G. Savage/ Engineering Failure Analysis 17 (2010)92-115 great as Table 1 implies because the fibres are extremely anisotropic, which must be accounted for in any design calculation In addition specific modulus(Elp)and strength(a/p)are only capable of specifying the performance under certain loading regimes. Specific strength and modulus are useful when considering materials for components under tensile loading such as, for example, wing support pillars( Fig. 9). The lightest component that will carry a tensile load without exceeding a predetermined deflection is defined by the high- est value of E/p A compression member such pension push rod on the other hand is limited by buckling such that the best material is that which exhibits the highest value of E//p( fig. 10) Similarly, a panel loaded in bending such as a rear wing(Fig. 11), will produce minimum deflection by optimising E lp. Nevertheless, weight savings of between 30% and 50% are readily achieved over equivalent metal components Designers of weight sensitive structures such as aircraft and racing cars require materials which combine good mechan- ical properties with low weight. Aircraft originally employed wood and fabric in their construction, but since the late 1930s aluminium alloys have been the dominant materials. during the last two decades guide the su te materials have been increas- ingly employed for stressed members in aircraft Composite structures are design ave a precisely defined quantity of fibres in the correct location and orientation with a minimum of polymer to provi upport. The composites industry achieves this precision using"prepreg"as an intermediate product(Fig. 12). 9aA Fig 9. Front wing pillars, loaded in tension. Fig. 10. Rear push rod-compression member
great as Table 1 implies because the fibres are extremely anisotropic, which must be accounted for in any design calculations. In addition specific modulus (E/q) and strength (r/q) are only capable of specifying the performance under certain loading regimes. Specific strength and modulus are useful when considering materials for components under tensile loading such as, for example, wing support pillars (Fig. 9). The lightest component that will carry a tensile load without exceeding a predetermined deflection is defined by the highest value of E/q. A compression member such as a suspension push rod on the other hand is limited by buckling such that the best material is that which exhibits the highest value of E1/2/q (Fig. 10). Similarly, a panel loaded in bending such as a rear wing (Fig. 11), will produce minimum deflection by optimising E1/3/q. Nevertheless, weight savings of between 30% and 50% are readily achieved over equivalent metal components. Designers of weight sensitive structures such as aircraft and racing cars require materials which combine good mechanical properties with low weight. Aircraft originally employed wood and fabric in their construction, but since the late 1930s aluminium alloys have been the dominant materials. During the last two decades composite materials have been increasingly employed for stressed members in aircraft. Composite structures are designed to have a precisely defined quantity of fibres in the correct location and orientation with a minimum of polymer to provide the support. The composites industry achieves this precision using ‘‘prepreg” as an intermediate product (Fig. 12). Fig. 9. Front wing pillars, loaded in tension. Fig. 10. Rear push rod – compression member. G. Savage / Engineering Failure Analysis 17 (2010) 92–115 97
G. Savage/ Engineering Failure Analysis 17(2010)92-115 Fig. 11. Rear wing, loaded in bending Fig. 12. Prepreg. m stiffness Strength 1.06 Fig. 13. Optimising strength and stiffness using"sandwich structures Prepreg is a broad tape of aligned(unidirectional, UD")or woven fibres, impregnated with polymer resin. A composite structure is fabricated by stacking successive layers of prepreg and curing under temperature and pressure. Many compo- nents consist of"sandwich construction"; thin, high strength composite skins are separated by and bonded to thick, light weight honeycomb cores. The thicker the core, the higher the stiffness and strength of the component, for minimal weight gain( Fig. 13). 3. Development of composite structures in Formula 1 racing The first documented uses of composite construction in racing cars date back to the late 1920s and early 1930s in the orm of wood and steel chassis. These early vehicles tended to be home built and raced so there is very little documented
Prepreg is a broad tape of aligned (unidirectional, ‘‘UD”) or woven fibres, impregnated with polymer resin. A composite structure is fabricated by stacking successive layers of prepreg and curing under temperature and pressure. Many components consist of ‘‘sandwich construction”; thin, high strength composite skins are separated by, and bonded to, thick, lightweight honeycomb cores. The thicker the core, the higher the stiffness and strength of the component, for minimal weight gain (Fig. 13). 3. Development of composite structures in Formula 1 racing The first documented uses of composite construction in racing cars date back to the late 1920s and early 1930s in the form of wood and steel chassis. These early vehicles tended to be home built and raced so there is very little documented Fig. 11. Rear wing, loaded in bending. Fig. 12. Prepreg. Fig. 13. Optimising strength and stiffness using ‘‘sandwich structures”. 98 G. Savage / Engineering Failure Analysis 17 (2010) 92–115
