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602 MRS BULLETIN • VOLUME 34 • AUGUST 2009 • www.mrs.org/bulletin

Materials at200 mph: MakingNASCAR Fasterand Safer

Diandra Leslie-PeleckyThe following article is based on the Symposium X: Frontiers of Materials Research presen-tation given by Diandra Leslie-Pelecky of the University of Texas at Dallas. The presentationwas delivered on December 1, 2008 at the Materials Research Society Fall Meeting in Boston.

IntroductionThe National Association for Stock Car

Auto Racing (NASCAR) is “stock car” rac-ing, in contrast to the open-wheel FormulaOne and Indy Car racing series. With aminimum weight of 1565 kg (3450 lbs),NASCAR stock cars are about twice asheavy as open-wheel cars. Their 5.87 L(358 in3) engines produce 6.3+ MW (850+horsepower), allowing the cars to reachspeeds of more than 329 kph (200 mph).

NASCAR has a challenging role as asanctioning body: developing rulesthat promote competitive racing whilekeeping costs in check and—most importantly—ensuring safety. Races ini-tially featured literal “stock” cars; how-ever, speed increased rapidly. Qualifyingspeeds at Daytona International Speed -way (Figure 1), for example, rose from 225

kph (140 mph) in the late 1950s to 312 kph(194 mph) in 1970, making safety modifi-cations necessary.

Building the CarEventually, it became easier (and safer)

to make race cars that look like stock carsthan it was to turn stock cars into racecars. In 2001, NASCAR started to designa new car, initially called the “Car ofTomorrow.” The new car was motivatedby three considerations: improving com-petition, lowering costs for owners, andimproving safety. The new car (shown inFigure 2) was introduced in 2007 and ranits first full season in 2008.

The cars, which are built largely byhand, start with a mild steel (1018 or sim-ilar) tube-frame chassis. Titanium alloys

or carbon-fiber composites would providebetter strength-to-weight ratios; however,the higher cost led NASCAR to limit chas-sis materials to “magnetic steel.” Each fin-ished chassis is inspected at the NASCARR&D Center using digitizing arms andthen certified with 10 strategically placedradio frequency identification tags that areused to confirm the chassis identificationat the racetrack.

The car’s body is surprisingly thin,with a minimum thickness of 24 gauge(about a half millimeter). The roof, hood,and decklid (trunk) are stamped, but therest of the car is shaped by hand usingan English wheel, a metalworking toolthat resembles two rolling pins, one ontop of the other. Sheet metal is compressedbetween the two wheels, forming thebody panels. Drawing quality alu-minum killed (DQAK) steel provides the formability necessary for the intricatecurves. A giant template grid fits overthe car to check that the body conformsto NASCAR rules.

Cars are painted or (more and more fre-quently) “wrapped.” Wrapping is essen-tially wallpapering a car with a polymerfilm onto which a design has been printed.A grid of micron-scale holes allow air toescape from under the plastic as it isapplied to the car.

Materials for SpeedSplitting the Air

A car’s grip is proportional to the forcepushing its tires into the track. That forcecomes from the car’s weight plus aerody-namic forces, the latter of which scale withthe speed squared. All but two of the 38races each season require only left-handturns. In response, the old car had evolvedinto a kidney-bean shape: Its body wasoffset to the left, and the left-side fenders

AbstractSpeed is the ultimate goal of racing, and materials are an increasingly important area

of research for making race cars faster. The splitter, which produces front downforce, ismade from Tegris, a polypropylene composite offering comparable stiffness and improvedimpact properties at significantly lower cost than alternative materials. Engine blocks mustbe cast iron, but careful control of microstructure using precision manufacturing methodsproduces a lighter engine block that generates more horsepower.

Speed and excitement must be balanced with safety, and materials are key playershere, as well. Energy-dissipating foams in the car and the barriers surrounding thetracks allow drivers to walk away uninjured from accidents. Fire-resistant polymersprotect drivers from high-temperature fuel fires, and technology transfer from theNational Aeronautics and Space Administration (NASA) to the National Association forStock Car Auto Racing (NASCAR) in the form of a low-temperature carbon monoxidecatalyst filters the drivers’ air.

Sports are an outstanding way of showing the public how materials science andengineering are relevant to their lives and interests. Materials science and engineeringis just that much more exciting when it’s traveling at two hundred miles an hour.

Figure 1. Qualifying speeds at DaytonaInternational Speedway 1959–2009.The two cusps in 1970 and 1989correspond to the implementation ofrestrictor plates, which limit enginepower by reducing airflow to the engine.

