PROJECT REPORT MEEG 4023 Shamus StewartMark Edwards

Composites in Automotive Racing

INTRODUCTION

In the past two decades, composite materials have become increasingly popular in

automotive racing. Most drastically in Formula 1 racing where teams are well funded and can

afford research and development of advanced composite materials. McLaren’s racing team

introduced the first entirely carbon fiber chassis in 1980 (pictured below). Excluding the wheels

and engine, 85% of a formula 1 race car is made from composite materials. This is largely due to

the competitive advantage that comes with minimizing the weight of each component on the car.

Formula 1, NASCAR, and other racing circuits have minimum vehicle weight regulations.

However, teams still strive to minimize weight wherever possible so weight ballast can be added

to the car allowing precise tuning of the vehicle’s center of gravity and handling characteristics.

There are numerous other benefits of composites including their durability, stiffness, thermal

conductivity, and energy absorption characteristics. Vehicle safety has been significantly

improved since the introduction of composite materials. Composite survival pods and impact

protection components have played huge roles in decreasing the fatality and serious injury

statistics in automotive racing.

Fig A. The original composite F1 chassis, McLaren MP4-1 [6]

VEHICLE SAFETY

The development of composite materials has led to many innovations in in vehicle safety.

F1 teams continue to develop extremely strong and durable carbon fiber survival pods and

energy absorption attenuators. NASCAR has introduced a composite driver’s seat that is much

stiffer than its aluminum predecessor [1]. During the 1960’s the rate of fatal and serious injury

within formula 1 was 1 in every 8 crashes [2]. Through implementation of many new safety

regulations by the FIA, the period of 1980-1992 saw a 6-fold reduction in fatalities and serious

injuries. Those new regulation were largely due to the introduction of composites into the sport

in 1980 by the Mclaren team with their composite chassis [2]. The phenomenal survivability of

race cars is accomplished with a combination structural stiffness and energy absorption

capabilities.

One of the most important traits of any racing vehicle is its ability to absorb impact

energy in the event of a crash. Most racing vehicles have “crumple zones”, as they’re known,

located at the front, rear, and sides. These crumple zones consist of structures which are designed

to dissipate energy through yielding. This dissipation of energy helps gradually bring the vehicle

to a stop and thus avoiding huge g loads being transferred to the driver. Historically, impact

attenuators have been of metallic composition. For metallic structures, the absorption of energy

is achieved by plastic deformation. Carbon fiber composites have been shown to have even

better energy absorption characteristics and are replacing metallic impact attenuators in many

racing circuits. As opposed to metallic materials, in composites energy absorption is achieved by

material diffuse fracture which is a brittle failure mode [3]. Because weight reduction and

vehicle stiffness are also of extreme importance, composites are the ideal material for most

impact attenuators in race cars. In many instances these impact absorption members must also

serve as load bearing members and are subject to tight geometrical constraints for packaging and

aerodynamic reasons. Obviously the shape of the nose on F1 cars is crucial to optimizing

aerodynamic performance of the vehicle but that same component must dissipate energy in the

event of a forward collision. Another example is the RIMP (rear impact member), shown in fig 1

below, which is an impact attenuator but also must react loads from the rear wing and rear

suspension linkages among other design constraints.

Fig 1. BAR Honda 050, Gearbox and RIMD Structure [2]

From an engineering standpoint, these types of components that are intended to catastrophically

fail in a controlled manner when an impact load is applied but still bear structural loads can

present immense challenges for the designer.

The energy dissipation that is achieved by metallic components is the result of the work

required to plastically deform the part and form “plastic hinges” which progress along the part.

This concept can be illustrated by examining the axial collapse of a metal tube. Figure 2 shows

the displacement to force behavior of a thin walled metal tube subject to impact loading.

Fig. 2. Axial collapse of ductile metal tube [2]

For composite materials the dissipation of energy is achieved by the work required to

fracture the brittle fibers imbedded in a brittle matrix. The primary energy absorbing mechanisms

of fiber-reinforced composites are:

Cracking and fracture of the fibers

Matrix fracture

De-bonding (pull-out) of fibers from the matrix

Delamination of the laminate

Figure 3 shows typical force displacement behavior for a composite tube. The photograph shows

successful failure modes of a 50mm cylindrical tube.

Fig. 3 axial crushing of composite tube [2, 3]

One of the major challenges in designing these components is avoiding global buckling of the

part (shown in Fig. 3 to the far left) and arranging the column of material such that a destructive

“process zone” can progress through the part in a stable manner without deceleration peaks [2].

