case study: polymer matrix composites in automobiles

Chapter 7

Case Study: PolymerMatrix Composites in

Automobiles

CONTENTS .Page

Findings..,. . . . . . . . ............... . . . 155Introduction . . . . . . . . . . . . . . . . . . . . . ...00 156B a c k g r o u n d . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 5 7Polymer Matrix Composite Materials ... ... ...l60Performance Criteria . .....................161

F a t i g u e . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 6 1Energy Absorption . . . . . . . . . . . . . . . . . . . . . .162Stiffness and Dam ping.... . . .. ...........164

Potential ManufacturingTechiques .. ..,....165. . . . . . . . . . . . . . . . . . . 1 6 5High-Speed Resin Transfer Molding. ... ....169Filament Winding.. . . . . . . . . . . . . . . . . . . . . .171

Impact on Production Methods . . . . . . . . . . ...173Manufacturing Approach . ................173Assembly Operation Impact . .............176Labor impact . . . . . . . . . . . . . . . . . . . . . . . . . .177

Impact on Support Industries....... . .......178Material Suppliers, Molders and Fabricators .178Steel Industry ...,...... . . . . . . . . ..* 179Repair Service Requirements . .............180PMC Vehicle/Component Recycling ... ... ..l80

Potential Effects of Governmental Regulations .181Hea l th Sa feguards . . . . . . . . . . . . . . . . . . . . . . 181Recyclability . . . . . . . . . . . . ...............181Crash Regulations . . .....................182Fuel Economy Standards . ................182

Technology Development Areas . ...........182Compression Molding . ..................182High-Speed Resin Transfer Molding.. ... ..182Fiber Technology . . . . . . .. .. .. ... + .......183Joining ● ....** ● *...... .**..... . . . . . . . . . 183R e q u i r e m e n t s . . . . . . . . . 1 8 3

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183S u m m a r y . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 8 3

FiguresFigure No. Page

7-1. Steel Body Shell Structure . . . . . . . ... ...1577-2. Ford GrFRP Vehicle . .................1587-3. Ford GrFRP Vehicle With the Composite

Components Shown. .. .. .. ... ... ... ..1597-4. Typical Fatigue Curves for (Unidirectional

GIFRP . . . . . . . . . . . . . . . . . . . ... .......1617.5. Typical Fatigue Curve for SMC.... .. ...16274. Tensile Stress-Strain Curves for Steel and

Aluminum . . . . . . . ...................1627-7, Tensile Stress-Strain Curves for Graphite

Fiber Composite, Kevlar Fiber Composite,and Glass Fiber Composite . ...........163

7-8. Energy Dissipation Mechanism inCeramics . . . . . . . . ...................163

7-9. Different Collapse Mechanisms in Metaland Composite Tubes . ...............164

Figure No. Page7-10. Relationship Between Performance and

Fabrication for Composites . . . . . . . . . . . .7-11. Sheet Molding Compound Material

7-12

7-13

7-147-15

7-167-177-18

Preparation and ComponentFabrication . . . . . . . . . . . . . . . . . . . . . . . . .Typical SMC Production AerostarTailgate . . . . . . . . . . . . . . . . . . . . . . . . . . . .Typical SMC Production AerostarHood. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Typical SMC Truck Cab. . . . . . . . . . . . . . .Prototype Escort Composite Rear FloorPan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Thermoplastic Compression Molding . . . .High-Speed Resin Transfer Molding . . . . .Squeeze Molding and Resin TransferMolding . . . . . . . . . . . . . . . . . . . . . . . . . . .

7-19. Filament Winding Process . . . . . . . . . . . . .7-20. Typical Assembly of (a) Steel Underbody

and (b) Underbody, Bodyside AssembliesEtc. into the Completed Steel BodyShell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

7-21. Typical Assembly of Composite BodysidePanel by Adhesive Bonding of lnner andOuter SMC Molded Panels . . . . . . . . . . . .

7-22. Typical One-Piece Composite BodysidePanel With Foam Core Molded byHSRTM . . . . . . . . . . . . . . . . . . . . . . . . . . . .

7-23. Typical Body Construction Assembly for

7-24

7-25

Composite Body Shell . . . . . . . . . . . . . . . .Typical Body Construction AssemblyUsing Two Major Composite Moldings . .Effect of Composite Use on Steel Use inAutomobiles . . . . . . . . . . . . . . . . . . . . . . . .

Tables

166

166

166

167167

168169170

171172

174

175

175

176

177

179

Table No. Page7-l, Major Weight Savings of GrFRP Over

Steel in Ford ’’Graphite LTD’’ VehicleP r o t o t y p e . . . . . . . . . . . . . . . . . . . . . . . . . . 1 5 9

7-2. Crash Energy Absorption Associated WithFracture of Composites ComparedWith Steel . . . . . . . ...................159

7-3. Typical Stiffness of SelectedComposites . . . . . . . ..................165

7-4. Typical Body Construction System: SteelPanels . . . . . . . . . . ...................174

7-5. Compression Molded Structural Panels ..1757-6. Preform Fabrication Sequence . ........1757-7. Foam Core Fabrication Sequence ... ....1757-8. HSRTM Molded Structural Panels. ... ...1767-9. Body Construction Assembly Sequence ..176

7-10. Effect of Composites on BodyComplexity . . . . . . . ..................177

7-11. Automotive Steel Usage .. .. ... ... ....179

Chapter 7

Case Study: Polymer MatrixComposites in Automobiles

FINDINGS

The increased use of advanced structural ma-terials may have significant impacts on basic man-ufacturing industries. The automotive industryprovides an excellent example, since it is widelyviewed as being the industry in which the great-est volume of advanced composite materials, par-ticularly polymer matrix composites (PMCs), willbe used in the future. Motivations for using PMCsinclude weight reduction for better fuel efficiency,improved ride quality, and corrosion resistance.Extensive use of composites in automobile bodystructures would have important impacts onmethods of fabrication, satellite industry restruc-turing, and creation of new industries such asrecycling.

The application of advanced materials to au-tomotive structures will require: 1 ) clear evidenceof the performance capabilities of the PMC struc-tures, including long-term effects; 2) the devel-opment of high-speed, reliable manufacturingand assembly processes with associated qualitycontrol; and 3) evidence of economic incentives(which will be sensitively dependent on the man-ufacturing processes).

The three performance criteria applicable to anew material for use in automotive structural ap-plications are fatigue (durability), energy absorp-tion (in a crash), and ride quality in terms of noise,vibration, and harshness (generally related to ma-terial stiffness). There is emerging evidence fromboth fundamental research data and field experi-ence that glass fiber-reinforced PMCs can be de-signed to fulfill these criteria.

At present, the successful application of PMCsto automobile body structures is more dependenton quick, low-cost processing methods and ma-terials than it is on performance characteristics.There are several good candidate methods of pro-duction, including high-speed resin transfer mold-ing, reaction molding, compression molding, and

filament winding, At this time, no method cansatisfy all of the requirements for production;however, resin transfer molding seems the mostpromising.

Clearly, the large-scale adoption of PMC con-struction for automobile structures would havea major impact on fabrication, assembly, and thesupply network. The industry infrastructure oftoday would completely change; e.g., the multi-tude of metal-forming presses would be replacedby a much smaller number of molding units, mul-tiple welding machines would be replaced by alimited number of adhesive bonding fixtures, andthe assembly sequence would be modified toreflect the tremendous reduction in parts. Thiscomplete revamping of the stamping and bodyconstruction faciIities wouId clearly entail a rev-olution (albeit at an evolutionary pace) in the in-dustry. However, there would probably not bea significant impact on the size of the overall la-bor force or the skill levels required.

Extensive use of PMCs by the automotive in-dustry would necessitate the development ofcompletely new supply industries geared to pro-viding inexpensive structures. It is anticipated thatsuch developments would take place throughtwo mechanisms. First, current automotive sup-pliers, particularly those with plastics expertise,would unquestionably expand and/or diversifyinto PMCs to maintain and possibly increase theircurrent level of business. Second, the currentlyfragmented PMCs industry, together with raw ma-terial suppliers, would generate new integratedcompanies with the required supply capability.In addition, completely new industries wouldhave to be developed, e.g., a comprehensive net-work of PMC repair facilities, and a recycling in-dustry based on new technologies,

Economic justifications for using PMCs in au-tomotive are not currently available. The eco-

155

156 ● Advanced Materials by Design

nomics will not become clear until the manufac-turing developments and associated experienceare in hand. Economics, customer perception,and functional improvements will dictate theeventual extent of usage. Present economic in-dicators suggest that PMCs would initially be usedonly for low-volume vehicles, and thus the mostlikely scenario would be limited usage of thesematerials. It is clear that a significant fraction of

annual U.S. auto production would have to con-vert to large-scale PMC usage before a major im-pact is felt by such related industries as the steelindustry, tool and die manufacturers, and chem-ical manufacturers. For example, it would takeproduction of 500,000 largely-PMC vehicles peryear to cause a 3 percent decrease in automo-tive steel use. The corresponding effect on theseindustries, therefore, would be minor.

INTRODUCTION

The use of PMC materials in the United Statesin automotive applications has gradually evolvedover the past two decades. With new materialsand processing techniques being continuouslydeveloped within the U.S. plastics and automo-tive industries, there is potential for a more rapidexpansion of these types of applications in thefuture. PMC applications, both for componentsand for major modular assemblies, appear to bea potential major growth area that could have asignificant impact on the U.S. automotive industryand associated supply industries if the requireddevelopments result in cost-effective manufactur-ing processes.

Extensive research and development (R&D) ef-forts currently underway are aimed at realizingeight potential benefits of PMC structures for theU.S. automotive industry:

●

●

●

●

●

●

weight reduction, which may be translatedinto improved fuel economy and performance;improved overall vehicle quality and consis-tency in manufacturing;part consolidation resulting in lower vehicleand manufacturing costs;improved ride performance (reduced noise,vibration, and harshness);vehicle style differentiation with acceptableor reduced cost;lower investment costs for plants, facilities,and tooling—depends on cost/volume rela-tionships;

‘This chapter is based on a contractor report prepared for theOffice of Technology Assessment, by P, Beardmore, C.F. johnson,and G.G. Strosberg, Ford Motor Co., entitled “Impact of New Ma-terials on Basic Manufacturing Industries—Case Study: CompositeAutomobile Structure, ” 1987.

● corrosion resistance; and● lower cost of vehicle ownership.

However, there are areas where major uncer-tainties exist that will require extensive researchand development prior to resolution. For example:

●

●

●

●

●

high-speed, high-quality manufacturing proc-esses with acceptable economics;satisfaction of all functional requirements,particularly crash integrity and long-termdurability;repairability;recyclability; andcustomer acceptance.

The purpose of this case study is to presentscenarios showing the potential impact of PMCson the U.S. automotive industry, its supplier base,and customers. These scenarios depict the effectslikely to be generated by implementation of thetypes of materials and process techniques thatcould find acceptance in the manufacturing in-dustries during the late 1990s, provided devel-opment and cost issues are favorably resolved,

To project the potential of PMCs for automo-tive applications, it is necessary to provide a rea-sonably extensive summary of the current stateof these materials from the U.S. automotive in-dustry’s perspective. In particular, the specifictypes of PMCs showing the most promise for struc-tural applications are described, as well as themost viable fabrication processes. The particu-lar properties of greatest relevance to automo-tive applications are presented, together with anagenda for gaining the knowledge required be-fore high confidence can be placed in the struc-tural application of the materials.

