measurements can be made, the LVDT signal must be calibrated and the

expansion of the quartz holder and probe with the steel clamps must be

measured. The LVDT is calibrated by measuring the distance between the hooks

with a micrometer and comparing this measurement to the LVDT signal on the

recorder. Calipers were used to initiate movement of the hooks and successive

measurements were made at small increments of length. The measurements from

the micrometer were plotted as a function of the readings from the analyzer.

The slope of this curve is the multiplicative LVDT calibration factor, which

is in units of mm/mV. The LVDT calibration factor for this test was 0.9860

mm/mV

As a sample is heated, the displacement of the probe is recorded as voltage

output by the LVDT. Corresponding temperature readings are measured by a

thermocouple and are also recorded. The LVDT factor is entered into the

DuPont Thermal Analyzer; during analysis, each displacement data point is

multiplied by the LVDT calibration factor. This multiplicative factor

converts the electronic readings from millivolts (mV) to millimeters (mm) . A

temperature region is selected from the generated curve, as in Figure 3, and

an initial CTE, Q:,^^, is calculated by the thermal analyzer using Equation 1,

The CTE value calculated by the thermal analyzer must be corrected to account

for the contributions of the quartz and steel. The correction^factor for the

quartz and steel, q^^ ^, has been determined to be 0.065 x 10 / C.

Thus, the final equation for the coefficient of thermal extension of the

sample is

F TA corr ^

^

where a^, is the final CTE of the sample corrected for the quartz holder and

probe and the steel clamps.

The TMA tests were run at a heating rate of 2°C/min. Each test began at

room temperature and ended at approximately 120 C.

SPECIMENS

Specimens of various thicknesses were cut to dimensions 38 mmx 2.5 mm (1.5 in

X 0.1 in). The specimen holder is designed to test films; it is necessary to

121
keep the films in tension in order to get accurate extension readings.

Weights must be added to the weight tray to keep the probe and film in tension

(Figure 1) . The range of weights that can be added to this system is from 1

gram to 10 grams. Thin films of thicknesses up to 2 mils cannot support even

the smallest applied load; specimens of 0.5 and 1 mil thicknesses could not

even withstand the load of the probe alone. In this study, it was found that

the applied load caused the thinner films to expand at an artificially high

rate; the weight caused the films to elongate so that the effects of

temperature were obscured by the effects of the applied load. It is for this

reason that thicker specimens and smaller loads are recommended. The

specimens in this discussion had a thickness of 5 mils (0.127 mm) and the

applied load was 1 gram; therefore, the applied stress to each film was 30.4

kPa.

MATERIAL

The film studied was a copolymer of polytetrafluoroethylene (PTFE) and

f luoroethylenepropylene (FEP) . Its tradename is FEP Teflon, and it is

manufactured by the DuPont Chemical Company. The chemical stucture of FEP

Teflon is given in Figure 4. The specific grade of FEP Teflon used was FEP

Teflon- 140; as discussed in Reference 3, the 140 indicates an intermediate

melt viscosity. FEP Teflon-140 is specifically designed for applications

involving high current loads or repeated thermal cycling. FEP Teflon is also

used on the Space Shuttle and is being studied for its Space Station

possibilities. In space, FEP Teflon is exposed to a wide range of

temperatures. It is for this reason that the National Aeronautics and Space

Administration (NASA) at Langley Research Center in Hampton, Virginia is

studying the effects of extreme temperatures on FEP Teflon. FEP Teflon was

exposed to temperatures between -150°F and +150°F in a thermal cycling

chamber for one thousand cycles. The effect of exposure to thermal extremes

on the coefficient of thermal extension of 5 -mil FEP Teflon was studied.

There were three test specimens for the baseline FEP Teflon and three for the

thermal cycled FEP Teflon.

ANALYSIS

A sample extension curve for baseline FEP Teflon-140 is given in Figure 3.

In Referenge^3, the value of a for FEP Teflon-140 is cited as^

13.9 X 10 / C for the temperature region between 0 C and 100 C. The

average a value for the three baseline Teflon specimens was (18.2 ± 0.3) x

10 ^/qC . For the thermal cycled specimens, it was (23.1 ± 1.6) x

10 / C. The temperature range used for both the baseline and thermal

cycled films was from 26°C to 100°C. This temperature range was chosen

because all the CTE curves were approximately linear in this region, and

because the region coincided well with the regions used for the reference

value for Teflon and the a value for the quartz and steel. The raw data are

given in Table 2

CONCLUSIONS

Two things can be concluded from these results. The first is that the

122
closeness of the baseline data to the cited value gives confidence to the

method used for this test. It can also be concluded that thermal cycling doe

affect the coefficient of thermal extension of Teflon. After exposure to

thermal extremes, such as those during cycling, Teflon showed a higher

coefficient of thermal extension. This demonstrates that FEP Teflon is

affected by thermal cycling.

ACKNOWLEDGMENTS

The authors of this paper would like to acknowledge Patricia D. Gillespie, of

the College of William and Mary, for her research on thermomechanical analysi

which contributed to the discussion presented here.

REFERENCES

1. Standard Test Method for Linear Thermal Expansion of Solid Materials by

Thermomechanical Analysis. ASTM Designation: E 831-86. VOL 14.02 of 1990

Annual Book of ASTM Standards, 1990, pp. 793-796.

2. Resnick, Robert; and Halliday, David: Physics, Part I. John Wiley &

Sons, 1977.

3. Encyclopedia of Polymer Science and Engineering, VOL 16. John Wiley &

Sons, 1989.

4. Du Pont Instruments Thermomechanical Analyzer 943: Operator's Manual.

E. I. du Pont de Nemours & Co., 1985.

1"

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

constitute endorsement, either expressed or implied, by the National

Aeronautics and Space Administration.

123
TABLE 1. Coefficients of Thermal Extension.

TEMPERATURE

MATERIAL a ( /°C) RANGE (°C) REFERENCE

Quartz 0.56 x 10"^ 20 - 700 1

Steel 1.1 X 10'^ 0-100 2

Altiminum 2.3 x 10'^ 0 - 100 2

Copper 1.7 x 10'^ 0-100 2

Glass (ordinary) 0.32 x 10'^ 0-100 2

FEP Teflon- 140 13.9 x 10'^ 0-100 3

TABLE 2. Data From Thermomechanical Analysis of FEP Teflon- 140,

BASELINE THERMAL CYCLED

18.2 X 10'^/°C 24.9 X 10"^/°C

18.0 X 10"^/°C 22.6 X 10'^/°C

18.5 X 10'^/°C 21.9 X 10'^/°C

124
LVDT Core

Quarlz Specimen

Holder - stationary

Applied Weight

4.

Thermocouple

Specimen

To Analyzer

(Extension)

To Analyzer

(Temperature)

Quartz Specimen

Probe - moves

relative to

specimen holder

Steel Specimen

Clamps (2)

FIGURE 1. DuPont 940 Thermomechanical Analysis (TMA) Film Extension Apparatus

(Reference 4)

125
38 mm

Specimen

Clamp Mounting Hole

FIGURE 2. Film Sample with Steel TMA Clamps (Reference 4).

126
0.7 r

0.6 -

0.5

Length

Change,

mm 0-^

0.3

0.2

0.1

0.0.

CTE = 182 uin/(m*C)

T(f) = 100 °C

T(i) = 2eX A

20 40 60 80 100

Temperature, °C

FIGURE 3. TMA Curve for Baseline FEP Teflon- 140.

Fluoroethylenepropylenepolytetrafluoroethylene

(FEP-PTFE)

1-25

n

FIGURE 4. Chemical Structure of FEP Teflon.

127

CHARPY V-NOTCH IMPACT TESTING

OF HOT ROLLED 1020 STEEL

TO EXPLORE

TEMPERATURE ~ IMPACT STRENGTH RELATIONSHIPS

Seth P. Bates, DJ.T.

Division of Technology

San Jose State University

SUMMARY

Temperature has a profound effect on the ductiUty of plain carbon steels, especially

within certain narrow temperature ranges known as ductile-brittle transition ranges. The

exploration of this relationship provides students with empirical support for intuitive notions,

and a great enhancement of the laboratory experience compared to the simple testing of

isolated samples to verify properties.

This experimental procedure uses pendulum impact testing of metals at varying temperatures to explore the temperature-toughness relationship. The data from the tests are

discussed, and alternatives to the procedures used are presented.

Students conducting these tests must attempt to explain the phenomena they observe, as

well as relate test results to published toughness /temperature curves, in order to provide additional reality and meaning to the experience.

INTRODUCTION

The effect of temperature on impact strength can be observed easily in any laboratory

with a pendulum type impact tester. The results of such experiments reinforce many

fundamental concepts of materials science, including failure mechanisms, mechanisms for

plastic deformation, ductile-brittle transition behavior, and basic concepts of energy and

work. In addition, this experiment can be a starting point for other experiments relating to

impact strength, such as the effect of striking velocity, notch sensitivity, and previous

conditioning (hot or cold working, or heat treatments) of the metal samples.

PROCEDURE

Overview

In this laboratory experiment, ten samples of hot rolled steel (SAE/ AISI 1020) are prepared for impact testing by machining to ASTM Standards (E23) (Charpy V-Notch sample

type), then conditioned at five temperatures (2 samples at each temperature) between -193 and

100 degrees Celcius. A wide range of temperatures can be attained without special equipment

129
through the use of liquid nitrogen, dry ice, an ordinary refrigerator, and a bunsen burner to

heat ordinary tap water. If temperatures are chosen over a suitable range, the Transition

Range of the metal will be made very clear through the results. In these tests, temperatures

of 25, 10, 0, -10, -20, and -30 degrees Celcius were used.

Safety

Pendulum impact test machines can be among the most dangerous of all mechanical test

devices in the materials laboratory (ASTM, E23-88). A careful explanation of the dangers of

the moving hammer to testers and bystanders in the lab. is essential with this experiment.

Students also love to leave the hammer swinging. This must also be discussed, both in terms

of danger and interms of wear on the vital pendulum bearing.

Equipment

These tests are designed to require a minimum of specialized test equipment. Most items

can be acquired easily and cheaply, but the test lab must have an impact tester capable of

breaking all the samples in the study. For ASTM standard Charpy impact tests of SAE/AISI

1020 hot rolled steel, approximately 180 to 210 foot pounds will be required. If a tester with

such capacity is not available, suitable modifications of this lab can include study of subsized

specimens (note that there is no ASTM standard for subsized metal impact test specimens).

Keyhole notch specimens can be used, though they are not usually used for such materials.

This type of specimen will require substantially less energy to fracture (mostly below 60 foot

pounds). Plastics can be used to study the glass transition temperature, if a much smaller tester

is all that is available (range required is from 8 to 16 foot pounds).

Other equipment that is required include:

Beakers

Bunsen burner and ring stand

Water and Methanol

Ice

Salt

Dry ice

Thermometers or thermocouple temperature sensors

Tongs

Prick Punch and (ball peen) hammer

Vernier or dial calipers

A hand lens (5 to 10 power) is handy for macroscopic evaluation

of the fracture surfaces.

Temperature Control

Temperature is controlled by using water baths that are either heated with the bunsen

burner, or cooled in various combinations of water, ice and water, and ice-water-salt (ice

brine). Additional cooling can be obtained by immersing dry ice in methanol. It will be ideal

if temperatures between -40 and +100 degrees Celcius can be obtained.

130
Samples

These tests are usually done with low carbon (SAE 1020) hot rolled steel. It is important

to be aware that metal processing (hot or cold) and carbon content have a profound effect on

both the shape and location of the transition temperature range. Lower carbon steels show a

slightly lower temprature range, and a much sharper drop. The drop for SAE 1008 steel is

nearly a vertical line at close to -10 degree C.

Advanced students can explore:

curves for different types of metals

notch sensitivity

unnotched samples

plastics

ASTM requirements for timing must be adhered to while conditioning the samples and

moving them from the cooling environment to the test fixture.

RESULTS

Data are compiled in tabular form, then reduced and presented in graphical form. Appropriate representative formulae and calculations are shown. The results are presented

without comment about their meaning, to separate data and discussion.

The results from these tests are as follows:

Table 1. Impact Test Results

Specimen Test Temp. Energy. % Lat. Exp. %Cleav.

1 20 170 11 0

2. 10 142 10 0

3 10 140 10 0

4 0 53 6 41

5 0 57 7 40

6 -10 29 2 65

7 -10 25 3 60

8 -20 30 2 68

9 -20 ' 22 2 65

10 -30 12.5 1 75

Students may be asked to prepare the graphs using computer software such as Excel or

Lotus, and this can lead into a discussion of tables, charts, and graphs as means of communication. The graph of these data is presented in figure 1, below.

131
DISCUSSION

These data provide a confirmation of the ductile-to-brittle transformation for low carbon

steel, and also show variations in the data that are to be expected from laboratory experiments.

These variations can be upsetting to students, just as variations in Gregor Mendel's genetic

studies of beans would have been upsetting to religious clergy in his day. After all, if God is

perfect, then his created phenomena would be perfect as well.

The discussion of such test results gives students a chance to demonstrate understanding of concepts presented through readings and lectures. Students must explain the results in

terms of what was expected and in terms of changes that are observed in the material under

the varying conditions. The depth of such discussions will be determined by the level of the

materials or metallurgy course in progress. This is a meaningful and satisfying experiment for

students, based on direct feedback during and after the experiment is over.

This experiment can be used to lead into or support discussions of plastic and brittle

failure mechanisms, and the effect of temperature on atoms in crystal lattice structures. In

addition. Professors will enjoy the opportunity to challenge the students to consider the

variables of concern to the tests, and what aspects of the test need to be understood simply

because they weaken the validity of the test.

Figure 1. Temperature vs. Impact Strength

Charpy V-Notch Impact Tests SAE/AISI 1020 Steel

Energy Absorbed, Ft-Lbs. 200 1

50-

0 H 1 1 1 \ 1

1 1 -40 -30 -20 -10 0 10 20 30

Temperature, Degrees F

Machine Design students may also enjoy discussing the inherent weaknesses of this test

and the equipment used to conduct it. Some relevant issues include:

friction in the pendulum bearing

windage, or friction between the moving pendulum and the air

friction between the sample and the anvil,

which goes through several stages

throw energy - the energy required to throw the sample after testing

132
ENHANCEMENTS OF THE METHOD

Needless to say, the results from such tests cannot be taken as highly precise. Variations

in pendulum bearing friction, windage, sample friction against the anvils, and throw energy

will result in numbers that include all of such errors. Today, technology exists which can

eliminate such concerns. The tools are sold by Tinius Olsen as well as several other companies

which manufacture or market impact testing equipment, but they can be built on-site by

enterprising faculty with the help of electronics students or faculty.

The technique is to attach a Piezo-electric sensor to the hammer, to sense the impact itself

and to provide an electronic impulse output that is exactly proportional to the energy absorbed

by the sample during fracture. The output is read through a storage oscilloscope equipped

with a triggering signal, and the area under the resulting curve can be integrated to determine

its magnitude. Implementing such a system would make a suitable senior or graduate project

for an enterprising student.

CONCLUDING REMARKS

The samples tested were of SAE/AISI hot rolled steel, tested in as-received condition.

Because of the sensitivity of impact test results and of the transition temperature range to small

variations in microconstituents and processing, it is advised that the instructor screen each lot

of samples before the students begin their work. Also, if technicians are involved in sample

preparation, it is important to watch that samples from different shipments or pieces of stock

do not get thrown together. This could result in a random scattergram of results, rather than

the exciting curve that should be discovered.

REFERENCES

1. Computer Aided Materials Testing. ASTM. American Society for Testing and Materials. Philadelphia, PA. 1981.

2. Principles of Materials Science and Engineering, William F. Smith, McGraw-Hill: New

York, 1990.

3. Standard Methods for Notched-Bar Impact Testing of Metallic Materials. ASTM Designation E 23-88. 1989 Annual Book of ASTM Standards, volume 3.01, pp. 198-213.

4. Structural Engineering Materials . 2nd. Edition. N. Jackson & R. K. Dhir. Hemisphere

Publishing Corp.: New York, 1988, pp. 34-35.

133
SAN JOSE STATE UNIVERSITY

DIVISION OF TECHNOLOGY

Industrial Materials Dr. Seth Bates

Lab Experiment:

Impact Testing of Carbon Steels

at Varying Temperatures

Introduction

The objectives of this experiment are:

1. To learn how to perform the Charpy impact test

2. To study how the impact toughness of a common engineering alloy varies with test

temperature

3. To examine how the fracture appearance correlates with impact toughness.

References

ASTM. "Standard Methods for Notched Bar Impact Testing of Metallic Materials", E23-82,

Annual Book of ASTM Standards, Author, Philadelphia.

Materials Tested

Ten steel bars supplied by your instructor will be tested at five temperatures between

-40 and +100 degrees Celcius. Be sure to look up the published values for these materials. If

you cannot find values, consult your instructor.

Procedure

NOTE: Be sure that the area of swing is clear before any use of the pendulum on this machine. It is very dangerous. Stop the pendulum after each single swing!

1. Obtain ten samples from your instructor, and complete their preparation according to

ASTM specifications for the 'V Notch' Charpy impact test. Review the ASTM procedure carefully, noting definitions, conditions of testing, and data to be collected and

reported.

2. Due precaution should be observed in the operation of the pendulum machine. Study

the machine and its operation by reading the instruction manual. Study the mechanism

for releasing the pendulum, making sure that it latches and locks properly and that you

understand its operation.

3. Raise the pendulum to the latch position and note the proper positioning of the sample.

Do not insert the sample yet. Set the energy indicator at the maximum scale reading,

and allow the pendulum to swing through one full swing to determine the energy in

the hammer. Record the reading.

3. Raise the pendulum to the latch position and set the energy indicator at the maximum

scale reading again. Take the test specimen from its cooling or heating medium (see

Note B); place it in the correct position in the specimen shroud.

4. Release the pendulum and record the energy absorbed. DO NOT allow the pendulum

to swing more than once!

134
Charpy V-Notch Impact Testing handout, page two

Notes:

A. Safety precautions should be taken to protect personnel from the swinging

pendulum, flying specimen fragments, and hazards associated with specimen

cooling and heating media.

B. While placing test specimens in the machine, be sure that the pendulum is

latched in the safety position.

C. Should any specimen jam in the machine, disregard the results and examine

the machine thoroughly for damage or maladjustment, which would affect its

calibration.

Results

1 . Inspect each broken specimen and sketch its fracture surface. Observe and calculate the

percent cleavage (brittle fracture) and shear (ductile fracture).

2. Compare the obtained impact energies with respect to the temperature changes, and

graph the results. Compare these results to pubUshed curves for this alloy.

3. Report measurements as indicated by ASTM guidelines.

4. Explain your conclusions regarding the behavior of this metal at different temperatures.

135

FIBER REINFORCED COMPOSITE MATERIALS

H. A. West and A. F. Sprecher

Department of Materials Science and Engineering

North Carolina State University

Raleigh, North Carolina

Key Words

Composite, anisotropy, fibers, matrix, reinforcement, shear distortion

Prerequisite Knowledge

This laboratory requires a general knowledge of the concepts and parameters

involved with the elastic behavior of materials, namely, stress, strain, elastic modulus,

and Poisson's ratio.

Objectives

In this laboratory, data will be collected in order to accomplish the folowing analyses

pertaining to the characterization and elastic behavior of fiber reinforced composite

materials.

1) Calculate the fiber volume fraction, Vf, for a composite sample from

sections oriented a) perpendicular to the fibers and b) 45° to the

fibers. Compare these two values and account for any differences.

2) Calculate the longitunal and transverse moduli, El and Ej, from data

provided for a nylon reinforced rubber composite and compare these

values to those observed in the laboratory.

3) Calculate the elastic modulus, Ej, at different angles (i.e. 6=15°, 30°,

45°, 60°, and 75°) and plot the values as a function of 9. On the same

graph, plot the theoretical curve from the equation given and compare

the two.

4) Obtain the major Poisson's ratio measured at the different angles

and plot the values along with a theoretical curve for comparison.

5) Plot the observed values of the shear coupling modulus, p, as a

function of 6.

137
Background

This laboratory is concerned with the mechanical behavior of fiber reinforced

composite materials. These types of materials are being used extensively in the

aerospace industry and in many other applications where high strength and low weight

are the primary design criteria. Generally, these materials consist of:

1) Fibers - long cylindrically shaped elements of high strength and/or

high modulus materials such as graphite, glass, Kevlar®,

boron, tungsten, aluminum oxide, etc., with diameters

ranging from 6 microns to 100 microns (1 micron = 10 %i).

2) Matrix - material which binds the fibers and transmits loads to the

fibers through chemical or mechanical bonds, and usually

has lower strength and modulus than the fiber material. The

most common matrix materials in use today are polymers

such as thermosetting epoxy resins and low-melting metals

such as aluminum. Other matrix materials such as thermoplastics of considerable toughness and heat resistant

ceramics are being developed for composite applications.

Fig. 1 Typical section of a fiber reinforced composite material

with unidirectionally oriented continuous fibers.

These composite materials (i.e. materials in which both constituents retain their

identities when "mixed" together) differ from most engineering materials in that their

mechanical properties are highly dependent on the direction in which the loads are applied.

Materials such as this are referred to as being anisotropic (just like a piece of wood).

Therefore, it is of considerable importance to the engineer to have a feel for this directional

dependence so that these materials may be utilized properly and safely.

138
DETERMINATION OF HBER CONTENT

The fiber content of a particular composite is generally expressed as the volume

fraction of fiber and is denoted Vf. Most structural composites contain between 50 to 60

percent fiber (0.5 < Vf < 0.6) while composites in other applications may contain less.

One method utilized for determining the fiber content is called the point count

method. This consists of the placement of a grid or an array of points over a

photomicrograph of a polished cross section of the composite material. Note that the

points must be small in comparison to the fiber diameter for an accurate measurement. By

counting the number of points or intersections which fall on the fibers and dividing by the

total number of points, the area fraction Af is calculated.

Referring to figure 2, the number of points falUng within fiber area is around 155 (not

everyone will count the same amount given the same picture). The total number of points

in the array is 630 (exactiy) so the area fraction of fiber in this example is 155/630 -0.25.

Fig. 2 Example of the point count method for a fiber-reinforced composite.

Notice that the fiber patches are elliptical; does this mean that these fibers are not

circular in cross section? Could they be circular but cut at an angle? Can the angle at

which the fibers are cut change the area fraction of fiber obtained by the point count

method?

Consider the case where the fibers are cut at a right angle to their lengths. The

patches would be circular and the area fraction could be obtained as above. Clearly, this area fraction Af is the same as the volume fraction Vf. Furthermore, it does not matter at

what angle the fibers are cut; even if the fibers are randomly oriented, such as in a

composite containing chopped fibers, the point count method gives, directly, the volume

fractions of the constituents.

In this lab, however, the total fiber area will be determined by counting the number of

fibers intersecting the surface of the sample and multipying by the area of the fiber. This

is possible due to the relatively large diameter of the nylon reinforcement and low fiber

content. This method will be employed on one surface oriented perpendicular to the fibers

and another oriented 45° to the fibers.

Fiber

Matrix

139
ELASTIC BEHAVIOR

As was previously mentioned, the mechanical behavior of fiber reinforced composite

materials is highly dependent on the direction in which the particular property is

measured. For instance, the elastic modulus along the fibers, El, is drastically different

from the elastic modulus transverse to the fibers, Ej. First order approximations of these

moduli can be caluclated from the elastic constants of the constituent materials by

considering the isostrain and isostress models shown in Figure 3:

Isostrain Isostress

Fig. 3 Geometry of idealized unidirectional composite materials.

The equation for the longitudinal modulus (along the fibers) can be derived from the

isostrain model as:

where,

El = E,v,+ E^v

Ef = elastic modulus of the fibers

V| = volume fraction of fiber in the composite = elastic modulus of the matrix material = volume fraction of matrix = (1 V^)

m

This equation is known as the rule ofmixtures and implies that the contribution of a

constituent is directiy proportional to its volume fraction. Clearly, the equation for the

density of the composite would be of the same form.

liie equation for the transverse modulus (perpendicular to the fiber direction) can be

derived from the isostress model as:

E

140
This equation is known as the inverse rule ofmixtures. Both equations are shown in

Figure 4 to illustrate the effect of fiber content on the elastic moduli. Notice that the

transverse modulus is not appreciably increased beyond the modulus of the less stiff

constituent, the matrix, at the fiber contents usually encountered in engineered

composites.

0 Vf 1

Fig. 4 Elastic modulus versus fiber volume fraction for the isostress and isostrain

models.

We can refer to the directions L and T as the material axes and, if the composite is

stressed in either of these directions, the corresponding strains can be calculated (on the

left in Figure 5). However, if a stress is applied at an acute angle, 0, to the fibers (on the

right in Figure 5), the elastic response along the loading axes (1 and 2) can be calculated

from the properties measured along the material axes (L and T).

Fig. 5 Illustration of material (L and T)and loading (1 and 2) geometries.

141
[E E

cos^e + ^sin*B + ^(-g*--2i;LT)sin22Bj

[E E

sin*e + -^cos*B + ^(-g^-2yLT)sin^2Bj

Notice that in the above equations the material parameters needed include 0, Glx»

and Vlt' ^^^^ ^T- The value of El can be calculated from the rule of

mixtures equation given previously and the value obtained will be satisfactorily close to

reality (even though the composite is made of fibers in a matrix instead of alternating

plates as utilized in the isostrain model). However, the value for Ej calculated from the

inverse rule of mixtures equation would not be close to reality because the isostress

model (stacked plates) is an oversimplification of a fiber composite loaded transversely.

Similarly, equations for Glj (the shear modulus obtained when a torque is applied in the

plane perpendicular to the fiber direction) do not always give accurate values; therefore,

Ej and Glt should be measured in the laboratory. The major Poisson's ratio, Vlt

longitudinal stress causes a strain in the transverse direction), can be calculated reliably

from a rule of mixtures type equation just like ElWhat about transverse stress causing a strain in the longitudinal direction)?

Would you expect it to be equal to Vlj? It is indeed different but easily calculable as

follows:

Et

^TL El LT

The transformation of Vlt (^0"g the material axes) into Vjj (along the loading

axes) is given in the following equation:

One of the most important phenomena which occur upon the off-axis loading of

unidirectionally reinforced fiber composites is the production of a shear strain from a purely tensile stress state. As illustrated in Figure 6, if a 90° reference angle is enscribed

on the sample (prior to loading), this angle will change as the sample is loaded uniaxially,

indicating the existence of a shear strain. This clearly would not happen with an isotropic

142
material (a square would become a rectangle but angles would not change) or on a composite sample loaded along the material axes (0=O° or 0=90°); but when 6 is

between 0° and 90°, a shear strain usually occurs. It may be positive, or negative, or

zero, depending on the value of 0, the elastic properties of the consitituents, and the fiber

content of the composite.

