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LAND TRANSPORTATION APPLICATIONS 41

Douglas L. Denton

41.1 INTRODUCTION

The use of polymer composite materials in land transportation is steadily increasing because of the cost and performance advantages that composites offer over competing materials. Today, composites are extensively used in well-established passenger car, van and truck applications. New applications demanding higher structural performance lev- els are under development. Railroad cars, mass transit vehicles and a wide range of military ground transportation systems offer expanding opportunities for composite materials.

Driving forces for the use of polymer composites in ground transportation applications include low manufacturing investment cost, cost reduction through parts consolidation, weight savings, good mechanical properties, 'Class A' surface quality, excellent durability characteristics, inherent dent and corrosion resistance, good noise and vibration dampen- ing, styling flexibility and dimensional stability. Factors which tend to mitigate against their use are high materials costs, low modulus and the reluctance to use materials perceived to be 'new and unproven'.

Only those materials and processes which provide required performance at the lowest cost achieve long-term commercial success in transportation applications. For high-volume automobile and truck applications, high-speed

Handbook of Composites, Edited by S.T. Peters. Published in 1998 by Chapman & Hall, London. ISBN 0 412 54020 7

processes must be used to manufacture parts rapidly enough to meet the production rates of the assembly plants. As a result, injection and compression molding processes are used extensively for these applications. Composites typically used in transportation applications consist of low-cost grades of thermoplastic or thermoset polymers reinforced with E-glass fibers. Often these composites also contain mineral particulate fillers. Composites containing high-modulus fibers, such as carbon, and higher-performance resins such as epox- ies, are used only where the higher cost can be justified to meet special product requirements. Metal matrix composites are used very spar- ingly in ground transportation.

Over the past 50 years, the use of polymer composites generally has progressed from low-performance applications towards more demanding applications requiring excellent surface appearance, high mechanical properties, increased temperature stability or improved durability. With increasing demands to reduce vehicle weight for improved fuel economy, and to reduce investment costs for greater competitiveness, the use of composites in ground transportation is expected to increase for many decades to come.

41.2 ECONOMICS AND MARKET GROWTH

The steady growth in the use of composites for land transportation is attributed primarily to the development and acceptance of new applications. From the late-1960s to the mid-1990s

906 Land transportation applications

composite usage in USA transportation more than quadrupled (Fig. 41.1), and since the early 1980s it has expanded at a faster rate than the total composites market. Land transportation use of polymer composites represents the largest segment (over 30%) of the total market and reached 430 000 metric tons in 1994 according to the SPI Composites Institute.

Year

Fig. 41.1 Growth in the shipments of polymer composites for use in land transportation. (Source: SPI Composites Institute.)

Composites have generally displaced metal alloys such as steel to gain new applications. In order for a material substitution to be successful, composites must provide all of the functions required by the part at a competitive cost. Because of strong competitive forces in the transportation industry original equip- ment manufacturers (OEMs) seldom pay higher cost for a new material to achieve desir- able functions beyond the part requirements. Therefore, composites must achieve cost effectiveness for long-term use in transportation applications.

On a price per unit weight basis, composite material costs are generally several times higher than the metals used in automobile and truck applications. However, when the total cost of component production and vehicle assembly is considered, composite parts can

be equal to or lower than stamped steel parts. A primary factor offsetting high materials cost is the lower investment needed to make parts from composites compared to steel. To produce a composite part generally only one mold and one press is needed whereas most steel parts require multiple stamping tools and presses to form the part. In addition, composites offer the opportunity to integrate several parts formed in steel into one part. This fur- ther reduces the number of tools and presses needed, and eliminates the welding operations required to join the stampings.

The cost advantage achieved or cost penalty incurred by composites depends upon the total volume of an application. As the number of parts produced becomes very high, the reduced investment in tools and presses is off- set by the higher materials cost for the composite. In the automobile industry the use of a composite part produced at a volume of several hundred thousand units per year may not be not cost effective. But production of the same composite part at volumes of tens of thousand units per year may be very competitive. The specific cost 'cross-over' point between composites and steel depends on a large number of factors and must be deter- mined for each specific application.