Materials at 200 mph: Making NASCAR Faster and Safer

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were broader than the right-side fendersso that when weight shifted to the right inleft-hand turns, the greater aerodyanmicdownforce would keep the left-sidewheels in contact with the track.

In the new car, the front valance wasreplaced by a splitter, and the rear spoiler(a flat metal blade standing up on the endof the trunk) was replaced by an invertedwing. Aerodynamic adjustability shiftedfrom the body, which cannot be changedeasily, to the front splitter and the rearwing, which can be adjusted at the track.The new body is much more symmetricand the new rules leave little room forshape modifications.

The front splitter produces downforceby literally splitting the air. Air above thesplitter has a higher pressure than airpassing below. After trying everythingfrom wood to carbon-fiber composites,the NASCAR R&D Center settled onTegris, a composite product with the necessary combination of strength andstiffness.

Tegris is a polypropylene compositethat starts with a tape yarn consisting ofan inner, highly oriented crystalline layerand an outer amorphous layer with alower melting temperature. The tape yarnis woven into a fabric, and sheets of fabricare pressed together under moderate tem-perature (138°C–160°C) and pressuresfrom 1380–2760 N/m2. The outer layer(~15 vol%) melts to form the matrix, whilethe inner layer provides the mechanicalproperties.

Tegris does not have a brittle failuremode—it delaminates, so it does not leavesharp pieces for other cars to run over.Consistent with NASCAR’s efforts toreduce costs for owners, Tegris offers com-parable stiffness and improved impactproperties at significantly lower costs thanalternative materials such as carbon-fibercomposites.

NASCAR uses Tegris primarily as asheet product, but Tegris has potentialapplications in other areas. The new car’sstatic center of gravity is 2–3 inches(5.0–7.6 cm) higher than in the old car, somore weight shifts on braking, accelerat-ing, and turning. Teams try to reduce theweight of components such as dashboardsto lower the center of gravity. The forma-bility of Tegris makes it an ideal candidatefor these applications, as well as for lower-speed use. For example, a Tegris kayak1

weighs in at only 16 kg, and 3 kg of that isthe seat.

EnginesNASCAR uses carbureted pushrod

engines that reach temperatures of 1200°Cin each of its eight cylinders. Engine

blocks are required to be cast iron, but notall cast iron is made equal.

Despite advantageous thermal proper-ties, gray cast iron (>95 wt% iron with2.1–4 wt% C and 1–3 wt% Si) is brittle dueto stress concentration at the edges of the

graphite flakes that form during process-ing (Figure 3a). Ductile iron, in whichmagnesium is added to produce roundgraphite structures, is less brittle but haslower thermal conductivity. As shown inFigure 3b, Mg additions in the narrow

Carbon-fiber composite wing

Tegris splitter

DQAK steel body

Kevlar/carbon-fiber fascia

Lexanwindshield

IMPAXXfoam

Mild steel tube-frame

chassis

CGl engine block

Figure 2. Race cars from Roush Fenway Racing (top) and Red Bull Racing (bottom) showa few of the places where advanced materials are used to improve speed and increasesafety. Images courtesy of Getty Images (top) and Thomas Hoeffgen (bottom). CGI,compacted graphite iron; DQAK, drawing quality aluminum killed.

50 µm 50 µm

a b

Figure 3. Deep-etched scanning electron microscope photos comparing (a) gray cast ironwith (b) compacted graphite iron, which is less brittle and stronger. Images courtesy ofSinterCast.



range of 0.007 wt% to 0.015 wt% changethe graphite from flakes into rounded,interlocking coral-like structures.2 Thiscompacted graphite iron (CGI) has at least75% higher tensile strength, 35% higherstiffness, and double the fatigurestrength of gray cast iron. Although CGIhas been known since the late 1940s, the need to control Mg additions precisely(a drop of just 0.001 wt% Mg can cause a25% reduction in tensile strength) precluded use in large-scale productionuntil computer controls became accurateenough to maintain the required Mg concentration.3

In addition to weight savings (10–30%on engine blocks), CGI blocks have lesscylinder bore distortion as the block heats,which means tighter sealing, higher cylin-der pressures, and, ultimately, morehorsepower.4 About 80% of all NASCARteams use CGI engine blocks. All of Audi’scommerical V-diesel engines rely on CGIcylinder blocks, and Ford is the globalleader in CGI, with five engines on theroad and two more to be launched in thenext year.

CoatingsTo limit cost, NASCAR specifies materi-

als for almost every part on the car. Forexample, engine valves may be titaniumalloys but not more expensive titaniumaluminides. Thin-film coatings not onlybroaden the range of possible mechanicalproperties but also are especially usefulwhen different areas of a single partrequire different properties.

