Engineering Failure Analysis 17(2010)92-115 Contents lists available at Science Direct NGINEFRING Engineering Failure Analysis ELSEVIER journalhomepagewww.elsevier.com/locate/engfailanal Formula 1 Composites Engineering G. Savage Brawn GP Formula 1 Team, Brackley, Northants NN137BD, UK ARTICLE IN FO ABSTRACT Any engineering structure, irrespective of its intended purpose, must be made of one or Received 9 April 2009 more materials. More often than not it is the choice and behaviour of those materials that Available online 3 May 2009 determine its mechanical performance. The introduction of fibre reinforced composite chassis was one of the most significant developments in the history of grand Prix motor racing. Technological advances gained from these advanced materials have produced cars hat are lighter faster and safer than ever before. The manufacture of Formula 1 cars is now Composite materials dominated by composites. A short introduction to the science of composite materials will be followed by a history of their use and development within the sport Design manufac- ture and operation of composite structures are reviewed. Reference is also made to their energy absorbing properties that have contributed so significantly to the improved safety record of formula 1 and posite materials, such as carbon-carbon used in brakes and clutches e 2009 Elsevier Ltd. All rights reserved. 1. The design of Formula 1 racing cars The general arrangement of single seat racing cars has remained the same since the early 1960s. The central component, which accommodates the driver, fuel cell and front suspension assembly, is the chassis( fig. 1). e This is a semi-monocoque shell structure which is more like a jet fighter aircraft cockpit, both in terms of shape and con- uction, than anything one would expect to find on the road. The engine, in addition to providing propulsion, is a structural member joining the front and rear of the chassis. It is attached directly to the rear of this unit by high strength metal studs ( Fig. 2 The assembly is completed by the addition of the gearbox and rear suspension assembly( fig 3 ). The gearbox, in addition to carrying the transmission is the rear section of the chassis. The cars primary structure of chas sis, engine and gearbox( Fig. 4)may be considered as a"torsion-beam"arrangement carrying the inertial loads to their reac- tion points at the four corners The secondary structures(bodywork, undertray, wing configurations and cooler ducting, etc )are arranged around and attached to the primary structure at various points( Fig. 5). A Formula 1 car is driven"on the limit, that is to say one aims to operate the car as close to the point where its longi- udinal g is just about to be overcome due to the lateral g from cornering(Fig. 6). The car must beset-up"for each individual circuit in order to optimise performance Changes are made to the aerody mic devices and the suspension elements(springs, dampers, anti-roll bars and so on)in an attempt to improve its lap time. Changes in the performance levels of the various sub-components must be manifest in the balance of the car. Clearly this not occur if the structure transmitting the loads is not of adequate stiffness. In common with many other engineering dis- ciplines, the designers of Formula 1 racing cars are required to comply with a stringent set of regulations. The rules are im- posed by the fla, the Sport s governing body. Constraints are laid down on geometry, strength and weight. Strict limitations E-mailaddressgsavageebrawngp.com 1350-6307/s doi: 10.1016/engfailanal
Formula 1 Composites Engineering G. Savage Brawn GP Formula 1 Team, Brackley, Northants NN137BD, UK article info Article history: Received 9 April 2009 Accepted 10 April 2009 Available online 3 May 2009 Keywords: Composite materials Design Manufacture Operations abstract Any engineering structure, irrespective of its intended purpose, must be made of one or more materials. More often than not it is the choice and behaviour of those materials that determine its mechanical performance. The introduction of fibre reinforced composite chassis was one of the most significant developments in the history of Grand Prix motor racing. Technological advances gained from these advanced materials have produced cars that are lighter, faster and safer than ever before. The manufacture of Formula 1 cars is now dominated by composites. A short introduction to the science of composite materials will be followed by a history of their use and development within the sport. Design manufacture and operation of composite structures are reviewed. Reference is also made to their energy absorbing properties that have contributed so significantly to the improved safety record of Formula 1 and the more specialist composite materials, such as carbon–carbon, used in brakes and clutches. 