41.3 HISTORICAL DEVELOPMENT OF APPLICATIONS

Polymer composites began to appear on cars shortly after World War I1 in small components under the hood and inside the passenger compartment. The first major milestone in exterior parts was the introduction of the Corvette in 1953 which sported body panels made of glass fiber reinforced polyester (Fig. 41.2). The body panels were produced with open mold and preform molding processes up to 1972, when the production was converted to compression molded sheet molding composite (SMC). The invention of the SMC process and the development of 'low profile' polyester resins, which provided

Historical development of applications 907

Fig. 41.2 Glass fiber reinforced polyester body panels on the 1953 Corvette was the first major application of composites in the automotive industry. Other composite applications introduced on the Corvette include bumper beams, leaf springs, radiator support, seat backs and rear floor pan. (Photo courtesy of General Motors Corporation.)

improved surface appearance, allowed the proliferation of composites into higher volume body applications.

SMC grille opening panels (GOP) were introduced in the late 1960s and rapidly spread throughout the industry because fiber glass GOPs saved weight and reduced cost through significant parts consolidation. With the introduction of composite panels on automobile assembly lines, the dimensional consistency of molded parts became well known. Manufacturers also recognized that the SMC panels could not be deformed to adjust for variations in the steel body structure. Modification of assembly plant procedures to accommodate the unique characteristics of composite parts continues to be an issue with new part introduction.

The need to reduce vehicle weight through materials substitution and downsizing to meet government mandated Corporate Average

Fuel Economy (CAFE) standards led to intense development of new composite applications and a significant upswing in composite usage in the late 1970s (Fig. 41.1). Composites not only expanded into additional cosmetic parts, but began to be seriously considered for use in structural components. Intense programs to develop radiator supports, transmission supports, leaf springs and wheels were initiated. Efforts to find additional under-the-hood and interior applications of composites were also intensified.

Improvements in composite surface quality and productivity lead to the introduction of the 1984 Fiero, the second high-volume vehicle with all exterior body panels made of composites. Using innovative body construction, exterior panels produced by the SMC and RRIM (reinforced reaction injection molding) processes were mechanically fastened onto a steel spaceframe. A similar design approach


was used for the construction of General Motor’s all purpose vehicles (APV). Introduced in 1989, these minivans used approximately 120 kg (260 lb) of SMC per vehicle (Fig. 41.3). With annual production volumes ranging from 90 000 to 148 000 vehicles per year this represented the largest single application of composites in the automotive industry.

The Dodge Viper was the first American vehicle to have all body panels produced by the resin transfer molding (RTM) process (Fig. 41.4). The low production volumes for the Viper (under 5000 per year) made this an ideal application for composites. The selection of an RTM process with low cost molds resulted in greater investment savings than could be achieved with SMC and RRIM. This milestone application was introduced in the early stages of an industry-wide effort to develop the RTM and SRIM (structural reaction injection molding) processes for the production of structural and Class A parts for the transportation market.

41.4 CURRENT APPLICATIONS

41.4.1 AUTOMOTIVE APPLICATIONS

On average, cars produced in USA in 1994 contained about 50 kg (110 lb) of fiber reinforced composites. The broad usage of composites in the automobiles and trucks is illustrated by the list of applications in Table 41.1. Distinctions can be made between applications that are experimental, have been in limited production or are well-established in production. In many cases, breakthrough composite applications are introduced by manufacturers of low volume specialty vehicles before they appear in high volume car lines produced by larger companies such as Chrysler, Ford or General Motors. These larger companies often will evaluate a new application on a low-volume specialty vehicle or on a customized segment of a high-volume vehicle before committing to high-volume production with a composite part.

Fig. 41.3 GM’s all purpose vehicle (APV) is the automotive industry’s largest application of composites. Each vehicle uses approximately 120 kg (260 lb) of SMC in addition to other polymer composites. (Photo courtesy of General Motors Corporation.)

Current applications 909

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Fig. 41.4 The Dodge Viper is the first American car to have ail Class A composite body panels produced by the resin transfer molding (RTM) process. (Photo courtesy of Chrysler Corporation.)

Automotive body applications

Composites have proven to be very successful in a wide range of exterior body panels and are used in hundreds of vehicle applications. Excellent surface finish, light weight, and a thermal coefficient of expansion near that of steel have made these applications successful. Customers appreciate the dent and corrosion resistance of composite panels.