Adding tetra-ethyl lead to gasolinewas primarily to prevent “pinging”–autoigniting the air-fuel mixture prior tothe spark. Lead gasoline additives fouledcatalytic converters and created concernover health and environmental safety,which led the United States to eliminateleaded gasoline. Auto-ignition can beaddressed by increasing gasoline octane,but lead also protects against valve seatrecession (wearing down of the valveseats). An engine valve operating at9500 rpm hits its valve seat 79 times eachsecond. BeCu25 is used for intake valveseats due to its high strength; however, thehigh temperatures of the exhaust valverequire BeCu3 or Moldstar 90 (a Be-free Cu), which have greater thermal conductivity.

The valve seat recession issue wasaddressed by coating the valve head seatangle (the part that mates with the valveseat) with diamond-like carbon (DLC) orchromium nitride. DLC transforms tographite at high temperatures, so its use inthe exhaust valve is limited, and metallichard coatings must be used.

Most valves have more than one type ofcoating. DLC or CrN coatings on the valvetips prevent lash cap wear. Valve stems(which pass through bronze valve guides)are highly polished to allow smaller toler-ances, and then they are coated with low-friction molybdenum-based alloys, suchas molybdenum disulfide. Valve-stemcoatings include some surface porosity(<2.0%) to minimize stress and promoteoil retention. Physical vapor deposition orplasma-assisted chemical vapor deposi-tion techniques commonly are used,although some coatings are plasmasprayed. Typical coating thicknessesrange from 1 to 5 μm, depending on thecoating and the part.

Coatings are not limited to valves, asshown in Figure 4. It is hard to find twocontacting metallic pieces in which at leastone member of the pair is not coated.Multilayered metal-containing DLC coat-ings are applied to parts that sustain highimpacts, such as gears. Piston rings arecoated with titanium or chromiumnitrides or metal-containing DLC todecrease friction while maintaining a tightseal. A nickel-silicon-carbide coating isused on cylinders or cylinder linings.Even fasteners in the engine are coated tofacilitate tearing down the engine, whichhappens after every race.

SafetyMaking Tracks SAFER

During a qualifying run at Texas MotorSpeedway in April 2008, MichaelMcDowell’s No. 00 Toyota Camry lost

grip in turn one and veered suddenly intothe outer wall. The impact spun the cararound, causing it to hit the wall again,followed by barrel rolls down the 24-degree banked turn.5 Within minutesof coming to rest at the bottom of thetrack, McDowell climbed out of the carand waved to the crowd before makingthe mandatory trip to the infield care cen-ter. One factor that allowed McDowell tobe out on the racetrack (in a backup car)the very next day was the SAFER (steeland foam energy reducing) barrier createdby Dean Sicking and his team at theMidwest Roadside Safety Facility at theUniversity of Nebraska–Lincoln.

The first racetrack barriers were con-crete walls, sometimes augmented bystacks of tires or plastic barrels filled withwater or sand. The formula for impulsetells us there are two ways to decrease theforce of an accident: decrease your speed(antithetical to racing) or increase the timeover which contact occurs. The idea of“soft walls” seems obvious, but theirimplementation poses challenges. Foam-lined walls, for example, can “catch” thecars, stopping them suddenly, or sendingthem back into the paths of other cars.

The polyethylene energy dissipatingsystem (PEDS) was installed at theIndianapolis Motor Speedway in 1998.The PEDS was composed of five-foot longsections of overlapping high density poly-ethylene (HDPE) plates separated fromthe outer walls by ~40 cm diameter HDPEcylinders. In principle, when a car hits thePEDS, the cylinders should deform, andthe smooth HDPE front should not snagthe car. The cylinders should reboundback to their original shape. In their firstrace test, the PEDS shattered, flingingdebris across the track; however, despite avery hard hit, the driver walked awayfrom the accident with nothing more thana concussion.

Tony George, owner of the Indy RacingLeague, got Sicking’s group involved in1998 on safety barriers, and NASCARjoined the effort in 2002. Many tracks hostIndy car and stock car races. Since the carmasses differ by a factor of two, the barriermust function over a range of energies.Sicking recommended an outer wall ofhollow square steel tubes (about 20 cm ona side), which have sufficient flexibilitybut will not scatter debris on the trackupon impact. The HDPE cylinders werereplaced by pyramidal foam wedges(Figure 5). Owens Corning Foamular150—an extruded polystyrene foam usedfor building insulation—absorbs energyand allows the outer wall to move. Theconstruction directs the car along the bar-rier and not back into traffic.

