COMPOSITE MATERIALS FOR OTHER APPLICATIONS We have given in Chapter 1 an idea on the diversity of the products which can be made using composite materials.'In this chapter we examine a few of these products,which form a good part in the evolution of these materials,excluding the aerospace sector presented in the previous chapter. 8.1 COMPOSITE MATERIALS AND THE MANUFACTURING OF AUTOMOBILES 8.1.1 Introduction Composite materials have been introduced progressively in automobiles,following polymer materials,a few of which have been used as matrices.It is interesting to examine the relative masses of different materials which are used in the construction of automobiles.This is shown in the graph in Figure 8.1.Even though the relative mass of polymer-based materials appears low,one needs to take into account that the specific mass of steel is about 4 times greater than that of polymers. This explains the higher percentage in terms of volume for the polymers.Among the polymers,the relative distribution can be shown as in Figure 8.2. The materials called "plastics"include those so-called "reinforced plastics"for composite pieces that do not have very high performance.The graph in Figure 8.3 gives an idea for the distribution by zone of the "plastic"pieces in an automobile and also shows the evolution in time.One can see the increasing importance of high-performance parts. 8.1.2 Evaluation and Evolution A few dates on the introduction of composite parts (fibers matrix)include: The antiques as shown in Figure 8.4 1968:wheel rims in glass/epoxy in automobile S.M.Citroen (FRA) 1970:shock absorber shield made of glass/polyester in automobile R5 Renault (FRA) TSee Section 1.3. 2003 by CRC Press LLC
8 COMPOSITE MATERIALS FOR OTHER APPLICATIONS We have given in Chapter 1 an idea on the diversity of the products which can be made using composite materials.1 In this chapter we examine a few of these products, which form a good part in the evolution of these materials, excluding the aerospace sector presented in the previous chapter. 8.1 COMPOSITE MATERIALS AND THE MANUFACTURING OF AUTOMOBILES 8.1.1 Introduction Composite materials have been introduced progressively in automobiles, following polymer materials, a few of which have been used as matrices. It is interesting to examine the relative masses of different materials which are used in the construction of automobiles. This is shown in the graph in Figure 8.1. Even though the relative mass of polymer-based materials appears low, one needs to take into account that the specific mass of steel is about 4 times greater than that of polymers. This explains the higher percentage in terms of volume for the polymers. Among the polymers, the relative distribution can be shown as in Figure 8.2. The materials called “plastics” include those so-called “reinforced plastics” for composite pieces that do not have very high performance. The graph in Figure 8.3 gives an idea for the distribution by zone of the “plastic” pieces in an automobile and also shows the evolution in time. One can see the increasing importance of high-performance parts. 8.1.2 Evaluation and Evolution A few dates on the introduction of composite parts (fibers + matrix) include: The antiques as shown in Figure 8.4 1968: wheel rims in glass/epoxy in automobile S.M.Citroen (FRA) 1970: shock absorber shield made of glass/polyester in automobile R5 Renault (FRA) 1 See Section 1.3. TX846_Frame_C08 Page 181 Monday, November 18, 2002 12:22 PM © 2003 by CRC Press LLC
mass distribution steel 75% polymers aluminum 16% textiles 9% #0.5% Figure 8.1 Use of Different Materials in Automobiles polymer mass distribution elastomers plastics (rubber) 45% 40% paints varnish in which tires:32% 15% Figure 8.2 Mass Distribution Among Polymer Materials Consequences of the introduction of composite pieces in automobiles are now well-known.They allow a number of advantages.One can find several common points with aeronautic construction.There are also disadvantages that are more specific to automobiles. ■Advantages include Lightening of the vehicles:A reduction of mass of 1 kg induces a final reduction of 1.5 kg,taking into account the consecutive lightening of the mechanical components. 2003 by CRC Press LLC