SMC dominates composite applications in horizontal panels such as hoods, roof and deck lids, and competes with RRIM for vertical panels such as fenders, doors and quarter panels. The use of unreinforced thermoplastic body panels on vehicles such as GMs Saturn and Chrysler 's Intrepid, Concorde, and Vision demonstrate the potential for the displacement of composites in some body applications.

Newly developed composites made from compression molded glass fiber mat thermoplastic sheet (GMT) or liquid molded (RTM/SRIM) thermoset resins may also compete with SMC for horizontal body panels.

The broader use of composites in body panels is restricted by their limited cost- effectiveness at very high production volumes. Composite panels are well-suited for niche vehicles and for providing economical opportunities to achieve styling differences within a body line, but they are seldom employed in high-volume applications. Another factor that precludes the use of some polymer composites in body panels is sensitivity to high temperature. In most assembly operations all body panels are subjected to a heat soak at 175-205°C (350400°F) for about 30 min fol- lowing the electrodeposition of a corrosion


coating (‘E-Coat’ or ’ELPO) to the steel body structure. Only a limited number of low-cost polymer composites can resist dimensional change or surface distortion during this heat treatment.

While composites are used in the body structure for several low-volume sports cars, this opportunity remains essentially untapped in the auto industry. The Lotus Esprit has an all-composite body produced by the VARI process (vacuum assisted resin injection) that is mounted on a steel frame. Lotus uses a sim- ilarly produced composite floor pan and body panels in the Elan. Consulier manufactures sports cars with all-composite monocoque bodies produced by vacuum bag molding of epoxy prepregs with E-glass, Sglass, carbon and KevlaP fibers. The entire body structure weighs only 125 kg (275 lb) and takes all structural loads. Higher volume applications in body structure includes the Corvette which has used composites in the floor pan, rear underbody and radiator support.

Since the early 1980s an evolving series of composite materials and processes have been used to produce front and rear bumper beams. SMC containing random chopped and/or continuous unidirectional fibers was initially used. Subsequently, stamped thermoplastic composites and SRIM bumper beams have been commercialized. Special design consider- ations and parts consolidation have lead to the use of glass-reinforced polypropylene (Azdel@) in the front bumper beams of Chrysler minivans, which are produced in volumes of more than 500 000 units per year.

Automotive chassis applications

While relatively few composite chassis components have been commercialized, notable applications have provided evidence of the performance level and durability offered by composites.

One of the most successful automotive stmc- tural applications to date is the composite leafspring. After decades of development work

and extensive testing, a transverse rear leaf spring was introduced on the 1981 Corvette. This 3.6 kg (8 lb) filament wound E-glass/epoxy monoleaf spring replaced a ten-leaf steel spring weighing 19 kg (421b). A front transverse spring was added to the Corvette in 1984 and the first composite longitudinal spring appeared on the General Motors Astro van in 1985. The use of composite springs rapidly spread across GM car lines in the late 1980s and early 1990s. In less than a decade from its introduction, the Inland Division of GM (now Delphi Chassis Systems) was manufacturing more than one million Liteflex@ composite springs per year (Fig. 41.5) to meet the demand.

Fig. 41.5 Composite leaf springs reduce vehicle weight, resist corrosion and outlast traditional steel leaf springs. (Photo courtesy of Delphi Chassis Systems.)

The exceptional weight savings and outstand- ing durability have been the keystones to the success of composite springs in cars and more recently, in heavy trucks. Composite springs last at least five times longer than steel coun- terparts in laboratory fatigue tests and in field service. Added advantages are improved packaging due to smaller size, and improved ride and handling characteristics. Their long- term field success has also clearly demonstrated the survivability of polymer composite materials in the harsh under-vehicle environment.


Another suspension application demon- strating the durability and load carrying capability of composites is wheels. The commercial introduction of polymer composite wheels was on the 1989 Shelby CSX modified version of the Dodge Shadow. Developed by the Motor Wheel Corporation, the Fiberide@ wheel uses a combination of structural SMC and XMC. These materials provided a mix- ture of chopped random and oriented continuous E-glass in a vinyl ester resin. At reduced weight, the composite wheel out- performed both steel and aluminum wheels in fatigue. The development of polymer composites that retained acceptable lug nut torque after wheel heating caused by extreme braking conditions was a technical advance that made this application possible.