2009 Elsevier Ltd. All rights reserved. 1. The design of Formula 1 racing cars The general arrangement of single seat racing cars has remained the same since the early 1960s. The central component, which accommodates the driver, fuel cell and front suspension assembly, is the chassis (Fig. 1). This is a semi-monocoque shell structure which is more like a jet fighter aircraft cockpit, both in terms of shape and construction, than anything one would expect to find on the road. The engine, in addition to providing propulsion, is a structural member joining the front and rear of the chassis. It is attached directly to the rear of this unit by high strength metal studs (Fig. 2). The assembly is completed by the addition of the gearbox and rear suspension assembly (Fig. 3.). The gearbox, in addition to carrying the transmission is the rear section of the chassis. The car’s primary structure of chassis, engine and gearbox (Fig. 4) may be considered as a ‘‘torsion-beam” arrangement carrying the inertial loads to their reaction points at the four corners. The secondary structures (bodywork, undertray, wing configurations and cooler ducting, etc.) are arranged around and attached to the primary structure at various points (Fig. 5). A Formula 1 car is driven ‘‘on the limit”, that is to say one aims to operate the car as close to the point where its longitudinal g is just about to be overcome due to the lateral g from cornering (Fig. 6). The car must be ‘‘set-up” for each individual circuit in order to optimise performance. Changes are made to the aerodynamic devices and the suspension elements (springs, dampers, anti-roll bars and so on) in an attempt to improve its lap time. Changes in the performance levels of the various sub-components must be manifest in the balance of the car. Clearly this will not occur if the structure transmitting the loads is not of adequate stiffness. In common with many other engineering disciplines, the designers of Formula 1 racing cars are required to comply with a stringent set of regulations. The rules are imposed by the FIA, the Sport’s governing body. Constraints are laid down on geometry, strength and weight. Strict limitations 1350-6307/$ - see front matter 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.engfailanal.2009.04.014 E-mail address: gsavage@brawnGP.com Engineering Failure Analysis 17 (2010) 92–115 Contents lists available at ScienceDirect Engineering Failure Analysis journal homepage: www.elsevier.com/locate/engfailanal
G. Savage/ Engineering Failure Analysis 17(2010)92-115 Fig. 1. The chassis is the central component of an F1 car Fig 3. Gearbox and rear suspension. are placed on the overall dimensions of the cars and the sizing of the driver envelope within the cockpit. A series of statutory regulations have been introduced over the years which are continually upd improve safety. Consequently, the chassis has developed a secondary function of survival cell"to protect the pilot vent of a crash. a number of tests must be performed in the presence of an official prior to the car being certified for Grand Prix usage. The regulation limiting the min- imum weight of the car plus driver to 605 kg is of great significance. Building a car to the weight limit is a vital task if it is to
are placed on the overall dimensions of the cars and the sizing of the driver envelope within the cockpit. A series of statutory regulations have been introduced over the years which are continually updated to improve safety. Consequently, the chassis has developed a secondary function of a ‘‘survival cell” to protect the pilot in the event of a crash. A number of tests must be performed in the presence of an official prior to the car being certified for Grand Prix usage. The regulation limiting the minimum weight of the car plus driver to 605 kg is of great significance. Building a car to the weight limit is a vital task if it is to be competitive. Fig. 1. The chassis is the central component of an F1 car. Fig. 3. Gearbox and rear suspension. Fig. 2. Engine. G. Savage / Engineering Failure Analysis 17 (2010) 92–115 93
G. Savage/ Engineering Failure Analysis 17(2010)92-115 4. The""primary structure" of a Formula 1 car consists of chassis, engine and gearbox. Fig. 5. Complete car with secondary structures added. lateral g Fig. 6. Driving"on the limit It has been estimated that a mass of 20 kg above the weight limit equates to a loss of 0. 4 s around a typical grand prix circuit. Less than half a second does not sound very much, but during a full race distance this amounts to half a lap or several grid positions during a qualifying session. with modern materials it is relatively easy to build a car which satisfies all of the statutory requirements whilst still being well under the minimum weight limit. As a consequence the majority of the cars are required to carry ballast (generally in the form of a heavy metal such as tungsten)in order to make up the deficit. At first glance therefore it may seem fruitless to continually aim to reduce the mass of components only to increase the amount of ballast carried. Lowering the weight of the chassis is still of benefit however when one considers Fig. 7. An Fl car is always accelerating, either positively under the influence of the engine or nega der braking. Lower mass enables the engineers to alter the position of the cars centre of gravity and thus greatly
