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1253

CHAPTER 40ADVANCED MATERIALS IN SPORTS

EQUIPMENT

F. H. FroesInstitute for Materials and Advanced Processes (IMAP)University of IdahoMoscow, Idaho

1 INTRODUCTION 1253

2 CHARACTERISTICS OFMATERIALS OF IMPORTANCEIN SPORTS EQUIPMENTDESIGN 1255

3 THE IMPACT OF ADVANCEDMATERIALS ON SPORTSPERFORMANCE 12573.1 Running 12573.2 Pole Vaulting 12593.3 Bicycling 12603.4 Tennis and Squash 1263

3.5 Cricket 12643.6 Golf 12643.7 Baseball /Softball 12663.8 Boats, Boards, and Wind-

Surfing Fins 12673.9 Javelin 12693.10 Skiing and Boards 12703.11 Hockey Equipment 1270

4 ETHICAL CONSIDERATIONS 1270

5 CONCLUDING REMARKS 1272

REFERENCES 1273

1 INTRODUCTION

Advanced materials can significantly enhance sports performance and dramati-cally tilt the playing field. This paper discusses the use of advanced materialsin sports and suggests that there are ethical questions surrounding their use.

Advanced materials with mechanical and physical behavior characteristicswell in excess of those exhibited by conventional high-volume materials such

as steels and aluminum alloys have contributed significantly to the increasedperformance of transportation systems in aerospace, automobiles, and rollingstock (trains). The important characteristics include strength, ductility, stiffness(modulus), temperature capability, forgiveness (a collective term including frac-ture toughness, fatigue crack growth rate, etc.), and low density. For many high-performance applications high cost can be accepted, although the level ofacceptance depends upon the industry in question (Fig. 1).

In this chapter the role of advanced materials in a number of sporting eventswill be addressed. At the highest professional level sports are a highly compet-

itive occupation with millions of dollars depending upon fractions of a secondor tenths of an inch. Even the dedicated amateur is willing to invest a great dealof money to improve performance, even though this may occur as infrequently

Handbook of Materials Selection, Edited by Myer KutzISBN 0-471-35924-6 2002 John Wiley & Sons, Inc., New York

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1254 ADVANCED MATERIALS IN SPORTS EQUIPMENT

Construction

Automotive

CommercialAerospace

Military

AerospaceBiomedical

Empha

sisoncos

t

Emphasis on performance

Fig. 1 Impact of cost in various industries.

Fig. 2 Graph showing how industries in advanced materials lead toenhanced performance, and a $17-billion sporting equipment market in the

United States in 1997 says the buying public agrees.

as once a month. Thus, just as in the industries mentioned earlier, if advanced

materials lead to enhanced performance, their use can be justified; and a $17billion sporting equipment market in the United States in 1997 says the buyingpublic agrees (Fig. 2). The characteristics of advanced materials that lend them-selves to this enhanced sporting behavior parallel those listed for other industriesabove.

Just as in the transportation industry the materials of choice for sports haveshown a major evolution over the last 100 years. From naturally occurring ma-terials such as wood, twine, gut, and rubber we have progressed to high-

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2 CHARACTERISTICS OF MATERIALS OF IMPORTANCE 1255

technology metals, polymers, ceramics, and synthetic hybrid materials, includingcomposites and cellular concepts.

In this chapter consideration is first given to a broad discussion of the me-chanical properties of materials that are significant in sporting equipment. Then

there is a more detailed examination of how advanced materials have impactedvarious specific sports. Here an attempt has been made to define how measurable(absolute) records have been influenced by these advanced materials. I haveattempted to subtract the portion of these improvements that are a result ofimprovements in the capability of the human body, whether this be a conse-quence of enhanced body function derived from superior training, diet, or willpower. Advanced materials have led to substantial improvement in some sports,much less in others. In addition, advanced materials have not only led to im-provements in performance for the paraplegic athlete, but in some cases partic-

ipation would not have been even possible without them. Finally, there is adiscussion of the ethics of the use of advanced materials in the sporting arena.The term technological momentum1once technological choices are made

(or allowed) and implemented, reversing the decision becomes difficultexists for sporting equipment. This is particularly the case when athletes andmanufacturers have a great deal invested in the new technology. Once a sportsorganization makes a technological choice, it is often a permanent decision.