Fig. 6 Illustration of shear strain produced by tensile loading of a fiber composite.

The amount of change in the 90° angle (measured in degrees) that occurs upon the

stressing of the composite is the shear strain 7j2- For the purpose of our simplified

experiment, we will define a shear coupling coefficient, P, to relate the the applied normal

stress, Oj, to the resulting shear strain as follows:

Instructor Notes

The composite samples currently used for this experiment consist of 7% by volume of

nylon cord in a cured rubber matrix. The raw material was originally obtained for a senior

project conducted by Mr. Yusef Fahmy. His investigation laid the groundwork for this

laboratory exercise and his assistance was gready appreciated. We cannot specify a

current vendor for such a nylon/rubber composite system, but can only suggest contacting

a tire manufacturer for uncured, unidirectionally reinforced material. A similar experiment

could be performed with fiberglass/epoxy or graphite/epoxy, but the deflections would only

be measureable with strain gages. Other commercially available reinforced sheet

materials could suffice as long as the extensibility was high enough to permit hand

measurement of strain and shear distortion. For this exercise, the students were able to

measure the elongations (and transverse contractions) with dial calipers and the shear

distortion angle was measured with a protractor. Samples of the results are given on the

proceeding page.

143
144
DIELECTRIC BEHAVIOR OF SUPERCONDUCTORS

AT MICROWAVE FREQUENCIES

J. N. Dahiya

Physics Department

Southeast Missouri State University

KEYWORDS

Superconductors; Microwave Resonant Cavity; Dielectric Constant; and

Dielectric Relaxation.

OBJECTIVES

1. To learn to operate a microwave spectrometer.

2. To tune the microwave resonant cavity at a certain frequency and

get resonant signal and frequency markers

3. To take data: Frequency shifts and Q-changes as a function of

temperature as the superconductor sample under investigation

goes through its transition temperature.

4. To analyze the data using a computer program.

SUMMARY

A cylindrical microwave resonant cavity in TEq^^ mode was used as a probe to study the dielectric behavior of two superconductors:

Y^-Ba2Cu30j^ and Bi2Sr2Ca2Cu3 at microwave frequency of 9.2 GHz. The

microwave cavity was used in a self designed microwave spectrometer

with a very efficient method of cooling. Dielectric relaxation of

these super-conductors was studied by cooling the sample to the

superconducting state. The frequency shifts and the Q-changes of the

cavity were monitored as the cavity temperature was varied.

145
INTRODUCTION

Dielectric properties of solids, liquids and gases have been studied

by different investigators (ref. 1-6). The present investigation

involves the use of a microwave resonant cavity to study the

dielectric response of two different samples of superconductors:

Y^Ba2Cu30j^ and Bi2Sr2Ca2Cu3.

The resonant circuit technique is a standard technique and has been

used by several workers. Bussey et al (ref. 7) and S. Chattarjee

(ref. 8) used a circular cavity resonating in TEq^q mode with

capillary tube specimen and tuning plunger. C. H. Collie et al (ref.

9) made use of a circular cavity resonating in TMq^ mode with a capillary tube specimen. K. H Hong and J. A. Roberts (ref. 10) used

a cylindrical cavity resonating near 10 GHz in TMq^q mode to

determine the dielectric properties of liquids and solids. Dahiya et

al (ref. 11 and 12) studied the dielectric behavior of various polar

and non-polar compounds using a microwave resonant cavity in TEq^j

mode.

Dielectric behavior of these superconductors was studied between 80 K

and 240 K while their superconducting temperatures were between 90 K

and 110 K. The microwave resonant cavity in this investigation was

cooled by flushing very cold nitrogen gas around the cavity. The

thermocouple was attached to the sample inside the cavity which in

turn was computerized by using microcomputer interfacing techniques

(ref. 13). The powdered sample of super-conductor was placed into

the resonant cavity through a capillary tube attached to a micrometer

drive which allowed a different mass of the sample into the cavity.

Dielectric behavior of these superconductors was studied by

introducing a fixed length of the sample into the resonant cavity and

then the cavity was cooled to achieve temperatures lower than the

superconducting temperatures. Slater's perturbation equations were

used to calculate the frequency shifts and Q-changes of the cavity.

THEORY

In a static field the displacement vector D and the electric field

vector t are proportional to each other.

5 = 6^ (1)

where e is the dielectric constant.

146
When a dielectric is subjected to an alternating field the

orientation of the dipoles, and hence the polarization, will tend

reverse every time the polarity of the field changes. As long as

field remains low (<10^ Hz), the polarization follows the

alternations of the field without any significant lag and the

permittivity is independent of the frequency and has the same

magnitude as in a static field. When the frequency is increased

dipoles will no longer be able to rotate sufficiently rapidly so

their oscillations will begin to lag behind those of the field,

the frequency is further raised the permanent dipoles will be

completely unable to follow the field and the contribution to the

static permittivity (e) from this molecular process, the

orientational polarization ceases and this usually occurs in the rf

to

the

the

that

As

range (10^ - 10^^ Hz).

For frequencies in the infrared (10 - 10^"* Hz) range there is no

contribution to e from atomic or ionic polarization and the only

polarization that contributes to e is the electronic polarization.

Therefore, the permittivity of a dielectric material decreases with

increasing frequency. This process is known as dielectric

dispersion.

At very high frequencies, E, D and e become complex quantities given

by

E= E, eJ"^

and e = e - j6

where e' and e" are the real and imaginary parts of the dielectric

contant.

(2)

(3)

(4)

Since

A

D

A

€

A A

eE

A

_D

A

E

Do eJ^"^"^)

Eo ejwt

(5)

(6)

or

A

6

=

D,

(7)

147
or e = -j^ (cos6-j sin6) (8)

Therefore, using eq. (4) €' = cos8 (9)

^0

e" = sin5 (10)

^0

The dielectric loss at a certain frequency is indicated by tan5 given

by equations (9) and (10) as follows

tan5 = -4 (11)

The frequency shifts and the Q-changes of a perturbed cavity are

functions of the dielectric properties of the cavity media and are

given by Slater's perturbation equations (ref. 12).

Af 1 , ^s'

^

f -7^-7 (12)

I - I dv

and A(l/Q) = e"

f — (13)

J ! • L dV

a

where E is the field of the unperturbed cavity, is the microwave

field as applied to the cavity and Eg is the field of the sample

itself, and v and V are the volumes of the sample and cavity

respectively.

By defintion

Q= \ (14)

where f^ is the resonant frequency of the system and W is the

frequency separation in Hertz, of the resonance half-power points.

148
Therefore, we have the following relation (with modulation

correction)

A(l/Q) = /3AW

(15)

0

The real and imaginary parts of the dielectric constant are further

related to the relaxation time (t) using Debye's equations (ref. 14)

as follows.

= WT (16)

where w = Ztif^, and is the value of the dielectric permittivity

for static field.

EXPERIMENTAL METHOD

Materials

Superconductors Y^-Ba2Cu30j^ and Bi2Sr2Ca2Cu3 in the powdered forms.

The transition temperatures for these superconductors were around

95 K and 106 K respectively.

(ii

(iv

(v

(vi

(vi i (vi 1 1 (ix

(X

(xi

(xi i (xi i i (xi V

(xv

Equipment and Supplies

Western electric 2K25 klystron

Hewlett Packard 715 A klystron power supply

Webster G40P5158 directional coupler

OKI 8-11 GHz wavemeter

Microwave resonant cavity in the TEq^^ mode designed in the

physics workshop at Southeast Missouri State University

Hewlett Packard x 485B tunable detector mount

Kenwood R-1000 radio receiver

Sencore FC71, 10 Hz - 1 GHz frequency counter

Hewlett Packard 612A UHF (450 MHz-1250 MHz) signal generator

Tektronix 533A dual channel oscilloscope

31 KHz bandpass amplifier designed in the physics workshop at

Southeast Missouri State University

Waveguides in the x-band of frequency (8-11 GHz)

Waveline attenuator for varying microwave power

Omega 6125A digital thermometer with a thermocouple attached

Large dewar to hold about 25 liters of liquid nitrogen for

149
cooling process.

(xvi) Thermal bath with copper coils to circulate cold dry nitrogen

gas around the sample placed in the microwave resonant cavity.

Procedure

A microwave spectrometer in the x-band of frequencies was put

together by collecting different components of the spectrometer and

this system is relatively very inexpensive as compared to the ESR

spectrometer. The details of the spectrometer have been discussed

elsewhere (ref. 12). A block diagram of the spectrometer is shown in

Fig. 1. A microwave signal of 9.2 GHz is produced by a 2K25 reflex

kylstron. The signal is modulated by applying a horizontal sawtooth

from the repel ler of the klystron to give a broader frequency

response of the microwave power. This signal is transmitted through

a waveguide as co-ax cables cannot be used because of very high

inductive reactance at that frequency. The directional coupler

divides this signal in two parts. A part of the signal goes to the

microwave resonant cavity and the reflected signal is detected by a microwave diode and the amplified signal looks like a butterfly. The

other part of the signal from the directional coupler is mixed with a

standard frequency signal to produce a series of markers. A radio

receiver is used to detect these markers which in turn are used to

study the frequency shifts and the width changes of the signal

produced by the resonant cavity as the sample is introduced in the

cavity. The frequency shifts and width changes or Q-changes of the

signal are related to the real and imaginary parts of the dielectric

constant through the Slater's perturbation equations 12 and 13.

The powdered samples of superconductors were provided by

Superconductive Components, Inc., Columbus, Ohio, and the purity

level was 99.9%. Each sample under investigation was taken into a

capillary tube that was sealed with a fine thermocouple wire attached

to the sample. It was then placed along the symmetry axis of the

cavity via a micrometer drive. The cavity resonating in TEq^j mode

was placed into a thermal bath. A block diagram of the microwave

resonant cavity is shown in Fig. 2. The cooling technique used in

this investigation is very efficient and has been discussed elsewhere

(ref. 12). Each sample of the superconductor was cooled below its

superconducting state and the temperature allowed to rise in suitable

steps with resonant frequency shifts Af and microwave loss parameter

A(l/Q) measured for each temperature until sufficient data were

obtained to determine the behavior of the dielectric response of the

system over the transition region. At each reading, sufficient time

was allowed to elapse so that the sample and cavity came to

temperature equilibrium.

150
RESULTS AND DISCUSSION

Microwave absorption technique has become very sensitive in

explaining the properties of high T^, superconductors (ref. 15,16).

The resonant cavity technique employed in this investigation

successfully monitored the dielectric relaxation phenomenon in

superconductors: Y^Ba2Cu30j^ and Bi2Sr2Ca2Cu3. Each sample of the

superconductor was found to show a dramatic behavior in the

dielectric properties near the super-conducting temperature. This

behavior can be seen in Figs. 3-6 with Figs. 3 and 4 showing the

behavior of microwave loss A(l/Q) and frequency shift Af/f^ vs.

temperature for the superconductor sample Y^-Ba2Cu30j^, and Figs. 5 and

6 showing the same behavior for the superconductor sample

Bi2Sr2Ca2Cu3.

The microwave resonant cavity technique employed in this investigation clearly identifies the superconducting temperature. The

microwave loss below the superconducting temperature is very

interesting. According to the Meissner effect, the microwave

frequency should be greater when the sample is in the superconducting

state because the magnetic component of the microwave field applied

is excluded from the sample. These measurements of microwave

absorption were made in the absence of an external magnetic field.

When a superconductor is in the normal state (above the superconducting temperature), this thickness is much greater than the skin

depth. Therefore, in the normal state the microwave field does not

penetrate the sample and only a fraction of it is absorbing the

microwaves.

The detailed results of the microwave loss measurements and the

frequency shifts in these superconductors will be presented elsewhere

as a continuation of this experiment. This experiment is presented

here as a technique to monitor the dielectric relaxation mechanism in

these and other supercondcutors and to identify their superconducting

temperatures.

151
ACKNOWLEDGEMENTS

The author wants to thank Melina Gray and Mark Wetzler, undergraduate physics majors for

their contribution to this work. I also wish to thank Ms. Theresa Buttry for typing this

manuscript and Mrs. Betty Black for preparing the figures.

152
REFERENCES

1. Baynham, A. Gibson, A. F., and Granville, J. W.: On the

Dielectric Constant of Germanium at Microwave Frequencies.

Proc. Phys. Soc, 75, 1960, p. 306.

2. Lurio, A., and Stern, E.: Measurements of the Dielectric

Constant of BaTi03 Single Crystals in the Paraelectric Region

at X-band. J. Appl . Phys., 31, I960, p. 1805.

3. Nishioka, A., and Takeuchi, M.: Dielectric Property of

Triglycine Sulphate Single Crystal in the 9,000 Mc/s Region.

J. Phys. Soc. Japan, 14, 1959, p. 971.

4. Surber, W. H., and Crouch, G. E.: Dielectric Measurement

Methods for Solids at Microwave Frequencies. J. Appl. Phys.,

19, 1948, p. 430.

5. Grant, E. H., Buchanan, T. J., and Cook, H. F.: Dielectric

Behavior of Water at Microwave Frequencies. J. Chem. Phys.,

2fi, 1957, p. 156.

6. Birnbaum, G., Kryder, S. J., and Lyons, J.: Microwave

Measurements of the Dielectric Properties of Gases. J. Appl.

Phys;, 22, 1951, p. 95.

7. Bussey, H. E., and Birnbaum, G.: Cavity Resonators for

Dielectric Spectroscopy of Compressed Gases. Rev. Sci.

Instrum., 30, 1959, p. 800.

8. Chatterjee, S. K.: An Approximate Theory of the CavityResonator Method of Determining the Dielectric Loss of Solids

at Microwave Frequencies. J. Indian Inst. Sci, 34B, 1952, p.

43.

9. Collie, C. H., Hasted, J. B., and Ritson, D. M.: The Cavity

Resonator Method of Measuring the Dielectric Constant of Polar

Liquids in the Centimetre Band. Proc. Phys. Soc, 1948,

p. 71.

10. Hong, K. H., and Roberts, J. A.: Microwave Properties of Liquids

and Solids Using a Resonant Microwave Cavity as a Probe. J.

Appl. Phys., 45(6) . 1974, p. 2452.

153
11. Jani, S. K., Dahiya, J. N. and Roberts, J. A.: Dielectric

Changes in Hyaluronate Solutions at Microwave Frequencies as a Function of Concentration, System pH and Temperature.

Bioplymers, 19, 1980, p. 931.

12. 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(6) . 1981, p. 3609.

13. Dahiya, J. N., and Freeman, R. W.: Computer Interfacing of a Microwave Resonant Cavity for Temperature Measurements During

Dielectric Relaxation. Computers in Physics, Jul /Aug. 1989,

p. 49.

14. Debye, P. Plar Molecules (Chemical Catalog, New York), 1929,

Chapter 5.

15. Durny, R., Hautala, J., Ducharme, S., Lee, B., Symko, 0. G.,

Taylor, P.C., and Zheng, D. J.: Microwave Absorption in the

Superconduci tng and Normal Phases of Y-Ba-Cu-0 Phys. Rev. B,

36(4) . 1987, p. 2361.

16. Pakulis, E. J., and Chandrashekhar, 6. V.: Anisotropic

Microwave Absorption of Bi-Sr-Ca-Cu-0 Single Crystals. Phys.

Rev. B, 38, 1988, p. 11974.

154
155
TUNING PISTON

THERMOCOUPLE

JUNCTION

COUPLING HOLES

MICROMETER

GLASS ROD

BRASS CAVITY

•TEFLON TUBINGS

SAMPLE HOLDER

R-4.9 cm.

2. Block diagram of the tunable microwave resonant cavity operated

in TEqjj mode used in this investigation.

156
o

o

-

o

o

o

o

o

o

o

o

o

o

o

% oo QiDDO OOOO ODq

1

1 1

CD

LO

CSJ

CM

CO

CO

LO

CM

O

1^

'q.

E

roCO

<o

s-o

=3

t.

0)

Q.

E

a> (U

4-> O

o

4-> CM E

U

e

00

CM

(/) N

<0 31

CD

cyosj

•—I

<a 4->

to

to X

o o — CO

a> o

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160
IT ' S HARD TO TEST HARDNESS

Edward L. Widener PE.

Purdue University-MET. Department

W. Lafayette, IN 47907

ABSTRACT

Hardness is essentially a mechanical property of uniform

materials, a surface indicator of other properties. It is hard

to define, hard to correlate different tests, and hard to

compare different materials. Nevertheless, hardness is broadly

considered as "resistance to penetration, elastic and/or

plastic." For metal alloys, commercial tests typically measure

plastic-strain or permanent-set for solids; resultant

scratches or dents are relatively non-destructive, unless

stress-concentrations in finished surfaces make trouble.

With dozens of hardness tests available, our conventional

lab experiments tend to focus on a pair of popular industrial

machines, Brinell and Rockwell, and to generate repetitive

data for common metals by routine operations. Technologists

are not clerks but problem-solvers, in need of an early

exposure to a variety of tests, which involve diverse

principles and definite applications. Selecting appropriate

methods and following published standards are priority lab

objectives. Details of several unconventional experiments,

with simple equipment and familiar samples, are suggested to

supplement certain well-established but lesser-known ASTM

hardness tests.

KEY WORDS

Hardness; Mohs-scratch ; Brine 1 1-stress ; Rockwel 1 -strain;

Plastic-dent; Elastic-rebound; Scleroscope.

PREREQUISITE KNOWLEGE

Definitions of Stress-Strain Test, Yield Point, Ultimate

Strength, Resilience, and Toughness.

OBJECTIVE

It is short-sighted to limit our technology labs to mere

measurements of "the plastic response of metals", typically

using Brinell and Rockwell machines. Pupils need a broad view

of the various ways to modify "materials" and a deeper

understanding of the many methods to assess "hardness" as

strength, firmness, rigidity, resilience, stiffness, solidity

or toughness.

INTRODUCTION

Hardening processes include: oxidizing and anodizing,

plating and coating, cold-working and heat-treating,

allotropic and precipitation quenching, alloying and

161
laminating, shot-peening and bal 1-peining, orienting and

cross-linking, irradiating and catalyzing. Testing processes

involve: filing and sawing, chiseling and tooling, twisting

and scratching, tumbling and breaking, milling and drilling,

grinding and sanding, sounding and pounding, magnetizing and

sparking, indenting and rebounding.

Commercial tests with standard procedures and plastic

strains include: Mohs scratch. Pencil number. File number.

Cloudburst shotting. Wheel abrator tumble-blast, Bierbaum plow.

Keep '

s

drill, L . A

.

rattler, Deval weight-loss, Charpy-Izod

toughness, Webster pliers, Barcol yoke. Sward rocker, Pfund

indenter, Telebrinel ler indent, Monotron stress.

Micro-character scratch width, Imbedded-bal 1 Newtons,

Penetrascope pressure , Wi Ison-King-Brinel

1

pressure

,

Bueh 1 er-Krautkramer-Tukon-Vi ckers-Knoop micropressure , New

Age-Wi 1 son-Rockwe 1

1

inverse strain. Superficial mini-Rockwel 1

,

New Age-Ames-Rockwel

1

portable.

Commercial tests with elastic strains include: Zwick-Shore

durometer, A.F. Shore scleroscope. Turner sclerometer, Barcol

yoke, Equot ip-Leeb rebound velocity, non-destructive sonagram,

Boyer-6a 1

1

-Lissa jou oscilloscope pattern, as well as the

Rockwe 1

1

test (minor-load remains as dial gage is read)

.

Indenters and penetrators include:

a) Brinel

1

hard-steel ball, Hul tgren cold-worked ball,

Sintered-carbide ball (WC) ; all have 10mm diameter and

500-3000 kgf loads.

b) Rockwell hard-steel balls (1/16" , l/8",l/4" , 1/2"

diameters) and cone-shaped diamond crystal "Brale", with

regular 60-100-150 kgf weights and superficial 15-30-45 kgf

weights.

c) Micro-hardness crystals shaped as (B) (Vickers, Pfund ) or (•«^^) lozenge® (Knoop) ; and diamond-tipped points or

carbide-disks ( Shore , Turner, Leep ) . So, to say

"diamond-indenter" is to confuse. Also, to distinguish between

inventers, machines, trademarks, and generic terms is

important

.

' SCRATCH TEST

Material removal (filing, sawing, drilling, milling,

planing, sanding, grinding) by hand or machine will produce

chips, noise, sparks, heat, odor, lost speed or power, and

tool marks or damage. Quantitative evidence, gathered under

controlled conditions to describe hardness variations, is

elusive. Fortunately, a box of rocks collected by Friedrich

Mohs (1812) established a "pecking order" (scratchabi 1 i ty ) for

a wide range of materials (#1-10) from softest talc to hardest

diamond.^ A modified selection (1822) of 15 minerals (#1-15)

provided better discrimination of materials. However, purchase

of a certified "Rock Kit" is not required to run these scratch

tests of HM (Hard Mohs' Numbers) or their half-points:

a) Hold a stick of chalk (say 10cm long) on a flat surface

and mark with a penci

1

(one stroke, about 1cm). Typically,

chalk (HM #2) scratches the softer graphite (HM #1.5) and gets

162
a grey mark. However, even a "soft lead" (HM #2 pencil) will

leave a "groove" when firmly scribed on the chalk (white

chalk-dust coats the pencil point). Obviously, the lead also

includes grit and binder (HM #6 to 8)

,

b) Mark the chalk with the tip of your thumbnai(HM #2.5)

or the edge of a copper penny (HM #3.5). Since your nail

elastically deflects, the "harder penny" cannot scratch it;

however, if you try to scratch the penny's edge with your

nail, the nail gets scraped.

c) Hold flat a piece of mild steel (HM #5) and mark with

the sharp edge of a broken piece of hacksaw blade (HM #6),

with one firm stroke (1cm) . However, a broken piece of

"white-iron" casting (chilled cementite) or "Duriron" pipe

(hi-silicon) is not scratched (HM #7); but, a flat sawblade

can be scratched with the sharp edge of such brittle iron.

d) Use other samples with broken edges: e.g., pottery,

concrete, glass, tile, file, arrow-head, cut-off saw, or

glass-cutter. Show how abrasives and refractories range

between HM #7-10. The coating on a "tin-can" is about HM #2.

Use all 5-senses to augment the "plastic-scratch" test; e.g.,

noting friability, sparks, and sounds.

BRINELL STRESS TESTS

Ultra-hard metals ( Martensite , Duriron ) are highly elastic

(stiff) and resilient (rebound), somewhat like elastomeric

polymers. Thus, a Brinell hardness test^of plastic (permanent)

indentation has serious limitations, which can be explored by

the lab to supplement routine tests normally run on mild

steel, brass, or aluminum:

a. ) Rubber specimens (hockey-pucks, old-tires) are tested

to show the dent disappears after a Brinell load (500-3,000

kg) is removed. The Brinell hardness is apparently infinite

(load H- zero area) and patently useless. Refer to

stress-strain curves of cast-iron, martensite, or ceramics to

show how resilient energy is recovered; i.e., brittle

materials are 75-95% "hockey-puck". Even if ultra-hard samples

are un-cracked by quenching or testing, and if the test-ball

is not damaged, the unreal istical ly small dents give too-high

hardness readings. Save and exhibit any broken balls and

samples, from deliberately overloaded trials.

b. ) In hard rubber, a "scuff-mark" can be measured with

the 20-power telescope (standard ASTM procedure #E 10)

Usually, vulcanized rubber lets the Brinell ball (10mm

diameter) sink to the holder (say 9mm) to establish a maximum

limit for "bearing stress".

Thus BHN (kg per square millimetre) is

calculated as load (kilograms) divided by

contact area (sq mm) , which is a

spherical-surface (plus flat-ring) as shown

ii^ Figure I . Incidentally, remember steel

quenched in cold "Brine" is hard as "'ell",

and never mis-spell Brinell or Rockwell;

mnemonics are an important part of lab.

163
c. ) Of course, non-standard weights less than 500 kgf can

be applied, so the ball-holder does not reach the specimen.

While yet loaded, the actual dent-diameter (d) can be measured

with thin calipers, or else marked with felt pen (fine point)

for later measuring by scope. Often, pre-coating specimen or

ball with chalk is sufficient to delineate dents.

d. ) For supplementary exercises, measure a metric-ruler,

with your "20-power scope", verifying length (not area) is

magnified 20X and is accurately read to half-a-tenth (1/20

mm). This converts by "factor-label" method (mm/20 X cm/lOmm X

1,000 mil/2. 54cm) to 1.9685 mils. So this "2-mil scope" is

about half as accurate as a machinist's micrometer.

e. ) Another exercise involves weighing a "500 kgf" Brinell

disk (about 19 pounds Avoirdupois) but calculating an 1,100

Ibf load on the test-ball at 453.6 g/lbf, say 2.2 Ibf/kgf )

Measure disk-diameter (a boss offsets a recess) and height;

subtract the rod-slot; calculate volume and then density (say

480 Ib/cuft) ; probably the disk-material is "steel".

f. ) Of course, when soft and/or resilient materials are

tested with weights below 500 kgf, direct loads may be applied

to specimens via an indenter-bal 1 . Friction in machine-levers

at low- loads is thus avoided.

g. ) Deriving the "Brinell Stress" formula is instructive,

as shown i n Figrure II : i

Similarly, standard tests of hardened-steels or cast-irons

(C-setup) can be supplemented with unorthodox (useless) tests

of aluminum and brass samples. A deep dent may read "HRC 88",

with diamond-cone "Brale" and full 150kgf load. However,

compared with "pin-pricks" in a standard C-gage block, this

soft sample obviously betrays an off-scale reading (minus 12

or minus 112), depending on the position of the "little-hand",

on the dial-gage. This is the time to warn against ultra-high

(above 80) or low (below 20) numbers, on a 1-100 scale.

