U.S. Department of Energy

Office of FreedomCAR and Vehicle Technologies

1000 Independence Avenue S.W.

Washington, DC 20585-0121

FY 2004

Progress Report for High Strength Weight Reduction

Materials

Energy Efficiency and Renewable Energy

Office of FreedomCAR and Vehicle Technologies

Advanced Materials Technologies

Edward Wall Program Manager, OFCVT

Rogelio Sullivan Advanced Materials Technologies Team Leader

Sidney Diamond Technology Development Area Specialist

April 2005

High Strength Weight Reduction Materials FY 2004 Progress Report 

iii

CONTENTS 

1 INTRODUCTION ............................................................................................................................. 1 

2 MATERIALS DEVELOPMENT ...................................................................................................... 7

A Integrated Approach for Development of Energy-Efficient Steel Components for 

Heavy Vehicle and Transportation Applications......................................................................... 7 

3 MATERIALS PROCESSING TECHNOLOGIES ............................................................................ 19 

A Oxidative Stabilization of PAN Fiber Precursor ......................................................................... 19 

B Wrought Magnesium Alloy/Process Development ..................................................................... 25 

C Equal Channel Angular Extrusion of Soft Ferromagnetic Materials........................................... 33 

D Equal Channel Angular Extrusion Processing of Alloys for 

Improved Mechanical Properties................................................................................................. 39 

E Development of an Advanced Squeeze Casting Process for the Production of 

High-Integrity Truck Components .............................................................................................. 49 

F Thermomechanical Processing of Ti and Ti-6Al-4V Sheet and Plate......................................... 53 

4 ENABLING TECHNOLOGIES........................................................................................................ 61 

A Improved Friction Tests for Engine Materials............................................................................. 61

B Laser Glazing of Railroad Rails to Reduce Friction.................................................................... 66 

C Laser Texturing of Materials ....................................................................................................... 71 

D Joining of Advanced Materials by Plastic Deformation.............................................................. 77 

E Friction Stir Joining and Processing of Advanced Materials Including 

Metal Matrix Composites ............................................................................................................ 85 

F Friction-Stir–Joined Aluminum Sheet Materials for Heavy Vehicle 

Cab Structures ............................................................................................................................. 95 

G Friction Stir Welding and Processing of Advanced Materials .................................................... 101 

H Basic Studies of Ultrasonic Welding for Advanced Transportation Systems ............................. 109 

I Attachment Techniques for Heavy Truck Composite Chassis Members.................................... 119 

J Rapid, Low-Cost Tooling Development ..................................................................................... 129 

K Inventory of Heavy-duty Truck Lightweighting Candidates....................................................... 35 

L Truck-to-Auto Technology Transfer for Lightweight Materials ................................................. 141 

5 LIGHTWEIGHT VEHICLE STRUCTURES ................................................................................... 143 

A Lightweight Stainless Steel Bus Frame―Phase III..................................................................... 143 

B Stainless Steel Bus Structure—Manufacturing Cost Analysis .................................................... 149 

C Side Impact Analysis of a Lightweight Stainless Steel Bus Structure ........................................ 153 

D New-Generation Frame for Pickup/Sport Utility Vehicle Application ....................................... 159 

E Lightweight Trailer—Liburndas Project ..................................................................................... 163 

6 APPLICATION OF INNOVATIVE MATERIALS.......................................................................... 169 

A Advanced Materials for Friction Brakes ..................................................................................... 169 

B Advanced Composite Structural Cab Components ..................................................................... 175 

C Advanced Composite Structural Chassis Components................................................................ 181 

D Carbon Fiber SMC for Class 8 Vehicle Hoods ........................................................................... 185 

E Advanced Composite Support Structures.................................................................................... 189

F Hybrid Composite Materials for Weight-Critical Structures....................................................... 199 

G Application of Carbon Fiber for Large Structural Components.................................................. 203 
FY 2004 Progress Report High Strength Weight Reduction Materials 

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High Strength Weight Reduction Materials FY 2004 Progress Report 

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1. INTRODUCTION 

As a major component of the U.S. Department of Energy’s (DOE’s) Office of FreedomCAR and Vehicle 

Technologies (OFCVT), the High-Strength Weight Reduction (HSWR) Materials Technology Development 

Area seeks to reduce parasitic energy losses due to the weight of heavy vehicles without reducing vehicle 

functionality, durability, reliability, or safety and to do so cost-effectively. The development area is focused 

on the development of materials and materials processing technologies that can contribute to weight 

reduction. In addition, it is recognized that improved materials may enable the implementation of other 

technologies that can further improve the fuel efficiency of the vehicles. Through many of its technology 

development programs, DOE supports the government/industry 21st Century Truck Partnership. 

The specific goals of the HSWR Materials Technology Development Area are 

• By 2010, reduce the weight of an unloaded tractor-trailer combination from the current 23,000 

pounds to 18,000 pounds, a 22% reduction in weight. 

• By 2010, develop and validate advanced material technologies needed to meet OFCVT goals. 

• Enable significant reductions in the weight of other classes of heavy vehicles (10–33% reduction 

in vehicle weight, depending on performance requirements and duty cycles). 

• Develop materials that exhibit performance, durability, reliability, and safety characteristics 

comparable to those of conventional vehicle materials and that are cost-competitive on a lifecycle basis. 

• Be consistent with the materials regulation requirements to maintain environmental 

responsibility. 

To reach the stated goals, the HSWR Materials Technology Development Area has been developing a 

broad spectrum of advanced materials technologies that can be applied to a wide array of body, chassis, and 

suspension components. The research required to develop these technologies is too high-risk to be pursued 

independently by the heavy vehicle industry because of substantial return-on-investment uncertainties. 

Research is focused on overcoming barriers to the widespread introduction of lightweight materials in the 

heavy vehicle industry. Major barriers exist in the following areas: cost; design and simulation technologies; 

manufacturability; prototyping and tooling; joining and assembly; and maintenance, repair, durability, and 

recycling. Priority materials include advanced high-strength steels, aluminum, magnesium, titanium, and 

composites such as metal matrix materials and glass- and carbon-fiber-reinforced thermosets and 

thermoplastics. 

Research and development (R&D) activities are being conducted through a variety of contractual 

mechanisms, including cooperative research and development agreements (CRADAs), university grants, 

R&D subcontracts, and directed research. Research partners include heavy vehicle manufacturers (including 

member companies of the 21st Century Truck Partnership), first-tier and materials suppliers, national 

laboratories, and other non-profit technology organizations. Laboratories include Argonne National 

Laboratory (ANL), Idaho National Engineering and Environmental Laboratory (INEEL), Los Alamos 

National Laboratory (LANL), Oak Ridge National Laboratory (ORNL), and Pacific Northwest National 

Laboratory (PNNL). Research is coordinated with various organizations―both government and private―as 

shown in the following table. 
FY 2004 Progress Report High Strength Weight Reduction Materials 

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Research Coordination 

Technology area Organization 

Production and fabrication of aluminum The Aluminum Association, DOE-Industrial 

Technologies Program (ITP), Natural Resources of 

Canada (NRCAN), Automotive Lightweighting 

Materials (ALM) Technology Development Area 

Production and fabrication of magnesium International Magnesium Association, NRCAN, 

ALM Technology Development Area 

Fabrication of steel and cast iron American Iron and Steel Institute, the Auto/Steel 

Partnership, ALM Technology Development Area 

Fundamental materials research DOE Office of Energy Research, National Science 

Foundation 

High-volume composite processing Department of Commerce—National Institute of 

Standards and Technology’s Advanced Technology 

Program, ALM Technology Development Area 

Materials research for defense applications Department of Defense 

Materials research for space applications National Aeronautics and Space Administration 

Crashworthiness Department of Transportation, ALM Technology 

Development Area 

International vehicle material R&D International Energy Association 

Production and fabrication of titanium The International Titanium Association, ALM 

Technology Development Area 

Production and fabrication of composites American Plastics Council 

FY 2004 Accomplishments 

Carbon-fiber-reinforced polymer composites have a great potential to reduce the weight of heavy 

vehicles. However, a number of technical and economic barriers prevent their widespread implementation. 

The National Composites Center is leading a team focused on enhancing the rapid implementation of 

lightweight composite materials in Class 7/Class 8 vehicles via the development of advanced composite 

support structures, specifically lateral braces. Mass reductions are targeted for 50%. 

The effort is focused in four areas: modeling, prototyping, molding, and materials characterization. 

Integration of progressive failure analysis using the Genoa software has successfully predicted fatigue 

behavior and elastic constants of test composite materials. In addition, the Genesis software was used to 

successfully develop an optimized design based on weight savings, cost, and manufacturing. A prototype 

lateral brace was successfully designed and fabricated by resin transfer molding and aluminum tooling in less 

than 4 weeks. 

A collaborative effort between ORNL and PNNL is focused on overcoming the technical issues 

associated with joining composite materials in heavy vehicles. The project supports the industry-led effort to 

develop advanced composite support structures, including chassis lateral braces and primary beams for Class 

7 and 8 vehicles (Figure 1). The initial focus of research is development and validation of one or more joint 

designs for a composite structural member attached to a metal member that together satisfy the truck chassis 

structural requirements both economically and reliably and with requisite durability. 
High Strength Weight Reduction Materials FY 2004 Progress Report 

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The multi-pronged approach includes evaluating a variety of 

hole fabrication techniques and their effects on subsequent 

performance (Figure 2); developing methods for detection of 

flaws and damage development during testing; static and fatigue 

testing under various environmental conditions; analyzing the 

effects of pre-load and bolt torque; and developing models for 

predicting the performance of joints. The results will be used to 

develop the first prototype composite component and joint for 

durability track testing in the latter part of 2005. 

Selective reinforcement of large truck cab components with 

higher-stiffness carbon fibers has the potential to reduce both 

cost and weight simultaneously while maintaining structural 

functionality. PNNL is leading a collaborative project to develop 

robust methods of forming glass and carbon fiber materials 

together, while meeting Class A surface finish requirements and 

meeting thermal and structural performance requirements. A 

series of factors associated with optimizing details of the process 

technology are being addressed, and the CRADA 

partner is developing an approach to molding fullscale parts that will ultimately be tested in over-theroad trials. To date, the team has been successful in 

molding structural carbon fiber Class A components 

with a cost-effective hybrid fiber system that has 

demonstrated significant structural performance in 

fatigue and impact tests (Figure 3). In addition, it 

has achieved molding of very thin section panels, 

which resulted in attractive weight savings. 

Magnesium alloys that have high specific 

strength (strength per unit of mass) are attractive 

materials for weight reduction. Presently, most 

magnesium use is limited to die-cast parts. Wrought 

magnesium alloys hold great promise for use in such 

components as hoods and doors. However, the need 

for a large number of processing steps and 

associated lengthy annealing times contributes to the 

high cost of sheet materials and presents one of the 

greatest barriers to the application of magnesium in 

these components. Researchers at ORNL, in 

collaboration with industry and universities, are 

applying infrared processing technology to reduce 

this barrier. A successful demonstration run made at 

a commercial rolling mill equipped with a bank of 

infrared lamps (Figure 4) produced materials with 

properties identical to those of materials produced 

with conventional techniques, but with much shorter 

annealing times and the potential for considerable 

cost savings. Future efforts will attempt to 

incorporate this technology with continuous twin 

roll casting to further reduce costs. 

Figure 1. Optimized geometry for lateral 

brace smoothed and drafted for 

manufacturability. 

0

20

40

60

80

100

120

100 1,000 10,000 100,000 1,000,000 10,000,000

Number of cycles to failure, Nf

Maximum stress level (MPa)

Forstner bit 

laser cut

water jet cut

punched

Figure 2. Fatigue testing results for specimens with holes 

fabricated with different methods. 

Figure 3. Resin system allowing excellent impact energy. 
FY 2004 Progress Report High Strength Weight Reduction Materials 

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Figure 4. Infrared lamp rolling mill at Manufacturing Sciences, Inc., and close-up of magnesium alloy 

sheet exiting the roll gap. 

As a result of a competitive solicitation, Heil Trailer International 

is working on a project to reduce the weight of an aluminum semitrailer tanker by 20% through innovative design and the assimilation 

of composite materials into select components. Excellent progress has 

been made on the vessel design and finite element analysis Figure 5). 

Analysis, testing, and manufacturing studies have been completed 

successfully for the vessel and for the run gear/ fifth 

wheel/bumper/underride. It is anticipated that the first full-scale 

prototype will be completed in early 2005. 

Future Direction 

The HSWR Materials Technology Development Area, for the 

most part, has addressed the near- and intermediate-term energy efficiency and safety technical needs of the 

heavy-duty transport sector (primarily class 7 and 8 trucks) in conjunction with the original equipment 

manufacturers and their suppliers. Metals and their alloys still dominate the material usage in these arenas, 

but over the longer term, composites of many types are expected to receive wider and significant applications. 

The makeup of the research portfolio of this technology development area reflects the current industry needs 

and these future expectations. 

As noted last year, several materials thrust areas have been identified, and exploratory efforts have been 

initiated within them. They are 

1. Advanced joining technologies 

2. Titanium use in heavy-duty structural and component applications 

3. Advanced surface modification technologies to tailor friction and wear characteristics and other surfacesensitive properties of materials. 

In area 1, advanced joining, DOE seeks to develop effective joining technologies that can enable the 

increased use of attractive advanced materials such as metal matrix composites without the severe alteration 

of microstructure and degradation of properties that are attendant upon conventional joining methods. The 

latter generally involve heating the materials adjacent to the joint into the liquid state. This technique results 

in significant phase redistribution, among other modifications that are deleterious to the properties of the 

resulting joint. Several promising joining techniques are in the early phases of evaluation to determine if they 

Figure 5. New-concept petroleum 

trailer 
High Strength Weight Reduction Materials FY 2004 Progress Report 

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can achieve the desired technical results. Economic assessment will follow to determine their cost 

competitiveness. 

In area 2, vigorous efforts are under way around the world that may result in the delivery of titanium 

feedstock at considerably lower costs than have prevailed up to this time. Anticipating this achievement, DOE 

has initiated activities to identify and develop applications of titanium and titanium alloys in various 

structural, engine, and transmission components for heavy vehicles because of their attractive lightweighting, 

high-strength, and high-temperature characteristics. In some of these applications, the significantly lower 

thermal conductivity of titanium may be an additional advantage for certain components. 

In area 3, advanced surface modification, a number of innovative technologies have been identified that 

can significantly reduce the friction coefficients and wear rates of many engine and transmission components 

of heavy vehicles. These can contribute to appreciable increases in the energy efficiency of the vehicles. In 

addition, optimizing lubricant–surface interaction through formulation modification may enable a total 

increase in energy efficiency of up to 5% in addition to improvements that may be gained in the combustion 

process. These technologies have been ranked in terms of their projected relative salubrious effects and are 

currently being systematically characterized and tested. Data from this work are being prepared for 

presentation via oral presentations at professional society meetings and in published papers. 

It is anticipated that collaborative efforts with the Automotive Lightweighting Materials Technology 

Development Area will be continued so that energy-efficient technologies may be developed expeditiously 

without duplication and introduced into both the heavy-duty and light-duty sectors to maximize the impact on 

reducing fuel consumption. The conventional near-term and intermediate-term R&D activities performed in 

conjunction with DOE’s industrial partners will, however, continue to make up the bulk of the project 

portfolio, with a modest number of projects of longer-term and more speculative nature. 

It is interesting and probably significant to note that just when an experienced , knowledgeable 

practitioner in the field of technology conception and development feels that he has seen all the major 

advances that he might reasonably expect to encounter, his superbly motivated technical colleagues, young 

and old alike, discover and share new and remarkable technologies that promise greater efficiency gains, 

improved properties, and even lower costs than the conventional materials of current use. This wonderfully 

innovative and exhilarating process is more than influential enough to keep old workhorses in harness, vying 

with and eventually winning over a harried and unreceptive user public and a generally otherwise directed 

political bureaucracy. 

Sidney Diamond 

Technology Development Area Specialist 

Office of FreedomCAR and Vehicle 

 Technologies 

Energy Efficiency and Renewable Energy 
FY 2004 Progress Report High Strength Weight Reduction Materials 

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High Strength Weight Reduction Materials FY 2004 Progress Report 

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2. MATERIALS DEVELOPMENT 

A. Integrated Approach for Development of Energy-Efficient Steel Components 

for Heavy Vehicle and Transportation Applications 

Co-Principal Investigator: Leo Chuzhoy 

Caterpillar, Inc. 

P.O. Box 1875, Peoria, IL 61656-1875 

(309) 578-6621; fax: (309) 578-2953; e-mail: chuzhoy_leo@cat.com 

Co-Principal Investigator: Gerard Ludtka 

Oak Ridge National Laboratory 

P.O. Box 2008, Oak Ridge, TN 37831-6064 

(865) 574-5098; fax: (865) 574-3940; e-mail: ludtkagm1@ornl.gov 

Co-Principal Investigator: Clyde Briant 

Brown University 

Box D, Brown University, Providence, RI 02912-D 

(401) 863-1422; fax: 401-863-1157; e-mail : clyde_briant@brown.edu 

Technology Development Area Specialist: Sidney Diamond 

(202) 586-8032; fax: (202) 586-1600; e-mail: sid.diamond@ee.doe.gov 

Field Technical Manager: Philip S. Sklad 

(865) 574-5069; fax: (865) 576-4963; e-mail: skladps@ornl.gov 

Contractor: Caterpillar Inc. 

Contract No.: DE-AC05-00OR22726

Objective 

• Develop methods and tools to achieve energy-efficient and environmentally benign steel components. 

• Develop microstructure-level (often called mesoscale) simulation tools to capture the formation and influence 

of non-homogeneous (real-life) microstructures in steel processing. The tools will be used to understand and 

predict microstructure evolution during processing and ultimately to predict the resultant component performance. 

• Use the information from the simulations to design steel microstructures and develop process roadmaps. 

• Demonstrate the developed techniques on a pilot project at Caterpillar involving a defined structural component, namely a track roller shaft, that represents a steel component with high production volume that can potentially benefit from microstructure-level improvements. 

Approach 

• Develop microstructure-level models to accurately predict the evolution and behavior of steel microstructures 

during component processing and performance. 

• Characterize thermomechanical properties of microstructural constituents as a function of temperature and 

composition for exact chemistries. 
FY 2004 Progress Report High Strength Weight Reduction Materials 

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• Develop the tools to assess required environmental resources and integrate them into the modeling simulation 

endeavor. 

Accomplishments 

• Acquired 1045 and 15V45 steel material. 

• Distributed the two alloys to be investigated to the project team members so that machining of the test specimens required for the tasks of microstructural characterization, machining experiments, and determination of 

strain-rate-dependent mechanical properties could be initiated during the first quarter of FY 2004. 

• Acquired two track roller shafts and distributed segments of these to the project team members. 

• Completed machining testing (round 1). 

• Completed mechanical testing for 1045. 

• Assessed resources for machining of track roller shafts. 

• Assessed resources for processing of track roller shafts. 

• Characterized ferrite and pearlite for the 1045 alloy. 

• Received three ultra-pure materials from CRIM. 

• Initiated simulation of heat treatment and machining operations. 

• Compared machining model predictions for different microstructures and machining parameters with experimental results from precision-controlled machining experiments. 

• Demonstrated that the machining model qualitatively predicts the adiabatic shear band formation and chip morphology observed in the machining chips obtained from the machining experiments. 

Future Direction 

• Develop and demonstrate a microstructure-level model incorporating phase transformation kinetics, but without 

chemical and microstructural inhomogeneities (to be implemented in year 3), for the heat treatment processes 

used by Caterpillar for the SAE 1045 and SAE 15V45 steel alloys (9/2005). 

• For both types of steel, produce in the laboratory the microstructures that evolve during these heat treatment 

processes and thoroughly characterize them to provide quantitative input data for the heat treatment simulation 

models. 

• Perform all mechanical tests on these microstructures that are required for inputs and validation of the heat 

treatment models. 

• Characterize the influence of mill thermomechanical processing (TMP) variables on deformation and recrystallization behavior for incorporation into coupled polycrystalline and recrystallization models developed during 

years 2 and 3 of this project. 

• Initiate development of coupled polycrystalline plasticity and recrystallization models to simulate mill TMP 

variable effects on austenite grain evolution behavior and characteristics. 

Introduction 

Product cost and performance are two major 

pressures influencing the acceptance of energysaving technologies by manufacturers, suppliers, and 

users in the heavy vehicle and transportation industries. Energy cost has become a significant portion 

of total product cost for steel applications. Major 

reductions in energy use are potentially achievable 

for the transportation and heavy vehicle industries 

through development and optimization of costeffective fabrication processes and enhanced product 

performance. The key enabling technologies to 

achieve these benefits are improved materials and 
High Strength Weight Reduction Materials FY 2004 Progress Report 

9

realistic, microstructure-level simulations to predict 

manufacturability and life-cycle performance. Over 

the past two decades, steel mills and forge shops 

have successfully implemented numerous energyefficient processes. The next logical step is to focus 

on the development of steel microstructures that are 

produced in such a way that they are energy efficient 

and environmentally benign over the entire manufacturing cycle. 

Structural materials used in critical steel components of machines have evolved to the point where 

further improvements in performance can be 

achieved only through a fundamental understanding 

of the mechanisms driving material behavior during 

processing and service. Microstructural elements 

such as grain size, inclusion and precipitate distributions, and chemistry control the performance of engineering materials. Variation in these microstructural elements leads to variation in such critical 

properties as fatigue life, toughness, and wear resistance. Therefore, understanding and developing the 

capability to control the formation of steel microstructures, and predicting their functional and environmental performance, are critical to moving the 

industry closer to its energy-efficiency, resourceefficiency, and pollution-prevention goals. The full 

realization of these benefits, however, requires a 

design tool that optimizes the micro-structure with 

respect to the mechanical and environmental performance throughout the life cycle of a particular 

steel component. 

To apply an integrated approach to development 

of energy-efficient steel components, the development of three major areas of research needs to be 

completed: 

• Micro-structure-level models to accurately predict 

evolution and behavior of steel microstructures during component processing and performance 

• thermomechanical properties of microstructural constituents as a function of temperature and composition for exact chemistries 

• tools to assess required environmental resources 

This project addresses activities required for the 

first of these three areas. The second and third tasks 

are either supported by current funding through the 

National Science Foundation (NSF) or are expected 

to be funded through the DOE Initiative for Proliferation Prevention. Through these integrated efforts, 

a design tool will be developed that optimizes the 

microstructure, manufacturability, and performance 

of components with respect to the mechanical and 

environmental performance required throughout the 

components’ life cycles. The overall benefit of this 

research will be the development and demonstration 

of a design methodology that will enable the domestic transportation and heavy vehicle industries to 

compete effectively in future worldwide markets 

through improved product performance and energy 

savings. Furthermore, the proposed design tool can 

be extended to other materials—i.e., cast iron, aluminum, titanium, magnesium, nickel-based alloys, 

ceramics, and composites—thus impacting virtually 

all industries. 

In addition to the significant energy and cost 

savings benefits that the transportation and steel industries will realize from microstructure-level modeling, virtually all industries will be impacted. 

Examples include aerospace (engines, transmissions, 

structural), marine (engines and drives), agricultural 

and construction equipment, oil and chemical processing (pumps and gear boxes), military vehicles, 

mining machinery, appliances (compressors, motors, 

gear boxes, shafts), power tools, and automotive 

aftermarket. 

Project Deliverables

The deliverables for the project will be 

• Microstructure-level methods for simulating the 

manufacturing cycle of steel products, coupled with 

material performance computations (Tasks 1, 2, 

and 3) 

• A specific chemical composition and processing map 

for a 1500-series steel and a microalloyed steel suitable for the application under consideration (Task 4) 

• A determination of the energy and environmental 

resources required to produce the selected steel component using at least two steels and processing 

schemes (Task 4) 

Project tasks will focus on three critical areas in 

the development of these models: heat treatment 

processing, machining, and materials performance in 

specific applications. These three processes have 

been chosen because they are critical steps toward 

the goal of developing a specific steel for a particular application, with a heavy reliance on modeling 

and with energy requirements optimized as an integral part of the development process. Casting and 
FY 2004 Progress Report High Strength Weight Reduction Materials 

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forming processing have been modeled under other 

programs, and Caterpillar has shown successful application and commercialization of these models. 

These existing models will be used, along with the 

heat treatment, machining, and specific applications 

models described in this report, to complete a suite 

of models for the manufacture of microalloyed 

steels. 

To accomplish the project objectives, a multidisciplinary team consisting of a national laboratory, 

a university, and a steel end-user has been assembled. The team will be supported by an international 

research institute for material characterization and 

by experts in environmental impact assessment. 

Technical Tasks 

Task 1: Heat Treating Process 

This task will quantify the influence of chemical 

and microstructural inhomogeneities in the austenite 

phase on the final heat-treatment response. The microstructure-level models incorporating phase transformation kinetics, polycrystalline plasticity, and 

recrystallization dynamics will be developed collaboratively by the Oak Ridge National Laboratory 

(ORNL), Brown University, and Caterpillar. Validation will be accomplished using the unique experimental capabilities and expertise at ORNL for 

conducting kinetic and metallurgical characterization and using Caterpillar’s capability to produce 

heat-treated specimens in precisely specified and 

controlled conditions. The modeling effort will draw 

on the programs at Brown and Caterpillar that have 

developed microstructural modeling capabilities. 

The coupled mesoscale deformation and recrystallization models developed cooperatively by the 

three team members will be implemented to study 

the influence of mill TMP variables and mesoscale 

composition variation on the grain size, grain-size 

distribution, and austenite grain-boundary character 

prior to the decomposition of austenite. The coupled 

deformation and recrystallization models will be 

used to predict the evolution of austenite grain structure and grain-boundary character distribution during the TMP steps involved during secondary 

fabrication. The output of these simulations will feed 

directly into an austenite decomposition code that 

predicts phase transformation during the heattreatment operation. 

Task 2: Machining Processing 

A microstructure-level model will be applied to 

machining simulation of steels to determine their 

machinability and material state after TMP. The 

model will consist of four main elements integrated 

into the finite element structure: microstructure 

simulation, material modeling, material characterization, and material flow and fracture. The microstructure simulation module will assemble individual 

constituents into a composite material based on microstructural composition, grain size, and grain-size 

distribution. This information, along with residual 

stress predictions for individual grains, will be obtained from Task 1. 

The material modeling module will account for 

the response of each constituent to high strains, 

strain rates, temperature, damage, and effects of 

loading paths associated with machining. The material characterization module will provide the material modeling module with parameters to define 

strain rate and temperature-dependent behavior of 

individual phases. The material flow and fracture 

module will periodically examine each grain for 

damage, locate deformed grain boundaries, and generate new boundaries. This module will compute 

stress, strain, temperature, and damage in each phase 

based on initial microstructure, material state, tool 

geometry, and process parameters. 

A concerted effort will be made to review and 

leverage all current developments in this materials 

and process-simulation field that is the scope of this 

project. Microstructure, residual stress, and cutting 

force measurements obtained by various research 

groups (e.g., ongoing research at Purdue University 

by S. Chandrasekar) will be used for model development and validation. 

Task 2 and Task 1 will be augmented by a parallel project among Caterpillar, Brown, and the Central Research Institute for Materials in St. 

Petersburg, Russia, in which a detailed examination 

is being performed of the relationship between composition, microstructure, and mechanical properties 

of steels of highly controlled purity and microstructure. 
High Strength Weight Reduction Materials FY 2004 Progress Report 

11

Task 3: Material Performance and Application 

After the materials have been processed and machined, the next concern is to predict their subsequent performance, that is, their strength and 

resistance to fracture. Thus the models for material 

performance need to be developed and validated. 

These models will explicitly include such microstructural elements as inclusions, precipitates, and 

grain boundaries and will be based on several finite 

element methods developed at Brown University. 

The first step will be to develop predictive models of damage initiation by either cracking or 

debonding of second-phase inclusions and precipitates. This modeling will be performed using a cohesive surface framework to model the interface 

between the inclusion (or precipitate) and the matrix 

and to model the initiation and growth of cracks 

within the second phase. Parameter studies will be 

undertaken to identify measurable and controllable 

features of the microstructure that are key for damage initiation. The results for damage initiation will 

be used in a modified Gurson model1

 to predict material performance. Of initial interest will be the prediction of performance in a suite of test specimens 

that give rise to different plastic strain-stress triaxiality histories so that the predictive capabilities of this 

modeling can be compared with experimental observations. Three-dimensional calculations of more 

complex geometries will also be performed to demonstrate the capability of predicting failure in component-like geometries. 

At the same time, experiments will be performed 

using specimens that have been carefully designed 

so that their mechanical response can be fully modeled. These specimens will be pulled in tension to 

various loads and then sectioned so that the microstructure can be observed. Particular attention will 

be given to identifying the second-phase particles 

that are present in the material and participate in 

crack nucleation. 

Task 4: Pilot Project 

The proposed research will focus on track roller 

shafts as a pilot component. The track roller shaft 

represents a component with high-productionvolume steel at Caterpillar. It transmits the weight of 

a tractor through the undercarriage (see Figure 1) 

and can be produced from either conventional steel 

(heat-treated for strength) or microstructurally improved microalloy steel. The use of microalloy steel 

has been demonstrated to reduce the cost and environmental impact of the heat-treatment stage, making it currently the preferred material in regions with 

high energy costs (such as Japan). The use of microstructure-level simulation and sustainability metrics 

to evaluate and optimize its environmental performance throughout the entire life cycle may lead to further improvements and serve as an example of the 

effectiveness of integrated methodology. 

Figure 1. The tractor undercarriage receives the weight of 

the tractor (a) through a track roller shaft (b). 

First, the entire life cycle of a track roller shaft 

made with a conventional 1500-series steel will be 

modeled, and the environmental resources needed 

throughout a component life cycle will be assessed. 

The chemical composition and processing map will 

be optimized to minimize the environmental impact 

and cost of the component. Then the modeling process will be repeated for using a microalloyed steel, 

which will be optimized for the same requirements. 

This study aims to provide optimum chemical compositions and processing road maps for a track roller 

shaft made with a conventional 1500-series steel and 

a microalloyed steel. In addition, the pilot project 

will quantify energy and environmental resources 

required for the entire life cycle of a track roller 

shaft made with the steels and processes mentioned 

above. 

A critical component in this task, as well as in 

the others, will be the quantification of energy use 

during production of a part, and optimization of the 

proposed process to minimize energy usage. Caterpillar has already established a project called 

“Bridges to Sustainability,” and NSF interns at 
FY 2004 Progress Report High Strength Weight Reduction Materials 

12

Brown worked in the summer of 2003 on this project. The tools developed by the NSF-sponsored project will be applied in this project to assess energy 

usage and savings for the processes used here. 

Current Period Progress

Microstructure-Level Modeling of Machining 

At the microstructural level, steel can no longer 

be treated as a homogeneous material. Different 

types of microstructures due to chemical composition and heat treatment cause the material to appear 

as a composite on the microscale. Thus material heterogeneity must be considered. Different microstructures—namely ferrite, pearlite, martensite, bainite, 

and tempered martensite—as well as inclusions, porosity, and precipitates, will have combined effects 

on the material behavior. By looking at deformation 

at the microstructural level, much detailed information can be obtained. Thus microstructure grains or 

colonies will be built into the model explicitly. A 

plasticity model based on dislocation interaction and 

evolution called the BCJ model will be used to describe the single-phase behavior of each microstructure. Owing to the nature of local high temperatures 

caused by mechanical deformation and high strain 

rate near the contact between tool and part, a material model should also be a function of temperature 

and strain rate. 

Since material behavior is a function of temperature, the thermal field also turns out to be very important for this current simulation. A coupled 

thermal-mechanical scheme is adopted in the analysis methodology. It shows significant impact on chip 

formation. Friction-generated heat is assumed to be 

important traditionally; therefore friction-generated 

heat and heat transferred between the contact interfaces of the tool and part are also included in the 

model. 

Machining test modeling input. Several orthogonal cutting tests have been done on different 

microstructures generated by different heat treatment 

operations. Microstructures before the machining 

operation have been recorded as modeling input. 

Microstructures in the chips and the machined surface after machining have also been checked for 

validation purposes. (These results were shown in 

this project’s prior semiannual report.) 

Microstructure evolution results. During the 

machining operation, individual microstructure 

grains and colonies will change significantly as a 

result of large shear deformation and even be broken 

into smaller grains or colony size. This microstructural change will affect the cutting process and the 

material properties after machining. The simulation 

results show steel with a ferrite/pearlite microstructure. The volume fraction of ferrite is about 30%, 

and the rest is pearlite. In an optical micrograph image, pearlite colonies are shown in black and ferrite 

grains are shown in white. Cutting was simulated for 

two speeds, 2m/s and 3.33m/s. Results for microstructure in the chip and the machining part from the 

simulation and test are shown in Figure 2 for the 

first speed. In the chip, grains are deformed in the 

direction of shear localization. Similar patterns of 

this deformation can be seen in both the simulation 

and the actual machining test. On the machined surface of the part, grains are separated by the cutting 

process and form a thin-layer shear zone. The simulation shows good agreement with testing. 

Chip morphology. Different chip shapes can have 

an impact on the machining operation. Figures 2 and 

3 show the chip shape under two different cutting 

speeds, for simulation and test. For the higher cutting speed, the chip appears to be more segmented. 

Also, chip thickness is reduced compared with the 

low cutting speed. Those changes are mainly due to 

different shear localization behaviors at the different 

cutting speeds. At high speed, the temperature increases locally because of the short transit time, 

which causes large local softening and a segmented 

chip. At low speed, heat generated by deformation 

will spread out and cause a more uniform temperature field. At the same time, the local temperature 

cannot go very high. A larger amount of material is 

softened to form the chip; this will cause the chip 

thickness to increase. 

Temperature field. Material response during 

machining is highly dependent on the temperature. 

The temperature field is also very important for 

cooling during machining. In some cases, material 

can become welded onto the tool, a behavior that 

can be related to the temperature field. Simulation 

results for the temperature field are shown in Figure 4 for the two different cutting speeds. It can 
High Strength Weight Reduction Materials FY 2004 Progress Report 

13

Figure 2. Microstructure evolution during cutting at 

2 m/s: (top) simulation shows microstructure in chip and 

part; (middle) microstructure in chip after testing; (bottom) microstructure for part after testing. 

Figure 3. Microstructure evolution during cutting at 

3.33 m/s: (top) simulation shows microstructure in chip 

and part; (middle) microstructure in chip after testing; 

(bottom) microstructure for part after testing. 

be seen that the maximum temperature occurs 

slightly above the tool nose. This is normally where 

welding of material onto the tool can occur. For 

high-speed machining, temperature is more localized 

and has a higher maximum value. 
FY 2004 Progress Report High Strength Weight Reduction Materials 

14

Figure 4. Temperature field for two different 

cutting speeds: 2 m/s (top) and 3.33 m/s (bottom). 

By comparison, chip shape is shown in Figure 5 for 

an adiabatic situation. It shows a significant difference from the case with heat conduction. The segmented chip shape shows an indication of adiabatic 

shear band formation. It can be concluded that at this 

cutting speed, heat conduction must be considered. 

Friction heat generation. Friction is another 

source of heat generation. A model was set up to 

account for heat generation by friction and account 

for the heat conduction between tool and part. A 

temperature field is shown in Figure 6 for cases with 

friction-generated heat and without. It can be seen 

that temperature increases directly as a result of the 

friction-generated heat. 

Figure 5. Chip formation for adiabatic condition at a 

cutting speed of 2 m/s. 

Effects on cutting force. Figure 7 shows several 

cutting force predictions and testing results resulting 

from different conditions of cutting speed and friction. 

The cutting force predicted in the simulation 

with a friction coefficient of 1.2 is in good agreement with testing results. In machining operations, 

the friction coefficient can vary from 0.6 to 2.0. 

Here, a constant value is assumed throughout the 

whole cutting time. Higher friction will increase the 

cutting force. At the extreme case of infinite friction, 

the cutting force goes up by about 10% compared 

with the friction coefficient of 1.2. The cutting force 

will also be affected by cutting speed; higher cutting 

speed results in a lower cutting force for the same 

material. 

Conclusions. A simulation model of the machining process at the mesoscale microstructure 

level has been set up. The model includes microstructural features such as grains and colonies. The 

material model is related to dislocation motion and 

interaction. A fully coupled thermal mechanical 

setup gives more realistic thermal field and chip 

formation. This model shows its capabilities in accurate prediction of chip shape, temperature field, and 

cutting force directly based on material microstructure. This simulation tool can also be extended 
High Strength Weight Reduction Materials FY 2004 Progress Report 

15

Figure 6. Temperature field with frictiongenerated heat (top) and without (bottom). 

to simulation of other manufacturing processes fairly 

easily. 

Future work. Currently, material properties 

have been characterized for only two types of microstructures, ferrite and pearlite. More material characterizations are needed; they are already included in 

another parallel material characterization project. A 

proper model for friction is needed for accurate predictions. 

Figure 7. Cutting force vs. distance. 

Development of Microstructure Evolution 

Module Using Cellular Automata 

As the first step in developing a robust microstructure evolution module for simulation of heat 

treatment, a single austenite grain transforming to 

multiple ferrite grains upon cooling was studied using cellular automata (CA) techniques coupled with 

a Monte Carlo approach. The cellular automation 

used in this study has been developed in two dimensions on a square grid, representing an austenite 

grain. The computation domain is one austenite 

grain with an ‘average’ grain size. The general approach is to calculate the total energy for a given cell 

in the austenite phase and the ferrite phase first. 

Then a probability is determined for that given volume to change from austenite to ferrite. The probability is calculated using Boltzmann statistics. 

Initial results (Figure 8) have shown that the CA 

modeling technique can be successfully used for 

phase transformation modeling that will provide information on microstructure evolution. This information can be combined with an MLS model to 

provide explicit microstructure information for material properties calculation in the heat treatment 

simulation. 
FY 2004 Progress Report High Strength Weight Reduction Materials 

16

Figure 8. Initial nuclei site of ferrite in austenite 

grain (top); ferrite grain growth (middle); ferrite 

grains when eutectoid temperature is reached 

(bottom). 

Material responses during quenching of steel.

The most critical issue in modeling heat treatment is 

the multiphase material constitutive relationship on a 

highly heterogeneous material found in a heat treatment process. The traditional approach has been to 

use an elastic-plastic or elastic-viscoplastic model 

based on a liner rule of mixtures (RM) or an average 

material property model. For microscale-level simulation, material properties for each individual phase 

can be accurately described according to the result 

of each individual phase characterized in a parallel 

project. Explicit microstructural descriptions can 

also be obtained from a microstructure evolution 

simulation based on stochastic modeling of microstructure. Using a macro/micro modeling technique, 

material properties for the multiphase structure during heat treatment can be calculated according to the 

MLS model. As an initial step, effective yield 

strength for 1045 steel with different constituent 

fractions of martensite and austenite phases was 

evaluated. These material properties for the martensite and austenite phases are given in Table 1. 

Table 1. Material properties for martensite and austenite 

Phase E(GPa) ν σy@ 

ε=0(MPa)

σy@ 

ε=0.04(MPa) 

Martensite 214 0.3 1550 2339 

Austenite 196 0.3 189 289 

A 2-dimensional finite element model (FEM) 

with random shape and orientation was created for 

the martensite and austenite phases. The mesh for 

31% martensite (dark grey) + 69% austenite (light 

grey) is shown in Figure 9. Periodic boundary conditions were prescribed at the edges by considering (1) 

symmetry along the left and bottom edge, (2) constraint of the nodes on the top edge to exhibit the 

same Y-displacement, and (3) constraint of the rightedge nodes to exhibit the same X-displacement. 

Displacement loading was applied to the right edge. 

The mechanical analysis was performed at room 

temperature using plane stress quadrilateral elements 

in ABAQUS. 

Figure 10 shows the stress-strain plot for different fractions of martensite and austenite. The solid 

line depicts the results from the FEM study, and the 

dotted line represents the yield strength values calculated using the linear RM. Figure 10 shows clearly 

that the composite of martensite and austen- 
High Strength Weight Reduction Materials FY 2004 Progress Report 

17

Figure 9. Finite element mesh. 

Figure 10. Stress-strain plot for different fractions of 

martensite (M) and austenite (A) phases. FEM results are 

represented by the solid line and dotted line shows the 

yield strength calculated using rule of mixtures (RM). 

ite shows considerably lower values of yield 

strength from FEM than the RM values. The difference is significant (200 to 300%) at higher fractions 

of austenite (85% A, 69% A and 50%A). At higher 

fractions of martensite (85% and 69% M), the difference between the yield strength values is around 

50%. This difference decreases at higher fractions of 

martensite, primarily because of the high yield 

strength of 100% martensite compared with 100% 

austenite. 

With this MLS approach to describe each individual phase explicitly, transformation-induced plasticity, a concept generally used in continuum 

models, can be explicitly modeled with great accuracy. The next step would be to incorporate material 

characterization results with the microstructure evolution model to implement an MLS scheme to provide material properties for a heat treatment 

simulation with a macro/micro model approach. 

Integrated heat treat model development.

Heat treatment simulation tool development is a key 

enabling part of the road map for resource-efficient 

steel components, as heat treatment provides the 

necessary material properties for many steel parts 

with great efficiency and minimum resource costs. 

In the case of the track roller shaft, quenching and 

tempering is applied after the forging process. Then 

induction heat treatment is applied again after the 

quenching and tempering process to create material 

properties that meet roller shaft design performance 

requirements. The manufacturing process is completed with a finish grinding after the induction 

process. To provide the final microstructure and 

predict roller shaft performance, an integrated computation method was developed to simulate the 

quenching/tempering process and the following induction hardening process. Microstructure and residual stress predicted from the quenching/tempering 

process were fed into an induction-hardening simulation model as input. The final microstructure, residual stress, and distortion could be predicted after 

the induction hardening process. 

 

Conclusions

This research has successfully accomplished its 

first-year goals. The microstructural characterization 

and mechanical property tasks are proceeding on 

schedule. These efforts have been completed for the 

initial microstructures of the SAE 1045 and 15V45 

steels in support of the heat treatment and machining 

simulation code development activities. In addition, 

the machining tests at two machining speeds for 

both alloys were accomplished. Finally, preliminary 

machining modeling results have been shown to 

qualitatively predict the chip morphology, including 

adiabatic shear band formation, for the as-quenched 

microstructure of the 15V45 steel alloy. 

References

1. A.L. Gurson, “Continuum Theory of Ductile 

Rupture, Void Nucleation and Growth,” Journal of 

Engineering Materials Technology, 99(2) (1977). 
FY 2004 Progress Report High Strength Weight Reduction Materials 

18
High Strength Weight Reduction Materials FY 2004 Progress Report 

19

3. MATERIALS PROCESSING TECHNOLOGIES 

A. Oxidative Stabilization of PAN Fiber Precursor 

Principal Investigator: Felix L. Paulauskas 

Oak Ridge National Laboratory 

Oak Ridge, TN 37831-8048 

(865) 576-3785; fax: (865) 574-8257; e-mail: paulauskasfl@ornl.gov 

Project Manager, Composites: C. David Warren 

Oak Ridge National Laboratory 

P.O. Box 2008, Oak Ridge, TN 37831-6065 

(865) 574-9693; fax: (865) 576-4963; e-mail: warrencd@ornl.gov 

Technology Development Area Specialist: Sidney Diamond 

(202) 586-8032; fax (202) 586-2476; e-mail: sid.diamond@hq.doe.gov 

Field Technical Manager: Philip S. Sklad 

(865) 574-5069; fax:(865) 576-4963; e-mail: skladps@ornl.gov 

Participants 

Terry L. White and Kenneth D. Yarborough, Oak Ridge National Laboratory 

Professor Joseph Spruiell, University of Tennessee 

Daniel Sherman, Atmospheric Glow Technologies 

Contractor: Oak Ridge National Laboratory 

Contract No.: DE-AC05-00OR22725 

Objectives 

• Develop an improved technique for oxidizing carbon fiber precursor with increased line speed, reduced carbon 

fiber cost, and reduced equipment footprint. 

• Verify that produced fiber properties satisfy automotive and heavy vehicle manufacturers’ requirements. 

• Conduct a preliminary evaluation of the cost impact of the new oxidation technique. 

Approach 

• Develop a plasma process for oxidation in an atmospheric-pressure plasma reactor. 

• Develop fiber handling protocols for continuous processing. 

• Conduct parametric studies to correlate processing parameters and fiber properties. 

• Characterize fibers to confirm that they satisfy program requirements. 

Accomplishments 

• Demonstrated the ability to oxidize fiber in atmospheric-pressure plasma in stages equivalent to those used in 

conventional oxidation furnaces. 

• Identified key process parameters and critical operating range and modified the reactor to achieve stable operation in the required parametric space. 
FY 2004 Progress Report High Strength Weight Reduction Materials 

20

• Identified the preferred range of feed gas compositions. 

• Improved dielectric properties monitoring technology and presented a conference paper on that topic. 

Future Direction 

• Continue refining the reactor design and processing protocols to achieve rapid, single-stage fiber oxidation. 

• Develop “pre-stabilization” technique. 

• Develop continuous processing protocols. 

• Conduct parametric studies and fiber characterization to better understand process effects and the processing 

window and to quantify fiber properties. 

• Conduct rate-effect studies and update cost analysis. 

Introduction

The purpose of this project is to investigate and 

develop a plasma processing technique to rapidly 

and inexpensively oxidize a polyacrylonitrile (PAN) 

precursor. Oxidative stabilization is a slow thermal 

process that typically consumes 70% or more of the 

processing time in a conventional carbon fiber conversion line. A rapid oxidation process could dramatically increase the conversion line throughput 

and appreciably lower the fiber cost. A related project has already demonstrated the potential for 

greatly increasing line speed in the carbonization 

and graphitization stages, but the oxidation time 

must be greatly reduced to fully exploit faster carbonization and graphitization. This project intends to 

develop a plasma oxidation module that integrates 

with other advanced fiber processing modules to 

produce inexpensive carbon fiber with properties 

suitable for use by the automotive industry. Critical 

technical criteria include (1) 25 Msi tensile modulus, 

250 ksi ultimate strength, and 1.0% ultimate strain in 

the finished fiber; (2) acceptably uniform properties 

over the length of the fiber tow; (3) repeatable and 

controllable processing; (4) and significant unit cost 

reduction compared with conventional processing. 

Project Deliverable

At the end of this project, we will have demonstrated satisfactory fiber oxidation in a multiple-tow 

plasma oxidation module operating at line speed 

exceeding that typical of conventional carbon fiber 

conversion lines. 

Technical Approach

We are investigating PAN precursor fiber oxidation by “direct exposure” in a nonequilibrium, 

nonthermal plasma at atmospheric pressure, with the 

fiber transported through the plasma. Plasma processing is believed to enhance oxygen diffusion and 

chemistry in the PAN oxidation process. Atmospheric-pressure plasma provides better control over 

the thermal environment and reaction rates than does 

evacuated plasma, in addition to eliminating the 

sealing problems accompanying evacuated plasma 

processing. Various fiber characterization tools and 

instruments are used to conduct parametric studies 

and physical, mechanical, and morphological 

evaluations of the fibers to optimize the process. An 

evacuated plasma reactor is useful for bench-scale 

studies, because it allows a greater degree of manipulation and control over reactive species and related parameters. Early in the project, processing 

tests were conducted in an evacuated plasma reactor, 

and that same reactor is now used for conducting the 

bench-scale parametric studies. 

Atmospheric-Pressure Plasma Processing 

Results

Exposure in plasma at or near atmospheric pressure provides superior thermal control because the 

gas flow should convectively heat or cool the fibers. 

This is deemed particularly important to avoid fiber 

melting from the exothermic reactions associated 

with the PAN cross-linking that occurs during stabilization. However, the mean free path of the chemically reactive species is shorter by orders of 

magnitude than it is in an evacuated environment, 

and this makes it very difficult to find a combination 
High Strength Weight Reduction Materials FY 2004 Progress Report 

21

of process parameters that will oxidize the fibers 

with acceptable residence time. 

Conventional PAN oxidation is typically accomplished in three or four thermal stages (stages 

can be physically separate furnaces or zones in a 

single physical furnace) in air, at temperatures increasing from about 200 to 250°C. In FY 2004, the 

researchers demonstrated the ability to reproduce the 

oxidation advancement in each of the conventional 

furnaces two, three, and four. The virgin PAN is 

chemically fragile; hence we have not yet discovered 

a satisfactory nonthermal processing protocol that 

reproduces the oxidation advancement in the first 

conventional furnace. Subsequent experiments have 

demonstrated the ability to advance the oxidation 

from the beginning of furnace two through the exit 

of furnace three in a single, uninterrupted process. 

These processing results are schematically illustrated in Figure 1. 

Figure 1. Schematic of conventional thermal oxidation 

process and progress in plasma oxidation process. 

A potentially very important discovery was that 

the cores of plasma-oxidized fibers are more chemically stable than those of conventionally processed 

fibers. Figure 2 illustrates the advancement of oxidation and stabilization through a filament crosssection. Most of the fiber must be oxidized, as represented by the outer region, before it can withstand 

carbonization. In thermal oxidation, the outer stabilized and oxidized region grows inward slowly, 

purely by diffusion. However, in plasma oxidation, 

we have observed that oxidation over the filament 

cross-section is much more uniform; and the entire 

fiber becomes highly oxidized at a lower fiber density (fiber density is normally used as an indicator of 

Figure 2. Illustration of advancing oxidation and stabilization through filament cross-section. 

degree of oxidation advancement). This suggests 

that plasma oxidation may allow onset of carbonization at a lower fiber density, a thesis that will be experimentally tested in future work. If carbonization 

can indeed commence at a lower fiber density, this 

could significantly reduce the residence time required for oxidation. 

The researchers have made good progress toward identifying the parameters that most affect the 

oxidation rate and optimizing those parameters 

within the reactor. For patent protection and export 

control reasons, the detailed results are not published, but they are periodically disclosed to the 

relevant program managers in oral briefings. 

Feed Gas Composition

The researchers investigated the effects of 

plasma oxidation with various gas compositions. It 

was confirmed that the chemistry can be quite sensitive to feed gas composition, as illustrated in Figure 3. A wide range of feed gas compositions were 

investigated and the results recorded. Specific compositions and processing parameters are not published for patent protection and export control 

reasons. 

Instrumentation

During this reporting period, the researchers 

continued developing techniques and hardware for 

measuring the fiber dielectric properties over a selected range of oxidation processing conditions. A 

dielectric measurement system, shown schematically 

in Figure 4, was validated. Several temperature 
FY 2004 Progress Report High Strength Weight Reduction Materials 

22 

Figure 3. Plasma with two different feed gas compositions in evacuated plasma reactor. 

Figure 4. Dielectric measurement system schematic. 

control problems were identified and corrected by 

adjusting control and operational parameters, modifying hardware, and changing the PAN cross-section 

in the instrument chamber. A large number of runs 

were conducted with PAN partially oxidized to differing degrees. The real and imaginary parts of the 

dielectric constant correlated well with the degree of 

PAN oxidation. A paper on this topic was presented 

at the 2004 SAMPE Symposium and Exposition in 

Long Beach CA. 

The researchers began creating a dielectric properties database for 3-k and 80-k PAN fiber tows that 

were partially oxidized in varying degrees by conventional means. Plasma-oxidized fiber properties 

can later be compared against this database as a selector for fiber specimens that will be further characterized by more time-consuming spectroscopy 

techniques. 

The researchers need a rapid turnaround technique for indicating oxidation trends, to quickly assess whether various parametric processing trials 

have successfully advanced the oxidation. Density 

measurements are frequently used by fiber manufacturers. In this project, dielectric measurement 

equipment and techniques have been successfully 

developed and validated, and morphology measurements are also used to characterize the fibers. However, density, dielectric, and morphology 

measurements all have turnaround times of hours to 

days because of measurement duration, instrument 

cost and location, required operator skill, and/or instrument time-sharing. The fiber changes color, 

starting from white and successively darkening until 

it turns completely black after it is about 10–20% 

oxidized. Therefore, color is a reasonable progress 

indicator in early oxidation, but another technique is 

needed for the remainder of oxidation. 

The researchers investigated dc electrical resistance measurement as an oxidation progress indicator. The very high tow resistance (1012 – 1015 ohms) 

is beyond the capability of most resistance meters 

and can be accurately measured only under exceedingly well-controlled environmental conditions. A 

high-resistance meter was purchased and tested. The 

PAN fiber must present the most conductive path 

between measurement terminals to achieve accurate 

resistance measurement. Since moisture, and even 

air, can provide a conductive “short,” the researchers 

concluded that dc resistance measurements are too 

unreliable, even with meters rated for ultra-high resistance. The researchers are still searching for a 

good, inexpensive, rapid turnaround technique for 

monitoring the relative oxidation progress. 

Economics

During FY 2004, Kline and Company completed 

a cost study of DOE’s entire carbon fiber development program, estimating profitable selling prices 

for baseline technology and if various technologies 

under development were implemented. Kline’s estimates generally indicated that advanced oxidation 

techniques should reduce fiber selling price by about 

6–8%. These estimates, however, were based on a 

line speed comparable to that of conventional conversion lines. Rough calculations suggest that if we 

can achieve much higher line speeds, the savings 

could increase dramatically. We have not discovered 

any inherent physics limits that would prevent us 
High Strength Weight Reduction Materials FY 2004 Progress Report 

23

from achieving a large increase in conversion line 

speed using plasma oxidation and microwaveassisted plasma carbonization. 

Education

The materials characterization has been conducted in partnership with the University of Tennessee’s (UT’s) materials science department. Two UT 

graduate students were engaged to provide characterization support to the project. 

Partners

ORNL gratefully acknowledges contributions to 

this project by Fortafil and Hexcel. Both have generously provided raw materials and offered technical 

consultation. An updated materials transfer agreement was executed with Hexcel during this reporting 

period. Additionally, technical and programmatic 

consultation has been provided by the Automotive 

Composites Consortium and by Delphi Corporation. 

Conclusions

The development of plasma-based oxidation 

technology has achieved a major milestone by demonstrating the feasibility of plasma processing to 

oxidize PAN precursor fibers. Preliminary data suggest that the plasma oxidation process may allow 

earlier onset of carbonization, thus reducing oxidation residence time. Understanding of the parametric 

processibility space has grown substantially during 

this period. Preliminary economics studies support 

the value of research in advanced oxidation. The 

researchers expect to demonstrate continuous 

plasma processing, and continue growing our understanding of the plasma oxidation process and its 

benefits, in FY 2005. 

Presentations

F. L. Paulauskas and T. L. White, “TemperatureDependent Dielectric Measurements of Polyacrylonitrile Fibers during Air Oxidation,” 49th International SAMPE Symposium 2004, Long Beach, CA. 

May 16–20, 2004. Published in the conference proceedings, 2004. 
FY 2004 Progress Report High Strength Weight Reduction Materials 

24 
High Strength Weight Reduction Materials FY 2004 Progress Report 

25 

B. Wrought Magnesium Alloy/Process Development 

Principal Investigator: J. A. Horton 

Oak Ridge National Laboratory 

P.O. Box 2008, Oak Ridge, TN 37831-6115 

(865) 74-5575; fax: (865) 574-825; hortonja@ornl.gov 

Principal Investigator: S. R. Agnew 

University of Virginia 

116 Engineer’s Way 

P.O. Box 400745, Charlottesville, VA 22904-4745 

Technology Development Area Specialist: Sidney Diamond 

(202) 586-8032; fax: (202) 586-1600; e-mail: sid.diamond@ee.doe.gov 

Field Technical Manager: Philip S. Sklad 

(865) 574-5069; fax: (865) 576-4963; e-mail: skladps@ornl.gov 

Contractor: Oak Ridge National Laboratory 

Contract No.: DE-AC05-00OR22725 

Objectives 

• Develop wrought magnesium alloys with better formability than current magnesium alloys. 

• Investigate new processing techniques for cost reduction and formability improvement. 

• Contribute to basic understanding of deformation, processing, and alloy behavior for this lightweight metal. 

Approach 

• Explore new processing schemes for magnesium alloy sheets. 

• Evaluate the practical formability of new alloys and after new processes. 

• Determine deformation mechanisms using experimentation and simulation. 

Accomplishments 

• Demonstrated feasibility of infrared sheet processing at a commercial facility, Manufacturing Sciences, Inc. 

• Designed warm formability testing tool based upon the “OSU test.” 

• Experimentally validated the dislocation-based mechanism hypotheses developed through simulation. 

• Collected data to determine if various dislocation-based mechanisms have distinct grain-size dependence. 

• Completed assessment of texture evolution during equal channel angular extrusion. 

Future Direction 

• Interact with an industrial partner to advance commercialization of infrared processing for cost reductions. 

• Define further correlations of microstructure, mechanisms, and anisotropy. 
FY 2004 Progress Report High Strength Weight Reduction Materials 

26 

• Further explore superplastic-type behavior observed at warm forming temperatures. 

• Investigate fundamental parameters affecting castability of the more creep-resistant alloys. 

Introduction

The world market for magnesium has changed 

substantially in recent years with the emergence of 

China as the leading producer (~50% of the market.) 

For instance, some western competitors have been 

driven out of business (e.g., Noranda in Canada) or 

have uncertain futures (e.g., AMC in Australia). It is 

still unclear what the final outcome will be, since at 

least one major western supplier (Norsk Hydro) has 

formed an alliance with a Chinese partner. 

Magnesium sheet manufacturers face a number of 

technical issues that we continue to research: 

• Rolling magnesium to thin-gage sheet currently 

leads to expensive solutions. 

• Obtaining an excellent surface finish is difficult. 

• Corrosion performance is poor vis-a-vis die-cast 

alloys. 

• Sheet formability is limited at low temperatures. 

During FY 2003, in addition to focusing on the 

sheet formability issues, we began addressing the 

concerns associated with the cost of sheet products. 

Demonstration of Infrared Processing at 

A Commercial Rolling Facility

After lab studies of the relevant infrared parameters, microstructures, and mechanical properties involved with infrared processing of sheet magnesium, 

a demonstration was performed at Manufacturing 

Sciences under the direction of Tom Muth. This 

commercial rolling mill facility has a 3 × 8 ft bank 

of infrared lamps at 12 W/cm2

 installed on one side 

of a reversing mill (Figure 1). Starting material for 

this demonstration was commercial sheets of 6-mmthick AZ31 tooling plate. Initial heatup required 5 

min; subsequent heatups with thinner sheet required 

less time until the last pass required approximately 2 

min. Newer designs of the infrared bank have an 

even higher output, promising even shorter anneal 

times. 

Sets of rolling sequences were performed aiming at 15%, 20%, and 40% rolling reductions for 

each pass until 1-mm thickness was obtained. A fiFigure 1. Commercial rolling mill facility has a 3 × 8 

ft bank of infrared lamps at 12 W/cm2

 installed on one 

side of a reversing mill. 

nal roll on a 6-mm plate was performed with as 

much reduction as we dared. Desired temperatures 

were 400 ̊C and 500 ̊C. However, 500 ̊C could not 

be reached because of the large airflow. Specimens 

were collected at several points in the rolling sequence. Table 1 lists the as-rolled mechanical properties for five test runs at various points during the 

rolling. The amount of cold work saturated after few 

passes. However, the tensile strengths and ductilities 

indicate that the magnesium was essentially coldrolled. Further experiments are under way to attempt 

to study actual rolling temperature effects on texture 

and properties. 

Figure 2 shows that the microstructure in the 

near-surface regions was similar to that of the cen- 
High Strength Weight Reduction Materials FY 2004 Progress Report 

27 

Table 1. As-rolled mechanical property data after infrared processing 

T 

( ̊C) 

Average 

reduction 

(%) 

Thickness 

(mm) Passes 

UTS 

(MPa) 

Elongation 

(%) 

400 16.5 2.1 6 275 6 

 1.3 9 285 5 

 1.0 10 307 4 

400 23 1.5 5 298 6 

 1.0 7 404 7 

~425 44 1.1 3 363 3 

~425 66 2.1 1 265 5 

Figure 2. Side and top views of the microstructure of 

1mm thick sheets after the 10th pass at average of 16.5% 

reduction showing that the near surface regions were 

similar to the center. 

Figure 3. Side and top views of the microstructure sheets 

after a single pass of 66% reduction showing evidence of 

dynamic recrystallization in the form of fine grain necklacses. 

ter. The largest reduction used, 66%, resulted in 

some dynamic recrystallization, as shown in Figure 3. Such an approach could be used to develop a 

very fine-grained structure appropriate for superplastic forming, as an example. In addition to microstructure, we examined the texture, since it is so 

significant for determining the properties of magnesium. The (0002) pole figure from the as-received 6-

mm tooling plate was little changed by the infrared 

rolling. 

These results were presented at the Magnesium 

2004 symposium at the TMS annual meeting and 

generated much interest. A member of the audience 

raised the concern that such large reductions could 

introduce microcracks or other defects during this 

processing, resulting in the low ductilities shown in 

Table 1. Subsequent annealing studies for 2 hours at 

185 ̊C and 345 ̊C resulted in much higher ductililties, suggesting that normal commercial wrought 

properties, or better, can be obtained (see Table 2). 