2 CHARACTERISTICS OF MATERIALS OF IMPORTANCE IN SPORTS

EQUIPMENT DESIGN

The optimum design of sports equipment requires the application of a numberof disciplines not only for the enhanced performance already mentioned but alsoto make the equipment as user friendlyas possible from the standpoint of theavoidance of injuries.2 Clearly sports equipment design encompasses materialsscience, mechanical engineering, and physics; however, it also necessitates aknowledge of anatomy, physiology, and biomechanics. Biomechanics can besimply defined as the science of how the body reacts to internal and externalforces.3 It is thus an attempt to apply the basic laws of physics and mechanicsto the joints, ligaments, and tissues of the body as they are subjected to loading

(Fig. 3).In designing sports equipment, various characteristics of materials must be

considered4,5:

Strength

Density

Ductility

Fatigue resistance

Toughness Modulus (damping)

Cost

To meet the requirements of sports equipment, the materials of choice oftenconsist of a mixture of material types, metals, ceramics, polymers, and compositeconcepts. They are fabricated into the desired equipment making use of creative

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Fig. 3 Biomechanics of sports addresses the analysis of forces and stresseswhich act on the body in various sports. (From Ref. 2.)

Table 1 Typical Mechanical Properties of Material Classes

Materials Classes

Youngs Modulus

E(MPa) 103

Density

(mg m3

) E/103

Metals 40210 28 2430

Glass 73 2.5 30

Ceramics 400700 3.5 100230

Fibers (B,C) 400 2.4 170

Carbonfiber composite 200 2.0 100

Wood 14 0.5 28

design concepts with due attention being given to biomechanical requirements.By comparing specific properties (i.e., taking the difference in density of com-peting materials into account), the attributes of different materials can be betterevaluated (Table 1). If we want a material that features the highest possiblestiffness for the least possible weight, we would select the materials with the

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3 THE IMPACT OF ADVANCED MATERIALS ON SPORTS PERFORMANCE 1257

Fig. 4 Parts of a running shoe. (From Ref. 2.)

highest specific stiffness. Cellular concepts win out compared to monolithic ma-terials in this regard because the density of cellular materials are less than thoseof solid articles. In the actual design of complex sports equipment, a specificdesign criterion needs to be defined to allow the optimum materials selection to

be made.3 THE IMPACT OF ADVANCED MATERIALS ON SPORTS

PERFORMANCE

To illustrate how advanced materials have impacted sports performance a num-ber of sporting events will be considered in which a contribution to the improvedperformance can be attributed to the materials used to construct equipment.Wherever possible, measurable quantities (distance, time) of improvements inperformance will be given.6

3.1 Running

Shoes have provided substantial improvements in the running events. The humanfeet are very complex biomechanical structures that are highly prone to stressand injury.2 Thus, a running shoe needs to be complex and consists of a varietyof different materials (Fig. 4),6 which are selected according to their resilience,strength, elasticity (stretchability), compression, durability, and wear resistance.About 80% of runners hit the ground on the center heel, roll onto the midfoot,and finally push off with the ball of the foot.2 The midsole is key in providingcushioning during impact with the ground. Usually, it is made from a plastic

foam that in some concepts includes air pockets(Air Max) filled with pres-surized gas. However, these cushioning effects break down with use (even afteronly 100 km of running) with reduced cushioning efficiency. For the future,better cushioning systems are likely with increased tailoring to the individual (ifyou can afford it).

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0

0.5

1

1.5

2

2.5

3

3.5

4

1880 1900 1920 1940 1960 1980 2000 2020

Years

MarathonRecordTime(hrs)

Fig. 5 Improvement in Olympic records for the mens marathon in the past 100 years.

9.5

10.0

10.5

11.0

11.5

12.0

12.5

Winn

ing

tim

ein100msprin

t(s)

1896

1900

1904

1908

1912

1916

1920

1924

1928

1932

1936

1940

1944

1948

1952

1956

1960

1964

1968

1972

1976

1980

1984

1988

1992

1996

Fig. 6 Winning times for the 100-m sprint at the Olympic Games since 1896.

This author contends that the improvements summarized above have beenmuch more in the comfort/avoidance of injury arena than in absolute perform-ance enhancement. In 1896 in the first modern-day Olympics when SpiridonLoues won the marathon (which was actually somewhat shorter in distance thanit is today), for all of Greece to celebrate with him, he barely broke 3 h (Fig.5). Almost 100 years later the Olympic marathon record is a little over 2 h,about a 30% improvement. The majority of this improvement can be attributed

to an improvement in human performance. The same can be said for the 100-m event (Fig. 6).

If we turn our attention to the paralympics, a totally different situation exists.There were no Olympic Games in 1896 for those requiring prosthetic limbs.The paraplegic could hardly move, never mind compete in athletic competition.But by 1992 the paraplegic could not only compete, but he could also outperformthe majority of us who have use of all our limbs.

Paraplegic Joe Gaetani broke world records in both the 100-m and 200-msprint events in Barcelona (Table 2). He made use of the amazing Springlite II

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Table 2 World Records Set by JoeGaetani in the 1992 Paralympics inBarcelonaa

Event (m) Time (s)

100 12.23

200 24.82

aBilateral below-knee amputee athlete (ClassA-3).