ROCKWELL STRAIN TESTS

measuring principle

{% inverse-strain)

of the"HR"

literal reading on

the dial-indicator

( Ficrure III ) and the

Then, the

reversed-scale can

be explained:

164
BOUNCING BALL TESTS

A ball-bearing (about 10 -mm diameter) is dropped through a

vertical glass or plastic tube (15mm O.D. X 30cm tall) to

rebound from the surface of a common commercial alloy (steel,

brass, aluminum). This is the principle of the "Scleroscope

Machine" : 5

a) Square bars (25mm X 25mm X 5cm long) or thick disks

(25mm X 5cm diameter) are placed on a solid bench, granite

block, or anvi 1

b) Elastic rebound can be measured (approximately) by a

metric-ruler, observing 5 or 10 trials and recording maximum

value (less rubbing against tube-wall).

c) As a measure of elastic hardness, a "coefficient of

restitution" (6) is calculated as the square-root of maximum

rebound-height ^ original drop-height. Velocity is the

square-root of 2 ^fh, where cf is the acceleration of gravity.

So, elastic hardness may be expressed as the inverted

restitution-coefficient, 1/0.

d) As a measure of plastic hardness, a Brinell scope (20

X) is used to measure dent-diameter (nearest twentieth of a

mm) . The "Impact Value" can be calculated as Energy

(ball-weight X drop-height) per Area (spherical contact). Thus

I.V. = (kgf x mm) per mm-squared. Prepare smooth specimens

(file or sand off any hacksaw marks). Students should know 20x

power means 20-times length.

e) Compare both values (elastic and plastic) to determine

which material is "harder". Generally, the higher the rebound

the smaller the dent. Thus, the greatest sum^l/£,+ I.V.)

identifies the hardest specimen.

f) Another plastic-strain test involves mounting a slender

bar (say 5mm square X 5cm long) of mild steel (or copper,

brass, bronze, aluminum) in a vise. Twisting 90° with a

torque-wrench (fitted with a square-socket) gives an initial

reading. Then, the return twist (minus 90°) gives a higher

reading (from work-hardening) . Report as torque (force X

distance) per degree.

CONCLUSION

For useful correlations of various hardness tests (elastic

and plastic), see "Ref erences"7 Absolute hardness of

soft-steel (annealed) is about 100 kg/sq mm (minimum)

precipitation-hard aluminum is about 100 kg/sq mm (maximum);

alloyed copper (brass) is about 60 kg/sq mm; soft-aluminum

(annealed) is about 30 kg/sq mm. These are comparable to

conventional U.S. values of elastic-modulus (E) ; i.e.,

30-million (psi) for steel, 20-million for brass, and

10-million for aluminum.

165
TERMS

1. Elastic strain - stress is proportional to strain

(Hooke's Law); strain returns to zero, when stress

is removed.

2. Force - time rate of change of momentum (mass times

velocity) ; commonly mass times acceleration of

constant mass; load or weight.

3. Hardness - resistance to penetration, elastic and/or

plastic; related to strength, stiffness,

resilience, toughness.

4. Hysteresis - energy left in a material, after

elastic-strain and stress-removal.

5. Impact - Potential energy absorbed by rapid blow.

(weight x height)

6. Mechanical - relating to forces (tension, compression,

shear)

7. Plastic strain - stress exceeds a material's elastic-limit

or yield-point) ; some permanent deformation then

remains, when stress is removed.

8. Resi 1 ience - Elastic energy absorbed (area under linear

plot) . 9. Rigidity - Torsional stiffness.

10. Scleros - Greek word for "hard" (root of scleroscope

skel eton, multiple-sclerosis)

11. Stiffness - Slope (stress per strain) of an elastic linear

plot

12. Strain - relative change of a key dimension (length,

area, volume); the result of stress.

13. Strength - Maximum or ultimate stress; so-called

"Tensile Strength" (T.S.).

14. Stress - Reaction of material to pressure (load per unit

area)

15. Toughness - Total energy absorbed (area under entire

stress-strain curve)

166
REFERENCES

1. ASM, "Hardness Testing", Materials Park, OH, 1987.

2. ASM, "Metals Handbook, Desk Edition", 1985 - Metals Park,

OH; Boyer, H.E. & Gall, T.L., editors, pp. 33-4.

3. T^erican Society For Testing and Materials (A.S.T.M.),

Standards E 10, E 18, E 33, E 48, E 92, E 110, E 140, E

384.

4. Brinell, J. A., "II Congress Int. des Methodes d'essai

(1900)

5. Budinski; "Engineering Materials; Properties and

Selection", 3rd ed; Prentice-Hall, Englewood Cliffs, N. J.

1989.

6. Encyclopaedia Britannica, Vol. 11, U. of Chicago, 1973,

"Hardness Testing"

7. Jacobs, J. A. & Kilduff, T.F. "Engineering Materials

Technology", Prentice-Hall, Englewood Cliffs, NJ., 1985.

8. Knoop, Peters, & Emerson, "A Sensitive Pyramidal Diamond

Tool for Indention Measurements to, J. Res. NBS, July

1939, V. 3, pp. 39-61.

9. Mohs, Friedrich, "Grundriss der Mineralogie" , 1822.

10. Sisco, F.T., "Modern Metallurgy For Engineers", 2nd ed..

Pitman Pub. Co., N.Y. , 1948, pp. 136, 137, 152, 153.

11. U.S. Steel Co., "The Making, Shaping, and Treating of

Steel", 9th ed. , 1971, pp. 1238-1239.

12. Van Vlack, L.H., "A Textbook of Materials Technology",

Add i son-Wesley, Reading, MA, 1973.

13. Vickers, "Accurate Determination of Hardness of Metals",

Engineering (April 25, 1924) pp. 518.

14. Winslow, D.N., "Experiments With Construction Materials: A

Laboratory Manual", McGraw-Hill, New York, N.Y., 1990.

15. Wood Handbook, "Wood as an Engineering. Material", Forest

Service, U.S. Dept. of Agriculture.

167

UNCONVENTIONAL IMPACT -TOUGHNESS EXPERIMENTS

Edward L. Widener

Department of Mechanical Engineering Technology

Purdue University - Knoy 119

West Lafayette, IN 47907

ABSTRACT

In the materials lab, various impact observations and exercises can

illustrate basic concepts of mechanics (Work, Kinetic Energy, Potential

Energy, Free-fall, and Friction), while defining Weight, Mass, Center- of

gravity. Velocity, and Acceleration. Unconventional impact- tests of unnotched specimens may exceed the capacity of a conventional but unanchored

pendulum-machine . This leads to adjusting toughness readings, for kinetic

and friction losses, before assessing the devastating effects of notching a

test-bar or changing the temperature.

Keywords: Impact- toughness ; Energy- absorption; Drop-weight; Pendulum- tup

Charpy-Izod Tests

Prerequisite Knowledge: Stress-Strain Test; Crystal Lattices (BCC, FCC);

Notch Sensitivity; Potential-Kinetic-Frictional Ene gy

Objectives: 1. To distinguish between slow absorption of energy (tensile

toughness) and fast absorption (impact toughness); 2. To compare notched

vs. un-notched samples of steel (BCC iron).

INTRODUCTION

Plain carbon steel is conventionally tested in tension, with slowly

increased axial-load at constant cross-head speed, per ASTM #A370

specification. Modulus -of- toughness is routinely measured as the area

under an engineering plot of stress (load/original cross -sectional area)

vs. strain (change in length/original gage length). Typical units are psi

(pounds per square inch) or N/m^ (Newtons per square meter); however,

toughness is not to be confused with stress, elastic-modulus, or elasticresilience (also psi). When reported as "inch-pounds per cubic inch" (or

Newton-metre per cubic metre), then tensile- toughness is seen as total

energy per unit-volume of test material. It involves both elastic and

plastic energy, slowly-absorbed.

By contrast, impact- toughness is perceived as rapidly-absorbed energy

per standard specimen, usually reported as "foot-pounds" (or Joule; Newtonmetre) of total shock-resistance. This is commonly mis-labeled "impactstrength." Of the 14-different "Bravais" crystal types, a body-centered

cubic (BCC) lattice of iron (steel) is exceptionally vulnerable to a shockload in a cold environment, as blemishes bring stress -concentration or

notch-sensitivity. Moreover, a coarser-grained metal, with higher areavolume ratio and lower strain- rate, tends toward lower impact- toughness

To avoid potential trouble in specific alloys or processes, a variety of

impact tests were developed for a falling-weight (tup) or swinging pendulum

(gravity) in several different setups:

169
1. Standard samples (notched or plain) are rapidly loaded in bending,

tension, or torsion.

2. Samples are supported as simple beams (Charpy) , cantilevers

(Izod) , or fixed beams (Both ends).

3. Notches are V, U, or keyhole shaped. Their surface smoothness is

a critical factor.

4. Toughness vs. temperature (y vs. x) is plotted, with constant tupspeed, for identical samples at various temperatures.

CONVENTIONAL IMPACT -TESTING

Results from different test-setups generally cannot be converted.

Probably the most popular test is with a gravity-pendulum, per ASTM #E23:

Samples of a specific metal are tested under constant conditions (Charpysupported, V-notched) except with varying temperatures; the objective is to

determine any "critical temperature," where ductile-brittle transformation

may occur. Common applications were the design of Alaska pipelines and the

modification of North Atlantic ships, where brittleness was a severe

problem in BCC steels.

Materials lab classes tend to neglect impact- testing , until a costly

pendulum-machine (with digital readout) is available. Most demonstrations

simply involve notching and breaking 1/4" x 1/4" x 2" steel bars (hotmedium-cold) to obtain readings of absorbed energy. Metric bars are

typically larger (10 mm x 10 mm x 60 mm long). Conveniently, boiling-water

(100°C) and dry- ice (-56°C) are equi-spaced (±78C° of temperature

difference) from room- temperature (22°C) . However, to contrast the notched

bars (brittle) to thicker un-notched bars (tough) may be desirable but

difficult: cross -sectional areas are unequal, machine -damage threatens the

anchored-machine, and energy- losses beset an unanchored-machine

.

UNCONVENTIONAL IMPACT -TESTING

Simplified demonstrations of dynamic material properties, varying with

strain-rate, can be done in the classroom:

1. Pitch will shatter, when hit with a hammer; but ductile -flow

ensues with slow pulling, even at room temperature.

2. "Silly-Putty" (trademarked silicone polymer) will snap like

brittle chalk, when jerked or sharply twisted; but ductile necking

will occur with slowl/4" loading. Also, a rolled-ball will

bounce like rubber (fast compression) ; but the same ball slowly

makes a puddle (viscous liquid) with gentle gravity.

3. Panes of window-glass will snap when notched, using a martensite

file or diamond cutter ,. especially when wetted; but an aged-pane

may exhibit a marked increase in calipered- thickness , from top to

bottom, with ductile -flow induced by gravity at moderate

temperature

.

170
4. Certain grades of glass - tubing , when heated red-hot, will snap if

jerked but will neck ductilely if slowly pulled.

5. Sugar cubes may "fluoresce" in the dark, when hammered.

Similarly, "Certs" (trademarked breath-mint) may "flash" with

piezoelectricity, when crunched and viewed in a dark room.

Quantitative measurements of impact- toughness are feasible, using an

inexpensive drop-weight tester. (See ASTM #E208 . ) The blunt "tup" slides

like a guillotine down an upright pair of guide-rods, striking the test

specimen placed on the base. Generally, this test precedes a standard

"guided-bend" test of strips cut from welded pipe. The drop-height is

increased until "work-to-break" is found (weight x height) when friction is

ignored. For unsatisfactory joints, this avoids the expense of guidedbends . Obvious classroom variations are: comparing different metals,

notches, temperatures, or processes; e.g., thick steel plates may be

brittler than thin ones; cold-worked steel may be tougher than air-cooled

products

A primitive pendulum can be made from a ball-bearing, swung from nylon

fish-line, supported by a ring-stand or easel-frame. Target samples could

be boiled eggs or blown shells. Energy (weight x height) to crack or break

the egg is determined by increasing the pendulum- angle and calculating

drop-height (from radius and angle). The ball's center is the pendulum's

"center-of -gravity , " neglecting the fish-line. A large protractor can

become a "direct-reading" quadrant, calibrated as N x m (or ft x lb).

Threads, wires, or film-strips can be stretched across the pendulum's

trajectory. Tear-resistances of papers and plastics (notched vs. plain)

can be compared. If excessive energy is used, the sample's absorption is

then figured as weight times loss - in-height (original- final)

A small inexpensive pendulum-machine (about $500) is available for

testing plastics. Typical specimens are small "dumbbells" (about 1 cm

long). Tensile- impact then decapitates one end and registers the energy

expended (N x m) . The specimens can be molded in the lab, using an

auxiliary unit (another $200).

A plain pendulum-machine (costing $5,000 to $10,000) will directly

indicate the energy absorbed by a struck specimen. Model #74 (Tinius -Olsen

Co.) has 264 ft-lb capacity (center-of -gravity of 60 lb tup x 4.4 ft

vertical fall) . Its 1500 lb frame has a "Charpy" simple-beam support for

the sample. Plastics bars are plied (say 30 mm x 10 mm) for adequate

cross-section. Obviously, it is wrong to compare un-notched tensiletoughness (in-lb per cu in) with notched impact- toughness (ft-lb). Just

comparing the un-notched vs. notched impact- toughness of standard (10 mm

square) steel bars (5-6 cm long) is complicated:

1. The pendulum will jam in an un-notched bar, like an axe in a

rotten stump, barely bending the sample bar and falsely reading

264 ft-lb (maximum).

2. Unless anchored, the machine will slide 2-4 cm (about 1") on a tile -floor; clearly the machine's capacity was exceeded, and

pendulum- energy was dissipated. Anchoring the base may lead to a

damaged pivot on the swing-arm, also giving false readings.

Eventual shaft- fatigue and failure can occur.

171
3. Visually comparing the tested specimens (un-notched vs. notched)

should convince students that "tough steel" (AX SI #1040) became

brittle (like cast-iron) when notched and hammered. But how can

this subjective observation be objectively quantified?

PROCEDURE

Perhaps an impact- toughness reading (for notched bar) should be

standardized, dividing a.:- : orbed e lergy (ft x lb x 12 in/ft) by the bar's

volume (cu in). Comparis jn wit i censile- toughness (psi) then seems

logical; however, ASEE recommends "all -SI" classwork; and comparing bending

mode vs. pulling is suspect. (See ASTM #E208.) With S.I. metric

equipment, the standardirad result would be in Pascals (N.m per cu m)

.

Perhaps a better approach is this:

a) Adjust the original "un-notched reading" (say 264 ft- lb) for

kinetic and friction losses. Machine weight (1500 lb) times

dynamic friction-coefficient (say 40%) times sliding distance

(1/12') is 50 ft-lb of sliding-work. Moreover, 20% reduction of

the indicated toughness for an un-notched (10 mm) bar (264 ft-lb)

is 53 ft-lb. Thus the pendulum really lost 103 ft-lb (39%) of its

original 264 ft-lb of potential energy. This lowers our

"reference toughness" to 161 ft-lb (264-103). Steel is still seen

to be plenty "tough," if not blemished.

b) Adjust the actual "notched reading" (say 7 ft-lb) for kinetic

energy loss of a "flying sample," at room temperature. Thus, a

1.5 oz bar (by postal scale) with 12 fps observed velocity (about

6' per half a second) has KE of 0.21 ft-lb; this is a 3% inflation

of the material's toughness.

c) Now compare "actual notched- toughness" (7 ft-lb) of Item (b) with

"reference toughness" (161 ft-lb) of Item (a). We may conclude

that V-notched steel is about 4% (7 vs 161) as tough as smooth

steel, when struck at room temperature.

As a final exercise, the class can estimate or calculate velocities:

a) Average velocity of the sliding 1500 lb machine is estimated by

equating kinetic energy with sliding-work (50 ft-lb) of Item (5a).

Thus, V- squared is 64.4 (50/1500), and 1.47 fps is slidingvelocity

.

b) Impact velocity of of the pendulum is estimated by equating

kinetic energy with potential energy (minus 1% lost arm- friction)

.

Thus, KE is (264-2.64) ft-lb; the pendulum velocity is 16.75 fps.

c) This velocity is checked, using Newton's "free-fall" formula, as

Initial velocity squared + 2gh is Final velocity squared. With

zero Initial velocity, the Final velocity squared is 64.4 times

4.4 ft per second squared; so, pendulum velocity is 16.83 fps.

Then, figure the percent difference, based on 16.75 fps (more

realistic)

.

172
d) All answers should then be converted to S.I. units.

Pound force (Avoirdupois) x 4.448222 is Newtons

.

Feet X 0.3048000 is metres.

e) Metric machines are recommended for all future acquisitions.

REFERENCES

1. ASEE Joint Regional Conference Proceedings, Sinclair Community

College; Dayton, OH; Oct. 10-12, 1985; pp. 341-343.

2. ASTM Std. E23, Mechanical Impact Testing.

3. Guy, A. G. , "Elements of Physical Metallurgy, 2""^ ed. , Addison-Wesley

,

Reading, MA, p. 339.

4. Marks, L. S., "Standard Handbook for Mechanical Engineers," 8*-^ ed.

(T. Baumeister et al.), McGraw-Hill, N.Y. , 1982, p. 3-24.

5. Van Vlack, L. H. , "A Textbook of Materials Technology," AddisonWesley, Reading, MA, 1973, pp. 16-17.

173

ADAPTING ARCHIMEDES' METHOD FOR DETERMINING DENSITIES

AND POROSITIES OF SMALL CERAMIC SAMPLES

Gail W. Jordan

Hocking Technical College

Key words: Archimedes' Method, bulk density, apparent

density, porosity

ABSTRACT

Nearly all materials contain at least two phases: solids and

pores. Many standard methods for determining densities and

porosities, especially for a variety of ceramic products,

employ various adaptations of Archimedes' Method. This

presentation demonstrates how the method can be extended

using an analytical balance and several precautions to

accurately determine physical properties of samples smaller

than one gram.

INTRODUCTION

Literally hundreds of specific test methods exist for

determining various densities of materials. Among those

standardized by the American Society for Testing and

Materials (ASTM), well over a dozen tests ( ref . 1) employ

Archimedes' Method directly to determine at least some of the

several properties of materials that can be calculated using

this simple technique. Many other tests for determining

densities (such as hydrometer, pycnometer, and porosimeter

methods) also use the principle of fluid displacement,

although not in the manner described here.

The method is sometimes used for cemented carbides, high

modulus fibers, electronic wire, asphalt, plastics,

bituminous coal, and even peat. However, the most common and

the most detailed uses occur for ceramic and related

products (refs. 2-4). Typical ASTM tests include:

C 20 Burned refractory brick, by boiling water

C 373 Ceramic whitewares

C 725 Semidense mineral fiber siding

C 830 Burned refractory brick, by vacuum pressure

C 914 Solid refractories, by wax immersion

C 948 Glass-fiber reinforced concrete

C 1039 Graphite electrodes

175
These tests, as written, all require relatively large

specimens with masses of at least 100 g to assure significant

results using balances with accuracies of no better than

0.01 g.

PREREQUISITES

A rudimentary understanding of the types of volumes,

densities, and porosities is required (refs. 5, 6). In

addition, the ability to determine masses using an analytical

balance is presumed.

OBJECTIVE

The purpose of this experiment is to demonstrate how

Archimedes' Method and an analytical balance can be used to

determine the mass bulk density and several other related

physical properties of a small (approximately 1 g) ceramic

specimen

.

EQUIPMENT AND SUPPLIES

In addition to basic laboratory supplies such as tweezers and

tissues, the following are required:

Analytical balance, mechanical, accurate to 0.0001 g

Bell jar (or vacuum type desiccator)

Vacuum pump

Thermometer, for room temperature

Copper or other non-corroding wire, 0.40 mm gauge or less

Jar or beaker, approximately 9 cm diameter x 9 cm high

(Small peanut butter jar works well!)

Di sti 1 1 ed water

3-legged stand

The 3-legged stand, which is used to hold the jar above and

away from the balance pan, can be constructed of any

materials on hand but needs to have: 1) a base approximately

8 cm X 14 cm, and 2) legs approximately 30 mm long.

PROCEDURE

1. Tare analytical balance. Then measure dry weight, , to

the nearest 0.0001 g; record.

2. Place specimen in its support in the jar and fill to

within approximately 1 cm of full with distilled water.

176
3. Place jar of water containing specimen inside of bell

jar

.

4. Connect vacuum pump to bell jar. (It is desirable to

place a trap in the line to prevent contaminating the

vacuum pump oil.)

5. Turn on vacuum pump for at least fifteen (15) minutes so

that the water boils, and water enters all open pores

within the specimen.

6. Remove the jar containing the specimen, and allow the

temperature to approach equilibrium. Record the

temperature

.

7. Place the 3-legged stand over the pan of the balance,

making sure it does not contact the pan. Then tare the

bal ance

.

8. Place the jar containing the specimen and its support on

the 3-legged stand.

9. Hang the support wire over the second hook below where

the pan bail is connected.

10. Measure the gross saturated suspended weight of the

specimen plus its support, W^^ ^, to the nearest

0.0001 g; record.

11. Use tweezers to dislodge the specimen from its support,

and either transfer it from the jar to another container

of water at the same temperature or allow it to fall to

the bottom of the jar.

12. Measure the tare weight of the support, Wgg ^ while

suspended; record.

13. Remove the jar and 3-legged stand from the balance, and

tare the balance again.

14. Daub surface of specimen with a wet tissue or cloth to

remove any droplets of water on the surface. Then

promptly measure the saturated weight, Wg ; record.

15. Measure the temperature of the water in. the jar. If

this has changed more than 0.2°C, then repeat steps

7-14. Otherwise, determine the water density, d^^ , corresponding to the average water temperature during

the determinations of the various saturated weights.

177
16. Calculate the bulk volume, bulk density, apparent

volume, apparent density, apparent porosity, and water

absorption using the equations provided.

SAMPLE DATA AND RESULTS

For a specimen of aluminum oxide, which had been sintered at

1667°C for ten (10) hours, the following were measured:

Dry wei ght , g 3.1127

Gross saturated suspended weight, g 2.7182

Tare weight, g 0.3869

Saturated weight, g 3.5281

Physical properties calculated from the above include:

Bulk volume, cm^ 1.197

Bulk density, g/cm^ 2.601

Apparent volume, cm^ 0.7814

Apparent density, g/cm^ 3.983

% apparent porosity 34.71

% water absorption 13.35

Although not part of the scope of this experiment, it can

further be shown that for a theoretical density of aluminum

oxide equal to 3.98 g/cm^ , other properties are:

% closed porosity 0.00

% total porosity 34.7

% apparent theoretical density 100.0

% theoretical density 65.3

INSTRUCTOR NOTES

Densi t y and Porosity Relationships

Archimedes' Method permits several physical properties

relating absorption, densities, and porosities of a specimen

to be calculated from just three weight measurements: dry

weight, saturated weight, and the net saturated suspended

wei ght

.

The table on the following page shows six (6) of the commonly

calculated properties using different notations.

178
ASTM Subscr i pted

Bulk volume V = M - S = - W^^ D —S ; S S

Bulk density B = D = D_ d^ = = Wp_x__dL

V M - S V, W3 - W33

Apparent volume = ~ (Impervious material) = D - S d^

Apparent density T = D = = x d

^ a D S S

Apparent porosity P = M - D = - W^^ x 100

s s s Water absorption A = M - D %A = W.._ - W, x 100 —w s —: D

where: M = = Saturated weight

S = Wgg = Saturated suspended weight

= Gross weight W„_ _ - Tare weight W-_ _ D = W = Dry weight

d|_ = Density of saturating liquid

= Water saturated weight

D S

M D

V

M D

D

Note that for the first four (4) ASTM relations the units do

not seem to be consistent. This is because the saturating

liquid is assumed to be water with a density of unity. For

other saturating liquids (such as for example when kerosene

is used for water soluble refractories), the complete

subscripted equations containing the liquid density factor

must be used.

For an excellent discussion of these and other related

properties, see Reference 6. This clearly explains the

differences between open (or apparent or i ntergranul ar ) and

closed (or intragranular) porosities. It also clarifies the

distinctions among bulk, apparent, and true densities.

Sources of Error

Primary causes of erroneous results include inadequate

attention to the following precautions:

1. Allow at least the minimum time (15 minutes) for the

"boiling in vacuum" absorption step so that the

specimen absorbs water (or other immersion liquid)

into as many of its open pores as possible.

179
2. Allow the water and specimens sufficient time to

approach a temperature equilibrium following the

absorption step — usually at least twenty (20)

mi nutes

.

3. Be sure to tare the balance, after placing the stand

over the pan, before determining the gross saturated

suspended weight and the tare weight of the support.

4. Do not take any more time than necessary to measure

the saturated weight; otherwise, some water from the

open pores may migrate to the surface and evaporate.

5. Take care that no water droplets fall onto the

balance pan. Also be sure that no water droplets

cling to the support wire loop.

6. If a basket is tied to the support wire, make sure

that only a single wire breaks the surface of the

water

.

7. Check that no air bubbles adhere to the specimens or

support. This is often the case if a mesh basket is

used. Light tapping will suffice to release these to

the surface.

Vari ati ons

This basic technique can be used for a variety of experiments

such as:

1. Compare the results obtained for a small piece of

refractory brick with those obtained using ASTM test

method C 20 on a half brick.

2. Determine gradient in density and porosity properties

between center and outside of a fired ceramic

arti cl e

.

3. Analyze errors and significant figures of results.

For example, what error is introduced if the

immersion density is assumed to be unity and the

effect of ambient temperature is neglected?

(Obviously, the calculations need not be done

manually, and the data can provide practice for

writing dedicated computer or spreadsheet macro

programs. In particular, the dependence of water

density upon temperature provides an excellent

exercise for fitting an empirical equation for use in

such programs .

)

180
4. For refractory specimens that slake, hydrate, or are

soluble in water, compare the results obtained by

using another liquid (such as kerosene) with the

results using ASTM test method C 914, which involves

coating the specimen with paraffin.

5. Compare the results with those obtained by using

geometric, pycnometric, sink-float, or other

determi nations

.

6. If the solid material is single phase (or ideally

so), then determine the theoretical density from

X-ray diffraction or other sources, and calculate the

percent theoretical density and the percent closed

porosi ty

.

REFERENCES

American Society for Testing and Materials. 1984.

Annual Book of ASTM Standards (Vol. 00.01 Subject Index;

Alphanumeric List). ASTM, Easton, Maryland. 724 pp.

American Society for Testing and Materials. 1990.

Annual Book of ASTM Standards (Vol. 4.05

Chemi cal -Resi stant Materials; Vitrified Clay, Concrete,

Fiber-Cement Products; Mortars; Masonry). ASTM, Easton,

Maryland. 810 pp.

American Society for Testing and Materials. 1987.