The typical design process for energy absorbing components can be broken down into three

different phases. The first is to develop analytical models that reproduce crash phenomenon, the

second is to implement numerical model to discretize the structure and perform FEA, and the last

is to perform experiments to prove out the design. Much research has been done to improve the

accuracy of numerical analysis methods used to predict a composite components impact loading

response. Because these impact attenuators play such a crucial role in driver safety, they must be

subject to rigorous static, dynamic, and fatigue testing before being cleared for installment on a

racing vehicle. The FIA requires official impact test of all energy absorption structures and has

set minimum peak force requirements for each component. These test usually involve impacting

the component with a large mass moving at a particular velocity. The photograph below is of an

official FIA test of a RIMP.

FIA rear impact test, impact structure is fitted on dummy gearbox [4]

The survival cell is the last defense a driver has against his/her body coming into contact with

outside entities in the event of a crash. The survival must be extremely strong, durable and, as

with all other racecar components, be as light as possible. For those reasons Fiber reinforced and

honeycomb composites are used in place of metallic material options. The standard construction

used in F1 monocoque consists of two thin carbon composites skins bonded to aluminum

honeycomb core [5]. As opposed to energy absorbing structures, the survival pod is designed not

to fail at the maxim loads that would ever be experienced in a racing crash. The FIA has

stringent requirements for the survival pod also, but these static test are intended to prove the

survival pods ability to deny intrusion of foreign objects. For example one requirement states the

side of the cell must hold a load of 30Kn for a period of 30s [3]. The addition of these

regulations to the design requirements have resulted in chassis that are designed to be very strong

and resilient to penetration as opposed to being primarily stiffness based. The FIA actually

requires a prescribed composite layer be added to the outermost layer of the side intrusion panel

to increase the intrusion reliance to an acceptable level. The laminate consist of PBO “Zylon”

fibers imbedded in one of two qualified toughed epoxy resin matrices and is of 16ply quasi-

isotropic layup, twill weave [5]. Figure 4 show a monococque with the Zylon panels being

impacted by a nose cone.

Fig. 4. Side intrusion and Zylon panels defeating an FIA frontal impact test. [5]

The introduction of composites has significantly improved the crashworthiness and

survivability of racing vehicles. The will always remain an inherent risk to the driver of racing

automobiles because that’s the nature of racing, but these technological advances in material

science help to minimize that risk. The aforementioned discussion pertains to formula 1 and

formula SAE racing, but similar examples can readily be found in other racing circuits. Still,

formula 1 teams are at the forefront of composites research as it applies to vehicle safety and

innovations made there usually find their way to the rest of the automotive racing world. At the

2003 Monaco green prix, Jenson button crashed sideways at 182mph into a tire barrier. The peak

load recorded was 32g and Jenson walked away unscathed [2].

SUSPENSION COMPONENTS

Composites have also made their way into almost every other aspect of the vehicles as

teams continue to strive for weight reduction. Every single suspension component on a formula 1

car has composite materials in some way shape or form. The recent development of thinner

fibers with greater tensile strength and high strength matrix materials has led to the propagation

of composite materials to even the highest stressed components on the vehicle. Composite

suspension components show advantageous durability when compared to the steel parts they’ve

replaced [6]. Advancements in structural adhesives have also helped, as composite parts are

often attached to metallic alloys through bonding. Figure 5 shows a formula 1 push rod designed

by Honda racing where titanium ends are bonded to a carbon fiber body.

Fig. 5, Honda RA106 front push rod [6]

In most cases, race car components are of the high complexity low volume variety. Even with

advancements in FEA software and computing power, the complexity of composite components

drives rigorous static and dynamic proof testing of components. Tensile and compression testing

can be carried out on simple two force members like push rods with uniaxial test rigs. Honda

Racing designs to a factor of safety of 1.3 so static test loads are approximately 30% higher then

what is expected in service [6]. For fatigue testing, sinusoidal dynamic loads are applied that

fluctuate between a maximum and minimum load. Some teams have acquired telemetry data for

particular racing circuits and, using multi-axis test rigs, can apply loads to the entire suspension

system that simulate those experienced by the race car for an entire lap. With this technology,

teams can run an excessive number of simulated laps on their vehicles components to verify the

vehicles durability. Often components are tested to failure to expose failure modes. For example,

figure 6 below shows the same push rod in figure 5 after being fatigue tested to failure. The test

showed the local compressive buckling of the carbon fiber close to the metal end was the effect

of bond failure in the joint [6]. Figure 7 shows the peeling failure of the adhesive. The colors

indicating that the disbonding propagated from left to right in the photo.

Fig. 6. Compression failure of push rod [6] Fig. 7. “Disbond” revealed by UT exam

Composites Effect in Racing Industry

Speed Increase vs. Year [7]

The use of composite materials has drastically changed the landscape of the racing

industry. The cars in the primary circuits of racing—NASCAR and Formula 1—are designed for

different purposes: Formula 1 cars are designed for quick acceleration and unmatched handling,

while the cars in NASCAR are designed for power and intense speed over a long period of time.