Table 2. Mechanical property data after 2-hour anneals 

Anneal T 

( ̊C) 

Yield 

(MPa) 

UTS 

(MPa) 

Elongation 

(%) 

As-rolled 262±57 312±49 5±2 

185 185±11 269±6 18±2 

345 141±14 247±6 24±2 

Design and Implementation of a Warm 

Formability Testing Apparatus

Throughout our research project, we have been 

continually pursuing the possibility of forming magnesium sheet metal at lower temperatures. Traditional wisdom states that the forming temperatures 

should be in the range of 250°C or higher. One problem is that there really is no standardized testing 

methodology for warm forming. In the past, we have 

used a high-temperature cylindrical cup drawing 

apparatus at Oak Ridge National Laboratory as an 

indicator of formability; and we have been able to 

make qualitative comparisons between alloys. However, there are a couple of problems with this ap-
FY 2004 Progress Report High Strength Weight Reduction Materials 

28 

proach: (1) Since our target applications are vehicles, the most important forming operations tend to 

be primarily stretching, as opposed to drawing. (2) 

The results of the cup drawing test are heavily influenced by thermal gradients. In our case, the die is 

heated, but the punch is not. While this actually 

leads to enhanced practical formability, it is not the 

best way to assess the intrinsic formability of the 

material at a given temperature and strain rate. 

We studied the literature and found a new test 

developed at Ohio State University (the OSU test) 

that actually deforms the sheet metal in a condition 

very close to plane strain tension. This is significant, 

since studies of technological forming failures have 

indicated 80% of stamping failures are under conditions of plane strain. This is also the division between the drawing and stretching halves of the 

forming limit diagram (FLD); it yields a result 

known as FLD0, which is the lowest point on the 

FLD. This test requires a relatively small die set-up 

and thus can fit within one of the furnaces mounted 

on mechanical testing frames at the University of 

Virginia (Figure 4). A few trial runs on copper and 

aluminum alloy sheets have been performed at ambient temperatures. Once a protocol has been developed, warm formability tests on aluminum and 

magnesium alloys will be performed. These may be 

conventional alloy sheets, sheets subjected to novel 

processing schemes, or experimental alloys. 

Figure 4. Warm formability testing apparatus based upon 

“the OSU test” shown (a) prior to deformation, as the 

metal is being clamped into the die, and (b) after deformation. 

Validation of Anisotropy and Simulation 

Approach to Mechanism Determination

It is of interest to determine the deformation 

mechanisms that control the deformation behavior of 

wrought magnesium. For instance, if particular 

mechanisms can be determined to be responsible for 

the cold-formability problems or the excellent formability at elevated temperatures, improvements may 

be made through targeted alloy or microstructure 

design. Our approach has been to probe the deformation mechanisms with the help of computer simulations based on polycrystal plasticity theory. 

Information about the material’s structure (i.e., crystallographic texture) and deformation mechanisms 

(solved for iteratively) serves as input, and the mechanical behavior and texture evolution are outputs. 

Experimentally, the initial texture, the mechanical 

response, including anisotropy, and the final texture 

are measured. When the simulations predict the observed behavior, it is an indication that the deformation mechanisms used as inputs are reflective of the 

material’s mechanisms. 

Last year it was demonstrated that alloy AZ31B 

sheet exhibits a strong correlation between the sharp 

increase in tensile ductility (and formability in general) at mildly elevated temperatures and a sharp 

decrease in anisotropy (Figure 5). Through the approach outlined, it was suggested that this strong 

decrease in anisotropy is associated with the activation of another deformation mechanism at elevated 

temperatures, pyramidal <c+a> slip. Of all the slip 

mechanisms known to operate within magnesium, 

this was the only one for which the simulations predicted the observed lowering of anisotropy. Provided the intrinsic assumptions of polycrystal 

plasticity are correct, this would represent a significant finding. 

Figure 5. The r-value measurements over a range of temperatures show that the r-value drops strongly in all directions as the temperature is raised. This behavior has been 

linked to an increase in the activity of pyramidal <c+a> 

slip as the temperature is raised. 
High Strength Weight Reduction Materials FY 2004 Progress Report 

29 

This year, efforts have been focused on demonstrating that the predictions of the approach are 

grounded in reality. Transmission electron microscope (TEM) dislocation analysis was used to examine deformed samples for evidence of mechanisms 

predicted to be operational by the modeling approach. As an initial step, samples deformed at room 

temperature were examined for evidence of nonbasal <a> slip. The simulations suggested that up to 

80% of strain is accommodated by non-basal slip. 

This is in stark contrast with magnesium singlecrystal observations of the 1950s and 1960s, which 

showed no evidence of non-basal slip below 

~180°C, even under constraint. The TEM study did 

show evidence of extensive non-basal <a> dislocation slip (Figure 6), and a preliminary report was 

published in the Proceedings of the Magnesium 

Technology 2004 Symposium of the TMS Annual 

Meeting. A full journal paper in the International 

Journal of Plasticity is in-press. 

Figure 6. TEM image of magnesium alloy AZ31B deformed in tension shows curved dislocations when viewing from a basal plane edge-on perspective. Thus the 

dislocations are gliding on non-basal planes. A complete 

Burgers vector analysis shows the majority of dislocations to have b = [1120] 3

1

 or [a3]. 

The same approach is being applied to determine 

(1) whether non-basal slip is strongly controlled by 

grain size and (2) whether our hypothesis that hightemperature formability is controlled by <c+a> slip 

is correct. Both of these findings would have significant practical implications, since processing can 

strongly affect the microstructure of magnesium (see 

following discussion), and secondary slip can be 

heavily influenced by alloying additions. 

Samples of alloy AZ31 sheet with different lineal intercept grain sizes (14–220 μm) have been produced through annealing for different times (1 h–1 

week) and temperatures (345–525°C). To date, the 

grain size has been assessed and tensile tests along 

the rolling (RD) and transverse (TD) directions have 

been performed, since these were previously shown 

to exhibit distinct behaviors connected with varying 

ratios of basal : non-basal dislocation slip (Figure 7a). Plotting the results in the conventional HallPetch fashion (Figure 7b) reveals a grain size dependence of this alloy’s yield strength similar to that 

published previously.1,2 

Figure 7. Grain size dependence of the (top) flow curves 

for transverse direction samples and (bottom) the yield 

stresses of both transverse and rolling direction samples 

of magnesium alloy AZ31 sheet. 

More interesting are the differences in the anisotropy that are exhibited by samples of different 
FY 2004 Progress Report High Strength Weight Reduction Materials 

30 

grain sizes (Figure 8). The as-received (not annealed) samples exhibit the lowest anisotropy. 

Annealing and grain growth actually appear to enhance the anisotropy, contrary to popular opinion. If 

the r-values are measured at a strain of 11%, as we 

have done previously, there appears to be only a 

slight change with annealing. 

A special extensometer has been obtained that 

can measure the Poisson strain along the sample’s 

width direction in-situ. The r-value evolution can be 

determined 

r = εw / εt = −εw / (εl + εw) 

by virtue of the incompressible nature of metal plasticity (εw + εt + εl = 0), where εw, εt, and εl are the 

strains along the sample’s width, thickness and 

length directions. This new tool shows the evolution 

of anisotropy is strikingly different between the 

samples of different grain sizes (Figure 8). 

Figure 8. Evolution of the anisotropy (r-value) with strain 

for samples of different grain sizes (H24 temper ~ 9 μm, 

O temper ~ 14 μm, and annealed at 475°C > 30 μm).

It was anticipated that larger grain samples 

might exhibit less non-basal slip and therefore lower 

r-values (using modeling arguments discussed earlier.) However, the initial results show that all of the 

larger grain samples have higher r-values. This fact 

may not be linked to mechanistic changes, since the 

higher overall anisotropy may be connected with a 

change in the texture during annealing; so we are 

now measuring the textures of samples in addition to 

their grain size. The final results will be important 

input for microstructure design of wrought magnesium. 

Texture Evolution during Equal Channel 

Angular Processing

This project focused on wrought magnesium began with an investigation of the potential of equal 

channel angular (ECA) processing to improve the 

mechanical properties of magnesium alloys by 

modifying the microstructure (i.e., reducing the 

grain size and heterogeneity.) The grain structure of 

bulk magnesium alloys was successfully modified 

and the elevated temperature ductility (e.g., superplasticity) improved early in the project. Later, a 

report published by a Japanese group led us to consider the possibility that the room-temperature ductility could be improved by ECA processing by 

reducing the crystallographic texture. We were able 

to duplicate the improvement in ductility; however, 

we found that the crystallographic texture of the 

samples was stronger than the initial texture. This 

sparked a renewed interest in the potential to improve the properties of magnesium alloys through 

texture modification. 

This year the possible texture evolutions of five 

different wrought alloys—AZ31, AZ80, ZK60, 

WE43—and an experimental alloy containing 

4 wt% Li were cataloged. These alloys were processed at a range of temperatures, different starting 

microstructures and textures, and a range of processing routes. The result of the study is an extensive 

database of texture evolutions. For the purpose of 

this short report, the results are described in Table 3. 

A couple of examples of the textures are shown in 

Figure 9. Another finding was that the texture 

throughout a sample is a strong function of position, 

particularly after processing by so-called route B 

(where the samples are rotated 90° between subsequent passes through the ECA die.) Analysis of how 

the deformation is actually introduced into a representative billet (Figure 10) has begun, and the differences in the textures from different parts of the 

samples can now be rationalized. 

References

1. F. E. Hauser, P. R. Langdon, J. E. Dorn, 

“Fracture of Magnesium Alloys at Low Temperature,” J Metals, Trans. AIME, 206, 589–93 (1956). 
High Strength Weight Reduction Materials FY 2004 Progress Report 

31 

Table 3. Summary of texture evolution of 5 magnesium alloys during ECA processing 

Alloy 

Initial 

state 

T 

(°C) Route Pass Texture description 

Peak 

(002) Classification 

AZ31 Plate 300 A 1 (002) tilted forward ~6 High temp, Al 

 2 “ ~8 “ 

 4 “ ~8 “ 

 8 “ ~8 “ 

“ Extru 200 A 1 (002) tilted backward ~6 Low temp, Al 

 2 “ ~6 “ 

 4 “ ~6 “ 

“ As-cast 200 A 1 (002) tilted backward ~6 “ 

AZ80 Extru 200 A 1 (002) tilted backward ~6 “ 

ZK60 Extru 260 A 1 (002) vertical, FPN ~4 High temp, Zr 

 2 (002) vertical ~6 “ 

 4 “ ~6 “ 

 8 “ ~8 “ 

WE43 Extru 325 A 2 (002) vertical, FPN ~4 “ 

 4 “ ~4 “ 

Mg4Li Extru 260 A 1 (002) vertical Li alloy 

 2 (002) vertical, FPN “ 

 4 (002) FPN, vertical “ 

ZK60 Extru 260 C 2 (002) tilted forw, back ~4 High temp, Zr 

“ “ “ “ 4 “ ~6 “ 

ZK60 Extru 260 B 4 (002) tilted forw, back ~4 “ 

AZ31 Extru 200 B 2 (002) tilt back, vertical ~6 Low temp, Al 

“ “ “ “ 8 (002) tilted back >10 “ 

“ Cast “ “ 2 “ >10 “ 

AZ80 Extru 200 B 2 (002) tilt back, vertical ~6 “ 

“ “ “ “ 4 “ ~6 “ 

“ “ “ “ 8 “ >10 “ 

2. N. Ono, K. Nakamura, S. Miura, “Influence of 

Grain Boundaries on Plastic Deformation in Pure 

Mg and AZ31 Mg alloy Polycrystals,” Mater. Sci. 

Forum, 419–422, 195–200 (2003). 

Publications and Presentations

S. R. Agnew, “Wrought Magnesium: A 21stCentury Outlook,” JOM 56(5), 20–21 (2004). 

S. R. Agnew and O. Duygulu, “Plastic Anisotropy and the Role of Non-basal Slip in Magnesium 

Alloy AZ31,” accepted for publication in Inter. J. 

Plasticity in 2005.

S. R. Agnew, J. A. Horton, T. M. Lillo, and 

D. W. Brown, “Enhanced Ductility in Strongly Textured Magnesium Produced by Equal Channel Angular (ECA) Processing,” Scripta Mater. 50, 377–381 

(2004). 

S. R. Agnew, C. N. Tomé, and D. W. Brown, 

“The Effect of Texture on the Deformation Mechanisms of AZ31B,” presented at Symposium on 

Phase Transformations and Deformation in Magnesium Alloys, TMS Annual Meeting, Charlotte, NC, 

March 16, 2004. 

A. L. Bowles, H. Dieringa, C. Blawert, N. Hort, 

K. U. Kainer, “Investigations in the Magnesium-Tin 

System,” in Proceedings of the International Conference on Magnesium—Science, Technology and 

Applications, Beijing, China. 

A. L. Bowles, H. Dieringa, C. Blawert, N. Hort, 

K. U. Kainer, “Investigations in the Magnesium-Tin 

System,” presented at International Conference on 

Magnesium—Science, Technology and Applications, Beijing, China, September 20–24, 2004. 

O. Duygulu and S. R. Agnew, “TEM Investigation of Dislocation Mechanisms in Mg Alloy 

AZ31B Sheet,” pp. 61–66 in Magnesium Technology 2004, Ed. A. A. Luo, TMS, Warrendale, PA, 

2004. 

O. Duygulu and S. R. Agnew, “TEM Investigation of Dislocation Mechanisms in Mg Alloy 
FY 2004 Progress Report High Strength Weight Reduction Materials 

32 

Figure 9. Representative textures from conventional extrusion, labeled 0, and the effect of 4 passes of ECA extrusion, labeled 4. Note strong differences between four 

of the alloys examined (a) AZ31, (b) ZK60, (c) WE43, 

and (d) Mg-4 wt % Li despite similarity of initial extrusion textures. Contours are on a logarithmic scale with a 

maximum (black) of eight multiples of a random distribution.

AZ31B Sheet,” presented at Magnesium Technology 

2004 Symposium, 2004 TMS Annual Meeting, 

Charlotte, NC, March 16, 2004. 

J. A. Horton, C. A. Blue, S. R. Agnew, and T. 

Muth, “Infrared Processing of Wrought Magnesium 

Alloys,” presented at Magnesium Technology 2004, 

TMS Annual Meeting, Charlotte, NC, March 16, 

2004. 

Figure 10. Schematics of the deformed regions of billets 

after 1, 2, 3, and 4 route A passes through the die, emphasizing the shrinking region, which is completely deformation. (1’s and 0’s indicate strained and unstrained portions 

during a given pass. For example, 1011 indicates the region was strained during the 1st, 3rd, and 4th passes, but 

not the 2nd.)

P. K. Liaw, G. M. Stoica, L. J. Chen, E. A. Payzant, C. Xu, T. G. Langdon, and D. E. Fielden, 

“Plastic Flow and Mechanical Behavior of Some 

Mg- and Al- Alloys Deformed by Equal Channel 

Angular Pressing,” presented at Third International 

Symposium on Ultrafine Grained Materials, TMS 

Annual Meeting, Charlotte, NC, March 16, 2004. 

G. Song, A. L. Bowles, and D. H. StJohn, “Effect of Aging on Yield Stress and Corrosion Resistance of Die Cast Magnesium Alloy,” in 

Proceedings of the International Conference on 

Magnesium—Science, Technology and Applications,

Beijing, China. 

G. Song, A. L. Bowles, and D. H. StJohn, “Effect of Aging on Yield Stress and Corrosion Resistance of Die Cast Magnesium alloy,” presented at 

International Conference on Magnesium—Science, 

Technology and Applications, Beijing, China, September 20–24, 2004. 
High Strength Weight Reduction Materials FY 2004 Progress Report 

33 

C. Equal Channel Angular Extrusion of Soft Ferromagnetic Materials 

Principal Investigator: R. B. Schwarz 

Los Alamos National Laboratory 

MST-8, Mail Stop G755, Los Alamos NM 87545 

(505) 667-8454; e-mail: rxzs@lanl.gov 

Co-Investigators: T. D. Shen, J. D. Thompson, J. I. Archuleta (LANL), and K. Mukherjee (UCDavis) 

Technology Development Area Specialist: Sidney Diamond 

(202) 586-8032; fax: (202) 586-1600; e-mail: sid.diamond@ee.doe.gov 

Field Technical Manager: Philip S. Sklad 

(865) 574-5069; fax: (865) 576-4963; e-mail: skladps@ornl.gov 

Contractor: Los Alamos National Laboratory 

Contract No.: W-31-109-Eng-38 

Objective 

• Conduct research on the theory, synthesis, and properties of soft ferromagnetic alloys having the potential to 

improve the efficiency of energy conversion devices in the U.S. transportation industry.

Approach 

• Use mechanical alloying (MA) (a high-energy ball milling technique) to prepare Fe-rich alloy powders. 

• Characterize the powder by X-ray diffraction, scanning differential calorimetry, and magnetometry. 

• Consolidate the mechanically alloyed powders by equal-channel angular extrusion and spark-plasma sintering. 

• Characterize the compacted alloys by ac and dc magnetic measurements. 

Accomplishments 

• Prepared nanocrystalline Fe-Al-Si powders by MA. We used differential scanning calorimetry and X-ray diffraction to determine the optimal annealing parameters for reducing the residual stress in the Fe-Al-Si powders, 

while maintaining the crystallite size below 20 nm, as required for soft ferromagnetic properties.

• Demonstrated that minimizing the magnetic coercivity requires annealing within a narrow temperature window 

at which residual stresses are eliminated, yet grain growth is avoided.

• Analyzed the effects of crystallite size and residual stress on the magnetic properties.

• Studied the consolidation of our mechanically alloyed Fe-Al-Si powders by spark plasma sintering (collaboration with Professor A. K. Mukherjee at the University of California, Davis). 

• Measured the magnetic properties of Fe-Al-Si alloys in both powder and consolidated form. 

Introduction

There is continued interest in increasing the efficiency of electrical energy-conversion devices.1

Here we are interested in ferromagnetic cores of motors and transformers and in magnetic material for 

switched-mode power supplies. The challenge for 

low-loss transformer applications is to develop ferromagnetic materials that have low coercivity, HC, 

and high magnetic saturation, MS. The challenge for 

efficient switched-mode power supply inductors is 
FY 2004 Progress Report High Strength Weight Reduction Materials 

34 

to develop ferromagnetic alloys with high saturation 

flux density, low permeability, and low losses at 

high frequencies. 

For the first application, the best results have 

been obtained with two-phase alloys consisting of 

nanosized bcc Fe particles embedded in an amorphous alloy matrix. Two nanocrystalline alloys, 

known under the trade names Nanoperm2

 and 

Finemet,3

 are prepared by the partial crystallization 

of 30- to 50-μm-thick rapidly quenched glassy ribbons. The saturation magnetization of these materials is approximately 1.4 T. Their main drawback is 

their thinness of gauge and brittleness, which are not 

optimal for the construction of power transformers. 

For the second application, industry has relied 

extensively on gapped ferrite cores and on “distributed-gap” cores made from pressed ferromagnetic 

powder or powder cast into a polymer. The last 

method has the advantage of a low manufacturing 

cost. 

In the present project, we are investigating the 

synthesis and magnetic properties of nanocrystalline 

ferromagnetic alloys. We prepare these alloys in 

powder form using mechanical alloying. We then 

consolidate them using a spark-plasma sintering 

technique. 

Magnetic Properties of Nanocrystalline 

Ferromagnetic Fe92Al2Si6 Alloy Powders

The synthesis of nanocrystalline alloy powders 

by MA was described in the FY 2003 report and 

thus will not be repeated here. In that earlier report, 

we also described the magnetic properties of 

Fe80Cu20 alloys prepared by MA. We then proposed 

to continue this work by studying the magnetic 

properties of Fe-Al-Si alloys. The reason for choosing this alloy was to raise the temperature at which 

one obtains optimal magnetic properties upon annealing, and to have an alloy of lower magnetostriction. 

We used MA to prepare Fe92Al2Si6 alloy powders. The as-prepared alloy powders have residual 

stresses, which have a detrimental effect on the 

magnetic properties of the alloy. The residual 

stresses must be eliminated through careful annealing. 

In the present study, it is imperative to have accurate measures of the residual stresses and of the 

crystallite size (more accurately, the size of crystalline domain that diffracts coherently). Most research 

to date has deduced these two quantities from an 

analysis of X-ray diffraction data using the Williamson-Hall method. In this method, for each Bragg 

reflection, the peak-width-at-half-maximum is plotted as a function of the scattering vector. The crystallite size and residual strain follow from the 

intercept and slope of a straight line plotted through 

the data. Figure 1(a) shows that the Williamson-Hall 

plot is inaccurate because the data have excessive 

scatter. The problem is that the Williamson-Hall 

method does not take into account the elastic anisotropy of the crystal, which affects each of the Bragg 

reflections differently. We used the recent methods 

of Ungar and co-workers4

 to calculate the contrast 

factors, C, needed to take into account the anisotropy. Figure 1(b) shows the modified plot. Here, all 

the diffraction data fit nicely a straight line. We used 

this method to analyze the diffraction data as a function of annealing temperature. 

Figure 2 shows the crystallite size D, square root 

of the dislocation density (proportional to the residual strain ε ), and coercivity Hc as a function of annealing temperature Ta for 1-h anneals. Each datum 

is for a different powder aliquot annealed at the 

stated temperature. The coercivity was measured 

using a well-calibrated superconducting quantuminterference device (SQUID), which has an accuracy 

of approximately ± 0.1 Oe. Annealing causes a 

monotonic decrease in the residual strain and a 

monotonic increase in the crystallite size. The coercivity, however, first decreases, reaching a sharp 

minimum for Ta ≈ 450o

C, and then increases for 

higher annealing temperatures. Notice the sharp 

minimum in the coercivity. We detected no phase 

separation on heating the Fe92Al2Si6 alloy up to 

600°C. Thus the increase in HC after annealing 

above 450°C is due to the increase in D. 

Our data demonstrate that in nanostructured materials, the coercivity Hc depends not only on the 

grain size D (as assumed by earlier theories) but also 

on the residual stress. This is a new result, as we 

explain next. 

Previous research on the magnetic properties of 

nanocrystalline alloys addressed the dependence of 

coercivity on grain size. In an extensively quoted 

paper, Herzer5

 proposed an explanation for the often 

observed decrease in the coercivity, HC ∝ D6

, for 

grain sizes below approximately 30 nm. Guided by 

this theory, researchers have studied nanostructured 

ferromagnetic alloys without paying attention to the 

residual stresses in the alloys. Although the residual 
High Strength Weight Reduction Materials FY 2004 Progress Report 

35 

Figure 1. Peak width at half maximum, ΔK, as a function 

of wavenumber, K, for as-mechanically-alloyed 

Fe92Al2Si6 powder: (a) using the Williamson-Hall 

method, and (b) using contrast-factors, C, according to 

Ungar [ref. 4]. 

Figure 2. Crystallite size, D, coercivity, HC, and residual 

strain, ε, (proportional to the square root of the dislocation 

density, ρ) in mechanically alloyed Fe92Al2Si6 powder as 

a function of annealing temperature. The annealing time is 

1 h. 

stress is low in rapidly quenched ribbons, it cannot 

be neglected in alloy powders prepared by mechanical alloying. 

The data in Figure 2 suggest two magnetic regimes. For Ta < 450°C, the decrease in coercivity is 

dominated by the residual stress in the material; and 

for Ta > 450°C, the increase in coercivity is due to 

the increase in the crystallite size D. 

The residual stress in our nanocrystalline alloys 

is of two types, microstress and macrostress. The 

microstresses are generated by dislocation walls that 

delimit the crystallite size D. The macrostresses are 

present because the total stress must average to zero. 

Because the microstress distribution is dominated by 

compressive components, the macrostress is dilatational in nature, as we confirmed by X-ray diffraction. Annealing facilitates the motion of the 

dislocations, leading to dislocation poligonization 

and/or annihilation. This process decreases both the 

microstresses and macrostresses. 

We have measured the residual microstress and 

macrostress independently. The microstress is proportional to the measured square root of the dislocation density and causes a broadening of the Bragg 

peaks. The macrostress is proportional to the overall 

lattice expansion, which causes a homogeneous shift 

of all the Bragg peaks versus diffracting angle. Figure 3 shows the macrostress in our Fe-Al-Si alloy 

powder as a function of annealing temperature. Notice that the macrostress vanishes at an annealing 

temperature of approximately 500°C. The microstress, deduced from the width of the Bragg peaks, 

shows a very similar dependence on annealing temperature. 

An important result to emerge from this work is 

that the coercivity correlates with the macrostress 

and not with the microstress. The reason is that the 

first Fourier component of the microstress distribution (the most important component) is shorter than 

the magnetic exchange length, Lex. This is to be expected because the crystallite size is less than 20 nm, 

whereas Lex is about 30 nm. Thus the motion of the 

magnetic Bloch walls is impervious to the presence 

of the random short-range microstresses. The domain walls do interact with the long-ranged macrostresses. Therefore, to obtain a magnetically soft 

nanocrystalline material, one has to first and foremost anneal out the macrostresses. However, the 

annealing temperature cannot be increased too 

much. Indeed, the data in Figure 2 show that annealing above 450°C causes an increase in the crystallite 
FY 2004 Progress Report High Strength Weight Reduction Materials 

36 

Figure 3. Macrostress in mechanically alloyed Fe92Al2Si6

powder as a function of annealing temperature. The annealing time for each sample was 1 h. 

size D. When D becomes comparable in size to Lex, 

then the coercivity increases rapidly because now 

the range of the microstresses becomes comparable 

to Lex. Then the coercivity increases proportionally 

to D6

 , as predicted by the random anisotropy 

model.5,6

Magnetic Properties of Consolidated 

Nanocrystalline Ferromagnetic Fe92Al2Si6

Alloy Powder

The mechanically alloyed Fe92Al2Si6 powder 

was consolidated by spark-plasma-sintering at UCDavis. In this technique, the powder is first cold 

pressed to about 300 MPa and heated to approximately 700°C. A series of current pulses are then 

sent through the compressed powder. The current 

heats preferentially the contact points between the 

particles, accelerating the sintering process. The 

consolidated disks were approximately 90% dense. 

The consolidated disks were cut (at Los Alamos 

National Laboratory) to prepare small toroid-shaped 

specimens. Primary and secondary solenoids were 

added to the toroids to create small transformers on 

which to measure magnetic properties. 

Figure 4 shows the B-H curve for such a toroid. 

The saturation magnetization is approximately 1.6 T, 

and the coercivity is approximately 4 Oe. The coercivity, although low compared with that of any ferromagnetic powder prepared by MA, is still too high 

for it to be used in ferromagnetic cores of low-loss 

transformers and motors. We attribute the finite coFigure 4. Induction, B, as a function of applied field, H, 

in a toroid-shaped sample made from Fe92Al2Si6 powder. 

The toroid was cut from a bulk disk made by consolidating the powder using spark-plasma-sintering at UC-Davis. 

ercivity to the presence of macrostresses introduced 

during the consolidation process. These macrostresses have not been reduced by annealing. In addition, during the consolidation at 700°C, the grain 

size grows to above 100 nm. 

Future Research

1. Optimize the temperature used during the sparkplasma-sintering consolidation to minimize the 

grain growth. 

2. Study the influence of post-annealing on reducing the macrostresses introduced during consolidation. 

3. Optimize the composition of the Fe-Al-Si to 

minimize the magnetostriction and magnetocrystalline anisotropy. 

4. Study the magnetic properties of two-phase materials consisting of Fe92Al2Si6 powder with 

nanosize grains and a ferromagnetic “glue” consisting of an amorphous ferromagnetic alloy 

with a glass transition temperature lower than 

450°C. The Fe92Al2Si6 alloy should provide a 

high saturation magnetization, whereas the 

amorphous phase will deform during sintering, 

closing the gaps and producing a fully dense ferromagnetic alloy. 
High Strength Weight Reduction Materials FY 2004 Progress Report 

37 

Acknowledgment

This work was supported by the DOE Office of 

FreedomCAR and Vehicle Technologies. 

References

1. U.S. Department of Energy, “Annual Energy Review 2001,” from www.eia.doe.gov. 

2. A. Kojima, H. Horikiri, Y. Kamamura, A. 

Makino, A. Inoue, and T. Matsumoto, “Production 

of Nanocrystalline bcc Fe-Nb-B Bulk Alloys by 

Warm Extrusion and Their Magnetic Properties,” 

Mater. Sci. Eng. A 179/180, 511 (1994). 

3. Y. Yoshizawa, S. Oguma, and K. Yamauchi, 

“New Fe-based Soft Magnetic Alloys Composed of 

Ultrafine Grain Structure,” J. Appl. Phys. 64, 6044 

(1988). 

4. T. Ungar, I. Dragomir, A. Revesz, and A. 

Borbely, “The Contrast Factors of Dislocations in 

Cubic Crystals: The Dislocation Model of Strain 

Anistrophy in Practice,” J. Appl. Cryst. 32, 992 

(1999). 

5. G. Herzer, in Handbook of Magnetic Materials, vol. 10, ed. K. H. J. Buschow, Elsevier Science B. V., Amsterdam, 1997, chap. 3. 

6. G. Herzer, “Grain Size Dependence of Coercivity and Permeability in Nanocrystalline Ferromagnets,” IEEE Trans. Magn. 26, 1397 (1990). 

Publications and Presentations

T. Li, F. Grignon, D. J. Benson, K. S. Vecchio, 

E. A. Olevsky, F. Jiang, A. Rohatgi, R. B. Schwarz, 

and M. A. Meyers, “Modeling the Elastic Properties 

and Damage Evolution in Ti-Al3Ti MetalIntermetallic Laminate (MIL) Composites,” Mater. 

Sci. and Eng. A 374, 10–26 (2004). 

R. B. Schwarz, “Synthesis and Properties of Ferromagnetic Bulk Metallic Glasses,” MST Division 

Seminar, Argonne National Laboratory, November 

7, 2003. 

R. B. Schwarz and T. Lillo, “Metal-Intermetallic 

Composites Prepared by Melt Reaction Synthesis,” 

presented at the Workshop on Ceramics Ductilization, Los Alamos National Laboratory, November 

15–18, 2004. 

R. B. Schwarz and T. D. Shen, “High-Strength, 

High Conductivity Bulk Nanostructured Alloys,” 

invited presentation at the Symposium on Processing 

and Properties of Structural Nanomaterials, 2003 

TMS Fall Meeting, Chicago, November 9–12, 2003. 

R. B. Schwarz, T. D. Shen, U. Harms, and T. 

Lillo, “Soft Ferromagnetism in Amorphous and 

Nanocrystalline Alloys,” Journal of Magnetism and 

Magnetic Materials 283, 223–230 (2004). 

R. B. Schwarz, T. D. Shen, T. Lillo, G. D. Zhan, 

and A. K. Mukherjee, “Soft Ferromagnetism in 

Nanocrystalline Alloys,” invited presentation at the 

10th International Symposium on Metastable, Mechanically Alloyed and Nanocrystalline Materials 

(ISMANAM 2003), Foz do Iguacu, Brazil, August 

22–26, 2003. 

T. D. Shen, U. Harms, and R. B. Schwarz, “Bulk 

Fe-based Metallic Glass with Extremely Soft Ferromagnetic Properties,” Materials Science Forum 

386–388, pp. 441–446 (2002). 

Awards

R. B. Schwarz was awarded the Von Humboldt 

Research Award for Senior U.S. Scientists for his 

research and teaching and was awarded the 

ISMANAM Medal for research in amorphous and 

nanocrystalline crystals at the International Symposium on Metastable, Mechanically Alloyed, and 

Nanocrystalline Materials. 
FY 2004 Progress Report High Strength Weight Reduction Materials 

38 
High Strength Weight Reduction Materials FY 2004 Progress Report 

D. Equal Channel Angular Extrusion Processing of Alloys for Improved 

Mechanical Properties 

Principal Investigator: Thomas M. Lillo 

Idaho National Engineering and Environmental Laboratory 

MS2218, P.O. Box 1625, Idaho Falls, ID 83415-2218 

(208) 526-9746; fax: (208) 526-4822; e-mail: tml@inel.gov 

Technology Development Area Specialist: Sidney Diamond 

(202) 586-8032; fax: (202) 586-1600; e-mail: sid.diamond@ee.doe.gov 

Field Technical Manager: Philip S. Sklad 

(865) 574-5069; fax: (865) 576-4963; e-mail: skladps@ornl.gov 

Contractor: Idaho National Engineering and Environmental Laboratory 

Contract No.: DE-AC07-99ID13727 

Objective 

• Investigate equal channel angular extrusion (ECAE) as a deformation processing technique to improve material 

properties such as strength, formability, fatigue, and corrosion. 

⎯ Apply ECAE processing to produce advanced, lightweight materials with enhanced formability, higher 

strength-to-weight ratio, and higher stiffness, ultimately leading to reductions in vehicle weight and thus 

more fuel-efficient vehicles. 

Approach 

• Assess the effects of ECAE processing parameters on the mechanical properties of a magnesium alloy 

(ZK60A) and an aluminum metal matrix composite (MMC) (AL6061+B4C). Both are lightweight alloys with 

potential for use in lightweight structural applications in vehicles. 

• Determine the optimum ECAE processing schedule for the maximum increase in mechanical properties. 

• Characterize the microstructure and mechanical properties of the ECAE-processed material. 

• Use microstructure and mechanical properties data to model the flow stress of materials processed with ECAE. 

Accomplishments 

• ECAE-processed five billets of ZK60A using new ECAE processing schedules and temperatures. 

⎯ CAE-processed eight billets of AL6061 + 10 wt% B4C using new ECAE processing schedules and temperatures. 

• Characterized microstructure and mechanical properties of ECAE-processed AL6061+10 wt% B4C. 

⎯ Improved ductility (>10% in some cases) and increased the modulus of elasticity from 70 GPa to over 85 

GPa, and in some cases >100 GPa, of AL6061+10 wt% B4C. 

• Performed strain rate jump tests on ECAE-processed ZK60A to determine superplastic behavior. 

⎯ Characterized the microstructure of various ECAE-processed and annealed brasses using orientation imaging microscopy (OIM) in support of flow-stress modeling work. 

39 
FY 2004 Progress Report High Strength Weight Reduction Materials 

Future Direction 

• Complete the superplastic behavior study of ECAE-processed ZK60A. 

⎯ Understand the variation in elastic modulus and tensile strength of MMCs with ECAE processing parameters through further ECAE processing, microstructural characterization, and mechanical testing. 

⎯ ECAE process an AL6061+ 20wt% B4C MMC, as well as other MMCs ,and evaluate mechanical properties to demonstrate the universal improvement in the mechanical properties associated with ECAE processing. 

⎯ Determine the modifications in ECAE die design and ECAE furnace design to ECAE process titaniumbased MMCs. 

⎯ Continue ECAE processing, characterization of microstructure, and characterization of mechanical properties in support of flow-stress modeling. 

Introduction 

Over the past years, this ECAE program has 

studied ECAE processing (Figure 1) of a wide variety of materials, from pure metals to alloys and 

MMCs. Initially it was surmised that ECAE processing might be a method of producing bulk nanocrystalline materials through grain refinement 

Figure 1. Schematic of ECAE 

processing.

associated with intense plastic deformation. Microstructural development and mechanical properties 

were tracked as a function of ECAE processing parameters such as processing route (Figure 2), number of passes through the ECAE die, processing 

temperature, and the level of back 

Figure 2. Schematic illustrating sample rotation between subsequent passes through the ECAE die.

stress during processing. A nano-crystalline grain 

size was difficult to obtain in most materials. Typically, the grain size stabilized after relatively few 

(4–10) passes through the ECAE die at a value determined by the metal or alloy being processed and 

the ECAE processing temperature. Although this 

grain size was generally sub-micron, it was not 

nano-crystalline ( <100 nm). Furthermore, the grain 

boundary structures were not in stable equilibrium; 

and the property improvements exhibited by ultrafine-grain materials made by other methods were not 

realized in ECAE-processed materials. 

40 
High Strength Weight Reduction Materials FY 2004 Progress Report 

However, most materials exhibited significant 

improvements in their mechanical properties as a 

result of ECAE processing with a subsequent annealing procedure. One example with potential 

lightweight vehicle applications was a commercial 

magnesium alloy ZK60A (Mg-5% Zn–0.5% Zr). 

During FY 2003, it was found that, with the appropriate combination of ECAE parameters, ZK60A 

could be ECAE-processed to a final grain size of 1–

2 μm. Alloys in this grain size range have been 

known to exhibit superplastic behavior. A subsequent superplastic study of this ECAE-processed 

material showed elongations of >200% at 200°C and 

a strain rate of 10−3

/sec. Since this was a first attempt, part of the focus during FY 2004 was to optimize the ECAE-processing schedule to obtain 

superplasticity at higher strain rates. 

Another material found to benefit from ECAE 

processing was an experimental MMC, AL6061 

with 10 wt% B4C particles, obtained from Dynamet 

Technologies. Dynamet desires to develop lightweight materials with high stiffness for structural 

applications. The composite was made by powder 

metallurgy techniques and suffered from very low 

ductility (virtually zero) and little enhancement to 

the stiffness over commercial AL6061. However, 

elongations as high as 10% and improvements to the 

stiffness (>10%) were found after ECAE processing. 

The elastic modulus (~80 GPa) was still significantly below the theoretical value of ~110 GPa. 

Again, since this was a first attempt, a portion of 

FY 2004 was devoted to exploring the optimization 

of ECAE processing to obtain greater improvements 

in the mechanical properties of this composite. Furthermore, work on this alloy will be useful in the 

processing of titanium MMCs that have greater application for lightweight, high-strength structural 

applications. Titanium MMCs will require modifications to the ECAE die and furnace, so the AL6061 

composite is used to demonstrate proof-of-principle.

Work in support of the effort to model the flow 

stress of metals and alloys also continued during FY 

2004. ECAE processing produces very fine-grainsize materials—finer than previously obtained by 

rolling, for instance. Determination of the 

relationship between flow stress and grain size at 

very small grain sizes aids in the elucidation of flow 

stress behavior. The data will eventually be 

integrated into a model capable of predicting grain 

size development and the resulting mechanical 

properties of thermomechanically-processed 

materials. 

Previous flow stress modeling work raised 

issues of the effect of stacking fault energy on the 

flow stress behavior. To answer these questions, 

various brasses, ranging from 30 to 5% Zn, with 

widely varying stacking fault energies, were ECAEprocessed and annealed to obtain a wide range of 

grain sizes. The microstructure was analyzed during 

FY 2004, and the flow stress behavior of these 

materials was determined and related back to the 

developing flow stress model. 

ECAE Processing of Magnesium Alloys

Previously, commercial-grade ZK60A (Mg-5% 

Zn–0.5% Zr) was ECAE-processed using three different sets of parameters: 

• Four passes by the B-route at 260°C and no applied 

back stress 

• Four passes by the B-route at 150oC and 18.3 ksi 

back stress 

• Six passes by the B-route at 150oC and 18.3 ksi back 

stress 

The results of the superplastic study on these 

samples seemed to indicate that lower ECAE temperatures and more passes through the die correlated 

with improvements in superplastic behavior. Therefore, new ECAE processing schedules, incorporating 

these insights, were devised. Specifically, billets 

were processed according to Table 1. 

Table 1. ZK60A ECAE processing schedules 

Sample

Initial 

billet 

condition 

ECAE temperature 

(

o

C) 

ECAE 

route 

Back 

stress 

level, ksi 

1 T5 150 8B 15.1 

2 T5 150 

135 

120 

2B 

1B 

1B 

15.1 

15.1 

19.7 

3 T5 150 

130 

2B 

4B 

15.1 

15.1 

4 Solution 

treated 

200 

150 

2B 

6B 

10.6 

21.2 

5 T5 150 2A 15.1 

Sample 1 explored the effect of the number of 

passes through the ECAE die on superplastic behavior; Sample 2 looked at ECAE processing temperature; and Sample 3 was processed with a 

combination of both variables. Sample 4 attempted 

41 
FY 2004 Progress Report High Strength Weight Reduction Materials 

to look at the effect of precipitation from solid solution during ECAE processing, and Sample 5 was to 

evaluate the uniformity of strain in the billet. 

At this time, tensile bars have been made and strain 

rate jump tests performed at 180, 225, 250 and 

275°C on Samples 1–4. The strain rate sensitivity 

factor, m, was calculated from: 

m = log(σ2/σ1)/log(¦2/¦1) , (1) 

where ¦ was the strain rate, σ was the flow stress 

and the subscripts 1 and 2 referred to the values before and after the strain rate jump, respectively. The 

m factors are plotted in Figure 3 as a function of 

strain rate for the test temperatures. (The strain rates 

in the plots are taken as the average of the strain rate 

before and after the strain rate jump.) Superplastic 

behavior is associated with m values near 0.5. At 

250 and 275°C, all samples behaved similarly, and 

presumably rapid grain growth out of the superplastic regime was occurring. At the two lower temperatures (180 and 225°C), only sample 4 showed 

significantly different behavior across the strain 

rates investigated. Sample 4 exhibited m ≈ 0.5 

around a strain rate of ~10−2

 sec−1 at 225°C. The 

other samples exhibited m ≈ 0.5 only at very low 

strain rates at all temperatures studied. Sample 4 was 

ECAE-processed in the solutionized state, and precipitation occurred during processing and possibly 

during testing to produce the different superplastic 

behavior. Microstructural examination of Sample 4 

will be performed to try to assess the effect of ECAE 

processing on precipitation. Finally, samples will be 

tested using the most promising combination of 

temperature and strain rate to determine the maximum elongation possible. 

It was also demonstrated during FY 2003 that a 

modified version of ZK60A (with additions of cerium and yttrium), provided by Daniel Schechtmen 

at NIST, demonstrated even better superplastic behavior than commercial ZK60A. 

Once the optimum ECAE processing schedule is 

developed and superplastic parameters (temperature 

and strain rate) are determined for commercial 

ZK60A, they will be applied to the modified ZK60A 

and the resulting superplastic behavior documented. 

Figure 3. Strain rate sensitivity of ECAE-processed 

ZK60A at 180 and 225°C.

These preliminary results suggest that it might 

be possible to develop a high-strain-rate superplastic 

magnesium alloy. This would facilitate the use of 

magnesium alloys in automotive applications. Superplastic forming would minimize fabrication waste 

for this relatively expensive alloy, making it more 

economically competitive with traditional iron-based 

materials. High-strain-rate superplastic forming also 

offers the potential for rapid fabrication, resulting in 

higher productivity and making this alloy more 

competitive with conventional materials of construction. Ultimately, vehicles incorporating magnesium 

alloys would be lighter 

42 
High Strength Weight Reduction Materials FY 2004 Progress Report 

than those that rely on traditional alloys, and therefore more fuel-efficient. 

Table 2. Processing schedules for AL6061+10wt% B4C 

Sample 

Initial 

condition 

ECAE 

temperature 

(

o

C) 

ECAE 

route 

Back 

stress 

(ksi) 

B3528-1 T0 300 

150

2A 

4B

10.6 

22.7

B3528-8 T0 300 

150 

2A 

4A

10.6 

22.7

B3528-

10 

T0 300 

150 

2B 

4B 

10.6 

22.7

ECAE Processing of Aluminum Alloy 

Composites

Additional billets of prototype MMCs were purchased from Dynamet Technology. The material 

consisted of an Al6061 matrix with boron carbide 

particles (~50 μm in dia-meter on average) present 

at a level of either 10 or 20 wt %. Additions of B4C 

particles increase the stiffness of the AL6061 matrix, 

making it more suitable for use in lightweight structural applications by reducing the deflection under 

load. The material was fabricated by powder metallurgy methods and contained agglomerates of boron 

carbide particles. During FY 2003, it was found that 

the B4C particles appeared to be concentrated around 

prior aluminum alloy powder particles. The interface 

between adjacent B4C particles was very weak and 

acted as a defect during tensile loading, causing 

premature fracture. The elongation/ductility of these 

composites was negligible in the as-received state. 

Table 3. Effect of ECAE processing on density 

Sample 

Average density 

(grams/cm3)

Relative 

densitya

 (%) 

As-received 2.55 94.9 

B3528-1 2.64 98.1 

B3528-8 2.64 98.1 

B3528-10 2.65 98.5 a

The theoretical density was taken as 2.69 g/cm3, based 

on a rule-of-mixtures calculation 

The tensile bars were heat treated to either the 

T4 (solid solution) or T6 (optimum aging treatment) 

condition. (The samples were heat treated to remove 

the grain size refinement due to ECAE processing. 

Only the effect of ECAE processing on the B4C particulate was of interest at this time.) Two tensile 

tests for each heat treatment condition were run at 

room temperature for each billet. The results are 

shown in Table 4. Significant increases in all properties resulted from ECAE processing compared with 

the as-received material, B3528 AR. Generally, the 

ductility in the T4 condition is greater than in the T6 

condition (~9% vs. ~3%, respectively); but both are 

much greater than in the as-received material, which 

exhibited virtually no ductility. The yield and ultimate tensile strength (UTS) increased by more than 

30% and 50%, respectively, with the UTS in some 

cases almost doubling that of the as-received material. The ECAE-processed materials also showed an 

increase in the yield and ultimate strengths, ~15% 

and ~5%, respectively, over commercial AL6061 

(without B4C reinforcement). The elastic modulus 

also increased and, in one case, Sample B3528 1-2, 

approached the theoretical value (~110 GPa) as calculated by the rule-of-mixtures. Overall, billet 

B3528-10 exhibited slightly better mechanical properties than billets ECAE-processed by other schedules, although the differences were not great. 

During FY 2003, it was found that considerable 

increases in density, elongation, and elastic modulus 

could be realized through ECAE processing. Relatively high ECAE processing temperatures closed 

residual porosity, while lower ECAE processing 

temperatures eliminated poorly bonded particle/particle interfaces (i.e., dispersed the particles in 

the agglomerates). Therefore, during the first half of 

FY 2004, ECAE processing schedules were devised 

that incorporated initial passes at relatively high 

temperatures (~300°C) to close porosity, followed 

by subsequent passes at lower temperatures 

(<150°C) to disperse B4C agglomerates. 

The specific schedules used are shown in Table 2. The ECAE-processed billets remained intact 

and were free of cracks and other flaws commonly 

found in ECAE-processed materials of low ductility. 

Tensile bars were prepared from each billet and oriented parallel to the ECAE direction. 

The density of each tensile bar was determined 

by the Archimedes principle, and the average density is shown in Table 3. ECAE processing significantly increased the density (~3.5%), but full density 

still was not achieved. There also is very little difference in density between the different ECAE processing routes. 

43 
FY 2004 Progress Report High Strength Weight Reduction Materials 

Table 4. Mechanical properties of ECAE-processed 

AL6061+10wt% B4C 

Modulus

Yield 

Heat treat- strength UTS Elongation RA

ment 

Specimen 

ID (GPa) (MPa) (MPa) (%) (%) 

B3528 1-2 115 158 248 9 10 

B3528 1-6 73 161 208 3 5 

B3528 8-2 59 140 198 3 4 

B3528 8-6 69 161 249 8 10 

B3528 10-2 94 163 260 9 11 

B3528 10-6 97 170 268 7 5 

T4 

B3528 AR 56 117 129 0.8 0 

B3528 1-1 75 326 337 2 4 

B3528 1-5 88 N/A 314 0.2 2 

B3528 8-1 59 279 298 1.6 1 

B3528 8-5 80 325 331 1.3 2 

B3528 10-1 73 333 351 3 6 

B3528 10-5 83 340 356 3.7 7 

T6 

B3528 AR 71 N/A 193 0 0 

Although increases in the mechanical properties 

are observed on average, significant variability was 

observed in specimens from the same billet with thesame heat treatment. This condition, most likely, 

arose from remaining B4C particle/particle weak 

interfaces and residual porosity. 

The ECAE-processed microstructures were significantly different from the as-received material. 

Figure 4 compares the microstructures of the asreceived and sample B3528-1. The micrographs 

were taken from samples in the T4 condition and 

were perpendicular to the extrusion axis. The asreceived material had more B4C agglomerates and 

voids within the agglomerates (at the arrows in Figure 4a) compared with ECAE-processed material 

(Figure 4b). Smaller agglomerates and a reduced 

number of voids were found in the ECAE-processed 

material. The B4C particles also were more evenly 

distributed throughout the material compared with 

the as-received sample. These factors undoubtedly 

contributed to the observed increase in mechanical 

properties. The microstructures of the other ECAEprocessed samples showed similar results and indicated the ECAE processing route had little influence 

on the microstructure. Only the number of passes 

seemed to significantly affect the boron carbide particle distribution. 

Figure 4. Microstructure of AL6061+ 10 wt% B4C of the 

(a) as-received and (b) B3528-1 in the T-4 condition.

Overall, the tensile results in FY 2004 confirmed 

the preliminary findings obtained in FY 2003 that 

ECAE can be used to significantly increase the mechanical properties of these MMCs. However, resid44 
High Strength Weight Reduction Materials FY 2004 Progress Report 

ual porosity and weak particle/ particle interfaces 

still existed even after ECAE processing with the 

new processing schedules. These defects, although 

greatly reduced, are still thought to adversely affect 

the mechanical properties. Therefore, new schedules 

were developed to further reduce residual porosity 

and eliminate B4C agglomerates and weak B4C particle/particle interfaces. Specifically, additional 

passes were added to the end of those outlined in 

Table 2 to further redistribute the particles and close 

any porosity generated during the low-temperature 

passes through the ECAE die. The elastic modulus 

was evaluated after various passes using ultrasonic 

methods. After the fourth pass, very little change in 

the elastic modulus was observed even up to a total 

of 8 passes. The elastic modulus stabilized at ~ 80–

85 GPa, which is still significantly lower than theoretical for this composite (~110 GPa). Tensile samples will be tested early in FY 2005. The mechanical 

properties of material processed by simplified ECAE 

processing schedules (only 4 passes through the 

ECAE die) also will be determined in early FY 2005 

for comparison with previous results. Heat treatment 

of the ECAE-processed material to promote better 

bonding of the B4C particles to the AL6061 matrix 

will be explored. The goal is to increase the elastic 

modulus to near theoretical values. Preliminary exploration of titanium MMCs will begin after these 

experiments and mechanical testing. 

ECAE processing of MMCs still appears to have 

the greatest potential for improving mechanical 

properties. The improved fabricability of ECAEprocessed MMCs may enable the use of these lightweight, high-stiffness materials in more transportation applications for increased fuel efficiency. 

Modeling Flow Stress

Brasses with 5%, 10%, or 30% zinc were ECAE 

processed during FY 2003 and then analyzed during 

the first half of FY 2004 for microstructure and mechanical properties. The goal is to relate the difference in stacking fault energy with the flow stress 

behavior. Tensile samples were annealed for 1 hour 

at 300, 400, and 600°C. Obvious differences in the 

room-temperature flow stress behavior between the 

different brasses were found (Figure 5). 

Samples were prepared from the failed tensile 

bars and sent out for OIM and analysis. Among 

other things, OIM analysis revealed that samples 

Figure 5. Flow stress behavior of various brasses ECAEprocessed and annealed at 600°C for 1 hour. 

BR16–1 and –2 were not fully recrystallized; the 

result was low Σ3 (twin) grain boundary fraction for 

these samples (Table 5). OIM analysis also revealed 

that the grain size at a given annealing temperature 

is influenced by the zinc content—the grain size increases with increasing zinc content. All fully recrystallized samples have a high twin grain 

boundary fraction (>50%). The OIM data will be 

combined with the tensile data and analyzed for the 

flow stress model under development. 

The OIM data also revealed one other noteworthy result. The Σ3 grain boundary content for Br2C14 (700°C, 1 hour) was significantly lower than expected (Table 5). A closer look at the OIM data revealed a fairly high fraction (~28%) of low-angle 

grain boundaries. Mapping of the low-angle grain 

boundaries revealed they were mainly associated 

Table 5. OIM analysis results for ECAE-processed and 

annealed brasses 

Sample Description 

Grain- Σ3 

size fraction 

Total 

CSL 

fraction 

BR16 Cu-5Zn 

-1 300oC 0.46 0.210 0.240 

-2 400o

C 0.70 0.361 0.410 

-3 600o

C 1.44 0.699 0.752 

BR17 Cu-10Zn 

-1 300o

C 0.57 0.561 0.634 

-2 400o

C 0.89 0.574 0.621 

-3 600o

C 11.77 0.593 0.605 

BR2C Cu-30Zn 

-7 400o

C 1.73 0.488 0.526 

-12 500o

C 7.63 0.514 0.529 

-8 600o

C 20.83 0.592 0.611 

-14 700o

C 53.24 0.398 0.406 

45 
FY 2004 Progress Report High Strength Weight Reduction Materials 

with twin grain boundaries (Figure 6). Three lowangle boundaries associated with twins are shown at 

the arrows, as examples. The low-angle grain 

boundaries (<10°) are shown in white. The grain 

boundaries near these low-angle grain boundaries no 

longer have a twin orientation. Therefore, it would 

appear that annealing at 700°C leads to the breakup 

of twin boundaries in this material. This also is 

shown by Figure 7, where the tolerance for what is 

considered a twin grain boundary has been varied. 

Twin boundaries in black represent deviations of up 

to about 8.7°, while those in white are within 2.9° of 

the exact twin orientation. For Br2C-8 (600°C, 1 

hour), nearly all of the twin boundaries are within 

2.9° of the exact twin orientation (Figure 7b), while 

the twin grain boundaries in the sample annealed at 

700°C show relatively large deviations from the exact twin orientation (Figure 7a). 

Figure 6. OIM image showing the low-angle grain 

boundary structure (white lines) in Cu-30% Zn sample 

annealed at 700°C for 1 hour.

This may provide evidence of twin grain 

boundaries acting as preferential dislocation sources. 

Decomposition of twin boundaries at high temperatures leaves behind a low-angle grain boundary and 

a grain boundary with a misorientation different 

from the original twin orientation. 

Figure 7. The Cu-30% Zn sample annealed at 700°C (a) 

exhibits twin boundaries that deviate up to about 9° from 

the exact twin boundary orientation (black boundaries). 

Annealing at 600°C (b) results in twin boundaries that 

deviate by <3° from exact coincidence (white boundaries).

This would support past findings that the flow stress 

correlates with the twin grain boundary density, implying that twin boundaries act as dislocation 

sources during deformation. Further analysis of this 

sample to confirm this finding is under way. The 

46 
High Strength Weight Reduction Materials FY 2004 Progress Report 

findings will be published in a peer-reviewed journal. 

Conclusions 

During FY 2004, work focused on developing 

ECAE processing schedules to optimize mechanical 

properties. Billets of a commercial magnesium alloy, 

ZK60A, have been ECAE processed by five new 

processing schedules. Preliminary superplastic studies show that the processing schedules may potentially yield a lightweight material capable of high 

strain rate superplasticity. Such a material will be 

more economically competitive (high production 

rate coupled with minimal scrap) with other traditional structural materials such as steel. Considerable 

weight savings and increased fuel efficiency could 

be realized by using magnesium alloys in place of 

iron-based materials. 

ECAE processing also appears to be a means of 

improving the mechanical properties of MMCs. The 

proper combinations of ECAE processing temperatures, back stress, and the number of passes through 

the ECAE die result in MMCs with better strength, 

ductility, and elastic modulus. The elastic modulus 

is still significantly lower than the theoretical value, 

and microstructural studies indicate residual porosity, both suggesting that further improvements can 

be made with optimized ECAE processing schedules. Increased ductility afforded by ECAE process 

ing offers the potential for improved fabricability 

and wider application of MMCs. Lightweight, highstiffness MMCs may then be employed as structural 

members in transportation applications, leading to 

more fuel-efficient vehicles. 

Publications and Presentations

S. R. Agnew, J. A. Horton, T. M. Lillo, D. W. 

Brown, “Enhanced Ductility in Strongly Textured 

Magnesium Produced by Equal Channel Angular 

Extrusion,” Scripta Mat., 50, 377–381 (2004). 

D. P. Field, M. M. Nowell, P. Trivedi, S. I. 

Wright, and T. M. Lillo, “Local Orientation Gradient and Recrystallization of Deformed Copper,” accepted for publication in Proceedings of the 

International Conference on Textures and Anisotropy of Polycrystalline Materials. 

D. P. Field, B. W. True, T. M. Lillo, J. E. Flinn, 

“Observation of Twin Boundary Migration in Copper During Deformation,” accepted for publication 

in Materials Science and Engineering A, 2004. 

M. M Nowell, D. P. Field, S. I. Wright, and 

T. M. Lillo, “In-Situ EBSD Investigation of Recrystallization in ECAE Processed Copper,” Malts. Sci. 

Forum, 467–470, 1401–1406 (2004). 

R. B. Schwarz, T. D. Shen, U. Harms, and T. 

Lillo, “Soft Ferromagnetism in Amorphous and 

Nanocrystalline Alloys,” Journal of Magnetism and 

Magnetic Materials, 283, 223–230 (2004). 

47 
FY 2004 Progress Report High Strength Weight Reduction Materials 

48 
High Strength Weight Reduction Materials FY 2004 Progress Report 

49 

E. Development of an Advanced Squeeze Casting Process for the Production of 

High-Integrity Truck Components 

Principal Investigator: David C. Weiss 

Eck Industries, Incorporated 

1602 North 8th Street, Manitowoc, WI 54221-0967 

(920) 682-4618; fax: (920) 682-9298; e-mail: dweiss@eckindustries.com 

Technology Development Area Specialist: Sidney Diamond 

(202) 586-8032; fax: (202) 586-1600; e-mail: sid.diamond@ee.doe.gov 

Field Technical Manager: Philip S. Sklad 

(865) 574-5069; fax: (865) 576-4963; e-mail: skladps@ornl.gov 

Contractor: Eck Industries, Incorporated

Contract No.: 4000022893 

Objective 

• Develop the equipment and process technology for an advanced squeeze casting (ASC) process to enable production of high-integrity cast metal components. 

⎯ Integrate the advantages of two casting methods—low-pressure permanent mold and direct squeeze casting 

—to attain non-turbulent fill of the die, high solidification rates to refine microstructural features, and solidification under pressure to minimize microporosity. 

⎯ Design and build a new kind of casting machine and develop process technologies needed to cast highintegrity truck components from nonferrous alloys. 

Approach 

• Design and construct a casting machine that integrates a low-pressure metal delivery system suitable for either 

aluminum or magnesium alloys, reliable gate shut-off technology, and direct application of squeeze pressures 

of up to 103 MPa (15,000 psi). This machine is intended for production. 

• Develop a gate shutoff mechanism that will operate reliably in a production environment. 

• Select a casting that will be produced in the casting machine built for this project. 

• Use fluid-flow and solidification analysis to predict optimum flow conditions for metal entering the mold and 

differential squeeze pressure requirements. 

• Design and build cast tooling. 

• Develop process technologies for the low-pressure/squeeze casting of aluminum alloys and evaluate the effect 

of various process parameters on casting integrity. 

• Apply developed technologies to the production of a selected automotive component. 

Accomplishments 

• Completed design of ASC machine. 

• Reached 80% completion of fabrication of ASC machine. 

• Designed and fabricated data acquisition system. 

• Designed and fabricated gate shutoff mechanism. 
FY 2004 Progress Report High Strength Weight Reduction Materials 

50 

• Designed and fabricated squeeze cast tooling. 

Future Direction 

• Complete fabrication of ASC machine and install data acquisition system. 

• Install ASC machine at Eck Industries. 

• Integrate operation of gate shutoff mechanism with the casting machine control system. 

• Develop and evaluate ASC process technologies. 

• Demonstrate production viability of ASC casting machine and process. 

Introduction 

Squeeze casting is the solidification of liquid 

metal under pressure in a closed metal die. The 

resulting casting has improved properties and a 

more uniform microstructure compared with those 

produced by traditional molten metal fabrication 

techniques. The higher properties are achieved 

through controlled entry of the metal into the die 

through large gates, which reduces turbulence, and 

high solidification rates, resulting in refinement of 

microstructural features. 

There are two squeeze casting methods—

direct and indirect. The method and efficiency of 

pressure application distinguish the two processes. 

Direct squeeze casting applies pressure directly on 

the casting. Indirect squeeze casting applies pressure via the gating system. The length of the gating system and any partial solidification prior to 

complete solidification of the part reduces the 

magnitude of the pressure applied and may result 

in casting porosity. For the indirect squeeze cast 

method, the dimensions of the die cavity control 

the part dimensions. For direct squeeze casting, 

the part dimensions are controlled by the die cavity dimensions and the finish position of the top 

die. Thus the direct squeeze cast method requires 

precise machine control to attain the desired part 

dimensions. In addition, the direct method requires 

in-gate shutoff technology to control pressure during cavity pressurization. Both methods suffer 

from poor metal handling from the furnace into 

the mold or gating system. Inadequate control of 

pouring speed generates turbulence and casting 

defects, such as oxide inclusions, that reduce fatigue properties. 

Earlier attempts to improve the squeeze casting process by combining the advantages of lowpressure die fill with those of squeeze casting 

demonstrated substantial mechanical property improvement and reduced component porosity. 