G. Savage/ Engineering Failure Analysis 17 (2010)92-115 data concerning their performance. It is most likely however that the use of wood as a chassis material was due in the main to cheapness and convenience rather than to enhance performance. Up until the early 1950s the predominant method of Formula 1 chassis construction consisted of a tubular aluminium space frame surrounded by hand worked aluminium body panels. At that time random orientation glass mat and polyester resins(Glass Reinforced Plastic)developed in wartime re- search became widely available. This material allowed the relatively cheap production of complex compound curvature bodywork which replaced aluminium. The use of grP panelling continued right through to the late 1980s. The first truly composite chassis was built in the early 1960s by Cooper cars. The structure consisted of a hand worked aluminium outer skin, an aluminium honeycomb core and a GRP inner skin. a single piece outer skin was produced from a number of panels to form the final aerodynamic surface of the car. The aluminium honeycomb core was then bonded to the inside of the outer skin using a phenolic resin film adhesive. The inner skin of grP was similarly bonded to the structure in a eparate operation. although the car never actually reached the track, it was to become the basis of Formula 1 chassis design for the next two decades. In the mid-to-late 1970s the preferred method of composite chassis construction used aluminium kinned, aluminium honeycomb material fabricated using the cut and fold"method. The tubs were formed from pre- bonded sheeting which was routed, folded and riveted into the appropriate shape( Fig. 14). The various teams involved later e-formed the skins prior to bonding to the core using an epoxy film adhesive. Carbon fibre composite chassis were first introduced by the Mclaren team in 1980 3. They consisted of pseud lithic arrangement laid up over a"male"mould or mandrel using unidirectional(UD)carbon fibre prepreg tape ( Fig. 15). The mandrel, made of cast and machined aluminium alloy was dismantled for removal through the cockpit opening following an autoclave cure of the composite. a three stage cure was required: one for the inner composite skin, a second to cure the epoxy film adhesive which attached the honeycomb core and a third for a further adhesive layer and the structure 's outer skin. The basic design and manufacturing process remained essentially unchanged for a number of years and was still the basis of chassis construction at McLaren up until the 1992 season. There is some debate as to which team was the first to produce a fibre reinforced composite chassis since the Lotus team were carrying out similar research in parallel with McLa- Fig. 14."Cut and fold"aluminium honeycomb chassis (late 1970s). Fig. 15."Male moulded"chassis manufactur
data concerning their performance. It is most likely however that the use of wood as a chassis material was due in the main to cheapness and convenience rather than to enhance performance. Up until the early 1950s the predominant method of Formula 1 chassis construction consisted of a tubular aluminium space frame surrounded by hand worked aluminium body panels. At that time random orientation glass mat and polyester resins (Glass Reinforced Plastic) developed in wartime research became widely available. This material allowed the relatively cheap production of complex compound curvature bodywork which replaced aluminium. The use of GRP panelling continued right through to the late 1980s. The first truly composite chassis was built in the early 1960s by Cooper cars. The structure consisted of a hand worked aluminium outer skin, an aluminium honeycomb core and a GRP inner skin. A single piece outer skin was produced from a number of panels to form the final aerodynamic surface of the car. The aluminium honeycomb core was then bonded to the inside of the outer skin using a phenolic resin film adhesive. The inner skin of GRP was similarly bonded to the structure in a separate operation. Although the car never actually reached the track, it was to become the basis of Formula 1 chassis design for the next two decades. In the mid-to-late 1970s the preferred method of composite chassis construction used aluminium skinned, aluminium honeycomb material fabricated using the ‘‘cut and fold” method. The tubs were formed from prebonded sheeting which was routed, folded and riveted into the appropriate shape (Fig. 14). The various teams involved later pre-formed the skins prior to bonding to the core using an epoxy film adhesive. Carbon fibre composite chassis were first introduced by the McLaren team in 1980 [3]. They consisted of pseudo-monolithic arrangement laid up over a ‘‘male” mould or mandrel using unidirectional (UD) carbon fibre prepreg tape (Fig. 15). The mandrel, made of cast and machined aluminium alloy, was dismantled for removal through the cockpit opening following an autoclave cure of the composite. A three stage cure was required: one for the inner composite skin, a second to cure the epoxy film adhesive which attached the honeycomb core and a third for a further adhesive layer and the structure’s outer skin. The basic design and manufacturing process remained essentially unchanged for a number of years and was still the basis of chassis construction at McLaren up until the 1992 season. There is some debate as to which team was the first to produce a fibre reinforced composite chassis since the Lotus team were carrying out similar research in parallel with McLaFig. 14. ‘‘Cut and fold” aluminium honeycomb chassis (late 1970s). Fig. 15. ‘‘Male moulded” chassis manufacture. G. Savage / Engineering Failure Analysis 17 (2010) 92–115 99