Ch. 7—Case Study: Polymer Matrix Composites in Automobiles w 157

This case study illustrates the potential of PMCsby examining the case of a highly integrated PMCbody shell, as depicted in figure 7-1. Basically,this body shell is the major load-bearing struc-ture of the automobile. This basic structure, which

Figure 7-1.—Steel

does not include the hood, decklid, and doors,has been chosen as representative of the type ofassembly that might be produced in moderatevolumes as PMC materials begin to penetrate theU.S. automobile

Body Shell Structure

industry.

wSOURCE P Beardmore, C.F. Johnson, and G.G. Strosberg, Ford Motor Co., “im-

pact of New Materials on Basic Manufacturing Industries, A CaseStudy’ Composite Automobile Structure,” contractor report for OTA,1987

BACKGROUND

The economic constraints in a mass-productionindustry such as the automotive industry are quitedifferent from the aerospace or even the specialty-vehicle industry. This is particularly true in thepotential application of high-performance PMCmaterials, which to date have primarily been de-veloped and applied in the aerospace industry.At present, virtually all uses of plastics and PMCsin high-volume vehicles are restricted to decora-tive or semistructural applications.

Sheet molding compound (SMC) materials arethe highest performance composites in generalautomotive use for bodies today. However, themost widely used SMC materials contain about25 percent chopped glass fibers by weight andcannot really be classified as high-performancecomposites. Typically, SMC materials are used forgrille-opening panels on many auto lines and clo-sure panels (hoods, decklids, doors) on a few se-lect models.

The next major step for PMCs in the automo-tive business is extension of usage into truly struc-tural applications such as the primary body struc-ture, and chassis/suspension systems. These arethe structures that have to sustain the major road-Ioads and crash loads. In addition, they must de-liver an acceptable level of vehicle dynamics suchthat the passengers enjoy a comfortable ride.

These functional requirements must be totallysatisfied for any new material to find extensiveapplication in body structures, and it is no smallchallenge to PMCs to meet these criteria effec-tively. These criteria must also be satisfied in acost-effective manner. Appropriate PMC fabrica-tion procedures must be applied or developedthat satisfy high production rates but still main-tain the critical control of fiber placement anddistribution.

PMC body structures have been used in a va-riety of specialty vehicles for the past three dec-

158 “ Advanced Materials by Design

ades; Lotus cars are a particularly well-known ex-ample. The PMC reinforcement used in thesespecialty vehicles is invariably glass fiber, typicallyin a polyester resin. A variety of production meth-ods have been used but perhaps the only thingthey have in common is that all the processes areslow, primarily because of the very low produc-tion rate of vehicles (typically, up to a maximumof 5,000 per year).2 Thus, there has been no in-centive to accelerate the development of theseprocesses for mass production. The other com-mon factor among these specialty vehicles is thegeneral use of some type of steel backbone orchassis, which is designed to absorb most of theroad loads and crash impact energy. Thus, whilethe composite body can be considered somewhatstructural, the major structural loads are not im-posed on the composite materials.

Current vehicles that include high volumes offiber-reinforced plastic (FRP) have been designedspecifically for FRP materials, as opposed to be-ing patterned after a steel vehicle. Consequently,it is not possible to make a direct comparison be-

2 lbid.

tween an FRP vehicle and an identical steel ve-hicle to derive baseline characteristics. Perhapsthe best comparison would be between the pro-totype “Graphite LTD” built by Ford, and a pro-duction steel vehicle.3 The vehicle was fabricatedby hand lay-up of graphite fiber prepreg.

This graphite fiber-reinforced plastic (GrFRP)auto is shown in figure 7-2, and an exploded sche-matic showing its composite parts is presentedin figure 7-3. The weight savings for the variousstructures are given in table 7-1. While theseweight savings (of the order of 55 to 65 percent)might be considered optimal because of the useof low density graphite fibers, other more cost-effective fibers are stiff enough to be able toachieve a major portion of these weight savings(with redesign).4 Although the GrFRP vehicleweighed 2,504 pounds compared to a similarsteel production vehicle of 3,750 pounds, vehi-cle evaluation tests indicated no perceptible dif-

3P. Beard more, J.J. Harwood, and E.J. Horton, paper presentedat the International Conference on Composite Materials, Paris, Au-gust 1980.

‘Beard more, Johnson, and Strosberg, op. cit., footnote 1.

Figure 7.2.—Ford Graphite Fiber Composite (GrFRP) Vehicle

SOURCE: P. Beardmore, C.F. Johnson, and G.G. Strosberg, Ford Motor Co., “Impact of New Materials on Basic Manufacturing Industries, A Case Study: CompositeAutomobile Structure, ” contractor report for OTA, 1987

Ch. 7—Case Study: Polymer Matrix Composites in Automobiles s 159

Figure 7-3.— Ford GrFRP Vehicle With the Composite Components Shown

SMC W , , ~production grilleopening panel

ers

lower control armsSOURCE: P Beardmore, C F Johnson, and G.G. Strosberq, Ford Motor Co., “lmpact of New Materials on Basic Manufacturing Industries, A Case Study Composite

Automobile Structure, ” contractor report for OTA, 1987

ference between the vehicles.5 The GrFRP auto’sride quality and vehicle dynamics were judgedat least equal to those of top-quality production

‘Ibid,

Table 7-1 .—Major Weight Savings of GrFRPa

Over Steel in Ford “Graphite LTD” Vehicle Prototype

Weight in pounds

Component Steel GrFRP Reduction

Body- in-whi te . . . . . . . . . . . . . . . .423.0 160.0 253.0Front end . . . . . . . . . . . . . . . . . . . 95.0 30.0 65.0Frame . . . . . . . . . . . . . . . . . . . . ..283.0 206.0 77,0Wheel(s) . . . . . . . . . . . . . . . . . . . . 91.7 49.0 42.7Hood . . . . . . . . . . . . . . . . . . . . . . . 49.0 17.2 32.3Decklid . . . . . . . . . . . . . . . . . . . . . 42.8 14.3 28.9Doors (4) . . . . . . . . . . . . . . . . . . . .141.0 55.5 85.5Bumpers (2) . ................123.0 44.0 79.0Driveshaft. . . . . . . . . . . . . . . . . . . 21.1 14.9 6.2— —

Total vehicle . .............3750 2504 1246aGrFRP = Graphite Fiber-Reinforced PlasticSOURCE: P. Beardmore, C F Johnson, and G.G. Strosberg, Ford Motor Co , “lm-

pact of New Materials on Basic Manufacturing Industries, A CaseStudy: Composite Automobile Structure, ” contractor report for OTA,1987

steel LTD autos. Thus, on a direct comparisonbasis, a vehicle with an entire FRP structure wasproven at least equivalent to a steel vehicle froma vehicle dynamics viewpoint at a weight levelonly 67 percent of the steel vehicle. b

The GrFRP auto clearly showed that high-costfibers (graphite) and high-cost fabrication tech-

Table 7-2.—Crash Energy Absorption AssociatedWith Fracture of Composites Compared With Steel

(typical properties)

Relative energy absorptionMaterial (per unit weight)

High performance composites . . . . . . . 100Commercial composites . . . . . . . . . . . . 60-75Mild steel . . . . . . . . . . . . . . . . . . . . . . . . . . 40a For example, graphite fiber-reinforced.b For example, glass fiber. reinforced.SOURCE: P. Beardmore, C.F. Johnson, and G.G. Strosberg, Ford Motor Co., “Im-

pact of New Materials on Basic Manufacturing Industries, A CaseStudy Composite Automobile Structure, ” contractor report for OTA,1987

160 . Advanced Materials by Design

niques (hand lay-up) can yield a vehicle that is quently, these vehicles cannot be used to developwholly acceptable in terms of handling, perform- guidelines for extensive PMC usage in high-vol-ance, and vehicle dynamics. However, crash and ume applications.durability performance were not demonstrated,and these issues will need serious developmentwork to achieve better-than-steel results. An evenbigger challenge is to translate the GrFRP auto’sperformance into realistic economics through theuse of cost-effective fibers, resins, and fabricationprocedures.

The governing design guidelines for PMCs needto be further developed to ascertain, for instance,how to design using low-cost PMC materials, andto ascertain allowable for stiffness in situationswhere major integration of parts in PMCs elimi-nates a myriad of joints. The following sectionssummarize information on composite materials,

Specialty autos of high PMC content use steel performance criteria, and potential manufactur-es the major load-carrying structure and are not ing techniques.generally priced on a competitive basis. Conse-

POLYMER MATRIX COMPOSITE MATERIALS

By far the most comprehensive property datahave been developed on aerospace-type PMCs,in particular graphite fiber-reinforced epoxiesfabricated by hand lay-up of prepreg materials.Relatively extensive databases are available onthese materials, and it would be very convenientto be able to build off this database for less eso-teric applications such as automobile structures.Graphite fibers are the favored choice in aero-space because of their superb combination ofstiffness, strength, and fatigue resistance. Unfor-tunately for the cost-conscious mass-productionindustries, these properties are attained only atsignificant expense. Typical graphite fibers costin the range of $25 per pound. There are inten-sive research efforts devoted to reducing thesecosts by using a pitch-based precursor but themost optimistic predictions are for fibers in therange of $5 to 10 per pound, which would stillkeep them in the realm of very restricted poten-tial for consumer-oriented industries.7

The fiber with the greatest potential for automo-bile structural applications is E-glass fiber–cur-rently, $0.80 per pound—based on the optimalcombination of cost and performance.8 Similarly,the resin systems likely to dominate at least in thenear term are polyester and vinyl-ester resinsbased primarily on a cost/processability trade-offversus epoxy. Higher performance resins will only

‘Ibid.8 lbid.

find specialized applications (in much the sameway as graphite fibers), even though their ultimateproperties may be somewhat superior.

The form of the glass fiber used will be veryapplication-specific, and both chopped and con-tinuous glass fibers should find extensive use.Most structural applications involving significantload inputs will probably use a combination ofboth chopped and continuous glass fibers withthe particular proportions of each depending onthe component or structure. Because all the fabri-cation processes likely to play a significant rolein automotive production are capable of handlingmixtures of continuous and chopped glass, thisrequirement should not present major restrictions.

One potential development likely to come aboutif glass fiber PMCs come to occupy a significantportion of the structural content of an automo-bile is the tailoring of glass fibers and correspond-ing specialty resin development. The size of theindustry (each pound of PMC per vehicle trans-lates into approximately 10 million pounds peryear in North America) dictates that it would beeconomically feasible to have fiber and resin pro-duction tailored exclusively for the automotivemarket. 9 The advantage of such an approach isthat these developments will lead to incrementalimprovements in specific PMC materials, whichin turn should lead to increased applications andincreased cost-effectiveness.