However, continuous production operation of the 

equipment was not achieved. The machines used 

were not specifically designed to meet the needs 

of the process. 

Technical Approach

The results of this project will provide (1) a 

production-viable ASC machine, (2) process technology that will improve the strength and reliability of cast automotive components, and (3) 

demonstrated production viability of the equipment and process. 

Machine Design. Previous efforts have demonstrated that modification of existing cast machine designs does not provide a productioncapable ASC machine. An assessment of the capabilities and limitations of existing machine designs 

demonstrated that 

• Low-pressure casting equipment typically does not 

have the structural rigidity needed to withstand the 

high pressures required of squeeze casting. 

• Die-casting and currently available squeeze casting 

machines are not designed for proper (nonturbulent) molten metal entry into the die cavity. 

• Neither type of equipment is typically available 

with the hydraulic and electronic controls necessary to attain the die cavity motions required for 

the direct squeeze casting process. 
High Strength Weight Reduction Materials FY 2004 Progress Report 

51 

After much consideration, the project team decided it was easier and more cost-effective to build 

a machine from the ground up than to modify an 

existing cast machine design. To facilitate this design and construction, the team partnered with 

Empire Castings, Inc., an experienced producer of 

low-pressure casting equipment. 

Process Development. Bendix, Inc. is an industrial manufacturer of truck components with an 

interest in reducing manufacturing cost by the use 

of high-quality castings. Consultation with Bendix 

led to the selection of an air compressor connecting rod for prototype production in the ASC machine. This component has a level of complexity 

that can demonstrate the production capability of 

the ASC machine and process and the need for 

mechanical properties higher than those attainable 

with commercially available castings, and it provides an opportunity for production with the ASC 

process. 

The cast part will be modeled for fluid flow 

and solidification. This work will be done in parallel with equipment design. Simulation will provide 

an understanding of optimum metal flow conditions and squeeze requirements, if any, to contend 

with solidification shrinkage. This is very important to the success of the program and potentially 

to the details of the machine design. The ASC machine will have two mechanisms to feed the casting—low-pressure, nonturbulent fill of the die 

cavity and high-pressure, direct squeeze to minimize solidification shrinkage. Modeling experiments will explore the interaction of the two feed 

mechanisms and select process parameters that 

lead to process optimization. Modeling results will 

be used to refine the die design and select initial 

casting process parameters. 

After tooling construction and ASC machine 

delivery, castings will be made under the range of 

process conditions anticipated during modeling. A 

variety of both cast and wrought alloys (Table 1) 

will be used. Evaluation of those castings will include radiography, die penetrant inspection, tensile testing, and functional component testing at 

Bendix. It is anticipated that this part of the program will require multiple iterations to produce 

the desired product quality. Some equipment and 

tooling modification may be required during this 

part of the program. 

Table 1. Aluminum alloys to be used for 

casting trials 

AA 380 AA 206 

AA 356 AA 6061 

AA 357 AA 535 

AA 319 AA 388 

After successful production of development 

castings, the production viability of the equipment 

and process will be demonstrated by 

• Production of a connecting rod with reduced porosity and improved mechanical properties compared with the current die-cast connecting rod used 

by Bendix. 

• Continuous production with the ASC machine and 

connecting rod tooling to include at least one 5-h 

continuous run with the equipment running at least 

3 days in a week. 

The goal of the project team is to implement 

part production on an ongoing basis. The production phase of the project will include detailed cost 

analysis of part production, determination of dielife parameters, and ongoing equipment and tooling development for maximum uptime. 

Program Status

ASC machine. The design (Figure 1) for the 

600-ton capacity ASC machine has been completed. Positioning of the top die is accomplished 

independently of the squeeze-cast cylinder. To 

maximize machine capability, the melting vessel is 

equipped with a crucible furnace. This facilitates 

the melting of both cast and wrought aluminum 

and magnesium alloys as well as aluminum and 

magnesium metal matrix composite alloys. 

To match the dimensional capabilities of the 

die-cast process, a closely controlled volume of 

liquid metal must be fed into the die cavity. Conventional low-pressure fill technology does not 

have the capability to accurately meter a fixed 

amount of liquid metal into the die. Therefore, we 

will accurately position (± 0.13 mm) the top die to 

obtain the desired fill volume and use a fill sensor 

and an independently controlled gate shutoff to 

control metal volume. Development of a reliable 

gate shutoff technology is a key part of the ex- 
FY 2004 Progress Report High Strength Weight Reduction Materials 

52 

Figure 1. Design for 600-ton ASC 

machine. 

perimental program. Gate shutoff system components are shown in Figure 2. 

Data acquisition system. A computerized 

data acquisition system has been designed to interface with the displacement, pressure, and temperature sensors located on the ASC press and cast 

tooling. Analysis of these data will be critical in 

understanding the operation of the ASC process. 

This system will be installed on the machine in 

early November. 

Figure 2. Components of the in-gate shutoff system. 

Cast tooling. The die for casting aircompressor connecting rods and tensile test bars 

has been completed. As shown in Figure 3, the 

tooling consists of a die holder and individual die 

inserts for the particular part being cast. This tooling will be used for the machine run-off. 

Figure 3. View of cast tooling. 

Conclusions

Good progress has been made on the project. 

The steel shortage and prior commitments of the 

machine builder delayed press construction by 

about 6 months. This is reflected in the revised 

schedule (Table 2). All other tasks of the project 

are on schedule. The results of casting simulation 

should decrease the process development time required to the 3 months reflected in the revised 

schedule. 
High Strength Weight Reduction Materials FY 2004 Progress Report 

53 

F. Thermomechanical Processing of Ti and Ti-6Al-4V Sheet and Plate 

Principal Investigator: Craig A. Blue 

Oak Ridge National Laboratory 

Oak Ridge, TN 37831-8063 

(865) 574-4351; fax (865) 574-4357; e-mail: blueca@ornl.gov 

Field Project Manager: John D. K. Rivard 

Oak Ridge National Laboratory 

Oak Ridge, TN 37831-8063 

(865) 241-8113; fax (865) 574-4357; e-mail: rivardjd@ornl.gov 

Technology Development Area Specialist: Sidney Diamond 

(202) 586-8032; fax: (202) 586-1600; e-mail: sid.diamond@ee.doe.gov 

Field Technical Manager: Philip S. Sklad 

(865) 574-5069; fax: (865) 576-4963; e-mail: skladps@ornl.gov 

Participants 

Evan K. Ohriner, Oak Ridge National Laboratory 

David C. Harper, Oak Ridge National Laboratory 

Jim O. Kiggins, Oak Ridge National Laboratory 

Paul A. Menchhofer, Oak Ridge National Laboratory 

Lance Jacobsen, International Titanium Powder, L.L.C. 

Dariusz Kogut, International Titanium Powder, L.L.C. 

Contractor: Oak Ridge National Laboratory 

Contract No.: DE-AC05-00OR22725 

Objective 

• Investigate and develop vacuum hot pressing (VHP) methods for the production of titanium (Ti) and Ti-6Al-4V 

plate from Ti and Ti-6Al-4V powder provided by International Titanium Powder, LLC (ITP). 

• Simulate a roll compaction method for the manufacturing of Ti and Ti-6Al-4V thin-gage sheet from Ti and Ti6Al-4V powder provided by ITP. 

• Demonstrate the ability to process thin-gage sheet using powder Ti precursor and plasma arc lamp processing. 

• Mechanically test Oak Ridge National Laboratory (ORNL)–produced materials 

• Optically and chemically analyze ORNL-produced materials. 

Approach 

• Conduct parametric studies using VHP to consolidate ITP Ti and Ti-6Al-4V powder to demonstrate the feasibility of powder use for further experiments. 

• Develop roll compaction techniques for the production of thin-gage Ti and Ti-6Al-4V from ITP powder using 

infrared (IR) heating from tungsten halogen lamp furnaces and plasma arc lamp. 
FY 2003 Progress Report High Strength Weight Reduction Materials 

54 

• Characterize ORNL-produced material properties. 

• Develop approach to scaling processing techniques for large-scale production applications. 

Accomplishments 

• Successfully consolidated ITP Ti and Ti-6Al-4V powder using VHP. 

• Developed processing techniques for production of thin-gage sheet using IR heating. 

• Evaluated physical, microstructural, and chemical properties of ORNL-produced materials 

Future Direction 

• Partner with ITP and Ametek to scale process to produce Ti and Ti-6Al-4V sheet and plate at substantially reduced cost using a lab-scale roll compaction process as a basis for commercial processing. 

• Partner with Universal Alloy Cooperation to extrude ITP Ti and Ti-6Al-4V rod and plate. Plates up to 40 in. 

wide can be extruded. 

Introduction

The aircraft industry is currently the single largest market for Ti and Ti alloy products primarily 

because of the exceptional strength-to-weight ratio, 

elevated temperature performance, and corrosion 

resistance. 

Titanium usage, however, is strongly limited 

outside the aerospace industry by its higher cost 

relative to competing materials, primarily aluminum 

alloys and steels. Although Ti possesses an attractive 

set of properties, including high specific strength 

and corrosion resistance, and allows for damagetolerant design, cost limits applications to selected 

markets. Many automotive systems would benefit 

from the use of Ti products. Automotive exhaust 

systems could save as much as 50% of their current 

weight by integrating Ti parts. Titanium valves and 

valve springs, connecting rods, suspension springs, 

wheels, drive shafts, underbody panels, side impact 

bars, and half shafts are just some of the automotive 

applications that could benefit from the use of Ti. 

The present market comparison for the use of 

engineering materials shows that steel is the most 

widely used material, with 800 million tons used 

each year. Aluminum, stainless steel, and copper are 

used at a rate of 22 million tons, 16 million tons, and 

12 million tons, respectively. Titanium is much less 

widely used at 0.05 millions tons per year. 

Potential technical problems preventing the integration of Ti, apart from cost of manufacturing, 

include wear resistance, a lower modulus than steel, 

and machining difficulties. Wear resistance can be 

addressed by coatings/reinforcements; the modulus 

can be increased by reinforcing the part with a second material; and the machining difficulties can be 

reduced by the production of near-net-shape parts. 

The major problem is that Ti costs substantially 

more than competing materials. 

Although the cost of Ti ore is significantly more 

than that of other competing materials, the difference in the cost of sheet is a result of processing. 

Processing of Ti from ingot to plate accounts for 

47% of the total cost of the material. 

Current melting techniques include vacuum arc 

remelting (VAR), electron beam melting, and 

plasma arc single-melt processes. VAR is used to 

clean and refine air-melted ingots and to improve 

homogeneity and refine grain size. To VAR-cast an 

ingot, a dc arc is struck between a Ti electrode and a 

base plate. The intense heat melts the electrode, and 

the Ti is cast into an ingot. VAR requires 20 hours 

and large-scale equipment. 

Electron beam and plasma arc single-melt processes have the advantage over VAR in that an airmelted ingot is not required. In these two processes, 

ingots are cast directly from melted feed sponge. But 

the cast ingot still requires post-processing, which 

accounts for 47% of the total cost. The plasma arc 

melt process is similar; plasma arc torches are used 

in place of electron beams for melting. 

Alternative processing methods such as casting, 

laser forming, and spray forming have also been explored. Casting is best suited for complex shape 

forming and is not economical for sheet processing. 

The process requires extensive tooling and frequent 
High Strength Weight Reduction Materials FY 2004 Progress Report 

55 

inspections. A post–hot isostatic pressing (HIP) is 

needed to eliminate porosity. Laser forming uses a 

raw powder stream injected into a rastered laser 

beam to melt, form, and build up sheet. Spray forming operates similarly, although a plasma torch melts 

the powder. Laser forming and spray forming have 

the advantages of using less material, requiring 

minimal tooling, and needing short cycle times. But 

it is difficult to control the thermal history of laser 

forming, and both methods suffer from residual porosity. In addition, both of these methods require 

conventionally produced and atomized powder, 

which is very costly. 

Although much time and effort has been invested in the development of these processing techniques, the cost of Ti still remains high because of 

the cost of raw materials, cost of post-processing, 

and yield losses. In recent work performed at the 

Infrared Processing Center at ORNL, new methods 

of Ti sheet and plate processing have been investigated. VHP, high-density infrared (HDI) processing, 

and roll compaction processing were explored. All 

three methods used powder provided by ITP. ITP 

has developed a new low-cost method of powder 

production and is currently running a pilot processing facility. 

Experimental Procedure

ITP Ti powder was processed into plate and 

sheet using three methods, VHP, HDI, and roll compaction. ITP Ti-6Al-4V was processed into plate and 

sheet using VHP and roll compaction. VHP, a batch 

process, was used to make Ti and Ti-6Al-4V plate. 

HDI and roll compaction were both used to make Ti 

sheet. Roll compaction also was used to make Ti6Al-4V sheet. HDI uses a plasma arc lamp to heat 

and liquid-phase-sinter vacuum-cold-pressed Armstrong Process Ti powder. Sintered compacts were 

repeatedly cold-rolled and flash-annealed under the 

plasma arc lamp in order to make sheet. Similarly, 

roll compaction uses medium-density tungstenhalogen–based radiant heating to solid-phase-sinter 

vacuum-cold-pressed Armstrong Process Ti and Ti6Al-4V powder. Sintered compacts were repeatedly 

cold-rolled and annealed until thin-gage sheet was 

produced. 

VHP was used to make four samples of Ti plate 

and one Ti-6Al-4V plate. Each of the four samples 

was pressed under vacuum in a graphite element 

radiant furnace. The three Ti samples and the Ti6Al-4V sample were pressed in a 63.5-mm-diam 

graphite die. The fourth sample was pressed in a 

178-mm-diam die. For each of the pressing operations, the die was lined with Grafoil and a measured 

amount of Ti powder was poured into the die. For 

the 63.5-mm-diam samples, the die was filled with 

36 g of Ti or Ti-6Al-4V powder. And for the 178-

mm-diam sample, the die was filled with 130 g of Ti 

powder. To prevent mechanical interaction between 

air and the powder, no pre-pressing was applied. A 

special collar was placed under the die to keep it in 

place while the powder was being pressed. When the 

rams were jogged into place, the furnace was closed, 

sealed, and evacuated. The furnace was back-filled 

with argon gas and evacuated three times in order to 

ensure a clean processing environment. The 63.5-

mm-diam Ti samples were pressed at a pressure of 

55.3 MPa. One sample was pressed at 750°C for 15 

min, another sample was pressed at 900°C for 15 

min, and the final sample was pressed at 900°C for 

30 min. The Ti-6Al-4V 63.5-mm-diam sample was 

pressed at a pressure of 55.3 MPa for 1 hour at 

950°C. The 178-mm-diam Ti sample was pressed at 

a pressure of 11.7 MPa for 1 hour at 900°C. All five 

samples were allowed to furnace cool after the heating cycle was completed. After the samples were 

removed from the furnace, the sample surfaces were 

ground and polished, and the densities were measured by immersion in ethanol (Archimedes method). 

Tensile specimens were machined from each 63.5-

mm-diam sample. The tensile specimens were machined to the SS3 standard. Mechanical testing, 

chemical analysis, and optical microscopy were performed on the samples. 

Roll compaction was developed by Ametek 

Corporation for the commercial production of nickel 

and other advanced alloy sheet. With ITP Ti powder 

costing as little as $4/lb, and with the greatly reduced effort needed to obtain sheet compared with 

the ingot processes, roll compaction could eliminate 

a large portion of total Ti sheet fabrication costs 

dedicated to forming. Roll compaction begins with 

raw powder fed into rolls from a hopper. The rolls 

compact the ductile powder into sheet. The sheet is 

then fed into a furnace where the sheet is sintered. 

Subsequent roll and sinter operations are performed 

continuously until a dense, thin-gage sheet is produced. 

To simulate a roll compaction process on a laboratory scale, thin-gage sheet was produced by sinter-
FY 2003 Progress Report High Strength Weight Reduction Materials 

56 

ing powder compacts in an IR furnace followed by 

cold rolling. First, 18 g of Ti or Ti-6Al-4V powder 

was vacuum-cold-pressed in a 50.8-mm-diam die at 

a pressure of 48.3 MPa. Powder compacts were 

heated in a 33-kW IR furnace that contains a 152-

mm-inside-diam quartz tube that allows for vacuum 

and argon gas flow in the chamber. 

The Ti sample was heated to 1200°C, held for 2 

hours, and then furnace-cooled and cold-rolled. The 

initial thickness was 3.25 mm; after rolling, it was 

1.29 mm. The sample was again heated at 1200°C 

for 2 hours in the IR furnace. The sample was then 

cold-rolled from 1.29 to 0.53 mm. A final anneal of 

1200°C for 1 hour was then performed on the sample. 

The Ti-6Al-4V sample was heated to 950°C and 

held for 2 hours and then furnace-cooled and coldrolled. The initial thickness was 4.06 mm, and 

thickness after rolling was 1.90 mm. The sample 

was again heated at 950°C for 30 min in the IR furnace. The sample was then cold-rolled from 1.90 to 

0.97 mm. Another intermediate anneal was performed by heating the sample to 950°C for 30 min. 

A final cold-roll was performed, and the final gage 

thickness was measured at 0.61 mm. A final 

950°C/30-min stress relief was also performed. 

From each final sheet, tensile specimens were 

machined and tested, chemical analysis was performed, and the microstructure was investigated. 

HDI processing is similar to roll compaction but 

uses heating the sample to the liquid phase to 

achieve bonding. In order to achieve temperatures 

above the 1650°C melting point of Ti, a plasma arc 

lamp is used to rapidly heat a vacuum-cold-pressed 

compact. The plasma arc lamps use a unique technology to produce extremely high power densities 

with a single lamp. Instead of an electrically heated 

resistive element, controlled and contained plasma is 

used. 

The lamp is sealed at the ends where the cathode 

and anode are located. Deionized water mixed with 

argon gas enters at the cathode side through highvelocity jets impinging at a given angle. Because of 

the high velocities and pressure, the deionized water 

is impelled to the wall of the quartz tube and spirals 

down the length of the tube in a uniform 2- to 3-

mm-thick film. This water film serves two purposes: 

to cool the quartz wall and to remove any tungsten 

particulates that may be expelled from the electrodes. The gas moves in a spiral fashion through the 

center of the tube, and a capacitative circuit initiates 

the plasma. The lamp operates at 750,000 W and is 

fitted with a reflector that illuminates a 20×15 cm 

area with a power density of up to 460 W/cm2

. The 

plasma, which has a temperature in excess of 10,000 

K, is stable and produces a radiant spectrum from 

0.2 to 1.4μm. 

The processing steps for HDI were very similar 

to those for roll compaction. First, 9 g of raw Ti 

powder was vacuum-cold-pressed in a 50.8-mmdiam steel die under 48.3 MPa pressure. The coldpressed compact was then placed in an environmentally controlled processing box. The box was water 

cooled and vacuum-tight. The box was evacuated 

and back-filled with argon gas to reduce oxidation 

during processing. 

The sample was moved into position under the 

lamp and liquid-phase-sintered at 280 W/cm2

 for 

8.5 s. The thickness after sintering was measured at 

1.8 mm. After a cold-rolling operation, the sample 

measured 0.95 mm. The cold-rolled sample was 

flash-annealed under the lamp at 280 W/cm2

 for 5 s. 

The sample was then rolled to 0.62 mm. A second 

flash anneal was performed at 280 W/cm2

 for 5 s. A 

final cold roll was performed, and the final thickness 

measured 0.40 mm. The sample was flash-annealed 

at 100 W/cm2

 for 5 s. The thin-gage, annealed sheet 

was mechanically tested, chemically analyzed, and 

observed under a light microscope. 

Results and Discussion

After the post-pressing grinding and machining 

was performed on the VHP Ti and Ti-6Al-4V consolidated powder, the samples were polished. Figure 1 shows the final Ti plates. 

The density of each plate was measured by the 

Archimedes method to be 100%. But metallographic 

observations performed on a light microscope 

showed differences in the levels of sintering obtained for the three pressing conditions. Figure 2 

shows the microstructure of the VHP samples 
High Strength Weight Reduction Materials FY 2004 Progress Report 

57 

Figure 1. As-VHP and machined Ti plates, 63.5 mm diameter and 178 mm diameter. 

at 750°C for 15 min, 900°C for 15 min, and 900°C 

for 30 min. 

Figure 2a shows that sintering in the 750°C/15 

min samples was incomplete, and many voids in the 

microstructure still remained. Figure 2b shows that 

increasing the pressing temperature to 900°C helps 

to reduce the amount of void present. But the best 

results were obtained by pressing at 900°C for 30 

min. Figure 2c shows the least amount of void after 

pressing at 900°C for 30 min and shows that grain 

growth has occurred, indicating that the particles 

have fully bonded to each other. Figure 2d shows 

the microstructure of the VHP Ti-6Al-4V samples. 

Figure 2. Microstructure for VHP samples (a) Ti 

750°C/15 min, (b) Ti 900°C/15 min, (c) Ti 900°C/30 min, 

and (d) Ti-6Al-4V 950°C/1h4. 

The lack of sintering at 750°C and 900°C/15 

min was also apparent in mechanical testing. Each of 

the SS3 tensile specimens machined from the 63.5-

mm-diam plates was tested in tension with a crosshead speed of 0.51 mm/min. The mechanical testing 

results are shown in Table 1. 

According to Allegheny Ludlum, Grade 2 Ti has 

comparable properties to the 930°C/30 min VHP 

samples. The Ti-6Al-4V VHP samples also exceeded the properties published for this material. 

Chemical analysis showed that the VHP Ti samples 

were all below the maximum allowable limits of O2, 

N2, and C for Grade 2 Ti. The O2 content of the 

VHP Ti-6Al-4V slightly exceeded the upper limits 

for Grade 5 Ti-6Al-4V, but the high oxygen level 

did not adversely affect mechanical testing results. 

The results of the chemical analysis are shown in 

Table 2. 

Microstructural investigations were performed 

on the HDI-processed roll-compacted Ti and on rollcompacted Ti-6Al-4V thin-gage sheet materials. 

Both samples were cut from the as-annealed sheet, 

mounted, polished, and etched with Kroll’s reagent. 

Optical microscopy revealed that the roll-compacted 

sample had a standard annealed Ti microstructure. 

Throughout the entire cross section, the rollcompacted sheet was virtually free of flaws with a 

very consistent microstructure. The HDI-processed 

material showed that the intense, short-duration, and 

directional heating of the plasma arc lamp caused 

large grains to grow on the top surface during the 

final anneal. But the structure remained equiaxed 

alpha with beta spheroids. Also, microscopy showed 

that many rolling lapses remained in the final HDIprocessed sheet. Investigation of the structure of the 

roll-compacted Ti-6Al-4V sheet showed that a significant amount of retained oxygen-stabilized-α was 

present. Figure 3 shows the microstructure of the 

HDI-processed Ti sheet, the roll-compacted Ti sheet, 

and the roll-compacted Ti-6Al-4V sheet. 

Mechanical testing of the HDI-processed and 

roll-compacted sheet was performed. Tensile testing 

results are shown in Table 3. 

The lack of ductility of the HDI-processed samples was due to the observed rolling lapses. This is 

similar to the lack of complete sintering in the 

750°C/15 min VHP sample. The mechanical properties of roll-compacted Ti sheet showed that the 

strengths are comparable to Grade 4 Ti. But the 

oxygen content of the roll-compacted samples exceeded the allowable limit for Grade 4, and the ductility suffered as a result. The chemical analysis 
FY 2003 Progress Report High Strength Weight Reduction Materials 

58 

Table 1. Mechanical testing results of VHP Ti and Ti-6Al-4V plates 

Sample Yield strength 

[MPa] 

Tensile strength 

[MPa] 

Elongation [%] 

Ti 750°C/15min 532 571 1.7 

Ti 915°C/15min 544 636 14.9 

Ti 930°C/30min 517 617 20.7 

Ti grade 2 (min values) 345 448 20.0 

Ti-6Al-4V 950°C/1 hour 963 994 13.8 

Ti-6Al-4V grade 5 (min values) 828 897 10.0 

Table 2. Chemical analysis of VHP Ti and 

Ti-6Al-4V plate (nominal %) 

Sample O2 [%] N2 [%] C [%] 

Ti 750°C/15min 0.23 0.01 0.05 

Ti 900°C/15min 0.25 0.01 0.06 

Ti 900°C/30min 0.24 0.01 0.03 

Ti grade 2 (max limits) 0.25 0.03 0.08 

Ti-6Al-4V 950°C/1hour 0.28 0.01 0.04 

Ti-6Al-4V grade 5 (max limits) 0.20 0.05 0.08 

Table 3. Mechanical testing results of HDI-processed and roll compacted Ti sheet 

Sample Yield strength [MPa] Tensile strength [MPa] Elongation [%] 

HDI-processed Ti 486 598 8.8 

Roll-compacted Ti 529 656 9.6 

Ti grade 4 483 552 15.0 

Figure 3. Microstructure for thin-gage sheet samples (a) 

roll-compacted Ti, (b) HDI-processed Ti, and (c) rollcompacted Ti-6Al-4V. 

of the HDI-processed and roll-compacted material is 

shown in Table 4. 

Summary

These are the highlights of the progress during 

FY 2004: 

1. Production of VHP Ti plate with mechanical properties comparable to those of commercially pure Ti 

grade 2. 

2. Production of VHP Ti-6Al-4V plate. 

3. Roll compaction of Ti and Ti-6Al-4V thin-gage 

sheet. 

4. Production of HDI-processed Ti thin-gage sheet. 

5. Mechanical, optical, and chemical analysis of 

ORNL-produced sheet. 

Conclusions

Although Ti and Ti-6Al-4V have attractive 

properties that would benefit a great number of engineering applications, their use is limited by the 

cost of the raw material and the processing that is 

necessary to make a usable product. But with the 

recent advancements in low-cost powder production 

at ITP, in conjunction with processing techniques 
High Strength Weight Reduction Materials FY 2004 Progress Report 

59 

Table 4. Chemical analysis of HDI-processed and roll compacted thin gage Ti sheet 

Sample O2 N2 C 

HDI-processed Ti 0.29 0.01 0.03 

Roll-compacted Ti 0.42 0.01 0.03 

Ti grade 4 (max limits) 0.40 0.05 0.08 

developed at ORNL, the cost of Ti sheet and plate is 

predicted to decrease. While VHP on a large scale 

may not be an economical method of plate production, it does demonstrate that ITP powder can produce a viable product. HDI-processing could be 

developed into a commercial process, but liquidphase processing may not be desirable. Furthermore, 

HDI-processed Ti sheet lacks the mechanical properties necessary. Roll compaction is the best alternative to the current VAR and other ingot metallurgy 

processes used to process Ti. Processing facilities 

are in place to produce nickel alloys and could easily 

be modified to process Ti. Lab-scale roll compaction 

produced thin-gage Ti sheet with the appropriate 

microstructure, mechanical properties, and chemical 

composition. Although the ductility is slightly below 

acceptable levels, a scaled-up facility will have better control over oxygen contamination, eliminating 

this problem. Results suggest that the roll compaction of Ti sheet should be further explored. 
FY 2003 Progress Report High Strength Weight Reduction Materials 

60 
High Strength Weight Reduction Materials FY 2004 Progress Report 

61 

4. ENABLING TECHNOLOGIES 

A. Improved Friction Tests for Engine Materials

Principal Investigator: P. J. Blau 

Oak Ridge National Laboratory 

P.O. Box 2008, Oak Ridge, TN 37831-6063 

(865) 574-5377; fax: (865) 574-6918; e-mail: blaupj@ornl.gov 

Technology Development Area Specialist: Sidney Diamond 

(202) 586-8032; fax: (202) 586-1600; e-mail: sid.diamond@ee.doe.gov 

Field Technical Manager: Philip S. Sklad 

(865) 574-5069; fax: (865) 576-4963; e-mail: skladps@ornl.gov 

Contractor: Oak Ridge National Laboratory 

Contract No.: DE-AC05-00OR22725 

Objectives 

• Develop a realistic, engine-correlated laboratory-scale test method to be used to evaluate new diesel engine piston ring and liner materials 

• Work with ASTM, through an industry-based advisory group, to establish a standard practice for testing the 

friction of piston ring and liner material combinations. 

• Investigate the ability of the new test method to detect small friction and wear differences due to the effects of 

engine conditioning of the lubricants. 

Approach 

• Review and critique past attempts to develop laboratory tests for piston ring and liner materials. 

• Develop a testing protocol for friction and wear in reciprocating, lubricated contacts that simulate key aspects 

of the diesel engine environment. 

• Study the characteristics of diesel-engine–conditioned oil and determine how to simulate its effects on the friction and wear response of candidate materials. 

• Work with ASTM through Committee G-2 on Wear and Erosion to develop and approve a standard practice for 

conducting laboratory-scale piston ring and liner friction and wear tests. 

Accomplishments 

• Published a report describing and critiquing past efforts to develop engine-correlated, laboratory-scale tests for 

materials and lubricants proposed for use in both spark-ignition and diesel engines. 

• Established an ASTM task group on Ring and Liner Wear within Committee G02.40 on Non-Abrasive Wear. 

Populated the task group with representatives from diesel engine companies, automotive companies, testing 

machine manufacturers, oil companies, government laboratories, and universities. 

• Developed a technique for simulating the surface finish of production cast iron cylinder liner bores on simple 

test coupons. 
FY 2004 Progress Report High-Strength Weight Reduction Materials 

62 

• Obtained samples of oils run in standardized engine tests and used them to determine the sensitivity of the new 

test method to delineate lubricant condition. 

• Prepared a draft standard practice for ASTM subcommittee review, submitted it for balloting, and revised it 

based on the results. The revised document is in process of final committee approval. 

Future Direction 

• Having established the standard, prepare a research report that documents its development, and use the standard 

to determine the friction of several promising engine ring and liner materials. 

Introduction 

Friction robs engines of useful energy and lowers the vehicle’s fuel economy. Depending on engine speed, the piston ring and liner system in an 

internal combustion engine can account for more 

than 50% of the total frictional losses in an engine. 

New materials, lubricants, and coatings offer the 

potential to reduce such frictional losses; but the 

development cost can be high, especially when fullscale engine tests are used. Smaller-scale, simulative 

laboratory tests are an attractive lower-cost alternative, but they are useful only if the results correlate 

well with the materials’ performance in fired engines. 

The design of cost-effective, laboratory-scale 

ring and liner simulations presents a complex challenge. Improperly designed simulations can produce 

misleading results. Materials and lubricants must be 

induced to react in tests as they would in actual service. Tests should enable the ranking of alternative 

materials and lubricants in the same order of merit as 

they would perform in service. That requires identifying and controlling the major mechanical, thermal, 

and chemical factors that influence the materials’ 

friction and wear characteristics. 

The development of a standard practice through 

ASTM was thought to be the best way to produce a 

rigorous friction test for ring and liner materials, one 

that would meet with industry approval through a 

consensus voting and approval process. ASTM is an 

international organization that develops consensus 

material testing standards. By working through 

ASTM Committee G-2, Oak Ridge National Laboratory (ORNL) was able to draw on dozens of experienced testing professionals. 

In FY 2001, key elements required for effective 

ring/liner simulation were identified. In FY 2002, 

the effort was focused on building an industry advisory group and involving ASTM. In FY 2003, friction and wear tests were conducted in new and used 

engine oils to refine the test methodology and prepare it for the rigorous ASTM standardization process. In FY 2004, the balloting process was 

conducted. The following section describes this evolutionary process. 

Development of the Standard 

This formal development of the standard document began with the establishment of a task group 

on Ring and Liner Wear, by ASTM Committee 

G02.40, under the auspices of the Subcommittee on 

Non-Abrasive Wear. In parallel, ORNL researchers 

began to evolve new laboratory testing procedures 

and to acquire samples of well-characterized, standard diesel engine test oils from Southwest Research 

Institute. These engine-conditioned oil samples were 

comprehensively characterized by sending them to a 

company that specializes in motor oil analysis. 

During that period, decisions had to be made regarding contact geometry, specimen fixturing, cylinder liner surface roughness, surface finish 

directionality (‘lay’), and the use of special runningin procedures to ensure proper specimen alignment. 

In fact, a special method to simulate the roughness 

of honed cylinder liners was developed in the course 

of this work and subsequently published in the Proceedings of the American Society of Mechanical Engineers, Internal Combustion Engine Division. 

Results of reciprocating friction tests on a Caterpillar 

diesel engine ring and liner combination revealed 

that the proposed standard could indeed discriminate 

between subtle changes in the oil condition. This 

first work was presented in December 2003 at a joint 

workshop between ASTM committees D-2 (Lubricants) and G-2 (Wear and Erosion). 

After an iterative review by task group members, balloting on the draft standard was conducted 

first at the subcommittee level and then at the main 
High Strength Weight Reduction Materials FY 2004 Progress Report 

63 

committee level. Results of the latter are scheduled 

for discussion and resolution at the November 2004 

ASTM G-2 Committee meeting in Washington, D.C. 

Description of the New Standard Practice 

The title of the document is Standard Practice 

for Conducting Friction Tests of Piston Ring and 

Cylinder Liner Materials Under Lubricated Conditions. It begins with a scope statement, followed by 

references to other applicable ASTM standards. The 

terminology section introduces a definition for engine-conditioned oil. The use of engine-conditioned 

lubricating oil is a key aspect of this practice because it provides the means to evaluate materials 

under conditions that simulate not only the mechanical and thermal aspects of a ring and liner interface, 

but the chemical aspects as well. 

The basic procedure involves the geometry 

shown in Figure 1. A piston ring segment oscillates 

with a load, stroke length, and rate appropriate for 

the engine of interest. Before the tests are conducted, 

the surfaces of the ring and liner are worn under low 

load to seat them properly. Early tests showed that 

failure to run-in the specimens carefully can increase 

the scatter and decrease repeatability of the test results. 

Figure 1. Side view schematic diagram of the ring-onliner test. 

Additional Use for Wear Measurement

The effects of oil condition on wear can also be 

studied using a variant of this test method. It is 

known that used engine oil tends to be depleted of 

its friction-reducing and wear-reducing additives. 

Such oils also contain soot, a by-product of combustion. The effects of oil condition on wear are illustrated in Figures 2 and 3. Both tests involved the 

same starting material combination (a chromiumplated diesel engine ring on cast iron). Tests were 

run for 6 h in oil at 100°C. In the first case, the lubricant was fresh 15W40 grade diesel engine oil 

(Cummins Blue); and in the second case, the lubricant was a high-soot test oil from Southwest Research Institute (called “M11 HST oil”). Using a 

surface profiling instrument, the wear volumes and 

wear rates of the specimens can be determined. In 

the example shown here, the wear rate of the cast 

iron in engine-conditioned test oil was four times 

higher than in the fresh oil. Therefore, as an added 

benefit, the basic friction test procedures developed 

in the course of this project can be extended, with 

minor procedural modifications, to measure the wear 

of new ring and liner materials as well. 

Plans for FY 2005

A workable method for friction testing of ring 

and liner materials having been established, three 

remaining tasks are planned for FY 2005: 

1. Resolve any negative votes that may arise from the 

fall 2004 main G-2 committee ballot. 

2. Prepare a research report that will be kept on file at 

ASTM headquarters. This is a society requirement 

Figure 2. Wear scar on cast iron produced by 6 h of testing at 240-N load, 10-mm stroke, 10 cycles/s, in fresh 

15W40 diesel oil. The normalized volumetric wear factor 

was 1.9 × 10–7 mm3/N-m. 

 

Figure 3. Wear scar on cast iron produced by 6 h of testing 

at 240-N load, 10-mm stroke, 10 cycles/s, in M11 HST test 

oil. The normalized volumetric wear factor was 7.7 × 10–7 

mm3/N-m. 
FY 2004 Progress Report High-Strength Weight Reduction Materials 

64 

 that serves to support the technical basis for each 

new standard. 

3. Use the new practice to evaluate a selection of candidate engine materials and surface treatments, thereby 

demonstrating the usefulness of the standard in supporting other heavy vehicle materials and surface engineering development efforts. 

A portion of the experimental findings on which 

the ASTM research report is to be based has been 

accepted for presentation at the 2005 International 

Conference on Wear of Materials and will be published in a special volume of the journal Wear. 

Conclusions 

Coupling a team of industry experts with laboratory experiments, ORNL has been able to develop a 

useful method for assessing the friction of piston 

ring and liner material combinations under mechanical, thermal, and chemical conditions that are similar 

to those in engines. The new method has been 

shown to discriminate between the frictional behavior of five standard test oils. Test oils can now be 

selected to evaluate new ring and liner materials under different degrees of lubricant deterioration and 

wear severity. A standard practice for lubricated diesel engine piston ring and liner materials testing is 

nearing final ASTM approval. Validation of the 

practice on other material pairs is planned for 

FY 2005. 

Publications 

J. J. Truhan, J. Qu, and P. J. Blau, “The Effect of 

Lubricating Oil Condition on the Friction and Wear 

of Piston Ring and Cylinder Liner Materials in a 

Reciprocating Bench Test,” accepted for publication 

in Wear.
High Strength Weight Reduction Materials FY 2004 Progress Report 

65 

B. Laser Glazing of Railroad Rails to Reduce Friction 

Principal Investigators: George Fenske, Saud Aldajah, Oyelayo Ajayi, and Ron DiMelfi 

Argonne National Laboratory 

9700 S. Cass Ave. 

Argonne, Illinois 60439 

(630) 252-5190; fax: ( 630) 252-4798; e-mail: gfenske@anl.gov 

Technology Development Area Specialist: Sidney Diamond 

(202) 586-8032; fax: (202) 586-1600; e-mail: sid.diamond@ee.doe.gov 

Field Technical Manager: Philip S. Sklad 

(865) 574-5069; fax: (865) 576-4963; e-mail: skladps@ornl.gov 

Contractor: Argonne National Laboratory] 

Contract No.: W-31-109-ENG-38

Objective 

• Determine the potential of laser glazing to lower parasitic energy losses between the flange and the rail in rail 

transport. 

• Develop a fundamental understanding of the metallurgy associated with the formation of low-friction surface 

layers during laser glazing processing and how these layers reduce friction between rail and wheel 

Approach 

• Develop advanced laser glazing processes to form glazed regions on carbon steels. 

• Perform benchtop tests, full-scale rig tests, and field tests of glazed steels and rails to quantify the impact of 

glazing on parasitic friction losses. 

• Characterize glazed and nonglazed steels to elucidate the impact of glazing on the microstructure. 

Accomplishments 

• Optimized laser processing conditions under which uniform glazed surfaces form on carbon steels. 

• Evaluated the friction and wear performance of glazed (and unglazed) rail steel by using benchtop and 

wheel/rail rig tests. 

• Characterized the microstructure and hardness of glazed steels. 

• Developed a deformation theory for nanocrystalline materials to model friction in glazed steel. 

• Demonstrated the efficacy of laser glazing to reduce friction on a full-scale test rig using prototype wheels, 

loads, and speeds. 

Future Direction 

• Perform high-tonnage field tests at the Association of American Railroads (AAR)/Transportation Technology 

Center, Inc. (TTCI) Facility for Accelerated Serving Testing (FAST) in Pueblo, CO. 

• Characterize the microstructure of a glazed rail subjected to AAR/TTCI FAST tests. 
FY 2004 Progress Report High Strength Weight Reduction Materials 

66 

• Make go/no-go decision to proceed with development of rail glazing technology. 

• If go/no-go decision is to proceed, establish project with a railroad track maintenance equipment and service 

organization 

Introduction 

Wheel/rail interaction accounts for a significant 

fraction of the energy consumed in rail transport. 

Past studies have indicated that energy savings could 

be as high as 24% when friction at the wheel/rail 

interface is properly managed. The key aspect is 

control of the friction forces. At the locomotive, 

high friction between the rail (specifically the top of 

the rail) and the wheel is desired to ensure adequate 

traction to keep wheels from slipping and sliding 

when power is applied. Friction is also required under braking conditions to control the speed of downhill-bound trains or to bring a train to a safe stop. 

The trailing cars, however, require much lower friction levels under normal train operations. At these 

cars, a low, controllable friction is desirable and can 

significantly reduce the energy required to pull a 

train. Two regions account for most of the frictional 

losses between the wheel and the rail: the region 

between the top of the rail and the wheel tread, and 

the region between the wheel flange and the gage 

face of the rail. Current wheel/rail lubrication (e.g., 

application of degradable greases and lubricants) is 

inconsistently applied and often disengaged by train 

crews. The research described herein focuses on the 

development of a laser glazing technique that imparts a durable, low-friction surface to the gage face 

of the rails to reduce parasitic frictional losses between the flange and rail gage. 

Approach

The objective of this activity was to develop an 

advanced laser modification process to form a glaze 

on the gage face of the rail. Initial results and models 

predicted the formation of a nanocrystalline surface 

layer that would impart low-friction properties at the 

interface. The tasks associated with this project involve 

• Process development (laser glazing) 

• Microstructural characterization of lasermodified surfaces 

• Development of a model (of surface deformation) 

• Lab-scale friction and wear testing of lasermodified surfaces (glazed and shot-peened) 

• Full-scale friction testing of laser-glazed steel 

Results

The development of the laser glazing processes 

used in these studies1,2 was documented in the 

FY 2003 Annual Report. Several approaches were 

investigated; two involved laser glazing, and a third 

investigated a laser shock-peening technique. Parametric studies were performed to optimize the conditions under which a glazed layer forms on 1080 

steel. For this purpose, an Electrox 1.6-kW pulsed 

Nd:YAG laser with fiber-optic beam delivery and 

special beam shaping optics was used in Argonne 

National Laboratory’s (ANL’s) Laser Applications 

Laboratory. Two approaches were developed: one 

involved a single pass of the laser over a given area, 

and the other involved multiple overlapping passes. 

The Knoop hardness of the martensitic glazed regions was 2–3 times greater than that of the substrate, depending on whether a single-pass (factor of 

3 times harder) or multipass (slightly over 2 times 

harder) process was employed. A commercial laser 

glazing process that used high-power diode laser 

technology was also investigated. In this case, bars 

of 1080 steel were processed by a commercial vendor (NuVonyx) and subsequently tested at ANL. 

Friction and wear studies were performed using 

a number of lab-scale systems. Block-on-ring tests 

performed by Falex Corp. showed static friction coefficients of ≈0.35–0.45 for untreated 1080 steel that 

dropped to values ranging from 0.2 to 0.4 for differing glazing conditions. Large-scale (using a glazed 

segment of rail and a full-size wheel) “block-onring” tests performed at the AAR/TTCI Pueblo facility showed the static friction coefficient of the untreated 1080 rail varied from 0.2 to 0.5, depending 

on the applied load, whereas the friction coefficient 

of the glazed regions varied from 0.1 to 0.25. Dynamic friction coefficients for the glazed regions 

varied from 0.2 to 0.35, depending on load, compared with 0.2 to 0.55 for unglazed regions. 
High Strength Weight Reduction Materials FY 2004 Progress Report 

67 

Benchtop pin-on-disc tests at ANL used flats of 

1080 steel, glazed and unglazed, that rubbed against 

stationary balls or pins (52100 steel, 1080 steel, 

440C steel, or alumina). The tests revealed that the 

composition of the pin/ball had a significant impact 

on the friction coefficient. The general trend was 

that the glazing reduced the friction coefficient by 

3–35%, depending on the material. The greatest reduction was for the alumina ball sliding against the 

1080 steel, suggesting that a strong chemical adhesion mechanism may be active with the metallic 

counterparts. 

Twin roller tests were conducted at ANL with 

1045 steel rail and wheel discs that were throughhardened (Rc 40) or glazed. The glazing effectively 

reduced the friction coefficient from roughly 0.4 for 

the unglazed condition to 0.3 for the glazed rail rotating against an unglazed 1045 steel counterpart. 

The most recent set of tests was performed in a 

twin-roller test rig at the Canadian National Research Center (CNRC) Wheel, Bearing, and Brake 

(WBB) facility in Ottawa, Ontario (Figure 1). The 

WBB Facility uses conventional and instrumented 

full-scale wheelsets loaded against large 63-in.-diam 

rims that simulate the track. The system is designed 

to operate at prototypical speeds and loads (30 mph 

and 33,000 lb in these tests). The instrumented 

wheelset allowed continuous monitoring of the lateral, longitudinal, and vertical forces during the 

tests—a feature that was used to measure differences 

between glazed and nonglazed regions on rim A in 

Figure 1. 

The WBB tests were performed to confirm the 

friction reductions observed in the lab-scale tests 

and to evaluate the durability of the glazed regions 

before glazed rail segments were installed in the 

FAST loop at the AAR/TTCI facilities. A 180° segment of rim A was sent to NuVonyx, where two 10–

12-mm-wide tracks were glazed along the circumference of the rim—one track along the gage face 

and the second track on the top of the rail approximately 5 mm from the gage point. 

A series of runs was performed over a 5-day period to evaluate the efficacy of the glazing to reduce 

lateral and longitudinal forces (e.g., reduce friction) 

and to evaluate the durability of the glazing after 

Figure 1. CNRC Wheel, Bearing, and Brake Test 

Facility. 

moderate tonnage. The friction measurements were 

performed with an instrumented wheelset that permitted direct measurement of the forces using strain 

gauges applied to the rotating wheels. These provided a continuous measurement of the lateral, longitudinal, and vertical forces. Figure 2 shows an 

example of the vertical load and friction coefficient 

measured during a lightly loaded (10,000 lb), lowspeed (6 mph) run at the start of the tests. 

Because the laser-glazed rim was not re-profiled 

before the start of the CNRC tests, the vertical loading trace (see Figure 2) provided an easy method to 

determine when the wheelsets were running against 

the 180° glazed segment or the non-glazed segment. 

As seen in Figure 2, the friction shows a cyclic period of approximately 2 seconds, corresponding to 

one revolution of the bottom rims (at 6 mph). When 

the wheelset is running on the smooth, nonglazed 

180° segment, the friction coefficient is high (approximately 0.18 in Figure 2). When the wheelset 

runs on the glazed segment, the friction drops to approximately 0.16—a decrease of 10 to 11%. 
FY 2004 Progress Report High Strength Weight Reduction Materials 

68 

Figure 2. Friction and WBB vertical load between 250 

and 260 seconds during run 1b of the ANL/CNRC rail 

glazing tests. 

The data shown in Figure 2 present a snapshot in 

time during this particular run, during which the top 

wheelset was gradually yawed with respect to the 

bottom rims—a process that simulates a train passing through a curve, or the wheels hunting back-andforth down a straight tangent run. Figure 3 summarizes the impact of the glazing observed during the 

entire duration of this particular run (run 1b). The 

magnitude of the friction reduction depends on a 

number of factors, including the yaw angle. As the 

yaw increases, the magnitude of the lateral and longitudinal forces increases and thus the friction coefficient increases, from values near 0.1 at low yaw to 

0.4 to 0.5 at high yaw. The impact of the glazing on 

reducing the friction was not as significant at higher 

yaw, where the lateral forces dominated the friction 

measurements. Overall, Figure 3 shows that the 

glazing treatment reduced the friction coefficient by 

8 to 50% depending on the yaw—with the greater 

friction reductions occurring at low yaw. 

After the initial series of friction tests, a conventional wheelset was installed and a series of longduration runs was initiated at high yaw and side 

loadings to expose the glazed regions to high tonnage to determine if the glazing was durable. Approximately 1 MGT (million gross tons) was applied 

to the glazed regions. The instrumented wheelset 

was then reinstalled and another series of friction 

measurements performed. 

The magnitude of the friction reduction decreased from values observed during the initial 

measurements (run 1b); nevertheless, friction reduce 

Figure 3. Friction reduction on glazed rim (normalized to 

the unglazed rim segment) for run 1b. 

tions in the range of 8 to 40% were consistently observed. 

Figure 4 shows a photograph of the bottom rim 

after the high-tonnage runs. These runs consisted of 

2–3 days of operation at high loads (33,000 lb), high 

speed (30 mph), and high yaw that accumulated 

roughly 6 hours of run time. White paint, applied 

early during the runs to adjust the position of the top 

wheelset to ensure it was running on the glazed 

tracks, indicated the glazed track on the top of the 

rail was in contact with the wheelset. Magnaflux 

characterization of the rim further indicated the 

Figure 4. Macrophoto of glazed rim after run 

4d. 
High Strength Weight Reduction Materials FY 2004 Progress Report 

69 

glazed track remained intact over most of the 180°

segment, although a short segment of glazed material (approximately 3 mm wide by 5 cm long) was 

removed after the severe high-load, high-yaw runs. 

The loss of the glazed material was aggravated because the glazed tracks were tested in the “as-glazed 

state” (a condition in which the glazed region was 

significantly rougher than a conventional rail profile), resulting in high contact stresses. Re-profiling 

the as-glazed track will reduce the high contact 

stresses and thus should mitigate fatigue-induced 

pullout/loss of glazed material. 

Conclusions

Testing of laser glazing to improve the friction 

(and wear) performance of steels continues to progress. Initial lab-scale tests showed significant friction reductions, and the more recent studies at 

CNRC Ottawa have confirmed the friction reductions using full-scale wheels under high loads and 

prototypical speeds. Friction reductions in the range 

of 10 to 40% have been observed—the magnitude 

of the reduction being dependent on the yaw and 

side loading. 

Efforts are in progress to establish a team to 

commercialize this technology with a rail maintenance firm. Plans are being developed to glaze a series of 20- to 40-foot-long track segments that will 

be installed in the FAST loop at the AAR/TTCI facility in Pueblo. The FAST loop tests will involve 

track segments in the as-glazed, and as-glazed and 

re-profiled state. The FAST loop tests are designed 

to put significant levels of tonnage on the treated 

track (upward of 100 MGT). If they are successful, 

arrangements are being made to incorporate a laserglazing system on a rail maintenance vehicle. 

References

1. S. H. Aldajah, O.O. Ajayi, G. R. Fenske, C. 

Reed, and Z. Xu, “Effect of Laser Surface Modifications on Tribological Performances of 1080 

Carbon Steel,” submitted to ASME Journal of 

Tribology, October 2004. 

2. Saud Aldajah, George Fenske, Layo Ajayi, 

Claude Reed, Zach Xu, and Ron DiMelfi, Laser 

Glazing of Rails—WBB/IWS Tests (CNRCOttawa), Argonne National Laboratory. 

Publications/Presentations

S. Aldajah, G. R. Fenske, O. O. Ajayi, and S. 

Kumar, “Investigation of Top of Rail Lubrication 

and Laser Glazing for Improved Railroad Energy 

Efficiency,” Journal of Tribology, 125, 643–648, 

July (2003). 

S. H. Aldajah, O. O. Ajayi and G. R. Fenske, 

“Effect of Laser Glazing and Laser Shock Peening 

on Tribological Performance of 1080 Carbon Steel,” 

presented at the 2004 STLE/ASME Intl. Joint Tribology Conference, Long Beach, CA, October 24–

27, 2004. 
FY 2004 Progress Report High Strength Weight Reduction Materials 

70 
High Strength Weight Reduction Materials FY 2004 Progress Report 

71 

C. Laser Texturing of Materials 

Principal Investigators: Ali Erdemir, Oyelayo Ajayi, Andriy Kovalchenko, Kursat Kazmanli, Robert 

Erck, Osman Eryilmaz, George Fenske 

Argonne National Laboratory 

Energy Technology Division, Argonne, IL 60439 

(630) 252-5190; fax: (630) 252-4798; e-mail: gfenske@anl.gov 

Principal Investigator: Izhak Etsion 

Technion University 

Technology Development Area Specialist: Sidney Diamond 

(202) 586-8032; fax: (202) 586-1600; e-mail: sid.diamond@ee.doe.gov 

Field Technical Manager: Philip S. Sklad 

(865) 574-5069; fax: (865) 576-4963; e-mail: skladps@ornl.gov 

Contractor: Argonne National Laboratory

Contract No.: W-31-109-ENG-38

Objectives 

• Assess and optimize the tribological performance of laser-textured (or -dimpled) surfaces under sliding and/or 

rotating contact conditions. 

• Determine durability and operational limits of dimpled surfaces with respect to dimple size, depth, and density. 

• Elucidate fundamental tribological mechanisms involved with laser-dimpled surfaces. 

• Design and produce novel hard coatings over dimpled surfaces and explore any beneficial synergistic effects 

that such coatings may have on friction and wear. 

Approach 

• Control and optimize parameters used in the laser-texturing process in order to obtain the most desired dimple 

size, depth, and density on a series of steel and SiC samples. 

• Control and eliminate bulges and other surface irregularities caused by the dimpling process on and around the 

rims of dimpled spots. Use a post-process grinding/polishing procedure to remove such irregularities. 

• Thoroughly examine and characterize dimpled surfaces by optical and electron microscopes and by a 3-

dimensional (3D) surface profilometer. Determine dimple size, depth, and density. Take several representative 

images. 

• Develop a test matrix, specify test conditions, and perform well-controlled tests with unidirectional and reciprocating wear test machines. 

• In collaboration with Izhak Etsion (who supplies the dimpled surfaces), analyze test results and make judgments on the performance of the dimpled surfaces. 

• Specify and apply hard coatings over laser-dimpled surfaces. Characterize and perform standard tests to assess 

performance improvements. 

• Promote/present findings at appropriate forums and generate more industrial interest. 
FY 2004 Progress Report High Strength Weight Reduction Materials 

72 

Accomplishments 

• Demonstrated lower friction and wear under mixed lubrication regimes using a unidirectional test rig. 

• Demonstrated an increase of up to 90% in resistance to scuffing on laser-dimpled surfaces using a reciprocating 

test rig. 

⎯ Modified a reciprocating test rig that can now simulate the motion between a piston ring (or skirt) and cylinder liner of an internal combustion engine. 

⎯ Initiated series of tests on cut segments of piston rings and cylinder liners using the modified reciprocating 

test rig. 

⎯ Successfully produced and optimized shallow (5 to 6 micrometers deep) dimples on mechanical face seals 

and demonstrated superior performance, lower torque (more than 40% lower), and minimal wear for dimpled surfaces (especially under lower face pressures). 

⎯ Performed series of tests on coated and laser-dimpled surfaces and determined operating conditions under 

which maximum beneficial synergistic effects can be realized. 

Future Direction 

• Concentrate on laser-dimpled piston rings and cylinder liners; perform friction and wear tests under conditions 

that represent actual engine applications. 

• Analyze friction and wear data; characterize worn surfaces; determine levels of improvements provided by 

dimpling process. 

• Assess friction reduction and energy-saving benefits of laser-dimpled rings and liners. 

• Perform more studies on laser-dimpled seal faces. 

• Determine effects of depth, size, and density of microdimpling on scuffing performance of surfaces coated with 

hard and soft films. Specifically, evaluate the effects of an MoN coating on friction and wear of laser surface 

texturing-treated surfaces. 

• Determine effects of oil viscosity and/or ambient temperature on friction and wear behavior of dimpled surfaces. 

• Determine microstructural, chemical, and mechanical characteristics of heat-affected zones at or near the dimpled areas and determine their impact on friction and wear. 

Introduction

Argonne National Laboratory has entered into 

an exploratory research program with Technion 

University to evaluate the potential usefulness of a 

laser surface texturing or dimpling technology for 

engine and drivetrain applications. This technology 

produces shallow dimples (typically 4–10 μm deep) 

70 to 100 μm in diameter on metallic or ceramic surfaces (see Figure 1). When such surfaces are used 

under mixed or hydrodynamic regimes of lubricated 

contacts, substantial reductions in friction and wear 

are observed. A major goal of this project is to produce and further optimize such dimples on sliding 

and rotating contact surfaces of critical engine parts 

and components to reduce friction and wear. Furthermore, synergistic effects of hard coatings on 

friction and wear of laser-dimpled surfaces are being 

explored. 

Laser texturing may be an ideal technology for 

applications in mechanical face seals, as well as in 

various engine and drivetrain components such as 

piston rings and cylinder liners and wrist pins. In 

such applications, shallow dimples can serve as reservoirs for fluid media (i.e., oil and/or water) and 

thus increase the hydrodynamic lubrication efficiency of these surfaces. Furthermore, dimples can 

effectively trap wear debris or third-body particles 

generating at sliding interfaces as a result of contact 
High Strength Weight Reduction Materials FY 2004 Progress Report 

73 

sliding and thus reduce wear. Overall, when such 

optimized dimples are produced on various engine 

and drivetrain components, much improved fuel 

economy due to reduced friction or torque can be 

expected, and reduced wear translates into longer 

durability and hence reliability. 

Accordingly, during this work period, we have 

prepared large numbers of SiC face seals, AISI H-13 

steel flats, and cut segments of piston rings and cylinder liners for laser texturing at SurTech. Dimpled 

samples were returned to Argonne for surface characterization and tribological testing. Some of the 

dimpled seals were subjected to rigorous wear testing, while others were used in a seal tester to measure torque. Some of the dimpled steel substrates 

were further coated with a superhard nanocomposite 

MoN film in order to further improve their friction 

and wear performance, especially under harsh sliding conditions that can lead to scuffing and hence 

major wear losses. 

Figure 1. 3D images of dimpled surface and individual 

dimple. 

Results

Effects of Point and Conformal Contacts on 

Friction and Wear 

Figure 2 shows surface conditions of three different samples (polished, ground, and dimpled) that 

were used in a series of sliding tests in a unidirec 

Figure 2. Surface conditions of H13 steel flats used in 

sliding experiments with point and conformal contacts. 

tionally sliding wear test machine. These samples 

were rubbed against both spherical balls (≈10 mm in 

diameter) and flat-ended pins under lubricated sliding conditions. Figure 3 shows the variation of friction coefficients of balls and flat pins against 

polished, ground, and dimpled H13 steel surfaces as 

a function of increasing sliding time and speed. As is 

clear, under both contact configurations, a dimpled 

surface (Disk #3) provided the lowest friction (especially against the flat-ended pin). However, the friction coefficient of dimpled surfaces was much 

higher than when they were rubbed against the 

spherical ball. This may have been due to the relatively high contact pressures that can be generated 

under such point contact situations. Formation of a 

complete or continuous hydrodynamic film (which 

is key for separation of the sliding surfaces) also 

becomes very difficult under high-pressure point 

contact. The higher overall roughness of the dimpled 

surfaces may also have an adverse effect on friction 

behavior. Specifically, relatively rough sur- 
FY 2004 Progress Report High Strength Weight Reduction Materials 

74 

Figure 3. Frictional performance of steel balls (point contact) and flat-ended pins (conformal contact) against polished, ground, and laser-dimpled H13 steel surfaces. 

faces of dimpled samples may adversely affect the 

formation of a continuous hydrodynamic film, leading to increased friction between the sliding surfaces. 

Figure 4 summarizes the friction and wear behavior of a polished and laser-dimpled H13 steel 

surface under boundary-lubricated sliding conditions 

during a constant-speed sliding test over a long duration. Highly polished surfaces of ball and flat samples become very rough as a result of wear under the 

severe contact pressures of point contact sliding condition, and the friction remains high (i.e., 0.09). For 

the laser-dimpled surface, friction is high initially 

but decreases steadily during successive sliding 

passes and eventually reaches a value of 0.05. The 

contact surfaces of steel balls wear out and become 

highly polished. It is quite possible that substantial 

reduction in friction during sliding may have resulted from ball wear and hence an increasingly conformal contact between ball and dimpled flat.

Integrating Dimpling with Hard Coatings 

Some of the laser-dimpled H13 steel flats were 

further given a superhard coating. Friction and wear 

tests were performed in a reciprocating test machine 

under both point and conformal contact conditions. 

Figure 5 shows the details of a dimple and the hard 

coating produced over it. 

Figure 6 compares the friction performance of 

as-received base steel, laser-dimpled steel, and suFigure 4. Friction and wear performance of M50 balls 

during sliding against polished and laser-dimpled H13 

steel flats. 

Figure 5. Hard coating applied over a dimple, and magnified details of segment showing coating and steel substrate. 

Figure 6. Friction behavior of as-received, laser-dimpled, 

and laser-dimpled + superhard MoN-coated surfaces under boundary-lubricated sliding conditions. 

perhard-coated + laser-dimpled steel surfaces under 

boundary-lubricated sliding conditions. 

Based on the results of Figure 6, it is clear that 

laser-dimpled and superhard-coated steel surfaces 

give fairly low friction coefficients, while the base 

steel and laser-dimpled + superhard-coated surfaces 

provide the same levels of friction. Surface studies 
High Strength Weight Reduction Materials FY 2004 Progress Report 

75 

after the tests indicated that despite their relatively 

higher friction, laser-dimpled + superhard-coated 

surfaces suffered the least wear regardless of contact 

loads (see Figure 7). 

Figure 7. Wear performance of sliding ball surfaces 

against laser-dimpled and laser-dimpled + superhard 

MoN-coated (SH) flat steel samples 

Laser-Dimpled SiC seals 

During this work period, we have performed 

numerous torque measurements on dimpled and asreceived (undimpled) SiC seal faces using an instrumented seal test machine. Figure 8 summarizes 

the results of these measurements. As is clear, frictional torque on undimpled seal faces increases almost linearly with increasing face pressure. The 

dimpled SiC seal faces show essentially the same 

trend, but the magnitude of frictional torque is at 

least 50% lower across the pressure range evaluated 

in these studies. Clearly, the dimpled seal faces provide much lower torque and hence may be very 

beneficial for demanding mechanical face-seal applications, including water pump seals of heavy-duty 

diesel engines. 