Table 3 Requirement for a Vaulting Pole

Requirements Possible Materials of Choice

Light (low density) Bamboo

Buckling resistance (stiffness) Aluminum

Strong (resistance to plastic strain) Steel

Minimal twisting (high torsional strain resistance)Cost

MagnesiumCarbon fiber composite

prosthetic device, which features a thin carbon fiber/epoxy pylon that providesthe right balance of stiffness andflex at a substantially reduced weight comparedto conventional materials (3 lb compared to 10 lb) such as wood. An energystorage return aids performance and contributes to the capability to walk or run

greater distances with much less fatigue and discomfort than with traditionaldevices. The cost of the Springlite II is about $850.

Born without feet, Tony Volpentest won gold medals in Barcelona in the 100-m (11.63 s) and the 200-m (23.07 s) events. He runs on carbongraphite feetbolted to carbon composite sockets that encase his legs (built by Flex-foot Inc.),the arrangement acts like a spring-board. With each step, the runner punches thetrack, which catapults him forward more efficiently than if he were running ontwo human feet. And the long-distance runner is not forgotten: This device isstiff and springey for sprinters but shock-absorbing for the marathoner.

3.2 Pole Vaulting

The requirements for a vault are shown in Table 3. The 1896 Olympics saw aheight of 3.30 m achieved with a bamboo pole in the pole-vault event. Figure 7shows the winning heights in the pole-vault discipline for all Olympic eventssince the first. The bamboo pole, which has more spring and is much lighter forthe same stiffness than the hickory pole, was introduced in 1904 by an Olympiadfrom my hometown of Moscow, Idaho, A. J. Gilbert (Dan OBrian is the secondOlympian from our town of 18,000). Initially this change in materials providedan advantage of about 200 mm in height. Improvements in coaching and tech-nique allowed a gradual increase in height over the years. By the late 1950s,however, the gains were starting to level off and lighter weight aluminum poleswere used for a short time. The greatest performance improvement occurred in1964 with a substantial gain of about 250 mm over the previous Olympics, toa height of 5.10 m. This improvement was caused by the introduction of glass-fiber composites, which were lightweight and had higher stiffness. Not only wasthis new material more efficient, it allowed athletes to change their style by

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2.5

3.0

3.5

4.0

4.55.0

5.5

6.0

6.5

Po

levau

lthe

ightjumpe

d(m)

1896

1900

1904

1908

1912

1916

1920

1924

1928

1932

1936

1940

1944

1948

1952

1956

1960

1964

1968

1972

1976

1980

1984

1988

1992

1996

Fig. 7 Winning heights in pole vaults since first Olympic event.

Longitudinal carbon fibers/epoxy

Glass fiber web/epoxyRings of glass fibers

Fig. 8 Adding in minimal twisting requirement, carbon fiber composite becomes more attrac-tive with three layers of different fibers being used to optimize the performance. (From Ref. 2.)

turning upside-down and gliding over the bar feet first. Improvements in tech-nique using the new pole once again lead to increases in performance that areonly just beginning to slow down.

If we refer to Table 1, and also add the requirement of durability, the materialof choice is the carbon fiber composite, with bamboo not too far behind. If weadd in the minimal twisting requirement, the carbon fiber composite becomes

even more attractive (Fig. 8) with three layers of different fibers being used tooptimize the performance. An outer layer of high-strength carbon fiber provideshigh stiffness, while an intermediate webbing of fibers together with an innerlayer of wound glass fiber, builds in resistance to twisting. The glass fiber con-sists of 80% longitudinal and 20% radial fibers. So for the pole vault advancedmaterials have a major influence on performance.

3.3 Bicycling

Cycling is a highly efficient form of transportation, with the energy consumptionlower than for walkers, and much lower than for powered vehicles.2,7,8 TheChinese, recognizing this, build over 10 million bicycles per year. The bicycle

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Fig. 9 Bicycle diamond frame. (From Ref. 2.)

has been around for almost 200 years maturing from the 1817 Draisienne (walk-ing device) to the modern-day Rover Safety Bicycle designed by J. K. Starleyin 1885. Nowadays, advanced materials, in combination with aerodynamic con-siderations, have led to vastly improved bicycles. When Greg LeMond won the

1989 Tour de France (3420 km) by only 8 s, for example, his success was madepossible by a clip-on extension of his handlebars with a padded tube, whichenhanced his aerodynamic shape.

The bicycle can be considered to be a modified space framesuch as thatfound in bridges, cranes, etc. For the bicycle this is the diamond frame(Fig.9).