When designing the cars, multiple things go into consideration; safety at high speeds,

maintaining high speeds, maintaining certain handling characteristics, and cost efficiency all play

a role. The majority of composite use comes from the Formula 1 circuit, although composites do

have their uses in NASCAR. Throughout the past half century, stock cars have gotten faster and

faster, which leads to more dangerous crashes due to such high speeds. The reason behind the

increase in speed is in part due to the decrease in the weights of the vehicles. Originally, actual

stock cars were used in NASCAR, but over the years, actual race cars have been used, and the

bodies have been formed to look like that of an actual stock car. These bodies are much lighter

than the original stock cars, and coupled with more powerful engines, the cars can go much

faster. Each of the racecars “starts with a mild steel (1018 or similar) tube-frame chassis.

Titanium alloys or carbon-fiber composites would provide better strength-to-weight ratios;

however, the higher cost led

NASCAR to limit chassis

materials” [7]. The regulation over

the chassis materials stems from the

fact that some of the teams have

stronger financial backing than

some others, which would put some

teams at a disadvantage at a

fundamental level. One area where

composites can be used is a part of

the car known as the ‘splitter,’

which provides down force on the

front end of the car. Prior to the introduction of composites on this portion of the vehicle, the

aerodynamics of the front-end was largely uncontrollable. With the introduction of a material

called Tegris, NASCAR finally had a material that met the necessary conditions for strength and

stiffness to develop the front splitter. An important characteristic about Tegris is that it “does not

have a brittle failure mode—it delaminates, so it does not leave sharp pieces for other cars to run

over” [7]. This introduction proved to be cheaper than a carbon-fiber composite, and it provided

safe impact characteristics and improved handling on the cars, which previously wasn’t as easy

to achieve without composites. While NASCAR has developed its uses for composites, Formula

1 has been the driving force in the advancement of composite use in racing. Without much of the

funding restrictions like NASCAR puts in place, Formula 1 teams are able to use the funding

they receive how they see best fit. [8] In the main introduction of composites to Formula 1 in the

1950’s, this generally resulted in teams making their chassis out of some form of glass/polyester

resin composite, which was developed during wartime research. This material provided cheap

production for complex curvature bodywork. Carbon fiber composites hit the scene when the

McLaren team in 1980 introduced the first carbon fiber composite chassis. Many teams were

concerned about the strength of the composites under high stress/strain situations, but after

multiple tests, and sometimes accidents on the tracks, the concerns were disproven. In fact, the

composites were shown to behave safer than other materials, minimizing damage from impacts

by localizing the damage to the region of impact—that is, if the impact wasn’t too strong. From

then on, teams tried to find other uses of composites, ranging from suspension members to

gearboxes. Looking back at the introduction of composite materials in Formula 1, to where it is

now, “carbon fiber composites now make up almost 85% of the volume of a contemporary

Formula 1 car whilst accounting for less than 25% 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 steering wheel and column” [8]. Due to the decrease in mass

because of composites whilst still making up the majority of the volume of the car, in order to

meet regulations, many F1 teams will place ballasts within the car. An inadvertent consequence,

albeit a positive one, of the decrease in mass is that it allows the teams to alter where the center

of gravity on the car is. The upside to this is that it allows the teams to have greater control over

the maneuverability and handling of the car prior to the race. Behind safety, this is one of the

most important aspects of F1 racing, considering many of the tracks don’t rely on a series of

gradual left turns like in NASCAR.

Composites in Commercial Automotive Industry

All of the advances made in racing not only affect racing, but also trickle down into

commercial automotive use. However, the commercial automotive industry has different focuses

on how to use the composites, primarily in safety and weight reduction. While NASCAR and

Formula 1 also focus on weight reduction, they do it for the purpose of being able to go faster

and to manipulate the center of gravities of the cars in order to have better handling. In

commercial use, the purpose of weight reduction is to enhance the fuel economy in

transportation. In the cyclical world of fuel prices, giving customers a car that prolongs the life of

its fuel tank is of extreme importance. Currently, practically all commercial vehicles rely on steel

and other metal alloys for most structural components due to the cost efficiency of their

development. However, the strength to weight ratio of steel and other metal alloys is worse

comparatively to composites. One application in commercial automobile use is in the suspension

of the vehicle, where the “introduction of composite materials made it possible to reduce the

weight of the leaf spring without any reduction on load carrying capacity and stiffness; since the

composite materials have more elastic strain energy storage capacity and high strength-to-weight

ratio as compared to those of

steel” [9]. In the figure below,

it’s shown that “there is much

weight reduction for composite

materials compared to steel.