A front suspension stabilizer link was introduced on the 1994 Ford Taurus and Mercury Sable. Made from a glass fiber reinforced copolymer polyacetal, this was the first use of a structural thermoplastic composites in such an application in North America. This durable part does not require painting and reportedly provides a 42% weight reduction and 33% cost reduction over the replaced steel part.

Automotive powertrain applications

The application of composites in the powertrain is extensive and is growing. In the past, only metals were considered for use in the demanding environment of the engine and transmission. Increasingly, composites are being selected to reduce weight and cost, and to improve NVH (noise, vibration and harsh- ness), engine efficiency, packaging and corrosion resistance.

Air intake manifolds are rapidly being converted from metal to injection molded thermoplastics reinforced with short glass fibers. Introduced on European cars in the 1970s, composite manifolds are predicted to be used on most vehicles by the turn of the century. Most intake manifolds are produced

by the 'lost-core' process in which a low temperature melting alloy such as tin-bismuth is used as a form to mold the hollow sections. The core is then melted away from the cured part in a subsequent operation. An alternative is to 'weld' two thermoplastic pieces to form the manifold. To reduce cost, some fuel intakes are being integrated with the air intake manifold.

Injection molded phenolic compounds are used in many engine and transmission applications because of dimensional stability and creep resistance at higher temperatures. Current applications include pulleys, torque converter reactors, thrust washers, water outlets, valve covers, radiator end caps, motor commutators and fuel rails (Fig. 41.6).

While the performance advantages of composite drive shafts and propeller shafts (lower weight, better NVH, increased durability) has been established, cost remains a barrier to their wide spread use. A composite drive shaft has an economic advantage, however, when it replaces two-piece metal shafts. The most successful designs have used glass and/or carbon fiber composite overwrapped on an aluminum tube using pultrusion or filament winding processes.

Fig. 41.6 Powertrain applications of phenolic composites include transmission torque converter reactors and thrust washers, poly-V pulleys, and water outlets. (Photo courtesy of Rogers Corporation.)


Experimental engines made almost exclu- sively of polymer composite materials,

rods, have been tested, but commercialization

41.4.2 TRUCK APPLICATIONS

Composites are widely used in the medium-

decrease weight, reduce manufacturing and

including block, head, pistons and connecting duty and heavy-duty truck industry to

is in the near future. Many maintenance costs, and extend the longevity of matrix (MMC) parts have been the vehicles. Lighter trucks allow increased prototyped for engine applicationsf payload capability and improved fuel econ- few have gone into production (Table 41.1). Aluminum reinforced with silicon carbide, alumina or carbon fibers offers the potential for good mechanical and thermal properties with large weight savings. However, factors such as high cost, low ductil- ity and machining difficulties have retarded the commercialization MMCs in transports- tion components.

Automotive interior applications

manufacturers make extensive use of polymeric materials on the interiors of cars

omy. Since trucks are generally not produced in high volumes, the lower tooling invesment favors composite parts. The durability is important since are used for many years.

Composites are commercially used for essentially all skin surfaces on truck cabs, air deflectors, hoods, fenders, roofs, side closure panels, sleeper box and doors. Mack Truck introduced the first structural SMC door in 1978 and two years later GM Truck and Coach made the first use of continuous fiber SMC in the door of the Astro and General truck cabs. In 1983 Mack Truck became the first manufac-

and trucks/ most do not require fiber rein- to meet performance requirements.

turer to introduce a cab with composites used in all exterior surfaces. These panels covered a

knee and instrument Pane' structural composite beams. Several all-composite truck cabs using monocoque structures

Some notable exceptions are seats, load floors, frame made of steel, aluminum, and

seat were first introduced on the 1975 Corvette. In have been prototyped and shown to meet all addition to stamped polypropylene, ther- performance requirements.

used in both seat back and seat pans. An injec- trailers when floor, wall and ceiling panels are tion seat with long fiber composite. In addition, refrigerated trailers

rently preferred for load floors in station wagons and extended pick-up truck cabs.