9Ibid.

Ch. 7—Case Study: Polymer Matrix Composites in Automobiles ● 161

Although thermoset matrix PMCs will probablyconstitute the buIk of the structural applications,thermoplastic-based PMCs formed by a compres-sion molding process may well have a significantbut lesser role to play.

Most of the compression-molded thermoplas-tics in commercial use today tend to concentrateon polypropylene or nylon as the base resin. Thereason is simply the economic fact that these ma-terials tend to be the least expensive of the engi-neering thermoplastics and are easily processed.Both of these materials are somewhat deficient

in heat resistance and/or environmental sensitivityrelative to vehicle requirements for high-perfor-mance structures.

Other thermoplastic matrices for glass fiber-reinforced PMCs are under development, andmaterials such as polyethyleneterephthalate (PET)hold significant promise for the future. The ex-tent to which thermoplastic PMCs will be usedin future structures will be directly dependent onmaterial developments and the associated eco-nomics.

PERFORMANCE CRITERIA

From a structural viewpoint, there are two ma-jor categories of material response critical to ap-plying PMCs to automobiles. These are fatigue(durability) and energy absorption. In addition,there is another critical vehicle requirement, ridequality, which is usually defined in terms of noise,vibration, and ride harshness, and is generallyperceived as directly related to vehicle stiffnessand damping. Material characteristics play a sig-nificant role i n this category of vehicle response.These three categories will be discussed below.

Fatigue

The specific fatigue resistance of glass fiber-reinforced plastics (GIFRP) is a sensitive functionof the precise constitution of the material. How-ever, there are also preliminary research indica-tions of the sensitivity to cyclic stresses. (For a fur-ther discussion of chopped and continuous glassfibers, see ch. 3.)

For unidirectional GIFRP materials, the fatiguebehavior can be characterized as illustrated in fig-ure 7-4. The most important characteristic in fig-ure 7-4 is the fairly well-defined fatigue limit ex-hibited by these materials; as a guiding principlethis limit can be estimated as approximately 35to 40 percent of the ultimate strength.10 A choppedglass PMC, by contrast, would have a fatigue limitcloser to 25 percent of the ultimate strength and

10 C.K. H. Dharan, Journal oiMater/a/s .$c/ence, VOI. 10, 1975, PP.1665-70.

Figure 7-4.—Typical Fatigue Curves forUnidirectional Glass Fiber Composite (GIFRP) as aFunction of Volume Fraction of Glass Fibers (VF)

1 10 102 103 104 10’ 10’ 107

2 NF

óA is defined as the amplitude of the cyclicly applied stress.NF is the number of cycles to failure.Fatigue is described by the number of cycles to failure at agiven cyclicly applied stress.

SOURCE: P. Beardmore, C.F. Johnson, and G.G. Strosberg, Ford Motor Co., “Im-pact of New Materials on Basic Manufacturing Industries, A CaseStudy: Composite Automobile Structure, ” contractor report for OTA,1987.

tends to produce less reliable fatigue test data.Figure 7-5 shows the scatter in fatigue test datafor SMC.11 12

It is also important to note that the different fail-ure modes in PMCs (in comparison to metals) can

I IT. R, Smith and M.). Owen, Modern P/astics, April 1969, pp.124-29.

12A, po t e m a n d z. Hashim, A / A A jourr?a/, VOI. 14, 1976, PP.

868-72.


a

Figure 7-5.—Typical Fatigue Curve forSheet Molding Compound

2.0

1.5

1.0

0.5

0 10 102 10’ 10’ 105 10’

Number of cycles to failureSMC exhibits significant scatter in fatigue test data.

SOURCE: P. Beardmore, CF. Johnson, and G.G. Strosberg, Ford Motor Co., “im-pact of New Materials on Basic Manufacturing Industries, A CaseStudy: Composite Automobile Structure, ” contractor report for OTA,1987.

result in different design criteria for these mate-rials, depending on the functionality involved. Forinstance, a decrease in stiffness can occur undercyclic stressing long before physical cracking andstrength deterioration occur. If stiffness is a criti-cal part of the component function, the loss instiffness under the cyclic road loads could resultin loss of the stiffness-controlled function with noaccompanying danger of any loss in mechanicalfunction. This phenomenon does not occur insteel.

As a guiding principle, it follows from the abovethat wherever possible, automotive structuresshould be designed such that continuous fiberstake the primary stresses and chopped fibersshould be present to develop some degree ofisotropic behavior. It is critical to minimize thestress levels, particularly fatigue stresses, that haveto be borne by the chopped fibers,

There is emerging evidence from both funda-mental research data and field experience withPMC components that glass fiber-reinforced PMCscan be designed to withstand the rigorous fatigueloads experienced under vehicle operating con-ditions. The success of PMC leaf springs and SMCcomponents attests to the capability of PMCs towithstand service environments.

Although the data for all combinations of PMCmaterials are not yet available, a sufficient data-

base is available such that conservative estimatescan be developed and lead to reliable designs.It should be emphasized, however, that the me-chanical properties of PMCs (much more thanisotropic materials) are very sensitive to the fabri-cation process. It is imperative that properties berelated to the relevant manufacturing techniqueto prevent misuse of baseline data.

Energy Absorption

The elongation (strain) behavior of a materialunder stress can indicate a great deal about thematerial’s ability to absorb crash energy. Metalsexhibit linear stress-strain behavior only up to acertain point, beyond which they plastically de-form (see figure 7-6). This plastic deformation ab-sorbs a large amount of crash energy that couldotherwise injure passengers.

The stress-strain curves of all high-performancePMCs are essentially linear in nature, as shownin figure 7-7. This resembles the behavior of brittlematerials such as ceramics. Materials that are es-

Figure 7-6.—Tensile Stress-Strain Curves for

50

40

30

20

10

Steel and Aluminum

350

300

250

200

150

100

50

0.002 0.006 0.01

StrainHRLC—hot rolled leaded carbon steel1100-H12—strain hardened low alloy aluminum

The plastic region of metal stress-strain behavior absorbscrash energy.

SOURCE: P. Beardmore, C.F. Johnson, and G.G. Strosberg, Ford Motor Co., “im-pact of New Materials on Basic Manufacturing Industries, A CaseStudy: Composite Automobile Structure,” contractor report for OTA,1987.

Ch. 7—Case Study: Polymer Matrix Composites in Automobiles “ 163

Figure 7-7.—Tensile Stress-Strain Curves for GraphiteFiber Composite (GrFRP), Kevlar Fiber Composite

(KFRP), and Glass Fiber Composite (GIFRP)

1.0 1.5 2.0 2.5 3.0 3.5

Strain, 0/0The linearity of the curves means that these composites be-have as brittle materials during fracture (cf fig. 7-6). There isno plastic region to absorb crash energy.

1 KSI = 103 psi

SOURCE’ P Beardmore, C.F. Johnson, and G.G. Slrosberg, Ford Motor Co., “im-pact of New Materials on Basic Manufacturing Industries, A CaseStudy Composite Automobile Structure, ” contractor report for OTA,1987

sentially elastic to failure (PMCs, ceramics) mightbe thought to have no capacity for energy ab-sorption since no energy can be absorbed throughplastic deformation. However, ceramics havebeen used for decades as armored protectionagainst high-velocity projectiles.

In fact, energy absorption is achieved by spread-ing the localized impact energy into a high-vol-ume cone of fractured ceramic material, as shownschematically in figure 7-8. A large amount offracture surface area is created by fragmentationof the solid ceramic, and the impact energy isconverted into surface energy resulting in suc-cessful protection and very efficient energy dis-sipation. Brittle materials can be very effectiveenergy absorbers, but the mechanism is fracturesurface energy rather than plastic deformation.

Figure 7.8.—Energy Dissipation Mechanism

D

Projectile

in- Ceramics

Energydissipation“cone”

Energy absorption occurs in ceramics and brittle PMCs byspreading local impact energy into a high-volume cone offractured material.

SOURCE: P. Beardmore, CF. Johnson, and G.G. Strosberg, Ford Motor Co., “im-pact of New Materials on Basic Manufacturing Industries, A CaseStudy: Composite Automobile Structure,” contractor report for OTA,1987,

This analogy leads directly to the conclusion thathigh-performance PMCs may well be able to ab-sorb energy by a controlled disintegration (frac-ture) process.

Evidence is emerging from laboratory test dataon the axial collapse of PMC tubes that efficientenergy absorption needed for vehicle structurescan be achieved in these materials. A compari-son between the collapse mechanisms of metalsand PMCs is shown in figure 7-9. Glass fiber- andgraphite fiber-reinforced PMCs behave as shownin figure 7-9(b). By contrast, PMCs using fibersconsisting of highly oriented long-chain polymers(e.g., Kevlar) collapse in a metal-like fashion usingplastic deformation as the energy absorbing mech-anism. The fragmentation/fracture mechanismtypical of glass fiber PMCs can be very effectivein absorbing energy, as illustrated in table 7-2.

It is particularly signif icant that although high-

per formance, h igh ly or iented PMCs prov ide the

maximum energy absorption, commercial-typePMCs yield specific energy numbers considera-bly superior to metals. Thornton and coworkershave accumulated extensive data on energy ab-sorption in composites .13 14 15

13p H . T~OrntOn and P.j. Edwards, journa/ of Composite Materi-als, vol. 13, 1979, pp. 274-82.

14P. H. Thornton and P.j. Edwards, Journa/ of cOrnP05;te Mater/-

d/s, VOI. 16, 1982, pp. 521 -45 .I sp H, Thornton, j.j. Harwood, and P. Beard more, International

Journal of Composite Structures, 1985.

164 Advanced Materials by Design

Figure 7-9.—C)ifferent Collapse Mechanisms in(a) Metal and (b) Composite Tubes, for

Energy Absorption

a) energy, absorption by plastic deformationb) fracture surface energy dissipation

SOURCE: P. Beardmore, C.F. Johnson, and G.G. Strosberg, Ford Motor Co., “lm.pact of New Materials on Basic Manufacturing Industries, A CaseStudy: Composite Automobile Structure,” contractor report for OTA,1987.

Virtually all the energy absorption data avail-able to date have been developed for axial col-lapse of relatively simple structures, usually tubes.The ability to generate the same effective fracturemechanisms in complex structures is still unre-solved. In addition, it is well known from obser-vations on metal vehicles that bending collapse

normally plays a significant part in the collapseof the vehicle structure, and it is consequentlyof considerable importance to evaluate energyabsorption of composites in bending failure.

Just as in metals, little data are available onenergy absorption characteristics in bending.There is no reason to believe that the energy ab-sorption values of metals relative to PMCs inbending should change significantly from the ra-tios in axial collapse except that bending failure(fracture) in PMCs may tend to occur on a morelocalized basis than plastic bending in metals. Ifthis does indeed occur, then the ratio couldchange in the favor of metals.

Other crash issues involve the capacity to ab-sorb multiple and angular impacts and the long-term effects of environment on energy absorp-tion capability. In general, practical data from arealistic, vehicle viewpoint are not yet in hand.An additional, significant factor is the consumeracceptance of these materials as perceived in re-lation to safety. A negative perception would bea serious issue on something as sensitive as safety,and better-than-steel crash behavior will be re-quired before wide-scale implementation of PMCscan occur. Conversely, a positive perceptionwould be a valuable marketing feature and pro-vide an additional impetus for PMC applications.