For E Glass Epoxy 88.4%, Graphite Epoxy 92.4%, Boron Aluminum 90.3%, Carbon Epoxy

92.3%, and Kevlar Epoxy 85.11% savings in the weight as compared to steel” [9]. These

decreases in weight go rather far in terms of improving fuel economy. Each 10% decrease in

total weight of the vehicle results in nearly a 7% increase in fuel economy. Not only does this

help the owner of the vehicle in terms of money spent on fuel, it also helps emissions reduction.

For every one kilogram in reduced weight, there’s a reduction of about 20 kg in carbon dioxide

emissions [10]. Another important use for composites in commercial vehicles is the safety. This

application has been most influenced by the advances in racing. The research in crashworthiness

that has gone into the use of composites in the racing industry has provided plenty of information

on how composites can be used to make commercial vehicles safer. In the standard vehicle

industry, many of the structural components are made of standard metals and metal alloys. In an

attempt to improve crashworthiness using these materials, crumple zones have been developed in

Material Behavior vs. Weight [9]

order to greater dissipate energy during crashes. However, the failure sequence for composites

occurs in a different fashion compared to metal structures. While metal structures collapse and

crumple under high stress and impact, composites, due to their brittle nature, fail through a in

multiple facets including fibre fracture, matrix crazing and cracking, fibre-matrix de-bonding,

de-lamination and interply separation. The types of failure that occur depend greatly on the

geometry of the structure and the laminate lay up, which can all be used as an advantage if

designed properly. With the right design, composites can be developed for use in high energy

absorption [10]. However, even with all the advantages that composites brings to the table, the

cost of the materials and production have been the main roadblock in their implementation in the

industry. Compared to conventional metals, the cost can reach up to 10 times the production cost

of conventional metals, depending on the composite being produced. Another roadblock that has

prevented composites from becoming a major factor in the commercial vehicle idnustry is the

issue it faces

in

manufacturability. The composites industry has yet to adequately develop methods for high-

volume production. Currently, there isn’t a process that provides cost-effective, rapid, repeatable

results while being environmentally consientious [10]. In the production of the body, although

the composites have a better strength to weight ratio, the cost to production ratio is much worse,

as seen in the following figure. When the total cost of production for a composite structural

piece costs at least an extra $1,000 per vehicle made, it’s clear to see why composites are having

trouble gaining traction in the general automotive industry.

Cost of Production for Different Materials [10]

CONCLUSION

The progression of fiber reinforced composites in automotive racing have made the race

cars both faster and safer. These improvements are mainly due to the advantages that fiber

reinforced composites have over metallic materials with regards to their mechanical properties.

Carbon fiber chassis are much stiffer and resistant to intrusion by foreign object while composite

crumple zones absorb energy to lessen g loads on the driver during a crash. Because of the high

cost associated with composite materials composites are not used to nearly the extent in typical

racing circuits like NASCAR as they are in Formula 1. Likewise, composites have enormous

advantageous applications in the commercial automotive industry. They provide safety, as seen

from the racing industry, as well as increased fuel economy due to their lighter weight. However,

due to their high production cost compared to conventional metals used today, composite

application in the commercial auto industry has yet to be heavily implemented.

References

[1] Ron Lemasters, Jr, Safety: Racing’s Burning Question, February 1, 2002http://www.hotrod.com/how-to/interior-electrical/nascar-safety-seat-cockpit-technology/

[2] Savage, Gary, (2004) Exploiting The Fracture Properties of Carbon Fibre Composites to Design Lightweight Energy Absorbing Structures, Engineering Failure Analysis, vol. 11, No. 5, pp. 677-694

[3] Jovan Obradovic, Simonetta Boria, Giovanni Belingardi, Lightweight design and crash analysis of composite frontal impact energy absorbing structures, September 2011

[4] http://www.formula1-dictionary.net/crash_test.html

[5] Savage, Gary, (2010) Development of penetration resistance in the survival cell of a Formula 1 racing car, Engineering Failure Analysis, vol. 17, pp. 116-127

[6] Savage, Gary,(2009) Sub-critical crack growth in highly stressed Formula 1 race car composite suspension components, Engineering Failure Analysis, vol. 16, pp. 608-617

[7] Leslie-Pelecky, Diandra, August 2009, Materials at 200 mph: Making NASCAR Faster and Safer, MRS Bulletin, vol. 34, No. 8

[8] Savage, Gary, July 2008, Composite Materials Technology in Formula 1 Motor Racing, Honda Racing F1

[9] B Raghu Kamar, R. Vijaya Prakash, N. Ramesh, February 2013, Static analysis of mono leaf spring with different composite materials, Journal of Mechanical Engineering Research, Vol. 5(2), pp. 32-37

[10] Elaheh Ghassemieh (2011). Materials in Automotive Application, State of the Art and Prospects, New Trends and Developments in Automotive Industry, Prof. Marcello Chiaberge (Ed.), ISBN: 978-953-307-999-8, InTech