Reciprocating Tests with Dimpled Piston 

Rings and Liner 

During this period, we have cut and prepared a 

number of segments of actual piston rings and cylinder liners for friction and wear studies using a reciprocating test machine. Figure 9 shows the layout of 

this machine, while Figure 10 shows a 3D image of 

a cut segment of a ring with dimples produced on 

Figure 8. Summary of torque measurements on dimpled 

and undimpled SiC seal faces. 

Figure 9. General layout of cut segments of dimpled piston ring and cylinder liner placed in its holder in a reciprocating test machine. 

its crown. Work is in progress, and the results of 

initial studies look very promising. 

Conclusions

During FY 2004, we have made great progress 

in the optimization, testing, and diverse utilization of 

a laser-texturing process. When used on coated or 

uncoated surfaces of steel or ceramic (SiC) test 

pairs, the process results in substantial reductions in 

friction and/or torque. When combined with a superhard coating technology, it can lead to superior 

wear performance. Used on SiC seal faces, it can 

reduce frictional torque by more than 50%. During 

this fiscal year, we have also produced wellcontrolled dimples on the surfaces of both piston 
FY 2004 Progress Report High Strength Weight Reduction Materials 

76 

Figure 10. 3D image of laser-dimpled ring sample to be 

tested in reciprocating test machine. 

rings and liners. A series of tests is currently under 

way and covers a wide range of test conditions. 

Patents

An invention disclose has been filed with Argonne’s Intellectual Property Department. This invention covers structural and chemical modulation 

of tribological surfaces by combined use of laser 

texturing and low-friction superhard coatings. 

Publications

A. Kovalchenko, O. Ajayi, A. Erdemir, G. Fenske, I. Etsion, “The Effect of Laser Texturing on 

Steel Surfaces and Speed-Load Parameters on the 

Transition of Lubrication Regime from Boundary to 

Hydrodynamic,” Tribology Transactions, 47(2), 

299–307 (2004). 

A. Erdemir, “Review of Engineered Tribological 

Interfaces for Improved Boundary Lubrication,” 

Tribology International, in press. 

A. Erdemir, “Smart Surface Engineering for Improved Boundary Lubrication,” pp. 13–20 in Proceedings of 14th International Colloquium on 

Tribology and Lubrication Engineering, Stuttgart, 

Germany, January 13–15, 2004 (invited keynote 

paper). 

C. Donnet and A. Erdemir, “Historical Developments and New Trends in Tribological and Solid 

Lubricant Coatings,” Surface and Coatings Technology, 180–81, 76–84 (2004). 

K. Kazmanli, O. L. Eryilmaz, O. Ajayi, A. Erdemir, I. Etsion, “Effects of Soft and Hard Coatings 

on Tribological Behavior of Laser Textured Surfaces,” submitted for presentation at the 60th Annual 

Meeting of the Society of Tribologists and Lubrication Engineers, May 15–19, 2005, Las Vegas. 

A. Erdemir, “Engineered Tribological Interfaces 

for Improved Friction, Wear and Lubrication in Engines,” invited panel presentation at Engine and 

Drivetrain Session of 59th Annual Meeting of the 

Society of Tribologists and Lubrication Engineers, 

Toronto, Canada, May 17–20, 2004. 

A. Kovalchenko, O. Ajayi, A. Erdemir, G. Fenske, I. Etsion, “The Effect of Laser Surface Texturing on Transitions in Lubrication Regimes during 

Unidirectional Sliding Contacts,” Tribology International, in press. 
High Strength Weight Reduction Materials FY 2004 Progress Report 

77 

D. Joining of Advanced Materials by Plastic Deformation 

Principal Investigator: J. L. Routbort 

Argonne National Laboratory 

9700 S. Cass Avenue, Argonne, IL 60439-4838 

(630) 252-5065; e-mail: routbort@anl.gov 

Technology Development Area Specialist: Sidney Diamond 

(202) 586-8032; fax: (202) 586-1600; e-mail: sid.diamond@ee.doe.gov 

Field Technical Manager: Philip S. Sklad 

(865) 574-5069; fax: (865) 576-4963; e-mail: skladps@ornl.gov 

Participants: 

D. Singh, Argonne National Laboratory 

F. Gutierrez-Mora, Argonne National Laboratory

K. C. Goretta, Argonne National Laboratory 

Contractor: Argonne National Laboratory 

Contract No.: W-31-109-Eng-38 

Objectives 

• Join advanced materials such as ceramics, cermets, intermetallics, composites, and biomaterials by plastic deformation.

• Collaborate with industry and universities to produce sensors.

• Characterize the interfaces.

Approach 

• Apply a modest compressive load to two pieces of similar or dissimilar materials that have had little surface 

preparation in the temperature region where the materials are known to deform by grain-boundary sliding. 

• Examine interfaces by scanning electron microscopy (SEM). 

• Measure residual stresses after joining dissimilar materials and compare with finite element analysis. 

• Measure strength of the interface by 4-point bend tests. 

• Characterize electrical properties of sensors. 

Accomplishments 

• Made strong, pore-free joints with various ceramics, cermets, intermetallics, composites, and more recently, 

biomaterials, with and without various interlayers. Fracture occurs away from the interface. 

• Achieved joint strength equal to that of the monolithic. 

• Filed patent disclosure for producing oxygen sensor.
FY 2004 Progress Report High Strength Weight Reduction Materials 

78

Future Direction 

• Join intermetallics to ceramics. 

• Join biomaterials. 

• Use functionally graded materials to distribute and reduce interfacial stress concentrations. 

• Measure in-situ grain rotation during deformation or joining using the Advanced Photon Source, pending funding.

Introduction

Joining by plastic deformation has been successfully applied in this program to various advanced ceramics: yttria-stabilized zirconia 

(YSZ)/alumina composites, mullite, silicon carbide and titanium carbide whiskers in a zirconiatoughened alumina (ZTA) matrix, metal-matrix 

composites and even an electronic ceramic, 

La0.85Sr0.15MnO3.

1–5 Techniques have been developed to minimize sample preparation procedures 

and the temperature at which the joining takes 

place. Among them, a spray application technique2

or use of nanocrystalline powders or dense interlayers stand out.2, 6 A patent application is pending. More recently, we have formed pore-free 

joints in Ni3Al. 

Although it is clear that joining by plastic deformation has few, if any, serious deficiencies for 

joining similar materials, some issues remain to be 

addressed when dissimilar materials are to be 

joined. The situation is different because of the 

residual stresses generated upon cooling after materials with different coefficients of thermal expansion (CTEs) are joined at the high temperatures 

required. The thermal residual-stress distribution 

has been characterized in YSZ-alumina composites by finite element analysis (FEA) simulation 

and later compared with experimental observation 

from Vickers indentation measurements.1

 

During FY 2004, we completed the 4-point 

bend tests on joined pieces of the same and different compositions of YSZ/alumina ceramics that 

were discussed in the annual report for FY 2003. 

Fracture mechanics principles, in conjunction with 

fractographic analysis, are used to explain 

strengths of joined ceramics in the presence of 

residual stresses. We have also characterized the 

high-temperature mechanical properties of hydroyapatite and successfully produced pore-free 

joints. Collaboration with Ohio State University 

has resulted in a patent application for an oxygen 

sensor with a built-in reference. 

Summary of 4-Point Bend Tests

Table 1 is a reproduction from the FY 2003 

annual report showing the fracture stress of the 

various monoliths of YSZ/alumina and of the 

ZT50A/ZT50A joint. The designation is YSZ containing 50% alumina. 

Table 1. Flexure data for monolithic ceramics. 

Al2O3 and ZTA from literature 

Material Strength (MPa) 

Al2O3 300 

ZT80A 560 ± 70 

ZT60A 580 ± 80 

ZT50A 650 ± 100 

ZT20A 1020 ± 150 

YSZ 1030 

ZT50A/ZT50A 620 ± 100 

The ZT50A/ZT50A joint fractured, on the average, about 2±1.5 mm from the interface, clearly 

indicating the strong nature of the joint. 

Table 2 presents the results of the flexure test 

data for dissimilar jointed materials.7, 8

Table 2. Flexure data for dissimilarly joined ceramics 

Joint Strength 

(MPa) 

Distance—

fracture to interface (μm) 

ZT50A/ZT50A 620 ± 100 1950±1540 

ZT60A/ZT40A 365 ± 135 335 ± 150 

AT60A/ZT40A 500 ± 50 690 ± 110 

ZT60A/ZT0A 440 ± 80 380 ± 1008 

FEA was conducted to determine the effect of 

residual stresses generated during joining of dissimilar materials on the mechanical behaviour of 

joined samples. Figure 1 shows the distribution of 

normal residual stresses generated as ZT60A 
High Strength Weight Reduction Materials FY 2004 Progress Report 

79 

joined to ZT20A cools from the joining temperature.1

 A high tensile stress (~250 MPa) perpendicular to the joint interface develops in the 

material with a lower CTE. In our case, this material corresponds to the composite with a lower 

YSZ volume fraction (ZT60A), because the CTE 

of the alumina is considerably lower than that of 

YSZ.1

 Also, the location of peak residual tensile 

stress normal to the interface is 150–200 μm away 

from the physical interface in the ZT60A composite. Moreover, normal stresses parallel to the interface are compressive in the material with lower 

CTE (ZT60A) and tensile for the material with 

higher CTE (ZT20A). This high tensile residual 

stress perpendicular to the interface has an important effect on mechanical performance of the 

joined dissimilar materials during flexure tests. 

Similar simulations were also conducted for 

ZT60A/ZT40A and ZT60A/ZT0A joined samples. 

Figure 1. Distribution of residual normal stresses per 

FEA simulation for a ZT20A/ZT60A joint. 

In addition to the normal stresses, shear 

stresses are also generated, and their variation for 

ZT60A/ZT0A joined samples determined by FEA 

is shown in Figure 2. Shear stresses are developed 

close to the interface; they fall off rapidly within a 

short distance from the interface. The magnitude 

of shear stresses is small compared with the normal tensile stresses. Thus it is expected that failure 

Figure 2. Distribution of residual surface shear stresses 

per FEA simulation for a ZT20A/ZT60A joint. 

will be controlled by the normal tensile stresses of 

these joined samples. 

Several key inferences can be drawn from the 

results of dissimilar joined samples. First, all samples failed in the ZT60A portion, the lowerstrength material with tensile stresses normal to 

the interface. Second, for ZT60A joined to ZT20A 

and ZT0A, the strength of joined samples decreased as the difference in composition between 

the parts joined or the CTE mismatch increased. 

For the experiment in which there was the largest 

difference in composition (YSZ joined to ZT60A), 

flexure strength decreased by 25% compared with 

the strength of monolithic ZT60A. However, 

strengths for ZT60A/ZT40A joined samples 

showed lower mean strength and large scatter 

compared with joined samples of ZT60A/ZT20A 

and ZT60A/ZT0A. Reasons for this will be discussed. Third, for all the dissimilar joints, failure 

was found to be away from the interface, again 

confirming the strong interface and efficacy of the 

joining process for materials with dissimilar compositions and CTEs. 

The decreased strength of ZT60A when joined 

to compositions with a lower volume fraction of 

alumina, compared with the strength of ZT60A, 

can be attributed to the presence of tensile residual 

stresses and the location and size of the failurecausing flaw. It is expected that the reduction in 

strength in the joined sample will depend on the 
FY 2004 Progress Report High Strength Weight Reduction Materials 

80

region of near-maximum tensile residual stresses. 

In this regard, the distance from the interface at 

which fracture occurred is especially revealing. 

For the ZT60A/ZT20A joint sample, the average 

failure location is about 700 μm away from the 

interface in the ZT60A section (Table 2). This corresponds to about 100 MPa tensile residual stress 

as per FEA simulations, as shown in Figure 1. By 

simple superposition of the residual stress intensities on the applied stress intensity during flexure 

tests, the failure strength for ZT60A should be 

reduced by 100 MPa. This is in agreement with 

the reduction of approximately 80 MPa in flexural 

strength of ZT60A when joined to ZT20A. Similar 

correlations between residual tensile stresses and 

flexural strength for ZT60A/ZT0A have been 

made. 

Strengths of ZT60A/ZT40A were somewhat 

lower and were 201, 360, and 530 MPa for the 

three joined samples tested. Close inspections of 

the fracture sites were made for all samples. The 

lower strengths of 360 and 201 MPa observed for 

the two samples is believed to be due to the presence of larger flaws. To confirm this, fractography 

was conducted on the two low-strength samples. 

SEM photomicrographs revealed surface damage 

on the tensile surfaces in the two low-strength 

samples. It is speculated that this damage was introduced during the sample preparation steps or 

handling. Typical lengths of this damage were 70–

90 μm. Using a nominal crack length of 80 μm, 

apparent toughness of 3.6 MPam1/2 for ZT60A, 

and fundamental fracture mechanics,9

 the fracture 

strength was calculated to be approximately 350 

MPa. This calculated fracture strength is consistent with the measured strength for the lowstrength ZT60A/ZT40A sample. Thus, in addition 

to the residual stresses, the size and distribution of 

failure-causing flaws in the ceramic materials will 

control the strength of the joint. This also explains 

why failure location in the joined samples does not 

necessarily coincide with the peak tensile residual 

stresses. 

Design and Fabrication of Air- Reference Free Potentiometric Planar 

A realistic miniaturization of a hightemperature, potentiometric planar oxygen sensor 

is possible by replacing the open-air reference column in current sensors with a metal/metal oxide 

Rhines pack at high temperatures. Gas-tight sealing of the internal reference oxygen pressure was a 

problem, but eventually perfect seals were obtained by joining the edges of the ceramic components by plastic deformation. This design, free of 

external reference,enables position flexibility and 

mobility of the sensor inside all combustion units. 

This report will detail the work that was performed in conjunction with a team from Ohio 

State University after it contacted ANL and detailed the sealing problems they were encountering 

using more conventional methods. 

The main components for the sensor fabrication are made of yttria-doped tetragonal zirconia 

polycrystalline (YTZP) ceramics, pellets, a ring, 

and green tapes. One YTZP pellet is partly covered with platinum ink, and a small-gauge platinum (Pt) wire is placed within intimate contact of 

the Pt ink in order to create a reference electrode. 

This electrode ink on the pellet (electrolyte) is 

fired at 1000°C in order to cure the electrode ink. 

The Pt wire is slipped between two rings of TYZP 

green tapes, and the pellet is placed wire-down 

onto the other fabrication components as shown in 

Figure 3. The components are joined together in a 

two-step process. The first joining step produces a 

cylinder, after which Ni/NiO powder is inserted 

into the cylinder and lightly compacted. Finally, 

the tapes and electrodes with the Pt wire are joined 

to the filled cylinder. Joining was readily achieved 

at 1200°C in an argon atmosphere using a nominal 

strain rate of 4 × 10−5

 s−1. 

Figure 3. Ceramic components and stacking of the internal reference planar oxygen sensor. 

An SEM micrograph of the top joint (with 

tapes) is shown in Figure 4. The sharply delineated 

edges of the joint shown in the low-magnification 

micrograph are the result of a slight offset between 
High Strength Weight Reduction Materials FY 2004 Progress Report 

81 

Figure 4. Top joint microstructure (with tapes). 

the top disk, the green tapes, and the cylinder. 

However, it can be seen that the joint contains 

only a very limited amount of porosity that was 

present in the initial materials. 

The electromotive force (EMF) as a function 

of oxygen partial pressure at 600°C is shown in 

Figure 5. These tests, performed as a function of 

time, indicate that the joints are indeed gas tight. 

Summary of Sensor Production

The plastic joining technique works and produces gas-tight seals. The sensor is viable and has 

the required sensitivity and response time. However, the EMF does not agree with the theoretical 

calculated EMF. This is most likely because the 

Ni/NiO was reduced by joining at 1200°C in an 

argon atmosphere. In the coming fiscal year, experiments will be performed to produce sensors 

joined in air or even in pure oxygen. Furthermore, 

several candidate reference materials under consideration may yield higher sensitivities. This 

work will form part of the Ph.D. thesis of John 

Spirig. 

Joining of Hydroxyapatite

Hydroxyapatite (HA) is a very common biomaterial that is generally used as a coating over a 

non-biocompatible material for implants such as 

teeth. Of course, coatings can be inexpensively 

applied using a number of different techniques. 

Figure 5. Oxygen sensing response at 600 °C of the 

fabricated sensor. Sensor has been gas-tight for several 

months. 

However, producing complex shapes by these 

techniques is difficult. Joining by plastic deformation presents a new possibility for production of 

complex pieces of HA. Therefore, the first phase 

of this work was to determine the conditions under 

which HA exhibits plasticity. 

HA was obtained from Professor Eldon Case 

of Michigan State University. The material was > 

98% of theoretical density and had a bimodal 

grain size distribution with the largest grains being 

≈ 5 μm and the smallest ≈ 1 μm. Figure 6 indicates 

that HA deforms into nearly a steady-state stress 

between 2.0 and 2.5 MPa at 1275°C at a strain rate 

of 10−5

 s−1. Strains of over 0.08 were achieved 

without fracture. 

Figure 6. Stress–strain data obtained from hydroxyapatite at 1275°C at a strain rate of 10-5 s-1. 
FY 2004 Progress Report High Strength Weight Reduction Materials 

82

Two pieces of HA were placed in the Instron and 

compressed to about 8% strain at 1275°C using a 

strain rate of 10−5

 s−1. The pore–free joint that was 

produced is shown in Figure 7. The joint is indistinguishable from the matrix. It is also noteworthy 

that the microstructure was unchanged. The next 

step will be to determine the temperature, strain, 

and strain rate region over which joining by plastic 

deformation is possible.

Figure 7. Joint in hydroxapatite produced at 1275°C at 

a strain rate of 10-5 s-1. Arrows indicate the interface 

between the two joined pieces.

Conclusions

We have shown that we can form pore-free, 

very strong joints in a wide variety of important 

materials by plasticity. Previously we have reported on joining structural and electronic ceramics, metal-matrix composites, Ni3Al, whiskerreinforced ceramics, and cermets. Previous work 

has shown that experimental determinations of the 

residual stress agree with calculated values. Little 

surface preparation and modest temperatures are 

required for deformation joining. Those factors 

make the process attractive for commercialization. 

Using the alumina/ zirconia system as a model 

material, we have shown that the fracture of a 

joined bar of the same composition has the same 

strength as the matrix. The fracture of a joined 4-

pt bend bar of dissimilar compositions does not 

fracture at the interface, but at a position near the 

maximum residual tensile stress. 

We have continued to expand the materials 

that can be joined by plastic deformation. In this 

fiscal year, we have studied high-temperature deformation and joined a biomaterial, HA. We have 

applied the technique to a practical problem, producing a gas-tight oxygen sensor. 

Future work will concentrate on joining dissimilar materials, such as intermetallics, to ceramics. We also plan to join optical materials and 

assess the quality of the join using optical transmission. Preliminary feasibility studies to perform 

an in-situ deformation study of grain rotation are 

under way. We are investigating the deformation 

characteristics of several possible candidate materials with a view of choosing one that has suitable 

X-ray transmission properties, but that deforms 

into steady state at modest temperatures by grain 

boundary sliding. Preliminary designs of a furnace 

and deformation apparatus will be considered in 

FY 2005, pending funding. 

References

1. F. Gutiérrez-Mora, K. C. Goretta, S. Majumdar, J. L. Routbort, M. Grimdisch, and A. 

Domínguez-Rodríguez, “Influence of Internal 

Stresses in Superplastic Joining of Zirconia 

Toughened Alumina,” Acta Materialia, 50, 3475–

3486 (2002). 

2. K. C. Goretta, F. Gutiérrez-Mora, J. J. Picciolo, and J. L. Routbort, “Joining Alumina/Zirconia Ceramics,” Mat. Sci. and Eng., 

A341, 158–162 (2003). 

3. F. Gutierrez-Mora, K. C. Goretta, J. L. 

Routbort, and A. Dominguez-Rodriguez, “Joining 

of Ceramics by Superplastic Flow,” in Advances 

in Ceramic Matrix Composites VII, Ceramic 

Transaction # 128, ed. N. P. Bansal, J. P. Singh, 

and H. T. Lin, p. 251, The American Ceramic Society, Westerville, Ohio (2002). 

4. N. Chen, F. Gutierrez-Mora, R. E. Koritala, 

K. C. Goretta, J. L. Routbort, and J. Pan, “Joining 

Particulate and Whisker Ceramic Composites by 

Plastic Flow,” Comp. Struct., 57, 135–139 (2002). 

5. F. Gutierrez-Mora and J. L. Routbort, 

“Electrical Characterization of a Joined Electroceramics La0.85Sr0.15MnO3, ” J. Am. Ceram. Soc., 

85(9), 2370–2372 (2002). 

6. F. Gutiérrez-Mora, A. DomínguezRodríguez, J. L. Routbort, R. Chaim and F. 

Guiberteau, “Joining of Yttria-Tetragonal Stabi-
High Strength Weight Reduction Materials FY 2004 Progress Report 

83 

lized Zirconia Polycrystals using Nanocrystals,” 

Scripta Mat. 41, 455–460 (1999). 

7. F. Gutierrez-Mora, D. Singh, N. Chen, K. 

C. Goretta, J. L. Routbort, and A. DominguezRodriguez, submitted to J. European Ceramic Society.

8. F. Gutierrez-Mora, K. C. Goretta, N. Chen, 

and J. L. Routbort, “Joining of Advanced Ceramics by Plastic Flow,” Ceramics Intl. 30, 1945–

1948 (2005). 

9. H. L. Ewalds and R. J. H. Wanhill, Fracture 

Mechanics, p. 37, Edward Arnold, Delftse, The 

Netherlands (1984). 

Publications and Presentations

A. Dominguez-Rodriguez, F. Gutierrez-Mora, 

M. Jimenez-Melendo, J. L. Routbort, and R. 

Chaim, “Current Understanding of Deformation of 

Y–TZP and Superplastic Joining of Ceramics,” J. 

Mater. Engr. A302, 154–161 (2001). 

A. Dominguez-Rodriguez, F. Gutierrez-Mora, 

M. Jimenez-Melendo, R. Chaim, and J. L. Routbort, “Superplasticity and Joining of Zirconia–

Based Ceramics,” presented at the Materials Research Society Symposium, Proceeding 601 99-

104, 2000. 

F. Gutierrez-Mora, K. C. Goretta, J. L. Routbort and A. Domínguez-Rodríguez, “Joining Ceramics by Superplastic Flow,” Ceramic 

Transactions 128, 252–258 (2002). 

K. C. Goretta, F. Gutierrez-Mora, J. J. Picciolo, and J. L. Routbort, “Joining Alumina/Zirconia Ceramics,” J. Mater. Engr. A341, 

158–162 (2003). 

A. R. De Arellano-Lopez, U. Balachandran, 

K. C. Goretta, B. Ma, and J. L. Routbort, “HighTemperature Deformation of Sr(FeCo)1.5Ox Ceramics,” Acta Materialia 49, 3109–3116 (2001). 

F. Gutierrez-Mora, K. C. Goretta, S. Majumdar, J. L. Routbort, M. Grimdisch, and A. Dominquez-Rodriguez, “Influence of Internal Stresses on 

Superplastic Joining of Zirconia-toughened Alumina,” Acta Materialia 50, 3475–3486 (2002). 

E. Wuchina, M. Opeka, F. Gutierrez-Mora, R. 

Koritala, K. C. Goretta, and J. L. Routbort, “Processing and Mechanical Properties of Solid-solutions of Hf-N,” J. European Ceramic Soc. 22, 

2571–2576 (2002). 

N. Chen, F. Gutierrez-Mora, R. E. Koritala, K. 

C. Goretta, J. L. Routbort, and J. Pan, “Joining 

Particulate and Whisker Ceramic Composites by 

Plastic Flow,” Composite Structures, 57, 135–139 

(2002). 

A. R. de Arellano-Lopez, J. J. MelendezMartinez, A. Dominguez-Rodriguez, T. A. Cruse, 

R. Koritala, J. L. Routbort, and K. C. Goretta, 

“Compressive Creep of Mullite Containing 

Y2O3,” Acta Materialia 50, 4325–4338 (2002). 

F. Gutierrez-Mora and J. L. Routbort, “Electrical Characterization of a Joined Electroceramic, 

La0.85Sr0.15MnO3,” J. American Ceramic Society 85, 2370–2372 (2002). 

F. Gutierrez-Mora, J. M. Ralph, and J. L. 

Routbort, “High-temperature Mechanical Properties of Anode-Supported Bilayers,” Solid State 

Ionics 149, 177–184 (2002). 

A. R de Arellano-Lopez, K. C. Goretta, E. T. 

Park, S. E. Dorris, U. Balchandran, and J. L. 

Routbort, “High-temperature Deformation of a 

BaCe0.8Y0.2O 3-y + Ni Composite,” J. European Ceramic Society 22, 2555-2560 (2002). 

J. L. Routbort, J. Ralph, R. E. Cook, C. 

Clauss, and A. R. de Arellano-López, “Creep of 

(La0.55Sr0.45)0.99Mn1-yGayO3,” Phys. Chem. 

Chem. Phys. 5, 2232–2236 (2003). 

K. C. Goretta, F. Gutierrez-Mora, N. Chen, J. 

L. Routbort, T. A. Orlova, B. I Smirnov, and A. R. 

de Arellano-López, “Solid-Particle Erosion and 

Strength Degradation of Si3N4/BN Fibrous Monoliths,” Wear 256, 233–242 (2004). 

J. Martinez-Fernandez, A. R. de ArellanoLopez, F. M. Varela-Feria, T. S. Orlova, K. C. 

Goretta, F. Gutierrez-Mora, Nan Chen, and J. L. 

Routbort, “Erosion and Strength Degradation of 

Biomorphic SiC,” J. European Ceramic Society

24, 861–870 (2004). 

K. C. Goretta, Nan Chen, F. Gutierrez-Mora, 

J. L. Routbort, G. C. Lukey, and J. S. J. van Deventer, “Solid-Particle Erosion of a Geopolymer 

Containing Fly Ash and Blast-Furnace Slag,” 

Wear 256, 714–719 (2004). 

F. Gutierrez-Mora, K. C. Goretta, Nan Chen, 

and J. L. Routbort, “Joining of Advanced Ceramics by Plastic Flow,” Ceramics International 30, 

1945–1948 (2004). 

F. Gutierrez-Mora, D. Singh, N. Chen, K. C. 

Goretta, J. L. Routbort, and A. DominguezRodriguez, “Fracture of Composite Alumina/Yttria-stabilized Joints,” J. European Ceramic Society, in press 
FY 2004 Progress Report High Strength Weight Reduction Materials 

84

K. C. Goretta, T. A. Cruse, D. Singh, J. L. 

Routbort, A. R. de Arellano-Lopez, T. S. Orlova, 

and B. I. Smirnov, “Ceramic Fibrous Monolithic 

Structures,” Composite Structures 66, 547–553 

(2004). 

D. Singh, F. Guiterrez-Mora, N. Chen, K. C. 

Goretta, and J. L. Routbort, “Joining of Advanced 

Structural Materials by Plastic Deformation,” Advances in Ceramics, in press. 

F. Guiterrez-Mora, K. C. Goretta, D. Singh, 

J. L. Routbort, S. Sambasivan and K. Steiner, 

“High-Temperature Mechanical Behavior of Aluminum-Phosphate Based Glass Ceramics (Cerablak),” J. European Ceramic Society, in press. 

Patent Applications

K. C. Goretta, J. L Routbort, and F. GutiérrezMora, “Joining of Advanced Materials by Plastic 

Deformation, invention report, 0003/00950. 

J. L. Routbort, et al., “Method Of Fabrication 

of a High-Temperature Potentiometric Oxygen 

Sensor,” invention report ANL-IN-04-105 
High Strength Weight Reduction Materials FY 2004 Progress Report 

85 

E. Friction Stir Joining and Processing of Advanced Materials Including Metal 

Matrix Composites 

Principal Investigator: Glenn J. Grant 

Pacific Northwest National Laboratory 

P.O. Box 999, 902 Battelle Blvd., Richland, WA 99352 

(509) 375-6890; fax: (509)375-44; e-mail: glenn.grant@pnl.gov 

Project Manager: Moe Khaleel 

Pacific Northwest National Laboratory 

P.O. Box 999, 902 Battelle Blvd., Richland, WA 99352 

(509) 375-2438; fax: (509) 375-6631; e-mail: moe.khaleel@pnl.gov 

Technology Development Area Specialist: Sidney Diamond 

(202) 586-8032; fax: (202) 586-1600; e-mail: sid.diamond@ee.doe.gov 

Field Technical Manager: Philip S. Sklad 

(865) 574-5069; fax: (865) 576-4963; e-mail: skladps@ornl.gov 

Participants 

Bill Arbegast, Glen Stone, Stan Howard, Casey Allen 

Advanced Materials Processing Center 

South Dakota School of Mines and Technology 

Rapid City, S.D. 

Contractor: Pacific Northwest National Laboratory 

Contract No.: DE-AC06-76RLO1830 

Objective 

• Investigate and develop friction stir joining (FSJ) and friction stir processing (FSP) as viable industrial joining 

and processing techniques for advanced materials, including aluminum metal matrix composites (MMCs), titanium, and advanced high-strength steel. During FY 2004, this project focused on two main task areas: the development of appropriate tooling and process parameters that will allow friction stir welding (FSW) to be used 

in abrasive and/or high-temperature materials, and the use of the FSP process to modify the surfaces of materials for advantageous near-surface mechanical and thermal properties. 

Approach 

• Develop new tooling designs and fabricate tools from advanced tooling materials (Ni-alloy and Fe-matrix TiC 

MMCs). 

• Develop weld process methods, such as induction preheating, to lower process forces and reduce wear or tool 

breakage issues in hard-to-weld materials. 

• Experimentally determine the feasibility of making near-surface graded composites by FSP in aluminum and 

steel to create functionally graded materials with enhanced surface-engineered properties. 

• Investigate the new method of friction surface reaction processing (FSRP) in which a friction stir tool is used to 

initiate in situ solid-state reactions that can stabilize new phases or ultra-fine grained phases in the near-surface 

regions of bulk materials for enhanced surface properties.
FY 2004 Progress Report High Strength Weight Reduction Materials 

86 

• Investigate the application of FSJ to ferritic oxygen-dispersion-strengthened (ODS) alloys, including MA957.

• Investigate the use of FSP to create robust thermal barrier coatings on steel. 

Accomplishments 

• Fabricated tools using new unique designs that will be used in coatings and wear studies. 

• Developed, at the South Dakota School of Mines and Technology, induction preheating techniques that facilitate FSJ/P in steels and cast iron. 

• Created near-surface regions in aluminum and steel that are enriched in ceramic particulate by physically stirring powders into the surface using a spinning friction stir tool. 

• Began experimental studies into FSRP by plasticizing and reacting elemental powders and oxides beneath a 

spinning tool during FSP. 

• Performed preliminary experiments on using FSP to plasticize MA957, a ferritic ODS alloy. 

• Used FSP to process pre-existing thermal barrier coatings on steel to create diffuse, interface-free, near-surface 

zones that have unique thermal properties. 

Future Direction 

• Further develop tool materials and designs for steel and titanium FSJ/P 

• Develop process parameters and conditions necessary for surface modifications of steel and titanium 

• Develop friction stir surface processing for thermal barrier applications 

• Develop the process of reaction surface processing to create, by solid-state chemical reaction, new phases at the 

surface. 

Introduction 

Friction Stir Joining 

One of the key strategies for making a vehicle 

energy-efficient is to manufacture it from lighter 

materials. Structural and functional requirements, 

however, lead to a situation where no single lightweight material is appropriate for all applications. A 

modern, weight-optimized vehicle structure is a hybrid of many materials. A critical problem that has 

emerged in the development of these hybrid structures is that for many material combinations, traditional joining technologies (e.g., fusion welding or 

mechanical fastening) are not appropriate. For some 

highly specialized materials, like aluminum MMCs, 

titanium, and advanced high-strength steels, a better 

joining technology can have significant impact on 

whether these materials have a role in future vehicle 

structures. 

In the last 15 years, the new joining technology 

FSJ has emerged that has the potential to join many 

lightweight materials. Invented by TWI, Ltd., FSJ is 

a solid state process that employs severe plastic deformation to create joints between a wide variety of 

different materials. A typical FSJ butt joint is depicted in Figure 1. The weld is created by clamping 

the materials to be joined and plunging a spinning 

tool into the surface. The spinning tool is then translated down the joint line, leaving behind a weld zone 

characterized by a fine-grained, dynamically recrystallized microstructure. Typically, the tool is spun at 

400 rpm to 2000 rpm and translated down the joint 

line at a rate of 4 to 300 in./min, depending on tool 

design, base material, and thickness. As the tool rotates and translates, complex flow patterns develop 

in the base material that create an intimate mixing of 

materials from both sides of the weld. Heat input 

during plastic deformation generally creates a temperature in the weld between 0.6 and 0.8 of the absolute melting temperature so that no liquid phase is 

generated. 

FSJ is capable of producing aluminum and magnesium alloy welds as good as or better than fusion 

welds in terms of joint efficiency, mechanical 
High Strength Weight Reduction Materials FY 2004 Progress Report 

87 

Figure 1. Friction stir joining and processing are accomplished by plunging a spinning tool into a material and 

translating the tool across the surface to form either a 

joint or a surface processed region (TWI, Ltd.). 

properties, and environmental robustness. A significant advantage of the process, for application to hybrid structures, is that since there is no melting 

during the process, a large variety of dissimilar material joints are possible, including dissimilar aluminum and magnesium joints that are not possible with 

conventional fusion welding. 

In the last five years, FSJ has been shown to be a 

commercially important, energy-efficient, and environmentally friendly process for joining aluminum. 

However, there are many opportunities for other 

higher-strength lightweight materials to be considered if there existed good joining technologies for 

these materials as well. The objective of this project 

is to investigate how FSJ can be applied to advanced 

materials including AL-MMCs, titanium, and steels. 

Moving the FSJ process from “soft” materials like 

aluminum and magnesium into advanced, higherstrength alloys has proved to be challenging because 

of the mechanical and thermal demands on the tool 

materials. In steels, for instance, the tools must survive high forge loads as well as tool temperatures of 

up to 1100°C. A primary challenge is to develop pin 

tool designs and materials that can survive the hightemperature and/or abrasive-wear conditions under 

which the tool will be forced to operate. 

Friction Stir Processing

Recently, a new research direction has emerged, 

as an outgrowth of FSJ, that recognizes that the same 

solid state deformation process can be used to modify the surface of a monolithic material for enhanced 

properties. This new research direction is called 

FSP. 

Several applications of FSP have been investigated during the course of this project including surface modification for wear resistance, for creation of 

bulk superplastic properties, and for improvement to 

the near-surface defect and porosity distribution in 

Al-MMC castings. Work during FY 2004 concentrated on creating wear-resistant surfaces by FSP 

particle incorporation, on creating engineered surfaces by solid state reaction- processing, and on basic experiments in creating thermal barrier coatings 

by FSP. 

This work was designed to test the feasibility of 

using FSP to create engineered surfaces. During 

previous years, this work demonstrated that it is possible to create a particle-reinforced zone of 20-

micron SiC or Al2O3 particles in a 6061 aluminum 

base alloy (Figure 2). Microscopy has shown that 

the stirred region is developed as deep as the pin 

probe (2–3 mm in our tests), which is defect-free 

and forms a graded metallurgical bond with the underlying surface. No interface is developed between 

Figure 2. Friction stir processed 6061 plate with ceramic 

particulate incorporated into the surface. 
FY 2004 Progress Report High Strength Weight Reduction Materials 

88 

the composite zone and the base material. The surface zone has the potential to be orders of magnitude 

thicker than conventional coating technologies; and 

it has the added benefit of producing a graded structure that does not have a sharp interface with the 

underlying substrate, thereby avoiding many of the 

problems seen in conventional coatings (coefficient 

of thermal expansion mismatch, etc.). 

While lightweight wear-resistant materials could 

benefit from this compositing technique, perhaps the 

greater application could be in ferrous or hard alloy 

systems. Hard particle reinforcement of the surfaces 

of steels, titanium, brasses, or cast iron may have 

numerous industrial applications in reciprocating 

assemblies, engines, brake disks, or other situations 

where both bulk strength and surface wear resistance 

is needed. Lightweight high-strength steels with surface wear resistance may have numerous applications in both lightweight structures and lightweight 

vehicle power systems. Work during FY 2004 focused on developing methodologies 

to successfully surface-process high-temperature 

materials including steels and cast iron. 

Approach

The basic objective of this project is to investigate and develop FSJ and FSP as viable industrial 

techniques for advanced lightweight materials. The 

approach used has been to (1) seek to develop new 

tool materials and designs that will allow successful 

joins to be made in Al-MMCs, titanium, and steel; 

and (2) explore the potential to modify the surfaces 

of both conventional aluminum and magnesium alloys and advanced materials toward the goal of improving wear, corrosion, or mechanical properties. 

The FY 2004 program is divided into three main 

tasks. The first task focused on developing tool designs and fabricating tools in some of the tool materials defined by last year’s efforts. The second task 

area broadly investigated using FSP to create engineered surfaces. Surface modification was investigated in three areas: (1) particle incorporation to 

create near-surface MMCs in aluminum and steel, 

(2) surface alloying by reaction processing, and (3) 

surface modification of pre-existing thermal barrier 

coatings to possibly create graded structures with 

unique thermal properties. In addition, to facilitate 

FSP in steels, we investigated the use of induction 

preheating to lower process forces in these hard-toprocess materials. Finally, the third main task was a 

small investigative effort into the feasibility of using 

FSJ to join or process a ferritic ODS alloy, MA957. 

This material is a creep- resistant high-temperature 

steel that has potential application in hightemperature environments such as solid oxide fuel 

cells. 

Results

Tool Materials and Designs 

During FY 2003, promising tool materials were 

identified for each material system. In FY 2004, 

tools were fabricated from some of these materials, 

and the tools were used to process aluminum and 

steel surfaces. Figure 3 shows several tools made 

from H13 (baseline), MP159 (a cobalt-nickel alloy), 

and FerroTiC (an iron-based TiC MMC). These tool 

materials show virtually no wear during FSJ of standard aluminum alloys. However, creating surfacemodified regions enriched in ceramic particles requires tool materials to have strong wear resistance. 

In aluminum MMC systems with either SiC or 

Al2O3 particulate, H13 and nickel alloy materials 

showed significant wear, while FerroTiC showed 

Figure 3. Tool materials clockwise from lower left: 

MP159 (a cobalt-nickel-chrome-moly alloy), H13 tool 

steel, and FerroTiC (35% TiC in a impact-resistant, ironbased tool steel) 
High Strength Weight Reduction Materials FY 2004 Progress Report 

89 

virtually no wear. This project also investigated stirring ceramic particulate into steel substrates. In these 

cases, tools were composed of tungsten 25% rhenium. 

Particle distribution within a surface- modified 

layer is dependent (among other things) on tool design. During FY 2004 this project investigated numerous tool designs in an effort to improve particle 

distribution and placement with a processed layer. 

Figure 4 shows tools of differing designs, including 

wide pins, narrow pins, scrolled shoulders, and 

multi-pin tools. The basic design philosophy is to 

create a wide stir zone (Figure 5) with a high degree 

of vertical mixing to drive the particulate from the 

surface to the deepest part of the processed region 

Figure 4. Different tool designs produce different particle distributions and flow characteristics. 

Figure 5. Wide stir zones can be created using three-pin 

tools. Wide zones are important to minimize passes required to process larger areas. 

(Figure 6). Experimental work has shown that both 

the three-pin designs and the wide stepped spirals 

can achieve this goal. 

Figure 6. Tool design affects material flow during FSP. 

Features on the tool surface can promote flow from surface to base of processed region and channel surface 

powders, for instance, to the pin root zone. 
FY 2004 Progress Report High Strength Weight Reduction Materials 

90 

Friction Stir Surface Processing

Much of the effort in FY 2004 was directed toward the new field of FSRP. Thermodynamic calculation of numerous potential solid state reactions 

indicates that energies available during FSJ/P may 

be high enough to initiate the formation of some 

compounds like TiB2 from elemental constituents, 

especially considering all the new surface being 

generated by the severe plastic deformation under 

the pin tool. This process opens the possibility of 

making very finely divided reaction products in the 

near-surface region of a bulk material (see Table 1). 

These reactions can be tailored by the composition 

of the elemental powders introduced on the surface. 

In addition, highly exothermic (thermite style) reactions may be possible that can put large amounts of 

heat into the surface and potentially reduce the flow 

stress of hard-to-weld alloys, or allow the FSJ process to occur without significant tool wear. Claddings 

of materials rich in fine oxide dispersions, or other 

in situ–formed ceramic-rich materials, may be possible on low-cost ferritic base alloys (creep-resistant 

surfaces for engine applications). 

from X-ray diffraction analysis. Despite the highly 

favorable Gibbs free energies for these reactions, 

only limited reaction products were formed. The 

large driving force for reaction with little reaction is 

a clear indication that the activation energy for the 

reaction was not satisfied. Higher temperatures decrease the activation energy, making spontaneous 

reaction more likely. In FY 2005, the project will 

investigate the FSRP process in higher-temperature 

processing environments like those found when 

processing iron- or titanium-based materials. In addition to higher temperatures, catalysts may also be 

employed as a means of lowering the activation energy. Additional work is planned on this as well as 

on other reaction systems, as outlined in Figure 9, 

including systems where the tool pin is a reactant 

and thermite-type systems. 

Work was also initiated on a study of the potential for using FSP to process previously deposited 

thermal barrier coatings (TBCs). In many applications, TBCs can show reliability problems as a result 

of cracking and spalling of the coating at the 

Table 1. Reaction modes 

Mode Reaction Examples 

I Base Metal (Al) + Reactant 

 Product 

3 SiO2 + 4Al 3Si + 2Al2O3

3 TiO2 + 4Al 3Ti + 2Al2O3

BN + Al AlN + B 

II Pin Tool (Ti) + Reactant 

 Product 

3 Ti + 2 BN 2 TiN + TiB2

Ti + AlN TiN + Al 

Ti + C TiC 

Ti + 2B TiB2

III A + B C + D 4Al(powder)+ 3SiO2 3Si + 2Al2O3

4Al(powder) + 3TiO2 3Ti + Al2O3

Work in FY 2004 concentrated on reactions in 

the aluminum system, as outlined in Table 1. 

Reactant powders were placed between plates of 

1100 alloy aluminum as shown in Figure 7. The assembly was then friction-stir-processed to produce a 

microstructure, as shown in Figure 8. The nugget 

region contains very finely dispersed precursor reactants but only a small amount of reactant product 

coating/substrate interface. FSP may be able to create more robust coatings by disrupting the sharp interface and creating a graded structure. Issues with 

coefficient of thermal expansion mismatch may be 

reduced by creating this graded stir zone. Most TBC 

systems are in materials that are very difficult to 

FSP because of their hot hardness or lack of plastic 

properties needed to form good FSP microstructure. 
High Strength Weight Reduction Materials FY 2004 Progress Report 

91 

Figure 7. Reactant oxide powders are placed between 

plates, and the stir tool processes the entire thickness 

Figure 8. Cross sections showing fully consolidated weld 

zone. FSRP zone is 3/8-in (9.52 mm) thick: (a) SiO2 and 

(b) TiO2. 

Figure 9. Different modes of reactions and experimental 

work planned in the current program. 

Most of the work in FY 2004 was directed at finding 

process conditions in which the coating, usually a 

zirconia-based material, could be successfully mixed 

into the substrate, usually a steel. Figure 10 shows 

typical flame spray coatings investigated in this 

study. These are usually characterized by a top coat 

of ceramic material underlain by a bond coat of 

NiCrAlY on a steel substrate. The project investigated various combinations of coating thicknesses 
FY 2004 Progress Report High Strength Weight Reduction Materials 

92 

Figure 10. Typical flame spray deposited thermal barrier 

coating. 

and graded metal ceramic coatings for their potential 

to be plasticized and processed using FSP. Figure 11 

shows an example of a processed plate both during 

and after FSP. In some cases, especially with thick 

ceramic top coats, a large percentage of the top coat 

was chipped off during processing; but in other 

cases of graded or mixed ceramic/bond metal coatings, much of the coating was stirred into the nugget 

region. 

Currently this project is investigating the thermal diffusivity/conductivity of these modified surfaces relative to the original coating; it is also 

investigating ways to better optimize the process so 

that less of the coating is lost during FSP. 

Research at the South Dakota School of Mines 

and Technology has shown that induction preheating 

of the substrate prior to FSP can have an important 

effect on process forces and perhaps on the quality 

of the weld in difficult-to-weld materials. Figure 12 

shows the induction heater mounted on the spindle 

head of the friction stir machine. Figure 13 shows 

that for 1018 steel, induction preheating can reduce 

process forces throughout the weld or processed region length.1

 Reduced process forces can be correlated with lower tool wear and better material flow 

in the weld. Additional work is planned in FY 2005 

to define the effects of induction preheating better in 

steel and difficult-to-process materials. 

Figure 11. Zirconia-based thermal barrier coatings undergoing friction stir processing to mix coating into base 

material. 

A final area investigated in FY 2004 was the 

applicability of FSJ/FSP to ferritic ODS alloys. 

These alloys have very good elevated-temperature 

creep properties resulting from the presence of fine 

dispersions of yttria in the steel matrix. One problem 

in using these materials for high-temperature applications is that they are very difficult to join. Few 

processes exist that can join these materials to other 

structures, or to themselves, without destroying the 

yttria dispersion and losing the high-temperature 

properties that make these materials attractive. Fusion welding can cause particle segregation, growth, 

or dissolution. FSP, however, is a solid state process 

and has the potential to join and process these alloys 

without destroying the yttria dispersion. Preliminary 

work during FY 2004 has shown that FSP can plasticize these alloys. Extruded tubes (25 mm in diameter with 3-mm wall thickness) of MA-957 with 

Inconel 625 inner rods were friction-stir-processed 

using a less than optimum 
High Strength Weight Reduction Materials FY 2004 Progress Report 

93 

Figure 12. Induction pre-heating head mounted to FSJ 

machine spindle. 

Figure 13. Work at South Dakota School of Mines and 

Technology has shown that induction preheating can 

lower process loads in difficult-to-weld materials like 

1018 steel. (Figure courtesy of Tweedy, Arbegast, Allen 

2004). 

tool. Figure 14 shows plasticized material in the 

processed region. Transmission electron microscopy 

analysis and mechanical testing are under way to 

Figure 14. Cross section of ODS alloy tube plasticized by 

friction stir processing. Processed region is not consolidated due to tool-part mismatch, but plasticized region 

shows nature of flow and confirms that ODS alloys can 

be processed using FSP. 

determine the effect of FSP on the yttria dispersion 

and whether creep properties are preserved. 

Conclusions 

FSJ and FSP are technologies that will enable 

the application of many lightweight materials in the 

next generation of transportation systems. Many 

advanced materials, such as Al-MMCs and certain 

high-strength steels (including ODS), are in need of 

effective joining technologies before their widespread use can be considered. Solid state FSJ/P 

avoids many of the problems with fusion joining and 

represents a revolutionary change in joining technology. FSP also has numerous opportunities in the 

growing field of surface engineering and thermal 

management. 

The results of this work will allow designers to 

anticipate and implement structures that are a hybrid 

of many different materials, facilitate new applications, and suggest new materials and engineered surfaces that can help deliver lighter and more fuelefficient vehicles. 

References

1. B. M. Tweedy, W. Abergast, and C. Allen, 

“Friction Stir Welding of Ferrous Alloys using Induction Preheating,” in Friction Stir Welding and 

Processing III, ed. K. V. Jata, M. W. Mahoney, and 

T J. Lienhert, TMS, 2005. 

Presentations/Publications

G. J. Grant, FY 2004 Semi-Annual Report: Friction Stir Joining and Processing of Advanced Materials, Including Metal Matrix Composites, June 

2004. 
FY 2004 Progress Report High Strength Weight Reduction Materials 

94 

G. J. Grant, PNNL Milestone Report PNNL 

15534: Project:Friction Stir Joining of Advanced 

Materials including AL-MMCs: Complete Analysis 

and Characterization of FSP Process Parameters 

Needed to Fabricate Surface-Modified, CeramicReinforced Metals, Pacific Northwest National 

Laboratory, June 30, 2004. 

S. M. Howard, W. Arbegast, B. Jasthi, G. J. 

Grant, D. R. Herling, “Friction Surface Reaction 

Processing On Aluminum Substrates,” abstract submitted for 2005 TMS Annual Meeting, San Francisco. 

S. M. Howard, W. Arbegast, B. Jasthi, G. J. 

Grant, D. R. Herling, “Friction Stir Welding Of Ma 

957 Oxide Dispersion Strengthened Ferritic Steel,” 

abstract submitted for 2005 TMS Annual Meeting, 

San Francisco. 

U. Ramasubramanian, W. Arbegast, G. Stone, 

G. J. Grant, “Friction Stir Processing Of Ferrous 

Alloys For Increased Wear Resistance,” abstract 

submitted for 2005 TMS Annual Meeting, San 

Francisco. 

R. L. Veluchamy, W. Arbegast, G. Stone, G. J. 

Grant, “Incorporating Titanium Powder to Create insitu Composites on the Surface of Cast Iron via Friction Stir Reaction Processing (FSRP),” abstract submitted for 2005 TMS Annual Meeting, San 

Francisco. 
High Strength Weight Reduction Materials FY 2004 Progress Report 

95 

F. Friction-Stir–Joined Aluminum Sheet Materials for Heavy Vehicle 

Cab Structures 

Principal Investigator: Richard W. Davies 

Pacific Northwest National Laboratory 

P.O. Box 999, Richland, WA 99352-0999 

(509) 375-6474; fax: (509) 375-4448; e-mail: rich.davies@pnl.gov 

Technology Development Area Specialist: Sidney Diamond 

(202) 586-8032; fax: (202) 586-1600; e-mail: sid.diamond@ee.doe.gov 

Field Technical Manager: Philip S. Sklad 

(865) 574-5069; fax: (865) 576-4963; e-mail: skladps@ornl.gov 

Participants: 

Scott Wazny, Leon Kaunitz, and Brian Fulbright, Freightliner LLC 

Douglas Waldron and Keith McTernan, Advanced Joining Technologies, Inc. 

Tom Sanor, Drive Automotive 

Gene Paik, Alcoa, Inc. 

Contractor: Pacific Northwest National Laboratory 

Contract No.: DE-AC06-76RL01830 

Objective 

• Develop and deploy friction stir joining (FSJ) as a weight- and cost-saving manufacturing technology for heavy 

vehicle cab structures. 

Approach 

• Demonstrate the use of aluminum tailor-welded blanks (TWBs) for heavy vehicle applications. 

• Develop and characterize TWBs prepared via FSJ. 

• Develop and prototype several cab-in-white structures for Class 8 trucks. 

Accomplishments 

• Conducted preliminary stamping trials, which indicated that some material combinations and weld geometries 

can be successfully stamped into parts; this application has the potential for a significant cost and weight savings in heavy vehicle cab structures. 

• Investigated new part configurations, using thin-gage heat-treatable alloys and dissimilar alloy combinations 

(5000 and 6000 series aluminum TWBs). 

• Developed welding process parameters to minimize cost and maximize performance of truck components. 

• Characterized the formability of welded assemblies through optical strain analysis. 

• Characterized the local mechanical properties of the weld metal and surrounding region of AA5052-H32 and 

AA5182-O TWBs to understand the effect of the welding process on the ductility of the weld metal. 

• Assembled successful parts into cabs and conducted full cab durability and crash testing at full truck load. 
FY 2004 Progress Report High Strength Weight Reduction Materials 

96 

Future Direction 

• Continue with the weld process development of 6000 series aluminum to increase the formability. 

• Continue with weld process development of aluminum alloy 5052-H32 TWBs and optimize the welding process parameters. 

• Investigate the interaction between the weld in the TWB and the joining method used to assemble the blank into 

the vehicle and determine how this interaction may influence long-term vehicle durability and crashworthiness. 

• Develop and optimize the welding process parameters of dissimilar aluminum alloys of different thicknesses 

(5182-O and 6022 aluminum alloys). 

• Conduct a design of experiments on tool development and design to determine the speeds and performances of 

different tools. 

• Focus on FSJ as a low-cost enabler of lightweight, low-cost vehicle assembly (non-TWB). 

Introduction

This work is a collaborative effort between Pacific Northwest National Laboratory (PNNL), 

Freightliner, LLC, Advanced Joining Technologies, 

Inc., Drive Automotive, and Alcoa. This project 

aims to develop and deploy FSJ as a cost- and 

weight-saving manufacturing technology for heavy 

vehicle cab structures. To date, the project has focused on (1) developing and characterizing TWBs 

prepared via FSJ and (2) demonstrating their use by 

prototyping several cab-in-white structures and body 

panels for Class 8 trucks. 

Aluminum TWBs consist of multiple-thickness 

and multiple-alloy sheet materials welded together 

into a single, variable-thickness blank. Figure 1 

shows a typical fusion-welded TWB before and after 

a stamping application. A TWB is assembled as a 

series of flat sheets joined together, which are then 

submitted to a stamping process. The technology 

allows production of a weight-optimized, variablethickness vehicle body component. TWB technology 

gives automotive and truck designers the ability to 

selectively vary body panel thickness to optimize the 

use of material. Successful use of the technology 

ultimately results in reducing vehicle weight without 

compromising final strength, stiffness, and durability. The manufacture of TWBs and their application 

in body panels requires that the weld material deform under biaxial loading during sheet metal 

stamping. The deformation of weld materials and 

their limits of formability are important aspects of 

TWB technology. 

The primary challenge of using aluminum 

TWBs in the past has been the relatively low quality 

Figure 1. Left: A TWB viewed in the as-welded condition, ready for submission to the stamping process. The 

shape shown is typical for a door inner stamping operation. Right: Aluminum TWB after stamping to produce a 

door inner panel. 

of aluminum fusion welds, which often results in 

premature fracture or lack of reliability of weld materials during stamping. Improving aluminum weld 

quality, understanding and describing the formability of the weld region, and predicting its formability 
High Strength Weight Reduction Materials FY 2004 Progress Report 

97 

are the primary technical challenges in using aluminum TWBs. 

FSJ is a revolutionary joining technology that 

employs severe plastic deformation to create solid 

state joints between wide varieties of different materials. Invented by TWI, Ltd., about 12 years ago, 

FSJ is capable of producing aluminum alloy welds 

as good as (or significantly better than) fusion welds 

in terms of joint efficiency, mechanical properties, 

and environmental robustness. The advantage of 

using this solid state joining technique is the ability 

to avoid liquid metal during joining, where aluminum has low molten viscosity, high reflectivity, and 

a relatively high propensity to form internal porosity 

because of the high solubility of hydrogen in liquid 

aluminum. 

Friction stir welding (FSW) can also eliminate 

hot cracking and minimize heat-affected-zone 

(HAZ) issues in 6000-series heat-treatable aluminum alloys. Avoiding the liquid phase of the materials also avoids the formation of various large 

eutectic constituent particles or other undesirable 

intermetallic particles that develop in particular alloys or with certain types of weld or materials contamination. The use of FSW also better facilitates 

welding of heat-treatable materials, since the HAZ is 

normally smaller or less pronounced compared with 

fusion welding. The use of solid state joining also 

enables a variety of types of dissimilar aluminum 

alloy joining not normally possible using fusion 

welding methods. 

FSJ Process Parameter Development

In a previous feasibility study, some alloy combinations were successfully stamped from TWBs 

fabricated by FSJ. However, weld line failures occurred in many other alloy combinations. The main 

thrust of this program is to better understand the 

weld process, forming parameters, and performance 

characteristics of TWBs and to apply them to a 

wider range of cab components. The use of FSJ to 

produce TWBs may result in dramatically improved 

weld quality and formability of aluminum TWBs—

thereby enabling this weight- and cost-saving technology. 

In order to develop and use FSJ to make highquality aluminum TWBs for intermediate- and highvolume truck applications, the FSJ process must be 

competitive with laser welding and other fusion 

welding technologies from a production rate perspective. The target weld speeds are 2–5+ meters/minute. The friction stir welds must be of 

significantly higher formability compared with conventional fusion welds. 

This project will develop process parameters to 

make successful welds in the following weld combinations, as they are representative of typical truck 

alloys and material thicknesses: 

• 5182-O 2 mm to 5182-O 2 mm 

• 6022-T4 2 mm to 5182-O 1.6 mm 

• 6022-T4 2 mm to 5182-O 2 mm 

• 5182-O 2 mm to 6022-T4 1.6 mm 

• 5182-O 2 mm to 5182-O 1.6 mm 

• 6022-T4 2 mm to 6022-T4 1.6 mm 

• 6022-T4 2 mm to 6022-T4 2 mm 

• 5052-H111 1.27 mm to 5052-H111 1.27 mm 

• 5052-H32 1.6 mm to 5052-H32 1.6 mm 

This project will determine, within the “defectfree” process window, where a set of parameters 

exists that produces a TWB with the best formability 

(see Figure 2). The process and forming parameters 

are being developed by FSW test coupons at a range 

of weld conditions, which are then subsequently 

tested for strength and formability to establish optimum weld conditions for each material and thickness combination of interest. The following section 

details the weld characterization performed to determine the optimum joining process parameters. 

Figure 2. An illustration of the process parameter window 

to determine the optimum set of parameters that produces 

a TWB with the best formability. 
FY 2004 Progress Report High Strength Weight Reduction Materials 

98 

Weld Characterization

Coupons of the material combinations were friction stir welded by AJT and sent to PNNL for testing 

and evaluation. These coupons were subjected to 

limited dome height (LDH) testing, mechanical tensile testing, and microscopic analysis. The results of 

these studies allow for bracketing of appropriate 

weld process parameters (i.e., weld speed, heat input, and tool design) that could produce TWBs with 

the best formability in a stamping process. 

LDH testing is used to provide joint metal formability data. Figure 3 shows a typical weld process 

parameter development matrix. For that particular 

material combination, the formability increased with 

weld speed up to 150 ipm, and then the weld quality 

degraded. Figure 4 shows typical punch-load versus 

LDH results for ductility and strength of a single 

Figure 3. LDH testing conducted to define appropriate 

weld parameters to produce the highest potential TWB 

ductility during stamping. 

Figure 4. A typical series of LDH tests illustrating ductility and strength trends with changing weld process parameters. 

population of welded blanks. LDH data also provide 

strain limits that guide weld placement in die design 

and predict the chances for successful stamping. 

Once the most formable FSW process parameters 

are established, LDH specimens are characterized 

for surface strains via strain grid analysis. LDH testing can help characterize the maximum strain that 

can be achieved in the weld or parent material adjacent to the weld. Figure 5 shows a typical illustration 

of the surface strains measured after LDH testing. 

Miniature tensile tests are conducted to characterize the local mechanical properties of the weld 

metal and surrounding region, as well as to ultimately understand the effects of the welding process 

on these mechanical properties. Figure 6 is an illustration of the miniature tensile specimen. 

Figure 5. Typical results from LDH strain analysis. Maximum achievable homogeneous true strain in the thin side 

sheet is 17 to 20% at the point when necking develops. 

Figure 6. A detailed drawing of the miniature tensile 

specimen. All dimensions are in millimeters. 

Figure 7 shows the location of some specimens 

extracted from a weld. The miniature tensile results 
High Strength Weight Reduction Materials FY 2004 Progress Report 

99 

Figure 7. An illustration of miniature tensile specimen 

locations superimposed in the weld region. 

show what mechanical property gradients exist in 

the weld metal, thermo-mechanically affected zone, 

HAZ, and parent material. The goal is to match weld 

metal and parent material flow stresses as well as 

minimize property gradient across the weld. 

For example, miniature tensile specimens were 

removed from the weld metal and surrounding region of 5052-H32 (1.6 to 1.6 mm) and 5182-O (2 to 

1.6 mm) friction-stir-joined TWBs. These experiments showed that significant variations in mechanical properties existed within the weld metal and 

surrounding regions for 5052-H32 aluminum TWBs, 

whereas little variation in mechanical properties was 

observed in 5182-O aluminum TWBs (Figures 8 and 

9, respectively). 

Figure 8. Miniature tensile test results for 5052-H32 aluminum TWB. Specimens shown were extracted from the 

weld metal and parent sheet material. 

Figure 8 shows that the 5052-H32 TWB weld 

metal is ductile; however, differences in flow stress 

Figure 9. Miniature tensile test results for 5182-O aluminum TWB. Specimens shown were extracted from the 

weld metal and parent sheet material. 

can lead to early localization during forming even 

though the weld metal shows good ductility. Therefore, one should expect that biaxial stretching 

(stamping) of the 5052-H32 TWB population will 

result in greater plastic deformation in the weld than 

in the parent sheet (and increasing weld failure 

probability); whereas biaxial stretching of the 5182-

O population should result in similar plastic deformation in the weld metal and parent sheet. Further 

development of the process parameters for 5052-

H32 TWBs is needed to determine the optimum 

joining process for formability. 