Stamped polypropylene has been used in numerous knee bolsters. This structural part at the bottom of the instrument panel helps to control occupant movement during a frontal crash. Composites and unreinforced thermoplastics are also being used in instrument panel supports to provide lower cost through parts integration and reduced weight. The use of composites in the front of vehicle interiors is expected to expand.

mosetting Polyurethanes and Polyester are Weight savings of 20% are achieved in truck

reinforcement Premiered On the 1993 Dodge sheet is cur-

made from composites are 25-30y0 more ther- mally efficient than metal trailers. In a recent application, Trail King has introduced a flat bed trailer with a fiber reinforced epoxy deck to achieve lower weight, corrosion resistance and lower cost.

One of the fastest growing application in heavy truck is composite leaf springs for large weight savings and greatly extended spring life.

41.4.3 RAILROAD APPLICATIONS

Durability and light weight make composites attractive for railroad applications, yet few


Table 41.1 Composite applications in automobiles and trucks'

Experimental Limited production Well established Body Front rails

A, B and C pillars Roof frame Rockers Rear underbody Pickup truck box Truck cab structure Truck trailer bed

Radiator support Floor pan Cowl panel Wheel housing Windshield surround Door surround Center tunnel Tanker truck trailers EV battery tray

Grille opening panel Grille opening reinforcement

Rear end panel Hood Deck lid Lift gate Rear hatch Roof panel Hardtop cover Fenders Quarter panels Doors outers Door inners Spoiler Headlamp cover Fuel filler doors Front bumper beams Rear bumper beams Truck air defector Truck trailer walls Truck trailer roof

Chassis Front cross member Wheels Leaf spring Transmission support Stabilizer bar links Disk brake pistons Brake rotors'

Powertrain Throttle body Oil pump - - Transmission valve body Hydraulic clutch actuator Engine - Pistons, block, head, piston pins3 connecting rods3 rocker arms2 bed plate2

Flywheel4 Drive shaft2

Drive shaft Propeller shafts Water pump housing Water pump impeller Fuel pump components Fuel rail Fuel tank supports Camshaft sprockets Oil pan Differential cover Valve lifter guides CNG storage cylinders5 Cylinder liners2 Pistons2

Air intake manifold Battery tray Fan shroud Radiator end caps Transmission torque converter reactor/stator

Transmission thrust washer Motor commutators Diesel electronic unit injector Valve cover Timing chain covers Poly-V pulleys Idler pulley Distributor cover

Interior Car jack Knee bolster Seat back Steering wheel Instrument panel support Seat support

Window frame/trim Load floor Plenum Glove box

Polymer composite unless noted otherwise Metal matrix composites Metal matrix or polymer matrix composites

Electric powered vehicles Natural gas vehicles


have been commercialized. Pultruded glass fiber reinforced thermoplastic composite panels are used to construct a 'Secured Modular Automotive Rail Transport' (SMART) for Union Pacific Railroad. Each three-tier structure serves as a 'car rack' to protect eighteen automobiles from damage and theft during transport to the dealer. The use of composites also significantly reduces the maintenance cost of the car rack.

Composite hopper car covers protect grain and other dry materials that need protection from moisture. The covers, which range from 9-15 m (3040 ft) in length, are fabricated by a hand lay-up process. Two prototype glass/polyester filament wound railroad cars termed the 'Glasshopper' have been in service since 1981 without failure. Produced in a joint venture by ACF Industries, Cargill and Southern Pacific, the corrosion resistant, lightweight composite car can carry a greater payload, but is significantly more expensive than a steel hopper car.

41.4.4 MASS TRANSIT APPLICATIONS

Buses and passenger rail systems offer many more opportunities for the application of composites than are presently in service. Some cosmetic and semi-structural applications have been successfully implemented, but few examples of structural components are found.

The durability of polymer composites has lead to extensive use in seats for buses, sub- ways, people movers and trains. Composite sandwich panels with glass fiber-phenolic skins over aramid or aluminum honeycomb are used in walls, ceilings and floors of many European mass transit cars. These rigid panels are very lightweight and the use of phenolic resins allows attainment of fire/emission standards. The end caps of transit cars are often molded composites. Pultruded exterior panels are being substituted for aluminum on buses to reduce weight and decrease assembly cost.

