automotive materials: …web.pdx.edu/~pmoeck/phy381/traub article.pdfautomotive materials technology...

336 MRS BULLETIN • VOLUME 31 • APRIL 2006

IntroductionThere’s good news and bad news about

the overall growth potential of the auto-motive industry.

First, the good news: Owning an auto-mobile and having personal mobility ap-pears to be global and universal in nature.For me, anything that can be representedon a sigmoidal curve (Figure 1) has theforce of a natural law, which in this casewould be, “when people can afford per-sonal mobility, they opt for it.” The growthin world population and the growth inglobal affluence, particularly in developingcountries, have very good implications forthe automotive business. Today, 12% ofthe world’s population owns a vehicle. By

2020, that figure could reach 15%, asshown in Figure 2. Factoring in the in-creased population, the result would be a50% increase in vehicle ownership in theworld. Those of us in the vehicle manu-facturing businesses definitely want to bea part of that growth story.

Now, for the bad news: This phenome-nal growth carries its own challenges andproblems. How can we grow the “vehicleparc”—the number of registered activevehicles—to 1 billion vehicles withoutadversely affecting the planet we live on?Sustainable growth is the primary chal-lenge for our industry. It is the theme thatdrives the technology agenda for General

Motors and probably for most of the otherautomotive OEMs (original equipmentmanufacturers).

GM’s sustainable growth agenda hasseveral key components:1. Fuel economy is one of the most criticalchallenges to our sustainability, and notjust in the United States or in the aftermathof Hurricane Katrina. Almost 98% of auto-motive vehicles are powered by petroleumproducts. We worry not only about the sus-tainability of that supply, but also aboutwhether its sources can be diversified, adevelopment that we favor.2. Emissions, both from our manufactur-ing plants and from our vehicles, are an-other major factor. Our emissions goal is totake the vehicle out of the environmentaldebate. That is another way of saying thatour company is working toward achievingzero tailpipe emissions. We are attackingthe problem not only at the tailpipe, but alsofrom the full “wells-to-the-wheels” cycle.In the end, that vision could be enabled bythe hydrogen economy and the fuel cellelectric vehicle.3. Infrastructure is yet another sustain-ability issue. Since the 1960s, the vehicleparc has been growing at a rate that is exceeding the number of roads availableinternationally. Congestion is one of therate-limiting steps that we are addressing.4. Safety is one of GM’s primary sustain-ability objectives. The World Health Orga-nization estimates that the number ofannual traffic-related fatalities globally isabout 1.2 million lives, including vehicleoccupants, cyclists, and pedestrians. Thisnumber is growing, particularly in the de-veloping world. On the positive side, weare going through a technology-enabledtransformation that will vastly improveautomotive safety. For the past 40 years,our focus has been to design vehicles sothat in the event of a crash, the chance ismaximized that the person will be able towalk away from the car or truck. To accom-plish this, we have developed seat belts,air bags, and crush zones. Now, throughtechnology such as electronics, controls,and software, we are moving toward thepoint where the crash could be avoided inthe first place.5. The experience of driving the vehicle,in terms of both safety and comfort, is an-other major factor in our industry. We arechanging the driver–vehicle relationshipthrough electronics technology. Today, ourhigh-end vehicles have almost 30 micro-processors in them, as well as safety devicessuch as our OnStar mobile communicationspackage, which provides 24-hour connec-tion to an OnStar center. In the same waythat iPods and Blackberrys have changedour daily lives in a personal way, electronic

Automotive Materials:Technology Trendsand Challenges inthe 21st Century

Alan I.Taub

AbstractThe following article is an edited transcript based on the plenary talk given by Alan I.

Taub of General Motors Corp. on November 28, 2005, at the Materials Research SocietyFall Meeting in Boston.

Fuel economy requirements, emissions regulations, and the push for energy inde-pendence are key factors driving the auto industry to increase vehicle efficiency.Themain avenues to efficiency improvement are powertrain enhancements and massreduction.This presentation details how General Motors is developing advancedpropulsion systems and using lightweight materials to achieve greater vehicle efficiency.Taub, who is executive director of General Motors Research and Development, outlinesGM’s strategy for advancing propulsion technology, from improvements in the internal-combustion engine to hybridization to full vehicle electrification. He then describes thecompany’s efforts to use lightweight materials such as aluminum and magnesium alloys,high-strength steels, and composites to reduce vehicle weight. Also highlighted is GM’ssuccess in employing novel materials in the development of advanced vehicle andpowertrain systems to achieve additional efficiencies. One example is the application ofsmart materials, which enable new features and functions by way of mechamatronicsolutions (the integration of smart materials with mechanical systems and electronics).Key technical hurdles that must be overcome to increase the use of these materials bythe automotive industry are also discussed.