A number of advances have contributed to the high efficiency of a modern-day bicycle including the development of spoke wheels, the chain concept, pneu-matic tires, and such accessories as seats, brake levers, and pedals. The two

major advances are in the frame and wheels, however, and we will now considerthese two components of the advanced bicycle.

Frame

The diamond frame and the alternate structure, the cross frame, are bothconstructed from thin-walled tubular components that must resist tension, com-pression, bending, and torsional stresses. The requirements for the materials ofconstruction of a bicycle are shown in Table 4.

These materials requirements can be simplified to the minimization of thebending of a cantilever beam; then the mass is given by

Mconst

E

Thus the optimum material is the material with the highest specific strength/E. Based upon the data shown in Table 1, carbon fiber composites are the

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Table 4 Materials Requirements for a Bicycle andPossible Materials of Choice

Requirements Possible Materials of Choice

Light (low density) Carbon fiber composites

Stiff Aluminum

Strong Titanium

Toughness Magnesium

Fatigue resistance Steel

Corrosion resistanceCost

Metal matrix composites

Fig. 10 Road bicycle made by Harry Havnoonian with a mix of materials using adhesive bond-ing for joints, investment-cast stainless steel lugs, Ti-3Al-2.5V head tube, SiC-fiber-reinforced

aluminum alloy front triangle, CRFP rear triangle, and CFRP rear wheel.

materials of choice if there is no concern over cost. Lightweight metalsaluminum, magnesium and titaniumare also attractive, as are metal matrix

composites (Fig. 109). If cost is a concern, then steel, which is not that far behindthe other materials, is the obvious material for selection.

In addition to the carbon fiber reinforced composite frames, recently frameshave been produced from magnesium, aluminum, titanium and metal matrixcomposites. In addition hybrid frames such as carbon fiber reinforced compositecombined with titanium have been produced.

Wheels

Advances here include wheels with increased stability and rigidity for off-road

bikes constructed from glassfiber reinforced nylon, and disc wheels. In the latterconcept discs made of aluminum alloys or carbon fiber reinforced compositesreplace the spokes in conventional wheels. Developments also include three orfive spoke wheels for rigidity and crosswind aerodynamics.

The improvements that advanced materials have produced in bicycling canbe gauged in the enhancement in the Olympic pursuit records shown in Table5.

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Table 5 Improvement in Olympic Records forthe Bicycle 4000-m Individual Pursuit

Competitor Year Time

Daler (CZE) 1964 5 min 5 s

Boardman (GB) 1992 3 min 22 s

Fig. 11 Dangerous vibration can lead to tennis elbow. (From Ref. 2.)

3.4 Tennis and Squash

Tennis is a sport in which absolute achievements cannot be compared. Who canargue with the notion that Bobby Riggs with his 1939 wooden racket wouldhave no chance against Pete Sampras armed with an oversized composite racketwith an enlarged sweet spot.In fact, this confrontation has been framed aslike fighting against rifles with bows and arrows.10

Until about 25 years ago, tennis rackets were made from wood with ash,maple, and okume leading the way. In the late 1960s metal frames, generallyfabricated from steel or aluminum, were introduced. At the present time, com-posite rackets are all the rage, not only from the viewpoint of efficiently accel-erating the ball across the net, but also in terms of damping dangerous vibration,which can lead to tennis elbow(Fig. 11).

The impact force experienced by a player on returning a tennis ball travelingat 160 km per hour (100 mph) is approximately equivalent to jerk-lifting aweight of about 75 kg (170 lb). These forces can transmit a high load to the

lateral epicondyle, located on the outer side of the elbow; leading to damage tothe small blood capillaries in the muscles and tendons around the elbow joint.Better technique can help, but improved rackets can also make a major contri-bution.

The goal in designing modern tennis rackets is to increase the size of thesweet spot, the central part of the racket, which leads to little or no shock tothe player and minimal vibration occurs upon impact with the ball. This depends

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upon the stiffness of the frame and the size and shape of the handle and head.The International Tennis Federation have now imposed an upper limit to the sizeof the racket.

Today tennis rackets are produced from monolithic metals, including steel,

aluminum, magnesium, and titanium and metal matrix composites. However, thehigh stiffness of carbon-fiber-reinforced composites makes them superior to themetals in imparting high forces to the ball. To reduce the high-frequency vibra-tion upon impact, racket handles are constructed of multiple fiber-reinforcedlayers wrapped around a soft inner core, which is often an injected polyurethanefoam or honeycomb construction.

An example of a state-of-the-art tennis racket is the Wilson FPK, which con-sists of a urethane core, 84% graphite, 12% Kevlar, and 4% fiber FP (a pureform of ceramic aluminum oxide). The graphite provides strength and stiffness,

thereby minimizing head deflection and helps to prevent twisting of the rackethead when the ball impacts outside the sweet spot. The Kevlar fibers lead toadditional strength and durability and contribute to damping vibration. The fiberFP produces even greater stiffness and damping to this type of tennis racket.