It has been estimated that a mass of 20 kg above the weight limit equates to a loss of 0.4 s around a typical Grand Prix circuit. Less than half a second does not sound very much, but during a full race distance this amounts to half a lap or several grid positions during a qualifying session. With modern materials it is relatively easy to build a car which satisfies all of the statutory requirements whilst still being well under the minimum weight limit. As a consequence the majority of the cars are required to carry ballast (generally in the form of a heavy metal such as tungsten) in order to make up the deficit. At first glance therefore it may seem fruitless to continually aim to reduce the mass of components only to increase the amount of ballast carried. Lowering the weight of the chassis is still of benefit however when one considers Fig. 7. An F1 car is always accelerating, either positively under the influence of the engine or negatively under braking. Lower mass enables the engineers to alter the position of the car’s centre of gravity and thus greatly influence its handling characFig. 4. The ‘‘primary structure” of a Formula 1 car consists of chassis, engine and gearbox. Fig. 5. Complete car with secondary structures added. Fig. 6. Driving ‘‘on the limit”. 94 G. Savage / Engineering Failure Analysis 17 (2010) 92–115
G. Savage/ Engineering Failure Analysis 17 (2010)92-115 Mr003Mx:421 Fig. 7. A Formula 1 car is always accelerating. teristics. The pursuit of lower weight and improved performance have both stimulated the introduction of new technology in both design and construction. The structural components of the car must be stiff, strong enough to satisfy the loading requirements, tolerant of and resistant to, impact damage and be of minimum weight. The solution to this problem is achieved by optimising the geometry the quality of construction and by using the most appropriate materials. The quest for maximum structural efficiency has resulted in a progression of different technologies throughout the history of Grand Prix racing. Much of the development within Formula 1 has shadowed that taking place within the aerospace industry This is not surprising when one considers the similarity of their objectives 2. Composite materials y opposites are defined as"materials in which two or more constituents have been brought together to produce a new material consisting of at least two chemically distinct components, with resultant properties significantly different to those of the individual constituents". A more complete description also demands that the constituents must also be present in rea- onable proportions. Five percent by weight is arbitrarily considered to be the minimum. The material must furthermore be considered to be"man made That is to say it must be produced deliberately by intimate mixing of the constituents. An alloy which forms a distinct two phase microstructure as a consequence of solidification or heat treatment would not therefore be considered as a composite. If on the other hand, ceramic fibres or particles were to be mixed with a metal to produce a mate- rial consisting of a dispersion of the ceramic within the metal; this would be regarded as a composite. On a microscopic scale composites have two or more chemically distinct phases separated by a distinct interface. This interface has a major influence on the properties of the composite. The continuous phase is known as the matrix. Generally the properties of the matrix are greatly improved by incorporating another constituent to produce a composite. A composite nay have a ceramic, metallic or polymeric matrix. The second phase is referred to as the reinforcement as it enhances the properties of the matrix and in most cases the reinforcement is harder, stronger and stiffer than the matrix [1]. The measured strengths of materials are several orders of magnitudes less than those calculated theoretically. Further ore the stress at which nominally identical specimens fail is subject to a marked variability. This occurs because of the presence of inherent flaws within the material [2]. There is always a distribution in the size of the flaws and failure under load initiates at the largest of these. Griffith derived an expression relating failure stress to flaw size(a) K (1) here af=failure stress, Kic is the material's fracture toughness and y a geometrical constant. As Eq (1)shows, the larger the flaw size the lower will be the failure stress( Fig 8)