Consequences of the introduction of composite pieces in automobiles are now well-known. They allow a number of advantages. One can find several common points with aeronautic construction. There are also disadvantages that are more specific to automobiles. Advantages include Lightening of the vehicles: A reduction of mass of 1 kg induces a final reduction of 1.5 kg, taking into account the consecutive lightening of the mechanical components. Figure 8.1 Use of Different Materials in Automobiles Figure 8.2 Mass Distribution Among Polymer Materials TX846_Frame_C08 Page 182 Monday, November 18, 2002 12:22 PM © 2003 by CRC Press LLC
mass distribution mass distribution body elements body elements elements under the hood elements under the hood passenger compartment passenger compartment 49% 56.7% electricity electricity transmission transmission motor motor 23.5% 21.5% chassis chassis 20.7% suspension suspension 2.8% 2.7% 16.8% 0.5% 2% 2% 1.7% 1982:101.000tons 1987:181.000tons Figure 8.3 Distribution of "Plastic"Components in an Automobile 1955.Citroen DS 19(FRA) 1953,Chevrolet Corvette (USA). roof in glass/polyester complete body in glass/polyester 70.000 cars/year 10,000 cars/year Figure 8.4 Composite Pieces in Antique Cars Cost reduction:This is due to the reduction of the number of pieces required for a certain component and to noise reduction and isolation. The better corrosion resistance of the composite pieces. Significant disadvantages are It is difficult,for fabrication in large volume,to obtain as good a surface finish as that of painted sheet metals. For the car body,the painting process and the treatment of the surfaces require high temperature exposure. 2003 by CRC Press LLC
Cost reduction: This is due to the reduction of the number of pieces required for a certain component and to noise reduction and isolation. The better corrosion resistance of the composite pieces. Significant disadvantages are It is difficult, for fabrication in large volume, to obtain as good a surface finish as that of painted sheet metals. For the car body, the painting process and the treatment of the surfaces require high temperature exposure. Figure 8.3 Distribution of “Plastic” Components in an Automobile Figure 8.4 Composite Pieces in Antique Cars TX846_Frame_C08 Page 183 Monday, November 18, 2002 12:22 PM © 2003 by CRC Press LLC
How to Evaluate the Gains: In theory:These are the experimental vehicles;Ford,Peugeot (1979).As com- pared with the metallic pieces,composite parts have obtained mass reduction of 20%to 30%on the pieces for the body. 40%to 60%on the mechanical pieces Example:Ford vehicle,which has a mass in metallic construction of 617 kg and a mass in composite construction of 300 kg for a global gain of 52%.It is convenient to consider this case as "technological prowess"far from the priority of economic constraints. In practice:Over the past years,an increasing number of pieces made of glass fibers/organic matrices have been introduced.The following list contains pieces that are in actual service or in development. Components for the body ■Motor cap ■Hood cover ■Hatchback door ■Fenders ■Roofs ■Opening roof ■Doors ■Shock absorber ■Interior components ■Seat frames Side panel and central consoles ■Holders Components under the hood ■Headlight supports ■Oil tanks ■Direction columns Cover for cylinder heads Cover for distributor ■Transmission shafts Motor and gearbox parts Components for the structure ■Chassis parts ■Leaf springs ■Floor elements Figure 8.5 shows the importance of the volumes actually occupied by the composites in an automobile. Example:Automobile BX Citroen (FRA)1983 with a total mass of 885 kg. Many of the molded pieces made of glass/resin composites as shown in Figure 8.6 are now commonly used by the automobile manufacturers.We note in particular the two elements below,the importance and large volume production of which (rate of production of more than 1000 pieces per day),indicate a significant penetration of composites in the manufacturing of automobiles. 2003 by CRC Press LLC