Squash rackets have shown similar trends to tennis rackets.2 Until 1983, theframe was constructed of wood. Since then, squash rackets have featured hollowextruded aluminum designs and fiber-reinforced plastics, the latter featuringlightness, strength, toughness, and reduced vibration.

Racket strings have transitioned from ox gut to the modern-day synthetic (e.g.,nylon) strings. This transition has not been without controversy. In the late1970s, so-called spaghetti stringing, which resulted in large amounts of spinbeing imparted to the ball and an unpredictable bounces, led to a rule requiringstrings to be interlaced and attachments for durability purposes only, not de-signed to alter the flight in the ball.11,12

Wheelchairs (Fig. 12) now allow the paraplegic athlete to compete in thissport, as well as others, including racing events, basketball, and rugby. No heavysteel frames hererather bikelike wheels, use of aerospace carbon fibers, andtitanium, as well as computer-aided design of the suspension. Now there is achair for each sport: basketball, racing, and even tennis. For example, tennis

chairs are built with sharply slanted back wheels so the athlete can move quicklyfrom side to side. In basketball, forwards have high seats, guards have moreslant in their chairs in order to turn quickly. Cost? Top wheelchairs are in therange of $2000$3300 apiece.

3.5 Cricket

As with tennis rackets, the manufacturers of cricket bats have been concernedwith the size of the sweet spot and the reduction offlexural vibrations.13 Threesignificant modes of flexural vibrations detract from the ideal rigid-body per-

formance, and whereas distributing the weight of the blade to the edges (perim-eter weighting) does not increase modal frequencies significantly, it may increasethe width of the sweet spot.

3.6 Golf

Paralleling the tennis situation, it is very difficult to compare many of theachievements of the past with those of today in absolute terms. Clubs have

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Fig. 12 Steve Meredith of Titanium Sports of Kennewick, WA (left) along with Alistair Godfreyand Malcolm Ward-Close of the Defense Evaluation and Research Agency (DERA), United King-

dom, are shown inspecting a titanium wheel chair.

evolved tremendously and it is difficult to imagine that Bobby Jones, usinghickory shafts, could compete, at least in length, with Tiger Woods, Ernie Els,

or David Duval armed with a shaft constructed from a graphite-epoxy and anover-sized hollow titanium head; albeit at a high price.

The materials evolution for the driver is dramatic. The overall weight hasbeen decreased and the length of the club increased from 100 cm to as muchas 125 cm. The grip and shaft weight has been reduced from 165 grams downto 115 grams or less. The weight of the head remains the same at about 200 gbut using a hollow titanium (casting) construction, the head is now much bigger,with the mass concentrated around the outside of the hitting face. The net resultis a club that is claimed to give greater distance (greater club head speed because

of the longer arc) but also a straighter (bigger sweet spot) shot.A concern of the U.S. Amateur Golf Association (USGA) is that technology

may dominate over skill, i.e., no spring-back(trampoline) effect should occurwhen the ball is struck by the clubface, which may add distance. When a golfball hits any surface it rebounds at a velocity less than that at which it hit thesurface (Physics 101).14 Materials with a high elasticity and high strength resultin a high rebound velocity (or high coefficient of restitution [COR]), especially

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when the impacted surface is thin (allowing the trampolineeffect). Thus thehitting surface can be tuned to increase the COR. However, this now puts us onthe ragged edge of the mechanical property limits of materials of construction.Thus you will hear of the proprietary heat treatments(simply an aging treat-

ment to increase the strength) to create a beta titanium alloy that is strong andcapable of resisting fracture (most of the time) even though it is thinner thanconventional titanium (e.g., Ti6Al4V) hitting faces.

With a tuned (nonconforming) face, the COR will exceed the USGA limit of0.83 (somewhat arbitrarily set to allow the majority of the drivers at the timethe limit was set to meet the requirement). However, the salient question is: Dothe nonconforming drivers actually lead to increased distance? Tests by Golf

Digest14 indicated that the trampoline effect is maximized only in a relativelysmall area of the clubface. This means that it requires the impact accuracy of a

robot or a professional to take full advantage of the effect. This has been con-firmed in robot testing of a nonconforming club head (COR 0.845) where a 2%increase in ball speed (over a confirming club with a COR of 0.81) increasedcarry distance by 12 yards for 220 yards shots and 46 yards for 270-yarddrives (the higher the swing speed, the greater the increase in ball speed andtherefore, carry distance). And to the crux of the matter: 40 players (0 to 22handicap) had essentially the same distance from both the conforming and non-conforming clubs. Worse: With off-center hits, there are indications that thenonconforming club hits the ball shorter distances than the confirming club.