Stiffness and Damping

Glass fiber-reinforced PMCs are inherently lessstiff than steel. Some typical values for varioustypes of PMC are listed in table 7-3. There aretwo offsetting factors to compensate for these ma-terial limitations. First, an increase in wall thick-ness can be used to offset partially the lesser ma-terial stiffness. Also, local areas can be thickenedas required to optimize properties. Because PMCshave a density approximately one-third that ofsteel, a significant increase in thickness can beachieved while maintaining an appreciable weightreduction.

The second, and perhaps the major, offsettingfactor is the additional stiffness attained in PMCsas a result of part integration. This integrationleads directly to the elimination of joints, whichresults in significant increases in effective stiffness.It is becoming increasingly evident that this syn-


Table 7-3.—Typical Stiffness of Selected Composites

Material Stiffness (lO6psi)

Unidirectional GrFRP . . . . . . . . . . . . . . . . . 20Unidirectional GIFRP . . . . . . . . . . . . . . . . . 6Unidirectional Kevlar. . . . . . . . . . . . . . . . . . 11XMC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5SMC-R50 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3SMC-25 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3SOURCE: P. Beardmore, C.F. Johnson, and G.G. Stromberg, Ford Motor Co. ’’lm-

pact of New Materials on Basic Manufacturing Industries, A CaseStudy: Composite Automobile Structure, ” contractor report for OTA,1987.

ergism is such that structures of acceptable stiff-ness and considerably reduced weight are feasi-ble in glass fiber-reinforced PMCs. As a rule ofthumb, a glass FRP structure with significant partintegration relative to the steel structure beingreplaced can be designed for a nominal stiffnesslevel of 50 to 60 percent of the steel structure.16

Such a design procedure should lead to adequatestiffness and to typical weight reductions of 20to 50 percent.17

lbgeardmore, Johnson, and Strosberg, Op. cit. , footnote 1,1‘Ibid.

The stiffness requirement for vehicles is nor-mally dictated by vehicle dynamics characteris-tics. The historical axiom in the vehicle engineer’sdesign principles is the stiffer the better. How-ever, there are some intangible factors that en-ter the overall picture, in particular the dampingfactor.

It is an oversimplification to assume stiffnessalone dictates vehicle dynamics, although it un-questionably dominates certain categories. Damp-ing effects can play an equally significant role i nmany categories of body dynamics, and the factthat the damping of PMC materials considerablyexceeds that of metals is relevant to the overallscenario. Most experts involved with PMC com-ponent/structure prototype development feel thatsome aspect of body dynamics (usually noise orvibration) is improved but few quantitative dataare available to document the degree of improve-ment. If customers share this perception, PMCswill receive impetus for structural usage.

POTENTIAL MANUFACTURING TECHNIQUES

The successful application of PMCs to automo-tive structures is more dependent on the abilityto use rapid, economic fabrication processes thanon any other single factor. The fabrication proc-esses must also be capable of close control ofPMC properties to achieve lightweight, efficientstructures.

Currently, the only commercial process thatcomes close to satisfying these requirements iscompression molding of sheet molding com-pounds (SMCs) or some variant on this process.There are, however, several developing processesthat hold distinct promise for the future in thatthey have the potential to combine high rates ofproduction, precise fiber control, and high degreesof part integration.

The requirements for precise fiber control, rapidproduction rates, and high complexity demandthat automotive processes be in the region of de-veloping processes shown schematically in fig-ure 7-10. The three most important evolving proc-esses are compression molding, high-speed resin

transfer molding, and filament winding. Each ofthese processes is examined below.

Compression Molding

This section discusses compression moldingtechniques; these are most often used with ther-mosetting resins but can be used with thermo-plastic resins.

Thermosetting Compression Molding

Figure 7-11 presents a schematic of the SMCprocess, depicting both the fabrication of theSMC material and the subsequent compressionmolding into a component. This technology hasbeen widely used in the automobile industry forthe fabrication of grille-opening panels on manyauto lines, and for some exterior panels on se-lected vehicles. Tailgates (figure 7-12), and hoods(figure 7-13) are examples on autos and lighttrucks; the entire cab on some heavy trucks (fig-ure 7-14) is constructed in this manner.


Figure 7-10.—Relationship Between Performance andFabrication for Composites

Automotive Composite Process Development

Size,complexity,performance

Handlay-up

/

/

Region of developing processes(i.e., high-speed resin transfer)

Thermoplastic stamping

Viable commercial processes must be able to produce a largenumber of high performance parts.SOURCE: P. Beardmore, C.F. Johnson, and G.G. Strosberg, Ford Motor Co., “im-

pact of New Materials on Basic Manufacturing Industries, A CaseStudy: Composite Automobile Structure,” contractor report for OTA,1987.

Figure 7-11 .—Sheet Molding Compound MaterialPreparation and Component Fabrication

Sheet Molding- Chopped

galss

SOURCE: P. Beardmore, CF. Johnson, and G.G. Strosberg, Ford Motor Co., “im-pact of New Materials on Basic Manufacturing Industries, A CaseStudy: Composite Automobile Structure, ” contractor report for OTA,1987.

The process consists of placing sheets of SMC(1 to 2 inch long chopped glass fibers in chemi-cally thickened thermoset resin) into a heatedmold (typically at 3000 F) and closing the moldunder pressures of 1,000 pounds per square inch(psi) for about 2 to 3 minutes to cure the mate-rial. Approximately 80 percent of the mold sur-face is covered by the SMC charge, and the ma-terial flows to fill the remaining mold cavity asthe mold closes.

The above description of the SMC process de-lineates material primarily used for semistructuralapplications rather than high load bearing seg-ments of the structure that must satisfy severedurability and energy absorption requirements.

Figure 7.12.—Typical Sheet Molding CompoundProduction Aerostar Tailgate

SOURCE: P. Beardmore, C.F. Johnson, and G.G. Strosberg, Ford Motor Co., “im-pact of New Materials on Basic Manufacturing Industries, A CaseStudy: Composite Automobile Structure,” contractor report for OTA,1987,


To sustain the more stringent structural demands,it is normalIy necessary to incorporate apprecia-

Figure 7-13.—Typical SMC Production Aerostar Hood

Figure 7-14.—Typical SMC Truck Cab

SOURCE: P. Beardmore, C.F. Johnson, and G.G. Strosberg, Ford Motor Co., “im-pact of New Materials on Basic Manufacturing Industries, A CaseStudy: Composite Automobile Structure, ” contractor report for OTA,1987.

ble amounts of continuous fibers in predesignatedlocations and orientations.

The same basic SMC operation can be used toincorporate such material modifications either byformulating the material to include the continu-ous fibers along with the chopped fibers or byusing separate charge patterns of two differenttypes of material. The complexity of shape anddegree of flow possible are governed by theamount and location of the continuous glass ma-terial. Careful charge pattern development is nec-essary for components of complex geometry. Atypical example of a prototype rear floor panfabricated by this technique is shown in figure7-15.18

The limitations of compression molding of SMC-type materials in truly structural applications haveyet to be established. Provided that continuousfiber is strategically incorporated, these materialspromise to be capable of providing high structuralintegrity and may well prove to be the pioneer-ing fabrication procedure in high load bearing ap-plications. The state of commercialization of thisprocess is advanced compared to other evolvingtechniques and this will provide a lead time for

SOURCE P Beardmore, CF. Johnson, and G G Strosberg, Ford Motor Co , “im-pact of New Materials on Basic Manufacturing Industries, A CaseStudy Composite Automobile Structure, ” contractor report for OTA,1987

18c, F. Johnson and N .G. Chavka, ‘‘An Escort Rear Floor pan,Proceedings ot’the 40th Annual TechrricJ/ Conference, Atlanta, GA,Society of the Plastics Industry, January 1985,


Figure 7-15.—Prototype Escort Composite RearFloor Pan

SOURCE: P. Beardmore, C.F. Johnson, and G.G. Strosberg, Ford Motor Co., “im-pact of New Materials on Basic Manufacturing Industries, A CaseStudy: Composite Automobile Structure,” contractor report for OTA,1987.

compression molding to branch into higher per-formance parts.

Although compression molding of SMC-typematerials is an economically viable, high produc-tion rate process in current use, there are somelimitations inherent in the process. In the longerterm, these will restrict applications and tend tofavor the developing processes. For instance, ma-terial flow in the compression step results inimprecise control of fiber location and orienta-tion. Typically, variations in mechanical proper-ties of a factor of 2 throughout the componentare not unusual based on an initial charge-patterncoverage of approximately 70 percent.

Such uncertainty in properties introduces relia-bility issues and encourages conservative designs

that yield a heavier-than-necessary componentor structure. Currently, extensive research effortsare underway to develop SMC-type materials thatwill allow 100 percent charge pattern coverageand that will attain high, uniform mechanicalproperties with minimal flow. These materials canalso be molded at lower pressures on smaller ca-pacity presses. Materials developments such asthese may well make the newer breed of SMCsmuch more applicable to highly loaded structuresthan has hitherto been envisioned.

Another potential limitation of compressionmolding is the degree of part integration that isattainable. The basic strategy in PMC applicationsis to integrate as many individual (steel) piecesas possible to minimize fabrication and assem-bly costs (which offsets increased material costs)and to minimize joints (which increases effectivestiffness). Compression molding requires fairlyhigh molding pressures (about 1,000 pounds psi)and thus limits potential structures in area sizeand complexity (particularly in three-dimensionalgeometries requiring foam cores).

Consequently, although compression moldingis likely to play a key role in the developmentof PMCs in structural automotive applications inthe next decade, ultimately the process is unlikelyto provide composite parts of optimum structuralefficiency and weight. Nevertheless, compressionmolding is currently the only commercial PMCprocess capable of satisfying the economic con-straints of a mass-production industry.

Thermoplastic Compression Molding

The process of thermoplastic compressionmolding (stamping) is attractive to the automo-tive industry because of the rapid cycle time andthe potential use of some existing metal stamp-ing equipment. Thermoplastic compression mold-ing at its current level of development achievescycle times of 1 minute for large components.

Figure 7-16 presents a schematic of the proc-ess. Typically, a sheet of premanufactured ther-moplastic and reinforcement is preheated abovethe melting point of the matrix material and thenrapidly transferred to the mold. The mold isquickly closed until the point where the mate-rial is contacted, and then the closing rate is


Figure 7-16.—Thermoplastic Compression Molding

Heated blank loaded Mold closing, compressinginto mold material to fill cavity

SOURCE” P. Beardmore, C F. Johnson, and G.G. Strosberg, Ford Motor Co., “im-pact of New Materials on Basic Manufacturing Industries, A CaseStudy: Composite Automobile Structure” contractor report for OTA,1987

slowed. The material is formed to shape and flowsto fill the mold cavity much the same as ther-moset compression-molded SMC. The materialis cooled in the mold for a short period of timeto allow the part to harden, and then the moldis opened and the component is removed.