Keywords: composite, energy storage, environmentally protective, H, nanoscale,nanostructure, polymer.

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Automotive Materials Technology Trends and Challenges in the 21st Century

MRS BULLETIN • VOLUME 31 • APRIL 2006 337

vehicle controls will alter the entire “lookand feel” of driving. Because of sophisti-cated on-board software, we are gettingever closer to our goal of being able to per-sonalize and adapt each vehicle to theindividual.

Cost also weighs in as a critical factor inthe sustainability equation. The era whenautomobiles were a cost � margin � pricebusiness ended around the mid-1990s. Sincethen, vehicle purchase prices have been lev-eling around the world, resulting in a re-versal of the equation, to price – margin �allowable cost. To continue the trend of a

growing vehicle parc, we must achieve in-creasingly lower costs while deliveringever-increasing features and functionality.

Considering that we have a broad arrayof challenges in the auto industry, I havedecided to selectively concentrate on twoof these challenges—advanced propul-sion and advanced materials. These topicsare reflected in a number of other sessionspresented at this meeting.

Advanced Propulsion SystemsThe primary challenge in improving

automotive propulsion systems is achiev-ing better fuel economy while retaining orimproving performance. For every unit ofenergy that is delivered to the wheels tomove the vehicle during city driving,nearly eight units of energy in gasoline arerequired. The example in Figure 3 is basedon city driving, the most demanding kindof use.

Improving the Internal-CombustionEngine

The greatest energy loss is in the effi-ciency of the engine. The internal-combustion engine has been developingand maturing for more than 100 years, butit can still be further improved.

As a result of research that is taking placetoday at laboratories and universitiesaround the world, we can now visualizethe entire combustion event inside thecylinder. Coupling that capability withflow modeling, thermal chemistry, andadvanced electronic controls, we can con-

trol a combustion event at each angle de-gree of the crank turn.

From a holistic point of view, it is possi-ble to squeeze an additional 10–20% effi-ciency out of the gasoline engine, today’sconventional powertrain. As an example,we were able to provide our new fleet oflight-duty trucks with “active fuel man-agement.” Since highway driving requiresonly about one-half of the engine cylin-ders, we have learned how to turn half ofthem off once the truck hits the highway,reducing the throttling losses.

Technologies like this start to attack the efficiency equation. Of course, withinternal-combustion engines, there is al-ways a certain amount of efficiency lossbecause of cold starting and because theengines are usually operating in transient,versus steady-state, mode.

Introducing HybridizationThe next step in improving engine effi-

ciency is to examine other energy losses inthe propulsion system, in particular, thelosses at idle and in kinetic energy. ForGM, the current response is to introducehybridization into our fleet.

First, hybrid technology allows shuttingoff the engine when the vehicle is not mov-ing and running the accessories off thebattery. The second major advantage ofhybrid technology is the recapture of ki-netic energy. Historically, the kinetic energyof a 4000-pound vehicle moving down theroad has been turned into heat in thebrakes. Hybridization allows that energyto be recouped through regenerative brak-ing, which involves converting the vehicle’skinetic energy during deceleration intostored electrical energy.

With improvements in conventionalpowertrains—that is, gasoline and dieselengines—as well as hybridization, we willbe able to improve the fuel efficiency ofour fleet by as much as 30–35%.

To take advantage of these efficiency im-provements, GM has an aggressive planfor rolling out its own hybrids. We havechosen to put the hybrid powertrains onthe most fuel-consuming vehicles—ourlarge trucks and SUVs.

In fact, we introduced our first hybridsystem in 2003 for transit buses after ourAllison transmission business came upwith a new hybrid transmission architec-ture called a “two-mode.” The first modeis used for launching the vehicle after astop and driving at low speeds, whenmore power is needed; the second mode isused for cruising at highway speeds, whenless power is required. A bus, with its nu-merous stops and waits, is the perfect ap-plication for hybrid technology, becausehybridization stops fuel loss when the

Figure 1. Relationship of vehicle sales to per capita income.Vehicle ownership correlatesalmost directly with rising per capita incomes. As a result, increasing affluence in both thedeveloped and developing countries is expected to drive substantial increases in vehiclesales in the future.