The USGA fears that trampolineclubs and other out theretechnologiescould add 30 yards to a drive.15 With a perfect center hit, a COR of 0.880/0.900(the maximum likely) and a 109-mph swing (a pros swing), the distance gapbetween a persimmon wood (COR 0.77) is about 25 yards.15 So potentially amaximum of another 25 yards is possible with a nonconforming driver (COR0.880/0.900) with an optimally struck approved golf ball. Thus there is a legit-imate concern with the professionals, probably none for the average golfer.

Driving distance is an absolute criterion, which can be tracked versus thematerial of construction, with a caveat that the modern top golfers on the PGAtour now realize that exercise and body-building help their performance, far from

a common practice in the past. The average PGA tour driving distance is shownin Fig. 13,15 with a spike in 1994 at the time of the introduction of the titaniumdriver. A complication here is that balls have also evolved tremendously, withthe most lively being banned because they would obsolete current golf courses.

3.7 Baseball/ Softball

Aluminum baseball bats are banned in the U.S. major leagues because theywould make current baseball stadiums obsolete. There would be too many homeruns. However, both new aluminum bat concepts such as the ultralight, with a

double-walled barrel construction, and titanium bats are revolutionizing softball.These bats have bigger sweet spots and lead to greater velocity off the bat.However, the Softball Association is concerned with an increase in injuries toinfielders who cannot react quickly enough to this higher velocity. An exampleof a softball bat produced from titanium using a powder metallurgy approach isshown in Fig. 14.

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Fig. 13 Average driving distance on the PGA tour. Note spike since the introductionof the titanium driver in 1994.

Fig. 14 Susan Abkowitz of Dynamet Technology, Inc. holds a softball batwith a titanium alloy outer shell.

3.8 Boats, Boards, and Wind-Surfing Fins

For all watercraft, there are four basic forces to contend with when consideringdesign: weight, lift, thrust, and drag (Fig. 15).2 Materials of construction areneeded that result in lightweight, low skin friction (to give smooth flow andreduced drag), increased toughness and a high level of safety. Modern craftconsist of a combination of several polymeric composite materials, often incor-porating cellular (sandwich) concepts.

The construction of a wind-surfing board is complex consisting of a core ofextruded foam polyestrene filler enclosed in fiberglass. This core is covered

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Fig. 15 Forces acting on a watercraft.

Fig. 16 Method of operation of hydroelastically tailored wind-surfing fin.

with graphite and glass fibers embedded in resin matrices, with an outer surfaceof glass-fiber-reinforced composite.

An interesting materials application involves the design of the wind-surfingfin. The challenge is to design a fin with optimal hydrodynamic shape becausesurfers need to perform equally in both directions, requiring a symmetric design.Innovation relied on a concept known as hydroelastic tailoring.16 Through thisprocess, structural deformation of the cross sections (Fig. 16) is induced by the

hydrodynamicpressure forces, with the internal structure encased in a flexibleelastomer material covering. As this section moves through the water (at anincidence angle), a surface pressure loading results, as shown. This surface pres-sure loading is of insufficient magnitude to deform the supporting internal struc-

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40

5060

70

80

90

100

1896 1916 1936 1956 1976 1996

Date

Distance(m)

Fig. 17 Winning Olympic Games javelin throws.

ture but is sufficiently strong to deform the elastomer region. As a result, thecross section will assume the cambered geometry shown. If a satisfactory shapeis achieved, the end result will be an increase in lift-to-drag ratio of the finone of the design parameters used to improve the fin performance. The material

of choice here is carbon fiber/Kevlar polymer composite.

3.9 Javelin

The javelin was an event enjoyed by the Mycenaeans at least 3000 years ago.17

The Greeks of 500 BC used a thin wooden javelin with a cord wrapped aroundits center of mass. When thrown, the thrower held onto the end of the cord tomake the javelin rotate through the air. The rotation acted to stabilize the javelinby averaging any non-symmetry in its construction about a central axis.

The modern javelin has relatively strict rules concerning its construction.17

Essentially, the modern javelin must be smooth and has strict geometric rules toensure the positioning of the center of mass. The reason for this can be seen inFig. 17 which shows winning throws at the Olympic Games from 1904 onward.At the Athens Olympic Games in 1908 the winning throw was just over 50 m.In 1984, Uwe Hohn (from the then East Germany) threw a staggering 104.80m. Given the dimensions of stadia and the fact that it was becoming unsafe forspectators, it was decided fairly quickly by the International Amatuer AthleticsFederation that the javelin had to be redesigned to under-perform.This wasdone by moving the center of mass forward by 4 cm, which caused a dramatic

loss in lift and a consequent reduction in the distance traveled.Figure 17 shows that the distances for the new-rules javelin were approxi-mately 15 m less after the center of mass rule change. As far as the rule makersare concerned there are two advantages: (1) the javelin does not fly as far and(2) the javelin clearly lands tip first. Although this reduces overall throw dis-tances, the new rule does give the athlete one advantage. The old-rules javelinwas very sensitive to the initial throw conditions and even a small change couldreduce distances by 20 m. The new-rules javelin is much less sensitive to initialconditions partly because it always has a negative pitching moment. This islikely to allow the athlete to produce more consistent throws.