Thermoplastic compression molding is cur-rently used in automobiles to form low-cost semi-structural components such as bumper backupbeams, seats, and load floors. Commercially avail-able materials range from wood-filled polypropy-lene and short glass-filled polypropylene withrelatively low physical properties, to continuousrandom glass-reinforced materials based on poly-propylene or PET which offer somewhat higherphysical properties. Other materials, based onhighly oriented reinforcements and such resinsas polyetheretherketone (PEEK) and polyphony -Iene sulfide (PPS), are in use in the aerospace in-dustry. These materials are expensive and arelimited in their conformability to complex shapes.

Higher levels of strength and stiffness must bedeveloped in low-cost materials before they canbe used in structural automotive applications. At-tempts have been made to improve the proper-ties of stampable materials through the use ofseparate, preimpregnated, unidirectional rein-forcement tapes. These materials are added tothe heated material charge at critical locationsto improve the local strength and stiffness. Usingthese materials adds to the cost of the materialand increases cycle times slightly.

Although effective for simple configurations,location of the oriented reinforcement and repro-ducibility of location are problems in complexparts. To be most effective, these types of rein-forcements ultimately will have to be part of thepremanufactured sheet or be robotically applied.Current research is in progress in the area of ther-moplastic sheet materials with oriented reinforce-ment in critical areas. For application to automo-tive structures, these materials will have to retainthe geometric flexibility in molding (i. e., abilityto form complex shapes with the reinforcementin the correct location) exhibited by today’s com-mercial materials.

The question of part integration is a major is-sue in the expanded use of this process. The highpressures (1 ,000 to 3,000 psi) required limit thesize of components that can be manufactured onconventional presses. Thermoplastic compressionmolding is also limited in its ability to incorporatecomplex three-dimensional cores required for op-timum part integration.

If very large integrated structures are requiredfrom an overall economic viewpoint, thermoplas-tic compression molding will be restricted tosmaller components such as door, hood, anddeck lid inner panels in which geometry is rela-tively simple and/or part integration is limited dueto physical part constraints. If very large-scale in-tegration proves too expensive, then thermoplas-tic compression molding will exhibit increasedmarket penetration. Ongoing long-range researchin the area of low-pressure systems and incorpo-ration of foam cores in moldings could signifi-cantly alter this outlook in the longer term.

High-Speed Resin Transfer Molding

Fabrication processes that permit precise fibercontrol with rapid processability would overcomemany of the deficiencies outlined above. The useof some kind of preform of oriented glass fiberspreplaced in the mold cavity, followed by the in-troduction of a resin with no resultant fiber move-ment would satisfy the requirements for optimumperformance and high reliability.

The basic concepts required for this process arepracticed fairly widely today in the boat-building


and specialty-auto business. However, with fewexceptions, the glass preform is hand-constructedand the resin injection and cure times are of theorder of tens of minutes or greater. Also, dimen-sional consistency necessary for assembling high-quality products has not been studied for thisprocess.

Major reductions in manufacturing time andautomation of all phases of the process are nec-essary to increase automotive production rates.However, the basic ingredients of precise fibercontrol and highly integrated complex part ge-ometries (including, for instance, box sections)are an integral part of this process and offer po-tentially large cost benefits.

There are two basic elements associated withthe high-speed resin transfer molding (HSRTM)process that must be developed. The assemblageof the glass preform must be developed such thatit can be placed in the mold as a single piece.In addition, the introduction of the resin into themold must be rapid and the cure cycle must beequally fast to provide a mold-closed/mold-opencycle time of only a few minutes, A schematicof the process is presented in figure 7-17.

There are two processes currently in use thatmay have the potential to offer rapid resin injec-tion and cure times. One is resin transfer mold-ing. Currently in widespread use at slow rates,

Dry glass

Figure 7-17.–High-Speed Resin Transfer Molding (HSRTM)

fiber

E p o x y shaping die J

Heated steel/aluminum die ‘“ Q

Resin pump

Glass preform

SOURCE: P. Beardmore, C.F, Johnson, and G.G. Strosberg, Ford Motor-Co., “Impact of New Materials on Basic Manufacturing Industries, A Case Study: CompositeAutomobile Structure,” contractor report for OTA, 1987.


it could be accelerated dramatically by the useof low-viscosity resins, multiport injection sites,computer-controlled feedback injection controls,and sophisticated heated steel tools. There do notappear to be any significant technological bar-riers to these kinds of developments, but it willrequire a strong financial commitment to proveout such a system. A schematic of the processis presented in figure 7- I 8, which also illustratesa variant on the process usually termed squeezemolding.

The second process that promises rapid injec-tion and cure cycles is reaction injection mold-ing (RIM). In reaction injection molding, twochemicals are mixed and injected simultaneously;during injection the chemicals react to form athermosetting resin. Once the dry glass preformis in the mold, the resin can be introduced byany appropriate procedure, and reaction injec-tion would be ideal, provided the resultant resinhas adequate mechanical properties. The inher-ent low viscosity of RIM resins would be idealfor rapid introduction into the mold.

Full three-dimensional geometries includingbox sections, are attainable by preform molding.In addition, only low-pressure presses are nec-essary. The high degree of part integration max-imizes effective stiffness and minimizes assembly.

In principle, major portions of vehicles couldbe molded in one piece; for instance, Lotus autobody structures consist of two major pieces (al-beit molded very slowly) with one circumferen-tial bond. If similar-size complex pieces could bemolded in minutes, a viable volume productiontechnique could result.

Filament Winding

Filament winding is a PMC fabrication processthat for some geometric shapes can bridge thegap between slow, labor-intensive aerospace fabri-cation techniques and the rapid, automated fabri-cation processes needed for automotive manu-facturing. The basic process uses a continuousfiber reinforcement to form a shape by windingover some predetermined path. Figure 7-19 pro-vides a process schematic.

Figure 7-18.—Squeeze Molding and Resin Transfer Molding

Squeeze molding

Resin transfer molding

Fiber preform.1 L

SOURCE: P. Beardmore, C.F. Johnson, and G.G, Strosberg, Ford Motor Co., “Impact of New Materials on Basic Manufacturing Industries, A Case Study: CompositeAutomobile Structure, ” contractor report for OTA, 1987.


Figure 7.19.—Filament Winding Process

Glass

Filamentimpregnated applicationreinforcement

/ .

headtape

Resinimpregnationbath

Rotating. —componentmandrel

SOURCE: P. Beardmore, C.F. Johnson, and G.G. Strosberg, Ford Motor Co., “Impact of New Materials on Basic Manufacturing Industries, A Case Study: CompositeAutomobile Structure,” contractor report for OTA, 1987.

The complexity and accuracy of the windingpath are highly controllable with microcomputer-controlled winding machines. Thin, hollow shapeshaving high fiber-to-resin ratios are possible,thereby making the process well suited to light-weight, high-performance components. Glass fi-ber, aramid, or carbon fiber can be used as thewinding material. Filament winding can use ei-ther thermosetting or thermoplastic resin systems.

The uniform fiber alignment afforded by theprocess provides high reliability and repeatabil-ity in filament-wound components. Some simpleshapes, such as leaf springs, can be fabricated bythis process and are currently in production ona limited basis.

Thermoset Filament Winding

The majority of filament winding done todayuses thermosetting resin systems. In the thermosetfilament-winding process, the resin and reinforce-

ment fibers are combined (referred to as wettingout of the reinforcement) immediately prior tothe winding of the fibers onto the part. Thewetting-out and winding processes require pre-cise control of several variables. Reinforcementtension, resin properties, and the fiber/resin ra-tio all relate directly to the final physical proper-ties of the part. As the winding speed and partcomplexity increase, these variables become in-creasingly difficult to control.

Winding of complex parts at automotive pro-duction rates will require major process devel-opments. The likely potential of thermoset fila-ment winding in automotive applications is in thefabrication of simple shapes such as leaf springs,in which the cost penalty involved due to slowproduction speeds can be offset by a need forhigh reliability and maximum use of materialproperties.


Thermoplastic Filament Winding

Filament winding of thermoplastic materialsrepresents both the leading edge of this technol-ogy and the area in which its potential benefitto the automotive industry is greatest.

Thermoplastic filament winding uses a rein-forcement preimpregnated with a thermoplasticresin rather than a reinforcement impregnatedwith a thermosetting resin at the time of wind-ing. The preimpregnated filament or, more often,tape, is wound into the appropriate shape in amanner similar to the thermosetting filament-winding process, with the exception of a localheating and compaction step.

The reinforcement tape is heated with hot airor laser energy as it first touches the mandrel. Theheat melts the thermoplastic matrix both on thetape and locally on the substrate permitting aslight pressure applied by a following roller toconsolidate the material in the heated area. Be-cause the reinforcement filament is already wetout in a prepregging process, the substrate is so-lidified over its entirety with the exception of asmall zone of molten material in the area of con-solidation.

The limitations with respect to filament tension,filament wet-out, and speed at which a wet fila-ment can be pulled through a payout eye are nolonger a major concern with thermoplastic fila-ment winding. Thick sections can be rapidlywound, and nongeodesic and concave sectionscan be formed. However, the applicability to ge-ometries as complex as body structures is notestablished. Currently, problem areas exist in thecarryover of physical properties due to the limitedamount of research that has been done on theprocess. There are problems with the control ofthe heating and consolidation of the thermoplas-tic materials that yield less than predicted valuesfor tensile strength and interlaminar shear strength.

Although the thermoplastic materials will likelyexpand the structural component applications inwhich thermoplastic filament winding can eco-nomically compete with thermoset filament wind-ing, the increased speed and shape capabilitieswill not entirely offset the limited degree of partintegration possible. The inability to integrate boxsections with large flat paneIs in a one-piece struc-ture having complex geometry will tend to limitthe penetration of filament winding in bodystructures.

IMPACT ON PRODUCTION METHODSThe following sections discuss the various im-

pacts of these candidate technologies on automo-bile production methods.

Manufacturing Approach

The manufacturing approach for producingautos with PMC structural parts will be consider-ably different from the methods employed forbuilding conventional vehicles with steel bodies.Currently, many domestic automotive assemblyplants for steel vehicles are used for very littlebasic manufacturing. Instead, high-volume sheetsteel stamping plants, geographically located toservice several assembly plants, produce bodycomponents and small assemblies and ship themto the assembly pIants. The plants assemble thesheet metal components into an auto body struc-ture as presented in table 7-4 and figure 7-20aand b.

An auto body is a complex structure, and itsdesign is influenced by many demanding factors.At the present time, it appears that two systemscan be considered as possible processes to buildthe structural panels for PMC auto bodies.

One system consists of compression molding.Compression molded thin-walled panels are firstbonded together to form structural panels (seefigure 7-21) and then the structural panels, areassembled to form auto bodies. The other sys-tem involves HSRTM, in which preforms of fiberreinforcement are combined with foam cores,placed in a mold, and resin-injected to form large,three-dimensional structural panels (see figure 7-22). These panels are then assembled into autobodies. It is important to note that the filament-winding process is viewed as a limited construc-tion method largely due to the restricted com-plexity that is available with this technique.