Conclusions

From this investigation, the following conclusions were derived: 

• FSJ appears suitable for fabricating aluminum 

TWBs. 

• The FSJ process is stable, is tolerant, and produces high-quality welds when the weld process 

parameters are defined. 

• The FSJ process is customizable. A wide range 

of weld heat, plastic work, and weld metal grainsize manipulation is possible with FSW by 

changing tool design and process parameters. 

These may be manipulated to achieve the opti-
FY 2004 Progress Report High Strength Weight Reduction Materials 

100 

mum joining process for formability and to create an even property gradient across the weld 

metal. 

• Process parameters can be refined for formability by choosing weld parameters from formability tests (LDH), by adjusting weld heat per unit 

of weld length to minimize the effect of thermal 

softening in the HAZ, and by closely matching 

the weld metal flow stress to that of the parent 

sheet. 

Publications/Presentations

“Evaluation of the Mechanical Performance of 

Self-Piercing Rivets in Friction Stir Welded Structures,” accepted for publication by Proceedings of 

Society of Automotive Engineers 2005 World Congress.

“The Formability of Friction Stir Welds in 

Automotive Stamping Environments,” accepted for 

publication by Proceedings of Society of Automotive 

Engineers 2005 World Congress.

“Friction Stir Welded Tailor Welded Blanks for 

Automotive Applications,” presented at 2004 TMS 

Annual Meeting and Exhibition, Charlotte, NC, 

March 16, 2004. 

“Weld Region Mechanical Properties of Friction 

Stir Welded 5052 and 5182 Aluminum TWBs,” 

proprietary technical report prepared for Freightliner 

LLC. 
High Strength Weight Reduction Materials FY 2004 Progress Report 

101 

G. Friction Stir Welding and Processing of Advanced Materials 

Principal Investigator: Zhili Feng 

Oak Ridge National Laboratory 

1 Bethel Valley Road, Oak Ridge, TN 37831 

(865) 576-3797; fax: (865) 574-4928; e-mail: fengz@ornl.gov 

Technology Development Area Specialist: Sidney Diamond 

(202) 586-8032; fax: (202) 586-1600; e-mail: sid.diamond@ee.doe.gov 

Field Technical Manager: Philip S. Sklad 

(865) 574-5069; fax: (865) 576-4963; e-mail: skladps@ornl.gov 

Participants: 

Michael L. Santella, Oak Ridge National Laboratory 

Tsung-Yu Pan, Ford Motor Company 

Naiyi Li, Ford Motor Company 

Contractor: Oak Ridge National Laboratory 

Contract No.: DE-AC05-00OR22725 

Objective 

• Develop the technological basis for friction stir welding and processing (FSW/P) of advanced high-strength 

and lightweight materials for the automotive industry. 

• Gain fundamental understanding of the relationships between workpiece and tool material properties during 

FSW/P. 

• Characterize the mechanical properties and microstructures of joints. 

• Correlate the proprieties and microstructures produced by FSW/P to the process conditions. 

Approach 

• Conduct experimental welding and processing tests on advanced materials using the state-of-the-art FSW/P 

process development system. 

• For particular workpiece materials, select the tool material based primarily on high-temperature strength, wear 

resistance, and chemical compatibility. 

• Evaluate mechanical properties and their correlation with microstructures produced by FSW/P. 

• Develop predictive modeling capability to study the properties as function of process conditions. 

Accomplishments 

• Achieved drastic improvements in the fatigue life of FSP cast aluminum alloys. 

• Completed a study on FSW of cast magnesium alloy AM60B. 

• Conducted FSW tests of high-temperature materials using the tool materials developed at Oak Ridge National 

Laboratory (ORNL). 

• Completed initial development of friction stir spot welding (FSSW) of aluminum alloys. 
FY 2004 Progress Report High Strength Weight Reduction Materials 

102 

• Developed an integrated thermal-mechanical-metallurgical model for FSW of aluminum alloy. 

Future Direction 

• Investigate the effects of heat treatment on the fatigue life of FSP cast aluminum alloys. 

• Carry out FSP of magnesium cast alloy. 

• Explore FSSW of advanced high-strength steels for automotive body structures. 

• Develop new approaches for FSSW without the exit hole for improved structural properties of the joint. 

• Carry out FSSW of other lightweight materials and dissimilar welds. 

• Use transmission electron microscopy to characterize the microstructure improvements to the cast surfaces. 

• Assess the ability of FSP to produce rapidly solidified surface microstructures. 

Introduction

FSW is a relatively new solid state joining 

method, invented in 1991. The process characteristics and advantages for joining materials that are 

difficult to join by conventional fusion welding 

processes were discussed in the 2003 annual report. 

Applications of FSW to aluminum alloys have 

been a great success. Currently, the technology forefronts are rapidly evolving: there is tremendous interest in and efforts to extend the technology to 

welding high-performance and high-meltingtemperature materials. Other novel applications of 

the process are emerging. For example, it can be 

used to thermomechanically process a material for 

microstructure refinement and property improvement. 

This program aims at advancing FSW/P technology to promote the increased use and adoption of 

high-strength lightweight materials in automotive 

structures, particularly heavy vehicles, to support the 

goals of the Office of Heavy Vehicle Technology to 

increase fuel efficiency and reduce emissions of 

heavy trucks by weight reduction without sacrificing 

strength and functionality. 

FSP Surface Modification of Aluminum

Castings

Last year, we began to investigate the application of FSP to modify the microstructures and properties of aluminum alloy castings. Two types of cast 

alloys were used: A319 (Al-6Si-3.5Cu wt %, nominal) and A356 (Al-7Si-0.3Mg wt %, nominal). Both 

alloys can be produced as either sand castings or 

permanent mold castings that are widely used in engine, driveline, and suspension components in a 

wide variety of automobiles and light trucks. Most 

of these applications involve dynamic loading, and 

the primary interest in FSP is for use as a means of 

improving the durability and reliability of a casting 

part by locally refining the cast microstructure at 

critically stressed locations. 

Experiments were conducted in collaboration 

with Ford Research and Advanced Engineering. 

Testing plates were machined from casting ingots to 

dimensions of 16 × 50 × 200 mm. FSP was applied 

on the face of the testing plate to produce an approximately 3-mm-deep processed surface layer. 

Optical microstructural examination showed that 

FSP breaks down the coarse dendrites and closes the 

solidification shrinkage porosity and voids in the 

original cast microstructure. The resulting refined 

uniform distribution of eutectic particles increases 

substantially the static strength and ductility of the 

FSP region. These results were reported in last 

year’s annual progress report. 

This year, the R&D efforts focused on the fatigue life of the FSP material. The procedure to obtain the fatigue life test specimen was the same as in 

last year’s static mechanical property test. A subsized tensile fatigue specimen with gage dimensions 

of 2 × 2 × 15 mm was then cut from the processed 

material. The testing gage length is entirely within 

the processed region and transverse to the FSP bead, 

as shown in Figure 1. 
High Strength Weight Reduction Materials FY 2004 Progress Report 

103 

Figure 1. Tensile specimens used for fatigue life 

testing of FSP aluminum castings. 

Tables 1 and 2 show fatigue life testing results 

for A356 and A319 cast alloys, respectively. It is 

evident that the FSP material showed drastic improvement in fatigue life, compared with the as-cast 

material, for both cast alloys. The increase in fatigue 

life can be attributed to the substantial strength and 

ductility improvements and the elimination of solidification shrinkage porosity (crack initiation sites) 

associated with the thermo-mechanical processing of 

cast microstructures during FSP. 

Table 1. Fatigue testing results for A356 cast aluminum alloy

Condition Applied 

strain 

Stress amplitude, 

ksi @ 1⁄2 life 

Neuber 

stress range 

ksi @ 1⁄2 life 

Life, # of 

reversals 

As-cast 2.0x10-3 15.5 39.0 7,700 

FS processed 2.0x10-3 19.4 43.9 93,848 

Table 2. Fatigue testing results for A319 cast aluminum alloy 

Condition Applied 

strain 

Stress amplitude, 

ksi @ 1⁄2 life 

Neuber 

stress range 

ksi @ 1⁄2 life 

Life, # of 

reversals 

As-cast 1.4x10-3 13.4 29.0 100,980 

FS processed 1.5x10-3 18.0 39.0 281,442 

The findings from this program show that FSP 

has potential as a very effective process to locally 

modify cast microstructures at critical locations to 

improve the overall durability of the component. 

This would open new opportunities to support wider 

use of aluminum castings in vehicles, which could 

directly impact weight reduction. We plan to conduct more comprehensive study on this subject in 

the future phases of this program. 

FSW of Cast Magesium Alloy

The use of magnesium has grown considerably 

in the past 10 years and continues to rise in the 

automotive industry. This increase is mainly attributed to the lightness of magnesium—it is one-third 

lighter than aluminum and four-fifths lighter than 

steel. Magnesium also has the highest strength-toweight ratio among the commonly used metals. 

Moreover, it has many other advantages, e.g., good 

castability, high die casting rates, electromagnetic 

interference shielding properties, parts consolidation, dimensional accuracy, and excellent machinability. With these characteristics, magnesium 

provides opportunities for the automotive industry, 

in which weight reduction, fuel economy, and environmental friendliness of vehicles are increasingly 

demanded. 

Despite its good castability, it is not always possible or economically viable to cast complex magnesium parts. Joining of the same or different types of 

magnesium alloys, as well as joining magnesium to 

other materials, is essential to enable the economical 

manufacturing of complex parts and structures. 

An increasing number of magnesium components for automotive applications are fabricated by 

high-pressure die-cast process. This type of magnesium casting has limited ductility, contains gas occlusions, and is generally difficult to weld 

satisfactorily by fusion welding techniques. 
FY 2004 Progress Report High Strength Weight Reduction Materials 

104 

In this part of the program, we conducted a 

study on FSW of AM60B, an Mg-Al-Mn cast alloy 

under development for automotive applications. The 

experiments were conducted in collaboration with 

the Research and Advanced Engineering Lab of 

Ford Motor Company. 

The AM60B cast plates were produced by the 

high-pressure die casting process. The nominal dimensions of the casting plate were 127 × 25.4 × 6 

mm. Two die-cast plates were FSW butt-welded 

along their long dimensions, as shown in Figure 2. 

In consideration of the typical automotive production environment, all welds were made without any 

special cleaning of the as-cast surface. In other 

words, the welds were made under the as-cast surface condition. In addition, no shielding gas was 

used during welding. 

Figure 2. A friction-stir butt weld between two 

casting plates (450 rpm). 

FSW was conducted using the FSW process development system acquired by ORNL with funding 

support from the HSWR Materials Program and 

other DOE programs. The machine is capable of 

simultaneous force-controlled or displacementcontrolled operation of three independent axes with 

adjustable, adaptable pin tools for on-the-fly mode 

switching between fixed, adjustable, and selfreacting welding modes. It also handles computercontrolled operation and key process parameter 

monitoring and is capable of making non-linear, 

variable-thickness, and double-curvature welds. 

The FSW tool was made of H13 tool steel. The 

shoulder diameter was 0.75 in. (19 mm), and the 

threaded pin was 0.25 in. (6.35 mm) in diameter. 

The length of the pin was 0.185 in. (4.7 mm), 

slightly shorter than the thickness of the plates. Two 

rotating speeds were used in this study, 375 and 

450 rpm. The linear welding speed was kept at 

152.4 mm/min. No elaborate attempt was conducted 

to optimize the process conditions in this phase of 

the study. 

The optical macroscopic photo in Figure 3 

shows the cross-section of the weld joint. The gas 

pores were clearly visible in the base metal as a result of the high gas content in the high-pressure die 

casting process. In the stir zone, the pores were significantly reduced on one side of the weld but still 

visible in the other side, which is characteristic of all 

the welds examined in this study. 

Figure 3. Transverse section of a friction stir weld 

of AM60B. 

To determine the strength of the welded joint, 

tensile testing samples were machined out from the 

middle of the specimen, as shown in Figure 4, and 

prepared in accordance with ASTM B557 specifications. Tensile properties of the base metal were also 

determined for comparison. 

Figure 4. Longitudinal tensile sample per ASTM 

B557 sub-size specimen. 

The tensile testing results are presented in 

Figure 5 and 6. The weld made under the low-rpm 

condition (M1) maintains the ultimate strength of 

the base metal but doubles the ductility. The highrpm condition (M2) slightly lowers the weld tensile 

strength but still offers significant improvement in 

ductility. 
High Strength Weight Reduction Materials FY 2004 Progress Report 

105 

Figure 5. Longitudinal tensile strength of FSW alloy 

AM60B. 

Figure 6. Longitudinal ductility of FSW alloy 

AM60B. 

FSW of High-Temperature Materials

In 2003, tool material design activities at ORNL 

led to the development of two new alloys for use as 

tool materials for FSW/P of high-temperature materials. In 2004, we conducted initial welding trials 

using the new tool materials developed by ORNL. 

Welds were successfully made for the following alloys: mild steel, stainless steel 304, CP Ti, and Ti6Al-4V. 

Initial testing showed that the ORNL tool materials exhibit minimal tool wear and deformation. The 

tungsten-based tool material has excellent toughness 

over the temperature range from the ambient to at 

least 1500°C. The tool material was very forgiving 

of unexpected sudden temperature and load changes 

during the welding trials, which would have led to 

premature failure of other tool materials under similar situations. Additional evaluations of the performance of the tool material, as well as the 

microstructure and properties of the friction stir 

welds of high-temperature materials, are currently 

under way. 

Figure 7 shows the tungsten-based and irridiumbased tool materials developed at ORNL. Figure 8 

shows the process in action in welding stainless steel 

304. Figure 9 shows two examples of hightemperature friction stir welds made with ORNL’s 

tungsten-based tool material. 

Figure 7. Two development-grade FSW tool 

materials developed at ORNL. 

Figure 8. FSW of stainless steel. 

Figure 9. Sample welds made with ONRL tool material. Above: stainless steel 304, below: Ti-6Al-4V. 

Plate thickness: 0.25 in. (6.35 mm). 

FSW of Aluminum Alloys

FSSW, or spot friction welding, is a new welding process invented by Mazda in 1993. It has been 

a subject of great interest for the U.S. automotive 

industry because of its process simplicity, low capital investment cost, and significant energy savings 

(up to 99% in the case of aluminum welding), compared with conventional resistance spot welding. 
FY 2004 Progress Report High Strength Weight Reduction Materials 

106 

We are collaborating with Ford to further advance 

the technology for the U.S. automotive industry. 

FSSW creates a spot lap-weld without bulk 

melting. The principles of the process are schematically illustrated in Figure 10. Similar to linear FSW, 

FSSW uses a cylindrical tool with a co-axial protruded pin. The welding cycle begins when the pin 

plunges into the upper sheet of the lap joint. The 

plunge load is supported from the bottom side with a 

backing plate or anvil to sustain the plunging load. 

The heat generated by the rotating pin softens the 

material and facilitates the penetration of the pin. 

Much more heat is generated to further soften a large 

region of the material underneath the tool shoulder 

after the tool shoulder contacts the top surface of the 

upper sheet. The softened material is pushed and 

stirred to form the metallurgical bond around the 

rotating pin. The forge pressure from the tool shoulder also keeps the interface between the two workpieces in intimate contact to facilitate the bonding. 

The tool is retracted at the end, leaving the characteristic hole in the middle of the weld. 

Figure 10. Principles of FSSW with fixed pin. 

Currently, FSSW is load controlled. This study 

was to develop a displacement-controlled operation 

mode that is more suitable for a high-volume production environment. 

Figure 11 illustrates schematically the basic operation of a displacement-controlled FSSW process. 

After the tool starts rotating, it is driven into the 

sample at a controlled plunging rate to reach a predetermined depth. The process then stops and the 

tool retracts. The normal force, recorded as an output, increases to a relatively low plateau when the 

pin initially plunges into the material. It then increases to a higher value when the shoulder of the 

tool touches the sample. 

Figure 11. Schematic diagram of a displacement controlled FSSW operation. 

The experiments were carried out on ORNL’s 

FSW process development system. Specimens of 

aluminum alloy 6111-T4, 25.4 mm in width, 101.6 

mm in length, and 0.94 mm in thickness were used. 

The standard overlapping distance of 25.4 mm was 

adopted. The weld was made at the center of the 

overlapping region. The spot weld was made at 2000 

rpm. The tool plunging displacement was set at between 1.6 and 1.9 mm. 

Figure 12 shows the lap shear tensile results of 

samples made between 1.6 and 1.9 mm in depth. 

Each data point represents an average of at least 

three samples. Initially the joint strength increased 

with the plunge depth. It reached a maximum value 

and then dropped off as plunge depths were further 

increased. The maximum lap-shear strength exceeded 3 KN at about 1.8 mm plunge depth. It is 

important to note that the tensile strength obtained in 

our study generally exceeded these reported with the 

load controlled operation. 
High Strength Weight Reduction Materials FY 2004 Progress Report 

107 

Figure 12. Lap-shear strength of spot friction welded 

6111-T4 samples at different insertion depths by displacement control welding. 

Figure 13 shows a micrograph of the crosssection of a sample with a plunge depth of 1.7 mm. 

Figure 14 (a) and (b) show the microstructures in the 

parent material region and stirred zone, respectively. 

The refinement of grain size in the stirred zone is 

obvious: it is about 3–5 times smaller compared with 

the grains in the parent material. 

Modeling of FSW

As with many other welding processes, residual 

stresses are expected in a friction stir weld. The 

welding thermal cycle also introduces microstructural changes in the weld region of many highperformance engineering materials. The resultant 

property and residual stress fields in a friction stir 

weld joint often govern the mechanical strength of 

the welded structures. For automobile structures, this 

affects both the durability of the vehicle in service 

and the formability of the welded part during postwelding forming and stamping operations. 

An integrated thermal-mechanical-metallurgical 

model was used to study the residual stress field and 

the spatial property gradient in an Al6061-T6 friction stir weld. The simulations were conducted using 

a 3-dimensional model, accounting for the frictional 

heating, aging, and dissolution processes 

Figure 14. Micrograph of the base metal 

(top) and stir zone (bottom) of SFW 6111-

T4. 

of the precipitates and the mechanical contact of the 

moving tool. 

Temperature-dependent material properties were 

used in the simulation. In addition, the residual 

stress fields were measured using the neutron diffraction mapping technique to validate the model 

predictions. 

The integrated model enables high-fidelity simulations of the thermal, mechanical, and metallurgical 

changes during the FSW process and the resulting 

microstructure, property, and residual stress inhomogeneity in the weld region. This type of model 

would make it possible to effectively interrogate the 

influence of various aspects of the process (process 

parameters, material, and geometry) on the performance of a friction stir weld under different postwelding fabrication conditions (such as stamping 

and forming) and in-service loading conditions. As 

an example, Figure 15 shows simulation results for 

temperature, hardness, and residual stress fields in 

the weld, and their combined effects on the deformation and failure behavior of an aluminum alloy 

Al6061-T6 friction stir weld in the tensile test. 

For the friction stir welds investigated, it was 

found that the residual stress distribution is strongly 

Figure 13. Macro cross-section of a spot friction stir 

weld of Al611-T6. 
FY 2004 Progress Report High Strength Weight Reduction Materials 

108 

Figure 15. Integrated thermal-mechanicalmetallurgical friction stir welding simulations provide 

insights into the performance of welded structures. 

dependent on the welding process parameters and 

the degree of material softening during welding. The 

failure of a friction stir weld under tensile load is 

controlled by a combination of material softening 

and the high residual stresses in the heat-affected 

zone. 

Conclusions

This program has made considerable progress in 

FY 2004 in advancing the FSW/P technology: FSP 

of cast aluminum alloys resulted in drastic microstructure and property improvement. A cast magnesium alloy was friction stir welded. FSW of hightemperature materials was explored, as well as 

FSSW of aluminum alloy. Integrated modeling was 

used to study the property and residual stresses and 

their effects on the performance of aluminum weld 

structures. 

Publications

N. Li, T-Y Pan, R. P. Cooper, D. Q. Houston, Z. 

Feng, and M. L. Santella, “Friction Stir Welding of 

Magnesium Am60 Alloy,” pp. 19–23 in Magnesium 

Technology 2004, 2004 TMS Annual Meeting, TMS, 

Charlotte, NC, 2004. 

Z. Feng, X-L Wang, S. A. David, and P. Sklad, 

“Modeling of Residual Stresses and Property Distributions in Friction Stir Welds of Aluminum Alloy 

6061-T6,” in 5th International Symposium on Friction Stir Welding, Metz, France, 2004. 

T-Y Pan, A. Joaquin, D. E. Wilkosz, 

L. Reatherford, J. M. Nicholson, Z. Feng, and M. L. 

Santella, “Spot Friction Welding for Sheet Aluminum Joining,” in 5th International Symposium on 

Friction Stir Welding, Metz, France, 2004. 
High Strength Weight Reduction Materials FY 2004 Progress Report 

H. Basic Studies of Ultrasonic Welding for Advanced Transportation Systems 

Principal Investigator: Zhili Feng 

Oak Ridge National Laboratory 

1 Bethel Valley Road, Oak Ridge, TN 37831 

(865) 576-3797; fax: (865) 574-4928; e-mail: fengz@ornl.gov 

Technology Development Area Specialist: Sidney Diamond 

(202) 586-8032; fax :(202) 586-1600; e-mail: sid.diamond@ee.doe.gov 

Field Technical Manager: Philip S. Sklad 

(865) 574-5069; fax: (865) 576-4963; e-mail: skladps@ornl.gov 

Participants: 

Michael L. Santella, Oak Ridge National Laboratory

Edward A. Kenik, Oak Ridge National Laboratory 

Xiaoguang Zhang, Oak Ridge National Laboratory

Hsin Wang, Oak Ridge National Laboratory

Keyu Li, Oakland University

Contractor: Oak Ridge National Laboratory

Contract No.: DE-AC05-00OR22725

Objective 

• Develop a fundamental understanding of the ultrasonic welding (UW) process. 

• Establish process conditions to optimize joint properties of aluminum alloys for auto body applications. 

• Explore opportunities for joining dissimilar materials. 

• Explore the feasibility of ultrasonic processing in other novel and unique situations in materials processing, 

such as making powders more dense, producing functionally graded components, modifying surface properties, 

and producing dissimilar material joints. 

Approach 

• Perform UW experiments to develop correlations of process parameters with joint properties. 

• Characterize details of joint microstructures. 

• Model the fundamental interactions of ultrasonic waves with solids. 

Accomplishments 

• Related the microscopic features at the interface region to process conditions. 

• Initiated a study toward the geometric effects on ultrasonic energy generation and dissipation during the welding process. 

• Completed a preliminary study of acoustic energy distribution by means of infrared thermography. 

• Initiated an experimental study of residual stress distribution in the bonding region. 

109 
FY 2003 Progress Report High Strength Weight Reduction Materials 

Future Direction 

• Continue welding process development for dissimilar materials, including joining of amorphous metals. 

• Study the structure-property relationship of joints. 

• Model the acoustic energy distribution in the weld joint. 

• Study the residual stress distribution in the bonding region. 

• Assess the ability of ultrasonic processing to enhance the densification of powder metal compacts. 

Introduction

UW uses high frequency mechanical vibrations 

to produce a solid-state metallurgical bond (weld) 

between metals. The basic process setup is illustrated in Figure 1 for a typical spot weld configuration. An electro-mechanical converter converts highfrequency electric current to mechanical vibrations. 

The mechanical vibration is then modulated and amplified by the booster/horn before it is applied to the 

overlapping workpiece through the sonotrode. A 

moderate clamping force is applied to ensure the 

mechanical vibration is transferred to the sheet-tosheet interface (the faying surface) where the weld is 

created. Typically, the mechanical vibration is at 

20–40 kHz with an amplitude range of 5–50 μm. 

The power delivered to the workpiece is in the range 

of several hundred to several thousand watts. 

Figure 1. Schematic setup of ultrasonic welding process. 

The principles for the formation of the metallurgical bond are illustrated in Figure 2. The combination of clamp pressure and mechanical vibration produces several important effects in the formation of 

the metallurgical bond at the workpiece interface. 

The lateral mechanical vibration of the sonotrode 

causes a small amount of relative motion at the interface between the two workpieces. The frictional action at the interface due to the relative motion and 

the pressure breaks the surface oxides and other contaminants. As a result, clean metal surfaces are 

brought into contact under pressure. Frictional heating also occurs at the bond interface. The heating 

promotes both localized deformation and diffusion 

in the region where the pressure is applied. When 

the process conditions are right, metallurgical bonds 

can be obtained without melting at the bonding interface. The self-cleaning nature of UW and its ability to form metallurgical bonds without melting are 

both important advantages of the process. 

Figure 2. Schematic representation of bond interface before (left) and after (right) UW. 

UW creates a joint without bulk melting. Thus 

the ultrasonic weld is inherently immune to welding 

defects associated with the solidification process in 

fusion welding. These include solidification cracking and porosity due to absorption of gaseous impurities (N, H, O) by the liquid metal that are common 

in electrical resistance spot welding (RSW) (the 

most widely used joining process in auto body assembly) of many classes of materials used in auto110 
High Strength Weight Reduction Materials FY 2004 Progress Report 

motive body structures. Also, unlike the copperbased electrode used in RSW, the sonotrode in UW 

can be made of high-strength materials that are inert 

to chemical attack from the material to be welded. 

Therefore, UW offers several significant potential 

advantages in joining aluminum alloys and other 

high-performance lightweight materials for auto 

body structures. 

This program started in FY 2003. The FY 2003 

study demonstrated the feasibility of UW of aluminum alloys, magnesium alloys, and steel to themselves, and the feasibility of joining dissimilar metals (aluminum alloy to steel). The FY 2004 efforts 

included microstructural characterization at the 

bonding interface, study of ultrasonic energy distribution in the weldment, and exploratory investigation of welding residual stresses. We also initiated 

the development of theoretical models that would 

eventually allow for interrogation of geometry effects on the distribution of acoustic energy, an important issue for application of the UW process. The 

variation of weld strength as a function of time was 

also observed. 

Welding

All welding trials were conducted on a Sonobond ultrasonic welder. The machine operated at 

20 kHz and had a maximum rated power output of 

2500 W. 

All welds were made using 25-mm-wide and 

100-mm-long specimens. This is a standard coupon 

dimension commonly used by the auto industry for 

weldability testing of resistance spot welds. All 

specimens had a nominal thickness of 1 mm. For 

bonding interface microstructural characterization, a 

standard 1-in overlapping configuration shown in 

Figure 3 was used. The weld was made at the center 

Figure 3. Weld coupon dimensions used in the study. 

of the overlapping region. For study of the geometry 

effects, the amount of overlap and the location of the 

weld were systematically varied. 

Microstructure Characterization

Because of the solid-state nature and minimal 

thermomechanical excursion of the ultrasonic bonding process, the bonding interface between the same 

metal (for example, Al6061 to Al6061) was difficult 

to observe experimentally. To aid the bonding interface study, a series of dissimilar welds between two 

different aluminum alloys (Al6061-T4 and Al2024-

T3) were used. These two aluminum alloys have 

very different etching responses to Keller’s reagent. 

This allowed for selective etching to reveal the interface region of the weld. 

The nominal mechanical properties of the two 

aluminum alloys are summarized in Table 1. As 

shown in the table, Al6061 is always softer and has 

better ductility than Al2024 over the entire temperature range. The differences in the mechanical properties of the two alloys are considerable at the ambient temperature, but they diminish as the temperature increases. At 370°C, the tensile strength and 

ductility of the two alloys are very close to each 

other. The differences in mechanical properties are 

considered to be an important factor affecting the 

interfacial deformation and bonding behavior during 

welding. 

Table 1. Mechanical properties of Al6061-T4 and Al2024-T3 at selected temperatures 

(Source: Properties of Aluminum Alloys, AMS International, 1999) 

25EC 260EC 370EC 

Yield 

(MPa) 

Tensile 

(MPa) 

Elon

g 

(%) 

Yield 

(MPa) 

Tensile 

(MPa) 

Elon

g 

(%) 

Yield 

(MPa) 

Tensile 

(MPa) 

Elong 

(%) 

6061-T4 145 241 25 165 172 17 55 59 35 

2024-T3 345 483 17 241 269 17 69 76 35 

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FY 2003 Progress Report High Strength Weight Reduction Materials 

We have discussed some of the general microstructural characteristics in the bonding interface 

region as a function of welding process parameters 

in the FY 2003 annual report. Additional observations are reported here. All the cross-sectional photos were taken along the plane cut through weld center, as depicted by the dashed line in Figure 3. 

Figure 4 shows the bonding interface at two different energy levels. The pictures were taken near 

the center of the weld (labeled A in Figure 5). At 

low energy levels, the bonding interface is quite flat 

microscopically. The interface becomes wavy, and 

considerable microscopic swirling deformation is 

evident at high energy levels. The microscopic 

swirling deformation is confined primarily on the 

softer Al6061 material side. 

Figure 4. Changes in bonding interface flatness as a function of UW energy level. Top: 750J; bottom: 950J. Other 

process conditions: 2400 W and 70 psi. Al2024 is the 

upper sheet. 

Figure 5. Macro view of the weld cross-section. The observation positions in Figure 4 and Figure 6 are labeled A 

and B, respectively. Point A is near the center of the 

weld; Point B is at the edge of the bonded region. 

Figure 6 shows the deformation near the periphery (region B in Figure 5) of the bonded interface in 

the low-energy-level case (750J). It was taken from 

the same 750J weld as the top photo of Figure 4. It 

suggested that, even though the interface was relatively flat when the energy level was low, the microscopic deformation was still extremely large and 

mainly confined on the softer Al6061 side. 

Figure 6. Local deformation of Al6061 at the periphery of the bonding interface. The photo was taken at 

position B of Figure 5. Arrow B points to the region 

where “coating” is formed. Energy level: 750 J. 

These observations suggest that there is considerable shearing deformation at the interface, under 

the lateral rubbing motion of the sonotrode, under all 

energy levels studied in this program. On the other 

hand, the material deformation or motion vertical to 

the interface is secondary to the bonding process and 

only becomes noticeable when the ultrasonic energy 

level is high. 

Another intriguing observation is the “coating” 

phenomenon at the interface. As pointed to by arrow 

B in Figure 6, a thin layer of Al6061 is “coated” and 

bonded onto the Al2024 side, while this thin layer is 

112 
High Strength Weight Reduction Materials FY 2004 Progress Report 

still disconnected with the bulk of the Al6061 material. This phenomenon is more evident in Figure 7, 

where only intermittent, partial bonding is achieved 

at the interface at a very low energy level (550J). 

Figure 7. Coating of Al6061 to Al2024 at a low energy 

level (550 J) that could form only partial bonding. 

Although the causes for formation of the coating 

layer are not clear at this time, the fact that it forms 

in the early stage of the bonding process would be 

an important aspect of the bonding process during 

UW. 

At higher energy levels, the bonding interface 

becomes wavy and is generally considered to be 

beneficial to the joint strength of the ultrasonic 

welds. However, excessive energy could cause 

cracking of the material, as shown in Figure 8. For 

the Al6061-to-Al2024 welds, the cracking always 

occurs on the Al2024 side, more or less parallel to 

the bonding interface at a distance about 50 to 

100 um from the interface. One possible cause 

would be related to the lower ductility of Al2024 

between the room-to-intermediate-temperature range 

as shown in Table 1. 

Geometric Effects on the Ultrasonic Bonding 

Process

We observed strong geometric dependence of 

the process: the weld quality, energy input, and energy distribution are all strongly dependent on the 

geometric arrangements of the test. Such dependency needs to be thoroughly understood because of 

Figure 8. Cracking at Al2024 side of bonding interface 

due to excessive energy input. 

its important implications in the industrial applications of the process. 

Effects of vibration direction relative to weld 

coupon orientation. Figure 9 compares two welds 

made when the direction of the applied lateral mechanical vibration from the sonotrode was changed 

relative to the specimen orientation. The direction of 

vibration is depicted by the arrow next to the weld in 

the figure. All other welding conditions were identical when these two welds were made. When the vibration was in the width direction of the specimen, 

two cracks formed at the edge of the specimen, as 

shown in the lower part of Figure 9. Such cracking 

was absent when the vibration was applied along the 

length direction of the specimen. This suggests that 

the acoustic energy distribution in the weld coupon 

(or welded structure) is strongly dependent on the 

vibration direction relative to the geometric orientation of the part. 

It is also important to note that, although the two 

cracks are relatively symmetric to the weld, they are 

not connected to the weld. This indicates that the 

cracks are not originated by the directly applied vibration of the sonotrode. Rather, there must be high 

energy concentration points (hot spots) near the edge 

of the plate, caused by the complex interaction of the 

propagating acoustic wave from the excitation 

source and the reflected wave from the free boundaries of the specimen. 

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FY 2003 Progress Report High Strength Weight Reduction Materials 

Figure 9. Effect of vibration direction for Al5754. 750 J, 

2400 W, 70 psi. Top: vibration parallel to specimen 

length. Bottom: vibration parallel to specimen width. 

Clearly, proper control and elimination of undesired hot spots would be a critical issue for the application of UW. 

Interactions of multiple welds. Auto body 

structures generally require multiple spot welds to 

connect two structural members. On average, about 

3000 to 5000 spot welds are used in assembling a 

passenger vehicle. In this study, the three-weld test 

arrangement commonly used in RSW was used to 

investigate the interactions between the adjacent ultrasonic welds, and the results are intriguing. 

Figure 10 shows the three-weld arrangement 

used in the study. The two 25 × 100 mm Al5754 

coupons were overlapped by approximately 75 mm 

in the length direction. The three welds were made 

one after another, following the sequence labeled in 

the figure. The first weld was placed at the center of 

the 75-mm overlap (i.e., 37.5 mm from the edge of 

the plate). The second and third weld were made 

respectively to the left and the right of the first weld, 

at a nominal distance of 20 mm from the first weld. 

The welds were produced with identical settings: 

2400 W, 70 psi, and 0.35 s. The vibration from the 

sonotrode was along the width direction of the 

specimen as illustrated in the figure. 

Figure 10. Interactions of multiple welds on the energy 

input level. All three welds were made with the same 

welding parameters: 2400 W, 70 psi, and a welding time 

set at 0.35 s. Weld ID = 4. Material: Al5754. 

The energy output as recorded by the ultrasonic 

machine was drastically different. The system delivered 813 J of energy when making the first weld, 

quite close to the theoretical value of 840 J (100% 

energy efficiency) under perfect acoustic impedance 

matching. However, because of the constraint 

changes induced by the first weld (as well as the 

location effect of the second weld), the energy output when making the second weld was only 230 J, 

less than 1/3 of the energy output in making the first 

weld. In this particular case, metallurgical bonding 

was not achieved in the second weld because of the 

inadequate energy input. The energy output in making third weld was 689 J. Note again the cracks near 

the third weld that were produced in making the 

third weld. 

The multiple-weld study clearly shows that the 

acoustic impedance of the UW system can be greatly 

affected by prior welds made during the assembly 

process. This would have profound influence on the 

energy output level and could cause considerable 

weld-to-weld quality variations. 

Infrared Thermography Study of the UW 

Process

The welding trials clearly show that the distribution of the acoustic energy in a UW workpiece is 

very complicated and has a profound influence on 

the weld quality. To further understand this matter, a 

study was initiated in FY 2004 in which real-time 

infrared (IR) thermography was used to capture the 

temperature changes during the UW process. Both 

the spatial distribution and the temporal variation of 

the temperature field were used to infer how the heat 

(the dissipative part of the acoustic energy) is generated and distributed during UW. 

114 
High Strength Weight Reduction Materials FY 2004 Progress Report 

The real-time IR measurements were conducted 

using a high-speed, high-sensitivity (0.015 K) and 

high-spatial-resolution (5 μm/pixel) IR camera. In 

the first test, the energy distribution across the 

workpiece thickness was captured with a special 

experimental set-up, as shown in Figure 11. The 

welds were made at the edge of the two workpieces, 

and the sonotrode vibration was parallel to the long 

side of the specimen. This special experimental 

setup preserved the process symmetry in an actual 

welding situation, while allowing the weld crosssection to be exposed to the IR camera during welding. 

Figure 11. Experimental setup for observing the heat 

distribution across the weld cross-section. 

Figure 12 shows the progression of the heat 

generation and distribution during welding. The 

three snap thermal image shots were taken, respectively, at the beginning, middle, and end of the welding cycle. The interfaces and the sonotrode are highlighted to provide the spatial reference frame. It is 

clear from these images that the heating is predominately generated at the interface and diffused into 

the workpiece and the sonotrode. 

IR thermography was also used to study the 

formation of cracks caused by the complex acoustic 

wave distribution in the workpiece. The results are 

presented in Figure 13. There are two hot spots at 

the edge of the specimen that were not connected to 

the main hot spot underneath the sonotrode. This 

suggests that high level of acoustic energy is concentrated at these locations and causes noticeable 

heating and cracking at these hot spots. 

Figure 12. Snapshots of thermal images captured by 

IR camera at three progressive time instances. 

Figure 13. Top: IR thermal image of the “hot” spot. 

Bottom: the corresponding cracked weld sample. 

115 
FY 2003 Progress Report High Strength Weight Reduction Materials 

Figure 14 presents a thermal image of a threeweld sample when the third weld was being made. 

The weld arrangement and the welding sequence are 

the same as for the weld sample shown in Figure 10. 

The concentration of the acoustic energy at the second weld is clearly observed. On the other hand, 

there is no noticeable heat generation at the first 

weld, although the first weld is closer to the source 

of vibration. Also, edge hot spots are evident near 

the third weld where cracking had been observed. 

Figure 14. IR Thermal image of multiple spot welds. 

The third weld is being made. 

The initial IR experiment conducted in FY 2004 

clearly showed the potential of IR thermography as a 

tool to study the fundamentals of the UW process. 

More detailed IR experiments are planned in 

FY 2005. 

Residual Stress Measurement

As in the case of many other welding processes, 

residual stresses are expected in an ultrasonic weld. 

High residual stress levels in the bonded region 

could affect the long-term stability of weld properties in aluminum welds. 

Because the bonded region in a spot weld is located between two thin workpieces, measurement of 

the residual stress in the bonded region is difficult 

for many measurement techniques such as X-ray 

diffraction and neutron diffraction. 

In this study, the interferometric strain/slope rosette (ISSR) measurement technique, developed by 

Li and colleagues of Oakland University, was used 

as an exploratory attempt to investigate the residual 

stress in a UW weld. The unique features of the 

ISSR technique include relatively small gauge size, 

high precision, and the ability to determine the stress 

gradient through the workpiece thickness. 

The measurement was taken at the center region 

of the spot weld of Al6061-T6 alloy. The residual 

stress distributions as a function of the depth from 

the back side of the weld sample are plotted in 

Figure 15. σxx and σyy are the two normal stress 

Figure 15. Residual stress as a function of the depth from 

the back side of an Al6061-T6 weld sample. 

components along the length and width of the 

specimen, respectively, and τxy is the shear stress 

component. 

The ISSR measurement shows that there are 

considerable tensile residual stresses in the center 

region of the ultrasonic weld. The maximum is at the 

surface of the specimen and reached the yield 

strength of the material (Table 1). Additional residual stress measurements are planned in FY 2005 to 

study the effect of welding process conditions on the 

residual stress. 

Conclusions

The research efforts during FY 2004 have resulted in considerable progress toward the understanding of UW process fundamentals. The bonding 

interface study on dissimilar aluminum alloy welds 

revealed several important aspects of the interface 

deformation and bonding process. The profound 

geometric effects on the acoustic energy propagation 

and dissipation and the resultant weld properties 

were identified and characterized. 

116 
High Strength Weight Reduction Materials FY 2004 Progress Report 

117 

Publications

W. Ren, K. Li, and Z. Feng, “Ultrasonic Welding Stress Distribution Measured with Optical Rosette/Ring-Core Method,” SAE 2005 Congress, 

SAE-International, Technical Paper No 2005-01-

1035, 2005. 
FY 2003 Progress Report High Strength Weight Reduction Materials 

118 
High Strength Weight Reduction Materials FY 2004 Annual Progress Report 

119 

I. Attachment Techniques for Heavy Truck Composite Chassis Members

Principal Investigator: Lynn B. Klett 

Oak Ridge National Laboratory 

P.O. Box 2008, Oak Ridge, TN 37831-6053 

(865) 241-8112; fax: (865) 574-8257; e-mail: klettlb@ornl.gov 

Principal Investigator: Darrell R. Herling 

Pacific Northwest National Laboratory 

P.O. Box 999, Richland, WA 99352-0999 

(509) 375-6905; fax: (509) 375-4448; e-mail: darrell.herling@pnl.gov 

 

Technology Development Manager: Sidney Diamond 

(202) 586-8032; fax: (202) 586-1600; e-mail: sid.diamond@ee.doe.gov 

Field Technical Manager: Philip S. Sklad 

(865) 574-5069; fax: (865) 576-4963; e-mail: skladps@ornl.gov 

Contractors: Oak Ridge National Laboratory, Pacific Northwest National Laboratory

Contract Nos.: DE-AC05-00OR22725, DE-AC06-76RL01830

Objectives 

• Overcome the technical issues associated with joining composite materials in heavy vehicles by developing 

technically robust and economically attractive joining techniques. 

• Develop and validate one or more joint designs for a composite structural member attached to a metal member 

that satisfy the truck chassis structural requirements both economically and reliably. 

• Solicit input from truck original equipment manufacturers (OEMs) and suppliers on the technical hurdles and 

needs associated with joining structural composite members in heavy vehicles. Use this information to guide 

the joint design and development activities. 

• Publish information on the design, modeling, and testing methodologies that are developed to support the incorporation of composite materials into other chassis components. 

Approach 

• Collaborate with Delphi and its OEM partners to identify and address technical needs related to the manufacturing, joining, and implementation of a composite chassis component. 

• Design attachment components and configurations in close coordination with the composite structural component development. 

• Use modeling techniques to predict the performance of various joint designs, taking into account damage 

mechanisms and fatigue/life requirements. 

• Characterize various composite materials and mechanical joint configurations through mechanical testing, considering variables such as hole size, hole fabrication method, bolt pre-load, inserts, combined loading, vibration, fatigue, and durability. 

• Validate joint design for the composite structural member through track testing. 
FY 2004 Semi-Annual Progress Report High Strength Weight Reduction Materials 

120 

Accomplishments 

• Conducted static and fatigue tests on a commercially available, component-independent, pultruded fiberglass 

composite material. 

• Investigated several hole fabrication techniques, including water jet cutting, laser cutting, punching, drilling 

with a standard drill bit and Forstner bit, and drilling undersized holes and then reaming. 

• Ran static and fatigue tests of composite specimens with holes fabricated by various methods to identify the 

method preferred for the least damage in the composite at an acceptable cost and complexity. 

• Identified thermography as a reliable nondestructive technique for evaluating damage due to hole fabrication. 

• Ran static and fatigue tests on Extren®/steel joints and baseline steel/steel joints (lap shear and cross tension). 

• Conducted finite element analysis (FEA) modeling to optimize the geometry of a metallic insert for an allcarbon-composite component to address the bolt loosening due to creep in the composite member. 

• Presented two papers at the 2004 SPE Automotive Composites Conference and Exposition in Detroit. 

Future Direction 

• Conduct bolt bearing and fatigue tests to investigate design modifications, such as inserts, molded-in holes, and 

3-dimensional (3D) reinforcement to minimize the damage in the composite and improve the fatigue life of a 

composite-to-steel joint. 

• Evaluate the impact of using adhesive bonding in place of and in combination with bolting, as well as the effects of environmental exposure and testing rate for the composite/steel Mode I and Mode II fatigue specimens. 

• Use FEA modeling with input from the composite and joint tests to optimize and predict the performance of the 

composite/steel joint. 

• Continue to work closely with the industrial team to develop the composite component and composite-to-steel 

joint design solutions to meet the demanding requirements of the heavy vehicle chassis environment. 

Introduction 

In May 2003, researchers at Oak Ridge National 

Laboratory (ORNL) and Pacific Northwest National 

Laboratory (PNNL) began collaboration on a 4-year 

research effort focused on developing technically 

robust and economically attractive joining techniques to overcome the technical issues associated 

with joining lightweight materials in heavy vehicles. 

This work is being performed concurrently with an 

industry program led by Delphi to develop and 

commercialize composite chassis components, 

which will require resolution of the joining challenges. The industry project serves as a “focal project” that provides real load and service data to this 

project and will potentially field-test and implement 

the technology developed in this project. The initial 

focus of research is development and validation of 

one or more joint designs for a composite structural 

member attached to a metal member that satisfy 

truck chassis structural requirements both economically and reliably. Broadening the effort to include 

other structural joints, including composite-tocomposite joints, is anticipated. Durability track testing of the first prototype composite component and 

joint is planned for the last half of 2005. 

Component-Independent Material Evaluation

To gain an understanding of the performance of 

composite materials in a heavy vehicle structural 

chassis application, a commercially available pultruded fiberglass composite—Extren®, manufactured by Strongwell—was chosen for initial 

component-independent study. The pultruded composite consists of a continuous-strand mat with unidirectional rovings in the axial direction and a 

surface veil for corrosion and ultraviolet protection. 

The results will serve as a baseline for further testing 

of composites with 3D reinforcement and with lowcost, lightweight design modifications—such as 
High Strength/Weight Reduction Materials FY 2004 Semi-Annual Progress Report 

121 

modified washers, inserts, or adhesive bonding— to 

improve performance at the joint. 

Hole Fabrication Techniques

The initial joint design for a composite component-to-steel member will likely include mechanical 

fasteners requiring holes in the composite member. 

The use of bolts through holes in the composite is a 

concern, especially because of the severe loading 

conditions and the long service life resulting in high 

cycle fatigue. Several hole fabrication techniques 

have been evaluated, including drilling with a 

Forstner bit, drilling with a standard tapered bit, laser cutting, water jet cutting, and punching. For each 

method, 12.7-mm-diam holes were machined in the 

center of 76.2 × 254 × 3.2 mm Extren® coupons. 

Many of the water jet cut specimens had visible 

delaminations and cracks around the hole diameter. 

In some cases, the damage produced at the edge of 

the hole spread through the laminate thickness, 

puckering the coupon’s surface layers around the 

hole at the back of the laminate during machining. 

Additionally, the cut was jagged instead of smooth 

and circular. This amount of damage was quite unexpected because of the prior success with the fiberglass composite for straight cuts. Two water jet 

cutting facilities, including one with significant experience with composite materials, attempted to machine the holes. In both cases, some of the 

specimens looked fairly good, but many had large 

areas of damage. 

Although the laser-machined holes (conventional laser with 127–152 cm/min linear feed rate) 

had no visible damage, there was some residual carbon dust on the cut surfaces, as is normal in lasermachined polymers. 

Open-hole tensile, static, and fatigue tests have 

been conducted on the specimens with holes fabricated with different methods. The results shown in 

Figure 1 indicate that the specimens drilled with the 

carbide-tipped Forstner bit have the highest average 

tensile strength with the least scatter in the data. As 

anticipated, the water-jet–cut specimens did not perform well because of the large amount of damage in 

many of the specimens. The results of the fatigue 

tests with R = 0.1 and a frequency of 5 Hz (Figure 2) 

at 70%, 50%, and 30% of ultimate stress do 

Figure 1. Comparison of ultimate tensile strengths for 

specimens with holes fabricated with different methods 

and the material with no hole. 

Figure 2. Fatigue testing results for specimens with holes 

fabricated with different methods. 

not show a dramatic difference in fatigue performance between the specimens with different hole fabrication techniques. However, a difference will 

likely be detected at higher stress levels because of 

the variations in the static failure stresses. Additional 

tests are under way. 

Specimens with a preferred hole fabrication 

method will be tested in bolt bearing and fatigue to 

evaluate design modifications, such as bolt pre-load, 

inserts, molded-in holes, and 3D reinforcement of 

the composite. The goal will be to minimize the 

damage in the composite and improve the fatigue 

performance of the resulting composite/metal joint.

Methods for Damage Detection

Several methods have been investigated for 

evaluating the damage associated with hole fabrica-
FY 2004 Semi-Annual Progress Report High Strength/Weight Reduction Materials 

122 

tion in the Extren® composite material, including 

dye penetrant analysis and flash thermography. The 

flash thermography method has good correlation 

with the X-ray dye-penetrant results. 

Although the results from dye penetrant can be 

very good, the drawbacks include the time required 

for soaking, the contamination of the composite with 

the solution, and the requirement for an X-ray 

source. Additionally, for each material density and 

thickness, the time of exposure and power level must 

be optimized to get the desired results. 

The flash thermography method was used to 

evaluate several of the water-jet–cut coupons. Thermography is a nondestructive technique that involves applying a heating (or cooling) stimulus to 

the surface of a test piece and imaging its thermal 

response with an infrared (IR) camera. In flash 

thermography, the thermal stimulus is in the form of 

a short-duration flash uniformly applied to one side 

of the part. The IR camera records the surface temperature of the opposite side of the part as a function 

of time. If sufficient temperature contrast can be obtained, changes in through-the-thickness diffusivity 

of the material can be measured. 

Thermal diffusivity is the property governing 

the rate at which heat flows within a material; and 

any delaminations or cracks will affect the heat diffusion rate, thereby changing the surface thermal 

response. Therefore, by studying the time evolution 

of the surface temperature distribution, it is possible 

to obtain information on the depth, spatial extent, 

and thermal character of subsurface structures and 

defects. 

The IR camera used in this study was a Raytheon Radiance-HS IR camera with a 50-mm lens, 

which operates in the 3–5 μm spectral range. With 

this camera, data are recorded as full field-of-view at 

a rate of 142 images/second and with a time resolution of 0.007 s. The flash system used was an 

Acute2 (2400 W·s) xenon flash lamp. The thermal 

images after flash were recorded for both sides of 

the coupons.

One advantage of flash thermography is that it 

can provide an indication of depth below surface 

that X-ray and visual examination cannot. The depth 

limit of flash thermography with this particular setup 

appeared to be about one-half of coupon thickness 

(1.5 mm). Possibilities to further enhance the thermal images and depth resolution of the flash thermography technique include the step-heat and lockin techniques. 

Additionally, because this is a nondestructive 

and noninvasive technique, flash thermography can 

be used during fatigue testing to monitor damage 

development and propagation in the composite material. 

Extren® Static and Fatigue Testing

Baseline static and fatigue tensile testing was 

conducted for the pultruded fiberglass material. The 

fatigue tests were run with R = 0.1 at 70%, 50%, and 

30% of ultimate stress at a frequency of 5 Hz (Figure 3). Although there was a fairly high level of 

scatter among the tensile specimens, the fatigue behavior was fairly consistent. Several of the specimens at 30% of ultimate stress reached runout with 

more than 1,000,000 cycles. As expected, the ultimate stress levels are significantly higher for the 

specimens with the loading axis in line with the axial reinforcing fibers. 

Figure 3. Tensile fatigue behavior of Extren® fiberglass 

composite. 

To determine the feasibility of testing at a higher 

rate, the surface temperature of the composite 

specimens was monitored at both 5 and 20 Hz. 

Room temperature was approximately 23°C. At 70% 

of ultimate (between 300 and 1250 cycles to failure), 

the maximum temperature of the samples at 5 Hz 

was 27.5°, compared with 34.5°C for 20 Hz. This is 

the most severe loading case; but it has the shortest 

life, so the temperature does not reach equilibrium. 

For tests at 40% ultimate (40,000–45,000 cycles), 

the specimens at 5 Hz reached 27.6°, while the 

20-Hz specimens reached 34.1°C. These temperature 

measurements are for the surface; the material is 
High Strength/Weight Reduction Materials FY 2004 Semi-Annual Progress Report 

123 

probably reaching a higher heat internally. In order 

to keep within the ASTM-recommended 10° temperature rise for these tests, the tests should be run 

slower than 20 Hz. However, the results indicate that 

a frequency greater than 5 Hz could possibly be 

used. 

Bolt Torque and Pre-Load Investigation

A test methodology has been developed to study 

the effects of bolt torque levels on composite materials. Information derived from this work will ultimately be used to support the characterization of 

bolted composite assemblies tested as part of this 

program, as well as provide insight into the design 

and manufacture of a composite truck chassis. 

When a composite assembly is bolted together, 

the tightened bolts and other hardware (e.g., washers, nuts) apply an external compressive stress to the 

composite through the thickness. This bolt pre-load 

may be beneficial or detrimental to the composite, 

depending on the amount of applied pressure. Snug 

bolts can minimize slippage or movement of the bolt 

shank in the composite hole, thereby reducing the 

possibility of wear and abrasion at the edge of the 

hole. The additional compressive force may also 

help “clamp” the individual composite layers together, resisting delamination propagation when 

other external forces are applied to the assembly. 

Alternatively, too high a pre-load could cause the 

clamping force to exceed the transverse compressive 

strength of the composite, essentially crushing the 

material or forcing penetration of the bolt hardware 

into the composite surface. 

Figure 4 is a schematic of the basic test setup 

used to characterize the effects of bolt pre-load on 

test specimens. An Interface washer load cell, model 

LW2050, was positioned between the composite 

laminate backed by a hardened flat steel backing 

plate, and a second backing plate. Applying a torque 

to the bolt applies a compressive force to the assembly, which is in turn measured by the washer load 

cell. 

For a given material and thickness, the washer 

load cell setup has proved useful to study the effects 

of a number of factors on joint design, including (1) 

composite pre-load as a function of bolt torque, (2) 

the effects of multiple bolt tightening/loosening cycles, (3) specimen-to-specimen variability, (4) the 

Figure 4. Bolt pre-load test schematic. 

effects of re-tightening bolts, and (5) the loss of bolt 

pre-load with time. 

Hardened flat steel plates are required on both 

sides of the washer load cell to ensure that the load 

is aligned correctly on the load cell. The use of this 

stack-up in bolted assemblies for static and fatigue 

testing may be impractical. Strain-gaged bolt load 

cells are under evaluation for use as an alternative to 

the washer load cells to monitor the bolt load during 

mechanical testing. 

Figure 5 shows the loss of pre-load as a function 

of time for various test materials that have been 

bolted together with a 67.8 N-m (50 ft-lb) applied 

torque. The loss of pre-load with time is relatively 

low for a steel-to-steel bolted assembly and increases for the composite assemblies. The greatest 

loss of pre-load occurs with the thick composite substrate (6.35 mm). This likely results from the increase in the thickness of the glass fiber mat in the 

thicker composite. 

A significant part of the loss of pre-load for 

these samples occurs during the first 5 minutes after 

the bolt has been tightened. A very rapid decrease in 

pre-load occurs within the first 30 seconds after application of the torque. Initial test results suggest 

that retightening the bolts within a few minutes of 

the initial assembly may help reduce the bolt’s preload loss rate with time, and the overall loss of preload. 

To determine the effects of the level of bolt preloading on the mechanical properties of the composite materials, bearing tensile and fatigue tests will be 
FY 2004 Semi-Annual Progress Report High Strength/Weight Reduction Materials 

124 

Figure 5. Loss of pre-load for various bolted assemblies. 

conducted on the pultruded fiberglass composites. 

Varying levels of torque on the bolts, as well as 

Huck bolts, will be evaluated. It is anticipated that 

the Huck bolts will yield a more consistent pre-load 

level. 

Evaluation of 3D Reinforced Composite 

Static tensile and fatigue tests have been conducted on 3D glass-reinforced composites to determine the effects of the 3D reinforcement and to 

evaluate their feasibility for use in the structural 

chassis component. The initial composites tested had 

both high levels of voids and a clay filler material 

that contributed to a decrease in static strength and 

poor fatigue performance. Once the processing was 

improved to eliminate the clay filler and reduce the 

void content, the static tension and fatigue properties 

improved significantly. Several material systems are 

under evaluation, and the fatigue curve for one of 

the 3D glass-reinforced polymers is shown in Figure 

6. 

Additionally, hole fabrication techniques were 

compared for the 3D reinforced material to ensure 

that the results seen in the pultruded polymer composite (with significant chopped glass mat) would 

translate for a highly oriented composite. For the 

Extren® material, the water jet cut specimens 

showed the most damage. However, the delamination occurring in the 3D reinforced material was limited to the midplane of the composite and did not 

appear at the surface. Again, the specimens cut with 

the carbide-tipped Forstner bit had the least visible 

damage. 

Figure 6. Tensile fatigue behavior of 3D reinforced 

glass/polymer composite. 

Steel-to-Steel Joint Evaluation

To establish design targets of an existing chassis 

joint, 6.35-mm-thick grade 6 steel plates were joined 

by a Huck bolt to achieve two testing configurations 

commonly used in joint performance evaluations, 

lap shear and cross tension. This baseline will be 

used to design and optimize the composite/steel 

joint. Static and fatigue tests were conducted to 

characterize the performance of the joints. In the 

static tests, a bearing failure mode (composite material shear-out) was observed for the lap shear specimens, whereas bolt failure (stripping of the nut 

collar) occurred in the cross tension specimens. The 

failure load for the lap shear specimens were approximately 128 kN, while the cross tension specimens failed at approximately 175 kN. 

Cyclic fatigue tests were also performed on the 

joints under a tension–tension ratio of R = 0.1 for 

both lap shear and cross tension configurations. Figure 7 illustrates the fatigue strength of the lap shear 

and cross tension specimens for all completed tests. 

Unlike for the static tests, the fatigue failure for the 

cross tension fatigue tests initiated from the steel/ 

steel contact periphery on the faying interface where 

the structural stress is maximum. Additional tests are 

ongoing. 

Extren®/Steel Joint Evaluation

Preliminary composite/steel joints (both lap 

shear and cross tension coupons) were assembled 

and tested to understand the fatigue behavior and 

failure mechanisms associated with joining the fi- 
High Strength/Weight Reduction Materials FY 2004 Semi-Annual Progress Report 

125 

Figure 7. Fatigue test results of the lap shear and cross 

tension steel assemblies joined by a Huck bolt. 

berglass composite to steel with a bolt. Joints were 

assembled using 3.2-mm-thick composite with 

1.4-mm-thick 1008 steel. All composite/steel joints 

were joined with 6.35-mm grade 5 bolts, torqued to 

13.6 N-m (10 ft-lb). 

The following joining and testing parameters for 

joint strength are under investigation: 

• Effect of washer size 

• Effect of fatigue test frequency and temperature 

rise 

• Effect of structural adhesive 

• Effect of environmental exposure 

Washer Size Effects

Figure 8 illustrates the static strength comparison among lap shear samples with a nominal size 

washer (15.9 mm diam), an oversize washer 

(25.4 mm diam), and a steel plate washer (50 × 35 

× 6 mm). Under lap shear loading, the static strength 

increases approximately 10% with an oversize 

washer and approximately 20% with a plate, compared with the nominal washer. The samples with 

nominal and large washers show the typical characteristics of a bearing type of failure, but the samples 

with the constraining plate do not show a clear load 

drop prior to the peak strength. A similar cleavage 

tension failure mode was observed in all three 

washer types, and the damage initiated from the periphery of the bolt hole. 

Figure 9 illustrates the fatigue strength comparison of lap shear and cross tension samples with the 

Figure 8. Static strength comparison of washer size effect. 

Figure 9. Fatigue strength comparison of washer size 

effect. 

nominal and oversize washer. On average, joints 

with larger washers yield higher fatigue strength 

than joints with nominal washers. This effect is more 

prominent under lap shear loading than under cross 

tension loading conditions. Under fatigue loading, 

damage on the composite plates initiated right underneath the periphery of the washer for both loading cases. 

Frequency Effects

Fatigue tests are normally carried out at the 

highest frequency possible in order to minimize test 

duration. Typically, the maximum temperature rise 

allowed in the test material should be less than 10°C 

during fatigue testing. To study the effects of frequency on the composite/steel joint, lap shear fatigue tests were conducted at 5, 15, and 20 Hz with 

R = 0.1. The coupon temperature was monitored 

with thermocouples, and the maximum temperature 

rise for each frequency was recorded. At a frequency 
FY 2004 Semi-Annual Progress Report High Strength/Weight Reduction Materials 

126 

of 15 Hz, the maximum temperature rise was 5°C; at 

20 Hz it was 9°C, which is just below the threshold 

value. Because of the degree of scatter in the material properties of this material, no significant change 

in the fatigue life at each fatigue level was apparent. 

Based on these results, a maximum test frequency of 

15 Hz was chosen for the composite/steel joints to 

avoid inducing significant temperature changes in 

the sample during fatigue testing. 

2D vs 3D Polymer Composites

Lap shear coupons were assembled with a 3D 

reinforced glass composite to investigate the fatigue 

behavior and failure mechanisms associated with 

joining the composite to steel with a bolt. The joint 

static and fatigue performance was then compared 

with the performance of the pultruded composite/steel joints. 

The 2.54-mm-thick composites were joined to 

steel in the same manner as the Extren®/steel bolted 

joints with a 25.4-mm washer. The static strength of 

the 3D composite is approximately 3 times greater 

than that of the 2D Extren® composite. However, 

hybrid joints assembled from each composite substrate with steel yielded comparable static strengths 

(Figure 10). A cleavage tension failure was observed 

in joints assembled with Extren®, and a shear-out 

failure mode was observed in joints assembled with 

the 3D composite. 