teristics. The pursuit of lower weight and improved performance have both stimulated the introduction of new technology in both design and construction. The structural components of the car must be stiff, strong enough to satisfy the loading requirements, tolerant of and resistant to, impact damage and be of minimum weight. The solution to this problem is achieved by optimising the geometry, the quality of construction and by using the most appropriate materials. The quest for maximum structural efficiency has resulted in a progression of different technologies throughout the history of Grand Prix racing. Much of the development within Formula 1 has shadowed that taking place within the aerospace industry. This is not surprising when one considers the similarity of their objectives. 2. Composite materials Composites are defined as ‘‘materials in which two or more constituents have been brought together to produce a new material consisting of at least two chemically distinct components, with resultant properties significantly different to those of the individual constituents”. A more complete description also demands that the constituents must also be present in reasonable proportions. Five percent by weight is arbitrarily considered to be the minimum. The material must furthermore be considered to be ‘‘man made”. That is to say it must be produced deliberately by intimate mixing of the constituents. An alloy which forms a distinct two phase microstructure as a consequence of solidification or heat treatment would not therefore be considered as a composite. If on the other hand, ceramic fibres or particles were to be mixed with a metal to produce a material consisting of a dispersion of the ceramic within the metal; this would be regarded as a composite. On a microscopic scale composites have two or more chemically distinct phases separated by a distinct interface. This interface has a major influence on the properties of the composite. The continuous phase is known as the matrix. Generally the properties of the matrix are greatly improved by incorporating another constituent to produce a composite. A composite may have a ceramic, metallic or polymeric matrix. The second phase is referred to as the reinforcement as it enhances the properties of the matrix and in most cases the reinforcement is harder, stronger and stiffer than the matrix [1]. The measured strengths of materials are several orders of magnitudes less than those calculated theoretically. Furthermore the stress at which nominally identical specimens fail is subject to a marked variability. This occurs because of the presence of inherent flaws within the material [2]. There is always a distribution in the size of the flaws and failure under load initiates at the largest of these. Griffith derived an expression relating failure stress to flaw size (a). rf ¼ KIC ya1=2 ð1Þ where rf = failure stress, KIC is the material’s fracture toughness and y a geometrical constant. As Eq. (1) shows, the larger the flaw size, the lower will be the failure stress (Fig. 8). Math_rmsAccel (G) -10 -8 -6 -4 -2 0 2 4 6 8 10 0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 Distance: 466.200 m 2 Accel Lat MCU 0.77 G Accel Long MCU -3.37 G Math_rmsAccel 3.44 G Speed 207 kph Math_rmsAccel (G) Min: 0.03 Max: 4.21 Mean: 1.45 Rate: 50 Hz Fig. 7. A Formula 1 car is always accelerating. G. Savage / Engineering Failure Analysis 17 (2010) 92–115 95
G. Savage/ Engineering Failure Analysis 17(2010)92-115 3500 30 2500 500 500 0100200300400 Fig. 8. Relationship between flaw size and failure stress of a material [2]- ws therefore that the strength of a material can be enhanced by eliminating or minimising such imperfections. Cracks lying perpendicular to the applied loads are the most detrimental to the strength. Fibrous or filamentary materials thus exhibit high strength and stiffness along their lengths because in this direction the large flaws present in the bulk mate- rial are minimised. Fibres will readily support tensile loads but offer almost no resistance and buckle under compression. In order to be directly usable in engineering applications they must be embedded in matrix materials to form fibrous compos ites. The matrix serves to bind the fibres together, transfer loads to the fibres and protect them against handling damage and environmental attack. Composites can be divided into two classes: those with long fibres(continuous fibre reinforced composites )and those ith short fibres(discontinuous fibre reinforced composites). In a discontinuous fibre composite, the material properties are affected by the fibre length, whereas in a continuous fibre composite