Table 7-4.—Typical Body Construction System:Steel Panels

●

●

●

●

●

●

●

●

●

●

●

●

●

�

Build front structure—assemble aprons, radiator support,torque boxes, etc. to dash panelBuild front floor pan assemblyAssemble front and rear floor pan into underbody assemblyComplete spot welding of underbody assemblyTransfer underbody to skidBuild left-hand and right-hand bodyside assembliesMove underbody, bodyside assemblies, cowl top, wind-shield header, rear header, etc. into body buck line andtack-weld partsComplete spot welding of bodyBraze and fusion-weld sheet metal where requiredAssemble, tack-weld and respot roof panel to bodyAssemble front fenders to bodyAssemble closure panels (doors, hood, decklid) to bodyFinish exterior surface where required

SOURCE: P. Beardmore, C.F. Johnson, and G.G. Strosberg, Ford Motor Co., “im-pact of New Materials on Basic Manufacturing Industries, A CaseStudy: Composite Automobile Structure, ” contractor report for OTA,1987.

Therefore, it cannot now be considered as a com-petitive process for high-volume body structurefabrication.

Compression Molded Structural Bodies

Compression molded structural panels mightbe produced as presented in table 7-5 and fig-ure 7-21. Panel assemblies (side panels, floorpans, roof panels, etc.) are produced from innerand outer components. First, SMC sheet must bemanufactured and blanks of proper size andweight arranged in a large predetermined patternon the die surface. The panels are then moldedin high-tonnage presses. After molding, the partsare processed in a number of secondary opera-tions, bonded together, and transported to thebody assembly line.

Body construction commences with the floorpanel being placed in an assembly fixture. Sidepanel assemblies and mating components arebonded in place. Attachment points for the ex-terior body panels are drilled and the body struc-ture is painted prior to transporting to the trimoperations. (The body construction sequence isdescribed later, see table 7-9 and figure 7-24.)

High-Speed Resin Transfer MoldedStructural Bodies

bining the preform with foam cores, and inject-ing resin into the mold to infiltrate the preform.

First, dry glass preform reinforcements must befabricated. The preform may be composed of pri-marily randomly oriented glass fibers with addeddirectional glass fibers or woven glass cloth for

Figure 7-20(a).-Typical Assembly of Steel Underbody

Figure 7=20(b). -Typical Assembly of Underbody,Bodyside Assemblies, Etc. into the Completed

Steel Body Shell

HSRTM processing consists of three stages thatinvolve making a dry glass fiber preform, com-

SOURCE: P. Beardmore, C.F. Johnson, and G.G. Strosberg, Ford Motor Co., “im-pact of New Materials on Basic Manufacturing Industries, A CaseStudy: Composite Automobile Structure)” contractor report for OTA,1907.

Ch. 7—Case Study: Polymer Matrix Composites in Automobiles c 175

Figure 7-21 .—Typical Assembly of CompositeBodyside Panel by Adhesive Bonding of Inner and

Outer SMC Molded Panels

Cross sectionBodysideSheet-molded compound(two piece)

SOURCE: P. Beardmore, C.F. Johnson, and G.G. Strosberg l Ford Motor Co., “im-pact of New Materials on Basic Manufacturing Industries, A CaseStudy: Composite Automobile Structure,” contractor report for OTA,1987.

Figure 7-22.—Typical One. Piece Composite BodysidePanel With Foam Core Molded by High-Speed Resin

Transfer Molding

1 piecemolding

BodysideResin transfer molding(one piece)

SOURCE: P. Beardmore, C.F. Johnson, and G.G. Strosberg, Ford Motor Co., ‘“im-pact of New Materials on Basic Manufacturing Industries, A CaseStudy: Composite Automobile Structure,” contractor report for OTA,1987.

local reinforcement of high-stress areas. To beeconomically viable, preform fabrication must beaccomplished by a highly automated technique.The process sequence is described in table 7-6.

Second, foam core reinforcements must befabricated to obtain three-dimensional inserts,such as those used in rockers and pillars. Local

Table 7-5.—Compression Molded Structural Panels

●

●

●

●

●

●

●

●

�

Fabricate and prepare SMC chargeLoad charge into die and mold panelRemove components from molding machine (inner and out-er panels), trim and drill parts as requiredAttach reinforcements, latches, etc., to inner and outerpanels, with adhesive/rivetsApply mixed, two component adhesive to outer panelAssemble inner and outer panels, clamp and cureRemove excess adhesiveRemove body panel from fixture and transport to body con-struction line’

SOURCE: P. Beardmorej C.F. Johnson, and G.G. Strosberg, Ford Motor Co., “lm-pact of New Materials on Basic Manufacturing Industries, A Case—- Study: Composite Automobile Structure, ” contractor report for OTA,1987.

Table 7-6.—Preform Fabrication Sequence

● Apply random glass fibers over mandrel● Apply directional fibers (or woven cloth) for local rein-

forcement● Stabilize preform● Remove preform and transfer to trim station● Trim excess fibers● Transfer to HSRTM panel molding lineSOURCE: P. Beardmore, C.F. Johnson, and G.G. Strosberg, Ford Motor Co., “im-

pact of New Materials on Basic Manufacturing Industries, A CaseStudy: Composite Automobile Structure, ” contractor report for OTA,1987,

metal reinforcements and fasteners can be pre-positioned in the mold at this point during foamfabrication. The chemicals are subsequently in-troduced into the mold and the resulting reactionyields an accurately shaped foam part. The proc-ess sequence is described in table 7-7.

Third, the body structural panel is molded. Agel coat may be sprayed in both the lower andupper mold cavities to obtain a smoother surfaceon the finished part. Preforms, foam cores, andany necessary additional local reinforcementsand fasteners are placed in the respective lowerand upper mold cavities. In high production,

Table 7.7.—Foam Core Fabrication Sequence

● Clean mold and apply part release● InstalI reinforcements and basic fasteners● Close mold● Mix resins and inject into mold● Chemicals react to form part● Open mold● Unload part and place on trim fixture● Trim and drill excess material● Transport to HSRTM body panel IineSOURCE; P. Beardmore, C.F. Johnson, and G.G. Strosberg, Ford Motor Co., “im-



these operations must be carried out robotically.The mold is closed and a vacuum may be ap-plied. The resin is injected, infiltrates the preform,and cures to form the body structural paneI. Themolding is then removed from the die andtrimmed. This process sequence is described intable 7-8 and illustrated in figure 7-22.

The final stage of body construction is the as-sembly of the individual panels, The underbodypanel is placed on the body construction line.Adhesive is applied to the side panels by robotsin the appropriate joint locations, the side panelsare mated to the underbody and clamped inplace, and the fasteners are added, Similarly, theremainder of the body structure is located andbonded to form a complete auto body. After cur-ing, the body is washed and dried, prior to trans-fer to trim operations. This process sequence isdescribed in table 7-9 and illustrated in figure7-23.

(Note that the body assembly sequence givenin table 7-9 is essentially common to both com-pression molding and HSRTM. This is only oneillustration of the assembly of a number of mold-ings to form the body—the number of moldingscould vary from 2 to 10 depending on the spe-cific design and manufacturing details,19)

lsBeardmOre, Johnson, and Strosberg, op. ci t . , footnote 1.

Table 7-8.—HSRTM Molded Structural Panels

Clean mold and apply part releaseSpray gel coat into mold (optional)Insert lower preforms and local woven fiber reinforcementsInsert specialized reinforcements and fastenersInsert foam coresInsert upper preforms and local woven fiber reinforcementsClose moldApply vacuum to mold (optional)Inject resin and allow chemicals to reactOpen moldRemove assembly and place in trim fixtureTrim and drill body panelTransport to body assembly line

SOURCE: P. Beardmore, C.F. Johnson, and G.G. Strosberg, Ford Motor Co.. “im-pact of New Materials on Basic Manufacturing Industries, A CaseStudy: Composite Automobile Structure,” contractor report for OTA,1987.

Table 7.9.—Body Construction Assembly Sequence

●

●

●

●

●

●

●

�

Place underbody in body build lineApply adhesive to bond lines of side panels and cowlMate side panels to underbody, clamp and insert fastenersApply adhesive to cowl top assembly, lower back panel andmateApply adhesive to roof panel and mate to body side panelsTransfer body to final trim operationsAfter final trim, the painted exterior body panels are as-sembled to the auto body

SOURCE: P. Beardmore, C.F. Johnson, and G.G. Strosberg, Ford Motor Co., “Im-pact of New Materials on Basic Manufacturing Industries, A CaseStudy: Composite Automobile Structure,” contractor report for OTA,1987.

As noted, figure 7-23 is a schematic of a mul-tipiece PMC body. For comparison, a two-pieceHSRTM body construction is illustrated in figure7-24 to indicate the various levels of part integra-tion that might be achieved using PMCs. In boththese scenarios, the body shell would consist ofPMC structure with no metal parts except formolded-in steel reinforcements.

Assembly Operation Impact

In both the compression molding and HSRTMscenarios, there would be a considerable change

Figure 7.23.–Typical Body Construction Assemblyfor Composite Body Shell



Figure 7-24.–Typical Body Construction AssemblyUsing Two Major Composite Moldings

Table 7-10.—Effect of Composites onBody Complexity

Typical number ofVehicle design major parts in Typical number ofand material body structure assembly robots

A. Conventional welded steelbody structure. . . . . . . ., 250 to 350 300

B. Molded SMC body structure. 10 to 30 100C. High-speed resin transfer

molded composite/bodystructure . . . . . ... 2 to 10 50

Estimated part reduction(A less B) . . . . . . . . . . . . . . . 240 to 320 200 to 250

Estimated part reduction(A less C) ,,, . . . . . . . . . . . . 248 to 340 250 to 280

SOURCE P Beardmore, C F Johnson, and G G Strosberg, Ford Motor Co , “Impact of NewMaterials on Basic Manufacturing Industries, A Case Study Composite Automobile Struc-ture, contractor report for OTA, 1987

SOURCE: P. Beardmore, C.F. Johnson, and G.G. Strosberg, Ford Motor Co., “im-pact of New Materials on Basic Manufacturing Industries, A CaseStudy Composite Automobile Structure,” contractor report for OTA,1987,

in the assembly operations for PMC vehiclesversus conventional steel vehicles. The numberof component parts in a typical body structure(body-in-white less hoods, doors, and decklids)varies with vehicle design and material, as pre-sented in table 7-IO.

The dramatic reduction in the number of partsto be assembled in a PMC vehicle would resultin a corresponding reduction in the number ofsubassembly operations and amount of subas-sembly equipment, as well as a reduction in therequired floorspace. For instance, robots used toproduce PMC assemblies can lay down an adhe-sive bead considerably faster than robots canspotweld a comparable distance on mating com-ponents. Therefore, it is anticipated that therewould be a considerable reduction in the num-ber of robots and complex welding fixtures re-quired.

Labor Impact

The design and engineering skills that wouldbe required to apply PMCs would be somewhat

different from the skills used for current metal ap-plications. A broader materials training curricu-lum would be required because the chemical,physical, and mechanical properties of PMCs dif-fer significantly from those of metals. These pro-grams are currently being developed at someuniversities but significant expansion would benecessary to ensure this trend on a broader scale.