Figure 10. Static joint strength comparisons of composite/steel joints. 

The fatigue strength of the hybrid joints assembled with the 3D composite was also comparable to 

that of the 2D composite. Figure 11 is an illustration 

of the fatigue strength comparison in terms of percentage of peak load. These testing results indicate 

that the fatigue strength of this type of hybrid joint is 

more sensitive to the geometry of the joint design 

than to the material substrate. 

Figure 11. Fatigue joint strength comparisons of composite/steel joints. 

Modeling

Genoa Evaluation 

The joining team has investigated the commercial software GENOA to evaluate the feasibility of 

using it to predict the static and fatigue strength of 

composite/steel joints. Three staff members from 

ORNL and PNNL attended the GEONA training 

classes. 

GENOA is an integrated structural analysis and 

design software that originated in the aerospace 

composite community. Its progressive failure analysis module predicts crack initiation, growth, and final failure for monolithic and 2D/3D braided, 

laminated, stitched, and woven composite materials 

based on the unit cell formulation originated by the 

National Aeronautics and Space Administration. The 

initiation and damage growth can be due to static, 

fatigue, thermal, and impact loading; and it is identified by the industrial team as the candidate software 

to be used in their project. 

The feedback on the software from the staff 

members that attended the training classes was 

mostly positive. GENOA couples analyses on different scales and provides progressive failure analysis capabilities that are specifically tailored for 

composites. However, the current version has the 

following limitations that may hamper its use for the 

joint analysis: 

• GENOA does not support more than one element type. Therefore, modeling of the joint area 
High Strength/Weight Reduction Materials FY 2004 Semi-Annual Progress Report 

127 

would have to be performed using solid elements. 

• GENOA does not have contact modeling capability. Therefore, the interaction between the 

fastener and the plate materials, critical for predicting the fatigue life of the joint, cannot be 

modeled with this contact included. 

• GENOA has demonstrated its ability to predict 

failures of composite samples with continuous 

fibers. Its capability to predict progressive damage for composites with randomly distributed 

chopped fibers needs to be further evaluated and 

established. 

Joint Modeling

ABAQUS was used to analyze the effect of 

washer size in a bolted joint consisting of pultruded 

fiberglass composite and steel. The solid models 

were linear elastic, and the pre-load was produced 

by turning the nut by 90°, simulating a torque of 

13.6 N-m (10 ft-lb). A small washer resulted in 20% 

more compressive strain in the composite than in the 

large washer. This prediction was validated through 

the joint mechanical testing results showing an improved static strength and fatigue resistance for a 

larger washer. 

For an all–carbon reinforced composite component bolted to a steel component (design provided by 

the industrial team), three insert geometries were 

evaluated under two loading conditions. The metal 

inserts were selected so that the compressive load 

caused by the bolt tightening is fully carried by the 

metal insert, and the load is transferred to the composite through the bond between the insert and the 

composite. This will mitigate the issues associated 

with bolt loosening due to creep and/or damage in 

the composite during bolt installation. 

The three insert designs include a cylindrical 

steel insert, a tapered insert with the large diameter 

at the bolt head side of the composite, and a tapered 

insert with the large diameter on the steel side of the 

composite. One assembly is shown in Figure 12. The 

model was evaluated under two loading conditions: 

a bending force and a lap shear force. The measure 

of performance to compare the different insert geometries was a component of traction norFigure 12. Finite element model of composite/steel 

bolted joint with tapered insert. 

mal to the composite/insert interface that would produce a peeling stress in the adhesive. Because actual 

loads are not yet available for the actual chassis 

component, failure stresses from the steel/steel joint 

testing for lap shear and cross tension (bending) 

were used with the model. This is a worst-case load 

application and is unrealistic because the pre-load in 

the bolt is overcome, and contact between the steel 

and the composite are lost. 

Qualitatively, the results match the results obtained for lower load levels: the tapered insert with 

the large diameter at the bolt head side of the composite exhibits the best performance. The model of 

the joint and insert will be added to the system 

model for additional investigation. As design and 

material changes are made and the loading cases are 

refined, further optimization of the joint, including 

inserts, will be possible. 

Fatigue 

Components in a truck chassis undergo complex 

random variable fatigue loading during their lifetime. The loading spectrum can be estimated from 

measurement results acquired in field tests or testtrack runs, where a component is instrumented with 

accelerometers, strain-gages, and linear variable differential transformers. A majority of the cycles reach 

low load levels and are generally of concern only if 

their frequency approaches a resonant frequency of 

the structure. Resonance issues can be eliminated by 

adequate design of a component. Higher loads 

commonly take place at lower frequencies. Repetitive loads below the static limit can initiate damage, 

especially in the vicinity of stress raisers such as bolt 

holes and contacts. Therefore, the prediction of low-
FY 2004 Semi-Annual Progress Report High Strength/Weight Reduction Materials 

128 

frequency fatigue life is of prime interest for chassis 

structural application. 

Cumulative damage caused by low-frequency 

cycles is estimated using certain damage laws in 

conjunction with the results of constant amplitude 

fatigue tests. One of the most common damage laws 

is the Palmgren-Miner linear relationship. This law 

assumes that fatigue cycles at a specific load level 

always result in the same damage regardless of the 

loading history. The Palmgren-Miner model yields 

acceptable results for metals and is almost exclusively used for life predictions in practical applications. A literature review has revealed that this 

relationship may grossly overestimate or underestimate the fatigue life of composites. Because of this, 

empirical and semi-empirical non-linear damage 

laws have been developed for a variety of composites. In addition, Goodman diagrams can be used to 

account for varying R ratios of constant amplitude 

fatigue tests that are used as a basis for fatigue life 

predictions. All these methods require significant 

testing. 

It will be necessary to evaluate the applicability 

of Palmgren-Miner’s law for selected materials as 

part of this project in order to predict long-term fatigue performance. If this law does not reasonably 

represent actual material behavior, then an appropriate nonlinear relationship must be determined 

through additional testing, or the uncertainty must be 

taken into account by using appropriate safety coefficients during design. Although GENOA has shown 

promise for predicting the fatigue performance of 

the 3D reinforced composite material at constant 

stress levels, the software uses Miner’s rule for variable stress levels. 

 

Presentations

L. Klett, B. Frame, and V. Kunc, “Damage at 

Holes in Bolted Composite/Steel Joints for Heavy 

Vehicle Chassis Components,” presented at the 2004 

SPE Automotive Composites Conference and Exposition, Detroit, September 14–15, 2004. 

X. Sun, D. Herling, and E. Stephens, “Static and 

Fatigue Strength Evaluations for Bolted Composite/Steel Joints for Heavy Vehicle Chassis Components,” presented at the 2004 SPE Automotive 

Composites Conference and Exposition, Detroit, 

September 14–15, 2004 . 

Acknowledgements

The principal investigators would like to acknowledge the valuable contributions of other members of the research team, including Barbara Frame 

and Vlasta Kunc at ORNL and Xin Sun and Elizabeth Stephens at PNNL. 
High Strength Weight Reduction Materials FY 2004 Progress Report 

129 

J. Rapid, Low-Cost Tooling Development 

Principal Investigators: 

Cliff Eberle

Oak Ridge National Laboratory, Oak Ridge, TN 37831-8048 

(865) 574-0302; fax: (865) 574-8257; e-mail: eberlecc@ornl.gov 

Curt Lavender 

Pacific Northwest National Laboratory, 902 Battelle Blvd, PO Box 999, Richland, WA 99352 

(509) 372-6770; fax: (509) 375-4448; e-mail: curt.lavender@pnl.gov 

Technology Development Area Specialist: Sidney Diamond 

(202) 586-8032; fax (202) 586-2476; e-mail: sid.diamond@hq.doe.gov 

Field Technical Manager: Philip S. Sklad 

(865) 574-5069; fax:(865) 576-4963; e-mail: skladps@ornl.gov 

Contractor: Oak Ridge National Laboratory 

Contract No.: DE-AC05-00OR22725 

Objectives 

• Assess status and need for low-cost tooling technologies for lightweighting materials. 

• Evaluate state-of-the-art capabilities for rapid, low-cost tooling approaches. 

• Determine the socioeconomic factors that are likely to significantly impact the development and implementation of advanced tooling technology. 

Approach 

• Conduct a workshop to solicit industry input. Follow the workshop by privately interviewing key participants 

throughout the value chain. 

• Conduct energy analysis to estimate potential energy savings from improved tooling technology. 

• Review tooling industry socioeconomics and potential impacts of technological change in the industry. 

• Report key findings and plan the path forward. 

Accomplishments 

• Conducted two industry workshop sessions. 

• Recorded preliminary findings from workshop sessions and published summaries on the web 

• Performed energy analysis. 

• Conducted follow-up interviews with key industry workshop contacts. 

• Reviewed socioeconomic indicators of tooling industry health and potential impacts of technological change or 

lack thereof. 

• Developed a plan to engage industry in roadmapping and collaborative technology development. 

• Issued draft report to DOE. 
FY 2004 Progress Report High Strength Weight Reduction Materials 

130 

Future Direction 

• Work with industry to foster communication and collaboration, and to develop an “industry-owned” roadmap. 

• Engage other interested government parties to co-sponsor research and development (R&D). 

• Commence performing selected R&D. 

Introduction

The introduction of advanced polymer-based 

composites and lightweight material manufacturing 

processes to commercial vehicle manufacturers and 

their supplier base is thought to be severely impacted by the high cost of tooling and long tooling 

development time. Often the use of lower-cost materials and less efficient structural designs is dictated 

by the fact that tooling for the manufacture of advanced composites and other lightweight materials 

cannot be justified from a cost-per-part basis, and 

from the long development times or procurement 

lead times that are required. In addition, the unique 

production volumes associated with commercial vehicles—which are significantly lower than automotive production volumes, yet well above aerospace 

production numbers—make current tooling design 

and development methods unsuitable. 

An example of the cost and schedule challenges 

faced by commercial vehicle manufacturers is that a 

fully tooled door system for a Class 8 tractor can 

cost upward of $20 million and require over 24 

months to fabricate and qualify the tooling. When 

advanced materials such as carbon fiber composites 

or lightweight metals such as aluminum or magnesium are considered, tooling design, material forming characteristics, and surface finish requirements 

make today’s manufacturing approaches very highrisk. The result is often that manufacturers fall back 

on less efficient structures that use conventional 

steel and fabricated structural designs. 

The purpose of this project is to assess current 

tooling technologies to identify key deficiencies in 

cost, prototype and fabrication methods, and design 

and modeling tools that prevent the increased use of 

lightweight metals and composites structures in lowand medium-volume commercial vehicles. Data 

have been gathered from government–industry 

workshops, published data sources, and numerous 

follow-up interviews with workshop participants and 

other key industry experts. The team intends to work 

with industry to develop a roadmap that will guide 

the development and implementation of advanced 

tooling technology that reduces the risk of using advanced lightweight materials in commercial vehicle 

applications. 

Project Deliverables

In late FY 2004, the project team delivered to 

DOE a draft report containing findings from the industry workshop, follow-up interviews, energy 

analysis, and socioeconomics review. The primary 

future deliverables are a roadmap for tooling technology development and implementation, and a list 

of co-sponsors that will share the R&D costs with 

DOE. 

Technical Approach

The technical approach for this project is largely 

based on gathering and analyzing information to 

enable informed decision-making regarding future 

R&D investments. A key part of the project has been 

to plan and conduct a workshop that served as a forum for soliciting information from industry experts 

and for networking among industry peers. The 

workshop was followed by interviews with selected 

key industry contacts, most of whom were attendees 

at one or more workshop sessions, to validate the 

workshop findings. Additionally, potential energy 

and socioeconomic impacts were analyzed. In the 

future, a roadmap and program plan will be developed. 

Industry Workshop

Oak Ridge National Laboratory (ORNL) and 

Pacific Northwest National Laboratory (PNNL) cohosted a two-session industry workshop entitled 

“Tooling Technology for Low-Volume Vehicle Production.” The workshop scope principally addressed 

tooling needs for large, lightweight components or 

parts, manufactured in production volumes from 

1,000 to 30,000 parts per year, using closed or two- 
High Strength Weight Reduction Materials FY 2004 Progress Report 

131 

sided forming or molding processes. Topics covered 

at the workshop included 

• Large class-A components 

• Large structural components 

• Computer-aided design/computer-aided engineering/computer-aided manufacturing/CIM 

(CAD/CAE/CAM/CIM) efficiencies 

• Rapid prototyping 

• Predictive modeling 

The target audience included truck, bus, automotive, recreational vehicle, and marine original 

equipment manufacturers (OEMs) and suppliers; 

tooling suppliers and designers; tooling material 

suppliers; rapid prototyping suppliers; CAD/CAE/ 

CAM/CIM suppliers and developers; and machine 

tool suppliers. 

Session one, hosted by PNNL in Seattle on October 28, 2003, focused on identifying needs and 

goals. It was attended by approximately 30 industry 

experts with a high representation from truck OEMs 

and upper-tier suppliers. Session two, hosted by 

ORNL in Detroit on November 18, 2003, focused on 

roadmapping solutions and strategies. It was attended by approximately 50 industry experts, with a 

high representation from companies that were offering new technology that they consider applicable to 

the tooling industry. 

Preliminary workshop observations included 

these: 

• Tooling technology development does not have 

a home or champion. 

- OEMs and upper tier suppliers push it down the 

supply chain. 

- Tool suppliers are too small to accept the risk (see 

socioeconomics discussion). 

- The value chain is very fragmented, and there is 

poor up-down communication. 

- This workshop appeared to be the first forum that 

had fostered communication throughout the tooling value chain.

• Tool manufacturing is moving offshore. 

• High tooling cost kills development projects. 

• Improved tooling technology may lead to reductions in vehicle mass and aerodynamic drag. 

• There are some novel technologies and ideas 

that merit further development. 

• The business case can favor composites (and 

perhaps other lightweighting materials) at low 

vehicle production volumes. 

To date, follow-up analysis has confirmed some 

of these observations and found others to be suspect. 

Workshop session summaries and invited presentations are posted on the worldwide web at 

http://www.pnl.gov/energy/tooling/default.htm. 

Energy Analysis 

An energy savings analysis was conducted by 

ORNL, using survey data from the workshop sessions. The results suggest that, at full market penetration, probable energy savings attributable to improved tooling are about 4% for heavy trucks and 

6% for passenger cars. Details of the analysis, such 

as assumptions and sensitivity estimates, are available in the full report.1

Socioeconomics

A socioeconomics review was conducted to assess the tooling industry’s health and impacts on 

U.S. economic prosperity. Key findings are discussed below. 

The U.S. tool, die, and mold (TDM) industry 

consists exclusively of small businesses and is a 

deeply distressed industry. In 1997, more than 75% 

of the companies employed fewer than 20 people, 

and 92% employed fewer than 50 people. In 2001, 

there were only 16 companies with revenues of $20 

million or more. The largest company had $80 million in revenues. In 1997, the industry had about 

7200 companies and was losing about 200 companies per year—before the most recent recession. 

Though Commerce Department data are not yet 

available for 2002 and 2003, our industry interviews 

suggest that the shake-out of independent TDMs 

accelerated in those years as a result of the recession. 

Apparent U.S. consumption of TDMs remained 

essentially flat during the 1997–2000 period at $15 

billion before declining in 2001 to $13.8 billion. Imports and exports showed the same general trend, 

essentially flat during the 1997–2000 period, followed by a significant decline in 2001. In 2001, the 

latest year for which data are available, domestic 

TDM manufacture was $13.2 billion, imports totaled 

$1.7 billion, and exports accounted for $1.1 billion. 

In follow-up interviews, we found that those who 

were importing tools usually were importing from 

high-cost-of-labor countries that gained their advan-
FY 2004 Progress Report High Strength Weight Reduction Materials 

132 

tage through technology. Although we do not doubt 

the workshop participants’ concerns over imports, it 

is difficult to ascribe the industry problems to this 

source. 

We discovered that during the 1997–2001 period, the TDM share of total U.S. manufactured 

goods value declined by 13%. It appears that U.S. 

manufacturers are reducing the value of TDMs in 

their finished manufactured products through TDM 

price reductions, longer use of existing tools, reduced prototyping, and fewer product changes. We 

believe that these reductions in TDM purchases are 

also related to increased stamping die production by 

the major automobile OEMs. Hence we conclude 

that the major source of the industry’s distress is a 

fundamental shift in its market drivers. 

Payment terms, which are driven by the OEMs, 

are a significant factor in the TDM industry’s distress. The OEM often does not pay the first-tier supplier until production begins, which is usually 18 

months or more after the TDM buys the tool material. The supplier frequently exacts the same terms 

from the tool maker. Hence the TDM is essentially 

compelled to make an interest-free loan to the OEM 

for several months. Being small companies, the 

TDMs will generally require bank financing, and 

banks discount the value of receivables over 30 

days. The strain put on banking relations by the recession was certainly a factor in the high rate of 

TDM company failures during the recession. The 

truck OEMs and those transplant automobile makers 

that were interviewed generally have payment policies that are more beneficial to the TDMs than do 

the U.S. “Big Three” OEMs. However, the domestic 

automakers comprise the lion’s share of independent 

TDM business in the United States; therefore, their 

procurement policies are a major factor in TDM industry health. 

New technology can significantly reduce the 

unit cost of tooling. However, the equipment embodying the technology is expensive, especially for 

small businesses in “cash flow distress,” and the resultant improvement in productivity increases the 

over-capacity in the industry. The reverse of this 

argument is that the survivors of the shake-out appear to have remained current with technology. This 

view was strongly reinforced in an interview with a 

small, but apparently successful, tool maker who 

suggested that if new technology could reduce tooling costs enough, that could change the paradigm 

and lead to more vehicle changes and more business 

for TDM builders. More vehicle changes translate 

into more rapid infusion of technology into the vehicles. 

Given all of the above, and only minimal government support from the Department of Defense 

and Department of Commerce, the technology development firms are struggling to survive. The technology developers would like direct government 

support. However, lacking financial support, they 

would like to see some mechanism by which the risk 

of new technology is shared among the TDM 

builder, the supplier, and the OEM. They feel that 

the OEM discourages new technology by not being 

willing to share the risk. Clearly, the TDM builder is 

the least able to afford the risk of new technology 

but is one of its biggest beneficiaries. Further, given 

the lack of real communication in the supply chain, 

the OEM is essentially oblivious to the problem 

faced by the TDM builder in adopting new technology. 

Conclusions

Tooling is a major expense in manufacturing 

vehicles, especially at low production volumes. The 

industry workshop sessions were well-attended, fostered a unique networking opportunity for industry, 

and provided important information. The energy 

savings analysis suggests that improved tooling 

technology should lead to appreciable reduction in 

petroleum demand. The socioeconomics review 

found a disconnected value chain, with the TDM 

manufacturing industry consisting entirely of small 

businesses and being in severe distress. The good 

news is that almost everyone with whom we have 

talked, including prospective co-sponsors such as 

other government agencies, wants to “do something.” It appears that there are opportunities to 

make a difference with properly planned and targeted technology development and implementation. 

In FY 2005, we plan to engage the stakeholders to 

develop a roadmap and begin its implementation. 

Acknowledgements

The principal investigators gratefully acknowledge key contributions from many sources. Special 

thanks is due Jeanne Phillips and Phil Sklad from 

ORNL, Suzanne Niemeyer and the web hosting 

group from PNNL, Allan Murray, a consultant to 

both laboratories, and David Stewart, President of 

Stewart Automotive Research, for their significant 
High Strength Weight Reduction Materials FY 2004 Progress Report 

133 

contributions to workshop planning and execution. 

Ed Ungar and other Taratec Corporation staff have 

led the workshop follow-up and socioeconomics 

review, and ORNL’s Rick Schmoyer conducted the 

energy savings analysis. 

References

1. R. L. Schmoyer and C. C. Eberle, “An Analysis of Energy Savings Possible Through Advances in 

Automotive Tooling Technology,” ORNL/TM2004/115, Oak Ridge National Laboratory, 2004. 

Publication

R. L. Schmoyer and C. C. Eberle, “An Analysis 

of Energy Savings Possible Through Advances in 

Automotive Tooling Technology,” ORNL/TM2004/115, Oak Ridge National Laboratory, 2004. 
FY 2004 Progress Report High Strength Weight Reduction Materials 

134 
High Strength Weight Reduction Materials FY 2004 Progress Report 

135 

K. Inventory of Heavy-duty Truck Lightweighting Candidates 

Principal Investigator: Edwin H. Kraft 

EHKTechnologies 

10917 SE Burlington Dr. 

Vancouver, WA 98664-5383 

(360) 896-0031; fax: (360) 896-0032; e-mail: ekraft@EHKTechnologies.com 

Technology Development Area Specialist: Sidney Diamond 

(202) 586-8032; fax: (202) 586-1600; e-mail: sid.diamond@ee.doe.gov 

Field Technical Manager: Philip S. Sklad 

(865) 574-5069; fax: (865) 576-4963; e-mail: skladps@ornl.gov 

Contractor: EHKTechnologies 

Subcontract No.: 4000031071 / 03/22/2004 

Objective 

• Identify components and systems of heavy-duty trucks that have the greatest total fleet weight savings potential 

for the purpose of increased fuel efficiency and productivity. 

- Inventory the systems and components of Class 8 tractor-trailers. 

- Model the miles traveled and weight factor for the major component-system-vehicle combinations. 

- Rank and estimate the fuel consumption contribution of the most significant components. 

- Provide a model usable by potential component lightweighting developers to estimate the relative weight–

miles contribution of candidate components. 

Approach 

• Define the industry segments: types of vehicle bodies and vehicle configurations; define the numbers and annual miles of vehicles by type and configuration. 

• Compile data on component and system configurations, weights, and materials of construction for the apparent 

major contributors to vehicle weight. 

• Aggregate data on specific component weights and materials to prevent disclosure of individual manufacturers’ 

proprietary information. Select representative values for component weights where a range of designs and 

weights are common. 

• Determine the fuel economy distribution of weight ranges of heavy-duty trucks and calculate a representative 

fuel consumption of components per pound-mile. 

• Design a model of the weight-miles traveled (pound-miles) and fuel consumption for any component or set of 

components to be considered for fleet weight savings and improved fuel economy. 

Accomplishments 

• Successfully used the various databases to calculate numbers and total annual miles of vehicles by body type, 

vehicle configuration (truck and truck-tractor, number of trailers pulled, number of axles and tires), weight subclassification, and type of cargo hauled. 

• Determined that buses and four types of trucks account for >90% of vehicle numbers and miles, and the four 

truck types account for the most trailer and haul unit miles. 

• Determined that weight regulations normally impact the operation of platform, dump, and tank body vehicles, 

causing them to be weight-limited (“gross out”). 
FY 2004 Progress Report High Strength Weight Reduction Materials 

136 

• Obtained representative weights of major components common to all vehicle types and those specific to the 

four primary body types. 

• Constructed an Excel-based model of component pound-miles and added a calculation of component fuel consumption. 

• Identified the most significant contributors to pound-miles. 

• Determined that extensive use of aluminum, high-strength steel, and new designs have already contributed to 

weight reduction and that further use these materials plus magnesium, titanium, and composites promises significant additional weight savings. 

Future Direction 

• Incorporate final manufacturer data in summaries and model. 

• Publish final report. 

• Present findings to selected industry, government, and professional associations. 

• Investigate opportunities and potential impact of materials such as aluminum, magnesium, and titanium. 

• Discuss findings with vehicle and component manufacturers for consideration of focused developments. 

• Discuss findings with military agencies for applicability to military ground vehicles. 

Introduction

The purpose of this project is to assist Oak 

Ridge National Laboratory (ORNL) and DOE in 

prioritizing lightweighting technologies for heavyduty trucks via an inventory of components that may 

aid in weight reduction. Identifying the components 

that contribute the most weight in the entire fleet of 

heavy trucks will enable ORNL/DOE to select projects with the greatest payoff in weight savings and 

reduced fuel consumption. The inventory must consider not only the weight of typical components but 

also the number of vehicle miles traveled by heavy 

trucks using that component over a typical year 

(pound-miles) and the fuel consumed carrying those 

components. A model will be provided that allows 

calculation of the pound-mile and fuel consumption 

figures for any component under consideration. It 

will incorporate the effect of applying the component to various truck body types and the miles traveled by trucks that use it. The model may be used to 

provide a quantitative estimate for comparing the 

weight and fuel consumption reduction potential of 

any proposed component. 

Project Deliverables

• A presentation has been made to DOE and 

ORNL personnel. 

• A final report will provide details of the methodology and findings. 

• A computer disk containing the model will be 

provided for use by DOE, ORNL, and potential 

component developers for calculating and identifying the weight and fuel savings potential of 

any proposed component. 

Heavy Vehicle Segments

Some components of heavy duty trucks and tractor trailers are used on every such vehicle; others 

may only be used on one vehicle type or configuration. In considering the development of a reducedweight component, it is therefore necessary to understand its potential contribution to weight reduction over the entire vehicle fleet. To do so, it is necessary to have data on the number of vehicles of 

various types, and the miles traveled by each type, 

over a representative year. The weight or weight 

reduction potential of a component is multiplied by 

the number used on each vehicle type and the miles 

traveled by that type to obtain the pound-miles for 

the component. Adding the pound-miles for all vehicle types where a component would be used gives 

the total pound-miles for that component. If an average fuel economy figure is available for heavy 

trucks, it may be used to calculate the fuel consumed 

by each pound of weight of an average vehicle. The 
High Strength Weight Reduction Materials FY 2004 Progress Report 

137 

product of the pound-miles and the fuel consumed is 

an estimate of the fuel savings if that component 

were implemented across all applicable vehicles. 

Several databases were used to construct a master database of numbers and miles traveled for all 

types of trucks in each weight range of Class 7 and 8 

vehicles. It lists 29 body styles, including dry van 

truck and trailer containers, refrigerated van truck 

and trailer containers, tank trucks and trailers, flat 

bed trucks and trailers, dump bodies, and cement 

mixers. Another truck-trailer classification includes 

the type of truck (truck or truck tractor), number of 

trailers pulled, number of axles, and number of 

wheels. Thus, for example, all tank trucks with 4 

axles and 14 wheels pulling a full tank trailer with 3 

axles and 12 wheels will have one estimated number 

with that configuration and total miles traveled. 

Three-axle, 10-wheel truck tractors pulling one 4-

axle, 16-wheel flatbed trailer will have a different 

estimated number and miles traveled. These differences have been found to be very significant. Analysis of these vehicle types was also expected to assist 

in focusing effort on the vehicle body types and 

components with the most contribution to poundmiles and fuel consumption. 

This last benefit of the analysis is best accomplished by charting the number and miles traveled 

for the various truck types, and the number of trailers and “haul units” traveled by those types. A haul 

unit is defined as one container or support structure 

for cargo carried by a truck or trailer (e.g., a tank 

truck pulling a tank trailer constitutes two haul 

units.) 

Figure 1 shows the number of vehicles by type 

with similar types combined. This result shows that 

relatively few body types account for the great majority of vehicles. This finding is even more pronounced when the results for body type by miles 

traveled are shown (Figure 2). We then find that just 

four body types account for 90% of the miles driven 

by heavy trucks/tractor trailers: the various forms of 

vans (dry, refer, insulated, and drop body), platforms 

(with and without added devices, and drop frame), 

dump bodies, and liquid haul tanks. Other body 

types travel far fewer miles and therefore contribute 

little to the overall miles driven by the total heavyduty fleet. 

Buses, including school, inter-urban, and city 

transit, have been included in this analysis thus far. 

It is apparent that they contribute significantly to the 

total miles driven by heavy vehicles. This analysis 

Figure 1. Number of vehicles by type. 

Figure 2. Number of vehicles by type; similar body types 

combined. 

was conducted even though the original project 

scope included only trucks. During the investigation, 

it was found that, while bus weight and miles may 

be significant, the operation of buses is limited by 

passenger capacity and not by weight in most cases. 

Fuel savings by reduced weight is a secondary consideration for this industry. Therefore, owners and 

operators are not generally willing to pay any premium for weight savings. Methods to reduce bus 

weight may have significant fuel economy payoff 

but are likely to be adopted only if they carry no cost 

penalty. Since this topic was not in the original project scope, and buses are not generally weight limited, no further analysis was performed. 

The number of trailer miles and of haul unit 

miles of the various types were analyzed to further 

confirm the overriding importance of the four types 

of vehicle bodies. Figure 3 shows the results for haul 

unit miles. 
FY 2004 Progress Report High Strength Weight Reduction Materials 

138 

Figure 3. Miles traveled by vehicles of each type; similar 

body types combined. 

We can definitively conclude that vehicles with 

body types including types of vans, flat beds, dump 

bodies, and tanks make the most significant contribution to miles traveled by heavy duty vehicles. It is 

also apparent that Class 8 vehicles other than buses 

travel far more miles than Class 7 vehicles, which 

may then be ignored in analysis of potential weight 

and fuel savings. Analysis of components used either on multiple-body type trucks or on these four 

primary types will provide the greatest potential for 

weight and fuel savings. 

Major Truck and Trailer Components

Some components of heavy vehicles are used on 

all body types and vehicle configurations, and others 

are specific to certain body types. Obviously, a relatively heavy component common to all types of vehicles will contribute much more to total poundmiles than a lighter component specific to only one 

body type. 

Data were collected on the weights of components of all the major systems of trucks, tractors, and 

trailers. Much of this specific data, however, is proprietary and may not be disclosed. Attempts were 

therefore made to collect data from multiple manufacturers so that aggregate weights could be used in 

the analysis. In some cases, particularly where a 

wide variety of designs and weights are available for 

a type of component, representative weights were 

selected to facilitate the comparative analysis. Individual component weights discussed in this report 

therefore do not represent those of components from 

any one manufacturer. 

Common Components. All truck and trucktractor components are used in all body types. Engines, transmissions, truck frames, exhaust systems, 

axles, suspensions, cab features, drivelines, wheels, 

and tires, among others, are common components. 

Since 70% of haul units are trailers, several other 

components, such as fifth wheels, couplers, landing 

gear, “bogie” sliders, bumpers, and underrides, are 

used by nearly all vehicles. Some components are 

used on several major body types, such as van and 

flatbed floors, lower and upper side rails, main and 

cross beams. It is also important to consider in our 

analysis that some components are used multiple 

times per vehicle, including tires, wheels, axles, 

brakes and suspensions; such multiple use may 

make a component of moderate weight significant. 

The engine is one of the heaviest components 

and is used on all vehicles. While there are numerous engine designs and engine sizes, many components are common to all or most designs. Figure 4 

shows the relative weights of many of the major 

components. It is apparent that the block and cylinder head are by far the heaviest components and 

most likely to be significant contributors to poundmiles and fuel consumption. Wheels and tires, used 

multiple times on all vehicles, have already been the 

subject of weight reduction efforts. Traditional steel 

wheels have been partially replaced by light steel 

and aluminum wheels, with the latter being used on 

40–50% of trucks but only about 10% of trailers. 

Super single aluminum wheel and tire combinations 

at ~240 lb per set are beginning to replace dual 

wheel/tires (~390 lb per set for conventional steel). 

Titanium provides weight and performance improvements for springs. 

Figure 4. Miles traveled by trailers of each type. 

Body-Type-Specific Components. Since four 

types of bodies predominate in numbers and miles 
High Strength Weight Reduction Materials FY 2004 Progress Report 

139 

traveled, we expect that some of their components 

will be among the largest contributors to poundmiles and fuel consumption. Among those components are the sides of van body trucks and trailers, 

with typical trailer side weights of 2000–3000 lb per 

set; the floors of van body vehicles and flatbed vehicles, which also weigh about 2000 lb; and parts such 

as base/side rails, top rails, floor crossmembers, rear 

frames, main beams, dump bodies, and liquid haul 

tanks. Data were collected on more than 100 such 

component types. 

Truck Fuel Economy

Various estimates of the fuel economy of heavy 

vehicles were encountered. To provide a supportable 

estimate for use in the comparison model, the VIUS 

database was exercised to provide the reported fuel 

economy of each 10,000 lb range in Classes 7 and 8. 

Class 8 fuel economy averages, weighted on miles 

reported, were calculated at 5.46 mpg, and the average vehicle weight at 64,400 lb. These points were 

used to calculate indicative fuel consumption by vehicle components of 2.84 × 10−6

 gallons per poundmile. 

Pound-Mile Comparison Model

For the purposes of this study, a computational 

model is needed that includes the effect of component weight plus the number of times a component 

may be used in the entire fleet of trucks, and the fuel 

consumption per pound of vehicle. An MS Excel 

spreadsheet model was constructed including all of 

these factors. The full model includes consideration 

of the nine most common body types and all 49 vehicle configurations. To operate the model, the user 

enters a component name and weight and then decides the applicability of that component to each of 

the nine body types. 

Applicability may be due to fundamental suitability or to an estimate of the portion of the entire 

fleet that is likely to adopt the component. The user 

will next enter the quantity of that component that 

would be used for each of the 49 configurations of 

truck and tractor trailer. The spreadsheet model then 

calculates the pound-miles of that component in the 

entire fleet, plus an estimate of the fuel that would 

be consumed by weight-limited vehicles over the 

entire fleet. 

Results

This procedure was followed for 74 of the 

heaviest components investigated. The results are 

shown in Figure 5 for the components with the 

greatest pound-mile and fuel consumption estimates. 

The values for the other 18 components are very 

small compared with these 56. 

Figure 5. Miles traveled by haul units of each type. 

Conclusions

Based on the results of the analysis of heavy vehicle fleet segments, component weights, and the 

Pound-Mile and Fuel Consumption model, we can 

provide the following conclusions: 

1. Class 8 trucks and tractor-trailers with four body 

types predominate in number of vehicles, miles 

traveled, number of trailers, and number of haul 

units. Weight reduction efforts will have the 

greatest payoff for vehicles with components 

common to all types, or to one or more of these 

four types. The four types are 

• Van bodies (basic enclosed vans, refrigerated vans, insulated vans and drop-frame 

vans) 

• Platform bodies (basic platforms, platforms 

with added devices, low boys) 

• Tank bodies (liquid or gas haul tank trucks 

and trailers) 

• Dump bodies (dump trucks, bottom and rear 

dump trailers) 

2. Several factors act to make some components 

more likely to be major contributors to total fleet 
FY 2004 Progress Report High Strength Weight Reduction Materials 

140 

weight and fuel consumption. They include 

these: 

• All truck and truck-tractor components, and 

many trailer components, are used by all body 

types. These include engine, transmission, truck 

frame, exhaust, axles, suspensions, cabs, drivelines, wheels, and tires. 

• Since 70% of haul units are trailers, several 

other components are used by nearly all vehicles, including fifth wheels, couplers, landing 

gear, suspension sliders, and bumpers. 

• Some components, such as floors, side rails, and 

main and cross beams, are used by several of the 

predominant body types. 

• Some components, such as tires, wheels, axles, 

brakes, support cross members, and suspensions, 

are used multiple times per vehicle. 

3. The pound-miles and fuel consumption contributions of a wide variety of components were 

determined so that they might be ranked in order 

of priority for lightweighting effort. The most 

significant contributors to pound-miles and fuel 

consumption include engines, tires and wheels, 

van sides, van and flatbed floors, suspensions, 

axles, brake drums, all frame members, cabs, 

couplers and fifth wheels, transmissions, and 

tanks. Some other component types are also significant contributors. 

4. Efforts to reduce the weight of engine blocks 

and heads, for example, the use of aluminum or 

titanium, would likely produce the greatest payoff. Application of aluminum to additional components and titanium, magnesium, and composites to many components would result in of 

many trillions of pound-miles of lightweighting 

and millions of gallons of fuel savings. 
High Strength Weight Reduction Materials FY 2004 Progress Report 

141 

L. Truck-to-Auto Technology Transfer for Lightweight Materials 

Principal Investigator: Edward Ungar 

Taratec Corporation 

1251 Dublin Road, Columbus, OH 43215 

614-291-2229; fax 614-291-2867; e-mail: eungar@tarateccorp.com 

Technology Development Area Specialist: Sidney Diamond 

(202) 586-8032; fax:(202) 586-1600; e-mail: sid.diamond@ee.doe.gov 

Field Technical Manager: Philip S. Sklad 

(865) 574-5069; fax: (865) 576-4963; e-mail: skladps@ornl.gov 

Participants 

Paula Dunnigan, Taratec Corporation 

Mike Carter, Taratec Corporation

Subcontractor: Taratec Corporation

Subcontract No.: 4000033939 under Contract No. DE-AC05-OR22725

Objectives 

• Determine the degree to which DOE technology development for heavy trucks is transferred through the supplier base to the automotive industry. 

• Determine if this process is applicable to the lightweight materials programs being funded by DOE. 

Approach 

• Identify suppliers in the DOE lightweight materials program who serve both truck and auto industries. 

• Identify individuals at the decision-making level. 

• Develop an interview script. 

• Conduct five supplier interviews. 

• Conduct five interviews with truck and auto original equipment manufacturers (OEMs) and industry groups. 

• Summarize findings. 

Accomplishments 

• Conducted interviews with materials decision-makers in the truck and auto industries to solicit their opinions 

on the potential for transfer of lightweight materials technologies between trucks and automobiles. 

Introduction 

Interviews were conducted with key materials 

decision-makers from the auto and truck industries. 

The purpose of these interviews was to better understand the potential for the transfer of lightweight 

materials technology from the truck to the auto industry. 

Comments from the interviewees indicated that 

some technology transfer between the truck and auto 

industries will occur spontaneously, but it will be 

limited. Regarding lightweight materials, there is the 

potential for significant truck-to-auto technology 
FY 2003 Progress Report High Strength Weight Reduction Materials 

142 

transfer with external stimulation of the process. 

Technologies that require significant change in legacy materials, processing, or auto assembly will require considerably longer for transfer than drop-in 

materials substitutions. 

The following findings represent the input provided by the interviewees. 

Key Findings

The technology transfer process is controlled by 

the advanced engineering groups at the truck and 

auto OEMs and by the first tier suppliers who serve 

both industries. 

Incentives for technology transfer for both the 

truck and auto industries stem from improvements in 

buyer economics or manufacturer’s costs. Transfer is 

hindered by the fact that the truck and auto industries have different production volumes, part sizes, 

buyer payback calculations, and long-term materials 

data requirements. 

Interviewees cited examples of technology 

transfer that has occurred previously in both directions. They feel that future technology transfer between the truck and auto industry is possible. Truckto-automotive technology transfer is likely to involve advanced materials for weight reduction, nonreinforced dicyclopentadiene for body panels and 

bumpers, adaptive cruise control, and electromagnetic retarder brake systems. 

For drop-in materials substitutions, it may take 

2–4 years for a product to be commercialized on the 

second vehicle platform. If the technology requires a 

change to current forming, joining, or finishing 

processes, commercialization may require up to 10 

years. 

The interviewees thought that DOE could catalyze technology transfer between the truck and auto 

industries by providing leadership, networking opportunities for gatekeepers, and project funding to 

support data collection for both industries. 

Interviewees thought DOE could play a key role 

in stimulating technology transfer to the auto industry. It would be important to involve the automotive 

gatekeepers in DOE’s lightweight materials truck 

projects. Projects should be structured to develop 

economic justification for both truck and auto applications. Long-term performance data should be generated to meet the concerns of both industries. A 

venue that provides neutral ground where auto and 

truck gatekeepers can routinely exchange information about new technologies would provide additional stimulus for the technology transfer process. 

Conclusions

DOE actions that were seen as particularly helpful in catalyzing technology transfer include these: 

• Support of dual-use (truck and auto) programs 

and forums on neutral ground 

• Development of economic justifications for both 

truck and auto applications 

• Investment in the demonstration of technologies 

at first tier suppliers serving both industries 

• Involvement of both truck and auto OEMs in 

those programs 

• Generation of long-term performance data under 

conditions appropriate for both trucks and autos 

• Involvement of industry crossover organizations, such as the U.S. Council for Auomotive 

Research 

DOE staff have been briefed on these results and 

are considering how DOE might best facilitate technology transfer of lightweight materials between the 

truck and auto industries. 
High Strength Weight Reduction Materials FY 2004 Progress Report 

143 

5. LIGHTWEIGHT VEHICLE STRUCTURES 

A. Lightweight Stainless Steel Bus Frame―Phase III 

Principal Investigator: J. Bruce Emmons 

Autokinetics Inc. 

1711 West Hamlin Road, Rochester Hills, MI 48309 

(248) 852-4450; fax: (248) 852-7182; e-mail: jbemmons@autokinetics.com 

Technology Development Area Specialist: Sidney Diamond 

(202) 586-8032; fax: (202) 586-1600; e-mail: sid.diamond@ee.doe.gov 

Field Technical Manager: Phillip S. Sklad 

(865) 574-5069; fax: (865) 576-4963; e-mail: skladps@ornl.gov 

Contractor: Autokinetics Inc. 

Contract No.: 4000010114 

Objectives 

• Investigate and demonstrate the mass savings potential of ultra-high-strength stainless steel as applied to the 

structure and chassis of a full-size urban transit bus. 

• Finalize design and analysis and build a full-scale prototype of the body structure and chassis. 

• Investigate all of the fundamental feasibility issues related to the structure and chassis: 

1. Fabricate and test large lightweight stainless steel sandwich panels 

2. Fabricate roll-formed, high-strength stainless steel sections 

3. Test the feasibility of lightweight stainless steel cantilever seats 

4. Design and fabricate lightweight stainless steel independent suspension 

5. Integrate the traction motors into the suspension design 

Approach 

• Execute the basic body structure, including the floor and roof sandwich panels, pillar assemblies, longitudinal 

rails, and suspension subframes. 

• Choose prototyping techniques that emulate the intended production process as closely as possible to aid in developing robust but cost-effective manufacturing techniques essential to meeting the objectives of the project. 

• As computer-based design and analysis details of the bus develop, conduct hands-on physical experimentation 

in parallel to support the concepts and methods. 

Accomplishments 

• Completed building a specialized resistance welder for joining sandwich panel segments. 

• Assembled the floor structure, including all floor sandwich panel segments and subframe subassemblies. 

• Assembled the roof structure, including all roof sandwich panel segments. 

• Produced a report documenting design enhancements for manufacturability. 

• Produced and documented fixture strategy for main assembly. 
FY 2004 Progress Report High Strength Weight Reduction Materials 

144 

• Completed assembly of primary structure. 

• Fabricated and assembled window and doorframe components. 

• Fabricated and assembled front and rear body end sheet metal components. 

• Created computer-aided design (CAD) model for seat design. 

• Conducted finite element analysis (FEA) for seat design. 

• Produced a report documenting side impact analysis results. 

• Performed a physical test of crash energy absorber tubes. 

• Received delivery of traction motors, inverters, and inverter software (propulsion components) 

• Modified design of suspension geometry for compatibility with new motor. 

• Modified design of suspension components for compatibility with new motor. 

• Provided support for independent cost analysis. 

Future Direction 

• Assemble closeout panels. 

• Complete the fabrication and installation of suspension, steering, and spring components. 

• Fabricate driver controls. 

• Prototype two seats. 

• Assemble propulsion components. 

• Testing of structure. 

Introduction

Advanced-technology transit bus concepts have 

made significant advancements in terms of low 

weight and fuel economy. However, these gains 

have come at the expense of higher manufacturing 

costs. In spite of attempts to use life-cycle costs to 

justify their purchase, initial cost remains a major 

obstacle to the introduction of fuel-efficient buses. 

Autokinetics was approached by DOE for help 

with solving this problem. Specifically, Autokinetics 

was asked to develop concepts for a lightweight urban transit bus based on the use of high-strength 

stainless steel. In the passenger car field, Autokinetics had developed structural and manufacturing 

techniques for the cost-effective use of stainless steel 

in spaceframes and suspensions. DOE wanted to 

determine whether this approach could be applied to 

transit buses as well. 

The program was structured in three phases: 

• Phase I—Initial Concept Development 

• Phase II—Concept Verification and Initial Design 

• Phase III—Final Design and Prototyping of 

Body and Chassis 

Phase I and Phase II have been successfully 

completed. Phase III will result in a full-size body 

structure and suspension that will be tested statically 

and dynamically. The development of an optimized 

hybrid powertrain and other vehicle systems will be 

addressed in a separate project. 

This project was unusual in that no formal mass 

or cost targets were given. The object was to save as 

much mass and cost as possible. 

Specialized Segment Welder

Preliminary welding tests indicate that the panel 

segments can be successfully joined together using 
High Strength Weight Reduction Materials FY 2004 Progress Report 

145 

resistance welding. This approach utilizes a joint 

configuration that reduces complexity and the need 

for extremely tight tolerances. To create a prototype, 

spot welds need to be placed along the nearly 8-ft 

seam between panel segments. 

To accomplish this, a special spot-weld gun was 

required that could reach at least halfway across the 

floor and roof. The design of this welder was reported on previously. A special support and backup 

structure were fabricated and fitted with conventional transformer gun components. This arrangement is shown in Figure 1. 

Figure 1. Specialized segment welder.

Special contact tips were also designed and fabricated to accommodate the slightly different configuration of the joint between the subframe and 

floor panel. As the joining of the panel segments 

progressed, the contact tips and the welding techniques were refined.

Floor, Roof and Primary Assembly

A major milestone was achieved as the primary 

body structure was assembled during this reporting 

period. 

The primary structure framing sequence shown 

in Figure 2 consists of three main elements. First, the 

floor panel components, including subframes, are 

located on the framing platform and joined together 

forming a completed floor assembly. 

Figure 2. Primary structure framing sequence. 

Next all side pillars and door frames are positioned and attached to the floor assembly. Positioning is controlled vertically by the floor, laterally by a 

taut wire running along the side, and longitudinally 

by a measured distance. The use of a simple temporary support aid maintains the pillar in a plumb orientation. 

Finally, the roof segments are hoisted into position and brought to rest on the pillar brackets. At this 

point, all roof segments are joined, forming a completed roof assembly. The pillars are then attached to 

the roof in a similar manner as with the floor. 

It was determined that a number of variations on 

this theme were possible. One such variation, to preassemble roof segments into three sub-assemblies, 

was used for the purposes of this prototype build. 

This reduced the amount of hoisting and overhead 

welding. Another was installing the door frames after the roof assembly was complete. 

Relative position between roof and floor assemblies was monitored throughout this sequence and 

found to be virtually self-locating. Figure 3 is a photograph of the completed primary structure. 

 Figure 3. Primary structure. 
FY 2004 Progress Report High Strength Weight Reduction Materials 

146 

Front and Rear End Sheet Metal

During this reporting, the sheet metal components, which close out the front and rear ends of the 

body, were fabricated and installed onto the primary 

structure. These components were fabricated to incorporate some design refinements for improved 

NVH (noise, vibration, and harshness) characteristics. For example, the lower edge of the rear window 

and front windshield apertures were reinforced, and 

the sheet gage of the seat pan, compartment bulkheads, and fascia was increased from .030 to .050 in. 

In Autokinetics’ judgment, improved NVH qualities 

gained by these refinements more than offset the 

slight weight increase. 

For prototype purposes, the large sheet components were fabricated in halves and joined along the 

vehicle centerline. This would not be necessary in 

series production. 

Figures 4 and 5 are photographs of the completed body end sheet metal. 

Figure 4. Rear end sheet metal. 

Figure 5. Front end sheet metal. 

Seat Design

Beginning with the initial passenger seat concept, a detailed design sufficient for prototyping was 

created. As shown in Figure 6, the design is a cantilevered type, which attaches by special brackets to 

two adjacent body pillars. On the seat side, each 

bracket is attached to a lateral beam. The arrangement is such that the brackets are rigid, movementcarrying connections. Therefore, vertical seat loads 

are transmitted into the pillar as bending loads. 

Figure 6. Front end sheet metal. 

Completing the design are two L-shaped end 

caps connecting the lateral beams, and perforated 

sheet forming the seating surface. A reinforcement 

pan is attached between the end caps to control local 

flexing of the seating surface. The entire seat structure will be fabricated in stainless steel and is expected to be lightweight and durable and exhibit 

very little deflection under normal load. 

An FEA model was constructed to verify load 

capacity and predict deflections. A proof load of 

1500 lb was applied to represent a 3-g loading condition with two 250-lb passengers on the seat. The 

plot shown in Figure 7 indicates the material will 

remain below yield, while deflection (including pillar deflection) will be on the order of 1.75 in., measured vertically at the most inboard edge of the seat. 

Crash Energy Management System

The crash energy management system, based on 

the principle of inverting stainless steel tubes to absorb crash energy, was described previously. During 

this reporting period, physical energy-absorbing 

(EA)) tubes were produced and tested. 
High Strength Weight Reduction Materials FY 2004 Progress Report 

147 

Figure 7. FEA model of passenger seat design. 

Autokinetics has specially constructed a machine that applies a force axially to a given tube and 

measures that force in real time as the tube is 

worked into an inverted state. Several such EA tube 

tests were performed on the physical specimens and 

data were collected. 

The tube inversion process inherently results in 

a very uniform, constant force. The level of this 

force can be set during design by adjusting certain 

parameters such as the diameter and wall thickness 

of the tube. A force level of about 12,000 lb per tube 

(there are 12 tubes in the front-end system) was chosen as the most appropriate for protecting the occupants of both the bus and the impacted vehicle. 

The crash energy management system is well 

suited for a front-end and rear-end crash event. 

However, of particular concern for a “low-floor” bus 

is the side impact crash event. The cause for concern 

is the fact that bumper of the impacting vehicle will 

strike the bus several inches above the floor. As a 

result, the pillars must engage the impacting vehicle 

and carry the load into the floor without excessive 

intrusion (3 in. is allowed). 

 To address this concern, a linear FEA model 

(shown in Figure 8) was constructed to roughly predict load capacity and deflection. It was determined 

that reinforcement of the lower inside portion of the 

pillar would be required to manage the load satisfactorily. In addition, a bumper engagement rail was 

added along the exterior to ensure a distribution of 

the load application. With these modifications, 

model data were prepared and sent to Oak Ridge 

National Laboratory (ORNL) for a more refined 

nonlinear analysis capable of predicting deflection 

beyond the elastic range of the structure. The ORNL 

analysis, while promising, indicates that more spot 

welds will be required to prevent detachment of the 

pillar reinforcement. Other detail design changes 

may also be required to fully meet the requirement. 

Additional funding will be required for ORNL to 

complete this additional analysis. 

Figure 8. FEA model for side impact study. 

Suspension /Driveline (New Motor)

With the vehicle body structure nearing completion, a greater emphasis has shifted to the suspension 

and driveline. 

As reported previously, traction motors and controllers were ordered from PreMag; however, PreMag experienced difficulty in molding the stators 

and was unable to deliver the motors in a timely 

manner. Therefore, the decision was made to implement a contingency plan to pursue an alternate 

motor supplier. 

Discussions were initiated with UQM. A motor 

currently being produced by UQM, the PowerPhase75, was identified as an appropriate selection. 

Recently developed technology allowing the power 

of the motor to be upgraded contributed to this decision. The first prototype bus will use the current 

PowerPhase75, with the intent to use the upgraded 

version in future buses. 

Because the PowerPhase75 is physically different in size and shape from the PreMag motor, a 

study was conducted to identify any packaging issues. A number of “short-coupled” and hubmounted concepts were explored. It was found that 

with some modification to the suspension design, the 

motors could be hub-mounted. This avoids consid-
FY 2004 Progress Report High Strength Weight Reduction Materials 

148 

erable complexity associated with the short-coupled 

or right angle drive approach. 

Given this information, Autokinetics selected 

the UQM PowerPhase75 and the hub-mounted configuration as the mainstream approach. Motors and 

controllers were ordered from UQM and delivered 

during this reporting period. 

The rear suspension design was adjusted to accommodate the increased length of the UQM motor. 

This required modifications to the upper and lower 

control arm as well as the knuckle designs. The 

modified rear suspension corner is shown with the 

new motor in Figure 9. 

Figure 9. Rear suspension with UQM motor. 

Dissemination and Commercialization

10/21/03―Meeting with Advanced Transportation Technology Institute (ATTI). Attended by Phil Sklad, Dick 

Ziegler, Richard Smith, (ORNL) and John Powell 

(ATTI). 

11/18/03―Emmons attended DOE workshop “Tooling 

Technology – Low Volume Vehicle Production.” 

12/05/03―Presentation to DOE: Entrepreneur John 

Friedl’s business plan to manufacture commercial vehicles using Autokinetics’ structure technology. 

3/10/04―Meeting with Transportation Design and Manufacturing Co. A discussion of hybrid systems integration 

was attended by Doug Mann and Greg Vanover. 

3/04/04―Meeting with Ricardo, Inc. Louis Infante (V.P., 

vehicle engineering) attended an introduction to the technology. Infante reviewed structural issues with a current 

project and expressed interest in the technology. 

3/19/04―Meeting with Ricardo. Follow-up meeting attended by Mick Winship and Abhay Bhivare. 

4/13/04—UQM press release announced UQM’s participation in the project. This statement was subsequently 

posted on the FreedomCAR website at 

http://www.eere.energy.gov/vehiclesandfuels/news/fcvt_

news_042004.shtml 

5/06/04—Meeting with IBIS Associates to initiate information gathering for its cost analysis. Attended by Tony 

Mascrin (IBIS) and Phil Sklad (ORNL). 

6/10/04—Commercialization discussion (under nondisclosure agreement). 

6/15/04—Commercialization discussion (under nondisclosure agreement). 

6/18/04—Emmons presented a project review at ORNL 

for Dr. Sidney Diamond (DOE). 

9/28/04—Commercialization discussion (under nondisclosure agreement). 

Conclusions

Autokinetics remains confident that highstrength stainless steel has the potential to achieve 

significant mass reductions of bus structures. The 

bus body structure is now nearly complete; most of 

the identified technical risk issues have been resolved, and only moderate mass gain has occurred 

compared with early predictions. Ongoing fabrication of the physical prototype has provided concrete 

mass numbers, and we now expect the actual mass 

reduction for the complete vehicle to be close to 

50%. 

It is also hoped that practical commercialization 

can be achieved in the not-too-distant future. Low 

capital investment and an ample knowledge base are 

key enablers for commercialization. Much has been 

learned thus far about processing and assembling the 

body structure, and many useful techniques have 

been developed. Given the relative ease of constructing this prototype within our own facility, it is quite 

apparent that capital requirements for commercializing this technology will be relatively small. It is anticipated this will be illustrated by the independent 

cost analysis commissioned by DOE. 
High Strength Weight Reduction Materials FY 2004 Progress Report 

149 

B. Stainless Steel Bus Structure—Manufacturing Cost Analysis 

Principal Investigator: Anthony E. Mascarin 

IBIS Associates, Inc. 

1601 Trapelo Road, Suite 164 

Waltham, MA 01720 

(781) 290-040; fax: (781) 290-0454; e-mail: tony@ibisassociates.com 

Technology Development Area Specialist: Sidney Diamond 

(202) 586-8032; fax: (202) 586-1600; e-mail: sid.diamond@ee.doe.gov 

Field Technical Manager: Philip S. Sklad 

(865) 574-5069; fax: (865) 576-4963; e-mail: skladps@ornl.gov 

Contractor: IBIS Associates, Inc. 

Contract No.: 4000030946 

Objectives 

• Provide the bus development program with manufacturing cost analysis and economic understanding to plan a 

technology and application development strategy. 

• Assess the cost of conventional bus structure fabrication. 

• Assess the cost of the proposed stainless steel structure. 

• Explore the impact of key design and process assumptions. 

• Characterize the potential commercial value of the concept. 

Approach 

• Collect data for scenario and process definition. 

• Assemble defining part and process data 

• Develop simulation model structure 

• Conduct baseline and scenario analyses and comparisons 

Accomplishments 

• Collected data on conventional bus manufacturing and visited production facilities. 

• Completed model development and scenario designs. 

• Presented side-by-side cost comparison of stainless steel concept to incumbent practice. 

• Analyzed sensitivities to annual production volume, throughput, assembly time, etc. 

• Assessed capital requirements, purchase facility investment, and scale-up schedule. 

Future Direction 

• Modify analyses to account for floor, skin, and roof. These are integral to the stainless steel bus concept but not 

part of the conventional bus structure. Including them will further improve the side-by-side economics 
FY 2004 Progress Report High Strength Weight Reduction Materials 

150 

• Assess the impact of powertrain and interior systems. 

• Analyze life-cycle and usage costs in terms of fuel, operation, and maintenance costs. 

Introduction 

 DOE, in conjunction with Autokinetics, is 

pursuing a design and process technology development program for alternative metropolitan bus structure manufacturing. Central to the effort is the 

stainless steel roll-formed design concepts developed by Autokinetics. Key to the success of this 

program is a demonstration of commercial viability: 

reduced piece cost, lower capital investment, or improved lifecycle economics relative to incumbent 

practices. Based on process and design scenario information provided to IBIS from the DOE/ 

Autokinetics team, IBIS has evaluated the alternative design concepts for these structures and provided an analysis of manufacturing economics. This 

analysis seeks to quantify the commercial production economics of the design and production techniques developed by Autokinetics relative to 

incumbent practices for conventional bus manufacturing. 

Bus Structure Scenarios

The basis for comparison of the conventional 

bus structure to the stainless steel concept is a 40-ft, 

low-floor metropolitan transit bus. 

In summary, the stainless steel concept involves 

a floor and roof composed of three-layer panels 

made from welded outer skins and a corrugated, rollformed core. Roll-formed pillars, rails, and sills 

complete the skeletal structure. Wheel wells and 

front and rear cap assemblies are welded from brake 

or press formings. The structure is assembled using 

spot welding. 

Conventional manufacturing involves laborintensive arc welding of tube stock. Sides, floors, 

roofs, and front and rear end units are made separately in subassembly cells on semi-dedicated fixtures (which can be modified for bus length). After 

final structure assembly, the frame is subjected to 

grit blasting and a zinc phosphate coating. 

Model Development

Existing models of automotive body-in-white 

manufacturing were used as the starting point for the 

bus structure technical cost model. This format has 

the capability to efficiently track the high piece 

count of individual components involved. IBIS collected additional roll-forming process data and specific stainless steel alloy material properties to 

update earlier information already in possession. 

The assembly operations, specifically the customdesigned panel fabrication, were defined in terms of 

commercial production-rate equipment. 

Separate model structures were constructed for 

conventional and roll-formed designs. Conventional 

manufacturing, relying principally on purchased 

tube stock, is modeled as a series of assembly cells. 

It accounts for material cost as the total of purchased 

components for each subassembly. A roll-formed 

structure, on the other hand, is modeled on the basis 

of each roll forming, with a major assembly operation into a unitized structure. 

Data Collection

Data used in the technical cost models were collected through interviews and site visits with many 

sources, principally existing transit bus and motor 

coach manufacturers. These include New Flyer, Advanced Bus Industries, North American Bus Industries, Gillis, Orion, and Motor Coach Industries. 

Equipment manufacturers and municipal transit authorities also provided useful information. Autokinetics provided design information for the stainless 

steel concept. 

Analyses

For comparison and simulation manageability, 

operations for each scenario were grouped as shown 

in Figures 1 and 2. The resulting cost comparison 

and sensitivities are shown in Figures 3 and 4. 
High Strength Weight Reduction Materials FY 2004 Progress Report 

151 

 Figure 1. Conventional process flow.

 Figure 2. Stainless steel concept flow. 

 Figure 3. Cost comparison table.

Figure 4. Cost comparison chart. 

Conclusions 

In addition to the weight savings gained from 

the stainless steel design (current numbers show approximately 1000 lb, not including additional savings of hundreds of pounds of flooring, skins, and 

roof already integral to the structure), the manufacturing economics of the stainless steel design are 

compelling. The combination of the novel design 

approach, using roll forming and high-rate spot 

welding (instead of arc welding), allows for a reduction in assembly labor and fixturing to offset the 

much greater material price of stainless steel relative 

to the steel tube stock. 

As the program moves into the next phase of 

demonstrating a working powertrain, the extended 

benefits of the lightweight structure on reduced 

power requirements and secondary mass savings can 

be explored. The economic analysis can also be employed to demonstrate to potential manufacturers the 

specific capital requirements needed for commercializing the proposed concept. 
FY 2004 Progress Report High Strength Weight Reduction Materials 

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High Strength Weight Reduction Materials FY 2004 Progress Report 

153

C. Side Impact Analysis of a Lightweight Stainless Steel Bus Structure 

Principal Investigator: Srdjan Simunovic 

Oak Ridge National Laboratory 

P.O. Box 2008, MS-6164 

(865) 241-3863; fax: (865) 574-7463; e-mail: simunovics@ornl.gov 

Technology Development Area Specialist: Sidney Diamond 

(202) 586-8032; fax: (202) 586-1600; e-mail: sid.diamond@ee.doe.gov 

Field Technical Manager: Philip S. Sklad 

(865) 574-5069; fax: (865) 576-4963; e-mail: skladps@ornl.gov 

Contractor: Oak Ridge National Laboratory 

Contract No.: DE-AC05-00OR22725 

Objective 

• Model and assess the structural performance of a lightweight stainless steel bus structure (LSSBS) during a side 

impact by a sport utility vehicle (SUV). 

Approach 

• Conduct the impact analysis simulation using finite element method (FEM) computer analysis. 