How to Evaluate the Gains: In theory: These are the experimental vehicles; Ford, Peugeot (1979). As compared with the metallic pieces, composite parts have obtained mass reduction of 20% to 30% on the pieces for the body. 40% to 60% on the mechanical pieces Example: Ford vehicle, which has a mass in metallic construction of 617 kg and a mass in composite construction of 300 kg for a global gain of 52%. It is convenient to consider this case as “technological prowess” far from the priority of economic constraints. In practice: Over the past years, an increasing number of pieces made of glass fibers/organic matrices have been introduced. The following list contains pieces that are in actual service or in development. Components for the body Motor cap Hood cover Hatchback door Fenders Roofs Opening roof Doors Shock absorber Interior components Seat frames Side panel and central consoles Holders Components under the hood Headlight supports Oil tanks Direction columns Cover for cylinder heads Cover for distributor Transmission shafts Motor and gearbox parts Components for the structure Chassis parts Leaf springs Floor elements Figure 8.5 shows the importance of the volumes actually occupied by the composites in an automobile. Example: Automobile BX Citroen (FRA)1983 with a total mass of 885 kg. Many of the molded pieces made of glass/resin composites as shown in Figure 8.6 are now commonly used by the automobile manufacturers. We note in particular the two elements below, the importance and large volume production of which (rate of production of more than 1000 pieces per day), indicate a significant penetration of composites in the manufacturing of automobiles. TX846_Frame_C08 Page 184 Monday, November 18, 2002 12:22 PM © 2003 by CRC Press LLC
rear window doorframe opening roof side aileron roof support for window wiper rear light box hood gas hatch rear shield hub cab front rim shield front lower grill body reinforcing rear view front wheel lateral rib mirror upper piece protection door panel front fender roof opening roof frame demister upper lining ducts board back cylinder head plate cover battery spare tire support hatch and cover front face leaf spring headlight socket back shock structure absorber seat shell self supporting wheel motor shock fuel floor space support beam line Figure 8.5 Composite Pieces in an Automobile The hood is made of glass/polyester molded at high temperature in a press (20,000 kN)with the deposition of a gel coat during molding'to assure the quality of the surface.The following comparison is eloquent: 2 See Section 2.1.1. 2003 by CRC Press LLC
The hood is made of glass/polyester molded at high temperature in a press (20,000 kN) with the deposition of a gel coat during molding2 to assure the quality of the surface. The following comparison is eloquent: Figure 8.5 Composite Pieces in an Automobile 2 See Section 2.1.1. TX846_Frame_C08 Page 185 Monday, November 18, 2002 12:22 PM © 2003 by CRC Press LLC
rear window guide air gnll rear hatch back hood glass/polyamide glass/polyamide glass/polyester glass/polyester decorating grill glass/polyamide head lamp socket glass/polyester gas hatch rim glass/polyamide glass/polyamide Figure 8.6 Composite Pieces in BX Citroen Figure 8.7 Automobile Alpine V6,Renault Conventional metallic construction (GS Citroen):7 elements Composite construction:1 element Mass gain:7.8 kg or 46%. The rear window frame is made of injection molded glass/polyester (23,000 kN press).The mechanical characteristics obtained with this method (frac- ture resistance,modulus,impact resistance)are in the vicinity of those obtained by compression molding.One obtains a single piece that can support the rear glass piece,the aerodynamic details,the hinges,and the lower part of the trunk.The advantages over the classical construction are great: Classical construction (GS Citroen):27 elements Composite construction:7 elements Mass reduction:1.7 kg or 16% Example:Automobile Alpine V6 Turbo,Renault (FRA),1986 (Figure 8.7).The entire body in glass/polyester composites is not obtained by molding according to 2003 by CRC Press LLC
Conventional metallic construction (GS Citroen): 7 elements Composite construction: 1 element Mass gain: 7.8 kg or 46%. The rear window frame is made of injection molded glass/polyester (23,000 kN press). The mechanical characteristics obtained with this method (fracture resistance, modulus, impact resistance) are in the vicinity of those obtained by compression molding. One obtains a single piece that can support the rear glass piece, the aerodynamic details, the hinges, and the lower part of the trunk. The advantages over the classical construction are great: Classical construction (GS Citroen): 27 elements Composite construction: 7 elements Mass reduction: 1.7 kg or 16% Example: Automobile Alpine V6 Turbo, Renault (FRA), 1986 (Figure 8.7). The entire body in glass/polyester composites is not obtained by molding according to Figure 8.6 Composite Pieces in BX Citroen Figure 8.7 Automobile Alpine V6, Renault TX846_Frame_C08 Page 186 Monday, November 18, 2002 12:22 PM © 2003 by CRC Press LLC