Annual Book of ASTM Standards (Vol. 15.01 Refractories;

Carbon and Graphite Products; Activated Carbon). ASTM,

Easton, Maryland. 570 pp.

American Society for Testing and Materials. 1987.

Annual Book of ASTM Standards (Vol. 15.02 Glass; Ceramic

Whitewares). ASTM, Easton, Maryland. 514 pp.

Richerson, D. W. 1982. Modern Ceramic Engineering.

Marcel Dekker, Inc., New York. 399 pp.

Jones, J. T., and M. F. Berard. 1972. Ceramics:

Industrial Processing and Testing. Iowa State University

Press, Ames, Iowa. 213 pp.

181

EFFECT OF HEAT TREATMENT ON MAGNETIC

PROPERTIES OF A METAL ALLOY

Wenchiang R. Chung and Margery L. Morse

Division of Technology

San Jose State University

ABSTRACT

An experiment is proposed using a non-destructive test method, Gaussmeter, to

observe the effects of heat treatment on the magnetic flux inductance of a soft magnetic

material. The material chosen for this exercise is a nickel alloy steel known as Alloy 48.

The chemical composition of this alloy is; 48% nickel, 0.25% manganese, 0.02% carbon,

0.001% sulfur, and 51.73% iron.

In this study, the Alloy 48 will be heat treated in an oven for four hours at 927°C.

Test samples wiU then be air cooled in the lab environment at ten minute intervals. Time

factor of heating is the test variable. Finally these heat treated samples will be magnetized

using a neodymium-iron hard magnet. The magnetic flux density or induction will be

measured using a Gaussmeter.

The results of this experiment could be used to help material technologists and

engineers determine heat treatment time factor needed for optimum permeability of a metal

alloy such as Alloy 48.

INTRODUCTION

Ferromagnetic materials are generally classified into two distinct groups, soft and

hard magnets. Soft magnets are the metals can be easily magnetized and demagnetized.

However, hard magnetic materials maintain a net magnetization after a magnetization

process. When a soft magnet is placed near a hard magnet, there will be attraction between

the two. The soft magnet will then become magnetized due to the induction of the magnetic

flux from the hard magnet. When the two magnets are separated, the soft magnet will

retum to its original unmagnetized state.

Permeability, is the ratio of magnetic flux induction and magnetizing force, or the ease at which a material will set up a magnetic field. The gaussmeter is an instrument that

measures the magnetic induction using the unit "Gauss" of the CGS system.

Alloy 48 is a nickel base metal alloy, designed for high permeability, high field

strength, and low core losses. It finds excellent applications in many industries such as instrument transformers, electronics relays, communication equipment devices and

magnetic shieldings. This experiment is designed to observe the effects of heat treatment

on the inductance of a soft magnetic material. Alloy 48. On the other hand, a hard magnetic

material, known as Neodymium-Iron alloy, is used as a magnetising force to induce

magnetic flux in the soft magnet. After heat treatment, both soft and hard magnets will be

examined using a Gaussmeter to see how would heating hours affect the future

magnetization process. The results of this experiment could be used in industry to indicate

the appropriate heat treatment time factor needed for optimum permeability of the material

,

Alloy 48.

183
EXPERIMENTAL PROCEDURE

Heat Treatment

Eleven metal samples were cut from a hot-rolled 0.25 inch thick Alloy 48 sheet

stock. After referring to ASTM standards and taking into account of the size of the

available furnace in Ae laboratory, the metal samples were further cut into 4.0 inch by 1.5

inch strips. The samples were then deburred, stamped with numbers 0-10. Sample 0 was

left untreated for comparison. According to the recommendation of materials supplier,

samples 1-10 were normalized in the furnace for 4+ hours at 927°C (1700°F). At four

hours the samples were taken out one by one, at ten minute intervals, so that they would

have varying time factors of heating. All heat-treated samples were allowed to have

sufficient air cooling. The attached oxidation was gently sanded off, and the samples were

further cleaned with rubbing alcohol (isopropyl alcohol). Six 0.75 inch square by 0.375

inch thick neodymium magnets were selected to be used as the magnetizers.

Magnetic Measurements

The gaussmeter Model 615 manufactured by F. W. Bell was employed to take

readings at specific locations on the surfaces of the Alloy 48 samples. It was decided to

use sample numbers 1, 3, 5, 7, and 9, in the test so that the intervals of heat treating would

be twenty minutes. The gaussmeter was calibrated to zero, then readings were taken off of

the six neodymium-iron magnetizers to characterize them. Readings were recorded at 0.25

inch intervals using an axial probe and a template to determine accurate locations (Figure

1). The soft magnets (Alloy 48 samples) were then characterized and the readings were

found to be zero. The magnetizers were then placed on top of the six heat treated Alloy 48

samples, directly in the center of the large surface. The magnets were then left to sit for

one hour so that the soft magnets hopefully could become magnetized. Magnetic

measurements were conducted using the probe at twelve points along the perimeter of the

soft magnets on both sides (see Figure 2). Hysteresis loops are plotted in Figure 3.

Figure 1. Points Locations Across Figure 2. Positions of Hard Magnet on

Hard Magnet Soft Magnet

184
RESULTS

Figure 3. Hysteresis Loops for Samples 0, 1, 3, 5, 7 and 9.

185
DISCUSSION

From analyzing the magnetic induction readings taken off the smaller hard magnet

alone, and the readings from when the hard magnet is situated on the soft magnet, it can be

determined that the magnetic induction across the hard magnet increased quite consistently

at corresponding points. The enhanced magnetic induction could be due to the sum of the

magnetic flux density of hard magnet itself and the external magnetic flux density of the

magnetized bar (soft magnet). It is also evident that there is no clear pattern between the

heat treated samples themselves, or in comparison to the untreated sample (Group 0). In

general, the readings lowered as the probe got closer to the center line, where the polarity

transformation occurs. Group 5 sample after being heated for five hours was found to

have lowest readings along the perimeter of the hard magnet.

Plots shown in Figure 3 reveal that there is a significant increase in the magnetic

induction over its control counterpart (Group 0). The best group in this experiment was

Group 1, which had been heat treated for four hours and air cooled. Sample 5 has least

amount of energy loss during the magnetization process. When samples were cooked too

long in an oven, they seemed difficult to be magnetized.

CONCLUSION

It is found in this study that normalizing of the AUoy 48 material can increase a

material's permeability during a magnetization process. The optimum condition was found

in the sample one which had been heat treated for four hours and then immediately air

cooled, if the core loss is not considered. Sample 5 has the least amount of core loss.

Other groups of samples generally have lower permeabilities and higher core losses

because of longer heating times. This experiment is found not a great determiner of the

variance of magnetization with heat treatment. Because it is difficult to see any changes

corresponding to the time/heat treatment factor. A systematic approach employing

annealing and quenching techniques and different heat treatment parameters can be utilized

to help understand the relationship between magnetization and heat treatment work.

REFERENCES

1. ASTM, "Direct Current Magnetic Measurements for Soft Magnetic Materials", (1970),

ASTM, Maryland, pp. 1-18.

2. ASTM, "Metals Test Methods and Analytical Procedures-- Magnetic Properties",

(1989), Vol. 3.04, ASTM, Philadelphia, Designations A 340-87, 34-83, & 753-85.

3. Schure, A., "Advanced Magnetism and Electromagnetism", (1959), John F. Rider

Publisher, New York, pp. 1-20.

186
ASTM

THE DEVELOPMENT

AND APPLICATION

OF STANDARDS

Presented by:

Drew 0. Azzara

Director, Technical Committee Support

187
STANDARDS

Nucleus of Sound Industrial and

Commercial Practice

promote understanding

advance technology

open trade channels

ensure quality

ensure safety

188
Knowledge of Standards

and

Standards Development

Organizations

critical to career success in any

technical field

faculty members and students

should be aware of, and

participate in, standards

activities

standards should form a part of

course curricula

189
More than 400 Standards-Writing

Organizations in U.S. Alone

ASTIVI:

One of the Oldest and Largest

in the World

190
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founded in 1898

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approximately 85% of inconne

from sales of publications
I

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producers users

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134 Main Technical Committees

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Technical Committees, continued

the environment

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and many other areas
What is a Standard?

As used in ASTIVI, a standard is a

document tliat lias been

developed and established within

the consensus principles of the

Society and that meets the

approval requirements of ASTM

procedures and regulations.

195
ASTM Develops Voluntary Full

Consensus Standards for:

materials products

systems services

196
Voluntary Standards

developed voluntarily

used voluntarily

Legally Binding Only When:

a government body nnandates

their use

cited in a contract

197
Full Consensus Standards

Standards developed through the

cooperation of all parties who

have an interest in participating in

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the standards.

198
ASTM develops full consensus

standards with the belief that input

from all concerned parties in the

development of a standard will

ensure technically competent

standards having the highest

credibility when critically examined

and used as the basis for

commercial, legal, or regulatory

actions.

199
Six Types of Standards

standard test method: a

definitive procedure for the

identification, measurement,

and evaluation of one or more

qualities, characteristics, or

properties of a material,

product, system, or service that

produces a test result.

200
standard specification: a

precise statement of a set of

requirements to be satisfied by

a material, product, system, or

service tliat also indicates the

procedures for determining

whetlier each of the

requirements is satisfied.

201
standard practice: a definitive

procedure for performing one or

more specific operations or

functions that does not produce

a test result.

202
standard terminology: a

document comprising of terms,

definitions, descriptions of

terms, explanations of symbols,

abbreviations or acronyms.

203
standard guide: a series of

options or instructions that do

not recommend a specific

course of action.

204
standard classification: a

systematic arrangement of

division of materials, products,

systems, or services into groups

based on similar characteristics

such as origin, composition,

properties, or use.

205
More than 8,000 standards are

published each year in the 68-

volume Annual Book of ASTM

Standards.

206
Credibility of ASTM Standards

voluntary, full-consensus

approach which brings together

people with a diversity of

backgrounds, expertise, and

knowledge

balanced representation of

interests at the standardswriting table

intense round-robin testing to

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207
Credibility of ASTM Standards,

continued

strict balloting and due process

procedures to guarantee

accurate, up-to-date information

an atmosphere that promotes

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208
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work begins when need is

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draft standard prepared

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negative votes cast at any level

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209
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final approval given by

Comnnittee on Standards, who

make sure proper procedures

were followed

standard published

reviewed every few years to

ensure timeliness of information

210
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for Non-Proprietary Input

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211
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Standards-Writing Process

through committee meetings

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212
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participate in discussions

relating to latest research and

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213
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proceedings often published

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214
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216
Benefits of Participating

in ASTIVI Activities

professional growth

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information

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papers
Benefits, continued

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benefits industry through ensuring

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communication. The development

of standards benefits the

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the reasons given above.

Academia is in a unique position

to aid in the standards

development process, and to

benefit from that participation.

219
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ASTM Headquarters

ASTM, 1916 Race Street, Philadelphia, PA 19103-1187, 215/299-5400

220
DETERMINING THE IMPACT OF ADJUSTING TEMPERATURE PROFILES

ON PHOTODEGRADABILITY OF LDPE/STARCH BLOWN FILM

Jerry L. Wickman Ph.D.

Scott M. Corbin

Ball State University

Muncie, Indiana

ABSTRACT

The major objective of this study was to develop a test

procedure to determine the impact of modifying temperature

profiles of extruded blown film on photodegradability

characteristics of a low density polyethylene (LDPE)/15 percent

starch blend.

Four sequential temperature adjustments, each of 2 percent

from the manufacturers recommended processing temperature for

polyethylene were used. Three barrel temperatures and two die

temperatures were adjusted accordingly throughout the test. The

blown film bubble and final film gage were stabilized previous to

the study to minimize any influences beyond typical processing

control

.

Three levels of lighting were used to determine the impact

of light on LDPE/starch film. The three conditions were as

follows: 1) control specimens were kept in total darkness, 2)

typical four foot office fluorescent lights with acrylic

diffusers were used to represent an average office environment,

and 3) an accelerated weathering unit was used to represent the

more intensive ultraviolet (UV) lighting conditions. Six samples

per processing temperature setting, per week, per environment

were prepared anticipating tensile tests relative to machine

direction of the blown film. Sample preparation and testing

procedures followed ASTM as close as practically possible. Total

time of exposure in all environments was limited to six weeks

with testing of 90 selected specimens weekly. This required a

minimum of 540 test specimens to be processed, documented,

handled, tested, and evaluated.

The test procedure provided information relative to the UV

light sensitivity of an LDPE/starch blend over a variety of light

conditions and processing temperatures sensitivity and

photodegradability characteristics. The study has the potential

to provide information for the processing characteristics of

temperature controllers relative to quality control.

221
INTRODUCTION

The development of the following test procedure, to

determine the impact of modifying temperature profiles of

photodegradable extruded blown film evolved as a result of

various discussions centered around plastics packaging and the

environment. Blown film was used as the processing method for

several reasons:

* the material was thin enough to show changes in tensile

test results in one 15 week semester

* the process could be stabilized and controlled

* large numbers of samples could be produced in a short . period of time

* test equipment was readily available

* storage, handling, and testing specimens presented the

fewest problems using blown film

* the film produced from LDPE represented the typical

packaging material.

Instead of the traditional processing and testing, the

environmental/photodegradability issue causes one to view the

dilemma from a systems approach. It forces students involved

with plastics manufacturing to consider the inevitable, to design

a product that is, in the long run, a greater part of the

solution to the environmental problem.

The exact amount of plastic that goes into Americas'

sanitary landfills is unknown but estimates vary from a low of 4

percent to a high of 35 percent by weight. Plastics are as

pervasive in landfills as they are in our daily lives. Any

material which is destined for a landfill should be either

photodegradable (light sensitive) or biodegradable (microorganism

sensitive) . Regardless of the environmental attitudes (pro or

con) on the part of the student we wanted to develop a test

procedure that caused the participants to think more

analytically.

When considering the equipment available, we had to

acknowledge what test procedures could be developed to adequately

evaluate the photodegradability of an LDPE/starch blend?

Equipment eventually selected consisted of:

* Davis Standard 1.250" extruder with blown film die and

tower

* Instron universal test center (model 1011)

* Q panel for accelerated exposure

Additional materials necessary to insure repeatability

consisted of various ASTM standards, sampling procedures,

statistical process control tools, and assorted handheld

measuring instruments

.

I

222
Material used throughout the test was an 85 percent blend by

weight of Dow polyethylene 533 low density film extrusion resin

and 15 percent by weight of Archer Danials Midland's (ADM)

Polyclean 012-400, general purpose starch based additive. The

additive is formulated such that it can be either extruded or

injection molded.

The major objective of this study was to develop a test

procedure to determine the impact of modifying temperature

profiles of extruded blown film on photodegradability

characteristics of an LDPE/15 percent starch blend. The film was

produced using five sets of processing parameters. Each

parameter set had an increase or decrease in the temperature

profile and screw speed in increments of 2 percent from the

manufacturers recommended settings. Three levels of lighting

were used to determine the impact of light on biodegradable film.

The three lighting conditions were as follows: 1) control

specimens kept in total darkness, 2) normal four foot fluorescent

tubes, and 3) an accelerated weathering unit. Six samples per

processing temperature setting, per week, per environment were

prepared anticipating tensile tests relative to the machine

direction of the blown film (Table 1)

.

PROCESSING MATERIAL PREPARATION

The resin and additive obtained both represented typical

materials as used in the production arena. The LDPE extrusion

film resin 533 was obtained from DOW Chemical company. The

following represents a brief listing of processing conditions,

and select physical and mechanical properties of resin 533

(Table 2)

.

It was assumed that the values from Table 2 represented

averages drawn from a normal distribution. Melt temperatures,

blow-up ratio and optimum gauge range were used to represent the

standard from which all tests were run.

The additive obtained from Archer Danials Midland's (ADM)

was Polyclean 012-400. It was recommended by representatives at

ADM that a 15 percent by weight blend of this material added to

the LDPE would represent the typical blends as used in industry.

7.5 lbs. of Polyclean were added to 50 lbs. of LDPE in a clean 55

gallon barrel and sealed. Care was taken to minimize exposure to

any form of light. The drum was rotated slowly (1 revolution

every 2 seconds) to thoroughly blend the LDPE and Polyclean. ASTM

D1898, Standard Practice for Sampling of Plastics was used to

insure the blend was homogeneous. If the blend was not

homogeneous, processing time and temperature would vary

excessively, material in contact with the screw and barrel walls

would not be uniform, gauge thickness would not be consistent and

the photodegradability results would be inconsistent.

223
MATERIAL PROCESSING

The LDPE/Polyclean blend was processed in a Davis Standard

1.250" (DSR-125) extruder with a Barber-Colman control system and

a Maco 8000 processor. The air ring, side fed die, cooling ladder

and mandrel were built from various industrial designs. The air

ring has eight equally spaced air ports for greater control when

producing the blown bubble. The ladder was leveled and centered

with the die before each production run. A LDPE curtain was

placed around the cooling ladder because of the adverse affects

of air from not only the air conditioning system but also

personnel in the area. Final layflat width was kept as close as

possible to 5" while film thickness varied from 0.0021" to

0.0024". ASTM D1248, Standard Specification for Polyethylene

Plastic Molding and Extrusion Materials was adhered to as close

as practically possible for an educational environment.

The film was produced using the following five sets of

processing parameters (Tables 3-7) . Each processing parameter

had an increase or decrease in the temperature profile and screw

speed in increments of 2 percent from the manufacturers

recommended settings. Through previous experiments it was

determined that a 2 percent adjustment was adequate to produce

results desired for this experiment.

TESTING MATERIAL PREPARATION

Subsequent to the processing of each of the five rolls of

blown film, samples were kept in darkened environments. As

needed each set of samples were prepared following ASTM 882,

Standard Test Methods for Tensile Properties of Thin Plastic

Sheeting using parallel knives designed specifically for thin

film sample preparation. The parallel knives provided specimens

with a uniform width of 1.0", care was taken to remove any

samples with notched or upset edges. Folded seams created at the

cooling ladder were avoided when cutting specimens, all specimens

were cut from the center portion of either the front or back of

the layflat. The width of each specimen should be no less than

0.02" and no greater than 1.0". The overall length of each

specimen was 6.5".

Each sample was then labeled with an alpha-numeric code for

identification. Table 8 represents the labeling procedure used.

ACCELERATED UV UNIT

ASTM G 53-84, Standard Practice for Operating Light- and

Water-Exposure Apparatus (Fluorescent UV-Condensation Type) for

Exposure of Nonmetallic Materials was referenced for use with the

Q-panel. The Q-panel is not intended to simulate the

deterioration caused by localized weather phenomena, such as

atmospheric pollution, biological attack, and water exposure.

Rather, it is intended to simulate the deterioration caused by

water as rain or dew and the ultraviolet (UV) energy of the sun.

224
The apparatus consists of: A test chamber made of corrosive

resistant material with a heated water pan and fluorescent UV

lamps, specimen racks, and provisions for controlling and

indicating operating times and temperatures. The lamps are rapid

start, medium bipin fluorescent UV lamp with a nominal rating of

40 Watts when in operation. Lamps used were UV-A 340 which

produces wavelengths in the 315 to 400 nanometers range. UV-A

340 represents sunlight not filtered through glass. The UV-A

causes slower degradation than the UV-B. UV-B lamps will produce

wavelengths in the 280 to 315 nanometers range. The eight lamps

were rotated every four-hundred hours as per manufacturers

recommendations. Samples in the Q Panel were exposed to lighted

conditions and condensation 12 hours per day for the duration of

the study. A condensation mechanism produced water vapor

generated by heating the water pan located under the entire

specimen area. The water supply in the water pan was regulated

with an automatic controller to provide a constant water level.

Specimens were mounted and secured with surgical tape. Surgical

tape was used because it provided the best method of securing the

samples when exposed to the UV light and water condensation.

NORMAL FLUORESCENT LIGHTING UNIT

The fixture was designed to secure samples to be placed in a

typical fluorescent lighted environment. The fixture was a wood

frame, 8.5" X 43.5", secured to a piece of hardboard of the same

size. The center section, 4.5" X 40.25" was removed with 30

wooden clothespins secured every 1.5" along the length of each

side. Each fixture secured 30 samples between the clothespins.

Six of these fixtures were required to provide the 180 test

samples. Each unit was hung directly beneath normal fluorescent

40 Watt light fixtures at a distance of 12". A constant

temperature of 72 was maintained while the relative humidity

was a constant 45 percent. Samples were exposed to lighted

conditions for an average of 70 hours per week for the duration

of the study.

CONTROL

A set (180) of control samples were kept in a darkened

environment at 72 °F while the relative humidity was 45 percent.

A total of 180 control samples were prepared such that each week

at each processing setting the exposed samples could be compared

to an equal number of control samples.

MATERIAL TESTING

An Instron Model 1011 was used in conjunction with ASTM 882

and the testing of the thin film. As per ASTM 882 the Instron

provided a device for recording the tensile load and the amount

of separation of the grips. As per ASTM 882 the rate of

separation of the jaws was to be uniform and capable of

adjustment from approximately 0.5 to 2 0.0 inches per minute. The

rate of grip separation used in this test was 12.0 inches/minute.

225
This was the accepted rate of grip separation used in related

industry tests. Data collected consisted of load, load

extension, and load at break. All data was analyzed and plotted

using a PC based statistics package. Numerical analysis

consisted of analysis of variance, hypothesis testing,

regression, and statistical process control procedures.

SUMMARY

Six samples were prepared for each processing parameter per

each week. Averages and standard deviations were calculated for

each set of six samples. The averages were arranged in a matrix

for each of the lighting conditions. The results of each test

consisted of load, load at break and elongation at break. It was

found that for our purposes elongation at break was the most

valuable. The matrices representing elongation at break had a

vertical axis of the five processing parameters while the

horizontal axis was represented by weeks 1 through 6.

This method of data representation allowed for analysis of

within processing parameter variation and differences, between

lighting condition variation and differences through the use of

analysis of variance, linear regression, and statistical process

control methodology.

RECOMMENDATIONS

1. The effect of the natural weather would be valuable to the

study. A roof top fixture integrated with this study is

essential

.

2. A chemical analysis of the film would be beneficial. Any or

all of the following would bring in valuable information.

Infrared Spectroscopy

X-Ray Defraction

UV Spectrophotometry

Gas Chromatography

3. A dedicated compressed air source would eliminate any

variation in air supply to the blown bubble and further

reduce processing variation.

4. Replicate this test using UV-B lamps in the Q-panel.

5. Six weeks as the exposure time using normal fluorescent

lights needs to be extended. Perhaps a separate study

emphasizing this portion could be further developed.

226
REFERENCES

1. Francis, Shelly. The Degradable-Plastics Debate. Plastics

Compounding. Volume 12, No. 7, 1989.

2. Standard Practice for Sampling of Plastics. ASTM

Designation: D1898-68. Volume 08.02 of 1986 Annual Book of

ASTM Standards, 1986, pp. 197-209.

3. Standard Specification for Polyethylene Plastics Molding and

Extrusion Materials. ASTM Designation: D1248-84. Volume

08.01 of 1986 Annual Book of ASTM Standards, 1986, pp. 584-

593.

4. Standard Test Methods for Tensile Properties of Thin Plastic

Sheeting. ASTM Designation: D882-83. Volume 08.01 of 1986

Annual Book of ASTM Standards, 1986, pp. 454-465.

5. Standard Practice for Operating Light- and Water-Exposure

Apparatus (Fluorescent UV-Condensation Type) for Exposure of

Nonmetallic Materials. ASTM Designation: G53-84. Volume

14.02 of 1984 Annual Book of ASTM Standards, 1984, pp. 948-

953.

227
WEEK NUMBER 1 2 3 4 5 6

Q-PANEL 30 30 30 30 30 30

TOTAL

DARKNESS

30 30 30 30 30 30

OFFICE LIGHT 30 30 30 30 30 30

TABLE 1. -QUANTITY OF SAMPLES REQUIRED PER WEEK/ENVIRONMENT

228
Melt IndexDensity , Outstanding Properties Fabrication CcxidititMis Coefficient •Excellent Processability Tubular Film Extrusion of Friction..., •Excellent Drawdown Melt Temperature .... 370'F/188°C Slip Additive

•Good Toughness Blow-up Ratio 2.25:1 Antiblock

•Good Optical Properties Optimum Gauge Range 0.8-2.0 mils Additive

Physical Properties' ASTM Method Value

Melt Index, gms/10 min D 1238 2.0

Density, gms/cc D 7922 .922

Vicat Softening Point, 'Y/'C D 1525 207/97

Tensile Yieldf, psi D 638 1625

Ultimate Tensilet, psi D 638 1375

Ultimate Elongationt, % D 638 630

Tensile Modulusf, 2% secant, psi D 638 34,000

Film Properties 1.5 mfl

Dart Impact, gms D 1709 130

Elmendorf Tear Strength, gms

Machine Direction D 1922 85

Cross Direction D 1922 175

Tensile Yield, psi

D 882 1475

Cross Direction D 882 1440

Ultimate Tensile, psi

Machine Direction D 882 2930

Cross Direction D 882 2725

Ultimate Elongation, %

Machine Direction D 882 470

Cross Direction D 882 585

Transparency, % D 1746 37

Gloss, 45 • D 2457 66

Haze, %...... D 1003 6.5

Heat Seal Range, -F 250-350

fCompression molded samples

^These typical property values are intended as guides only, and not as specification limits. ^Method B Dow modification.