• Develop a detailed model of a central five-column-long section of the LSSBS to model the area of collision, 

with two semi-rigid components on each end of the deformable section representing the remainder of the bus. 

• Simulate a side impact collision scenario using LS-DYNA on supercomputers at the Oak Ridge National 

Laboratory Center for Computational Sciences. 

Accomplishments 

• Developed the detailed model of the center section of the LSSBS, including key structural features of the bus 

relevant to the side impact. The simulations showed overall satisfactory structural response. 

Future Direction 

• Use the results of the study to modify the bus design to reduce the damage and intrusion resulting from the 

collision and analyze the design modifications using the same approach. 

Introduction

The ultralight stainless steel urban bus concept 

was developed by Autokinetics, Inc.1

 with the 

objective of demonstrating the feasibility of a 

stainless steel structural design for weight reduction 

in mass-transit vehicles. The resulting bus employs 

high-strength stainless steels and monocoque design 

to simultaneously achieve the weight reduction and 

maintain or surpass the performance of conventional 

bus designs. The bus body structure is shown in 

Figure 1. 

Bus performance with respect to torsional and 

flexural rigidities and axial impact has been 

investigated using computational models. However, 

side-impact response has not been fully addressed 

yet; it is the subject of this research. A collision 

scenario that is considered to be a good measure of 

the side-impact performance of the bus is an impact 

of a mid-size SUV-class vehicle into the half span of 
High Strength Weight Reduction Materials FY 2004 Progress Report 

154

Figure 1. Ultralight stainless steel bus 

structure. 

the bus. SUVs usually have a high ground clearance, 

and an SUV chassis may not coincide in height with 

the bus floor. In the case of the current design, it 

would obviously be desirable to transfer the impact 

loads into the rigid floor as efficiently as possible 

without allowing for a significant intrusion into the 

bus passenger space. The other essential structural 

component that comes directly into contact with the 

impacting vehicle is the lower reinforcement rail. 

This rail is supposed to distribute the impact force 

between the neighboring pillars. The bus floor and, 

to a lesser extent, the roof are the final destinations 

of the SUV impact load. In order to achieve a 

controlled load transfer into the floor and roof, it is 

necessary to maintain reasonable stability of the 

pillars and the reinforcement rail. Joints connecting 

pillars into the floor/roof must distribute the load 

very quickly without creating local instabilities or 

joint failure. Figure 2 shows the pillar joint with the 

roof. 

Location, geometry, and bonding of the joint 

brackets are important for local load transfer; 

therefore, it is necessary to model them in sufficient 

detail to determine the local stability of the 

connection. Detailed computational models have 

been developed to adequately address these issues 

and provide a basis for further performance 

investigations that require high-resolution, nonlinear 

FEM analysis. 

Development of the FEM Model

The finite element model of the bus structure 

involves several steps. The basic geometry of the 

Figure 2. Pillar joint detail. 

bus was provided by Autokinetics in the IGES 

format. The geometry data are used to generate 

surfaces that are used as projection targets for the 

FEM mesh generation. The data were provided for a 

single typical section (‘segment’) of the structure; 

Figure 3 shows the segment model. Repeated 

reflections and translations are used for the 

generation of the model used in the analysis. 

Figure 3. ViewPoint surfaces of bus ‘segment’ model. 

The integrity of the body structure is provided 

almost exclusively by spot welds. Therefore, in 

order to create a realistic model for side impact it 

was essential to include them in the model. The 
High Strength Weight Reduction Materials FY 2004 Progress Report 

155

location of the spot welds was provided in IGES 

format. A graphical representation of this data is 

shown in Figure 4. 

Figure 4. Spot welds in the bus segment. 

The FEM model was developed using the spot 

weld locations as key locations for the mesh 

generation so that the locations of the spot welds 

exactly match the locations specified in the IGES 

geometry. The developed FEM model for the ten 

base segments, where spot weld locations are 

denoted by black dots, is shown in Figure 5. 

Figure 5. FEM model; black dots denote locations of 

spot welds. 

FEM Simulations of Side Impact

The FEM model of the bus consists of a 

representative section and approximations of the 

front and rear of the bus. The approximate parts are 

modeled as stiff, elastic materials that approximate 

the areas of the bus that are not going to deform in 

the impact and provide vertical support relative to 

the ground of the bus assembly. Ideally, the actual 

bus geometry could have been modeled, but it was 

not available at the time of model creation. 

Figure 6 shows the entire analysis model of the 

bus used in the analysis. This model has 287680 

nodal points, 280148 shell elements, and 34567 

beam elements. 

Figure 6. Finite element model of the LSSBS concept.

The FEM model used in the study of the side 

impact analysis includes a ‘bullet’ vehicle. For this 

analysis, the bullet vehicle is an 1998 Explorer 

SUV.2

 The representation of the merged busExplorer model is shown in Figure 7. Two cases 

have been considered for the impact analysis: the 

first one considers the case when the center (across 

the width) of the SUV engages the bus at a pillar 

location, and the second case considers the case 

when the center of the SUV engages the bus at the 

midpoint between pillars. Figure 7 shows the model 

of the first case. 

The combined model has 427675 nodal points, 

281102 hexahedral elements, 414942 shell elements, 

280677 beam elements, and 8653 spot welds. 

The analysis considers the impact of the SUV 

traveling at 25 mph at the time of engagement with 
High Strength Weight Reduction Materials FY 2004 Progress Report 

156

Figure 7. Finite element model for the SUV-LSSBS 

impact at column. 

the stationary bus. The analysis has been performed 

using the computer program LS-DYNA.3

The following paragraphs discuss the results of 

the analysis performed to assess the bus integrity 

when the SUV traveling at 25 mph impacts the bus 

so that the center of the SUV is between the two bus 

pillars. 

The configuration of the model at a time when 

the elastic deformation of the bus reaches a 

condition of quasi-steady state is shown in Figure 8. 

At this point in the analysis, the SUV–LSSBS 

assembly moves as a rigid body, and very little 

relative deformation is imposed upon the bus 

structure beyond the end time of the analysis. 

The intrusion into the bus body, defined as the 

reduction in width between the outward pillar and 

the corresponding pillar near the point of impact, 

was calculated. Two locations along the height of 

the pillar were chosen for the determination of this 

parameter: at the vertical level that corresponds to 

the bumper height of the bullet vehicle, and at the 

sill level of the bus window opening. Figure 9 shows 

the time history of these intrusion measurements. 

The top curve corresponds to the bumper height 

location; the lower curve corresponds to the sill 

location. Final intrusion values are 195 mm and 

145 mm at the bumper height and sill level 

locations, respectively. 

Figure 8. Side view (top) and top view with roof 

panels removed (bottom) of model configuration 

at end of simulation. 

Figure 9. Width measured between columns at center 

column line. 

The integrity of the bus structure can be 

evaluated in terms of the ability of the brackets to 

maintain the connection between the floor assembly 

and the lower pillar sections. Failure of the spot 

welds at the bracket interface between the floor 

plates and the lower section of the pillar 

compromises the integrity of the structure, as most 

of the stiffness of the assembly depends on the 
High Strength Weight Reduction Materials FY 2004 Progress Report 

157

integrity of the side components. The analysis shows 

that the lower row of spot welds can fail in the 

vertical leg of the top brackets that connect to the 

pillar. The analysis also shows that the connection 

between the horizontal legs of the bracket that 

connects to the top floor plate undergoes relatively 

large deformation. This is attributed to the topology 

of the spot welds at this interface; only the inner part 

of the horizontal part of the bracket is attached to the 

floor plate. The result is a cantilever mode of 

deformation for the bracket. Potential improvement 

in the performance of the structure could be 

achieved if additional reinforcement were provided 

between the horizontal section of the lower bracket 

and the floor rail and between the horizontal section 

of the top bracket and the roof rail. Another possible 

design modification is reinforcement of the pillar. 

The corresponding design modifications will be 

addressed in the continuation of the study. 

Conclusions 

We have developed an FEM model for the 

structural analysis of a side impact against a LSSBS. 

Results of the study point to areas that may 

warrant some design modifications in order to 

reduce the damage and the intrusion of the SUV into 

the LSSBS. The model can be further refined to 

allow for more accurate simulation and flexibility 

for modeling of different loading situations. 

References 

1. J. B. Emmons, and L. J. Blessing, “Ultralight 

Stainless Steel Urban Bus Concept,” SAE Technical 

Paper 2001-01-2073, Government/Industry Meeting, 

Washington, D.C., 2001. 

2. G. Aramayo, “Parametric Finite Element 

Model of a Sport Utility Vehicle: Development and 

Validation, in Proceedings of the 7th International 

LS-DYNA Users Conference, Dearborn, MI, 2002. 

3. J. O. Hallquist, DYNA-Keyword User’s 

Manual, Version 970, LSTC, April 2003. 
High Strength Weight Reduction Materials FY 2004 Progress Report 

158
High Strength Weight Reduction Materials FY 2004 Progress Report 

159 

D. New-Generation Frame for Pickup/Sport Utility Vehicle Application 

Principal Investigator: Curt A. Lavender 

Pacific Northwest National Laboratory 

P.O. Box 999, M/S K2-03, Richland, WA 99352 

(509) 372-6770; fax: (509) 375-4448; e-mail: curt.lavender@pnl.gov 

Kurt M. Knop 

DaimlerChrysler Corporation 

14250 Plymouth Road 

Detroit, MI 48227 

(313) 659-6076; fax: (313) 635-5221; e-mail: kmk4@daimlerchrysler.com 

Technology Development Area Specialist: Sidney Diamond 

(202) 586-8032; fax: (202) 586-1600; e-mail: sid.diamond@ee.doe.gov 

Field Technical Manager: Philip S. Sklad 

(865) 574-5069; fax: (865) 576-4963; e-mail: skladps@ornl.gov 

Contractor: Pacific Northwest National Laboratory 

Contract No. DE-AC06-76RLO 1830 

Objective 

• Evaluate the design of an optimized hybrid materials frame that represents a new generation of pickup/sport 

utility vehicle (PU/SUV) frame applications and vehicle architecture. 

Approach 

• Apply high-risk manufacturing and design methods to the PU/SUV frame to reduce mass while meeting cost 

goals consistent with a high-production vehicle. 

Accomplishments 

• Established performance, packaging, and weight targets for the second iteration of the new-generation frame, 

“the next-generation frame” (NGF). 

• Created a design for the NGF that projects a greater weight reduction and a decrease in the number of parts 

compared with the current steel baseline frame. 

• Created a computer-aided engineering (CAE) model of the NGF to evaluate impact; noise, vibration, and harshness (NVH); and durability. 

• Completed CAE and design iterations to meet impact, NVH, and durability requirements. 

• Successfully demonstrated the “5-star” crash rating. 

• Established a preliminary cost estimate for frame production and prototyping. 

• Established initial cost estimates for the frame that are 12% higher than the current frame with a 200-lb weight 

savings. The initial cost projections are favorable and are being evaluated in more detail. 
FY 2004 Progress Report High Strength Weight Reduction Materials 

160 

Future Direction 

• Construct the full NGF frame and perform vehicle testing to validate the CAE-designed NGF. 

• Complete prototype frame component design and procure parts for DCX assembly. 

• Validate the CAE analysis by DCX in a full-frame test to be determined by identifying needs from CAE testing. 

Introduction

Increased consumer demand for PUs/SUVs has 

resulted in increased fleet fuel consumption, and the 

trend toward consumer demand for PUs/SUVs has 

been predicted to increase. By 2005 the fuel demand 

for this class of vehicle will exceed that for passenger automobiles.1, 2 The objective of this project is to 

explore manufacturing methods and materials to reduce the mass of the SUV/PU frame, thereby reducing fuel consumption for this class of vehicle. 

During the second quarter of FY 2003, DaimlerChrysler completed vehicle testing at the DCX 

Proving Grounds using an SUV/PU platform 

equipped with a hybrid frame. Results of the accelerated testing have proved that (1) the hybrid frame 

design had sufficient strength and durability to meet 

the vehicle performance requirements, and (2) the 

frame was probably somewhat overbuilt and heavier 

than required, even with a substantial weight savings 

over the current baseline steel frame. 

The next phase of the project will evaluate the 

use of a lighter frame, the NGF (Figure 1). The NGF 

uses a CAE approach and higher-risk manufacturing 

technologies. The projected weight for the NGF is 

less than that for the previously tested newgeneration frame, and it requires 35% fewer components. 

Approach

A CAE model of the NGF was created and design iterations were performed to meet the NVH, 

impact, and durability requirements for a DCX 5-star 

rating. A prototype of the frame will be fabricated 

and evaluated by frame flexure and road tests. 

Figure 1. Next-generation frame design. 

Progress

CAE analyses of the frame are completed and 

have satisfied all requirements for impact, NVH, and 

durability analyses. Owing to the large section 

height of the aluminum extrusions, intrusion into the 

passenger compartment during impact analysis 

proved to be the most challenging problem. 

 Complete CAE impact analyses (like those 

shown in Figure 2) have been reiterated upon and 

reduced the intrusion into an acceptable range. A 

full 5-star rating has been attained with only minor 

frame modifications. Intrusion into the vehicle is 

measured in terms of the maximum displacement of 

the vehicle into the passenger compartment. The 5-

star rating is achieved when all intrusion values are 

below a “good” rating as determined by DCX safety 

review. Reiteration on the original NGF design has 

resulted in all values below the “good” rating, as 

shown in Figure 3. 
High Strength Weight Reduction Materials FY 2004 Progress Report 

161 

Figure 2. Frontal impact analysis of the NGF. 

The aluminum frame complicates the design for 

intrusion because of the increased section size. The 

aluminum extrusions are 5 cm taller than the steel 

frame sections. In order to have an equivalent intrusion, the NGF must be designed not to deflect as 

much as the steel version. The actual magnitude of 

deflection at each passenger compartment location, 

shown in Figure 3, indicates that the additional 5 cm 

of frame height reduces the allowable deflection of 

the frame by approximately 30% in locations where 

a total intrusion of 15 cm is allowed. 

The design of the frame has been completed, and 

a bill of materials (BOM) has been created and used 

for prototype and future production cost quota 

Figure 3. Intrusion measurements for 40% offset frontal 

impact for the NGF. 

tions. Initial cost analysis shows that a 200-lb savings can be achieved with a 12% cost penalty. Additional analyses of cost and re-design for production 

will be performed. 

Future Direction

The CAE/design for the NGF is complete, a 

BOM has been created, and a suitable frame that 

shows a weight savings of 200 lb has been proposed. 

The next step in the frame project will be validation 

of the CAE results through full-scale vehicle testing 

and frame flexure tests. A prototype frame will be 

fabricated, and flexure will be tested by twisting. 

After flexure testing, the full-scale frame will be 

assembled into a DCX vehicle platform and evaluated on the test track for durability and driver-felt 

comfort and performance. 

References

1. EIA Annual Energy Outlook 2002, 

DOE/EIA-0383 (2000), Energy Information Administration, December 2001. 

2. Transportation Energy Data Book: Edition 

21, ORNL-6970, Oak Ridge National Laboratory, 

September 2001. 
FY 2004 Progress Report High Strength Weight Reduction Materials 

162 
High Strength Weight Reduction Materials FY 2004 Progress Report 

163 

E. Lightweight Trailer—Liburndas Project 

Principal Investigator/Team Leader: Travis McCloud 

Heil Trailer International 

1125 Congress Parkway, Athens, TN 37303-0160 

(423) 745-5830; fax:(423) 745-1943; e-mail:tmcloud@heiltrailer.com 

Co-Team Leader/Marketing Liaison: Bill Harris 

Heil Trailer International 

5741 Cornelison Rd, 6400 Bldg A, Chattanooga, TN 37411 

(423) 855-3492; fax:(423) 855-3459 ; e-mail:bharris@heiltrailer.com 

Technology Development Manager: Sidney Diamond 

(202) 586-8032; fax: (202) 586-1600; e-mail: sid.diamond@ee.doe.gov 

Field Technical Manager: Philip S. Sklad 

(865) 574-5069; fax: (865) 576-4963; e-mail: skladps@ornl.gov 

Contractor: Heil Trailer International 

Contract No.: 4000027094 

Objective 

• Reduce the net weight of an aluminum tank semi-trailer by 20% by using a cylindrical design and assimilating 

available composite technology for functional components. 

Approach 

• Develop a new frameless vessel design incorporating a new cross-section, flangeless heads, and internal rings. 

• Optimize design through finite element analysis (FEA) and testing. 

• Explore existing composite accessories. 

• Conduct a focus group and a marketing study, including a campaign for the new design. 

• Complete a manufacturing study, including a labor rate analysis. 

• Manufacture and test prototype. 

Accomplishments 

• Completed vessel and bogie (run gear suspension frame) design. 

• Completed FEA of vessel and bogie. 

• Completed evaluation of friction stir welding samples. 

• Completed initial testing of flangeless, dishless head design. 

• Defined and approved loading head parameters. 

• Completed focus group. 

• Started marketing and manufacturing study. 
FY 2004 Progress Report High Strength Weight Reduction Materials 

164 

Future Direction 

• Complete fifth-wheel design and FEA. 

• Complete accessory design and FEA. 

• Validate possible composite accessories. 

• Complete manufacturing study and marketing report. 

• Manufacture prototype and conduct track test. 

• Conduct marketing and sales campaign. 

Introduction 

 The Liburndas Project is Heil Trailer International’s effort to design and build an aluminum 

semi-trailer for petroleum products that is lighter, 

stronger, and safer than any before it. By using a 

cylindrical cross section and assimilating composites 

into select trailer components, Heil’s Research and 

Development (R&D) Group proposes to reduce the 

aluminum tank semi-trailer’s net weight by 20 %. 

 Just changing the geometry of the vessel by redesigning it to a cylindrical shape will allow a reduction in shell thickness and elimination of 

historical strengthening structures that have plagued 

equipment with parasitic mass. This new design will 

also lower the center of gravity (CG) by 25–30%, 

which enhances the safety of the trailer with respect 

to roll-over potential (see Figure 1). 

Figure 1. New concept petroleum trailer.

 Investigating a new aluminum alloy for weight 

reduction in areas not regulated by the U.S. Department of Transportation (DOT) is an objective of the 

project as well. Areas such as the frame rails for the 

suspension and fifth-wheel plate are valid candidates. Although some weight savings is possible, 

this is secondary to the contributions the new cylindrical design and composite accessories will make to 

Heil’s overall weight reduction goals. 

 Accessories made from composites are critical 

to meeting weight reduction goals and will ultimately reduce the mass of the trailer and improve 

corrosion resistance. This project’s purpose is not to 

create or test a new composite for these areas. Existing composites will be explored that have proved 

successful in the market. Areas that are likely candidates for composites are fenders, cabinets, hose 

holders, ladders, and suspension support structures. 

 Although a successful vessel design and notable 

composite integration will result in reaching weight 

reduction goals, it is paramount to the project’s success that the market accept the new design. Because 

of the competitive nature of the market, data will be 

collected covertly, without divulging the new 

trailer’s design or benefit. Therefore, the marketing 

study initially will determine acceptable envelopes 

for piping and discharge outlets, as well as conduct a 

preliminary commercial viability study based on the 

design’s limits and/or restraints. A marketing campaign to bolster product acceptance will take place 

near the end of the project. The initial marketing 

study began during Phase 1 of the project and should 

be completed before the first prototype is built. The 

marketing campaign will take place during Phase 3 

(after the successful field testing of the second prototype) and should result in orders for production 

models. 

 A successful product resulting from this project 

would allow carriers to safely deliver 2000–2500 lb 

more payload per trip, ultimately reducing the daily 

average number of miles required to deliver product 
High Strength Weight Reduction Materials FY 2004 Progress Report 

165 

by about 1%. On a national level (the current population of petroleum tank trailers is approximately 

50,000 units), this could equate to over 200,000 

miles per year saved, or 30,000 gallons of fuel per 

year.

Vessel Design

Cross Section 

 An important part of Heil’s new design concept 

for its petroleum trailer is the cross section of the 

vessel. In today’s petroleum trailers, the most common cross section used is an elliptical shape, used to 

lower the overall height and center of gravity of the 

trailer. Since petroleum trailers are not unloaded or 

loaded with pressure, the elliptical shape works well. 

 When the structure of a petroleum trailer’s vessel is studied, it is simply analyzed as a supported 

beam with reactions at the suspension and kingpin 

plate. This condition places the bottom of the trailer 

vessel in tension and the top in compression. The 

advantage of a round cross section under these loads 

is that the radius of the top is tighter or smaller and 

therefore more resistant to buckling under the compression loads. This allows the shell thickness of the 

vessel to be thinned, compared with an elliptical 

cross section, and thus saves weight and material. 

 Even though petroleum trailers are not pressurized, they do occasionally see some low vacuum or 

pressure differentials during loading and unloading. 

Today’s trailers are equipped with vents to prevent 

damage to the vessel if this condition becomes excessive. In the event of a vent failure, a round vessel 

is more likely to survive a pressure or vacuum overload, whereas an elliptical vessel will tend to fail. 

 A round vessel is therefore stronger, lighter, 

safer, and more stable than an elliptical vessel for an 

equivalent cross sectional area. The only advantage 

of an elliptical trailer is its overall lower height and 

center of gravity. Designing a round vessel with a 

drop center can offset this advantage (Figure 2). 

Drop Center Design 

Dropping the center of the vessel in relation to the 

front and rear not only lowers the center of gravity 

but also causes the lateral center of mass to stay near 

the longitudinal center of the trailer, as shown in 

Figure 3. 

Figure 2. Height and center of gravity comparison. 

Figure 3. Drop center design. 

 Federal weight laws call for manufacturers to 

design trailers with equal loads on the tractor’s drive 

axles and the trailer’s suspension. By designing a 

lower front and rear end section of the vessel, we 

can engineer the trailer so that the mass is equally 

distributed over the rear of the trailer (bogie) and the 

tractor’s rear axles. 

Elimination of Surge Heads 

 Petroleum tank trailers are designed to DOT 406 

specifications as found in the Code of Federal Regulations Title 49. Section 178.345-7 of this code discusses circumferential reinforcements in trailers and 

mandates that the maximum unreinforced portion of 

the vessel’s shell not exceed 60 in. Traditionally, 

this has been accomplished in petroleum trailers 

through the use of surge heads or baffles. These 

surge baffles are the same heads that separate the 

trailer’s compartments, but they have holes formed 

in them to allow product to flow through them. 

These surge baffles help with the surge of the product during acceleration and deceleration and serve as 

the circumferential reinforcements. 

 Replacing these surge baffles with an adequately 

designed internal ring can achieve a considerable 

weight savings. However, rings will not help with 

product surge, and drivers will have to be trained to 

handle the “feel” of the tank in certain road condi-
FY 2004 Progress Report High Strength Weight Reduction Materials 

166 

tions. The market’s opinion (business owners and 

drivers) on internal rings and their advantages and 

disadvantages will be one of the topics for the focus 

group and marketing study. 

Liquid trailers without surge baffles are not uncommon in the chemical and food industry, where 

the cleanability of the inside of the trailer is important. Drivers in these industries have learned to drive 

safely without baffles; therefore, it is anticipated that 

the weight benefits will outweigh the surge issue. It 

should also be noted that there is no product surge 

when a trailer is completely full or empty. 

Flangeless, Dishless Heads 

A new concept with regard to the vessel design 

is being applied to the Liburndas Project. This is a 

redesign of the compartment heads that separate different commodities in a petroleum trailer. These 

heads are typically dished and flanged bulkheads 

that are connected to the shell via a single fillet 

weld. The Liburndas vessel will use a flangeless, 

dishless head, which will be connected to the shell 

via two fillet welds. A Pro-E model of the head is 

depicted in Figure 4. 

Figure 4. Flangeless head concept. 

The Liburndas vessel is a perfect application for 

the flangeless head—it is lighter, the welds are 

stronger, the strength is comparable, and the manufacturability is more precise than for the current 

style head. The flangeless head is much easier to 

manufacture and should offset part of the cost of the 

composites. One of the goals of marketing goals is 

to ensure that the R&D group’s new design—lighter, 

stronger, and more stable—does not cost more than 

the market will bear for those benefits. This offset 

strategy should keep the price of the new design 

within acceptable limits for the market. 

Heil has been working on forming techniques 

for this new head with the Alcoa Technical Center 

and has already conducted preliminary testing of a 

“simulated” prototype head at its Athens, Tennessee, 

R&D facility. The prototype head can be seen in 

Figure 5. Initial testing was promising, and advanced prototypes are planned for continued testing. 

Figure 5. Flangeless head test vessel. 

Framing 

The final design and FEA of the bogie frame has 

been successfully completed. It eliminated some 

framing requirements (and weight) for both bogie 

and vessel structure mounting compared with current framing designs. The Liburndas bogie design 

can be seen in Figure 6 below. 
High Strength Weight Reduction Materials FY 2004 Progress Report 

167 

Figure 6. Liburndas bogie frame. 

 The bogie frame is one of the most critical design areas for a petroleum trailer. The vessel experiences not only loads from the force of gravity acting 

on the payload but also loads due to articulation or 

twisting as it maneuvers over the road around corners. Consequently, a leak due to weld fatigue would 

most likely occur in this area. To simulate road conditions, FEA on the frame was completed for four 

load cases: (1) 2-G downward, vertical inertial; (2) 

2-G forward, horizontal inertial; (3) 1-G lateral, 

horizontal inertial (10-ton axle load traveling around 

curves); and (4) 1-G lateral horizontal inertial load 

(turning on the spot). 

The initial analysis indicated that the mild steel 

crossmember structure gave cause for concern with 

unacceptable stress levels under the load cases specified. However, the initial FEA model did not take 

into account the link of the top crossmember to the 

frame or the correct welding techniques. After further review and FEA remodeling, the bogie frame 

design actually experienced acceptable stress levels. 

To confirm our results, the bogie frame design was 

also tested by Hendrickson, the air ride suspension 

manufacturer. Hendrickson conducted similar FEA 

modeling and confirmed our final test results. 

Overturn Rails/Vapor Manifold 

 Finally, the vessel design will eliminate the need 

for overturn rails on the top of the trailer. The overturn rails act as guards to prevent a manhole from 

opening during a rollover situation. The flashing 

rails also act as a manifold for vapor collection and 

recovery during the loading and unloading of a 

trailer. A significant amount of weight can be saved 

by the successful elimination of the rails. It can be 

done with the installation of recessed manholes, 

which are widely used in Europe (see Figure 7). 

Figure 7. Recessed manhole. 

 Vapor collection and recovery will be completed 

using internal vapor lines that drop down through 

each compartment from the manholes. Lines will be 

manifolded outside and under the vessel. This configuration has been successfully designed and tested 

by Heil in Europe. Its application to the Liburndas 

vessel will save approximately 400 lb, the weight of 

both flashing rails. 

Vessel Weight Reduction 

 To date, the total weight reduction goals are as 

follows: from the shell, 15%; from the heads, 20%; 

by eliminating the overturn/flashing rails, 20%. The 

remaining 45% will come from the framing and accessories design. 

Friction Stir Welding

 During the project, Heil is also working closely 

with Oak Ridge National Laboratory to determine 

the feasibility of applying friction stir welding 

(FSW) to the manufacturing process for the Liburndas vessel. The most likely area will be the large, 

flat aluminum sheets that make up the barrel proper 

(currently done on a plasma table). FSW samples 

have been collected, along with both gas tungsten 

arc and gas metal arc samples, and bend and tensile 

testing will begin this phase. 
FY 2004 Progress Report High Strength Weight Reduction Materials 

168 

Marketing 

Focus Group 

 Heil invited five customers representing a cross 

section of the industry (major oil companies, jobbers 

and common carriers) to participate in a focus group 

this past October. The customers in attendance were 

positive and encouraged by the information presented. They ranked their needs and wants as follows: first, the capability to haul more payload; 

second, better operational efficiency; finally, a design as safe as, if not safer than, than current trailers. 

As anticipated, an increase in payload capability 

was the customer’s number one requirement for the 

new design. If afforded the capability to haul more 

product, they can increase revenue on a per-load 

basis and reduce maintenance and operational expenses over the life of the trailer. 

Although recessed manholes were not seen as an 

advantage to the customer, they would be “tolerated” if they created the weight savings advertised. 

Concerns exist over weather caps, internal drains, 

and internal vapor piping that would exist with the 

manholes. 

The customer’s operational and safety requirements may drive a redesign of the accessory location 

and possibly the vessel diameter. Currently, the Liburndas cabinet and accessories are located at the 

rear of the trailer, which would be unacceptable to 

the operators. It was determined during the focus 

group that the operators’ perceptions of the new design will have an important bearing on the success 

of the Liburndas trailer in the market. 

The low belly height was actually a concern because of the potential for side collisions, which was 

perceived to outweigh the advantages of a lower 

center of gravity. The trailer may perform better in a 

rollover situation, but it may be more susceptible to 

loss of load in a side impact collision. The customers 

in the focus group recommended we limit the 

amount of drop to 50% of the planned design and 

move the accessories to the side of the vessel. This 

would make the trailer operationally acceptable and 

still improve on the safety of the existing trailer in 

the market. 

The project leader is considering reducing the 

major diameter and increasing the minor end tube 

diameters to maintain capacity and provide more 

room for accessories on the side of the trailer, the 

typical location for accessories in today’s trailers. 

Conclusions 

 Excellent progress has been made on the vessel 

and bogie design and FEA during the first year of 

the project. Design and FEA of the fifth-wheel plate 

are now on schedule and should be completed by the 

end of the month. All Phase 1 deliverables should be 

completed by the end of the year, according to the 

project schedule. 

 Continued study and testing will take place on 

the flangless head design. Once a die is acquired and 

actual test heads are constructed, mock-up prototype 

testing will be completed. It is anticipated that the 

flangeless head design will be very successful, 

which will accelerate the project into Phase 3—field 

testing of a prototype. 

 The marketing research completed to date reflects initial acceptance of the new design, with the 

exception of the existing accessory locations. 

Redesign of the accessories will take place quickly 

over the next month. Market acceptance of the cylindrical design, flangeless heads, and internal rings 

will make the Liburndas trailer a viable alternative 

to and inevitable replacement for the elliptical 

trailer. Once it is in the market, the popularity of the 

trailer is expected to increase exponentially because 

of its improved fuel delivery capabilities and roll 

stability. 
High Strength Weight Reduction Materials FY 2004 Progress Report 

169

6. APPLICATION OF INNOVATIVE MATERIALS 

A. Advanced Materials for Friction Brakes

Principal Investigator: P. J. Blau 

Oak Ridge National Laboratory 

P.O. Box 2008, Oak Ridge, TN 37831-6063 

(865) 574-5377; fax: (865) 574-6918; e-mail: blaupj@ornl.gov 

Technology Development Area Specialist: Sidney Diamond 

(202) 586-8032; fax: (202) 586-1600; e-mail: sid.diamond@ee.doe.gov 

Field Technical Manager: Philip S. Sklad 

(865) 574-5069; fax: (865) 576-4963; e-mail: skladps@ornl.gov 

Contractor: Oak Ridge National Laboratory 

Contract No.: DE-AC05-00OR22725 

Objectives 

• Identify, test, and analyze the friction and wear characteristics of advanced materials and surface treatments 

that enable weight reduction in truck brake components while equaling or bettering their performance. 

Materials of interest include intermetallic alloys, ceramic composites, titanium alloys, and novel surface 

treatments. 

Approach 

• Design and build a subscale brake material testing apparatus to investigate the friction and frictional heating 

characteristics of advanced materials at speeds and contact pressures similar to those in full-sized brakes. 

• Investigate the nature of changes to the surfaces of materials that occur as a result of frictional contact under 

high energy input conditions—especially the formation of friction-induced films. 

• Evaluate friction and thermal characteristics of candidate lightweight materials for heavy vehicle brakes. These 

include titanium alloys and ceramic matrix composites. 

• Examine the characteristics of brake material wear particles, an environmental consequence of braking. 

• Understand and model frictional energy dissipation and apply that knowledge to the evaluation of advanced 

brake materials. 

Accomplishments 

• Selected and tested a variety of metals, ceramics, and composite materials with the potential to serve as 

lightweight brake components. Down-selected two material systems, titanium-based materials and ceramic 

composite materials, for further study during the coming year. 

• Worked with a visiting university faculty member to understand and model frictional heat partition. 

• Evaluated the effects of wear testing methodology on the relative wear rankings of a series of commercial brake 

lining materials. Identified the role of entrapped wear particles in affecting these rankings. 

• Compared the frictional characteristics of two titanium-based disc materials with those of two ceramic 

composite disc materials using several candidate lining materials. Compared results with traditional cast iron 

combinations. 
FY 2004 Progress Report High Strength Weight Reduction Materials 

170

Future Direction 

• Evaluate currently available commercial coatings and explore new coating technologies for use on titanium 

alloys for lightweight brake rotor materials. 

• Understand the role of particle loading on friction performance and thermal transport in candidate titaniumbased composites. 

• Identify lining materials that are frictionally compatible with advanced disc materials. 

Introduction 

Advanced aerodynamic designs and tires with 

lower rolling resistance can improve fuel efficiency 

of trucks. However, as these approaches decrease the 

drag forces on trucks, the demands on truck braking 

systems increase. Brake engineering involves 

design, instrumentation and controls, and materials 

development. This project specifically addresses the 

latter. Brake materials must exhibit a balance of 

properties, including frictional stability over a wide 

temperature range, appropriate thermal properties, 

dimensional stability, corrosion resistance to road 

deicers, and wear resistance. From a practical 

standpoint, they must also be cost-competitive. 

Opportunities exist to employ advanced materials to 

create lighter-weight braking systems that will 

enable new technologies to raise the fuel efficiency 

of a vehicle without compromising its safety and 

reliability. 

This project addresses the science and 

engineering of advanced structural materials and 

surface treatments that show potential as truck brake 

friction materials. Testing of such new materials is 

made more cost-effective by using small specimens 

to screen the most promising candidates. To this 

end, a subscale brake tester (SSBT) was designed 

and built. It was instrumented to measure normal 

force, friction force, surface temperature, and 

vibrations during braking. An attachable water spray 

system enables study of the effects of wet and dry 

braking. The SSBT has been a workhorse in recent 

studies involving a variety of both traditional and 

nontraditional brake materials. Analysis of SSBT 

results is supplemented by optical microscopy, 

electron microscopy, and transmission electron 

microscopy of friction-induced films. 

Selection of Candidate Materials

Studies of the structure, composition, and 

physical properties of candidate materials have 

eliminated those with low softening points, brittle 

behavior, corrosion sensitivity, and environmentally 

unacceptable wear byproducts. A list of the 

materials evaluated, along with comments on their 

advantages and disadvantages, was presented in the 

FY 2003 Annual Progress Report. Table 1 provides 

a summary of the materials tested to date. Most of 

the disc materials, particularly the composites, are 

not mass produced; therefore, special samples were 

Table 1. Candidate friction material combinations

Disc specimen material Mating material(s) 

Traditional gray cast iron Jurid 539 disc brake lining 

Performance friction carbonmetallic pad (type 10) 

Armada AR2, AR4, AR5 

drum brake lining materials 

SiC particle–reinforced 

aluminum alloy 

(Al-MMC) 

Specially formulated lining 

for Al-MMC (Plymouth 

Prowler) 

Fe3Al intermetallic alloy Jurid 539 disc brake lining 

Ceramic composite 

(C/SiC)—GE Power 

Systems, LLC 

Jurid 539 disc brake lining 

Same material as the disc 

Ceramic composite 

(SiC/Si)—Redunndant 

Materials 

Same material as the disc 

Ceramic composite 

(C/SiC)—Starfire Systems 

Carbon felt composite 

Copper-carbon composite 

Titanium alloys (Ti-6Al4V, and Ti-6Al-2Sn-4Zr2Mo)—TIMET 

Jurid 539 disc brake lining 

Titanium matrix 

composite (TiC)—

CermeTi C-10, Dynamet 

Tech 

Jurid 539 disc brake lining 

Performance friction carbonmetallic pad (type 10) 

Thermally-sprayed 

titanium—Red Devil 

Brakes 

Metallic and semimetallic 

pads materials supplied by 

Red Devil Brakes 
High Strength Weight Reduction Materials FY 2004 Progress Report 

171

purchased specifically for our tests. The sliding 

partners (linings) for the disc materials were selected 

based on factors such as comparison with similar 

linings tested against cast iron, recommendations 

from suppliers, and materials having thermophysical properties that made them likely partners 

for given disc materials. 

After evaluating the materials in Table 1 from an 

overall performance and cost standpoint, we decided 

to limit our studies to (1) titanium-based alloys, 

including composites and coated alloys, and (2) 

ceramic composites that had shown encouraging 

results both in our work and in limited vehicle 

braking tests. 

During FY 2004, dozens of experiments were 

conducted to characterize the effects of speed and 

contact pressure on the friction coefficient and 

frictional temperature rise for both titanium-based 

and ceramic composite disc materials. Results are 

summarized in the following sections. Polished cross 

sections of the materials were examined to document 

their structure, and thermal property measurements 

were made for use in modeling. 

Titanium-Based Disc Materials

Titanium-based materials offer higher 

temperature resistance and better corrosion 

resistance than aluminum-based composites, but 

they are not widely used in brakes. In fact, the 

current applications for titanium lie mainly in 

automotive racing (Red Devil Brakes Co., Mt. 

Pleasant, Pennsylvania). Disc friction surfaces of the 

titanium alloys are thermal-spray-coated. Such 

materials were included in our investigation using 

fully metallic pad materials supplied by Red Devil 

Brakes. 

It was also of interest to determine whether 

noncoated titanium alloys could be used for brake 

discs. Therefore, we purchased titanium-based 

composite material discs from Dynamet (Burlington, 

Massachusetts) whose CermeTi materials contain 

hard particles in a titanium alloy matrix. 

Figures 1 and 2 summarize friction data on the 

effects of sliding speed and contact pressure on the 

friction of titanium-based disc materials against 

several pad materials. Figures 1 and 2, respectively, 

show data for 150 N and 300 N applied force. Data 

for Jurid 539 against gray cast iron (GCI) are also 

plotted for comparison. 

Figure 1. Effect of sliding speed on the friction of 

several titanium-based disc materials (low applied 

force). 

Figure 2. Effect of sliding speed on the friction of 

several titanium-based disc materials (high applied 

force). 

Friction coefficients for the various 

combinations spanned a relatively wide range, 

depending on applied conditions. Other things being 

equal, the lower the friction coefficient, the more 

applied force is required to produce the same 

stopping distance. 

At both levels of applied force, the highest 

friction coefficients were obtained from Jurid 539 

sliding on GCI; those for the other material 

combinations, involving titanium-based discs, 

tended to be about 1⁄2 to 3⁄4 as high. However, these 

results must be viewed with the understanding that 

our tests do not simulate every aspect of actual truck 
FY 2004 Progress Report High Strength Weight Reduction Materials 

172

braking characteristics. Transfer films seemed to be 

more difficult to create on the nonferrous materials 

and took place over a period of time. To 

precondition the surfaces before taking data, we 

began with coarsely abraded surfaces and ran a 

series of conditioning stops. Surface engineering 

may be required to facilitate transfer film formation, 

and that subject remains for further investigation. 

In general, to obtain the higher levels of friction 

typical of commercial materials sliding on cast iron, 

it was necessary that the disc materials be 

frictionally heated until they became very hot. This 

temperature characteristic is both an advantage and a 

disadvantage. The advantage is that titanium-based 

materials seem less prone to ‘fade’ (loss of braking 

at high temperature) and in fact probably behave 

better at high temperature. The disadvantage is that 

the titanium brakes tend to run hotter than cast iron 

brakes, and thermal management would need to be 

applied in order to use them effectively. Use of 

vented rotors or other designs to induce forced 

cooling in the wheel well are other options for 

addressing that issue. 

Ceramic Composite Disc Materials

Ceramic composite materials (CCMs) have been 

of interest for high-energy braking applications such 

as high-speed trains, race cars, and highperformance sports cars. Their low density offers the 

potential for significant weight savings; their high 

hardness suggests wear resistance; and their hightemperature resistance is attractive. However, the 

costs and special procedures associated with 

processing, handling, and finishing CCMs have been 

significant impediments to their widespread use. 

CCMs were included in this project to assess any 

relative performance benefits over titanium materials 

or conventional materials. Furthermore, there have 

been limited field trials of lightweight CCM brakes 

that showed up to 8% fuel economy savings on a 

GM sports utility vehicle. 

Carbon/SiC ceramics were previously tested 

under a joint project with GE Power Systems. Now 

we are working with two other CCM suppliers: 

Starfire Systems (Malta, New York) and 

Redunndant Materials, Inc. (Clarence Center, New 

York). Test discs were purchased from both of these 

companies. Previous experience from the GE carbon 

composites program indicated that good results 

could be obtained from self-mated sliding 

combinations. In addition, two candidate lining 

materials were provided by Starfire Systems (a 

carbon-felt composite and a carbon-copper 

composite). Using the same testing protocols as for 

the titanium-based materials, a series of friction tests 

were performed on CCM combinations. Results are 

summarized in Figures 3 and 4. 

Figure 3. Effect of sliding speed on the friction of 

various CCM disc/lining material combinations at 150 

N force. 

Figure 4. Effect of sliding speed on the friction of 

various CCM disc/lining material combinations at 300 

N force. 

Several trends are evident from the data in 

Figures 3 and 4. The friction coefficients of the 

CCMs tend to decrease as the sliding speed 

increases. This is somewhat unexpected, because for 
High Strength Weight Reduction Materials FY 2004 Progress Report 

173

carbon-based brakes, like those used in racing and 

aircraft brakes, friction tends to increase with 

severity of use (repeated braking or high-pressure 

application that increases the brake temperature). 

Second, the copper-carbon lining material against 

the Starfire Systems materials produced better 

results than the carbon felt. Recent discussions with 

Starfire engineers suggest that further improvements 

are possible using a new pad formulation against 

their CCM, and ORNL is in the process of obtaining 

this material for further testing. 

The SiC/silicon material prepared by 

Redunndant Materials had the highest friction 

coefficients at both low and high pressure, but it 

suffered from brittleness resulting from the layers of 

silicon within the composite. 

Temperature Modeling

While this report has primarily addressed results 

from friction measurements, considerable data on 

temperature rises were also obtained for analysis. 

One measure of the efficiency by which the energy 

of braking is converted into heat is the thermal 

conversion parameter (Qf) defined here as follows: 

Qf = c(ΔT/Fx) 

where ΔT is the temperature rise of the disc 

specimen surface during a constant speed drag, F is 

the average measured friction force, and x is the 

distance slid during the drag. The constant c is a 

function of the testing geometry and the fact that 

only the heating of the disc is considered, not the 

heating of the pad as well. Qf can be thought of as 

the efficiency of a given rotor material to covert 

frictional work (Fx) into a certain surface temperature rise (ΔT). The higher Qf, the more readily the 

frictional work of braking translates into the heating 

of the disc surface. Table 2 lists experimentally 

obtained values for several of the material combinations. For example, for our particular testing 

configuration, Jurid 539 against CermeTi discs 

results in (5.9/1.1 =) 5.36 times more temperature 

rise per unit of frictional work than Jurid against 

GCI. 

Table 2. Thermal conversion parameter (Qf) for various material combinations (300 N test results)

Disc material Sliding partner Qf 

(

o

C/N-m) 

GCI Jurid 539 1.1 × 10–3

GCI Perf. friction 1.5 × 10–3

CermeTi C10 Jurid 539 5.9 × 10–3

CermeTi C10 Perf. friction 6.7 × 10–3

Red Devil Ti Pad type 14 15.4 × 10–3

Starfire CCM Carbon felt 17.6 × 10–3

Starfire CCM Copper carbon 12.4 × 10–3

Redunndant CCM Redunndant CCM 2.70 × 10–3

During the summer of 2004, ORNL was joined 

by Timothy Ovaert, University of Notre Dame. He 

analyzed several current models for heat partition in 

braking and developed a new model that allows 

estimation of the partitioning of heat between the 

slider (pad) and rotor. His model will be used during 

FY 2005 to help understand the implications of 

relative heat transfer characteristics when optimizing 

material combinations for brakes. 

Conclusions

Studies have been conducted of a variety of 

candidate lightweight truck brake materials. Of 

these, titanium alloys offer a number of attractive 

characteristics, but their low thermal conductivity 

and wear behavior must be considered as well. The 

use of surface coatings or treatments is expected to 

enable the materials to perform quite well as brakes. 

Further work in FY 2004 is planned to better 

understand the friction and wear behavior of 

titanium alloys and to evaluate several alternative 

coating methods for rotor surfaces. 

Publications

M. Mosleh, P. J. Blau, and D. Dumitrescu, 

“Characteristics and Morphology of Wear Particles 

from Laboratory Testing of Disk Brake Materials,” 

Wear 256, 1128–34 (2004). 

J. Qu, P. J. Blau, T. R. Watkins, O. B. Cavin, 

and N. S. Kulkarni, “Friction and Wear of Titanium 

Alloys Sliding against Metal, Ceramic, and Polymer 

Counterfaces,” Tribology International, accepted for 

publication (2004). 
FY 2004 Progress Report High Strength Weight Reduction Materials 

174
High Strength Weight Reduction Materials FY 2004 Progress Report 

175 

B. Advanced Composite Structural Cab Components 

Principal Investigator: Michael A. Wieck 

Delphi Automotive Systems 

Delphi Steering Division 

3900 Holland Road, MDC-2 

Saginaw, MI 48601-9494 

(989) 757- 4283; fax:(989) 757-4295; e-mail: michael.a.wieck@delphi.com 

Technology Development Area Specialist: Sidney Diamond 

(202) 586-8032; fax: (202) 586-1600; e-mail: sid.diamond@ee.doe.gov 

Field Technical Manager: Philip S. Sklad 

(865) 574-5069; fax:(865) 576-4963; e-mail: skladps@ornl.gov 

Contractor: Delphi Corporation 

Contract No.: 4000009401 

Objectives 

• Develop an advanced composite cab structural component for a Class 8 tractor: 

⎯ Develop the design, materials, and manufacturing process for using continuous-oriented, fiber-reinforced 

composites for affordable commercialization within 5 years of beginning the project. 

⎯ Reduce the existing mass by at least 30% from 22.8 to 15.96 kg. 

⎯ Meet or exceed the performance of existing materials. 

⎯ Meet customer target cost. 

Approach 

• Organize a value analysis/value engineering (VAVE) workshop to generate different options for design and 

manufacturing. 

• Develop finite element analysis (FEA) to develop and optimize design options. 

• Perform a process cycle study, make necessary panels, and study Class B surfaces. 

• Conduct design failure modes effects and analysis (DFMEA). 

• Construct prototype parts and verify the proposed design using a design validation (DV) test. 

• Release final designs, construct production tools, perform process failure mode and effects analysis (PFMEA), and 

undergo process validation (PV) of the production phase. 

• Commercialize and start production. 

Accomplishments 

• During the first half of the fiscal year, completed a proof-of-process study with generic block mold, which 

demonstrates the feasibility of infusing thin-walled laminates. Then completed a pre-PV study with production foam 

core and prototype composite mold for areas 3 and 4 of the lower B-pillar. 

• Completed DV testing of prototype components in full cab build. (Door slam test had gone through three life cycles 

and sustained no structural issues) Completed fastener torque studies in molded sample blocks. 
FY 2004 Progress Report High Strength Weight Reduction Materials 

176 

• Updated the system DFMEA with suppliers and customer. 

• Refined FEA models to include material properties from actual material test data, developed local composite 

reinforcements to improve stiffness, and studied the effect of processing tolerances for an affordable product. 

• Simplified construction in the air duct area by making the air duct a separate, post-mold fastened part. 

• Reduced metal usage by eliminating large steel plate and using more localized attachments with composite 

reinforcements. 

• Produced assembly drawings, CAD models, some design details, and specifications for quote packages. 

• Selected a production source for final assembly. 

• Reduced flange areas to 3 mm in thickness. 

• Performed cure-cycle study, made composite panels, conducted Class B surface activities. 

• Made plaques and part skins using a conductive gel coat to demonstrate elimination of post-mold spray conductive 

primer. Validated conductive gel coat to replace post-mold spray primer system (cost savings). 

• Finalized metal hardware material specifications. 

• Determined optimal machining process parameters (tool shapes, feeds, and speeds for drill/tap of composite laminate 

over metal hardware). 

• Created 2-dimensional (2D) lay-flat fabric patterns from 3D part geometry with slits and darts to minimize fabric 

shear and to optimize the overall fabric blank size. 

• Completed environmental testing. 

• Finished final design math model and process. 

Future Direction 

• Conduct PFMEA with sourced supplier and customer. 

• Finalize specifications, assembly, and detail drawings. 

• Release final design, release remaining production tools, and validate the production phase. 

• Begin production. 

Introduction 

Significant strides forward were made in 

FY 2004 on the Advanced Composite Cab 

Structures project. Within Delphi, the project moved 

from a development activity to an implementation 

team; and with the progress outlined in this report, 

both cost and mass targets were achieved. 

To accomplish the project objectives, the 

Delphi-led team replaced the present production 

liquid-compression-molded two-component postbonded assembly made of non-oriented chopped 

fiberglass with a single resin-transfer-molding 

(RTM) processed foam core structure enclosed with 

a thin laminate of oriented and continuous-length 

fiberglass. 

Design and Process Failure Modes and 

Effects Analysis

A system-based DFMEA was initiated at the 

Delphi facility in early 2003 and was periodically 

updated as the production intent design was refined. 

It included a review at Delphi’s original equipment 

manufacturer (OEM) partner’s assembly plant with 

representation from engineering, quality, and 

purchasing. Another DFMEA was held in June 2004 

with the OEM engineers after the DV tests were 

completed. The suppliers of individual components 

and final molder have responsibility for performing 

PFMEA and creating process control plans after 

final sourcing. Delphi participates in each FMEA. 
High Strength Weight Reduction Materials FY 2004 Progress Report 

177 

Pre-PV Development: Resin Cure Times 

and Thin-Walled Infused Laminates

To determine the proper tooling and cure cycle, 

Delphi and Reichhold, a leading resin supplier, 

conducted multiple cure-cycle studies at Delphi’s 

Composite Lab in Salt Lake City. The goal was to 

make a resin recipe that would meet a requirement 

for a 22-min full-cure cycle at 120oF. Initial studies 

completed in February 2004 indicated that a 

processing temperature of 120oF for the cure cycle 

was possible. 

One of the major design obstacles of this project 

was the processing of thin (1.0–1.5 mm) laminates 

with RTM. Some of the concerns originated around 

tolerances and geometric stack-ups of all the 

components within the molded assembly. Secondary 

concerns included the response of the foam core, 

tooling, and hardware during infusion. Multiple 

layers of fabric and reinforcement were located 

between various foam cores. 

To expedite pre-PV development, we selected a 

small section of the molded assembly, rather than 

work with the complete assembly. Pre-PV 

development used results from early proof-ofconcept development. 

Proof-of-concept development used a 

rectangular box (4×6×16 in.), a cross section of 

which is shown in Figure 1. This shape closely 

represents one of the longest infusion sections of the 

actual component. The tool was designed to infuse 

the 16-in. length, with an injection and a vacuum 

port on opposite ends. The cover of the tool was 

made of clear glass to allow visual inspection and 

videotaping of the resin flow front. 

Figure 1. Proof-of-process mold block. 

Almost 50 individual infusion runs were 

conducted with very positive end results. In the 

course of the proof-of-concept study, it was 

determined that laminate thicknesses of less than 

1.5 mm were achievable. The limiting factors in 

achieving thin laminates were the tolerances of the 

tooling and the foam cores; but even on areas where 

the fabric was pinched because of irregularities or 

multiple plies, it was still possible to infuse. To 

maintain regular laminate thicknesses between the 

top and bottom surfaces, because of pressure 

gradients, special geometries were added to the foam 

cores. With respect to internal supports and multiple 

plies, the development showed a process that was 

able to fully infuse any of the combinations we were 

able to create. A close-up view of a proof-of-process

through-part reinforcement is shown in Figure 2. 

Figure 2. Close-up view of proof-of-process composite 

block with reinforcement. 

Other findings from process development were 

that pressure/vacuum values as well as the foam 

density were optimized. With a low-density foam 

core, vacuum assist, and low resin pressure, 

consistent processing results were obtained with few 

air voids and an infusion time of 1 minute. High 

pressure resulted in foam compression, allowing 

more resin into the part, and did not shorten the 

injection time. Finally, a modified resin with less 

inhibitor was used to allow the cure cycle (from 

mixing to cured part) to meet an acceptable cycle 

time (<22 minutes) at a heated tool temperature of 

<120°F. 

The next step in developing the pre-PV molding 

process was to build a larger tool with the actual part 

geometry (foam core areas 3 and 4) to ensure pre-PV 

process capability. Two production-level foam core 

tools were made to allow refinement of the process 
FY 2004 Progress Report High Strength Weight Reduction Materials 

178 

on an actual production geometry tool. Figure 3 

shows a view of an open aluminum-based RTM prePV tool. Figure 4 shows the first part made out of an 

aluminum-based pre-PV tool, and Figure 5 shows a 

cutout portion of a molded part section view from 

the aluminum pre-PV tool. The part was made using 

production-intent resin with a low inhibitor level and 

production-intent foam. The resulting composite part 

was very close to the targeted weight. 

Figure 3. Open view of aluminum-based RTM pre-PV 

tool for sections 3 and 4. 

Figure 4. First pre-PV part made out of aluminum-based 

RTM tool. 

Figure 5. A cutout portion of molded pre-PV part 

from aluminum tool. 

Hardware: Secondary Machining Operations

A key design element to minimize cost was 

insert molding of the metal fasteners into the foam 

cores. Another cost-saving method was to ensure 

that drilling and tapping time were optimized. To 

ensure optimal drill and tap cycle time after parts 

were made, a study was conducted. Figure 6 shows a 

robotic machine cell that was used to optimize the 

drilling method. Various drill bits and speeds were 

determined to help remove chips, and countersink 

methods were developed to avoid composite damage 

during tapping. 

Figure 6. Drill and tap time study fixture for hardware 

molded test block. 
High Strength Weight Reduction Materials FY 2004 Progress Report 

179 

Analytical Work—FEA and Fabric Pattern Development

The production design direction has been 

finalized, and FEA and CAD data files are 

undergoing final updates before production release. 

FEA indicates that all performance requirements 

will meet or exceed requirements. 

Fifteen individual fabric pieces are required in 

the molding operation. The initial lay-flat patterns 

developed did not drape well over the foam cores or 

into the molding tool. Alternative lay-flat software is 

being investigated. 

Cost Reduction: Conductive Gel Coat 

A systematic review of the final assembly cost 

indicated that masking, conductive spray primer, and 

finish were areas with great cost reduction potential. 

By implementing a conductive gel coating in the 

composite molding, preliminary estimates showed 

that finished assembly cost could be reduced by up 

to 10%. Delphi identified a conductive gel coat 

system that had already been approved by the OEM 

partner in other applications and fabricated flat 

panels representative of exterior part surfaces (see 

Figure 7) with this conductive gel coat. These 

samples were forwarded to the OEM partner for 

oven and environmental conditioning. Following 

this conditioning, surface finish and resistivity will 

be evaluated. 

Testing Activities

Fastener testing. Tests for torque and pullout 

load had been conducted on several M5 and M6 

threaded fastener designs in composite panels with 

steel plates. Other sizes were also tested according to 

their application category [e.g., Federal Motor 

Vehicle Safety Standard (FMVSS), heavy load 

bearing, interior to the door seal, exterior to the door 

seal]. 

The foam block with hardware after drilling and 

tapping can be seen in Figure 8. To ensure that new 

hardware will work, a study of hardware bonding 

and corrosion resistance were conducted. 

Torque and pullout load between composite and 

metal hardware embedded in foam was determined 

using various surface preparations for metal 

hardware. The torque fixture used for the study is 

shown in Figure 9. The purpose was to determine 

Figure 7. Exterior surface showing conductive gelcoat. 

Figure 8. Hardware molded block after drilling and tapping. 

that threaded fasteners meet FMVSS requirements. 

The results showed that all various surface 

preparations were acceptable for bonding with the 

proposed composite materials. 

Expansion testing. Blocks of the same 

composition of composite and foam design have 

been heated to process temperatures of 225oF for 
FY 2004 Progress Report High Strength Weight Reduction Materials 

180 

Figure 9. Torque test fixture for hardware molded test 

block. 

one hour with no effects on the part due to variations 

in expansion rate among the differing materials. 

Environmental testing. Environmental testing 

was conducted on both composite test blocks and 

cut-away sections of prototype parts (Figure 10). 

The effect on the foam, the hardware, and the 

laminate was determined. The results, as expected, 

verified that the foam and composite laminate 

construction protect the hardware from the 

environment and resist moisture penetration into the 

structure. 

Figure 10. Hardware molded block after corrosion. 

To meet the corrosion requirement, it was 

decided, with customer approval, to use stainless 

steel for machined and tapped holes outside the seal 

and carbon steel material in areas inside the seal. 

The corrosion resistance test was performed 

according to the OEM’s standard practice on drilled 

metal fasteners. The results showed that Dupont’s Ecoated steel exhibited similar result as current 

production parts. Since the cost difference was 

minimal, the team decided to use E-coat to keep 

with the customer specifications. 

Summary

These are the highlights for the progress during 

FY 2004. 

1. Reduced laminate thickness from 3.0 to 1.5 mm 

using 30% fiber volume with production-intent 

resin and process. The visual inspection looked 

good. Performed mechanical testing of the 

panels and used the test properties to refine the 

FEA model of the cab structure. 

2. Reduced component mass by 32% over current 

composite technology. 

3. In-molded hardware to meet process 

requirements. 

4. Proved 1.5-mm-thick molding process with area 

3 and 4 pre-PV tools using foams from 

production-intent 3 and 4 foam tools. 

5. Used in-mold conductive gel coating to reduce 

process steps and material cost of conductive 

spray primer. 

6. Successfully completed cab shake testing of the 

cab structure using VARTM thin-walled 

laminates over foam cores with embedded metal 

hardware. This same cab structure completed the 

final stages of DV testing, again with no 

failures. Torsion and pullout testing also have 

met specifications. 

7. Met all mass, performance, and cost objectives. 
High Strength Weight Reduction Materials FY 2004 Progress Report 

181

C. Advanced Composite Structural Chassis Components 

Principal Investigator: David E. Witucki, PE 

Delphi Corporation— Saginaw Steering Systems Division 

3900 Holland Ave., Saginaw, MI, 48601 

(989) 757-4984; fax: (989) 757-4295; e-mail:david.witucki@delphi.com 

Technology Development Area Specialist: Sidney Diamond 

(202) 586-8032; fax: (202) 586-1600; e-mail:sid.diamond@ee.doe.gov 

Field Technical Manager: Philip S. Sklad 

(865) 574-5069; fax:(865) 576-4963; e-mail:skladps@ornl.gov 

Contractor: Oak Ridge National Laboratory 

Contract No.: DE-AC05-00OR22725 

Objectives 

• Develop an economical, long-fiber–reinforced manufacturing procedure using continuous and/or oriented 

chopped fibers for structural chassis components for Class 7&8 trucks. 

• Reduce the mass of these components by 60%. 

• Commercialize and annually produce these components, reducing vehicle mass by about 50 kg/vehicle and 

significantly increasing North American carbon fiber demand annually, within 5 years of project commencement. 

Approach 

• Conduct value analysis/value engineering workshop(s) to conduct function analysis and brainstorm composite 

solutions to each component function. 

• Develop finite element analysis (FEA) models on both the component and system level. Conduct structural 

optimization (topology and shape/sizing) of components for “material-efficient” designs. 

• Build and test prototypes. 

• Secure production orders for the components developed within the scope of the project. 

Accomplishments 

• Received production purchase orders from two customers for four different models of composite tie rod tubes 

to be supplied by Delphi. Current total volume is approximately 6000 units per year. Samples have been 

supplied to three additional customers. 

• Presented the paper “Composite Tie Rods for HD Truck Applications” at the Society of Plastics Engineers 

(SPE), Automotive Composite Conference. In addition, this product was nominated for SPE’s Plastics 

Innovation award and has been named a finalist in the run for the award in the Chassis category. 

• Completed initial durability and stiffness testing on a “proof-of-concept” composite-reinforced, thin-wall steel 

tube main support. 

• Used composites research/design concepts to develop and commercialize an aluminum z-beam that resulted in 

over 27 kg mass savings per system. 

• Achieved 32 kg of the 50 kg target for system mass reduction with the combined mass savings of the composite 

tie rod tube and aluminum z-beam. 
FY 2004 Progress Report High Strength Weight Reduction Materials 

182

Future Direction 

• Continue investigation into lower-cost tie rod tube designs and processes. 

• Validate composite tie rod tube for higher-volume, front steer applications. 

• Investigate follow-up project for main support development with second tier-one chassis system supplier. 

Introduction

In response to a request for proposals from UTBattelle/Oak Ridge National Laboratory (ORNL) in 

February 2001, a submission from Delphi 

Corporation led to the award of a subcontract for the 

development of advanced composite structural 

chassis components with the objectives listed earlier. 