it is assumed that the load is transferred directly to the fibres and that the fibres in the direction of the applied load are the principal load-bearing constituent. Polymeric materials are the most common matrices for fibre reinforced composites. They can be subdivided into two distinct types thermosetting and thermoplastic Thermosetting polymers are resins which cross-link during curing into a glassy brittle so- id, examples being polyesters and epoxies Thermoplastic polymers are high molecular weight, long chain molecules which an either become entangled (amorphous)such as polycarbonate, or partially crystalline, such as nylon, at room temperature to provide strength and shape. In common with all structural applications of polymer matrix composites, Formula 1 is dom inated by those based on thermoset resins, particularly epoxies. The driving force for the increasing substitution of metal alloys is demonstrated in Table 1 Contrary to many a widely held belief, composites are not"wonder materials". Indeed their mechanical properties are roughly of the same order as their metal competitors. Furthermore they exhibit lower extensions to failure then metallic al- loys of comparable strength. What is important however is that they possess much lower densities Fibre reinforced com- posites thus exhibit vastly improved specific properties, strength and stiffness per unit mass for example. The higher specific properties enable the production of lower weight components. The weight savings obtained in practice are not Table 1 Comparison of mechanical properties of metallic and composite materials. Density (g cm) le strength, a(MPa) Tensile modulus, E(GPa) Specific strength(alp) gnetum HM carbon 1550
It follows therefore that the strength of a material can be enhanced by eliminating or minimising such imperfections. Cracks lying perpendicular to the applied loads are the most detrimental to the strength. Fibrous or filamentary materials thus exhibit high strength and stiffness along their lengths because in this direction the large flaws present in the bulk material are minimised. Fibres will readily support tensile loads but offer almost no resistance and buckle under compression. In order to be directly usable in engineering applications they must be embedded in matrix materials to form fibrous composites. The matrix serves to bind the fibres together, transfer loads to the fibres and protect them against handling damage and environmental attack. Composites can be divided into two classes: those with long fibres (continuous fibre reinforced composites) and those with short fibres (discontinuous fibre reinforced composites). In a discontinuous fibre composite, the material properties are affected by the fibre length, whereas in a continuous fibre composite it is assumed that the load is transferred directly to the fibres and that the fibres in the direction of the applied load are the principal load-bearing constituent. Polymeric materials are the most common matrices for fibre reinforced composites. They can be subdivided into two distinct types: thermosetting and thermoplastic. Thermosetting polymers are resins which cross-link during curing into a glassy brittle solid, examples being polyesters and epoxies. Thermoplastic polymers are high molecular weight, long chain molecules which can either become entangled (amorphous) such as polycarbonate, or partially crystalline, such as nylon, at room temperature to provide strength and shape. In common with all structural applications of polymer matrix composites, Formula 1 is dominated by those based on thermoset resins, particularly epoxies. The driving force for the increasing substitution of metal alloys is demonstrated in Table 1. Contrary to many a widely held belief, composites are not ‘‘wonder materials”. Indeed their mechanical properties are roughly of the same order as their metal competitors. Furthermore they exhibit lower extensions to failure then metallic alloys of comparable strength. What is important however is that they possess much lower densities. Fibre reinforced composites thus exhibit vastly improved specific properties, strength and stiffness per unit mass for example. The higher specific properties enable the production of lower weight components. The weight savings obtained in practice are not as Fig. 8. Relationship between flaw size and failure stress of a material [2]. Table 1 Comparison of mechanical properties of metallic and composite materials. Material Density (g cm3 ) Tensile strength, r (MPa) Tensile modulus, E (GPa) Specific strength (r/q) Specific modulus Steel 7.8 1300 200 167 26 Aluminium 2.81 350 73 124 26 Titanium 4 900 108 204 25 Magnesium 1.8 270 45 150 25 E glass 2.10 1100 75 524 21.5 Aramid 1.32 1400 45 1060 57 IM carbon 1.51 2500 151 1656 100 HM carbon 1.54 1550 212 1006 138 96 G. Savage / Engineering Failure Analysis 17 (2010) 92–115