TABLE 2.-DOW POLYETHYLENE RESIN 533

2.0 .922

0.20

Med

Low

229
RUN ONE

BARREL 1

288

BARREL 2

336

SCREW SPEED==> 25 RPM

AIR RING PRESSURE==> 43 psi

NIP SPEED==> 20%

WIND SPEED==> 40%

FILM WIDTH==> 5"

BARREL 3

346

DIE 1

356

DIE 2

361

MELT PRESSURE==> 800 psi

AIR RING OPENING==> 2

NIP TORQUE==> 100%

WIND TORQUE==> 85%

FILM THICKNESS==> .0021"

TABLE 3

. -PROCESSING CONDITION AT MANUFACTURERS RECOMMENDED

TEMPERATURE SETTINGS MINUS 4 PERCENT

RUN TWO

BARREL 1

294

BARREL 2

343

SCREW SPEED==> 30 RPM

AIR RING PRESSURE==> 51 psi

NIP SPEED==> 20-

WIND SPEED==> 40^

FILM WIDTH==> 5"

BARREL 3

353

DIE 1

363

DIE 2

368

MELT PRESSURE==> 755 psi

AIR RING OPENING==> 2

NIP TORQUE==> 100%

WIND TORQUE==> 85%

FILM THICKNESS==> .002 3"

TABLE 4. -PROCESSING CONDITIONS AT MANUFACTURERS RECOMMENDED

TEMPERATURE SETTINGS MINUS 2 PERCENT

230
RUN THREE

BARREL 1

300

BARREL 2

350

SCREW SPEED==> 35 RPM

AIR RING PRESSURE==> 62 psi

NIP SPEED==> 20%

WIND SPEED==> 40%

FILM WIDTH==> 5"

BARREL 3

360

DIE 1

370

DIE 2

375

MELT PRESSURE==> 850 psi

AIR RING OPENING==> 2

NIP TORQUE==> 100%

WIND TORQUE==> 85%

FILM THICKNESS==> .0023"

TABLE 5. -PROCESSING CONDITIONS AT MANUFACTURERS

RECOMMENDED TEMPERATURE SETTINGS

RUN FOUR

BARREL 1

306

BARREL 2

357

SCREW SPEED==> 40 RPM

AIR RING PRESSURE==> 74 psi

NIP SPEED==> 3 0%

p

WIND SPEED==> 65%

FILM WIDTH==> 5"

BARREL 3

367

DIE 1

377

DIE 2

383

MELT PRESSURE==> 850 psi

AIR RING OPENING==> 2

NIP TORQUE==> 100%

WIND TORQUE==> 85%

FILM THICKNESS==> .0024"

TABLE 6. -PROCESSING CONDITIONS AT MANUFACTURERS RECOMMENDED

TEMPERATURE SETTINGS PLUS 2 PERCENT

231
RUN FIVE

BARREL 1

312

BARREL 2

364

SCREW SPEED==> 45 RPM

AIR RING PRESSURE==> 78 psi

NIP SPEED==> 3 0%

WIND SPEED==> 65%

FILM WIDTH==> 5"

BARREL 3

374

DIE 1

385

DIE 2

391

MELT PRESSURE==> 850 psi

AIR RING OPENING==> 3.5

NIP TORQUE==> 100%

WIND TORQUE==> 85%

FILM THICKNESS==> .0024"

TABLE 7. -PROCESSING CONDITIONS AT MANUFACTURERS RECOMMENDED

TEMPERATURE SETTINGS PLUS 4 PERCENT

A-216

A - CONTROLLED CONDITION

A - OFFICE LIGHT

B - Q PANEL (Accelerated UV Exposure)

C - TOTAL DARKNESS

2 - WEEK NUMBER

1 - PROCESSING PARAMETER

6 - SAMPLE NUMBER

TABLE 8

. -ALPHA-NUMERIC LABELING PROCEDURE USED

IN PHOTODEGRADABILITY STUDY

232
TITLE: DEMONSTRATION OF A SIMPLE SCREENING STRATEGY

FOR MULTIFACTOR EXPERIMENTS IN ENGINEERING

BY LARRY PANCHULA AND JOHN W. PATTERSON

DEPARTMENT OF MATERIALS SCIENCE AND ENGINEERING

IOWA STATE UNIVERSITY

AMES, lA 50011

INTRODUCTION

One of the more serious problems in engineering today is the widespread use of

poorly designed experiments in engineering investigations. Most of us use the

strategies learned in our college lab courses, but these are often ill-suited

for engineering research. In college labs, as in most basic research, a welldefined theoretical idea is being investigated and this greatly simplifies the

task of data interpretation. We use the data used to obtain best fit values

for the parameters in our favorite theoretical formulas, but rarely consider

how well alternative theories and their formulas might have explained the

data. Usually such alternatives will contain other independent variables and

this could greatly expand the scope of the investigation, not to mention the

level of confusion. Indeed most projects in basic research and college labs

are designed to be narrow in scope for precisely these reasons.

In engineering studies almost none of the above applies. Often there is no

well-defined theory or formula for relating the variables one can control to

1

233
the responses one hopes to influence. In some cases it turns out that none

of the factors that we can control will significantly influence the important

responses in the process of interest. Moreover, we often have to consider a

large number of candidate control variables, at least in the early stages of

the study, and the experimental strategies used in college labs do not teach

one how to efficiently sort the "vital few" controllable variables from the

"trivial many," particularly when no theory or well-defined fitting formula

are available.

Fortunately, some very efficient, statistically-based strategies exist which

can handle these kinds of problems, but engineers are gaining little or no

exposure to them during their college years. This is probably because their

mentors are not well versed in them either. At present, almost all the

engineers using statistically designed methods of experimentation have learned

them after graduating from college and probably at considerable expense to

their employer. We hope this will change soon and that this paper helps speed

the transition.

THE PAPER HELICOPTER EXPERIMENT: ITS FEATURES AND PURPOSE

Described below is an easy to run project called the "paper helicopter

experiment."^ We think it originated with Mr. C. B. "Kip" Rogers, a

consultant quality engineer with Digital Equipment Corp., Maynard MA 01754,

who conceived it as a teaching tool for courses in the design of experiments.

234
We chose it because it is simple, quick, and inexpensive to run and because it

entails many of the bewidering experimental problems encountered in

engineering studies. There is no "pat answer" that can be looked up in a

physics book and, in our version, a total of eight controllable variables are

to be sorted into the vital few as opposed to the trivial many. (Instructors

can easily modify the project, however, so as to either shrink or expand the

number of candidate control factors.) In real life, these control factors may

act alone or in concert with one or more of the others to dramatically affect

the response variable; in such cases we speak of interaction effects.

Interaction effects are investigated after sorting, especially when four or

more control factors are in the offing, so we willleave the treatment of

interactions for another time. Also, only one response variable— the flight

timeupon dropping the helicopter— will be considered here, tough we shall

comment later on how to simultaneously monitor others as well.

The sorting strategy employed here is called a linear screening design. Its

primary purpose is to distinguish the most important control variables from

those which are of such minor importance that studying them any further would

(probably) be a waste of time and effort.

.r

EXPERIMENTAL PROCEDURE

Figure 1 shows a small drawing of a typical helicopter, along with a generic

pattern for making the crafts. Only four of the eight control factors are

235
clearly described in figure 1; namely. Body Width (B), Body Length (L), Wing

Length (W) and Fold (F) . Whereas these all change in value from craft to

craft, the dimensions shown as 3" and 8.5" on Figure 1 are kept the same on

all the crafts. (We chose 3" and 8.5" only because they happen to fit

conveniently on 8.5" x 11" paper. However, other values could certainly be

substituted if desired, or if another size of paper is used. ) In addition, we

also included four other factors as follows: Paper Type (P), Tape on the Body

(T) and Tape on the Wings (M) . Table 1 lists all eight of the design

(control) factors and gives the high and low settings we used for each.

The design matrix of Table 2 lists all sixteen combinations of control

settings used in our version of this experiment. For example, craft #1 is made

with the settings given in row #1 of the design matrix, craft #2 is made with

those of row #2 and so on for all 16. Because we are only doing a linear

screening experiment, each variable has only two settings; one high and one

low, which are designated respectively as +'s and -'s in the table. There is

one helicopter for each trial in the design and we recommend that each team

construct all sixteen and number them accordingly. That way the results of

the various teams can be compared and disussed afterwards.

Figures 2 (A) through (C) can be photocopied as templates to save time.

Together they contain all the unique patterns needed for this experiment;

this is eight in total. One set is fabricated from regular paper and the

other from construction paper, bringing the grand total to sixteen. Each

pattern has two numbers associated with it, one odd and one even. The odd

236
numbered crafts are fashioned from regular paper (-) and the evens from

construction paper (+). So much for the P factor column of Table 2.

The next three columns— B, L and W— should be fairly obvious in that they

only involve cutting and folding to get the appropriate high (+) and low (-)

settings. The last four factors, however, may need a little further

explanation. We added a paper clip at the bottom or foot of the body,

essentially as a means of increasing the weight of the craft. So, a "+" in

the W column means "add a paper clip," whereas a "-" means "no paper clip".

A "+" in the F column means fold the bottom inch of the body upwards and tape

it in place. (We attached a similar piece of tape to each body whether or not

it has been folded to avoid a possible confounding effect between the fold and

weight variables.) A "+" in the Taped Body or the Taped Wing columns simply

means the body or wing was stiffened by covering it with scotch tape.

COLLECTING THE RESPONSE DATA

When all sixteen crafts are in hand, the teams are ready to collect their data.

Again, we recommend labeling the helicopters from 1 - 16 at the outset. They

are then to be dropped (from the same height 1) and timed, but in a randomized

order. Randomization is important for it randomly distributes the noise from

background or uncontrolled factors among the various high and low settings.

This minimizes the possibility that chance noise variations will contribute

systematically to one or more of the main effects. Because the runs were so

237
easy and inexpensive to execute, we dropped each helicopter five times and

used the average of the five flight times as the response value. The best

place to enter each response value is to the immediate right of the

appropriate row in the design matrix of Table 2. (This will be the row whose

number also appears on the helicopter being dropped. ) These entries will form

a column and should be labled "response" or "ave. t" as was done in Table 2.

We suggest distributing photocopies of Table 2, with our response values

blanked out, for use as data recording sheets.

Incidentally, it should now be clear how one can follow any number of responses

simultaneously. Had we wished to also study, say, the variation in flight time

as a second response variable, we could have calculated the standard deviation

for each sample of five drops and entered that value under a second response

column named "S.D. 5 DROPS". It would be located to the immediate right of

the "AVE. 5 DROPS" column of our Table 2. We might also have considered a kind

of signal-to-noise ratio as yet another response variable. To do this, we

would simply add a third response column to receive the ratios— "AVE. 5

DROPS" divided by the "S.D. 5 DROPS" — as could be readily calculated from

entries in the previous two response columns. Clearly any number of other

response variables can be added in a similar fashion, but in our version of

the experiment, we considered only the average flight time so that only one

response column appears in our Table 2

.

238
ANALYSIS OF THE RESPONSE DATA

After all the response values have been entered, there begins the task of

evaluating the effect that each control factor has on the flight time response.

Our detailed calculations are given in Table 3.^ To begin the analysis, pick

any particular control factor, say L, and merely add all the response values

for the high (+) settings— for L this would be eight runs (5 through 8 and 13

through 16) as can be seen from Table 2 — and then divide by the number of

+'s or eight in this case. This gives a kind of "average of the highs".

Subtracting from this the same kind of "average of the lows (-)" gives the

main effect of control factor L on the flight time response. It is the

difference .142 in Table 3.

For the variable P, eight other runs (helicopters) have P set high (+) and

eight with P low {-). Hence to get the overall effect on flight time of

changing P from low to high, we proceed as before: simply add all the

responses with P high and divide by eight, then do the same for all the

helicopters with P low and then subtract the latter average from the former.

For our data, the effect of P on flight time turned out to be the difference

of .011 in Table 3.

When the effects for all the control variables have been calculated in this

fashion, a so-called scree plot (a kind of "Pareto Diagram", actually) is

constructed with the effects plotted in descending order. "Scree" is from a

Scandinavian word meaning "rock slide" or "pebble debris." The "vital few"

239
factors are those located at the upper left, while the "trivial many" show up

as the "scree" points or "debris" at the lower right. The scree plots of

Figure 3 were constructed from effects as calculated in Table 3. In fact the

heights of the solid black bars in Figure 3 are precisely equal to the "diff."

values reported in Table 3, all of which are based on five-run samples. The

other bars in Figure 3 are included only to show that the scree plots didn't

change much when we cut the number of drops per sample back to three, two and

even to one. (None of the data analyses from those additional experiments

have been included here.

)

For us, the most significant control factor by far was the wing length, with

taped body being the next most important. All the other factors are clearly

relegated to the debris or "scree" part of the plot.

CONCLUDING REMARKS

Once the vital few control factors have been identified as outlined above, one

may go on to consider a more detailed study. Does the response exhibit any

nonlinear dependences on the control factos? Are there significant interaction

effects among the most important control variables? We prefer to use ECHIP

a software package of computer-assisted response surface methods-^ — for

handling the various nonlinear and interaction effects that can show up.

Computer assistance is recommended because such analyses require rather

advanced and time consuming algorithms and these, too, are well beyond the

240
intended scope of this paper. However it should be noted that if one were to

attempt to ferret out such effects before reducing the control factors from

eight to our vital two, the number of trials (helicopters or flights in this

case) could prove too much even for the most sophisticated software packages.

One final point. Had the effort and expense of gathering all the flight time

data been beyond our research budget, we might have considered using fewer

flights for each helicopter. After all. Figure 2 shows that cutting back the

number of flights, at least in this experiment, would not have changed the

conclusions we reached as to which control factors are the most important.

However, there are penalties to be paid for doing this. For example, one could

totally undermine certain tests of statistical significance that statisticians

consider to be very important. Such significance tests, however, are also

beyond the intended scope of this paper.

241
REFERENCES

1. Rogers, C. B., "Design of Experiments", Trans. Amer. Soc» Quality Control

Congress of 1986 in Anaheim, CA

2. Box, G. E. P., Hunter, W. G. and Hunter, J. S.; Statistics for Experimenters .

1978, John Wiley & Sons, Inc. (especially Pp 309-313 and 322-324)

3. Wheeler, R. , ECHIP SOFTWARE fAND TEXT) . 1989, ECHIP, Inc., 7640 Lancaster

Pike, Suite 6, Hockessin, DE 19707. (302) 239-5429.

242
TABLE 1. EIGHT CONTROL FACTORS WHOSE EFFECTS ARE TO BE STUDIED

Variable Low setting (-) High Setting (+)

8

Paper (P) Regular

Body Width (B) 1"

Body Length (L) 1.5"

Wing Length (W)

Paper Clip (C)

Fold (F)

Taped Body (T)

Taped Wing (M)

2"

no

no

no

no

Construction

1.5"

3"

4"

yes

yes

yes

yes

243
TABLE 2. THE RESPONSE VALUES AND DESIGN MATRIX OF SIXTEEN

UNIQUE COMBINATIONS OF THE CONTROL FACTOR SETTINGS — ONE FOR EACH HELICOPTER USED —

RESPONSE

Number PBLWCFTM AVE. 5 DROPS

1 ________ 1.474

2 + ___- + + + 1.102

3 _ + __ + _ + + 1.084

4 + + -- + + -- 1.260

5 - - + - + + + - 0.928

6 + - + - + -- + 1.232

7 - + + -- + -+ 1.310

8 + + + -- - + - 1.306

9 - -- + + + -+ 2.078

10 + -- + + - + - 1.808

11 _ + _ + _ + + _ 2.006

12 + + - + -- -+ 2.122

13 __ + + __ + + 1.530

14 + - + + - + -- 1.988

15 - + + + + -- - 2.000

16 + + + + + + + + 1.502

244
TABLE 3. TABULATION OF HIGH VS. LOW SETTINGS

P HIGH = {2+4+6+8+10+12+14+16)/8

( 1.102+1. 260+1. 232+1. 306+1. 808+2. 122+1. 988+1. 502 )/8=l. 540

P LOW =(l+3+5+7+9+ll+13+15)/8 DIFF = .011

( 1.474+1. 084+0. 928+1. 310+2. 078+2. 006+1. 530+2. 000 )/8=l. 551

B HIGH = (3+4+7+8+11+12+15+16) /8

( 1 . 084+1 . 260+1 . 310+1 . 306+2 . 006+2 . 122+2 . 000+1 . 502 ) /8=1 . 574

B LOW = (l+2+5+6+9+10+13+14)/8 DIFF = .056

( 1.474+1. 102+0. 928+1. 232+2. 078+1. 808+1. 530+1. 988 )/8=l. 518

L HIGH = (5+6+7+8+13+14+15+16) /8

( 0.928+1. 232+1. 310+1. 306+1. 530+1. 988+2. 000+1. 502 )/8=l. 475

L LOW = ( 1+2+3+4+9+10+11+12 )/8 DIFF = .142

( 1.474+1. 102+1. 084+1. 260+2. 078+1. 808+2. 006+2. 122 )/8=l. 617

W HIGH = (9+10+ll+12+13+14+15+16)/8

( 2 . 078+1 . 808+2 . 006+2 . 122+1 . 530+1 . 988+2 . 000+1 . 502 ) /8=1 . 879

W LOW = (1+2+3+4+5+6+7+8) /8 DIFF = .667

( 1.474+1. 102+1. 084+1. 260+0. 928+1. 232+1. 310+1. 306 )/8=l. 212

C HIGH = (3+4+5+6+9+10+15+16)/8

( 1.084+1. 260+0. 928+1. 232+2. 078+1. 808+2. 000+1. 502 )/8=l. 487

C LOW = (l+2+7+8+ll+12+13+14)/8 DIFF = .118

( 1.474+1. 102+1. 310+1. 306+2. 006+2. 122+1. 530+1. 988 )/8=l. 605

F HIGH = (2+4+5+7+9+11+14+16) /8

( 1.102+1. 260+0. 928+1. 310+2. 078+2. 006+1. 988+1. 502 )/8=l. 523

F LOW = (l+3+6+8+10+12+13+15)/8 DIFF = .048

( 1.474+1. 084+1. 232+1. 306+1. 808+2. 122+1. 530+2. 000 )/8=l. 570

T HIGH = (2+3+5+8+10+ll+13+16)/8

( 1.102+1. 084+0. 928+1. 306+1. 808+2. 006+1. 530+1. 502 )/8=l. 408

T LOW = ( 1+4+6+7+9+12+14+15 )/8 DIFF = .275

( 1.474+1. 260+1. 232+1. 310+2. 078+2. 122+1. 988+2. 000 )/8=l. 683

M HIGH = (2+3+6+7+9+12+13+16) /8

( 1.102+1. 084+1. 232+1. 310+2. 078+2. 122+1. 530+1. 502 )/8=l. 495

M LOW = (1+4+5+8+10+11+14+15) /8 DIFF = .101

( 1.474+1. 260+0. 928+1. 306+1. 808+2. 006+1. 988+2. 000 )/8=l. 596

245
FIGURE CAPTIONS

FIGURE 1. DRAWING AND GENERALIZED TEMPLATE FOR THE HELICOPTERS

FIGURE 2. TEMPLATES FOR CONSTRUCTING ALL SIXTEEN HELICOPTERS

FIGURE 3. SCREE PLOTS FOR VARIOUS NUMBERS OF DROPS PER SAMPLE

246
CUT

W INOBOPY

WIPTH

247
5,6

3,4

I

1,2

FIGURE 2(A)

(Reduced 80%)

248
11,12

9,10

7,8

HGURE 2(B)

(Reduced 80%)

249
FIGURE 2(C)

(Reduced 80%)

250
Absolute Value of Effect

0.50

0.25

0.00

U T L C M B F P

Factor Involved

FIGURE 3. SCREE PLOTS FOR VARIOUS NUMBERS OF DROPS PER SAMPLE

251

ENVIRONMENTAL STRESS CRACKING OF

RECYCLED THERMOPLASTICS

Nikhil K. Kundu

Purdue University

Statewide Technology

Elkhart, Indiana

SUMMARY

The high processing temperature of polymers cause what is

called thermo-oxidat ive degradation which results in the rapid

decrease in molecular weights. Due to various processing

parameters all materials in fabricated form contain microscopic

defects in the form of voids, contamination, or material

discontinuities and grain boundaries. Testing for environmental

stress cracking involves inducing mechanical stress in the test

specimens under a controlled environment in the presence of

specific reagents. Application of stress causes localized failures

at the defects, which acts like a stress concentrator and promotes

crack propagation.

The purpose of this experiment is to investigate the

environmental stress cracking characteristics of recycled

thermoplastics. Two types of polycarbonate materials were selected

for investigation, one plain polycarbonate and one 30^6 glass fiber

reinforced polycarbonate (abbreviated as PC). The degree of

environmentcil stress cracking is expressed by the flexural

strength with the level of induced stress as a parameter.

INTRODUCTION

As the polymer degrades to a lower molecular species, it is

weakened to the point where it will no longer stand the load and

will fail catastrophical ly . Mechanical properties such as flexural

strength and impact resistance deteriorate drastically with

repeated processing. Test specimens were molded according to DIN

53449 and stress was induced simply by pressing an oversized steel

ball into a drilled hole in the specimen. Tests were performed

under controlled conditions. The damage to the specimens caused by

a specific reagent was determined by the flexural strength of

the treated specimens.

Test specimens of a plain PC and a 30% glass fiber reinforced

PC were molded at molding temperature of 300 ''C and 310''C. Then the

specimens were tested and compared for their sensitivity towards

environmental stress cracking. Variations in the stress level

demonstrate the relationship of thermal damage to molecular chains

with molding temperatures.

253
TESTING OF FLEXURAL STRENGTH

purpose of this experiment was to determine the flexural

or the stress level at which cracks propagates to

failure in presence of a reagent as a medium. The medium

was toluol normal propanol ( 1 : 10 ) which simulates an

testing period in a normal environment.

EQUIPMENT

Flexural stress tester and a mechanical device for introducing

oversized balls into the test specimens

TEST SPECIMENS

50mmx6mmx4mm test specimens were molded according to DIN

53449 in an injection molding machine at molding temperatures of

300C and 310C. A 3.0 mm diameter hole was drilled at the center of

the specimen as shown in fig.l. And a 15^m oversized steel ball

was introduced into the drilled hole to induce stress. Four .sets

of specimens were prepared as follows:

A. Plain PC molded at 300C

a. with 15^m oversized balls

b. without balls

B. Plain PC molded at 310*C

a. with 15^m oversized balls

b. withot balls

C. 30% glass fiber reinforced PC

molded at 300C

a. with ISQ/om oversized balls

b. without balls

D. 30% glass fiber reinforced PC

molded at 310°C

a. with 150Ani oversized balls

b. without balls

TEST PROCEDURE

For every processing five specimens were tested for flexural

strength. The specimens were placed on supports at both ends and

load applied at the center until failure. The flexural stress was

calculated using the applied load, the bending moment, and the

moment of inertia of the sample.

Flexural Stress Cj^= M/(I/C)

I/C= bh"/6

b=width, h=height, M=bending moment.

The

strength

ul t imate

selected

extended

254
RESULTS AND DISCUSSION

One set of sample test results for only the first moldings

are given in table 1 and 2. Table 1 shows the f lexural test

results for plain PC molded at 300C with and without induced

stress. Table 2 shows the same for plain PC specimens molded at

Slot. A summary of test results for plain PC is given in table 3

and for 30% glass fiber reinforced PC is given in table 4.

Fig 2A and 2B shows the change in f lexural strength as a

function of repeated processing. No.l refers to the very first

processing and no. 2 refers to the second processing or the first

recycle. Samples from the first molding are assumed to have 100%

strength and the subsequent recycling are rated accordingly.

a In case of plain PC specimens from 300C molding temperature

show gradual drop in strength. The specimens from 310'c molding

temperature show some strength upto the second processing only,

which suggests higher thermal damage and faster development and

propagation of environmental stress cracking. Specimens without

induced stress does not show any drop in strength upto the third

processing or second recycle. Even at the third recycle

considerable amount of strength was maintained.

Glassfiber reinforced PC suffers sharper drop in strength due

to induced stress. The specimens without induced stress maintained

their strength through the recycle.

Some samples failed instantly when came in contact with the

reagent. Plain PC showed far more resistance to stress cracking

than the reinforced type. Plain PC with induced stress (molded at

300C) maintained 76% of its original strength after the first

recycle and the reinforced PC (molded at 300*C)

maintained 56% of its original strength after the first

recycle.

In reinforced PC due to the presence of glass as a foreign

material, the crack propagation was drastic, and the specimens

could not be tested for the second recycle. Fig. 3 and fig. 4 show

flexural strength as a function of excess ball diameter which is

an indirect measure of the induced stresses.

Fig. 5 shows specimens of plain PC for all four processings.

Fig. 6 shows the gradual progress of failure in plain PC specimens

of subsequent processings and fig. 7 shows a drastic development of

environmental stress cracking of a sample of fourth processing

even without any induced stress. This is due to the residence

stresses developed during repeated processing.

In practice environmental stresses develop due to adverse

environmental conditions that leads to stress cracking and

eventual failure of plastic parts.

255
ENVIRONMENTAL STRESS CRACKING

FLEXURAL TESTS

Table 1 Table 2

Makrolon 3000W

First Molding

Molding Temp 3 IOC

(Excess ball dia 150,«an)

Specimen no,

12

3

45

Load{N)

37.28

25.51

37,28

37.37

39.24

©"J, = 42.91 MPa

(Excess ball dia Oi«m)

12

34

5

76.52

78.48

77.50

76.52

80.44

97.34 MPa

Molding Temp 300C

(Excess ball dia 150/<m)

Specimen no.

12

3

4

5

Load(N)

80.44

69.65

70.63

73.58

79.46

Sr = 93.18

(Excess ball dia 0/tm)

Table 3 SUMMARY OF TEST RESULTS /MAKROLON 3000W

73.58

82.40

74.56

76.52

82.40

97.34 MPa

Molding Temp 300C

1 50,'«m excess ball dia Without ball

Molding

12

3

4

Flexural

Strength (MPa)

93.18

71 .1

1

7,36

1 00%

76%

8%

Flexural

Strength (MPa)

97,34

95,63

98,08

56,40

1 00%

98%

1 01 % 58%

Molding Temp 31 OC

1242 , 29,

91

42

1 00%

69%

97,34

106,05

1 00%

1 09%

Table 4 SUMMARY OF TEST RESULTS/ MAKROLON GV 30

Molding Temp .300C

(150/m excess ball dia)

Molding

12

Flexural

Strength (MPa)

(Without ball)

Flexural

Strength (MPa)

96,85 "lOO* 111.81 100%

53,94 56% 109,11 98%

Molding Temp 31 OC

12

90,97 100% 112,79 100%

36,78 40% 113,28 100%

256
1

i AW'

0

50-

4+0.2

FIG 1

257
ENVIRONMENTAL STRESS CRACKING WITH INDUCED STRESS

PERCENT OF FLEXURAL STRENGTH MAINTAINED

VS. RECYCLING

PLAIN POLYCARBONATE 30% GLASS FIBER

REINFORCED POLYCARBONATE

1 00 |r=^'---_ ^T80 -

z

^^60

ElW

<

cmD

«40

fa

20

2 3

RECYCLING RECYCLING

T

MOLDING TEMP 300 C

2 MOLDING TEMP 310 C

FIG 2A

EXCESS BALL DIA 150/^m

EXCESS BALL DIA 0 y**^

FIG 2B

258
FLEXURAL STRENGTH OF SPECIMENS

WITH INDUCED STRESS

0 0 150/^'^

- EXCESS BALL. DIA EXCESS BALL DIA

PLAIN POLYCARBONATE

FIG 3

MOLDING TEMP 300 ''C MOLDING TEMP 310''C

0 150/<'>^ 0 150/^-^

EXCESS BALL DIA EXCESS BALL DIA

30% FIBER GLASS REINFORCED POLYCARBONATE

FIG 4

259
260
HOW DOES C3iANGE IN TEMPERATURE AFFECT RESISTANCE?