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Fig. 18 Forces acting on a skier. (From Ref. 2.)

As with the pole vault, technology strongly influences the performance ofjavelin throwers, and the IAAF successfully used an equipment change to reducethe length of throws from the mid 1980s. As Fig. 17 shows, however, it mightnot be too long until a further rule change is required!

3.10 Skiing and Boards

Skis need to provide for good longitudinal torsional rigidity to allow for goodweight/pressure distribution while being flexible enough to respond to differentsurface properties (snow conditions) to dampen vibrations that could lead to hipand knee injuries (Fig. 18).2 Modern skis consist of a cellular core (of polymericor metal construction) and layered material around this core (including metalsand polymer composites reinforced with Kevlar, aramid, and carbon fibers) withmetal edges of steel or high-strength aluminum alloys. Debatably, the top-of-the-line skis, at the present time is the Volant titanium model, again with steeledges for high hardness, toughness, and wears resistance18 (Fig. 19).

3.11 Hockey Equipment

The hockey stick has changed dramatically over the years, transitioning fromwooden handles and paddles to hybrids of wood and fiberglass composites, andrecently to include aluminum and carbon or graphite composite shafts.19 Thelatter concept giving improved performance and player comfort.

4 ETHICAL CONSIDERATIONS

The use of advanced materials in sporting goods has been discussed with someexamples being given; but certainly not all that are possible. Where the sportingachievement can be gauged in absolute terms, tremendous improvements havebeen made in those sports where equipment is critical. However, use of advancedmaterials in sports equipment presents us with some ethical questions.20 We canclearly enhance behavior by allowing the use of advanced materials, but where

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4 ETHICAL CONSIDERATIONS 1271

Fig. 19 Volant titanium skis.

should the line be drawn? Or should there be no restrictions? The solution,according to a young man in one of my classes at the University of Idaho, isthat if you have the patent, you (and only you) can use this material or designno matter what it is.

This then brings us to a second question. Should we allow competition at thehighest level to be only affordable to the elite because of the high cost of equip-ment? In turn this leads into what is perhaps the most controversial question. Ifwe allow certain classes of materials and designs, but not others, we can actuallyfavor the class of people who will excel! Let us briefly examine these questions.

The carbonfiber vaulting pole, javelins with spiral tails, golf balls with specialdimple patterns, stiffer carbon fiber tennis rackets, bicycles with new types ofwheels, and the egg position,discuses with their weight distributed as closeas possible to their perimeter, and Americas Cup yachts (forget it, this one istoo complex) all lead to further and faster.We should not be Luddites but

where should this end? Can we ensure that it is people who are competing andnot the advanced materials? For sure, we do not want to force the paraplegicathlete to go back to a wooden pylon. But how about electronically guided darts,heat-seeking missiles for grouse shooting (allowable, provided the grouse is stilledible, according to a young lady in one of my classes at the University ofIdaho), solar-energy-enhanced bicycles, and terrain-following golf balls, whichautomaticallyfind the lowest local elevation on a putting surface (the bottom ofthe hole).

Returning to running, consider the advanced devices that allow the runner to

be catapulted forward more efficiently than if he were running on two humanfeet (cost up to $7000). So lets develop similar devices to be incorporated intothe shoes of Donovan Bailey (winner of the 100 m in Atlanta in a world record9.84 s) and Michael Johnson (winner of the 200 m in Atlanta in a world recordof 19.32 s). Any bets on whether Donovan and Michael could then break 9 sand 18 s in their respective events? Is the answer here that nothing beyond thenaturalspringiness should be allowed?

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What is the answer to high costs? Many sports rules committees feel that areasonable compromise is to keep their sport affordable to many athletes ratherthan the elite few. For example, disk wheels were initially banned from Olympicbicycling competition because they were so expensive that they could not be

considered as available to most cyclists. Should all canoes and kayaks conformto a single-hull design? Should the Hoyt bow,comprised of tiny glass beadsembedded in a rigid foam matrix, be allowed to compete against the traditionalwooden bow? The lack of change in behavior with temperature and minimalmoisture absorption of the new bow has led to winning scores of 1350 (out of1440) compared to about 1100 thirty years agobut at a price.