the technique used for the previous model A 310(contact molding).3 It is made by bonding around fifty elements in glass/polyester on a tubular chassis. The panels are made by molding using a press at low pressure and temperature (6 minutes at 45C). Contouring is done using a high-speed water jet. Structural bonding is done on a frame at 60C.Robots control it.The classical mechanical nuts and bolts are replaced by 15 kg of adhesives. Significant advantages include the following: There is reduction in fabrication time:80 hours versus 120 hours for the construction of the previous model A 310. Excellent fatigue resistance is realized:(mileage 300,000 km). There is good filter for noise from mechanical sources. The flexibility in the method of fabrication:The tooling in the press is inter- changeable in order to produce small series of different pieces on the same press.This process is well adapted to a low rate of fabrication (10 cars per day). Mass reduction-as compared with the technique used in the previous model,which itself was using composites-is 100 kg. For a cylinder size of 2500 cm2(power of 147 kW or 240 CV),it is one of the most rapid series of vehicles ever produced in France previously (250 km/h)with a remarkable ratio of quality/price as compared with other competing European vehicles (Germany in particular). Example:Racing car"F.1"Ferrari (ITA)(Figure 8.8).This car body is a sandwich made of NOMEX honeycomb/carbon/epoxy.In addition,a crossing tube made of carbon/epoxy transmits to the chassis aerodynamic effects that act on the rear flap. This is attached to the chassis by light alloy parts,bonded to the composite part with structural araldite epoxy adhesive.There is weight reduction compared with previous metallic solution,and one also sees very good fatigue resistance,which is important in regard to mechanical vibrations. 8.1.3 Research and Development A number of working pieces-traditionally made of metallic alloys-of road vehicles have been designed and constructed in composite materials,and they have actually been tested and commercialized: 8.1.3.1 Chassis Components Research and Development work has been concerned with the spars,floors,front structures,rear structures,and also the complete structure. Principal advantage:Reduction in the number of parts and thus in the cost. Secondary advantage:Mass reduction (beams for truck chassis in Kevlar/ carbon/epoxy lead to a mass reduction of 38%-46 kg versus 74 kg for metal). 3See Section 2.1.1. See Section 2.2.5. 2003 by CRC Press LLC
the technique used for the previous model A 310 (contact molding).3 It is made by bonding around fifty elements in glass/polyester on a tubular chassis. The panels are made by molding using a press at low pressure and temperature (6 minutes at 45∞C). Contouring is done using a high-speed water jet.4 Structural bonding is done on a frame at 60∞C. Robots control it. The classical mechanical nuts and bolts are replaced by 15 kg of adhesives. Significant advantages include the following: There is reduction in fabrication time: 80 hours versus 120 hours for the construction of the previous model A 310. Excellent fatigue resistance is realized: (mileage > 300,000 km). There is good filter for noise from mechanical sources. The flexibility in the method of fabrication: The tooling in the press is interchangeable in order to produce small series of different pieces on the same press. This process is well adapted to a low rate of fabrication (10 cars per day). Mass reduction—as compared with the technique used in the previous model, which itself was using composites—is 100 kg. For a cylinder size of 2500 cm 3 (power of 147 kW or 240 CV), it is one of the most rapid series of vehicles ever produced in France previously (250 km/h) with a remarkable ratio of quality/price as compared with other competing European vehicles (Germany in particular). Example: Racing car “F.1” Ferrari (ITA) (Figure 8.8). This car body is a sandwich made of NOMEX honeycomb/carbon/epoxy. In addition, a crossing tube made of carbon/epoxy transmits to the chassis aerodynamic effects that act on the rear flap. This is attached to the chassis by light alloy parts, bonded to the composite part with structural araldite epoxy adhesive. There is weight reduction compared with previous metallic solution, and one also sees very good fatigue resistance, which is important in regard to mechanical vibrations. 