Figure 2. World population and theglobal vehicle parc.Vehicle ownership isa universal, but largely unmet, aspiration.Today, only about 12% of the world’spopulation owns a vehicle. By 2020,with 15% of 7.5 billion people projectedto own an automobile, the global vehicleparc could surpass 1 billion vehicles.Source: U.S. Census BureauInternational Population Database, GM Global Market & Industry Analysis.



vehicle is idling and recaptures kinetic en-ergy through regenerative braking. Hy-brid technology is resulting in a 25–50%improvement in fuel economy, dependingon driving conditions.

In 2007, we will begin offering a newhybrid powertrain intended for use in ourmid-sized SUVs and sedans. We also aredownsizing the two-mode from our bussystem and plan to roll out this new sys-tem on our full-sized trucks in 2008.

Reducing costs in hybrid vehicles is stilldifficult to achieve, however, because it in-volves carrying essentially two systems:an internal-combustion engine and anelectric drive system. Even though bothsystems are downsized, it is difficult torun them in combination at equivalentcost to a conventional gasoline engine. Webelieve that the fully electric vehicle, pow-ered by the fuel cell, will enable that.

Moving Toward Full ElectrificationGM’s foray into electric propulsion took

place in 1996, when we commercialized afully electric vehicle, the EV1. The first testmarkets were California and Arizona, andwe leased about a thousand of our electricvehicles to customers in these states. Thiswas a big technology gamble, and in theend the marketplace rejected it.

Some in the automotive business be-lieve that the ultimate lack of success withEV1 resulted from the limitations of bat-tery technology. GM had counted on abreakthrough in battery energy density,that is, the number of kilojoules that canbe stored in the battery as a function of itssize and weight. Although most peopleactually drive less than 100 miles in a day,the marketplace saw the limitations of a

100-mile range as a flaw. The lack of acharging infrastructure was also an issue.

Now, ten years later, we may be on thethreshold of that battery breakthrough. In-dications from some research areas showthat lithium-ion battery technology mayhave achieved not only some cost break-throughs, but also (and more importantly)a fast recharge rate and good cold-weatherperformance. Supercapacitors also havegreat potential and could represent a para-digm shift for our hybrid-electric vehicleadvancements.

Hydrogen-Powered Fuel CellsWhile GM’s first electric car failed to ig-

nite the market, the company did not backoff from its goal of achieving full vehicleelectrification. Instead, when we could notacquire enough energy density in the bat-tery, we sought an alternative technologyin the hydrogen-powered fuel cell. The goalwas to use gaseous hydrogen to achievethe required energy density in a fuel cell.The vehicle would still be fully electric butwould operate in a different way to get ca-pacity and energy in range.

Fuel cells operate by a process that iselectrolysis in reverse—getting hydrogenand oxygen to combine to generate elec-tricity (Figure 4). The proton exchangemembrane (PEM) fuel cell preferred forautomobile applications consists of a hy-drogen fuel anode, an oxygen cathode,and a membrane made from a specializedpolymer–electrolyte material. At the anode,hydrogen molecules split into protons andelectrons. The electrons that are generatedcan perform electrical work as they passthrough a circuit to the cathode. The pro-tons, meanwhile, migrate through the

membrane to the cathode, where they arereunited with the electrons and then com-bine with oxygen to create water. The onlyother byproduct is heat. In a vehicle, mul-tiple fuel cells are connected in series tocreate a fuel cell stack capable of providingthe electricity required to power the vehicle.The electricity propels the electric motor,which turns the vehicle wheels. Whenfueled by pure hydrogen, a fuel cell car isa zero-emission vehicle, because it pro-duces no exhaust emissions or greenhousegases. This seemingly simple technicalbreakthrough is, like every breakthrough,materials-enabled. I work in what is basi-cally a mechanical–electrical engineeringcompany and I need to keep remindingmy co-workers that the world is made ofmaterials.

In working toward our vision of ahydrogen-powered fuel cell, we faced sev-eral challenges. The first was packaging thefuel cell in a conventional vehicle. The fuelcell had to be designed so that the propul-sion system would not end up taking allthe cargo and passenger space. Because ofthe nature of our product, system engi-neering requirements mandate achievinga certain energy density and a certainweight density to produce the 75 kWneeded to propel the vehicle. Not onlyhave we demonstrated that principle, wehave also exceeded that target. We haveshown the possibility of packaging anddesigning a fuel-cell-powered vehicle withnumerous advantages over a conventionalpowertrain-driven vehicle. We have de-veloped fuel tanks for storing liquid andgaseous hydrogen. And we have designedvehicle systems to be operated electroni-

Figure 3. Energy distribution for a typical mid-sized vehicle. Each number represents theenergy units used in an urban test cycle (city driving). Out of 100% of the fuel’s energyinput, only about 13% reaches the vehicle wheels. Essentially, every subsystem andcomponent on the car has to get lighter and better.