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
G. Savage/ Engineering Failure Analysis 17(2010)92-115 ren. Unlike the former, the Lotus chassis followed the previous"cut and fold "methodology simply replacing the pre-bonded luminium skins with a hybrid composite of carbon and Kevlar reinforced epoxy. As such they can be considered to have followed a technological cul-de-sac"and the mclaren chassis must be recognised as the forerunner of those used today In 1980 the reputation of composites with respect to impact loading was very poor as a result of problems experienced in aero-engine components in the early 1970s and some dramatic in-service failures of early race car components. Indeed lany designers of repute expressed grave doubts as to the suitability of such brittle materials in what is a highly stressed application. Despite the reservations of many of their competitors, the McLaren MP4/1, the first carbon fibre monocoque rac- ing car(Fig. 16) proved so successful that it was soon copied, in one form or another, by every other team. The 1981 season became something of a"war of attrition"for McLaren with a number of cars being accidentally crashed everal times during both testing and racing. It became clear that in addition to improved mechanical properties and lower weight of the composite chassis, the damage caused by accidents was constrained in the locality of the impact. Repairs could be executed quickly and effectively with little or no loss in performance. the ability to sustain and undergo repair to minor damage is all very well, but what concerned the designers most was the ability to withstand a major collision. At the 1981 Italian Grand Prix, John Watson lost control of his McLaren and smashed violently into the barriers. He was able to walk away from the debris unscathed(Fig. 17). This incident went a long way to removing the doubts in the minds of those uncon- vinced of the safety of carbon fibre composites under high strain rate loading. The energy absorbing properties of composites have subsequently made a great contribution to the safety record of the sport. The next major advance in chassis construction occurred in 1983 at one of the smaller teams. The German AtS team developed a tub fabricated inside female composite tooling. The two halves of the structure were made from woven fabric reinforced prepreg and joined at the centre line( Fig. 18). Female moulding makes far more efficient use of the available aero- dynamic envelope since only a minimum of secondary bodywork is needed to cover it. It also provides an opportunity to Fig. 16. The first carbon monocoque Mclaren MP4/1(1980) Marlboro Fig. 17. MP4/1 chassis following large impact
ren. Unlike the former, the Lotus chassis followed the previous ‘‘cut and fold” methodology simply replacing the pre-bonded aluminium skins with a hybrid composite of carbon and Kevlar reinforced epoxy. As such they can be considered to have followed a ‘‘technological cul-de-sac” and the McLaren chassis must be recognised as the forerunner of those used today. In 1980 the reputation of composites with respect to impact loading was very poor as a result of problems experienced in aero-engine components in the early 1970s and some dramatic in-service failures of early race car components. Indeed many designers of repute expressed grave doubts as to the suitability of such brittle materials in what is a highly stressed application. Despite the reservations of many of their competitors, the McLaren MP4/1, the first carbon fibre monocoque racing car (Fig. 16) proved so successful that it was soon copied, in one form or another, by every other team. The 1981 season became something of a ‘‘war of attrition” for McLaren with a number of cars being accidentally crashed several times during both testing and racing. It became clear that in addition to improved mechanical properties and lower weight of the composite chassis, the damage caused by accidents was constrained in the locality of the impact. Repairs could be executed quickly and effectively with little or no loss in performance. The ability to sustain and undergo repair to minor damage is all very well, but what concerned the designers most was the ability to withstand a major collision. At the 1981 Italian Grand Prix, John Watson lost control of his McLaren and smashed violently into the barriers. He was able to walk away from the debris unscathed (Fig. 17). This incident went a long way to removing the doubts in the minds of those unconvinced of the safety of carbon fibre composites under high strain rate loading. The energy absorbing properties of composites have subsequently made a great contribution to the safety record of the sport. The next major advance in chassis construction occurred in 1983 at one of the smaller teams. The German ATS team developed a tub fabricated inside female composite tooling. The two halves of the structure were made from woven fabric reinforced prepreg and joined at the centre line (Fig. 18). Female moulding makes far more efficient use of the available aerodynamic envelope since only a minimum of secondary bodywork is needed to cover it. It also provides an opportunity to Fig. 17. MP4/1 chassis following large impact. Fig. 16. The first carbon monocoque McLaren MP4/1 (1980). 100 G. Savage / Engineering Failure Analysis 17 (2010) 92–115