8.1.3 Research and Development A number of working pieces—traditionally made of metallic alloys—of road vehicles have been designed and constructed in composite materials, and they have actually been tested and commercialized: 8.1.3.1 Chassis Components Research and Development work has been concerned with the spars, floors, front structures, rear structures, and also the complete structure. Principal advantage: Reduction in the number of parts and thus in the cost. Secondary advantage: Mass reduction (beams for truck chassis in Kevlar/ carbon/epoxy lead to a mass reduction of 38%—46 kg versus 74 kg for metal). 3 See Section 2.1.1. 4 See Section 2.2.5. TX846_Frame_C08 Page 187 Monday, November 18, 2002 12:22 PM © 2003 by CRC Press LLC
cross beam carbon/epoxy body honey comb/carbon/epoxy Figure 8.8 Ferrari F.1 Racing Car Figure 8.9 Front Face of 405 Peugeot The problems involved are numerous: How to assemble the pieces. What will be the mechanical behavior when subjected to strong impacts? How is the rate of production to be augmented?The actual fabrication methods are too slow (decrease in the cycle time by using automation). Example:The superior cross beam or "front face"of the automobile 405 Peugeot (FRA).This component (see Figure 8.9)is subjected to repeated load cycles in tension,flexure,and torsion.It also supports several dozens of 2003 by CRC Press LLC
The problems involved are numerous: How to assemble the pieces. What will be the mechanical behavior when subjected to strong impacts? How is the rate of production to be augmented? The actual fabrication methods are too slow (decrease in the cycle time by using automation). Example: The superior cross beam or “front face” of the automobile 405 Peugeot (FRA). This component (see Figure 8.9) is subjected to repeated load cycles in tension, flexure, and torsion. It also supports several dozens of Figure 8.8 Ferrari F.1 Racing Car Figure 8.9 Front Face of 405 Peugeot TX846_Frame_C08 Page 188 Monday, November 18, 2002 12:22 PM © 2003 by CRC Press LLC
mass metallic system metallic composite system spnng composite junctions spnng junctions:.. Figure 8.10 Comparison Between Metallic and Composite Springs components and equipment that form the front face of the vehicle.Characteristics include: Part molded in glass/polyester (V=42%) Fabrication process:SMC:Press 15,000 N Rate of production:1200 pieces/day Machining/drilling (70 holes);installation of inserts(30)and components made by laser,numerical machining,and robots 8.1.3.2 Suspension Components Springs:One of the principal characteristics of the unidirectionals (namely glass/resin)is their capacity to accumulate elastic energy.Herein lies the interest in making composite springs.In theory,a glass/resin spring is capable of storing 5 to 7 times more elastic energy than a steel spring of the same mass. Other advantages include: The composite springs are "nonbreakable."Damage only translates into a minor modification of the behavior of the component. It is possible to integrate many functions in one particular system,leading to a reduction in the number of parts,an optimal occupation of space, and an improvement in road behavior. The mass reduction is important (see Figure 8.10) The disadvantages:It is difficult to adapt the product to the requirements of the production.It is not sufficient to demonstrate the technical feasibility;one must optimize the three-criteria product-process-production rate (rates of production of 5S.M.C.process:See Section 2.1.3 and 3.2. 6See Section 3.3.2.comparison of load-elongation diagrams for a metal and a unidirectional. 2003 by CRC Press LLC