Sponsored by DOE, the duration of the 

subcontract is 3 years with an estimated cost of 

$2.5 million. This project is a 50/50 cost share 

between ORNL and industry. In this project, Delphi 

Corporation, the world’s largest automotive Tier 1 

supplier, partnered with an industry leading Tier 1 

supplier to the truck and trailer industry and focused 

on three components in a chassis/suspension system: 

lateral links, main supports, and z-beams. 

Composite Tie Rod Tube Status 

Through the third quarter of 2004, more than 

6000 carbon-fiber–reinforced tie rod tubes have 

been installed on passive-steer, auxiliary lift axle 

systems. Delphi has secured production orders for 

tubes of four lengths for two customers. Samples 

have been supplied to three additional customers. 

This tube was nominated for the SPE 

Automotive Division Innovation Award in the 

Chassis Category and was selected by SPE’s board 

of directors as a finalist. A formal presentation will 

be made to a blue ribbon panel composed of 

technical trade publication and industry experts for 

final evaluation. For more information on the SPE 

and the award program, visit http://www. 

speautomotive.com/inno.html. 

Production tooling has been released for a 

lower-cost tube assembly, and production-intent 

samples are currently undergoing validation testing 

for both auxiliary lift axles and front steer 

applications. Test results have been mixed so far; 

durability testing has been favorable, but buckling 

capacity has degraded with the new design. 

Additional samples are being fabricated with 

alternative lay-up and materials, and preliminary 

results have been encouraging. Unfortunately, these 

design changes are beginning to erode the original 

forecast of 20% cost savings for this design. 

Z-Beam Status

Delphi’s Tier 1 partner has introduced a cast 

aluminum z-beam based on FEA topology 

optimization completed for a composite design. 

Figure 1 illustrates both a preliminary composite 

concept and the similar final production aluminum 

design. The cast aluminum solution reduced the 

mass by approximately 7 kg and was at cost parity 

or below current welded steel designs. Since four zbeams are used in each system, 28 kg of total system 

mass was eliminated. 

Figure 1. Composite z-beam concept (left) and current 

production cast aluminum beam. 

Main Support Status

Testing has been completed on the first proofof-concept main support. This assembly consisted of 

a relatively thin-wall steel tube, welded-in end 

fittings, and epoxy/carbon fiber composite 

reinforcement. The test sample completed the side 

load test schedule but failed approximately twothirds of the way through the brake load schedule. 

The failure occurred in the welded joint between the 

inner steel tube and the end fitting (see Figure 2). It 

is anticipated that this can be overcome with a slight 

redesign to the interface of the metal parts and the 

addition of composite reinforcement around the end 

fitting.
High Strength Weight Reduction Materials FY 2004 Progress Report 

183

Figure 2. Proof-of-concept main support after side and 

brake load testing. 

Vertical stiffness measurements were taken of 

the baseline, current production steel main support, 

thin-walled steel tube, and final compositereinforced tube. Stiffness data are shown in Figure 3. 

The composite-reinforced axle beam very closely 

matched the stiffness of the baseline steel beam, 

validating the previous FEA and structural 

optimization efforts. 

Figure 3. Main support stiffness testing. 

The prototype proof-of-concept samples were 

26.3% lighter (20.9k kg or 46 lb) than the baseline 

and employed 5.9 kg (13 lb) of dry carbon fiber 

fabric. Further mass reduction is anticipated because 

the tubing selection for fabrication of the prototype 

was based on availability. The fully optimized 

design calls for thinner steel tubing. 
FY 2004 Progress Report High Strength Weight Reduction Materials 

184
High Strength Weight Reduction Materials FY 2004 Progress Report 

185

D. Carbon Fiber SMC for Class 8 Vehicle Hoods 

Principal Investigator: Nicholas A. Rini 

Volvo Trucks North America, Inc. 

P.O. Box 26115, Greensboro, NC 27402-6115 

(366) 393-2771; fax: (336) 393-2773; e-mail: nicholas.rini@consultant.volvo.com 

Cliff Eberle, Project Manager 

(865) 574-0302; fax: (865) 574-8257; e-mail: eberlecc@ornl.gov 

Technology Development Area Specialist: Sidney Diamond 

(202) 586-8032; fax: (202) 586-1600; e-mail: sid.diamond@ee.doe.gov 

Field Technical Manager: Philip S. Sklad 

(865) 574-5069; fax: (865) 576-4963; e-mail: skladps@ornl.gov 

Contractor: Volvo Trucks North America 

Contract No.: 4000010928 

Objective 

• Develop carbon-fiber (CF) sheet molding compounds (SMCs) and processing techniques that will enable serial 

production of Class 8 truck hoods with structural integrity, class A surface quality, significantly reduced mass 

and will be competitive in cost with existing glass-fiber SMC molded components. 

Approach 

• Accumulate material property data to establish reliable design properties that can be utilized for engineering 

design analysis. 

• Perform finite-element analysis of a CF SMC-based Class 8 hood design. 

• Evaluate consistency and repeatability of CF SMC material properties, processing techniques, and surface 

quality. 

• Evaluate mass savings and costs. 

• Confirm predicted results by constructing prototype hoods and performing accelerated endurance tests. 

Accomplishments 

• Designed, built, and used a development tool in CF SMC molding trials. 

• Successfully molded CF SMC materials in thicknesses ranging from 1.0 to 3.0 mm. 

• Attained CF SMC material for structural applications in near final form, exhibiting good molding 

characteristics and using manufacturing processes very similar to those for glass-fiber SMC. Costs are reduced 

by approximately 50% compared with currently available commercial CF bulk molding compound materials. 

• Performed initial work on CF SMC with Class A surface quality that has eliminated several proposed surface 

enhancement materials and processes. 

• Conducted adhesive bonding prescreening trials of the CF SMC structural material that have produced data 

indicating lap-shear values generally two times that of comparative glass-fiber SMC. 

• Completed preliminary cost and weight evaluations for the CF SMC hood. 
FY 2004 Progress Report High-Strength Weight Reduction Materials 

186

• Completed the design, procurement, building, and installation of a CF SMC compounding line to supply 

materials supporting this research and development project. 

• Built eight prototype hoods using existing production tools to evaluate processing characteristics of various 

combinations of lightweight SMC materials. 

Future Direction 

• Continue evaluation of CF materials and surface treatments from various suppliers. 

• Pursue cost reduction and supply stabilization of CF SMC materials. 

• Pursue low-density glass-fiber-reinforced materials and process developments to provide lightweight Class A 

surface quality exterior panels. 

• Use the CF SMC compounding line to produce CF materials to support ongoing development. 

• Follow up Class 8 truck hood costs and weights based on CF SMC material and process developments. 

• Evaluate CF SMC hood development status and determine if a business case can be made to pursue serial 

production of CF-reinforced heavy truck hoods. 

Introduction 

The mass of light automotive and commercial 

heavy-duty vehicles can be reduced using modern 

lightweight, high-performance composite materials. 

The reduction in vehicle mass translates into an 

increase in fuel efficiency. Currently, polymeric CF 

composites are used in low-volume, highperformance applications such as spacecraft, aircraft, 

and racecars. The CF-reinforced composites can 

reduce vehicle body mass by 40% to 60%. However, 

market conditions and technical barriers inhibit their 

use in high-volume automotive applications. 

Class 7 and 8 trucks offer a lower production 

volume, lower technical barriers, and financial 

incentives that can justify a modest price premium 

for competent lightweight materials. The aim of this 

project is to accelerate the commercial 

implementation of high-performance, lower-cost CF 

SMC material body components for Class 7 and 8 

trucks. As utilization of CF SMC develops and the 

technology matures, it is foreseeable that CF SMC 

will migrate into the high-volume automotive 

market. 

The project was initiated by performing a 

comparative finite-element analysis of a hood 

configuration made of glass-fiber SMC material that 

had been validated through modeling, accelerated 

endurance tests, and field test. Based on expected 

CF physical and mechanical properties, hood 

structural and surface component material 

thicknesses were reduced through several iterations 

to determine the effect on hood system stress states 

and displacements. Modal analyses were performed 

to determine mode shapes, and complete vehicle 

models were used to obtain dynamic responses in 

the frequency domain. Fatigue life comparisons 

were made based on the complete vehicle model 

transient analyses. 

Based on the initial investigation, it was 

concluded that a competent hood could be produced 

with a 40% to 60% reduction in hood mass if a CF 

SMC material could be produced that would 

consistently provide the physical and mechanical 

properties targeted.

CF SMC Material Search and Comparative Testing

A search was initiated to find suppliers of 

polymers and CFs combined in a useable SMC. 

Materials from Zoltek, SGL, Toray, Grafil, and 

others were evaluated. Early on, two significant 

obstacles became evident: completely wetting out 

the CF and defilamentizing the fiber bundles. Work 

with suppliers is ongoing to optimize chemistry and 

processes to consistently provide CF SMC material 

with the targeted material properties. Short beam 

shear tests based on ASTM D2344/D 2344M were 

used to screen material samples with various 

combinations of resins and additives. More than 

150 samples were evaluated. Materials that 

performed well in the short beam shear screening 

were used to make plaques to measure material 
High Strength Weight Reduction Materials FY 2004 Progress Report 

187

properties. Good progress has been made in 

obtaining the targeted mechanical properties, as 

shown in Table 1. 

Table 1. Percentage of target values achieved 

(updated April 2004) 

Class A Surface Quality Development

The development tool was used for Class A 

surface quality development trials. Parts were 

molded using combinations of two CF loadings, 

three resins, two surfacing veils, and in-mold 

coating. Processing parameters were set similar to 

those of the glass-fiber SMC components. Although 

some progress was made, several of the materials 

and processes were eliminated from further 

consideration. It appears that a substantial effort will 

be required in materials and process development to 

achieve CF SMC panels with Class A surface 

quality. Because of the anticipated higher cycle 

times and additional processing steps, the projected 

cost of CF SMC for Class A surface components 

was estimated to be too high for commercial truck 

applications. Therefore, development of CF SMC 

for exterior Class A surface quality components was 

held in abeyance in order to pursue lower-cost, 

lightweight, low-density, glass-fiber-reinforced 

SMC for Class A surface components. 

Assembly Process Evaluation 

Preliminary evaluations of bond strength were 

made for CF SMC plaques at adhesive bond gaps 

ranging from 0.5 to 3.0 mm. Lap shear tests run at 

ambient and elevated temperature show CF SMC 

bond strengths generally twice those of glass-fiber 

SMC. The evaluation confirmed that the bond 

strength decreases as the bond gap increases. 

Ongoing investigations to provide bond performance 

data for alternative constructions will be required. 

The data developed will be used in hood finiteelement analysis calculations. 

To evaluate the processing characteristics of 

various combinations of lightweight SMC materials, 

prototype hoods are being built using the production 

tooling for an existing hood. The prototype hoods 

are being fabricated using low-density glass-fiber 

SMC Class A outer panels and inner reinforcements 

constructed of glass- or CF-reinforced SMC. The 

prototype hoods will be used to assess 

manufacturing process variability, dimensional 

stability, and adhesive bonding characteristics. To 

evaluate the viability of the lightweight materials in 

the production environment, the hoods will be run 

through the normal assembly plant production 

processes and evaluated for surface quality, paint 

quality, and bond read-through. 

Cost and Weight Evaluation

Initial concept work has concluded that a 40% to 

60% weight reduction is within range, as samples in 

the required reduced material thickness have been 

successfully molded. Preliminary cost estimates of 

the CF SMC hood indicated a higher-than-expected 

cost premium based on the current best estimate of 

CF SMC material costs. Because CF costs have risen 

recently as a result of increased world demand and 

insufficient supply capacity, alternative 

constructions are under review to reduce CFreinforced truck hood costs. At this time, it is 

anticipated that CF production capacity will 

increase. However, it is difficult to predict whether 

world demand will also increase and thereby keep 

CF material costs high. To build a business case for 

a lightweight CF SMC truck hood, CF material costs 

must come down and a stable supply must be 

ensured. 

Conclusions 

The project has made good progress in finding 

promising materials and developing processes. The 

early work is very encouraging because material 

properties for structural applications are generally on 

target. Molding processes similar to those for current 

glass-fiber SMC can be used for structural 

applications. Assembly bonding processes appear to 

follow those of glass-fiber SMCs, with significantly 

increased bond strength. Most of the potential 

weight reduction has been achieved. CF SMC 

material costs for components requiring Class A 

surface quality are projected to be too high for 

Property Tensile Tensile Flexural Flexural

strength modulus strength modulus

Percent

 achieved 86% 97% 118% 107%

Coefficient

 of variation 0.05 0.09 0.09 0.10

Percent (%) of Target Value
FY 2004 Progress Report High-Strength Weight Reduction Materials

188

commercial vehicle applications. Alternative

constructions appear to present a more reasonable

cost/weight value.
High Strength Weight Reduction Materials FY 2004 Progress Report 

189

E. Advanced Composite Support Structures 

Principal Investigator: Brian Knouff, PhD 

National Composite Center. 

2000 Composite Drive 

Kettering, OH 45420 

(937 -297-9458; fax (937) 297-9440; e-mail: bknouff@compositecenter.org 

Project Manager: Jay Batten 

Delphi Corp. 

3900 Holland Rd 

Saginaw, MI 48601-9494 

(989-757-3895; fax (989) 757-42950; e-mail: jay.batten@delphi.com 

ORNL Project Manager: Cliff Eberle 

(865) 574-0302; fax: (865) 574-8257; e-mail: eberlecc@ornl.gov 

DOE Technology Development Area Specialist: Sidney Diamond 

(202) 586-8032; fax: (202) 586-1600; e-mail: sid.diamond@ee.doe.gov 

ORNL Field Technical Manager: Philip S. Sklad 

(865) 574-5069; fax: (865) 576-4963; e-mail: skladps@ornl.gov 

Contractor: Oak Ridge National Laboratory 

Delphi/ORNL Contract No.: 4000021806 

Objective 

• Lead the rapid implementation of lightweight composite materials in Class 7/Class 8 vehicles via the 

development of advanced composite support structures, specifically chassis lateral braces, which can number 

up to six per vehicle. Mass reductions are targeted for 50%. 

Approach 

• Model composite support structures using progressive failure analysis (PFA) software and finite element 

analysis (FEA). 

• Fabricate prototypes of designed structures. 

• Mold composite test plaques to be used in the task on “Attachment Techniques for Heavy Truck Composite 

Chassis Members.” The data from those tests will be integrated into our design models. 

• Analyze materials characteristics of the test plaques such as fracture toughness and fatigue life. 

Accomplishments 

Modeling 

• Used PFA software to provide a means of modeling damage and failure in composites, accurately predict the 

number of cycles to failure as a function of void fraction, and predict the elastic constants. 

• Designed all carbon and all glass composite lateral braces using six load cases. 

• Optimized the geometry by transforming the current U-channel into a box beam and integrating the end 

brackets into the center piece. 
FY 2004 Progress Report High Strength Weight Reduction Materials 

190

• Demonstrated weight savings of 70%. 

• Fed results in the design iterations back to the Joining Team, which then requested that plaques be molded for 

various tests. 

• Displayed the second all-composite prototype model at the ACSS Program Review and 2nd value 

analysis/value engineering meeting (VAVE) on August 10, 2004. 

• Fabricated several different composite test panels to support both the joining and modeling database programs. 

• Discovered that the void content had a dramatic effect on fatigue life and that the plaques were not reaching 

their ultimate Tg (glass transition temperature) without a postcure. 

• Conducted Mode I fracture toughness studies and fabricated Mode II fracture toughness fixtures. 

Future Direction 

• Complete design validation for this application and then pursue a new application. Associated with this 

program will be a higher-level effort in composite-to-composite joint design with the added variable of hole 

placement. 

Introduction

The purpose of this effort is to lead the rapid 

implementation of lightweight composite materials 

in Class 7/Class 8 vehicles via the development of 

advanced composite support structures. This task 

specifically addresses lateral braces; primary beams 

are being targeted for future work. The mass 

reduction target is 50%. The benefits of mass 

reduction in commercial vehicle applications are 

well known. They include increased fuel economy 

and a larger payload, which translate into fewer total 

trips and thus fewer vehicles on the road. This leads 

to less traffic, which aids highway safety, and 

decreased emissions. Support structures offer an 

opportunity for significant weight savings. However, 

this area of the vehicle also represents a large hurdle 

in terms of composite applications and market 

acceptance. 

The application of focus is a Class 8 tractor 

lateral brace (Figure 1). The estimated total annual 

usage of Class 8 lateral braces could exceed 1 

million by 2007. At a current typical weight of 9 kg 

for Class 8 tractors, weight savings would be 4.5 kg 

per part. With up to six braces per vehicle, the 

resulting total weight savings would be 27 kg per 

Class 8 tractor. 

To facilitate this work and future endeavors, 

advanced FEA and PFA software is being employed 

and developed. The FEA software contains a unique 

Figure 1. Schematic showing logical synergism between PFA, FEA, and experimental data. 

optimization algorithm that allows for the rapid 

optimization of such design variables as part 

thickness, fiber angle, fiber type, and even part 

shape while minimizing mass, strain, or even cost. 

PFA, although in development for composites, 

will provide the ability to model composite behavior 

in durability and fatigue situations—unlike any 

other software our team has examined or is aware of. 

Modeling

The modeling effort was separated into two 

parts: 

1. PFA 

2. Prototype design with FEA 

GENOA

Micro- & Macro-Mechanical 

Integrated Software 

EXPERIMENTAL 

ARRANGEMENT

VALIDATION & 

VERIFICATION

(V & V)

BENCHMARK 

• Uniaxial Tensile Tests

• Tension-Tension Fatigue 

Test

• Other Tests (Joining, etc.)

FEA

MATERIAL 

DATA INPUT

Math-Based Methodology for Advanced Composites

FEA Models 

Development 

(TCI/DRL)
High Strength Weight Reduction Materials FY 2004 Progress Report 

191

Fatigue Life Prediction Using GENOA

10

15

20

25

30

35

40

45

2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0

Log(Number of Cycles)

Maximum Stress (ksi)

EXP (10-13% voids) EXP (10%)

EXP (2%) DRL (2%)

DRL (10%) DRL (13%)

40 times

PFA was used to satisfy the following 

requirements: 

• Generate required material database for microand macro-mechanical simulation of fracture 

and fatigue of composite joining systems. 

• Develop predictive models of composite joint 

failure based upon failure mechanics theories. 

Figure 1 shows the relationship between 

physical testing, FEA, and PFA used to develop the 

math-based methodology for advanced composites. 

The physical testing of the composites in both static 

and fatigue supplied the database to model these 

conditions. In this case, the material was a 3-

dimensional (3D) fabric reinforcing a vinyl ester 

thermoset. An S/N curve of the neat resin matrix 

was produced (Figure 2). It was required to model 

the resin behavior for complex geometries, such as 

the 3D composite material employed. 

Figure 2. S/N curve for neat resin polyurethane 

modified vinyl ester system. 

Initial results have been promising. PFA has 

been able to accurately represent the Poisson ratios 

as well as longitudinal and transverse elastic moduli. 

An attempt was also made to determine a “Miner’s 

Rule” for composites, but that has been determined 

to be somewhat complex and requires further 

investigation. 

The main accomplishment to date is the ability 

to model the effect of void content on fatigue 

behavior in the test plaques. Figure 3 shows 

experimental data with symbols and predictions with 

lines. For 13% and 10% void content, the prediction 

line fell within the scatter from the data. For 2% 

void content, it actually coincided with the data. 

This is a major breakthrough, as a void content of 10 

to 13% has been shown to decrease fatigue life by a 

factor of 40 compared with a void content of 2%. 

This phenomenon has now been not only 

documented but also modeled and predicted. 

Without this capability, predictive modeling would 

have to be generated from empirical correlations. 

Figure 3. Good correlation between PFA (lines) and data 

(symbols) for S/N curves at different void concentrations. 

Prototype Design with FEA

Actual design requirements of the application 

lateral brace were not available from the customer. 

However, the current steel design was in IGES 

format. This file was imported and meshed for FEA. 

No design requirements were associated with 

this application. In other words, the customer did not 

know what load levels the part would experience in 

its life nor how stiff it had to be to perform properly. 

This is not unusual in the Class 8 truck market. Steel 

with a thickness of 0.25 in. is an industry standard, 

and it has been shown to perform well in chassis 

applications. The customer supplied IGES files of 

both the center steel brace (stamped) and the cast 

end brackets. 

Each part will experience six basic load cases: 

• Axial extension: a tensile or compressive load 

along the length of the brace, perpendicular to 

the primary beams. This load case will occur 

during lane changes and cornering, for example. 

• Racking: an applied load on the brace flanges 

parallel to the primary beams. It can also occur 

during cornering and braking, as one side of the 

chassis lags briefly behind the other. 

0.

2.

4.

6.

8.

10.

12.

14.

0 123 456 7

Log (Number of 

Cycles)

Max 

Stress 

(ksi)
FY 2004 Progress Report High Strength Weight Reduction Materials 

192

• Rolling: a result of one wheel being elevated 

above the other on the same axle. Potholes or 

road debris will cause rolling, which is a force 

perpendicular to the road surface. 

• Torsion: a twisting motion that can also occur 

during a pothole or debris hit. One side of the 

chassis lifts and pivots to accompany the terrain, 

resulting in a twisting of the lateral brace. 

• In-plane bending: a movement applied on one 

side of the flange around the primary beam. It 

can occur when one side lifts or when the 

chassis experiences a jarring motion from rough 

terrain. 

• Out-of-plane bending: one primary beam 

trying to circle the other. Sharp turns can cause 

this load case to be applied. 

The center steel section was first meshed and 

modeled in FEA. The constraints and loads were 

applied evenly along the ends. Using the exact same 

mesh, composite properties were applied to the 

model and FEA optimized the design variables to 

satisfy the stiffness requirement. Specifically, the 

design variables were the thickness and fiber angles 

of each of eight plies, the single point constraints 

were all nodes at one end constrained in all six 

degrees of freedom, the load case was 2000 N-mm at 

the other end, the design constraint was a maximum 

deflection of 1.2 mm, and the design objective was 

the minimization of mass. 

The optimization resulted in a lay-up of three 

stacks of [02/90/236/-236]s of prepreg with each ply 

0.15 mm thick. The total thickness of the part was 

13.5 mm and the part weighed 5.3 kg, resulting in a 

mass savings of 58%. 

After this design, a meeting with the customer 

was held to determine what other options were 

available. It was determined that the holes were not 

needed in the center section. Additionally, it was 

discovered that torsional rigidity was further 

improved by adding a fourth wall to the bottom, 

thereby making the brace a box beam. 

To minimize assembly time, the design was 

further optimized by combining the end brackets 

with the centerpiece. The material was changed from 

carbon prepreg to 3D carbon fabric to reduce the 

material cost. A topology was then performed to 

determine the areas of most required mass, or 

stiffness. Figure 4 represents the thick areas with the 

darker gray areas that make an ‘X’ shape on both 

sides of the part. Also, notice the darker areas calling 

for reinforcement of ends on top and bottom. Using 

the topology results, the part was then divided into 

finite elements parts with each part optimized for 

thickness. The result was an end thicknesses of 

5 mm with 1-mm thicknesses for the rest of the part. 

Figure 4. Topology shows areas of high profile (thickness) to accommodate higher-stress 

regions. 

Up to this point, only the torsional load case was 

considered because of our impression that it was the 

worst-case scenario. However, with the optimization 

to a box beam, that was shown to no longer be the 

case. 

Therefore, the additional five load cases were 

also used for design optimization. All six load cases 

are shown in Table 1. In the general coordinate 

system, the X-axis runs longitudinally through the 

lateral brace itself, the Y-axis is parallel to the 

primary beams, and the Z-axis is perpendicular to 

the ground. 

For the design of the composite part, the steel 

lateral brace was loaded until 90% of yield stress 

failure in each load case. This load then was applied 

to the composite, which was designed with a safety 

factor of 2 using Tsai-Wu failure criteria. Table 1 

shows the resulting loads used for each case and the 

corresponding reaction (deflection) of the steel 

brace. 
High Strength Weight Reduction Materials FY 2004 Progress Report 

193

Table 1. Loads calculated in FEA analysis on steel section to achieve 90% von 

Mises yield stress. The deflection is also shown. 

Load case Load (kN) 

(kN-mm) 

Max VM 

(MPa) DOF Deflection (mm) 

1. Axial 28.08 527.40 Fx 6.32 

2. Racking 8.00 527.34 Fy 52.7 

3. Roll 8.86 526.90 Fz 12.6 

4. Torsion 1003.42 527.11 Mx 40.8 

5. In-plane bending 3882.45 525.00 My 2.76 

6. Out-of-plane bending 1045.29 527.39 Mz 17.7 

It was also determined that the brace could be 

processed much more easily (with less cost and 

increased yield) by removing the scallop on the 

underside and making the box beam straighter. In 

this design, a 7-mm backing plate was also added to 

represent the attachment to the primary beam. 

Topology and part optimization was used again to 

design this iteration. This iteration was used for the 

prototyping. Figure 5 shows the model after it was 

optimized for manufacturability. 

Figure 5. Optimized geometry smoothed and 

drafted for manufacturability. 

Further investigation took place to optimize the 

design. Two hybrid designs of steel and glass were 

investigated first. Both of these hybrid concepts use 

traditional joining methods because of the steel 

endplates and offer a potential low-cost alternative. 

Five different all-glass composite designs were 

also considered. The flanges of the endplates are 

reinforced by geometric hollow ribs in the first 

concept, whereas these ribs are replaced with an 

expanding tube at the end in the second. The third 

concept attempts to decrease the middle section 

geometry from the previous design. A more radical 

conceptual design is offered in the fourth: Ribs are 

placed longitudinally along the tube, thereby also 

serving as the attachment flanges. This can be 

accomplished process-wise by employing foam 

inserts that remain in the part or using metal inserts 

that disassemble. The fifth concept uses flat 

attachment plates instead of the rib design in all four 

corners of the tube. The novelty of this analysis is 

that the lateral braces were attached to sections of 

the primary beams, to which the loads were applied. 

Each of the designs has been compared in all six 

load cases in terms of displacements. These six load 

cases are 

1. Axial extension in the X direction (11-X) 

2. Racking in the Y direction (12-Y) 

3. Rolling in the Z direction (13-Z) 

4. Torsion around the tube (14-MXX) 

5. In-plane bending (15-MYY) 

6. Out-of-plane bending (16-MZZ) 

Table 2 lists the load cases as well as the 

normalized deflection of each design, with the steel 

base case having a deflection of 100%. A percentage 

less than 100% means the composite design was 

stiffer. Alternatively, a value higher than 100% 

means it is less stiff, or deflects more as a result of 

similar applied loads. 

In the extensional load case, the hybrid designs 

were slightly stiffer than the base case. However, 

each one of the glass designs showed stiffness 

decreases. The hybrid designs also showed stiffness 

increases in the racking loadcase, with only 

concept 2, of the all glass designs, showing a 

significant increase in stiffness. 

None of the designs fared better in rolling than 

the base design. However, the hybrids performed the 

best. Contrary to this fact, all of the concepts were 

torsionally stiffer than the baseline case. However, 

the in-plane and out-plane-bending cases showed 
FY 2004 Progress Report High Strength Weight Reduction Materials 

194

Table 2. Comparison of seven designs to baseline in the six load cases

Load 

case Baseline Hybrid-1 Hybrid-2 Concept-1 Concept-2 Concept-3 Concept-4 Concept-5

11-X 0.080 0.072 0.079 0.135 0.101 0.113 0.126 0.180 

% 100% 91% 99% 169% 126% 142% 158% 226% 

12-Y 2.859 1.132 1.212 3.445 1.882 2.631 3.243 4.255 

% 100% 40% 42% 120% 66% 92% 113% 149% 

13-Z 1.972 2.113 2.320 4.271 2.697 3.182 5.556 6.353 

% 100% 107% 118% 217% 137% 161% 282% 322% 

14- 

MXX 3.243E-02 7.168E-04 6.251E-04 4.392E-03 3.442E-03 5.293E-03 4.579E-03 4.159E-03 

% 100% 2% 2% 14% 11% 16% 14% 13% 

15-MYY 1.981E-05 3.076E-05 5.834E-05 7.315E-05 2.936E-04 3.902E-05 7.241E-05 1.097E-04 

% 100% 155% 295% 369% 1482% 197% 366% 554% 

16-MZZ 1.279E-03 1.327E-03 1.402E-03 4.603E-03 2.684E-03 4.052E-03 3.862E-03 5.025E-03 

% 100% 104% 110% 360% 210% 317% 302% 393% 

there to be a considerable need for redesign in each 

of the seven concepts. 

Prototyping

Figure 5 was used as the design for the 

prototype model. The resin transfer molding (RTM) 

process with fiber architecture achieved via a biaxial braided fabric was chosen to fabricate the 

prototypes. Table 3 lists this architecture. The 

braided fabric took the form of several layers of a 

braided sock that could be threaded over a two-piece 

mandrel and the assembly loaded into a multi-piece 

aluminum mold. 

The aluminum mold (Figures 6 and 7) consisted 

of six pieces that encapsulated and located the twopiece mandrel covered with the fiber assembly. The 

mold was cored to allow temperature control via 

ancillary thermolators to aid in the curing of the 

injected matrix. The matrix chosen was a twocomponent epoxy system with good thermal and 

environmental properties. The resin was injected at 

an elevated temperature to lower its viscosity and 

reduce the infusion time. The mold design 

incorporated a bleeder system that created minimal 

flash even though the resin injection pressures 

exceeded 100 psi. The infusion time was less than 

5 minutes; however, the cure–demold time took 

several hours because of the ramp-up and cool-down 

thermal requirements for the several hundred pounds 

of aluminum mold. In addition, the multi-piece mold 

was assembled and disassembled by hand. 

Production tools will incorporate much easier 

assembly/disassembly and will be water-cooled to 

allow for rapid cycle times. 

The parts weighed 7.7 lb with a targeted fiber 

volume of 55%. Constant fiber content was 

maintained in the varying cross-section by placing 

additional layers of braided sock as needed. Bi-axial 

braided preforms conform much more easily to the 

variations in the mandrel geometry as opposed to triaxial braids. Computer-aided part design and tool 

manufacturing contributed significantly to a time 

frame of less than 4 weeks from concept to the part 

shown in Figure 8. 

Molding

The fabrics used for this project were 

• 3D glass 96 oz/yd2

 

• 3D carbon 32 oz/yd2

• Stitched glass 0–90o 17.8 oz/yd2

• Plain-weave glass 10.5 oz/yd2

 

• Unidirectional glass 10 oz/yd2

All panels were molded to a nominal thickness 

of 0.100 in. To achieve this, the following lay-ups 

were used: 

• 3D glass 96 oz/yd2

—1 layer 

• 3D carbon 32 oz/yd2

—5 layers 

• Stitched glass 0–90o 17.8 oz/yd2—5 layers 

• Plain-weave glass 10.5 oz/yd2

—9 layers 

• Unidirectional glass 10 oz/yd2—10 layers 
High Strength Weight Reduction Materials FY 2004 Progress Report 

195

Table 3. Braided fiber architecture used for the prototypes

Braid laminate design for National Composite Center demonstration structure 

 Full-length sleeves Full-length sleeves Patch plies 

Product code Y56L800R MM26L700R AP5574 

Box width 4.897 4.897 4.897 4.897 Braid width = 59.2 

Box height 5.358 7.022 5.358 7.022 

Box perimeter 19.179 24.047 19.179 24.047 

Braid condition Nominal Use diameter Nominal Use diameter Bias Warp Total 

Diameter 8.000 6.015 7.65 7.000 6.105 7.65 18.844 18.84 

Angle 45.0 32.7 42.6 45.0 38.1 50.6 60.0 0.0 

Raw Yd/Lb 620 620 620 1800 1800 1800 620 620 

Carrier 272 272 272 500 500 500 336 168 

Ends per carrier 1 1 1 1 1 1 1 2 

Fiber density lb/in.3 0.065 0.065 0.065 0.092 0.092 0.092 0.065 0.065 

Part fiber volume (%) 51.8% 51.8 51.8 51.8 51.8 51.8 51.8 51.8 

Outputs 

One layer thickness 0.0204 0.0224 0.0204 0.0104 0.0107 0.0106 0.0151 0.0076 0.0227 

Number of layers 3 1 ?? 

Local laminate thickness 0.0780 0.0719 0.2039 

Overall fiber volume in patch area for an overall laminate thickness of 0.275 in. 52.0% 

Percent coverage (%) 58.5 63.0 45.9 

Oz per yd2 14.2 15.6 14.3 10.3 10.6 10.5 10.5 5.3 15.8 

Ft/lb 4.84 5.76 5.04 7.64 8.50 6.85 2.77 5.54 1.85 

ppi 5.4 4.5 5.2 11.4 10.2 12.7 4.9 0.0 

Mtl. reqd. for 3 performs (lb) 6.1 1.4 17.1 

Figure 6. Four corners plus two mandrels (ends 

have been removed). 

Two resins were used for the matrix, a 

polyurethane/vinyl ester blend and a polyurethane 

modified vinyl ester. 

The process chosen to consolidate the 

constituents was vacuum infusion. Some of the 

fabric/resin combinations were not infusible. 

Although the blend of polyurethane and vinyl ester 

allowed for some gel time extension by changing the 

chemistry (catalyst, accelerator, and promoter 

Figure 7. Both top corners removed. 

concentrations), the ceiling was found to be between 

24 and 30 minutes. 

The other resin used in this project was a vinyl 

ester resin base. This resin showed better infusion 

properties. The gel time for this resin was extended 

from 8 minutes (first iteration) to 50 minutes (third 

iteration), making this resin more infusible. A 

consistent pattern of bubbles or voids occurred at the 

intersection of the fiber tows when infusing this 

resin into a 3D glass 96-oz fabric. 
FY 2004 Progress Report High Strength Weight Reduction Materials 

196

Figure 8. Second prototype part. 

This project helped to shed light on the 

mechanisms of infusion and the importance of fabric 

orientation. It was noticed that orienting the fiber 

parallel to the infusion line produced a slower 

infusion than orienting the main fiber perpendicular 

to the infusion line. In one case, when the 3D glass 

96-oz fabric was oriented parallel to the infusion 

line, the total infusion time was 20 minutes; but 

when the main fiber was oriented perpendicular to 

the infusion line, the infusion time was only 4 

minutes. 

A second important point for infusion is the 

effect of changing the layup schedule. For this trial, 

the stitched 17.8-oz fabric was used with five layers 

per panel. Two sequences were used: Panel A: 

[0–90o, 0–90o]2S and Panel B: [0–90o, 90–0o]2s 

Panel A infused faster than panel B. The reason 

is that in panel A, the infusion speed tended to be 

constant; meanwhile, in panel B, the fiber 

perpendicular to the resin line (0o direction) flowed 

faster than the fibers parallel to the infusion line (90o 

direction), which flowed at half the speed of the zero 

fiber orientation. In panel A, the resin that flowed 

along the 0o fibers also was able to transfer to the 

90o fibers on both sides. However, in Panel B, a 

‘dead’ zone was created between each of the two 90o 

layers and resin infusion was impeded. 

Material Characterization

Molding 

It was found that the initial composite specimens 

made were performing unacceptably in fatigue. This 

was found to be the result of having too much clay 

in the formulation, incomplete cure, and high void 

content. The elimination of clay in the formulation 

was easily accomplished, and a post-cure schedule 

was added to each panel to ensure completion of the 

polymerization. The thrust of this investigation was 

the cause and elimination of voids. Voids are 

detrimental to fatigue properties of composites. 

By degassing the resin before infusion and using 

vertical infusion, the void content was successfully 

minimized. Figure 9 shows a comparison between 

an initial plaque (10 to 13% voids) and one of the 

latest plaques (2% voids). 

Figure 9. Side-by-side comparison of 10% 

void plaque and 2% void plaque. 

It was necessary to generate and test neat resin 

samples for input into the PFA database. The resins 

were characterized under a dynamic mechanical 

analyzer. This unit, used to measure the glass 

transition temperature, showed that all the samples 

needed a post-cure to obtain a saturated cross-link 

density. 

Fracture Toughness 

Another method of obtaining material data to 

support PFA was the use of fracture mechanics. 

Mode I fracture toughness testing initially gave 

mixed results, but the testing technique has now 

been improved. A fixture for Mode II has been 

fabricated. 
High Strength Weight Reduction Materials FY 2004 Progress Report 

197

The results include an interesting observation of 

the stitched or z-fibers in the 3D fiber architecture. 

The fibers not only prevent catastrophic crack 

growth but also actually impede it to the point of 

rerouting the crack through the thickness of the 

specimen. Possibly, the fracture toughness could be 

increased by decreasing the proportion of z fibers. 

Testing with the neat resin showed a continuous 

fracture toughness (~ 590 J/m) regardless of crack 

length, thereby providing a noncatastrophic Mode I 

failure. 

Conclusions

Accomplishments in FY 2004 include the 

following: 

• Integrated PFA to help design composite parts in 

durability and fatigue environments. 

• Successfully predicted S/N curves of composite 

plaques with varied levels of void content. 

• Successfully predicted elastic constants of 3D 

fabric composites. 

• Brought an optimized design close to 

completion on the lateral brace using 3D fabrics. 

FEA was used to generate the designs. 

• Achieved weight savings of more than 50%. 

• Integrated a cost model into the optimization 

program. 

• Considered all-carbon, all-glass, and hybrid 

materials. 

• Successfully designed a manufacturable 

prototype. 

• Successfully fabricated a prototype using 

aluminum tooling and displayed it at the August 

VAVE workshop. Design to fabrication took 

4 weeks. 

• Determined that the aluminum tool can fabricate 

up to 500 parts. 

• Employed both vacuum infusion and RTM to 

mold plaques for the process development 

(elimination of voids) and fatigue and durability 

testing for input into the PFA database, and for 

the “Attachment Techniques for Heavy Truck 

Composite Chassis Members” project. 

• Successfully measured the mode I fracture 

toughness for the 3D fabric. It has been 

determined that the frequency and placement of 

the ‘z’ fibers can have a major effect on this 

value. 

Future Direction

Results from the VAVE workshop produced the 

functional analysis system technique model shown 

in the following chart. The chart envelopes several 

paths for the design, processing, and attachment of 

the lateral braces in the tractor suspension. Once 

design validation is successful, a new application 

will be pursued. 
FY 2004 Progress Report High Strength Weight Reduction Materials 

198
High Strength Weight Reduction Materials FY 2004 Progress Report 

199

F. Hybrid Composite Materials for Weight-Critical Structures 

Principal Investigator: Mark T. Smith 

Pacific Northwest National Laboratory 

P.O. Box 999 Richland, Washington 99352 

(509) 375-4478; fax: (509) 375-4448; e-mail: mark.smith@pnl.gov 

Principal Investigator: Bill Roberts 

PACCAR Technical Center 

12479 Farm to Market Road, Mount Vernon, Washington 98273 

(360) 757-5286; fax: (360) 757-5370; e-mail: broberts@paccar.com 

Technology Development Area Specialist: Sidney Diamond 

(202) 586-8032; fax: (202) 586-1600; e-mail: sid.diamond@ee.doe.gov 

Field Technical Manager: Philip S. Sklad 

(865) 574-5069; fax: (865) 576-4963; e-mail: skladps@ornl.gov 

Contractor: Pacific Northwest National Laboratory 

Contract No.: DE-AC06-76RLO1830 

Objective 

• Develop and demonstrate (1) the application of hybrid composites and composite/metal hybrids to heavy-duty 

vehicles and (2) the capability to integrate these materials choices into moderate-volume production. 

⎯ Develop and demonstrate the potential for major weight savings (>50% on a component basis) in critical 

structures applicable to truck cabs and support components. 

⎯ Demonstrate the basis for use of hybrid metal-composite systems to reduce weight via proof-of-principle 

experimentation. 

Approach 

• Investigate the potential of new materials and manufacturing technologies to effect major weight reductions for 

heavy-duty vehicles. 

• Assist in demonstrating the applicability of composites and composite/metal hybrids to operational vehicles 

with little or no cost impact. 

• Provide the experience base to develop the design and analysis tools, as well as the scientific understanding of 

the factors affecting molding and materials performance. 

• Provide the materials suppliers with a market that can stimulate demand, leading to an increase in their production capacity. This will help reduce materials costs by creating higher volumes. 

Accomplishments 

• Completed three sets of prototype hybrid door components, which were delivered to Pacific Northwest National Laboratory (PNNL) by the subcontractors. The key components include sand cast magnesium door inners (Style and Tech) and molded hybrid glass/carbon fiber upper door frames (Profile Composites). 

• Initiated door hardware fitting and assembly tasks at PACCAR and PNNL. These include dimensional inspection and fitting of the magnesium lowers to the hybrid composite uppers, as well as initiation of material adhesive bonding tests at the PACCAR Tech Center. 
FY 2004 Progress Report High Strength Weight Reduction Materials 

200

• Completed bonding adhesion testing of composite and metal systems at PACCAR Tech Center and demonstrated excellent bond strengths and desired bond failure behavior. 

• Received fitted hardware at the PACCAR Tech Center for final prototype assembly and bonding. Assembled 

prototype doors will be placed in the PACCAR cab shaker test system for simulated durability testing. The assembly and testing milestone has been delayed until early 2005 in order to successfully complete bonding adhesion development tests. 

Future Direction 

• Assemble three prototype hybrid material doors for testing by PACCAR. Plans call for cab shaker tests to be 

conducted in the first half of 2005. 

• Based on component design and assembly tasks, update door manufacturing cost models for PACCAR (PNNL 

and Mercia).

• Compile a final report at the conclusion of the prototype demonstration phase. 

Introduction 

Current materials and manufacturing 

technologies used for heavy vehicle door systems 

are often dictated by the high cost of tooling and the 

relatively low production volumes for Class 8 

trucks. Automotive-style stamped door designs, 

whether of steel or aluminum, require multistage 

stamping dies that are generally cost-prohibitive at 

lower production volumes (<50,000 units per year). 

Alternate materials, such as glass-reinforced sheet 

molding compound (SMC), require less expensive 

tooling and can provide a Class A finish; but the 

relatively poor specific properties of SMC tend to 

compromise design and result in a heavier door 

system. For many production truck cabs, a simple 

aluminum extrusion frame is used with a flat 

aluminum sheet riveted to the frame. Although this 

approach does not require expensive tooling, the use 

of constant cross-section extrusions in the frame is 

less than optimum, and it requires more assembly 

labor than other approaches. PACCAR, a world 

leader in Class 8 truck design and manufacturing, 

teamed with PNNL to explore alternate “hybrid” 

door system designs that minimize tooling cost and 

per/part door cost, while providing a lightweight, 

structurally stiff, automotive-style door. 

Project Approach 

The initial approach to development of the 

hybrid door system was to perform a structural 

analysis of an existing PACCAR door design and 

determine what the design and performance goals 

should be for new-generation door systems. 

PACCAR provided a number of weight, cost, and 

performance parameters that it considered important 

for future door designs. PNNL was tasked to survey 

existing and emerging materials and manufacturing 

approaches that could be applied to a new door 

design. Following completion of this survey and 

analysis of existing door designs, PNNL, with 

design assistance from Mercia, Ltd., developed a 

series of five door design concepts that included 

combinations of large die castings, extrusions, 

carbon- and glass-reinforced composites, and 

conventional SMC and stamped aluminum exterior 

panels. 

Following a concept review meeting with 

PACCAR, an optimized hybrid door design concept 

was selected. The door concept was then defined 

using computer-aided-design tools and analyzed 

with finite element models to validate performance, 

weight, and cost. After determining that the 

prototype design met or exceeded all performance 

and projected cost targets, PNNL and PACCAR 

selected methods to produce prototype components 

for the full-scale assembly and testing phase of the 

project. The finite element model of the prototype 

door system is shown in Figure 1. 
High Strength Weight Reduction Materials FY 2004 Progress Report 

201

Figure 1. Finite element model of 

prototype door system under simulated loading conditions. 

Conclusions 

The prototype development of hybrid materials 

components for an advanced heavy truck door was 

completed by the team and its selected 

subcontractors. Initial prototype assembly has been 

initiated by the team, including inspection and 

assembly fitting, as well as adhesive bonding 

development. Three prototype doors will be 

assembled by the team for cab testing and evaluation 

during the first half of 2005. The hybrid door design 

that will be prototype-tested reduces door weight by 

37%. If the hybrid design were to move into 

production, the use of a stamped aluminum outer 

panel (cost-prohibitive during the prototype stage) 

would improve structural performance, reduce cost 

to project goals, and increase weight savings to 55%. 
High Strength Weight Reduction Materials FY 2003 Progress Report 

202
High Strength Weight Reduction Materials FY 2004 Progress Report 

203

G. Application of Carbon Fiber for Large Structural Components 

Principal Investigator: Kevin L. Simmons 

Pacific Northwest National Laboratory 

P.O. Box 999, MSIN: K2-44, Richland, WA 99352 

(509) 375-3651; fax: (509) 375-2186; e-mail: kl.simmons@pnl.gov 

Technology Development Area Specialist: Sidney Diamond 

(202) 586-8032; fax: (202) 586-1600; e-mail: sid.diamond@ee.doe.gov 

Field Technical Manager: Philip S. Sklad 

(865) 574-5069; fax: (865) 576-4963; e-mail: skladps@ornl.gov 

Contractor: Pacific Northwest National Laboratory 

Contract No.: DE-AC06-76RLO1830 

Objective 

• Develop selective reinforcement technology that can be applied to large cab components to improve specific 

stiffness and strength, while reducing overall component weight. 

Approach 

• Determine the capability of low-cost carbon fibers to be hybridized with glass fibers to provide substantial 

weight and cost reductions in large cab components. 

• Develop a system for preforming carbon and glass fibers together that will allow components to take maximum 

advantage of the capabilities of selective reinforcement alignment and property contribution. 

• Develop models for the analysis of hybrid chopped-fiber preforms and composites that allow the thermal and 

structural properties to be developed and compared with experimental analysis. 

• Perform structural testing to define the limits of the applicability of the carbon/glass hybrid reinforcement 

materials to the large structures and develop guidelines for applications that may be used by original equipment 

manufacturers (OEMs). 

• Design and develop critical subsection components of large structures to use in correlation with the predictive 

models and to validate the structural application criteria. Determine the capability of the materials to be 

fabricated in full-scale components and determine the performance of these full-scale components in real 

application scenarios. 

Accomplishments 

• Developed the first Class A structural carbon composite panels for truck applications. 

• Showed impact performance that is 2–3 times higher than performance values of standard structural 

composites. 

• Developed hybrid carbon composite with improved impact performance over fiberglass composites. 

• Demonstrated thin (2.5 mm) panel fabrication and resin transfer molding capability. 

• Demonstrated panel molding with varying cross-sections from 2.5 to 7 mm in a single component. 

• Performed panel molding with various filler types and loading, and selected optimum fillers for achieving 

Class A surface. 
FY 2004 Progress Report High Strength Weight Reduction Materials 

204

• Performed mechanical and impact tests on a range of panels. 

• Developed and performed process trials with a new tooling system that allowed the system to work together, 

including improving thermodynamic control necessary for achieving mechanical and impact properties. 

Future Direction 

• Scale up to test a production component selected by the cooperative research and development agreement 

(CRADA) partner. 

• Optimize the resin system using different fillers. 

• Test and validate thickness constraints on panels to achieve structural performance on surface-coated thin 

hybrid panels. 

• Fabricate test tooling for production-level component. 

• Test and validate barrier coat and optimize for surface profile. 

• Verify tooling performance and long-term viability. 

Introduction

Selective reinforcements with stiffer fibers have 

the potential to reduce both costs and weight 

simultaneously even at current price points. Their 

introduction is hindered by a lack of understanding 

of the fibers in existing processes and the need to 

develop robust methods of preforming glass and 

carbon fiber materials together. In addition, the 

capability to attain Class A surface finish is 

required; and potential development of bonding 

agents and the ability to model thermal and 

structural performance of the materials in a hybrid 

system are needed. The recent development of 

composite systems combining carbon fiber 

reinforcement with low-cost automotive and marine 

resin systems provides the opportunity for selective 

reinforcement of a broad range of structural 

composite components. 

The purpose of this project is to develop the 

design and materials processing technology that will 

facilitate the application of low-cost hybrid glass 

fiber and carbon fiber reinforcements in large 

composite components, resulting in reduced weight 

and improved structural performance. This project 

will also seek to advance low-cost carbon fiber 

materials developed by industry by advancing the 

introduction of low-cost resin systems that are 

compatible with current heavy vehicle structural 

composites. 

Fiber Preform Development and 

Evaluation

The requirement for a discontinuous fiber 

preform that can accommodate multiple project 

objectives was a key issue in the project. Critical 

aspects included allowable loft and compressibility, 

capability to achieve Class A surface, ease of fiber 

placement, ability to tailor for placement of local 

additional carbon fiber reinforcement, minimum 

processing cost, and repeatability of processing. The 

approach calls for a given amount of loft to be 

available but for both compressibility and the 

capability to provide a high-permeability resin flow 

path. The method and application of the surface 

fibers have provided benefits in tailoring fiber 

content and have assisted in achieving success in the 

Class A arena. 

To supply the various molding trial 

requirements, different core densities and fiber 

surface densities were evaluated. Packing levels 

were from net to 60% compaction, which varied 

fiber loading in the composite from effective values 

of 25% to well over 45%. Fiber loading in the 

carbon fraction was approximately 50% and allowed 

excellent surface density and allowed fabrication of 

a thin, high-stiffness panel. This is clearly seen in 

the test results for flexural properties versus the 

results for tensile properties. Figure 1 shows the 

surface available from the sample panel. 
High Strength Weight Reduction Materials FY 2004 Progress Report 

205

Figure 1. Molded preform indicating 

discontinuous fiber surface. 

Hybrid Resin Evaluation

The development effort has remained focused on 

using a carbon- and fiberglass-compatible resin 

system. This has proved to be a valid selection based 

on impact test data that indicate excellent 

performance with carbon fiber systems as well as 

glass and other systems (Figure 2). The resin is 

tailored for use in a resin transfer molding (RTM) 

process. Several features of the development project 

have been mentioned by the resin supplier as being 

unique and beneficial based on the project. The 

capabilities to develop a truck-quality Class A 

surface without low-profile additives (which 

compromise toughness) and to achieve consistent 

molding are both new to the industry. The excellent 

toughness seen in carbon hybrid composites is also 

an industry first, described with enthusiasm by the 

resin supplier as “ballistic performance.” One 

significant issue with carbon composites is their lack 

of toughness and brittle failure nature. The team had 

concerns about the minimum achievable panel 

thickness because of this issue. Limiting panel 

thickness would have severely hindered capability to 

be cost-competitive and provide the weight savings 

desirable. Resin and process evaluation indicated a 

need for a system with close temperature control, 

which required development of tight tolerances on 

the process and equipment. 

Figure 2. Resin system allowing excellent impact 

energy. 

Molding Trials

Molding trials have consisted of flat panels and 

large test tool molding trials. Flat plaques were made 

primarily at Pacific Northwest National Laboratory 

to develop and verify resin and additive processing 

conditions as well as to determine the flow rates 

achievable through preforms of different thicknesses 

and compaction. Full-scale test tools (approximately 

3 × 5 ft mold) were fabricated (Figure 1) to translate 

these results into a size and form that could 

demonstrate the effects of different geometries, fiber 

loadings, and resin flow paths. Experimental results 

for each provided a process map for the CRADA 

partner’s confidence in molding actual on-vehicle 

test components to be provided later this fiscal year. 

Local condition variability was a key issue in the 

process control and development efforts, especially 

as the resin rheometry effects varied with time as 

reactions occurred. 

Several different conditions had to be addressed 

in order to achieve consistent and reproducible 

moldings. These included density and 

compressibility of the pre-form, wettability of the 

surface fibers, surface energy of the mold’s A and B 

sides (provided by the particular mold releases), 

flow-rate into the mold and lag between flow front 

and fiber wetting front, vacuum level, injection 

pressures, and mold and materials temperatures. 

Their effects were often interrelated as regards 

quality of the components produced. Studies were 

developed to evaluate common mold release agents 

and to determine the level of “slip” required to 
FY 2004 Progress Report High Strength Weight Reduction Materials 

206

effectively de-mold parts without causing prerelease at the part surface. This surface requirement 

proved difficult to achieve, since the materials with 

medium slip would build up on the tooling and 

degrade the surface finish. High-slip materials 

almost always resulted in pre-release at the tool 

surface, resulting in degradation of the Class A 

finish capability. Systems evaluated included 

primarily semi-permanent films. A combination of 

materials was developed to provide excellent release 

off the B-side tool and limited release off the A-side 

to achieve the Class A finish required. Testing is 

continuing with newly developed formulations for 

decreased buildup and with internal gylceride-based 

fatty acid release agents. Surface wettability also 

impacted the molding quality and the surface pinholes and voids based on wetting of the fibers in 

direct contact with the surface. 

Four different fabric carriers were evaluated to 

provide control of resin-injection back-pressure and 

to determine effective properties with different 

compressibilities. The best surface finishes achieved 

were provided by materials that had lower-thandesired permeability and restricted resin flow on the 

thinner areas (2.7–3.5 mm) of the test parts. After 

analysis of flow rate and injection pressure 

parametric studies, vendors have been approached to 

modify their materials for optimum functionality. 

New materials to achieve both flow rates required at 

optimum process pressures and required 

compressibility of the preforms should be available 

to us in early FY 2005. 

Although temperature has a very significant 

effect on resin viscosity, cure times, and fiber 

wetting, it was determined in studies that a very 

limited temperature range was feasible for this 

system, based on resin off-gassing and void 

formation, catalyst selection, and flow. To achieve 

viable system performance, equipment specifically 

designed for these resin systems will need to be 

developed. Pump and feed/storage system 

customization was required for the experimental 

trials, which was not an optimal solution. 

Gel-coats from several different manufacturers 

were tested for performance against the A-side tool. 

Although all performed adequately, a clear choice 

emerged out of the five tested to meet the CRADA 

partner’s guidelines. The partner desired a system 

that needed no post-molding sanding and one that 

could be scuffed with Scotch-BriteTM or a similar 

material and sent straight to paint. A study of gelcoat thicknesses and optimum application 

parameters was initiated, but it had to be stopped 

because of environmental concerns. A new air 

handling system is being installed to mitigate this 

problem and to allow completion of the study. This 

system should be operational by early November 

2004. 

Experimental Testing

Mechanical and impact tests were performed on 

the panels, and excellent translation of properties for 

all fiber systems was noted. In an unusual departure 

from common practice, the impact performance of 

the carbon fiber panels was better than that of the 

glass fiber panels. The somewhat brittle nature of the 

fibers in failure was suppressed by a combination of 

materials and design. The improvements seen were 

dramatic and bode well for the usefulness of ultrathin panels. 

Specimens were machined and finished on 

diamond tools and tested with combination 

extensometers. Results and failure modes were 

consistent with previously reported testing on the 

hybrid system that had used different resin systems, 

except that the performance was significantly better 

and reflected the improved adhesion to both material 

phases. 

Flexural fatigue testing was performed on 

several sets of data to determine the durability. The 

CRADA partner suggested that the material must be 

able to endure at least one million cycles. Figure 3 

Figure 3. Flexural fatigue comparison at both 40 and 

60% of flexural strength. 

illustrates the fatigue resistance of the developed 

system at both 40% and 60% of flexural strength. 

Most specimens were stopped at three million 
High Strength Weight Reduction Materials FY 2004 Progress Report 

207

cycles, but there are data for up to seven million 

cycles. It was decided to stop the testing at three 

million cycles so that more samples could be tested. 

Fatigue testing on the tooling skin was also 

conducted to determine the durability of flexing 

large tooling skins. The material was determined to 

be suitable, but a more durable surface coating will 

continue to be investigated. 

Rheology measurements were taken on different 

solids loading of the filler. An optimum range of 

filler content and particle size was studied and is the 

basis of future work. 

Flow testing under a glass top tooling was 

accomplished on the four different preform 

materials. Data showing the different preform 

materials and the optimized rheology were 

combined to enhance the understanding of needs and 

upper limitations. 

 

Cost Analysis

A cost analysis of a large (proprietary) 

component was performed to determine the breakeven points for materials and processes in a typical 

truck production environment. The effects of a much 

reduced tooling budget were not factored in because 

the CRADA partner could not define exactly how 

and over how many components its internal costing 

amortized up-front tooling costs. 

Tool cost factors would generally sway the 

costing option in favor of the carbon composite 

approach. This is because a typical fiberglass 

injection/compression mold is 4 to 7 times the cost 

of the RTM tools used in this process. Cost analysis 

indicated cost parity if carbon fiber is available for 

approximately $5/pound and allows for equivalent 

costing of process ancillaries. The weight savings 

amounts to 53% over a traditional wet/preform 

component in production currently. 

With tooling cost differentials amortized over 

two years of production, the break-even point for 

cost parity is with carbon fiber at just under 

$6/pound. Although carbon fiber prices have risen 

substantially in the past year because of materials 

shortages, several options for low-cost carbon are 

being developed. One manufacturer is starting 

several moth-balled production lines that will ease 

supply pressures. Aerospace sector supply should 

increase significantly in 2006 to meet the demand, 

and these factors will bring pricing back to preshortage levels. Long-term pricing for large-volume 

orders in FY 2003 was near $6.10/lb, which is in 

line with cost parity for this technology given 

appropriate tool amortization models. 

Large Evaluation Tool

In order to evaluate the capability of the process 

and materials to meet the demands of industry, a 

proof test component tool was developed. This tool 

has all the features anticipated in designs, and it was 

used to evaluate the hybrid process for achieving 

performance given the requirements of these 

features. It is not expected that all features can be 

molded and perform as expected, since the goal of 

the development is to determine the limitations of 

the hybrid fiber system as well as provide designers 

and OEMs with guidelines as to where lightweight 

materials will be applicable and how to design and 

manufacture them accordingly. 

A new cell was set up for R&D purposes with 

preforming modifications and resin modification 

possible in a more appropriate environment. Also, 

several options for molding were built in that were 

not possible in the existing production environment 

but that could easily be implemented once proven. 

Running this cell, several successful test panel runs 

were made late in the year using hybrid preforms 

while meeting requirements of the overall process. 

Figure 4 illustrates the flexibility of the molding cell 

and the capability to rotate the position of the mold 

to change the flow behavior throughout the tool. 

Samples were provided to be tested early in the next 

phase. Development of parameters has been much 

more controllable; and several advanced options for 

preforming, molding, and materials are being 

investigated. 

A unique proprietary development in a low-cost 

tooling approach is being used in the test tool. The 

new technology will be transferred in the scaled-up 

prototype runs for the client’s proprietary 

component. 
FY 2004 Progress Report High Strength Weight Reduction Materials 

208

Figure 4. Mold cell for test tool setup for large part 

molding. 

Summary

Highlights of progress during FY 2004: 

• Molded structural carbon-fiber–based Class A 

components with a cost-effective hybrid fiber 

system. 

• Achieved significant structural performance in 

fatigue and impact resistance not previously 

seen with these composites. 

• Achieved molding of very thin section panels 

and demonstrated weight savings. 

• Filed several inventions and potential patents on 

the process and technology. 

• Proved the performance of the tooling approach. 

• Demonstrated a system meeting requirements 

for no sanding prior to paint (all of the partners’ 

current components go through a 100% sanding 

operation prior to paint.) 

• Published results in peer-reviewed compilation 

and presentation at American Composites 

Manufacturers Association Annual Meeting. 

Conclusions 

Initial work has provided some very specific 

process and product molding parameter goals that 

needed to be addressed to make a system with 

proven capability to move toward 

commercialization. A series of factors associated 

with optimizing details of the process technology are 

being addressed; the CRADA partner is developing 

an approach to mold full-scale parts that will 

ultimately go on over-the-road trials. These parts 

have been chosen to demonstrate the most 

challenging aspects of the process capability: 

namely, highly structural, Class A surfaces in direct 

line-of-sight, with some complex process details 

required for success. Tooling quotes and 

negotiations are ongoing, and several aspects of the 

process are anticipated to go forward for patent 

protection. Alternative U.S. government applications 

have been identified that can benefit significantly 

from this technology. These will be investigated 

over the coming fiscal year. 

Presentations

K. L. Simmons, G. G. Jones, S. P. Walsh, and G. 

M. Wood, “High-Performance Laminates Using 

Blended Urethane Resin Chemistry,” Composites 

2004 Convention and Trade Show, American 

Composites Manufacturers Association, Tampa, 

Florida; October 6–8, 2004. 

“Application of Carbon Fiber for Large 

Structural Components,” Pacific Northwest National 

Laboratory On-site Review, April 21, 2004. 

Invention Disclosures

“Development of Improved Carbon Fiber Based 

Hybrid Fiber Structures,” IPID 14431-E, submitted 

May 21, 2004. 

“Tooling Method for Application in Rapid 

Fabrication of Thin-walled Composite Structures,” 

IPID #14430-E, submitted May 21, 2004. 

“A Method for Reducing Inter-laminar Stresses 

in Chopped Fiber Hybrid Composites,” IPID 

#14421-E, submitted May 21, 2004.