The development of high speed rail systems, which attain speeds up to 480km/h

(300 miles per hour), may offer an opportunity for composites because of the need to mini- mize weight. Weight reduction is especially important for magnetic levitation (MAGLEV) systems where the vehicle is suspended above the guideway to provide friction free movement.

41.4.5 MILITARY APPLICATIONS

Limited applications of composites are found in combat and non-combat ground vehicles in the US military, but if current development programs are successful, much greater use of composites should result. Modern warfare requires rapidly deployable, survivable vehicle systems. Thus, weight reduction in all vehicles, including armored vehicles, is desir- able. In addition to weight savings, composites can potentially offer increased durability, improved signature management! better personnel protection and lower production cost.

The goal of an ongoing Army project, the Composite Armored Vehicle Advanced Technology Demonstrator (CAV ATD), is to establish the feasibility of using polymer composites in the primary structure of a 20 tonne (22 ton) combat vehicle to achieve a 33% weight saving over a traditional metal vehicle. Composites are also being considered for combat vehicle armor - used either alone or in conjunction with ceramics and/or metals - to provide significant weight savings over current materials. The High Mobility Multi-purpose Wheeled Vehicle (HMMWV), which is currently in production, utilizes an integrated hood/fender assembly molded from SMC. In upgraded versions, composite armor is attached to the HMMWV.

Phenolic spa11 liners containing Kevlar or S-2 Glass@ fibers are used in the M113A3 Armored Personnel Carrier and Bradley Fighting Vehicle to provide troop protection. Longer service life and chemical protection were the motivation for the incorporation of composite seats and side racks in 2.2 tonne

Conclusions 915

(2.5 ton) and 4.4 tonne (5 ton) trucks. Other potential composite applications such as M1 Abrams Main Battle Tank components (dri- ver’s seat, air intake plenum, stowage box, and power pack container), tactical vehicle body, fuel tanker and HMMWV drive shaft are under consideration for production after the turn of the century.

41.5 FUTURE DIRECTIONS

The growth of the transportation market is expected to continue, and potentially acceler- ate, into the 21st century. As composites become better understood by designers, and as the reliability and advantages of these materials are more clearly demonstrated, they will be used increasingly in more demanding structural applications. Body structure, chassis and powertrain offer tremendous opportunities for the utilization of composite materials. Improved manufacturing capability to rapidly produce composite parts will boost their economic viability in high volume applications. The development of a commercial infrastruc- ture and market for the large scale recycling and reuse of polymeric materials will also increase the growth opportunity for composites.

The potential economic advantages and weight reductions afforded by the use of composites in integrated body structure and chassis components has driven development programs since the 1980s. In 1988 Chrysler, Ford and General Motors formed the Automotive Composites Consortium (ACC) to conduct joint R&D on structural polymer composites with a focus on these structural applications. Operating under the United States Council on Automotive Research (USCAR), the ACC works with supplier companies and uni- versities to develop the processing, materials, design and joining technology needed to achieve production worthiness and cost effectiveness of composite structures. Currently, the US Federal Government is providing resources

and technical expertise acquired in defense programs to the development of composite technology needed to improve the competitiveness of American industries with a particular emphasis on the automotive industry. Numerous federal programs are directing dollars and technical expertise resident in the National Laboratories into ground transportation programs. A notable example is the ’Partnership for a New Generation of Vehicles’ program, which teams the government with the automotive industry to produce the technology to make safe, comfortable, and affordable cars that achieve up to 30 km/l (82 miles per gallon) of gasoline with low emis- sions. Composite materials are expected to play a key role in meeting this challenging goal. Successful implementation of the tech- nologies developed in these cooperative programs could have an enormous impact on the usage of composites in future vehicles.

41.6 CONCLUSIONS

Ground transportation is the largest and one of the fastest growing segments of the polymer composites market. While transportation use of composites is expected to expand, the rate of growth depends on a number of factors. Improvements in technology are needed to increase high volume production capability and increase the cost competitiveness of composites relative to other materials. The performance and durability of composites in a wide range of structural applications must be demonstrated. More designers and engineers need to become familiar with the unique characteristics of composites and learn to develop designs that use the full potential of these materials. An economically viable infrastruc- ture for dealing with post-consumer waste must be established. With these advances, composites are expected to play an important role as industry meets the increasing world- wide demand for safe, clean, energy efficient land transportation.

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