G. Savage/ Engineering Failure Analysis 17 (2010)92-115 optimise the geometry and thus improve its structural efficiency. The bmw powered atS was never a leading contender but generally considered to be one of the strongest and stiffest chassis on the circuit. This method of manufacture does however ecessitate a join in the main shell and a great degree of laminator skill in order to produce a consistent, repeatable com- ponent. Developments in aerodynamic shaping, structural analysis and laminating techniques have ensured continuous development of the chassis and other composite pieces. During the design of the MP4/1, Mclaren used carbon composites wherever they offered advantages in mechanical prop- erties or a reduction in complexity of design. Since that time there has been a continual process of metals replacement within he sport. In the early 1990s, Savage and Leaper from McLaren developed composite suspension members (4 Composite suspension components are now used by the all of teams (Fig 19). In addition to the obvious weight savings, composite push rods and wishbones have almost infinite fatigue durability and so can be made far more cost effective than the steel parts which they replaced. The latest innovation was the introduction of ite gearbox by the arrows and Stewart teams in 1998 although the true potential of these structures was only fully realised from 2004 by the BAr-Honda team [5. Composite gearboxes( Fig. 20)are significantly lighter than traditional alloy oxes, up to 25% st can be operated at higher temperatures and are easy to modify and repair. The design and logistics. tc are not insignificant such that to this day they are not universally used on the Fl grid Carbon fibre composites now make up almost 85% of the volume of a contemporary Formula 1 car whilst accounting for less than 30% of its mass. In addition to the chassis there is composite bodywork, cooling ducts for the radiators and brakes, front, rear and side crash structures, suspension, gearbox and the steering wheel and column. In addition to the structural Fig. 18. Female moulded ATS D6 (1983). Fig. 19. Composite suspension
optimise the geometry and thus improve its structural efficiency. The BMW powered ATS was never a leading contender but generally considered to be one of the strongest and stiffest chassis on the circuit. This method of manufacture does however necessitate a join in the main shell and a great degree of laminator skill in order to produce a consistent, repeatable component. Developments in aerodynamic shaping, structural analysis and laminating techniques have ensured continuous development of the chassis and other composite pieces. During the design of the MP4/1, McLaren used carbon composites wherever they offered advantages in mechanical properties or a reduction in complexity of design. Since that time there has been a continual process of metals replacement within the sport. In the early 1990s, Savage and Leaper from McLaren developed composite suspension members [4]. Composite suspension components are now used by the all of teams (Fig. 19). In addition to the obvious weight savings, composite push rods and wishbones have almost infinite fatigue durability and so can be made far more cost effective than the steel parts which they replaced. The latest innovation was the introduction of a composite gearbox by the Arrows and Stewart teams in 1998 although the true potential of these structures was only fully realised from 2004 by the BAR-Honda team [5]. Composite gearboxes (Fig. 20) are significantly lighter than traditional alloy boxes, up to 25% stiffer, can be operated at higher temperatures and are easy to modify and repair. The design and logistics, etc. are not insignificant such that to this day they are not universally used on the F1 grid. Carbon fibre composites now make up almost 85% of the volume of a contemporary Formula 1 car whilst accounting for less than 30% of its mass. In addition to the chassis there is composite bodywork, cooling ducts for the radiators and brakes, front, rear and side crash structures, suspension, gearbox and the steering wheel and column. In addition to the structural Fig. 18. Female moulded ATS D6 (1983). Fig. 19. Composite suspension. G. Savage / Engineering Failure Analysis 17 (2010) 92–115 101