The overall labor content for producing a PMCbody would similarly be reduced as numerousoperations would be eliminated. However, it isimportant to note that body assembly is not alabor-intensive segment of total assembly. Otherassembly operations that are more labor-intensive(e.g., trim) would not be significantly affected,Thus, the overall labor decrease due to PMCsmight be relatively small.

The level of skills involved in PMC assemblyline operations (e.g., bonding operations) is notexpected to be any more demanding than theskill level currently required for spotwelding con-ventional body assemblies. In either case, goodproduct design practice dictates that product as-sembly skill requirements be matched with theskill levels of the available workers to obtain aconsistently high-quality level.


IMPACT ON SUPPORT INDUSTRIESThe increased use of polymer composites could

strongly affect the existing automotive support in-dustries as well as promote the development ofnew ones.

Material Suppliers, Molders, andFabricators

PMC vehicle body structures of the future,whether built with compression-molded or HSRTMparts, are expected to be designed with compo-nents integrated into modular subassemblies.Therefore, these units will be of considerable sizeand are not conducive to long-range shipping.Manufacturing on site in a dedicated plant formolding body construction and assembly oper-ations, just prior to trim and final assembly of thevehicle, will become necessary.

PMC automobile production, in relatively highvolumes, will require additional qualified suppliercapacity. The extent of these requirements willbe dependent on the economic attractivenessand incentives for developing in-house capacityby the automotive manufacturers. Fortunately,these demands are likely to be evolutionary, inthat the automotive industry would undoubtedlycommence with low annual volume (10,000 to60,000) PMC body production units.20 When(and if) higher volume production of PMC bod-ies is planned, additional supplier capacity canbe put in place as a result of supplier/manufac-turer cooperation throughout the normal leadtime (4 to 6 years) for the planning, design, andrelease of a new vehicle to manufacturing.21

Although compression molding is the most ma-ture of the evolving PMC production techniques,a major conversion to SMC for body structureswould require a substantial increase in resin andreinforcement output, mold-building capacity,molding machine construction, component mold-ing, subassembly facilities, adhesives, and qual-ity control tools, etc.

If the HSRTM processing concept is used, resinand reinforcement suppliers would need to sub-

Zolbid .

ZI Ibid.

stantially expand their output (as in the case ofcompression molding) and perhaps develop newproducts to meet the unique demands of theprocess. Tooling is similar in construction to thatused in injection molding, and therefore manu-facturers of this type of tooling would likely ex-pand to fill the need. If inexpensive electroformedmolds, which consist of 0.25 inch of electroplatednickel facing on a filled epoxy backing (usedtoday for low-pressure or vacuum-assisted mold-ing) become feasible, this phase of the industrywould have to be developed and expanded. Be-cause molding pressures for this process are low,high-tonnage hydraulic presses would not beneeded. However, companies specializing inautomation and resin handling equipment wouldplay an increased role.

If PMC structures were suddenly implemented,there would bean expected shortfall of qualifiedmolders and fabricators regardless of the proc-ess chosen. It is more likely, however, that im-plementation would be evolutionary, and thesupply base would be addressed during the PMCvehicle planning and design stage. To enlarge thesupply base, the auto industry is currently work-ing with, and encouraging, qualified vendors toexpand and/or diversify, as required, to supportproduct plans. Additionally, with growth in PMCdemand, new suppliers would be expected to be-come qualified.

Current suppliers may also form joint venturesand/or make acquisitions to expand capabilitiesduring the phase-in period of PMC structures.Along with the need to expand materials supplyand facilities, there is the significant need to de-velop and retrain qualified personnel to providesupport for both supplier and automotive indus-try operations.

The current molding capacity for SMC devotedto the automotive industry is of the order of 500million to 750 million pounds annually.22 Figure7-25 projects the additional volume of PMCs thatwould be needed as a function of producing ahigh volume of autos with a high content of com-posites. The data are based on a substitution for

22 lbid.

Ch. 7—Case Study: Polymer Matrix Composites in Automobiles 179

Figure 7-25.—Effect of Composite Use on Steel Usein Automobiles

Decrease in steel usage (106 tons)

x

o 1 2 3

Composite usage (106 tons)

Increase in composites usage and associated decrease insteel usage for various production volumes of composite-intensive vehicles. Assumes 1,000 lb. of steel is replaced by650 lb. of composites in a typical vehicle weighing 2,700 lb.that contains 1,600 lb. of steel.Two million composite-intensive vehicles per year causes aloss of one million tons of steel, which is roughly 12 percentof steel usage in automobiles, see table 7-11.


a typical vehicle weighing 2,700 pounds and con-taining 1,600 pounds of steel. Of this 1,600 poundsof steel, 1,000 pounds of steel have been replacedby 650 pounds of PMCs. It is evident that therewouId be a relatively massive incremental amountof PMCs needed for even 1 million vehicles peryear–about 300,000 tons (650 million pounds);i.e., roughly a doubling of current SMC capac-ity.23 Each additional million vehicles would re-quire the same increase, creating (ultimately) anenormous new industry.

Steel Industry

The implementation of PMCs in automobileswould clearly have an impact on the steel indus-try. As with the plastics industry, this impactwould be volume-dependent. In the initial stages,with volumes in the range of 10,000 to 60,000

231 bid.

vehicles per year, there would be only a mini-mal effect-a small loss in steel tonnage, someexcess press capacity, and some additional stamp-ing die building capacity. 24 The loss of steel ton-nage from the steel mills would cause additionalproblems for this already beleaguered segmentof industry. Both captive and/or supplier stamp-ing plants would have idle capacity. Stamping diebuilders would lose orders, unless they could alsobuild molds for plastics. However, these poten-tial problems for the steel industry would beevolutionary and would take several years to oc-cur after the successful introduction of vehiclesusing this technology.

Figure 7-25 can be used to place this potentialimpact in perspective. The decrease in steel useas a function of increasing production volume ofcars with a high PMC content would become sig-nificant only at intermediate volume levels. Thedata reproduced in table 7-11 show that at vol-umes of up to 500,000 PMC vehicles per year,automotive use of steel would drop only about250,000 tons (or 3 percent) per year.25 Since mo-tor vehicle manufacturing uses about 15 percentof all steel consumption in the U.S.,26 steel con-sumption would drop 0.45 percent for volumesof 500,000 PMC vehicles per year. Major steelproduction decreases would result only from amajor change in PMC vehicle volume—e.g., 2million vehicles or more.27

zqlbid.zslf a vehicle is specifically designed for PMCS instead of steel,

and, for instance, the volume is on the order of 500,000 units, theimpact would be greater.

26 U.S. Department of Commerce, Bureau of Economic Analysis,

The Detailed Input-Output Structure of the U.S. Economy, 1977,vol. 1, Washington, DC, 1984.

z7Beardmore, johnson, and Strosberg, op. cit.

Table 7-11.—Automotive Steel Usage(based on annual volume of 107 vehicles)

Production volume of Steel usagecomposite-intensive vehicles (106) tons

o 850,000 7.975

500,000 7.755,000,000 5.5

10,000,000 3.0SOURCE: P. Beardmore, C.F, Johnson, and G.G. Strosberg, Ford Motor Co., “Im-


180 “ Advanced Materials by Design

It is also recognized that the steel industry andits suppliers are aggressively seeking methods toreduce costs and provide a wider range of steels.This healthy economic competition between steeland PMCs will have an effect on the timing ofPMC auto introductions and the volumes to beproduced. World competition in the steel indus-try is leading to the availability of a wider rangeof high-strength steels with improved quality, re-sulting in an increase in productivity for the enduser. The balance between improved economicfactors for steel use and the rate of improvementof PMCs processing will dictate the use, rate ofgrowth, and timing of the introduction of PMCvehicles.

Repair Service Requirements

Another support industry of importance is thePMC repair service required to repair vehicledamage caused in accidents, etc. During the de-sign process, automobile engineers will designcomponents and body parts to simplify fieldrepairs. For repair of major damage, large replace-ment components or modules will have to besupplied. At the present time, the comparativeexpense of repairing PMC structures relative tosteel is unclear. Replacement parts or sections willtend to be more expensive. However, low-energycollisions are expected to result in less damageto the vehicle. Thus, the overall repair costsacross a broad spectrum of vehicles and damagelevels are not anticipated to be any higher thancurrent levels.

Exterior SMC body panel repair procedures arealready in existence at automotive dealershipsand independent repair shops specializing infiberglass repairs. With additional PMC use, it isexpected that the number of these repair serv-ice facilities will increase. To repair the PMCstructure, dealers and independent repair centerswill need new repair procedures and repair ma-terials. The development of the appropriate re-pair procedures will be contained well within thetime frame of PMC vehicle introduction. Therewill be new business opportunities to establishadditional independent shops.

As with any new vehicle design, PMC repairprocedures must be fully developed and stand-

ardized, along with the additional training of re-pair personnel. This training will require skilllevels equivalent to those required for steel repair.

PMC Vehicle/Component Recycling

The recycling industry is another support in-dustry that will undergo significant change in thelonger term if PMC vehicles become a significantportion of the volume of scrapped vehicles. Cur-rent steel vehicle recycling techniques (shreddersand magnetic separators) will not be applicable,and cost-effective recycling methods will need tobe developed exclusively for PMCs. Low volumesof scrap PMC vehicles will have minimal effect,but the problems will increase as the volumereaches a significant level. This level is estimatedto be in the range of 20 percent or more of thetotal vehicles to be salvaged .28

Plastics must be segregated into types prior torecycling. Currently, only clean, unreinforcedthermoplastic materials can readily be reclaimed,but the techniques are somewhat inadequate andtend to be very expensive. Fortunately, the calo-rific value of many thermoplastics approachesthat of fuel oil. Some waste-incinerating plantsnow operate with various types of plastics as fuel.One developing use for plastic waste involvespulverizing plastics and using their calorific valueas a partial substitute for fuel oil in cement kilns.Some plastics in automobiles can be recycled bymelt recovery, pyrolysis, and hydrolysis, but cost-effective methods are not yet in place.

Thermoset plastic components, such as SMCpanels and other PMC body components, cur-rently cannot easily be reclaimed because of theirrelatively infusible state and low resin content.Grinding, followed by reuse in less demandingapplications such as roadfill or building materi-als, is possible, but is not currently economical.Consequently, these kinds of parts are used aslandfill or are incinerated. Again, at low volumes,these recycling procedures are acceptable, butthey would not be viable at high scrap rates.

Without the advent of some unforeseen recy-cling procedures, it appears likely that incinera-tion will have to be the major process for the fu-

*81 bid.


ture. The viability of incineration will either have more favorable economics or some penalty willto be improved by more efficient techniques for likely have to be absorbed by the product.