components and equipment that form the front face of the vehicle. Characteristics include: Part molded in glass/polyester (Vf = 42%) Fabrication process: SMC5 : Press 15,000 N Rate of production: 1200 pieces/day Machining/drilling (70 holes); installation of inserts (30) and components made by laser, numerical machining, and robots 8.1.3.2 Suspension Components Springs: One of the principal characteristics of the unidirectionals (namely glass/resin) is their capacity to accumulate elastic energy. 6 Herein lies the interest in making composite springs. In theory, a glass/resin spring is capable of storing 5 to 7 times more elastic energy than a steel spring of the same mass. Other advantages include: The composite springs are “nonbreakable.” Damage only translates into a minor modification of the behavior of the component. It is possible to integrate many functions in one particular system, leading to a reduction in the number of parts, an optimal occupation of space, and an improvement in road behavior. The mass reduction is important (see Figure 8.10) The disadvantages: It is difficult to adapt the product to the requirements of the production. It is not sufficient to demonstrate the technical feasibility; one must optimize the three-criteria product-process-production rate (rates of production of Figure 8.10 Comparison Between Metallic and Composite Springs 5 S.M.C. process: See Section 2.1.3 and 3.2. 6 See Section 3.3.2, comparison of load-elongation diagrams for a metal and a unidirectional. TX846_Frame_C08 Page 189 Monday, November 18, 2002 12:22 PM © 2003 by CRC Press LLC
Renault "traffic". useful load:1300 kg 40 cars/day mass gain:17 kg cost:identical to a conventional system Figure 8.11 Leaf Spring ●spring 。rolling retum .wheel guide unidirectional connecting rod glass/carbon/epoxy Figure 8.12 Combination of Functions several thousands of parts per day in the automotive industry,to be made using a few processes,i.e.,filament winding,compression molding,pultrusion,and pultrusion-forming). The current development and commercialization efforts deal with leaf springs and torsion beam springs. Example:Single leaf spring (see Figure 8.11).A spring made of many metallic leaves is replaced by a single leaf spring made of composite in glass/epoxy.Many vehicles are sold with this type of spring,for example,Rover-GB;Nissan-JAP; General Motors-USA:Renault-FRA). Example:Multifunctional system (Bertin-FRA).This prototype for the front suspension of the automobile combines the different functions of spring,rolling return,and wheel guide (see Figure 8.12). Example:Stabilizing system.This is used for the connection between an automobile and a caravan (Bertin/Tunesi-FRA).The combined functions are shown schematically in Figure 8.13.The mass is divided by 4.5 in comparison with an“all metal'”solution. Example:The automobile suspension triangle has two parts (FRA)that are bonded to make a box (see Figure 8.14). 8.1.3.3 Mechanical Pieces Motor:The parts shown schematically in Figure 8.15 are in the experimental stage or in service in thermal motors.For pieces that have to operate at high temperatures,one should use the high temperature material system See Chapter 2. 2003 by CRC Press LLC
several thousands of parts per day in the automotive industry, to be made using a few processes, i.e., filament winding, compression molding, pultrusion, and pultrusion-forming).7 The current development and commercialization efforts deal with leaf springs and torsion beam springs. Example: Single leaf spring (see Figure 8.11). A spring made of many metallic leaves is replaced by a single leaf spring made of composite in glass/epoxy. Many vehicles are sold with this type of spring, for example, Rover–GB; Nissan–JAP; General Motors–USA; Renault–FRA). Example: Multifunctional system (Bertin–FRA). This prototype for the front suspension of the automobile combines the different functions of spring, rolling return, and wheel guide (see Figure 8.12). Example: Stabilizing system. This is used for the connection between an automobile and a caravan (Bertin/Tunesi–FRA). The combined functions are shown schematically in Figure 8.13. The mass is divided by 4.5 in comparison with an “all metal” solution. Example: The automobile suspension triangle has two parts (FRA) that are bonded to make a box (see Figure 8.14). 8.1.3.3 Mechanical Pieces Motor: The parts shown schematically in Figure 8.15 are in the experimental stage or in service in thermal motors. For pieces that have to operate at high temperatures, one should use the high temperature material system Figure 8.11 Leaf Spring Figure 8.12 Combination of Functions 7 See Chapter 2. TX846_Frame_C08 Page 190 Monday, November 18, 2002 12:22 PM © 2003 by CRC Press LLC