Let us take two examples of how legislation regarding advanced materialscan significantly determine who wins an event. Elite rowers stand 6 ft 6 in. andweigh about 210 lb. In contrast elite kayakers stand 612 in. smaller and weigh

30 lb less. This relates to allowable boat dimensionsa rowing boat can be aslong as desired, favoring strength even at higher weights (longer boats can dis-tribute more weight over a larger area without riding too low in the water, whichleads to excessive drag). In contrast the length of a kayak is restricted, leadingto an optimized aerobic strength-to-weight ratio.

When the javelin was redesigned to be lighter and more aerodynamic, finessewas required to make it floatcorrectly. Masters of this new art, such as Uwet-lohn of East Germany (1984), deftly projected the javelin over 100 m, much tothe danger of spectators and other athletics warming up on the far side of thestadium. The 1986 ban on the new design led to a dramatic drop in the worldrecord by 20 m, with the finesse floaterfading to the second rank, and thestrong-arm boysonce again leading the way.

Lots of questions, few answers.

5 CONCLUDING REMARKS

In this chapter, I have chosen a number of sporting events to illustrate how themagnitude of the effect of advanced materials differs depending upon the sportin question. I then presented some ethical issues regarding the use of advancedmaterials in sports, with the issues outnumbering the answers. Clearly different

sports have been affected by quite different amounts, in some cases to an extentthat has required legislation restricting certain materials and designs (titaniumbaseball bats, floating javelins, nonconforming golf club drivers, etc.). However,perhaps the best approach would be to define acceptable performance standardsrather than the conventional ad hoc regulation focused on design standards.11

This should protect the essential skills of the sport, preventing it from becomingtoo easy or distancing it from historic or aesthetic origins. For further details onthe use of advanced materials in sports, the interested reader is referred to tworecent conference proceedings.21,22

Acknowledgments

The author would like to thank C. Shira, S. Haake, S. Fagg, K. A. Prisbrey, K.Tabeshfar, and X. Velay for useful input into this chapter, and the assistanceprovided by Mrs. Marlane Martonick in manuscript preparation. Acknowledg-ment is also made to Dr. Sharon Stoll, Director of the Sports Ethics Center atthe University of Idaho (UI) and to UI students who have forced me to thinkdeeper about some of the ethical questions presented in this chapter.

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REFERENCES

1. T. P. Hughes, Networks of Powder: Electrification in Western Society 18801930, John HopkinsUniversity Press, Baltimore, 1983, p. 15.

2. K. E. Easterling, Advanced Materials for Sports Equipment, Chapman and Hall, 2-6 BoundaryRow, London, 1993.

3. R. Wirhead, Athletic Ability and the Anatomy of Motion, Wolfe Medical Publication, London,1989.

4. D. Bjerklie, High-Tech Olympians,Tech. Rev., 96,22 (1993).

5. N. Russell, High-Tech Sport,Economist, 324,17 (1992).

6. Atlanta 96, The Official Commemorative Book of the Centennial Olympic Games, WoodfordPress, San Francisco, 1996.

7. G. Lea, On Your Bicycle,Economist, 330,94 (1994).

8. M. F. Ashby, Met. and Mats. Trans., 26A(Dec.), 3057 (1995).

9. Anon, High Performance Composites,July/ August 48 (1999), C. Grant,MRS Bull.March 50(1998).

10. M. Fisher, Atlantic Monthly, 271(1), 78 (1995).11. J. N. Gelberg, MRS Bull., 23(3), 39 (1998).

12. Rules of Tennis Amendment ITF upheld, July 13, 1978, Presidents Newsletter,July 31, 1978.

13. C. Grant, MRS Bull. 23(3), 50 (1998).

14. A. Chou, Golf Digest,Dec., 96 (1999).

15. V. Klinkerborg, Golf Digest,Dec., 94 (2000).

16. F. H. Froes, S. Haake, S. Fagg, K. Tabeshfar, and X. Velay, Gold Digest,Dec., 32 (2000).

17. S. J. Haake, The Chronicle of the Olympics, 18961996.

18. H. Casey, private communication with F. H. (Sam) Froes, March 7, 2001.

19. E. M. Lenoe, MRS Bull., 23(3), 47 (1998).

20. F. H. Froes, Is the Use of Advanced Materials in Sports Equipment Unethical?, JOM,Feb.,15 (1997).

21. A. J. Subic and S. J. Haake, (eds.), The Engineering of SportsResearch, Development andInnovation,Blackwell Science, London, 2000.

22. Proceedings of Materials and Science in Sports Conference, San Diego, CA, F. H. (Sam) Froesand S. J. Haake (eds.), TMS, Warrendale, PA, April 2001.

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