POTENTIAL EFFECTS OF GOVERNMENTAL REGULATIONSAny major potential changes in automotive in-

dustrial practice, such as the large-scale substi-tution of a new structural material, must take intoconsideration not only current regulations butalso future regulations that may already be un-der consideration or that may be initiated be-cause of the potential changes in industrial prac-tice. One example is the increased safety (crash-resistance) requirements already under activeconsideration. Another is the potential increasesin CAFE standards for the 1990s. Although thefollowing discussion of such potential regulationsis not comprehensive, it serves to illustrate theimportance of such considerations in introduc-ing major materials changes to the automotiveindustry.

Health Safeguards

The introduction of fiber-reinforced plastics insignificant volumes into the automotive work-place may raise health and environment con-cerns. Any fibers in very fine form have the po-tential to create lung and skin problems, andalthough glass fibers may be among the more in-ert types of fiber, there must still be adequateprecautions taken in handling these fibers.

Currently, glass fibers are widely used in vari-ous industries such as molding industries, boatbuilding, and home construction; extension tothe automotive industry would probably not re-quire development of safeguards other than thoseused within those existing industries.

However, the widespread nature of the auto-motive business would undoubtedly raise aware-ness of potential health risks and could precipi-tate more stringent requirements for the workplace.Although such additional precautions may notpose a technological problem, the extent of theregulations could have a significant effect on theeconomic viability of the use of composites.

Similarly, the same problems could arise withthe resin matrix materials of these PMCs. It is notclear which specific resin materials will be dom-inant for PMCs use, but there is a widespreadconcern regarding all chemicals in the workplaceand in the environment.

There are already strong regulations concern-ing chemical use and handling, but again, thesheer magnitude of the automotive industry islikely to bring such requirements to the forefrontof interest and may result in additional legisla-tion. This could result in limitation of the typesof resins used and implementation of additionalsafeguards. The impact is less likely to preventimplementation of PMCs technology than it is toaffect the economic viability and timing of theintroduction of this technology.

Recyclability

The current recycling of scrap automobiles isa major industry. Sophisticated techniques havebeen developed for separating the various ma-terials, and cost-effective recycling procedures arean integral part of the total automotive scene. Be-cause steel constitutes 60 percent (by weight) ofa current automobile, the recycling of steel is themajor portion of the recycling industry. Recyclingof PMCs is a radically different proposition, anduse of these materials will necessitate develop-ment of new industrial recycling processes if largevolumes are manufactured.

If PMCs are only applied in low-volume spe-cialty vehicles, however, current recycling tech-niques of landfill and incineration will probablybe adequate.

The potential for large numbers of composite-intensive vehicles to be scrapped will undoubt-edly raise the issue of disposal to the nationalspotlight. One concern is that there would be adisposal problem due to a lack of economic in-

.—


centives to recycle. Consequently, this problemmay need to be addressed by legislation beforewidespread use of these materials is permitted.The result of such legislation could be the com-mitment of resources at an early stage of devel-opment with payback as part of the. overall costof PMC development.

Crash Regulations

There are regulations in existence, and othersproposed, that set or would set impact-survivalcriteria in frontal impacts, side crash tests, andvehicle-to-vehicle impacts. Various scenarios havebeen proposed for making these standards morestringent (e.g., raising frontal-impact criteria from30 to 35 miles per hour, and possibly higher).

Basic experience to date in crash-energy man-agement has primarily been with steel vehiclesand, consequently, the specific wording of theregulations is based on the characteristics of thesevehicles. Vehicles consisting largely of PMC ma-terials absorb energy by significantly differentmechanisms, and the details of impact would bevery different from those of steel vehicles, eventhough the objective of occupant protectionwould be the same.

Thus, new regulations in this area could con-tain provisions that would preclude the use ofPMCs because of the lack of information. For in-stance, if a requirement were promulgated thatstated no fracture of a major body structure shalloccur during a certain impact, PMCs would beexcluded because, unlike steels, internal fractureof the PMCs is a critical part of energy absorp-tion. Thus, detailed wording of crash regulationsbased on steel experience could inadvertentlyjeopardize the potential use of PMC structuralmaterials.

Fuel Economy Standards

Just as some regulations might produce deter-rents to PMCs use, others might promote devel-opment and use. If CAFE requirements were drasti-cally increased, there would be a limited numberof options for increasing fuel efficiency-down-sizing, increased power train efficiency, andweight reduction. In terms of weight reduction,aluminum alloys and PMCs would represent per-haps the major options. Thus, legislation requir-ing a marked increase in fuel economy mighttend to promote the development and use ofPMCs, providing that functional requirements,manufacturing feasibility, and overall economicfactors are proven.

TECHNOLOGY DEVELOPMENT AREAS

Although years of development efforts have ad-vanced structural composites so that they con-stitute a significant material for use in the avia-tion and aerospace industries, the cost-effectiveuse of these materials in the automotive indus-try requires considerable additional developmen-tal work in the following areas.

Compression Molding

Improvements in SMC technology are requiredin the areas of reduced cycle times, reproduci-bility of physical properties and material handle-ability. A major improvement would be a signif-icant reduction in manufacturing cycle time.Current objectives are to cut the conventionaltime from 2 to 3 minutes to 1 minute or less. De-

velopment of materials requiring less flow toachieve optimum physical properties would per-mit more reproducible moldings to be made.Other potential technology improvements forSMC include a reduction in the aging time for ma-terial prior to molding, an internal mold releasein the material, an improved cutting operationto prepare a loading charge for the molding ma-chine, automated loading and unloading of mold-ing machines, and improved dimensional con-trol of final parts.

High-Speed Resin Transfer Molding

There are two critical segments of this processthat require major developments to achieve via-bility. One is reduction in manufacturing cycle


time, and new, faster curing resins currently un-der development should make significant con-tributions in this area. The other is developmentof automated preform technology (foam core de-velopment and subassembly), which is critical toachieving cost-effectiveness. This is perhaps thearea requiring major innovation and invention,but it has yet to be perceived by the existing fi-ber and fiber-manipulation industry to be a ma-jor area for development.

Fiber Technology

There are three major areas in fiber technol-ogy that must be optimized to promote fiber usein high-production industries: 1 ) improved phys-ical properties of the composite, 2) improved fi-ber handling and placement techniques, and 3)improved high-volume production techniquesproviding fibers at lower cost. Superior physicalproperties would result from improved sizings (fi-ber coatings) to reduce fiber damage during proc-essing and provide improved mechanical prop-erties in the finished components. Fiber-handlingequipment permitting high-speed, precise fiberplacement with minimal effect on fiber proper-ties is a vital requirement for the developmentof stable, three-dimensional preforms. Cost mini-mization is a critical factor in using glass fibersbut also should be considered from the viewpointof generating other fibers (e.g., carbon fibers) atcosts amenable to mass-production use.

Joining

Two key areas dominate the category of join-ing technology. First, adhesives and mechanicalfasteners must be tailored for PMC construction,to develop the necessary combination of produc-tion rate and mechanical reliability. Second, there

is a need for the development of design criteriaand design methodologies for adhesive joints.Neither of these areas have been systemically de-veloped for a mass-production industry and fargreater attention must be paid to joining materi-als and to methods for alleviating any problemsin this element of the overall PMCs technology.

General Technology Requirements

Design methodologies for use with PMCs tocover all aspects of vehicle requirements mustbe developed to a degree comparable to currentsteel knowledge. The ability to tailor PMCs forspecific requirements must be integrated intosuch design guides, and this makes the task morecomplex than the equivalent guidelines for iso-tropic materials (e.g., metals). Manufacturingknowledge and experience, which provide con-straints for the design process, must be fully doc-umented to optimize product quality, reliability,and cost-effectiveness, The degree of componentintegration must be a key factor in determiningmanufacturing rates, and this interdependenceof design and manufacturing will evolve only overa protracted time period. This buildup of experi-ence will be the key factor in resolving overalleconomic factors for the production of compos-ite vehicles.

Standards

The complexity of PMC materials relative tometals will require the development of standardtesting procedures and material specifications asis discussed in chapter 5. The rapid proliferationof materials in the PMC arena will not permit fi-nal establishment of these generic standards un-til PMC technology matures. It is likely that spe-cific corporate standards will be used in theinterim prior to professional society actions.

SUMMARYThe extension of PMCs use to automotive struc- ogies. There is abundant laboratory evidence and

tures will require an expanded knowledge of the some limited vehicle evidence that strongly in-design parameters for these materials, together dicates that glass fiber-reinforced PMCs are ca-with major innovations in fabrication technol- pable of meeting the functional requirements of


the most highly loaded automotive structures.There are, however, sufficient uncertainties (e.g.,long-term environmental effects, complex crashbehavior) that applications will be developedslowly until adequate confidence is gained. Never-theless, it seems inevitable that the functionalquestions will be answered, and it only remainsto be seen how soon.

perhaps the most imperative requirement is thecost-effective development of fabrication tech-niques. There will be a prerequisite to widespreaduse of PMCs in automotive structures. High-vol-ume, less-stringent performance components canbe manufactured by variations of compressionmolding techniques. it is the high-volume, high-performance manufacturing technology that needsdevelopment, and the HSRTM process appearsto be a sleeping fabrication giant with the poten-tial of developing into just such a process.

All the elements for resolving the rapid, high-performance issue are scattered around the some-what fragmented PMCs industry. It will requirethe appropriate combination of fiber manufac-turers, resin technologists, fabrication specialists,and industrial end users to encourage the nec-essary developments.

The advent of composite-intensive vehicles willbe evolutionary. The most likely scenario wouldbe pilot programs of large PMC substructures asinitial developments to evaluate these materialsrealistically in field experience. This would be fol-lowed by low annual production volumes (20,000to 60,000 units) of a composite-intensive vehiclethat would achieve the extensive manufacturingexperience vital to the determination of realisticfabrication guidelines and true economics.29 The

29 lbid ,

data derived from such introduction would de-termine the potential for high-volume production.

Currently, the industry infrastructure is not inplace for PMC-intensive vehicles. In addition, thesupply base could presently respond to only low-volume production of PMC vehicles. Neither ofthese situations is a major restriction in that theanticipated long development time would per-mit the appropriate changes to occur over a pro-tracted period. Rather, the initial decisions tomake the necessary changes and (substantial) fi-nancial commitments will have to be based onsignificant evidence that PMC vehicles are via-ble economically and will offer customer benefits.

irrespective of the scenario for the eventual in-troduction of PMC vehicles, there are probablysome general conclusions that can be drawn rela-tive to the impact of these materials. PMC appli-cations are unlikely to have a large effect on thesize of the labor force because the major changesare not in labor-intensive areas of vehicle manu-facture and assembly. Likewise, the necessaryskill levels for both the fabrication of the PMCparts and assembly of the body should not be sig-nificantly changed. Engineering know-how wouldbe very different, but the needed skill levelswould be similar to those already in place.

Perhaps the largest effect would be on the sup-ply industries, which would need to implementproduction of PMCs. This would involve both achange in technology for many current suppliers,together with the development of a new supplybase. The steel industry would experience a cor-responding decrease in output, but the decreasewould only be of major proportion if PMC vehi-cles became a significant proportion of total ve-hicle output. The repair and recycling industrieswould similarly undergo a major change to ac-commodate the radical change in the vehicle ma-terials.

case study: polymer matrix composites in automobiles

Documents