Jenifer A.T. Taylor, NYS College of Ceramics, Alfred University

KEY WORDS

Resistance, conductivity as function of temperature.

PREREQUISITE KNOWLEDGE

Chemical bonding types, specifically metallic and covalent. This

experiment illustrates elementary band gap theory. Familiarity

of the equation relating resistivity to measured resistance is

assumed.

OBJECTIVE

The two materials you are going to investigate are silicon (the

shiny rod) and copper (a coil made of fine copper wire stolen

from a computer corpse). Before you leave this station, you

should be able to say how resistance and resistivity change with

temperature for these two materials.

EQUIPMENT AND SUPPLIES

Piece of a silicon boule a few inches long with low megohms

resistance.

Coil made of fine copper wire long enough to have resistance

measureable on available ohmmeters.

Either a hot plate or an ice bag to change the temperature of the

boule about 20 degrees C. It might be possible to cool the boule

in the same medium used for the coil but the problem of making

electrical contact to the wet surface is not trivial.

Both a thermos of ice water and a Dewar of liquid nitrogen.

Ohmmeter with appropriate leads

Safety glasses

PROCEDURE '~

1. The shiny rod is a single crystal of silicon, called a boule.

Adjust the meter to measure ohms and hold the probes against

the silver painted spots on the end. Be gentle, force will

break the probes and not improve your measurement. You may

also flake off the silver painted electrodes.

If the area of the electrode is decreased, what happens to

the measured Resistance?

261
The silver electrodes painted on the ends inprove the contact

between the Si and the probes. Whenever electrons have to

leave one materials and enter another, problems can occur.

The reading should be stable and less than one megohm

(substitute for actual sample here) if the T is about 20 C.

(If not, call for help.)

a. Record the room temperature value of resistance and then

set the boule on the hot plate, being careful not to let

it roll off. (The hot plate should be only medium warm,

not hot .

)

b. Record the resistance at a slightly warmer temperature.

It should not be necessary to heat the boule for more

than a few minutes to see the relationship. (If when you

get to this station, the boule is already warm to the

touch, how can you adjust the procedure to suit the

situation?*)

a. Room temperature value for Si boule:

b. Warmed boule:

2. Hook the meter onto the ends of the Cu wire that is wound in

the coil.

a. Adjust the meter to measure Resistance; and record the

room temperature value.

b. Carefully lower the coil into the ice water that should

be available nearby and get a value of R after the coil

cools to 0 C.

PUT ON SAFETY GLASSES BEFORE PROCEEDING.

c. Carefully lower the coil into the Dewar of liquid

nitrogen, using the wires from the meter as a sky hook.

Cool until the nitrogen quits boiling vigorously and the

R value has stabilized. Record the R values below.

a. Room temperature R for Cu coili

b. 0 C Resistance for Cu coil:

c. 77 K Resistance for Cu coil:

REPORT

1. In one or two short paragraphs, explain how the resistivity

of these two materials changes with temperature and explain

why they change the way they do.

2. Graph the R vs. T curve for Cu using the 3 different

teirperatures for which you have data. Do you think this

curve is truly representative?

* Take a measurement immediately and let the boule cool while

you mess with the coil; then take a measurement of the

cooled boule.

262
INSTRUCTOR NOTES

Resistance of Si boule may change because the Ag paint flakes

off, readings become unstable and high.

As Area decreases, R increases.

Question about graph: not enough points.

A hair dryer is handy to warm the coil between groups.

The boule might crack if put in the liquid nitrogen.

The wires from the coil frequently break so stabilizing the coil

in a plastic holder of some kind to reduce stress is advised.

Good follow up to the graphing question is to collect data from a

superconductor or present R vs T data from a superconductor

showing the difference of several orders of magnitude at room T

with Cu lower followed by the switch to zero resistance by the

superconductor. Comparison of same three points for

superconductor makes the futility of three point graphs apparent.

REFERENCES

For basic theory about band gap, any introductory materials

science book, such as Shackleford or Van Vlack.

An equation describing the change in R of Cu with teirperature is

usually found in the same text or in CRC Handbook of Chemistry

and Physics.

SOURCE OF SUPPLIES

A company that works with semiconductors should be able to help

locate a boule of Si. Richard Lane at Rochester Institute of

Technology's Microelectronics Laboratory might be able to suggest

a source. (716) 475-6911 (Don't tell him where you got his

name .

)

Air dry silver paint: GC Electronics, Rockford, IL 61125

Cat. #22-246.

r

263

DEMONSTRATION OF KINETIC RELATIONSHIPS

BY PRECIPITATION-HARDENING EXPERIMENTS

Philip J. Guichelaar, Associate Professor

Department of Mechanical Engineering

and

Molly W. Williams, Associate Dean

College of Engineering and Applied Sciences

Western Michigan University

Kalamazoo, MI 49008

(616) 387-3373

Abstract

The laboratory experiment on age-hardening that is included in many

undergraduate metallurgy courses considers the changes in hardness

that occur as Guinier-Preston zones form, grow, and eventually become

noncoherent precipitates. If the solution and aging temperatures are

carefully controlled, the resulting hardness/ time data clearly show

how mechanical properties can be manipulated by changing the microstructure of an alloy.

If we expand the experimental matrix to include additional aging

temperatures, the family of hardness/ time curves that results can also

be used to illustrate diffusion kinetics. Aluminum alloy 2024 is

particularly well suited to this scheme because aging can be retarded

by storage in a freezer; natural aging starts to develop within the

time limits of a laboratory session; and overaging can be developed in

a simple oven. A two week sequence of laboratory instructions thus

provides sufficient data for a thorough discussion and explanation of

the kinetic principles underlying precipitation hardening and the more

general consideration of the effect of temperature on diffusion rates.

I

265
Key Words ; Aluminum Alloy, Precipitation Hardening,

Kinetic Relationships, Laboratory Experiments.

Prerequisite

Knowledge;

Concurrent with classroom lectures on precipitation

hardening, subsequent to laboratory and classroom

discussions on cold working and hardness measurement.

Objective ; Reinforce understanding of age-hardening and demonstrate the effect of temperature on diffusion rates.

Equipment

and Supplies ; Aluminum alloy 2024-T4 bar stock.Suggested dimensions - 25mm x 5mm x 3m.

Quench Tank - Water

Furnace for solution-treating - 650°C capability

Furnaces for artificial aging - 220°C, 175°C capability

Tongs and Gloves

Freezer - 0°C

Rolling Mill

Shear or Bandsaw

Abrasive Belt Grinder

Hardness Testing Machines - Rockwell B scale

Procedure;

Two separate laboratory sessions are required to complete the three

elements of the experiment:

Artificially age solution-treated aluminum alloy samples, measuring their hardness after selected times,

Suppress aging by holding solution-treated samples in a freezer

for an extended time.

Cold work solution-treated samples to accelerate the age hardening reaction.

First Session;

Prior to the session, the instructor should place four pieces of

aluminum alloy (suggested dimensions 150mm x 25mm x 5mm) in the 650°C

solution-treating furnace. The pieces should be in the furnace for

about one hour.

Begin the session by acquainting the students with the nomenclature

for aluminum alloy tempers - O, T3 , T4 and T6. Then ask one of the

students to take the aluminum alloy pieces from the furnace and

immediately quench each one in room temperature water. As promptly as

possible.

266
one piece should be put into the freezer until the next session,

one piece should be sawed or sheared into six smaller pieces and

all of these should be put into the 220°C furnace, and

one piece should be sawed or sheared into six smaller pieces and

all of these should be put into the 175°C furnace.

one piece will be used to establish the hardness in the solutiontreated condition and the initial portion of the natural age

hardening response.

After quenching the last piece, carefully grind opposite surfaces flat

with an abrasive belt grinder. Then measure the hardness of the

sample in at least three places. Record the elapsed time between

quenching and hardness testing, which should be mo more than five

minutes. Continue to measure the hardness of the piece in at least

three places at time intervals of 15, 30, 60, 90, 120 and 150 minutes

after quenching. This piece should be stored by the instructor at

room temperature until the next session.

Remove one sample from each of the furnaces after soaking times of 15,

30, 60, 90, 120 and 150 minutes. The samples can be cooled in water.

Again, carefully grind opposite surfaces flat with an abrasive belt.

Measure the hardness of each sample in at least three places.

Post each hardness measurement on a blackboard so that all participants can record and discuss the data.

Second Session:

For this session, the instructor should place three pieces of aluminum

alloy (suggested dimensions 150mm x 25mm x 5mm) in the 650°C solutiontreating furnace prior to the session. The pieces should be in the

furnace for about one hour and then individually quenched in room

temperature water. As promptly as possible,

cold roll one piece about 5%, measure its thickness after rolling, cut or saw it into six pieces and put all of them into the

220°C furnace,

cold roll one piece about 5%, measure its thickness after rolling, cut or saw it into six pieces and put all of them into the

175°C furnace,

cold roll one piece about 5%, measure its thickness after rolling, grind opposite faces flat and then measure its hardness in at

least three places; make subsequent hardness measurements at

intervals of 15, 30, 60, 90, 120 and 150 minutes after cold

rolling.

267
Remove one sample from each furnace after soaking times of 15, 30, 60,

90, 120 and 150 minutes, cool it in water, grind opposite surfaces

flat and then measure the hardness in at least three places.

Retrieve the sample that has been held in the freezer for one week,

warm it to room temperature by immersing it in water, grind opposite

surfaces flat and then measure the hardness in at least three places

immediately and after 15, 30, 60, 90, 120 and 150 minutes.

Measure the hardness of the sample from the previous session that was

held by the instructor. This sample has now been naturally aged one

week

.

Post all hardness measurements on a blackboard so that all participants can record the data and discuss the trends.

Student's Reports;

Summary

Description of the Experiment

Draw a simple block diagram flowsheet that shows the steps

used to develop each temper, including the grinding and the

hardness measurements. Explain each step carefully.

Include a discussion of

phase solubility changes with temperature,

the change in solute atom diffusion rate that occurs as

temperatures are lowered, and

the effect that work hardening has on the age hardening

reaction.

This discussion should reference the textbook and other

selected handbooks and journals that may be available.

Analysis of Data

Construct a graph that shows each hardness reading on the

ordinate and the logarithm of the elapsed time on the abscissa. Draw a curve through the family of points that

represents each aging treatment.

Conclusion

Note the time required to achieve peak hardness for each

aging treatment and the value of that hardness. Discuss the

agreement of these experimental results with theory and give

reasonable explanations for any gross discrepancies. Do not

attribute discrepancies to "variability" of the sample.

268
******************************************************

Notes for the Instructor

The underlying theory for the experiment is covered in all undergraduate metallurgy texts and will not be repeated here. You may wish to

refer to the Metals Handbook Volume 2 for a particularly good explanation of the strength and hardness changes that can be expected for

2024 alloy.

We have found that students will obtain confusing and contradictory

data if certain precautions are not taken.

Hardness tests have a tolerance band of at least 4 points when

the Rockwell B scale is used. Students will likely record

hardness readings to one decimal place accuracy and will take

more than one reading only if prompted. Take full advantage of

the potential in this exercise to introduce the real world of

measurement accuracy and experimental variation. Explain that at

least four hardness readings and preferably six should be taken

of each sample. Take as many readings as possible given limitations on sample size and hardness testing machine availability

for other samples. Students should list all readings in the

report and use their average for all graphs.

The hardness reading variation problem will be exacerbated if

sample faces are not parallel, freshly ground and dry. A few low

hardness readings indicate poor sample preparation, especially if

they are the initial hardness readings on a given sample.

Laboratory furnaces commonly have a low thermal mass and inexpensive temperature controllers. Therefore, large temperature

excursions can occur when cold samples are placed into a furnace

or when the furnace is opened to remove samples. Aging may be

accelerated if the furnace temperature overshoots. If a 9mm

thick piece of stainless steel is laid onto the hearth of the

furnace, the added thermal mass will lessen this problem.

The aging temperatures that we list above are arbitrary. However, if you use temperatures higher than 220°C, overaging may

occur too quickly to catch the peak hardness. If temperatures

lower than 175°C are used, overaging may not occur within the

time limits of a laboratory session.

Although the recommended solution treating temperature for 2024

Aluminum is given as 493°C, we found it necessary to exceed that

temperature considerably in order to effect solution treatment

within one hour. The high reflectivity of aluminum, as well as

its high heat capacity, makes thermal equilibrium difficult to

achieve. Even though the phase diagram indicates that 650°C is

well above the solidus line and into the liquid-solid 2-phase

region for aluminum - 4.4% copper, we found that full solution

269
treatment did not occur at lower furnace temperatures within a

reasonable length of time. We recommend that persons replicating

this experiment devote some time to finding solution treatment

conditions appropriate to their own situation.

The effect of cold work on aging kinetics is interesting but

optional if you do not have access to a small rolling mill. If

you do, determine the roll opening that corresponds to about 5%

cold work with a scrap piece of aluminum alloy before quenching

the sample from the solution-treating furnace.

The microstructural changes that occur in the samples of this

experiment are on too fine a scale to observe with optical

microscopy. Therefore, the discussion portion of the student

reports should include, for each of the various processing

schemes, a simple flow sheet and a discussion of the fundamental

theory of the precipitation hardening process. A suggested

format for the flow sheets is shown in Fig. 1. Require a hypothesis statement—for the given process scheme, will the peak

hardness be higher or lower than that for other aging treatments

and will the peak hardness be achieved in less or more time?

Encourage the use of the textbook and selected references for the

preparation of this section.

The kinetic relationships among the various aging schemes are

best understood if the data are graphed as the average hardness

versus the elapsed aging time with the latter on a logarithmic

scale. You may wish to briefly review with your students the

first-order kinetics basis for using a logarithmic transformation

of the data. To avoid confusion over plotting the point which

represents the solution-treated condition, do not use zero but

instead use the time at which the hardness readings were taken,

presumably two or three minutes. A sample graph is shown in

Fig. 2. This graph was constructed using spreadsheet software.

Encourage students to use this tool for enhanced productivity and

accuracy.

References

Boyer, Howard E. and Timothy L. Gall, ed, Metals Handbook Desk Edition, ASM International, 1985, pp 6-3 to 6-11.

Flinn, Richard A. and Paul K. Trojan, Engineering Materials and Their

Applications, 4th edition, Houghton Mifflin Company, 1990, pp 244-248.

Canister, William D. , Materials Science and Engineering, John Wiley,

1985, pp. 236-241.

Metals Handbook (Ninth Edition), Volume 2, Properties and Selection:

Nonferrous Alloys and Pure Metals, ASM, 1979, pp 24-43, 72-75.

270
Solution-Treat

650°C, 1 Hour

Quench in

Room Temp. Water

Cold Roll 5%

Cut into Six Pieces

Age at 175 °C

15, 30, 60, 90, 120

and 150 Minutes

Quench in

Room Temp. Water

Grind Parallel

Faces Flat

Measure Hardness

Rockwell B Scale

Fig. 1. Sample of format for flow sheets; T8 temper shown.

271
55

50-

^45

I 40

|35-

30

25

Age Hardening Curves

Aluminum Alloy 2024

I I I I I I I

1 1—I I I I I I I

1 1—I MINI 1 1—I I I I I I 10 1 00 1 000

Aging Time, Minutes

10000

-B- Room Temp. Age -- 0 C-7 Days, RT Age -t— Aged at 1 75C -Ar Aged at 220C

Fig. 2 Suggested format for age hardening curves.

T4 and T6 tempers shown

272
SIMPLE STRESSED-SKIN COMPOSITES USING

PAPER REINFORCEMENT

L. R. Bunnell

October 1990

Presented at

National Educator's Workshop: Update

November 13-15, 1990

Gaithersburg, Maryland

Prepared for

the U.S. Department of Energy

under Contract DE-AC06-76RL0 1830

Pacific Northwest Laboratory

Richland, Washington 99352

273
SIMPLE STRESSED-SKIN COMPOSITES USING PAPER REINFORCEMENT

L. Roy Bunnell

Pacific Northwest Laboratory, Richland, WA

KEY WORDS : composite, stressed skin, polyurethane foam, paper, cantilever

beam, Young's modulus, elasticity.

PREREQUISITE KNOWLEDGE : This material could be taught to a tjrpical student of

materials science, at the high school level or above. The student should understand

the concept of Young's modulus of elasticity, which is a measure of a material's

stiffness

OBJECTIVES : To demonstrate the composite reinforcement concept in a hands-on

manner, using readily available materials. To demonstrate the consequences of

certain defects in these structures. To quantify the gains made by engineered composite construction, using a simple measurement of Young's modulus of elasticity.

EQUIPMENT AND SUPPLIES : 1) Foam rubber beam about 8 cm by 8 cm by 30 cm, with

vertical lines on all of the 8-cra faces; 2) polystyrene or polyurethane insulating

foam; 3) heavy paper such as construction paper; 4) waxed paper or polyethylene;

5) slow-setting (>3 h) non- allergenic epoxy resin curable at room temperature;

6) cantilever beam loading device constructed as per instructions in this writeup

7) known weights of about 100 g; 8) dial -gauge indicator capable of measuring to

0.025 mm (although most will measure in thousandths of an inch); 9) calculator.

PROCEDURE: Demonstrate by bending the foam rubber beam that the initially

parallel lines get further apart on one side (the tensile side) and closer together

on the other side (the compressive side), see Figure 1. Introduce the concept of

stressed-skin composites by stating that a strong and stiff material, if attached to

these faces, will provide substantial reinforcement to the structure by resisting

such tensile or compressive forces. Next, students bend by hand precut pieces of

polystyrene or polyurethane foam insulation 1 cm by 3 cm by 18 cm, bending the beam

in the 1-cm direction. They will soon note that the beam is not very stiff and will

not bend very far before breaking. Students will then weigh four more foam beams

identical to the first, to a precision of 0.1 gram, and record the weights permanently on the ends of the beams. They should then prepare stressed-skin composites

as follows: one beam is left as is; one beam has construction paper bonded to one

of its 3 X 18 faces; one beam has construction paper bonded to both of its 3 x 18

faces; the fourth beam is made just as the third but has an intentional disbond

that is made by placing a piece of waxed paper or polyethylene 3 cm by 6 cm at the

midpoint of one of its paper-reinforced faces. To achieve the best possible bond,

minimal epoxy should be used and the beams should be weighted during the curing

process. Use waxed paper or polyethylene to separate the composites from surfaces

such as tabletops where bonding is not desired.

The first part of the testing will be done by hand. First, the students weigh

the beams after any necessary trimming and record the weight gains for reference.

Students then bend the nonreinfcreed beams again for calibration purposes. The

single-sided beam is next bent, with the nonreinforced face first on the tensile

side; the beam should be bent only slightly, taking care not to break it. Note that

274
Before Bending

Tension

39008069.2 FIGURE 1. Foam-Rubber Beam Used to Illustrate Tensile and Compressive

Forces Resulting From Bending

this one-sided reinforcement does not have much effect on the stiffness. Finally,

the beam should be bent so that the nonreinforced face is on the compressive side

until it breaks. Note that the foam collapses on the compressive side. This is

because the reinforcement has made the beam much stronger on the tensile side. Now

the students should bend the two-faced reinforced beam without the intentional

debond; it is noticeably stiffer than either of the two preceding beams. Some of

the students may want to break these beams to observe whether failure occurs on the

tensile or compressive face. Next, the defected beam should be bent but not to the

breaking point, with the defect on the tensile side; note that the defect has essentially no effect. Finally, the defected beam should be bent with the defect on the

compressive side until it fails. Note that the nonbonded paper pops away from the

foam in what is known as buckling. Buckling is a fairly common failure mode for

this kind of composite and can be avoided by close attention to construction.

Students may want to quantify the gains made by reinforcing the beams. This

can be done by using the simple testing device in Figure 2. Start with a nonreinforced beam, clamping it in place as shown and barely contacting its bottom face

with the dial indicator. Zero the indicator, or note its reading before loading.

Next, place a weight of 50-100 g on the beam, directly in line with the dial

indicator. If washers are used as weights, it may be useful to push a nail into the

275
Clamp

W

Specimen ]3"

6

Steel Base

Dial Indicator

39008069.1

FIGURE 2. Apparatus Used to Evaluate Stiffness of Composite Beams by

Measuring Deflection of a Cantilever Beam in Bending

beam to prevent them from sliding off. The beam will then bend, and the deflection

should be noted and converted to centimeters. Using the formula, calculate the

Young's modulus of the beam:

Young's Modulus (in Pascals, Pa) =4 (98) W L^/D B H"^

where W = weight, g, L = unsupported length, cm, D = deflection, cm; B = width, cm;

H = height, cm; and 98 is the conversion factor necessary to change from g/cm^ to

Pascals, the SI units for elastic modulus or pressure.

Do the same with one-sided and two-sided reinforced beams. The deflection

should be at least 0.25 mm; if not, apply more weight until it is. It will be noted

that the beam reinforced on one side is not a great deal stiffer than the one without reinforcement, just as was learned by hand bending. Similarly, the two-sided

reinforcement produces impressive gains in stiffness. Some students may wish to

relate the stiffness gains to the weight gains involved in the various reinforcements. Although the stiffness of the foam beams has been increased greatly by using

only paper reinforcement, the resulting composites are not very stiff when compared

276
with other materials. However, the density of the foam beams is very low compared

with other solid materials. The following values of Young's modulus for some common

materials may be useful for comparison:

SAMPLE DATA SHEETS : Self -Evident

.

INSTRUCTOR NOTES : The experiment outlined here is designed for minimal

expense per concept learned. If students are interested in exploring the capabilities of different reinforcement fibers, such materials as Fiberglass cloth, woven

Kevlar, or woven graphite fibers can all be used to make additional beams that can

be evaluated by the cantilever beam test above. Additionally, other fabrication

techniques such as vacuum bagging may be used to achieve better bonding while using

even less epoxy. To save on supplies and time, the instructor may wish to prepare

demonstration beams using the more exotic materials rather than have each student

make all the beams. These demo beams may then be measured for stiffness using the

cantilever beam apparatus

.

REFERENCES : Timoshenko, S., and D. H. Young, Elements of Strength of

Materials . Fourth Edition, Van Nostrand, 1962. p. 212.

SOURCES OF SUPPLIES : Polystyrene or polyurethane foam- -available from any

building supply store, in pieces about 2.5 m by 0.6 m by several different thicknesses. The pink board is much more uniform than the white type made from expanded

beads and is much preferred. The test beams can be cut with a table saw or band

saw, using a fine, sharp blade to produce a good surface finish. Epoxy- -one epoxy,

used successfully with no signs of skin reactions to date, is Vinacron Epoxy, available from lasco, 5724 W. 36th St., Minneapolis, MN 55416.

Dial Indicator and Support- -available from Sears Catalog Sales, both for a total of about $125.

r

Weights --use calibrated weights made for that purpose, or use large preweighed

steel washers with their weights written on them.

Material E. GPa

Aluminum

Steel

Many Solid Polymers

Glass

Note: 1 GPa = 10^ Pa.

69

207

3

69

277
I
EFFECT OF STRAIN RATE ON TENSILE PROPERTIES OF PLASTICS

L. R. Cornwell, R. B. Griffin, W. A. Massarweh

Mechanical Engineering , Texas A&M University

College Station, TX 77843-3123

SUMMARY

Polypropylene specimens were tested in a uniaxial tensile testing machine

to illustrate the effects of varying strain rates on the final elongation and yield

strength of the material. As the rate increases, the strain to failure decreases

while the yield stress increases. These results provide a nice contrast with metallic

systems which are nearly independent of strain rate effect, at least at room

temparature. All of the tests were conducted at 300° K which is above

polypropylene's glass transition temperature of 253° K.

INTRODUCTION

The purpose of this experiment is to demonstrate the variation in tensile

properties as a function of crosshead rate on uniaxial tensile machine. A specimen

is prepared in the form of a sheet tensile specimens and pulled to failure in a

uniaxial tensile test machine(Instron). This provides an excellent demonstration

of the sensitivity of polymeric materials to the loading conditions.^

PROCEDURE

Sheet tensile specimens of common plastic materials are formed in a Boy

injection molding machine. We have had made specimens from polyethylene,

polypropylene, and polystyrene. For demonstrating the effect of varying crosshead

rate, polyethylene is probably the most dramatic. The overall dimensions of the

specimen are 5" long, 0.125" thick, and 0.500" wide in the gage length which is

1.875". The students remove the flash along the parting line and measure each

specimen. Sheet metal tensile grips are used to hold the specimens. For

convenience, the gage length is taken from the ends of the specimen holders. The

crosshead rate is set and then the test is begun. It is crucial to record the

temperature of the room.' A copy of the laboratory handout is given in Appendix

1.

279
DATA

Table 1 provides the crosshead speed, the final elongation and yield stress,

the true strain, and the true strain rate for the polypropylene specimens. Figure

1 a and b gives the stress-strain curves for polypropylene at crosshead rates of 0.4

to 20 in/min.

DISCUSSION

As the data in Table 1 and Figure 2 show the strain to failure decreases as

the crosshead rate or true strain increases. For example, at a crosshead rate of 0.2

in/min the strain to failure was between 140 and 170%, while at a crosshead rate

of 20 in/min the strain to failure was between 54 to 66%. There is also a steady

increase in the yield strength from about 3170 Ib/in^ at 0.4 in/min crosshead rate

to 3620 Ib/in^ at 20 in/min crosshead rate.

Polymers have a range of mechanical property behavior. Depending on the

glass transition temperature (Tg), the properties can vary from brittle-elastic at low

temperatures, to plastic, to viscoelastic or leathery, to rubbery, and finally viscous

at high temperature.^ The Tg for-polypropylene is 253° K and laboratory tests were

conducted at about 300° K. The polypropylene will be in the glass transition or the

rubbery region during testing.

The modulus of elasticity for the 0.4 in/min specimen is approximately 55000

lb/in^(0.38 GPa). Compared with published results, this value is about half the

smallest value reported for polypropylene, 10000 Ib/in^ (0.69 GPa). This great

inaccuracy is attributed to the lack of direct strain measurements using either an

extensiometer or a strain gage mounted on the specimen. Without the direct strain

measurements, specimen elongation will be overestimated due to structural

deflection in the tensile testing machine, thus resulting in underestimate of the

modulus of elasticity.