Head Seat (wear)

Stem (lowfriction)

Tip (wear)

Figure 4. Most valves have differentcoatings on different parts. Decreasingfriction is critical on the stem, whilewear resistance is the primary concernfor the head. The photo also showsvalve spring retainers, valve locks, andpiston wrist pins, all of which are alsocoated. Images courtesy of Xceldyneand CV Products.


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Energy-absorbing foam is also foundinside the car. Dow Automotive’s IMPAXXfoam is sandwiched between the out-sides of the chassis bars and the car’s bodyon both sides. A 90-mil (2.3-mm) steel platein the driver’s side door and a piece ofTegris in the right-side door preventsharp objects from getting into the driver’scockpit.

IMPAXX is a closed-cell extruded poly-styrene foam. The isolated pores of closed-cell foams make them more rigid thanopen-cell foams, which have a percolativepath of pores through which gas canescape when the foam is compressed.Most closed-cell foams obey Hooke’s lawto about 5% strain. Higher strain deformsthe cell walls (at nearly constant stress)until they touch, at which point the engi-neering stress-strain curve rises sharply,6as shown in Figure 6. IMPAXX’s ability toabsorb large amounts of energy is due tothe foam’s specific cell-wall architecture,which can withstand large applied forcesbefore buckling.7 The combination ofenergy dissipation in the track and in thecar greatly minimizes the impact driversfeel in accidents.

Driver GearJeff Gordon’s No. 24 car is sponsored by

DuPont, which means that materials occa-sionally are not just in the car—they are onthe car. Nomex and Kevlar have both beenfeatured on the rear panel of Gordon’s car.

Kevlar reinforces the front and rear carbon-fiber-composite fascia, whileNomex provides fire protection.

Nomex (poly-meta-phenylene tereph-thalamide) and Kevlar (poly-para- phenylene terephthalamide) are siblingaramids (aromatic polyamides), withKevlar being the para form and Nomex the meta form. The monomers consist of the same atoms in the same order(Figure 7); however, Kevlar forms verystraight chains due to steric hindrance,whereas Nomex has a kink. This makesKevlar (a highly crystalline fiber thathydrogen bonds) extremely strong, butstrength is not the top priority in caseof fire.

NASCAR requires fire suits to protectthe driver from a 982°C (1800°F) flame forfive seconds. Kevlar starts to decomposebetween 427°C and 482°C. Nomex is notnearly as strong as Kevlar; however, itdoes not decompose when heated.Instead, the outer layer of the Nomex fiberforms a “char”—a carbon layer that sur-rounds the fiber and prevents it frombeing used as fuel.8

Chapman Industries’ CarbonX is apolyacrylonitrile polymer that is heated tohigh temperatures during processing.Essentially, the char is created ahead oftime. CarbonX will not ignite or burn,even when exposed to 1400°C for twominutes. Because it is essentially pre-burned, CarbonX currently comes only in

dark colors. Since fire suits are part per-sonal protective apparatus and part bill-board, most drivers wear Nomex firesuits,with either Nomex or CarbonX under-wear.

Fire is an obvious danger, but carbonmonoxide is colorless and odorless. Stockcars have neither mufflers nor catalyticconverters, as high engine throughput isessential for high horsepower. Efforts tominimimize CO exposure were stepped

Extruded polystyrene foam

Square hollow steel tubing

Concrete wall

Figure 5. The SAFER (steel and foam energy reducing) barrier features hollow squaresteel tubing on the side closest to the cars and extruded polystyrene foam trapezoids thatcompress between the steel and the concrete wall when hit. Photo by Robert Hilborn.

Strain

Str

ess

Linear-elastic region

Cell wall deformation, collapse

Cell walls touch

Traditional Closed-Cell Foam

IMPAXX

Figure 6. Schematic illustration of theengineering stress-strain relationship fora standard closed-cell foam (red) andIMPAXX (blue) foam showing thatIMPAXX absorbs significantly moreenergy than traditional closed-cell foam.7

C C

O

O

N NH

H

Kevlar

C

O

O

C N

HN

H

Nomex

a

b

Figure 7. (a) Kevlar and (b) Nomexmolecules share the same atoms, butthe straight Kevlar molecules allowgreater alignment, giving Kevlar highstrength. The kink in Nomex precludesalignment, so Nomex is not as strongas Kevlar; however, Kevlar starts todecompose between 427°C and 482°C,whereas Nomex carbonizes instead ofburning, melting, or decomposing.