Since polymeric materials are strain rate sensitive, the strain is a function

of both time and temperature. As the strain rate is increased, the strength of the

material will increase while the strain to failure will decrease. Figure 2

demonstrates the decrease that occurs in the final elongation as the crosshead

rate is increased and correspondingly the true strain rate is increased as shown in

Table 1. The true stain rate can be obtained from the following expression,^

280
8 ^ = true strain

= original gage length

V = crosshead speed

Although the above experiment does not hold the strain rate constant during

the entire test, using the crosshead rate is representative of the actual strain rate

and plotting this versus the final elongation provides a very useful demonstration

of the effect of varying loading rates on a polymeric material. Figure 3 illustrates

the increase in yield strength that occur as the crosshead rate is increased.

Very similar data can be obtained for polyethylene and Figure 4 shows the

final strain plotted against the crosshead rate for polyethylene. The strain

decreases from more than 600% at the lowest rates to less than 10% at the highest

crosshead rates. A simple explanation of the processes occurring in the structure

is given to the students following Ashby and Jones.^

CONCLUSIONS

This experiment demonstrates the significant effect varying the crosshead

rate (strain rate) has on the elongation and yield strength for the polyolefins. In

particular, this experiment used polypropylene. There are several additional

things that could be done to improve or enhance the experiment. A constant

temperature cell could be built to surround the specimen and then the data as a

function of temperature could be obtained. With more sophisticated test machine,

one could actually perform the tests at a constant strain rate. Another possibility

would be to obtain the strain rate exponent by performing rate change tests.^

281
REFERENCES

1. Engineered Materials Handbook, Vol. 2, Engineering Plastics. ASM

International, Metals Park, OH., 1988.

2. M. F. Ashby and D. R. H. Jones, Engineering Materials 2: An Introduction

to Microstructure. Processing and Design. Pergamon Press, Elmsford,

NY,1986.

3 G. E. Dieter, Mechanical Metallurgy. 3'** ed., McGraw-Hill, 1986.

4. ASM Engineered Materials Reference Book. ASM International, Metal

Park, OH.

* We had an interesting experience when one lab session took place when the

room was about 10 degrees cooler than normal. The results differed dramatically

from previous tests and we concluded that the temperature was the reason the

results were different.

TABLE 1. MECHANICAL PROPERTIES OF POLYPROPYLENE.

Crosshead Engr. Strain Yield True strain True Strain

rate (in/in) Strength Rate (s

(in/min) (lb/in')

0.2 1.681 3172 0.986 0.050

0.2 1.391 3161 0.872 0.056

0.4 1.402 3141 0.876 0.111

0.4 0.951 3200 0.668 0.137

0.6 0.667 3271 0.511 0.240

0.6 0.712 3203 0.537 0.234

0.8 0.657 3318 0.505 0.322

0.8 0.936 3234 0.661 0.336

1.0 0.981 3383 0.684 0.336

1.0 0.661 3318 0.507 0.402

5.0 0.667 3402 0.511 2.000

5.0 0.653 3454 0.503 2.016

10.0 0.510 3498 0.412 4.415

10.0 0.596 3517 0.468 4.175

15.0 0.594 3588 0.466 6.275

15.0 0.458 3563 0.377 6.859

20.0 0.537 3576 0.430 8.673

20.0 0.661 3666 0.507 8.031

282
0-

-500H i

\ \ \ \ 1 1 \ \

1 0 0.2 0.4 0.6 0.8 1

0.1 0.3 0.5 0.7 0.9

Engineering Strain (in/in)

r

C.H Speed 0.4 in/m

Fig 1 a: Engineering stress strain curve for polypropylene,

crosshead speed of 0.4 in./min.

283
4000

0 0.2 0.4 0.6

0.1 0.3 0.5

Engineering Strain (in/in)

f- C.H Speed 15 in/m C.H Speed 20 in/m

Fig 1 b: Engineering stress strain curve for polypropylene,

crosshead speeds of 15 and 20 in./min.

284
Polypropylene

Crosshead Vs. Engineering Strain

1.6--

1.4-

0.1 10

1Crosshead Rate (in/min)

100

Fig 2: Plot of engineering strain as a funcion of crosshead

rate for polypropylene

285
Polypropylene

Crosshead Rate vs. Ult. Tensile Stress

3700-1 \

1 I I I I I I I

\

1 I I I I I I I

1 r—

(0

(00

0)0

c

O)

c

LU

3600

3500

% 3400

3300

3200

3100

0.1 10

Crosshead Rate (in/min)

100

Fig 3 : Plot of UTS of polypropylene as a function of

crosshead rate.

286
LU

Q.

(u!/U!) uoub6uoi3 |BU!J

287
TENSILE TESTING OF PLASTICS

OBJECTIVE: To determine the effect of varying strain rates on the

mechanical properties of an engineering plastic.

EQUIPMENT: - Plastic tensile specimens.

Instron test machine.

Micrometer and scale.

Thermometer.

PROCEDURE: - Measure the gauge length and cross sectional area of

specimens.

Determine required crosshead speed testing range,

tabulate speeds required, and then select a random

sequence for performing the tests.

Setup Instron and recording computer.

After test, measure final elongation and area.

ANALYSIS: Determine the following properties:

maximum elongation

% reduction area

modules of elasticity

yield strength

fracture stress

flow stress

REPORT:

O INTRODUCTION:(25%)

Importance of plastics as an engineering material.

Discuss the different mechanical properties of plastics and how

they are utilized in selecting appropriate materials for a given

application, give examples.

Discuss the particular type of plastic used in this experiment

including structure, type (thermoset vs. thermoplastic),

applications ..etc.

Discuss any environmental issues associated with the tested

material including ease of recycling, biodegradability, toxic

byproducts ...etc (EXTRA CREDIT).

288
o EXPERIMENTAL PROCEDURE:(15%)

Mention all testing parameters including material type,

crosshead speed range and increments, and room temperature.

Briefly, describe the test setup including tensile testing

machine, and data recording method.

Describe test specimens, including all the relevant dimensions,

use an illustration.

Did the test conform with any ASTM standard?

O ANALYSIS OF DATA:(15%)

Describe data reduction procedure including:

* all relevant formulas.

* software used.

O RESULTS:(10%)

Tabulate test results and relevant published data. Include

measured temperature as part of your results.

Generate plots displaying the relationship between the

different mechanical properties and crosshead speed.

Describe the necking behavior at different crosshead speeds.

O DISCUSSION OF RESULTS:(25%)

Explain the necking behavior. Use a stress-strain curve

generated during the experiment as an example.

Compare data for various crosshead speeds.

Explain the effect of crosshead rate on the material.

Contrast with tabulated values.

Compare and contrast the behavior of the polymer used with

that of a metal of your choice.

Explain the effect of temperature on the test results.

O REPORT FORMAT (10%)

REFERENCES:

ASM Engineered Materials Handbook- Plastics.

Engineering Materials and Their application, Flinn/Trojan.

The Science and Engineering of Materials, Askland.

289

BIODEGRADABLE PLASTICS:

AN INFORMATIVE LABORATORY APPROACH

Jeffery S. Humble

Shawnee State University-Portsmouth, Ohio

Department of Plastics Engineering Technology

ABSTRACT

Simple laboratory procedures are outlined for class participative

sessions on the subject of testing the new claims of polymer

biodegradat ion . These claims are being brought out by major chemical

companies pertaining to their new polymer products. Both long term and

short term, accelerated tests are cited using published standards.

INTRODUCTION

Due to the increasing awareness of the public toward disposable

trash items, the plastics industry has begun to respond to eyer

increasing pressures from both the public and politicians to enhance

the biodegradation of polymeric materials. This is very problematic

for the industry as polymers are virtually stable and inert to the

elements when added to land fills. By their very chemical nature,

polymeric materials are resistant to degradation by sunlight, water

exposure or oxygenation. Only polymers that contain more unstable

components in their chemical structure, such as Vinyls or Chlorides

tend to degrade over time when exposed to weathering. Normally only

the excessive energy exerted by short wave ultraviolet light (UV-B)

emitted by the sun can destroy the bond integrity and thus destroy the

polymer. Polymers ("plastics") such as Polypropylene (disposable

squeeze bottles), Polyethylene (disposable bottles and films).

Polystyrene (disposable utensils and dinnerware) and other food

packaging materials are for all practical purposes chemically stable

and will withstand the tests of time and elements very well.

The solution then, must come from some alternative method of

material manufacture. The industry has responded with an organic

additive to the polymer matrix called corn starch. This material is

touted as being totally biodegradable and as having the ability to rot

and fade away in a few short years. The question to the student and

instructor alike is whether the claims are accurate. The questions are

answered by following national standard test procedures for weathering

(in order to expose the material to the elements to be encountered in a

dump, excluding bacteria and micro-organisms which are very important

to the "degradation" of the new polymer matrices) and for testing

physical characteristics ( in order to detect changes in matrix

integrity, i.e. biodegradation).

291
EQUIPMENT

1. An outside weathering apparatus built in accordance to ASTM test

number D1435-85.

2. Tensile testing apparatus meeting ASTM standards for pulling the

material apart in order to simulate polymer matrix integrity.

3. Accelerated weathering apparatus capable of generating UV-B light

and of varying both the relative humidity and heat in the chamber.

4. Dial micrometer reading to .0001".

5. Digital scales with at least .001 gram accuracy,

6. New household biodegradable trash bags.

EXPERIMENTAL

The most effective visual aid for demonstrating the effects of

adding corn starch to a polymer matrix is to wrap a ball of any

composition (representing the starch particle) with string

(representative of polymer chains). This polymeric theory is made more

apparent by wrapping a sugar cube (the starch) with stiff wire (the

molecular chains) and submerging the model in water. The theory states

that as the starch is removed from the system, the molecular structure

falls apart. This is to promote biodegradat ion

.

Using a sharp razor or knife, the trash bag must be cut into

sample strips that are in accordance with ASTM D882-83 (Test Methods

for Tensile Properties of Thin Plastic Sheet). These strips are for

use in the tensile tester which will allow us to test the pull strength

of the polymer. This will give an indication of the matrix integrity

and allow conclusions to be drawn as to the effect of starch loss.

The prepared samples must then be mounted on an environmental test

stand as described in ASTM D1435-85 (Practice for Outdoor Weathering of

Plastics). This stand must set in a place free of any objects that

might cast a shadow on the samples at any time during the day. The

angle of the apparatus should be at 45 degrees. The stand should point

to the South so as to give it the maximum exposure to the Sun (it is

interesting to note that the UV absorption of a black trash bag is

greater than that of a lighter colored bag. The time factor can be

shortened by simply using a dark colored bag so that more UV energy is

absorbed). If the stand is erected and the samples prepared in the

Fall of the school year, the sample testing will occur throughout the

full year and quite possible into the next year. This factor of a long

exposure period of time in order to affect a change is the one major

drawback to the testing procedures.

The answer to the problem of excessive time limitations is to be

found with the uses of accelerated testing apparatuses. An apparatus

of this type can significantly reduce the amount of time that it takes

to get significant changes in the properties of the polymer to occur.

A proper weather accelerator will expose the samples to UV-B light and

will vary the temperature and the humidity levels within the chamber

its self. This has the effect of simulating conditions on the outside

292
of the building, but due to the severity of the conditions within the

chamber, the time factor is greatly reduced (reference ASTM D756-78,

Practice for Determination of Weight and Shape Changes of Plastics

Under Accelerated Service Conditions for proper accelerated testing

procedures).

As the sample progresses in the elements and "degrades" we can

pull samples off of the test stand or out of the accelerated chamber

and run a simple tensile test on them (or a test for Initial Tear

Resistance of Plastic Film and Sheet, ASTM D1004-66, could be

substituted as it uses the tensile tester as well). The output of the

tester will show that the material starts to lose it's strength as the

starch is dissolved. The amount of starch loss can be calculated by

weighing the samples before testing in the tensile machine. Accurate

numbering of the samples when they are first placed on the stand or in

the chamber is essential and accurate weights must be made so that

future determination of weight loss can be accounted for. This

accounting for the starch loss may not show immediate correlation to

the tensile data as the actual amount lost may be too small to

accurately determine.

It is extremely interesting to keep record of the temperature and

humidity of the test site so that these conditions can be correlated

with the speed of degradation. Simple, periodic checks will suffice in

getting the information needed to determine whether changing weather

conditions drastically effect the rate of biodegradat ion (variables

such as amount of rain, temperature of the specimen, relative humidity,

length of time frozen in air or in ice, etc.)

One of the easiest ways of determining the concentration and

therefore the biodegradabil ity of the polymer is to take the trash bag

and boil it in water. The reason is obviously to remove the starch

additive. Weigh the remaining polymer structure to see what amount of

loss occurs over the life of the material in the ground. By boiling

the material and continually weighing the sample until a constant

weight is achieved, we can calculate the percentage of additive used.

Care must be taken when boiling the material as some Polyethylene

materials that are used in trash bags will melt totally at this

temperature. The molecules will re-form as the temperature lowers to

below the melting point of the bag.

Whatever the preferred method of analyzing the effects of corn

starch loss may be, the ultimate goal is to determine how long it would

take for the material to completely degrade. This is a paradox in the

testing as the polymer matrix may fall apart, but it will never

completely dissolve under the conditions found in public land fills.

The test stand and the accelerated chamber have one thing in common

with each other which is that we are supplying all of the necessary

ingredients necessary for complete degradation of any substance: light,

heat, moisture and oxygen (air). Public land fills on the other hand

do not supply these ingredients after we have buried materials over a

certain depth (approximately six feet down). The testing performed

with these procedures are of the type that assume the "best case"

scenario which is when all of the necessary components are present.

293
EXPERIMENTAL ORDER

1. --PURCHASE BIODEGRADABLE TRASH BAGS

2 . --CONDITION BAG SAMPLES ACCORDING TO ASTM STANDARDS

3. —CONSTRUCT ASTM WEATHERING SAMPLE FIXTURE OR PREPARE THE

ACCELERATED WEATHERING APPARATUS IN ACCORDANCE TO THE

RECOMMENDED MANUFACTURERS DIRECTIVES

4. —WEIGH EACH SAMPLE ACCURATELY BEFORE AND AFTER LABELING

IN ORDER TO DETERMINE ACCURATE WEIGHT LOSS OF THE SAMPLE

DURING TESTING (CORN STARCH LOSS)

5. —RECORD TEST CONDITIONS AT THE BEGINNING OF THE TEST AND

AT EACH SAMPLE POINT ALONG WITH THE SAMPLES EXPOSURE

LIMITS DURING TESTING (TEMP., WEATHER CONDITIONS, ETC.)

6. --PULL A REPRESENTATIVE SAMPLE OF PRE-TEST CONDITIONED

SAMPLES AND TEST THEM USING THE TENSILE TESTER IN ORDER

TO GET A STARTING POINT FOR THE DATA COLLECTION

7. —MOUNT THE TEST STRIPS TO THE WEATHERING APPARATUS IN

ACCORDANCE TO ASTM PROCEDURE

8. —PULL A REPRESENTATIVE SAMPLE FROM THE TEST APPARATUS

AT REGULAR INTERVALS AND CHECK FOR WEIGHT LOSS. IF NO

MEASURABLE LOSS HAS OCCURED, RE-MOUNT THE SAMPLES AND

CONTINUE TO LET THEM AGE. IF WEIGHT LOSS IS DETECTED,

CONDITION THE SAMPLES AND TEST USING THE TENSILE TESTER.

KEEP CORRECT DATA CORRELATIONS WITH THE TIME, TEMPS." AND

CONDITIONS IF POSSIBLE (THIS IS WHERE THE ACCELERATED

TESTING APPARATUS IS IDEAL AS YOU CAN RECORD THE EXACT

CONDITIONS EXPERIENCED BY THE SAMPLES.).

9. —CONTINUE TO TEST UNTIL COMPLETE LOSS OF STRENGTH IS

EXPERIENCED ON A CONSTANT BASIS (LOSS OF POLYMER MATRIX

INTEGRITY) AT WHICH TIME YOU MAY CONSIDER THE MATERIAL TO

BE DEGRADED ENOUGH TO END THE EXPERIMENT. YOU WILL NO

DOUBT NOTICE THAT ALTHOUGH THE PROPERTIES ARE TOTALLY

RUINED, THE MATERIAL IS STILL INTACT AS FAR AS IT'S

PHYSICAL BULK IS CONCERNED.

NOTE: FOR AN INTERESTING COMPARISON, PERFORM THE EXACT SAME TESTING

THAT IS OUTLINED ABOVE WITH A REGULAR TRASH BAG TO CORRELATE THE

DIFFERENCES ENCOUNTERED WITH THE "BIO-DEGRADABLE" MATERIAL.

RESULTS AND DISCUSSION

What the students (and the un-informed instructor) will ultimatel

conclude is that unlike food stuffs, polymer materials, even with the

corn starch additive are for the most part resistant to biodegradat ion

Even when the additive is removed the polymeric chains are still

present in a far less space consuming form, but they are still present

As the plastics industry is reported to only contribute approximately

5% of the total land fill composition (by weight), we find that the

problem of eliminating the materials through biodegradat ion is of

questionable benefit. The one positive solution to the problem is to

be found in such programs as source recycling whereby the materials ar

re-used. This is, in fact, one of the plastics industry's most

endearing qualities with it's ability to recycle it's waste materials.

294
The test will however, demonstrate the effects of using special

additives to polymeric materials to help achieve desired end results.

The corn starch additive it must be recognized, does not alter the

molecular structure of the polymer. It is instead simply being used as

a sort of "space or place holder" that is later dissolved and eaten

away by micro-organisms. When the starch dissolves, the hole left by

the eroded mass is responsible for the collapse of the structure, but

not the decomposition of the polymer matrix its self. We have had

samples hanging outside for nearly a year now and have seen only

minimal changes in a disposable (biodegradable) trash bag that is used

in automobiles. This item was given to me to use when I took aluminum

cans to a recycling drive. The item obviously had a curious attraction

for me to test the properties of the "new" biodegradable polymers. The

bag has proved to be as strong as the non-biodegradable bag that was

hung next to it. The other bag is being used as a standard with which

we have to compare to. The data for these tests is still forthcoming

and I therefore have no sound correlations to report.

PERSONAL INSTRUCTION NOTES

If it if feasible from a financial standpoint, I feel strongly

that the accelerated chamber method of sample preparation is .the most

effective. The amount of time required to get good results by hanging

the samples outside is prohibitive to the success of these tests.

This test provides the essential elements of student interaction

and curiosity as the subject matter is a newer, more current issue that

has been given maximum air time on the different media services. Most

people have already formed an opinion as to the causes of public land

fill problems and are therefore startled to find that the plastic or

polymer content of the dump is relatively small. The problem still

exists for the industry to address, however. Additives in the matrix

of polymeric materials is only one of the answers to a very complex

problem.

295
BIBLIOGRAPHY

American Society for Testing and Materials. 1988 Annual Book

of ASTM St andards. Section 8. Plastics . Maryland

ASTM, 1988.

Grossman, Douglas M. Know Your Enemy: The Weather and How to

Reproduce It in the L a boratory. Informational paper

presented to customers of The Q-Panel Company, Cleveland,

Ohio

296
Freshman Chemistry and Materials Science:

Merging the Microscopic With the Macroscopic

Gary E. Wnek^ and Peter J. Ficalora'*

^ Department of Chemistry and ^ Department of Materials Engineering

Rensselaer Polytechnic Institute

Troy, NY 12180-2590

Introduction

Among the most exciting prospects for the benefit of society are high temperature

superconductors, organic thin films for optical communication, and polymers which can function as

prostheses. Each presents a "materials problem," and engineering undergraduates from virtually all

disciplines will encounter problems like these. Solutions to these challenges demand an appreciation

of many issues, including the chemical route(s) by which a material is synthesized, the effect the

preparation and processing steps have on various levels of structure (atomic to 'bulk'), and how

structure ultimately affects properties. Thus, a solution to a materials problem requires

understanding of both microscopic (e.g., electronic structure and bonding) and macroscopic (e.g.,

fracture strength, electrical conductivity) phenomena. What we wish to advocate in this article is a

merging ofthe microscopic with the macroscopic in undergraduate chemical education, beginning

withfreshman chemistry. The key difference in a freshman chemistry course with a more

macroscopic emphasis is the set of examples selected to illustrate chemical principles. We present

here motivations for this shift in direction, and offer an approach to implement the integration of the

microscopic with the macroscopic.

Chemistry and materials science are inextricably linked. In fact, in the National Research

Council's "Opportunities in Chemistry," famiharly known as the Pimentel Report,^ can be found the

following definitions from Webster: a material is "the substance or substances out of which a thing

297
is constructed," and chemistry is "the science that deals with the composition, properties, and

changes of properties of substances." However, there is a perception that chemistry is concerned

primarily with microscopic phenomena. Nowhere is this attitude more evident than in a freshman

chemistry textbook. While occasional chapters on the solid state can be found, these typically dwell

on atomic packing. Virtually no mention is made of material properties such as modulus, electrical

conductivity, and transparency, and how these are dictated by atomic and molecular composition and

structure. If solids are discussed, imperfections such as point and line defects are almost never

mentioned, and yet these dictate, for example, mechanical properties. This approach is unfortunate,

as it has been pointed out quite clearly that tremendous opportunities exist for chemists to participate

in the exciting area of materials science. For example, in the Pimentel Report, materials chemistry

played a prominent role, and the interdisciplinary nature of materials chemistry was stressed. It was

stated that "chemists are increasingly joining and expanding the specialist communities concerned

with glasses, ceramics, polymers, alloys, and refractory materials." Furthermore, the report

predicted that "coming years will see entirely new structural materials, liquids with orientational

regularity, self-organizing solids, organic and ionic conductors, acentric and refractory materials."

It should be noted that a companion report, "Frontiers in Chemical Engineering" (National Research

Council, 1988), expressed similar opportunities in the materials area for chemical engineers.'^ That

more and more chemical research activity is indeed being directed toward the materials area was

responsible for the American Chemical Society's launching of a new journal. Chemistry of

Materials, in 1989. Dr. Mary Good, former ACS President, recently edited a book published by the

American Chemical Society which speaks directly to the point.^ The title? "Biotechnology and

Materials Science: Chemistry for the Future." In order to meet these challenges, it has been

suggested that changes in chemical education may be needed "to keep chemists in the center of

revolutions in materials and biological sciences."^

Perhaps the most compelling arguement for at least considering a shift toward a more

macroscopic focus in freshman chemistry comes from engineering faculty. At a number of

298
institutions, engineering faculty have complained that introductory chemistry is not terribly relevant

to the needs of their undergraduates. What they mean (in part) is that their students are not learning

enough about the solid state and, hence, about materials. For example, many electrical engineering

faculty believe that students should be exposed to semiconductors and how simple devices can be

constructed from them. Another way of saying it is that freshman chemistry is not applied enough

for engineering needs. But is it not, afterall, the application of chemistry that fascinates chemists?

The reluctance of chemistry faculty to respond to these needs has led to the initiation of

'alternative' chemistry courses taught by engineering faculty. For example, for the about the last 15

years, freshmen at MIT may elect to take their one-semester requirement in chemistry in the form of

"Introduction to Solid State Chemistry." This course is taught exclusively by the Materials Science

and Engineering Department. Roughly one-half of the freshman class takes this course instead of

the Chemistry Department's offering. Northeastern University now teaches a second semester

freshman course emphasizing materials chemistry for honors students. At the University of

Pennsylvania and the University of Arizona, freshmen engineering majors can take their second

semester chemistry course in solid state chemistry, again taught by materials science and engineering

faculty. While these are programs are ones with which the authors are familiar, there are likely to be

many more in progress or in the planning stages.

Should this shift toward materials chemistry be taken seriously? The answer in brief is 'yes' if

students are consulted - materials topics bring vitality to freshman chemistry, which should be

fascinating but many times falls short of this goal.

An Approach to the Microscopic/Macroscopic Merger

At Rensselaer Polytechnic Institute, we are in the third year of teaching a two-semester

freshman chemistry course which emphasizes materials chemistry. This 'pilot' course, being taken

by about 180 engineering students selected at random in 1990-1991, is co-taught by faculty from the

299
Departments of Chemistry and Materials Engineering. Tiie development of course materials, as well

as the staffing of both lectures and recitations, are shared equally by the two Departments, as this is

in the truest sense a cooperative venture. Summarized in this section are the philosophies about the

operation of the course and an outline the subject matter.

The organization of a typical freshman chemistry textbook is inappropriate for a course aimed

at teaching the basics of chemistry using materials examples. Chapters on bonding, for example, are

frequently in the middle of a book, whereas we insist that bonding be the first subject discussed in

detail. We strongly believe that what is required is a hierarchical approach which begins with the

structure of the atom and continues to molecules and then collections of atoms or molecules into

various superstructures (i.e., condensed phases). The fundamentals of thermodynamics, kinetics

and the solid state are discussed next to prepare students for the remainder of the course. Students

will learn, for example, in detail why metals are electrical conductors and malleable, whereas most

ceramics are insulators and are brittle. They also learn why structural metals are not as strong as one

might predict based upon an ideal (perfect) crystal lattice, and how it is possible for solid-state

chemical reactions to alter the strength of an alloy. To understand macroscopic properties, it is

absolutely essential that the microscopic world of atoms and electrons be understood. This is

modem chemistry, and it epitomizes what is meant by a microscopic/macroscopic merger.

Because no chemistry textbook had an order of presentation which was deemed appropriate,

we developed the course outline (Table 1) without reference to any particular text. It reflects the

hierarchical approach mentioned earlier. Once this was established, readings were assigned from the

texts selected (Gillespie et al., Chemistry, 2nd ed., AUyn & Bacon, 1989; Shsicktlford, Introduction

to Materials Sciencefor Engineers, 2nd ed., Macmillan (1988)). In many instances, the texts'

treatment of a particular subject may be weak or non-existant, and therefore we provide students

with detailed lecture notes. Students meet for two large lectures per week and two smaller (ca. 25

student) recitations. The first of the two recitations takes on the character of a small but more

300
personal lecture, where concepts presented in the texts and in the main lectures are built upon. The

relevance of the course material to the 'real world' is particularly stressed. The second recitation

serves as a problem-solving session, and weekly quizzes are given here to monitor student progress.

Table 1. Abbreviated RPI Freshman Chemistrv/Materials Course Outline

Part 1: Structure and Bonding

Nuclear and electronic structure; properties of light; simple quantum theory; the

periodic table; creation of elements; bonding; hybridization and molecular geometry;

resonance; the states of matter.

Part 2: Thermodynamics and Kinetics

Equilibrium; acids and bases; thermochemistry and bond energies; the laws of

thermodynamics; kinetics: simple collision theory and activation energy; chain vs. non-chain

reactions; catalysis.

Part 3: The 'Ideal' Solid State

Atomic, ionic, covalent and network solids; bonding and packing of spheres; band

theory; cubic crystals; evidence for periodicity (x-ray diffraction); metallurgy; mechanical

properties of 'ideal' crystals.

Part 4: The Imperfect Solid State

'Real' crystals. Compositional and structural imperfections; their influence on material

properties. Glasses.

Part 5: Phase Diagrams: EquUbrium 'Maps'

Two-component diagrams with and without solid solubiUty; the Gibbs phase rule;

lever rule; illustrative systems (e.g., Pb/Sn solder, and Fe/FeC (steel)).

Part 6: Kinetic Processes in Solids

Diffusion; reactions in/on solids; sintering.

301
Part 7: Classes of Materials

Metals (conduction, mechanical properties); ceramics (brittle fracture, glasses);

polymers (synthesis and properties of macromolecules); electronic materials (semiconductors,

simple electronic devices, device fabrication).

Part 8: Materials Synthesis

Inorganic and organic reactions; use of thermodynamic and kinetic arguments to select

reaction conditions; influence of synthesis pathway on structure.

It should be emphasized that the order of the presentation allows continuous reinforcement of

concepts. For example. Part 6 calls for an appreciation of activation energy, a concept already

discussed in Part 2 using gas-phase kinetics but now applied to kinetic processes in solids. Parts 7

and 8, which last about eight weeks, provide the opportunity to 'put it all together.' For example,

among the many phenomena discussed in Part 7 is the fracturing of glass.^ The rate of crack

propagation is known to be enhanced in the presence of water. Hydrolysis of Si-O-Si bonds occurs

and is facilitated by bond angle strain at the crack tip, the latter being dependent on the magnitude of

the applied stress. A detailed discussion serves to illustrate, among other things, (1) nucleophilic

attack by water on Si and why silicon is more reactive than carbon towards nucleophilic attack, (2)

the effect of bond angle strain on chemical reactivity, (3) the effect of molecular size on reactivity at

the restricted geometry of the crack tip (methanol and aniline react more slowly than water), and (4)

a macroscopic phenomenon is dictated by events occurring at the microscopic (atomic) level. These

ideas are important, and the interesting example of glass fracture provides a vehicle to promote an

interest in learning chemistry. Part 8 attempts to merge what chemists know how to do particularly

well, that is to make things, with a materials scientists' detailed knowledge of how atomic and

molecular structure affects properties. Virtually all Of the concepts presented earlier are reinforced

here.

302
The outline mentioned above is obviously quite different from that of a typical freshman

course. While many traditional experiments can be readily employed, the course content calls for

new experiments. Our goal for the coming year is to develop interesting laboratory experiments

which are relevant to the lecture material and which can be performed with the large throughput of

students in a freshman course. Experiments under development include precipitadon hardening of

an aluminum alloy, the synthesis of diamonds, the growth of a metal/semiconductor junction and its

electrical properties, anisotropic etching of Si single crystals, absorption spectroscopy of transition

metal ions in glasses, and construction of a phase diagram. Each is intended to provide a conceptual

Unk between a macroscopic property and its atomic/molecular level origin. The near-term plan is to

offer the course in 1991-1992 to all engineering freshmen at Rensselaer (approximately 700

students). Our longer-range goals are to develop a textbook based upon the outline in Table 1 along

with a laboratory manual.

Additional details and course material will be provided for the asking.

Acknowledgements

The authors wish to thank their colleagues D. A. Aikens, R. H. Doremus, D. J. Duquette, J.

B. Hudson, K. J. Miller, J. A. Moore, C. T. Moynihan, S. Murarka, K. Rajan, R. R. Reeves, C.

Steinbruchel, R. L. Strong, and S. E. Wiberley for their effort in making the course described a

reality. Financial support from Rensselaer's Office of the Provost, the Deans of the Schools of

Science and Engineering and the Departments of Chemistry and Materials Engineering, and the

General Electric Company Foundation is gratefully acknowledged. We thank our 'pilot' students

for their thoughtful comments and suggestions.

303
References

1. G. C. Pimentel, "Opportunities in Chemistry," National Research Council, Washington

(1985).

2. N. Amundson, "Frontiers in Chemical Engineering," National Research Council, Washingt

(1988).

3. M. Good, "Biotechnology and Materials Science: Chemistry for the Future," ACS,

Washington, 1987.

4. B. Hileman, Chemical and Engineering News, Oct. 26, 1987, p. 34.

5. T. A. Michalske and B. C. Bunker, Sci. Am., 257, 122 (1987).

304
INTRODUCTORY MATERIALS LAB

Sayyed M. Kazem

MET Department, Purdue University

West Lafayette, Indiana 47907

INTRODUCTION

Freshmen in Engineering Technology at Purdue must take a basic "core" course

in Materials and Processes (MET 141) with two one -hour lectures and one two -hour

laboratory. As usually scheduled, our initial lab session precedes the first

lecture. Also half of these students have had little or no math and science since

junior high school. The first lab is designed to serve as an orientation to draw

students' attention and create a need for understanding engineering materials; to

arouse students' curiosity and give insight into some principles of science; and

to encourage students to develop general technical skills in the field of

materials technology. The objectives of this lab are: (1) establish a broad

outlook for classification of engineering materials; (2) introduce basic concepts

and vocabulary in materials technology; (3) make qualitative observations and

measure or gage quantitatively; (4) use and review basic math and science.

The instructor gives an overview of engineering materials, classifications,

and properties. Complex tests like specific gravity and thermal conductivity may

be demonstrated for the whole class. Then with 12 -students per lab, individual

students (or teams) may select a task (or setup) . Observations (or data) are

recorded on the WOEIKSHEET (see page 2). Students then move to the next setup.

Some tasks are "fill-in- the-blank" ; others require "homework calculations," neatly

and legibly written on separate sheets, stapled to the "WORKSHEET."

Grading is based on logical answers, correct conversions, and appearance.

Scoring (24 points) is about 10% of total lab points (25% of course grade)

.

Different samples and types of materials are introduced each semester, to

encourage "student initiative" and "foil the files." Alternative setups can be

introduced as desired or required to elucidate other "PHENOMENA" (see page 3).

Materials and exhibits may be selected from discarded test specimens, broken

parts, or household items. Each setup can be stored in boxes or stacked trays.

Standard sets of metallics, plastics, and ceramics may be purchased:

PROCEDURE

COSTS

Metals kit (36 pieces)

Plastics kit (25 pieces)

Ceramics kit (12 pieces)

Baby scale, for weighing kilograms, or pounds

Beam balance, for buoyancy/density experiments

Magnifiers (lOx)

Brinell scope (20x)

Micrometer caliper

Vernier caliper

Torque wrench (with socket)

$200

60

10

50

200

5

20-300

50

50

50

305
MET 141L, DIV. #

WORKSHEET

DATE: NAME:

INTRODUCTION TO MATERIALS

1 . METALS

:

Main Color?

Oxide Tint?

Al Brass Cu Mg Nb Sn Ta Ti

2. DENSITY:

Weight?

Volume?

.-. Ib/ft3 =

Metal (steel) Ceramic (glass) Plastic (acrylic)

3. SPECIFIC GRAVITY/RELATIVE DENSITY:

Dry Sample = kg, Wet Sample =

S.G. = . Sample is (Mg

kg, Lost = kg.

1.7, Al = 2.7, Ti = 4.5 Fe = 7.9)

4. GRAINS: Galv. Zn Plate

Grains/in2 - N -

Brass

N =

Al Elbow

N -

ASTM Chart

N -

If N - 2<''"i\ then n = n = n - n =

5. MAGNET: List the materials which the magnet attracts

6. BRINELL SCOPE: What is its magnifying power?

Does the scope read (a) cm and tenths, or (b) mm and tenths?

Does "power" multiply (c) Length, or (d) Area?

7. MICROMETER: Read mils (1/1,000 in) and tenths (1/10,000 in).

The dry IBM card is mils. The wet IBM card is mils.

(thickness) (thickness)

8. TEMPERATURE vs. COLOR: Heated steel will oxidize and cool to various colors,

so light yellow forms at °C, and light blue forms at °C.

.". Plain steel conducts heat (a) faster, or (b) slower than stainless?

9. METRIC RULER (Stainless Steel): Measure a large paper clip.

Width — cm. Length = cm. Wire dia. = mm. And 1-inch = cm. (S.I. metric units).

10. SHEARED EDGE: (a) a shiny -cut occurs in ductile-metal.

(b) a dull -break occurs in work-hardened-metal. In a punch-disk, what occurs

first?

11. TENSILE BAR: Dp = ", Dq = ", Lp = ", Lq = 2".

Ductility index — % area reduction = 100 (Aq - Ap) + Ao = %.

Elongation = linear strain = (Lp - Lq) -»- Lq = in/in.

12. SPARKS: Using electrical grinder and chart, identify the "unknown metal

bar" as ?

306
PHENOMENA

Surface Grains- -Frost , zinc, brass, aluminum.

Fractures- -Cast iron, Duriron (with silicon). Aluminum plug, Brass piece

Welded steel pieces; Blistered Steel.

Fatigue rods (steel, brass, aluminum); Torsion shaft and bolt.

Machining- -Stainless steel, Mild steel. Brass, Aluminum, Copper.

Shearing and Punching- -Aluminum and Steel strips, discs.

Sounds- -Hit and drop specimens.

Ball and Tube- -Simple rebound scleroscope; Rough surfaces; Dents.

Penetration- -Using hammer, awl, knife, chisel, file, saw.

Making dent, scratch, cut, chip/burr, dust/groove.

Vise- -Bending tin specimens (creaky) and solder bar (silent).

Sparking cerium specimen (Ce) .

Grinder- -Shower of sparks; vary Carbon %; need chart and experience.

Magnet- -Ferrous metals. Nickel electrode. Stainless steels;

Non-ferrous metals; Non-metals; Ceramics.

Specific Gravity- -Zero the scale; Weigh sample in air and in water.

Calculate S.G. = Air Wt./Wt. Loss.

Compare published values (ABS , Steel, Cu, Pb, Brass).

Thermal Conductivity- -Time to melt wax at end of rod. Specimens of

Stainless and Mild Steel, Cu, Brass and Aluminum. Compare published

values (thermal and electric).

Thermal Heat Capacity- -Constant weight specimens (Cu, Al, Brass, Steel,

Stainless) and constant volumes of water; measure maximum temperature

rise; compare published values.

Melting Temperatures - -Time to melt same size ball (Pb, Sn, Solder of 50%

Lead/50% Tin) . Refer to "Equilibrium Phase Diagram" and predict melting

point of "Eutectic mix" (63% Tin, 37% Lead) . Discuss wiping solder (non

eutectic) and potable water (no lead) in copper pipes (95% Sn, 5% Sb)

.

Oxidation and Corrosion- -Hot steel colors; Cold oxide colors; Crayons

("Tempil Stix"); Rust and Tarnish (Fe, Cu, Brass); Brass tubing (Sulfur

Natural Gas); PVC (plastic degradation).

307
REFERENCES

1. DeGarmo, E. R. , "Materials and Processes In Manufacturing," 5^^ Ed.,

Macmillan, Inc., NY, 1979.

2. Jacobs, J. A., and Kilduff , T. F. , "Engineering Materials Technology,"

Prentice- Hall, NJ , 1985.

3. Widener, E. L. , "Materials Labs: MET Department, Purdue University," Kinko's

Copies, West Lafayette, IN, 1989.

308
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331

Simple Strategies for Improving Retention of Women

In Technical Studies

Jenifer A. T. Taylor

New York State College of Ceramics at Alfred University

Alfred, New York 14802

The United States is facing a serious shortage of

engineers and decreasing numbers of young people interested

in pursuing technical careers. To alleviate this situation,

engineering students must be recruited from populations not

traditionally well represented. Women are one such group.

Despite the best intentions and determined efforts made

by engineering schools over the last ten years, women still

account for only 7% of the American engineering workforce.

[1] This paper addresses two facets of this situation. One

aspect is related to the cultural attitudes that are

responsible for the problem. The second is a qualitative

description of painless techniques that can be implemented

by engineering faculty to provide moral support for the

women who do make it to college in an engineering major.

I. The Roots of the Problem

We are all products of our upbringing and under

scrutiny will find that much of our interpretation of the

behavior of others is based on the premise that their

motives are the same as ours. Often, this not the case. We

of the Caucasian majority in the U.S. tend to think that

culture is something only minorities have. Try standing less

than 28 inches from a typical American and you are aware

that something is wrong; a manifestation of your

encul turation . For a WASP, a person who encroaches on your

personal space is sending a message, with sexual and/or

sinister overtones. More likely, the person is hard of

hearing or comes from a subculture where twenty inches or

less is the appropriate distance between people in

conversation

.

We have definite cultural values that condition us to

expect certain patterns of behavior that are often

gender-specific. I would like to mention a few of these, on

the grounds that being aware of them will in itself be

helpful in understanding why so few women become engineers.

In years past, it has been a popular conception that

women are not as good at math and science as men. When men

study young males and females to ascertain whether there is

a measureable difference in mathematical ability, the

conclusion is usually that there is. [2] When women conduct

the study, no difference can be documented. [3] This

prejudice still influences many, properly enculturated

individuals, both men and women. Math phobia among young

females is a recognized problem; a manifestation of a

self-fulfilling prophesy.

333
As small children, males and females in our culture are

usually trained to express anger in different fashions. If a

three or four year old child lets go with a stream of

obsenities, the response of the adults in the immediate

proximity will depend to some extent on what gender the

child is believed to possess. Since, at that age, gender is

mostly determined by apparel or name, the perception of

gender is no more than exactly that. A girl child who

indulges in such expressions of anger or hurt will be

considered the unfortunate product of poor parenting,

probably a profane mother. A boy child might be

remonstrated, depending on the relationship of those within

hearing distance, but the behavior will be considered much

less shameful, perhaps even boyish. The girl can cry with

complete immunity but the boy is likely to be told that men

do not cry and keep a stiff upper lip, etc. Which behavior

is going to be considered acceptable in young engineering

students running up against a frustrating problem or bad

grade? After years of training to be typical females, young

women suddenly find their cultural conditioning is crippling

them. Men are not sure how to work with a person who

expresses anger or frustration by crying.

Similarly, most children are taught not to interrupt

other people when they are speaking. However, consideration

for others and nurturant behavior is part of what our

culture considers especially proper female training. Boys

are taught to be polite also but are treated much less

severely when they are not. Some recent studies [4] showed

men start more than 90% of their conversations by

interrupting whoever has the floor. Women seldom begin a

conversation by interruption. They wait for a break to occur

which means in some cases they can wait a long time. Of

course there are exceptions to this cultural pattern; men

who find it difficult if not impossible to interrupt a

speaker and women who have no problem initiating a statement

in the middle of another's discourse.

I was present at a meeting of about ten faculty

discussing the selection of a new chair not long ago and was

able to observe this phenomenon in action. In the first

twenty minutes of the meeting, eight people spoke, not one

began his comments at a period. The two of us who did not

feel comfortable with that procedure waited hopefully for

order to prevail. (I was the only woman; the other

nonspeaker was a male.) Reluctance to begin speaking by

interruption does not mean that a person has less to say,

which is the conclusion drawn by typically enculturated

males. In some cases, probably a direct result of child

rearing practice, the cultural prohibition on rudeness has

been engrained more thoroughly.

Some years ago, one of the more perceptive

psychologists studying our culture presented his

observations on the natural proclivity of preadolescent

334
girls to plan the interior of rooms and boys to build

rockets and tall buildings, when encouraged to design an

environment with a collection of props. [5] From these

observations, he concluded that the presence of the womb in

even young girls led them to an interest in the interior of

domiciles while the young boys were taken with phallic

images. This study was widely accepted and considered a good

example of how men and women are naturally different. I was

rearing young girls at the time and was appalled at the lack

of sensitivity the author showed to the extent of

enculturation that girls had been subjected to by the time

they were preadolescent . When asked why this was the case,

the daughter of this eminent phychologist said he was too

busy developing his theories to notice how she was subjected

to cultural values. Girls are "nice" when they are quiet,

clean, helpful; boys are "all boy" when they are active,

loud, dirty, investigating everything. (Which set of

character traits do you suppose will lead a young person to

be interested in engineering?)

The above examples of how our culture influences our

response to the gender of a person have been cited only to

heighten awareness on the part of engineering educators (who

are predominatly male). I am not trying to make males feel

guilty because they are a product of their upbringing. A

more appropriate goal is to help formulate patterns of

behavior that will make the four years (minimum) a young

woman spends in the classroom more pleasant, so the word

will spread to younger students that engineering is OK.

II. Cultural Remediation in the Engineering Classroom

Some techniques suggest themselves, based on the

examples above. Allow uninterrupted speaking time to both

men and women. You will never know what good ideas some

people have if they have to interrupt or bear interruption

to share them. It can be argued that these people should

just learn to function like "real men" but there is a fair

amount of evidence accumulating that competition for the

floor does not result in very good communication in the best

of times. [6] Tentative broaching of a solution or question

is more common from females than males and must be handled

carefully to avoid squelching participation. Listening for

the idea rather than dismissing the contribution because of

overly polite phrasing or questioning intonation is not easy

for a typical, properly brought-up male of my generation.

The immediate impulse is to interrupt and rephrase,

regardless of the validity of the response. [6] Women are

taught to be indirect in their approach by our culture. Ask

a question that brings up your point rather than make the

point bluntly; good psychology for smart females but poor

practice in a male-dominated classroom. A professor might

respond with a tentative expression or ask supporting

questions when faced with encouraging a non-assertive

335
student. Students of both sexes have been shown to

participate significantly more often in classes taught by

women, who are more accepting of the tentative "female"

approach. [6]

EXAMPLE: The instructor asks: "What determines

thermal shock resistance in a ceramic?" (Looking for thermal

expansion, thermal conductivity and tensile strength) A

tentative answer from a student: "The thermal gradient

across the sample is important?" (Misinterpreted question;

missed "property" and is not thinking in the same path as

the professor) Positive response by professor: "Yes, that

will certainly affect the likelihood of fracture due to

thermal shock. Could we divide the important properties in

environmental and material related? Thermal gradient is the

most important environmental factor. What would be the most

important material related factors? The properties of the

material." Note the use of some of the same words the

student used; that is great for the self concept of the

student. So is reference to the student by name. "As Joan

mentioned, thermal gradient must always be considered when

evaluating the likelihood of thermal shock cracking." The

professor has in this reply interpreted a response as

correct in the manner the student intended it, encouraged

that student and others to ask questions, helped the class

make an important distinction, and steered them in the

direction s/he wanted to go.

Professors should not be afraid to call on women for

fear of embarrassing them, even if there are only two or

three in the class. Female students should be treated as

individuals and expected to respond in the same manner as

the man, keeping in mind that many women (and some men) will

not respond well to being interrupted and may be

"unbecomingly tentative" (cultural interpretation) in their

responses. Encouraging the classroom attitude that every

student is worthwhile and probably has good ideas will

result in more learning and will make females more

comfortable.

Be sensitive to your proxemic behavior. Male professors

tend to aviod eye contact with female students. [6] The

message this gives the women is that they probably do not

have anything to contribute, because our culture encourages

eye contact during serious conversation. If you would not

put your arm around a male student who was talking to you as

you walked down the hall, don't do it to a female. Many of

us automatically respond differently to males as opposed to

females; it is part of our encul turation and we must be very

sensitive to avoid creating the wrong impression.

EXAMPLE: Talking about how different people act often

relaxes tension and allows for open discussion of what can

be very disturbing behavior patterns. I recently taught a

lab class to senior engineers with two teaching assistants

336
who represented both extremes in the need for personal

space. One was Latin and always had his body next to

whomever he was talking to, touched everyone and generally

could have been perceived as a real menace by both genders.

The other T.A. was a typical American, 28 to 30 inches and

never touch anyone. The first semester I worked with these

two gentlemen I got many complaints about the Latin T.A.

from student evaluations. Knowing the person well, I was

quite confident that his intentions were honorable and

friendly. The second semester I introduced them with

comments about the spectrum represented by the three of us.

I was somewhere in the middle, often touching when I should

not have. I told the students that the Latin couldn't help

himself. After 25 years of being trained by his culture, he

wasn't going to change and they should just kick him right

above the ankle if he bothered them by his proxemic

behavior. I was a hopeless case also, having been a mother

for almost 25 years (a difficult disease from which most

people never fully recover) and they should likewise make it

clear to me that I was bothering them. They all laughed at

this and with subsequent encouragement, were able to joke

about proxemic behavior during the semester. The important

point is to make discussion easy because a strained

classroom is not an easy place to learn. No one complained

about the Latin T.A. the second semester.

Another culturally initiated difference that can be

addressed in the classroom with perfect honesty is how men

and women respond to failure. Men tend to blame the

textbook, the professor, time spent on sports, and similar

external influences. Women almost always blame themselves.

They think they are not smart enough or something serious is

wrong with their background. [7] I have found joking about

this when someone (male) makes excuses a good way to bring

it up and a source of tremendous interest to the women. It

is easier to address directly in a meeting of female

undergraduates, but that format is often unavailable.

Knowing this reaction is common from females as opposed to

males often allows the women to build defenses against

self-doubt, since most modern young women are not willing to

allow their success to be hindered by gender-specific

behavior.

To support this point, a recent study at the University

of Illinois revealed that after two years of college, women

who were top high school students have significantly lower

self-images than do their male counterparts, and that their

perceptions had no correlation to the students' actual

academic performance. The study also revealed that, by their

sophomore year in college, women had lowered their career

aspirations more than men had. [7]

Well enculturated women tend to feel that they are

obligated to nurture the world. This conditioning has been

very helpful to our society over the years but results in

337
women seeking service professions rather than what are

perceived as materialistic endeavors. A recent Office of

Technology Assessment study reported that young people in

general would be more attracted to the field if engineering

were perceived as directly serving people and the public

interest. [8] The idealism of the young (may it never fail!)

leads to questions like: What is engineering? What does

engineering contribute to humanity? What does it stand for?

A big picture description of engineers as problem solvers - people who enjoy trying to develop new and better ways of

doing things - is often helpful in addressing these

concerns, which are expressed by both genders.

Since women usually picture themselves as being

nurturant they may respond more actively to this picture of

engineering as a profession that contributes significantly

to the well being of humanity. When asked what an engineer

does, most of us tend to focus on our own branch and start

outlining the various specializations when the question is

generally prompted by more global concerns.

EXAMPLE: Engineers work at solving problems such as

environmental pollution. Ceramic engineers are trying to

make a ceramic engine that will run at higher temperatures

to get more energy from a gallon of gasoline. Automotive

engineers are trying to design a more efficient engine.

Petroleum engineers are trying to find better ways of

extracting gasoline from oil. Chemical engineers are trying

to develop alternative fuels that are less polluting.

Be sensitive to the fact that the male gender dominates

in all textbooks, articles, examples and problems in

engineering. When you make up problems, include reference to

females.

EXAMPLE: When the engineer evaluated the glass batch

as specified by the customer, SHE discovered the weight

percents did not add up to 100.

III. Summary

The number of women who begin engineering studies and

the number who finish and go on to work in the field are

influenced by cultural attitudes; their own, their peers'

and their professors'. I believe we can, as engineering

faculty, have a significant, positive impact on the

percentage of women actually working in the field by being

more sensitive to our gender-specific behavior, as described

above. In addition, the following general approaches are

recommended. [6]

1. Pay particular attention to classroom interaction

patterns during the first few weeks of class and

make a special effort to draw women into discussion

during that time. The pattern that is estalished

early in the term will likely continue.

338
2. Notice whether the "feminine" or "masculine" style

of a student's comments, question or response

affects your own perception of its importance.

3. Intervene in communication patterns among students

that may shut out women.

4. Note patterns of interruption to determine if women

students are interrupted more than men, by yourself

or by other students.

5. Ask women and men qualitatively similar questions;

critical and factual.

6. Avoid using the generic "he" whenever possible.

7. Watch for and respond to nonverbal cues that

indicate women students' readiness to participate

in class.

8. Use the same tone of voice when talking to women as

with men.

9. Ensure that women are not squeezed out by male

classmates from viewing a laboratory demonstration

or engaging in other group activities.

10. Assume an attentive posture when responding to

women's questions or listening to their comments.

11. Ask a colleague to visit your classroom and

observe; watching for inadvertent gender-specific

behavior on your part.

REFERENCES

1. from Relations With Industry Division of ASEE

Newsletter, Fall, 1988 "Startling Statements"

2. for example, see C. Benlow and J. Stanley, Science

Dec. 12, 1980, "Math Abilities of Gifted Children"

3. for example, see the "Armstong Report" by Jane M.

Armstrong, "A National Assessment of Achievement

and Participation of Women in Mathematics" for

National Institute for Education, 1977

4. Chicago Sun-Times 28 Dec. 1987 p. 23 "When women

can't get a word in edgewise" and Discover,

aproximately Winter 1985-86

5. Erik H. Erikson, Ch. 6 in CHILDHOOD AND SOCIETY 2nd

Edition, W.W. Norton New York 1964

6. Roberta M. Hall, "The Classroom Climate: A Chilly

One for Women" Report from the Project on the

Status and Education of Women sponsored by the

Association of American Colleges Feb. 1982

7. Theresa Johnston reporting at the "You Can Make a

Difference Conference" on a network established at

Stanford to encourage undergraduate women to

persevere in their science and engineering studies.

8. Robert P. Morgan, "Educating Scientists and

Engineers: The View From OTA" Engineering

Education 79 [1] 1989

U.S. GOVERNMENT PRINTING OFFICE: 1991 — 31 3- 89 1' It0't96

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National Educators Workshop: Update '90

Standard Experiments in Engineering Materials Science and Technology

5. AUTHOR(S)

Jonice S. Harris and James A. Jacobs

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U.S. DEPARTMENT OF COMMERCE

NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY

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in Gaithersburg, Maryland, November 13-15, 1990. The workshop theme was

strengthening materials education. Material in this publication can serve

as a valuable guide to faculty who are interested in useful experiments for

their students. There was a blend of experiments on new materials and

traditional materials. Uses of computers in MS&E, experimental design and

an approach to systematic materials are among the topics presented.

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