up in 2002 at the urging of drivers. At thattime, the National Aeronautics and SpaceAdministration (NASA) was preparing tolaunch a CO2 laser as part of a LaserAtmospheric Wind Sounder satellite.Given the difficulty of regular CO2 deliv-ery to space, a catalyst was needed to con-vert CO output by the laser back to CO2.Space is cold, however, and known cata-lysts needed heat to work. NASA inventeda plantinized tin oxide catalyst thatworked to −26°C. Then the solid-state laserwas invented. There was no need for thenew catalyst in space, but it turned out tobe the perfect solution for NASCAR drivers.9,10 Air passes through a series offilters, catalysts (including the NASA cata-lyst), and a cool box before entering thedriver’s helmet. The tubes entering thehelmet sometimes are visible in in-carshots during races. NASA and NASCARalso collaborated in the mid-1990s todevelop thermal blankets made from spunceramic and glass materials that reduce theheat in the driver’s cockpit by up to 10°C.

The FutureThe National Association for Stock Car

Auto Racing (NASCAR) is a technologicalenigma. While the cars themselves are rel-atively low-tech, an ever-expanding arrayof advanced technology (e.g., finite ele-ment analysis, computational fluiddynamics, and wind tunnels) is usedbehind the scenes to increase speed andimprove safety. Many of the materialsused in NASCAR are finding their waysinto passenger cars, whether they be compacted graphite iron (CGI) engineblocks that reduce weight and save fuel,

advanced coatings that decrease frictionallosses in the engine, or foams that dissi-pate energy in collisions.

Sports are a great way to show the pub-lic how materials science and engineeringimpact their lives. An estimated 75 millionpeople in the United States are NASCARfans, watching races at tracks fromCalifornia to Florida and New Hampshireto Phoenix. Like most sports fans,NASCAR fans are passionate about theirinterest, which means they are willing togo the extra mile to understand why theirdriver is (or is not) winning races.Materials are ubiquitous. It is hard to findplaces where they are not important.Materials moving at 322 kph (200 mph)open new avenues for us to share ourwork with the public.

AcknowledgmentsThank you to Jeff Bulmer of IonBond,

Steve Dawson of SinterCast, HeatherHayes of Milliken & Co., NASCAR histo-rian Buz McKim, Andy Randolph ofEarnhardt Childress Racing Engines, JoeRogers of Xceldyne & CV Products, andMarie Winkler-Sink of Dow Automotivefor their assistance with research andhelpful comments on the manuscript.

References1. www.nativewatercraft.com/ult_12_tegris.cfm.2. S. Dawson, 106th AFS Casting Congress,Kansas City, KS, 4–7 May 2002.3. S. Dawson, T. Schroeder, “AFS Transactions,”(Paper 04-047, American Foundry Society, 2005).4. R.J. Warrick, G.G. Ellis, C.C. Grupke, A.R.Khamseh, T.H. McLachlan, C. Gerkits, SAEPaper 1999-01-0325, International Congress and

Exposition, Society of Automotive Engineers,Detroit, MI, 1–4 March 1999.5. B. Halford, Chem. Eng. News 87, 12 (2009).6. S.K. Maiti, Acta Metall. 32, 1963 (1984).7. G. Slik, G. Vogel, V. Chawda, Proceedings ofthe 5th LS-DYNA Forum (2006).8. S. Villar-Rodil, J.I. Paredes, A. Martinez-Alonso, J.M.D. Tascon, Chem. Mater. 13, 4297(2001).9. NASA Technical Brief, “From NASA toNASCAR: Space-Age Technology Finds ItsWay into Auto Racing” (2008).10. NASA Technology Innovation, PartnershipHelps Virginia Company Grow, Racers BreatheBetter 12, 20 (2005).

Diandra L. Leslie-Pelecky is a professor ofphysics at the Universityof Texas at Dallas. Afterearning her PhD degree incondensed matter physicsat Michigan StateUniversity, she joined thefaculty at the University of

Nebraska—Lincoln before starting her currentposition in 2008. In addition to research in thebiomedical applications of magnetic nanoparti-cles, Leslie-Pelecky engages the public in sci-ence and engineering through K–12 schools,public outreach, and authoring The Physicsof NASCAR. More information about materi-als and motorsports can be found atwww.stockcarscience.com. Leslie-Pelecky canbe reached at the Department of Physics, TheUniversity of Texas at Dallas, 800 W. Camp -bell Rd., EC 36, Richardson, TX 75080, USA;tel. 972-883-4631; fax 972-883-2848; and-mail [email protected].

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