Figure 4.The proton exchangemembrane (PEM) fuel cell preferred forautomobile applications consists of ahydrogen fuel anode, an oxygencathode, and a membrane made from aspecialized polymer–electrolyte mate-rial. Green dots are hydrogen, blue areoxygen, and red are electrons.



cally—or, as we say in the industry, “bywire.” Many of the constraints inherent inmechanical systems, with all of theirdriveline connections, are eliminated.

Our efforts to package our fuel cellpropulsion system into a fairly conven-tional vehicle resulted in the HydroGen3(see Figure 5). The HydroGen3 is a con-verted Opel Zafira minivan from whichthe internal-combustion engine and fueltank were removed and replaced with afuel cell propulsion system and either acompressed hydrogen tank or a cryogenicliquid hydrogen storage system.

In addition to the HydroGen3, we havealso created a revolutionary vehicle designthat we call the “reinvented” automobile.Our AUTOnomy vehicle, which debutedin January 2002, was the first to be designedaround a fuel cell system and by-wire con-trols. We followed it with the Hy-wire ve-hicle, introduced in September 2003, and,most recently, the Sequel concept car, whichdebuted in January 2005 (see Figure 5).The Sequel is the first fuel cell vehicle cap-able of being driven 300 miles betweenfill-ups, and this range is for a five-passenger SUV.

Once we reduced the fuel cell to a man-ageable size and weight, we faced addi-tional challenges. First, we needed toassure the durability of the fuel cell. Be-cause of the way a fuel cell is structured, asingle pinhole in the membrane can dis-able it. Second, because our industry is op-erating in a competitive environment, ourtarget is to develop a fuel cell propulsionsystem at the same $50/kW cost associ-

ated with today’s conventional internal-combustion engines.

Fuel Cell Development ChallengesIn addressing the fuel cell durability

and cost issues, we are looking at threemajor areas:

Our first area of concern is catalyst ma-terials. We need to find ways, just as wedid for the engine catalytic converter, toreduce platinum catalyst loading for thefuel cell. In addition, we need to improvethe support system for the catalyst itself,particularly for corrosion problems.

The membrane is the second area weneed to address. Because fluorinated mem-branes are costly, we are searching for adifferent material system that will allowus not only to control the cost and struc-tural performance of the membrane, butalso to allow the membrane to work athigher temperatures where we can gainmore efficiency, particularly at heat extrac-tion and at lower humidities.

One of the largest system challengesposed by the fuel cell stack today is con-trolling humidification. Current mem-branes lose function at low humiditybecause protons are carried by water. Tothe extent that we can get a membraneand catalyst system that will work atlower humidities, we will change both theeconomics and the system engineering ofthe fuel cell itself.

Diffusion media, the third area of thefuel cell stack that we are developing, controls much of the flow and mechanicalperformance of the stack. A solution would

be an optimized diffusion medium, realized through top-notch research relative to hydrophilic and hydrophobiccoatings.

Hydrogen Storage ChallengesAnother problem that arises in adapting

fuel cells for vehicles is hydrogen storage.This area, more than any other, needs tocapture the attention of the world’s mate-rials community. Ironically, when I was ingraduate school, hydrogen storage activi-ties were very prominent, driven to a greatextent by the space program. Today, thisresearch area is re-emerging, and it pres-ents a major opportunity for scientists be-cause hydrogen storage is the potentialAchilles’ heel for our fuel cell strategy.

Right now, we are pursuing four op-tions for solving the hydrogen storageproblem. Each area has its challenges, andall of them are materials-based.

First, we are looking at compressed gas,which is the default storage medium today.Compressed gas packages hydrogen effi-ciently but is too costly because it involveshigh-strength carbon fiber in the compositetank. For 20 years, GM has been waiting fora breakthrough that would lower carbonfiber costs, which could completely changethe research parameters not just for fuelcells but for automotive bodies as well.

An alternative is to use liquid hydrogenstorage. We have been able to show that itpackages well and we have built vehiclesthat run on it. Of the various options, itprobably constitutes the best financialsolution. The drawbacks associated withliquid hydrogen storage are based on fun-damental physics and thermodynamics.We do not know how to take advantage ofthe energy we use to liquefy the hydrogenonce that hydrogen is in the fuel tank.About half of the efficiency we get fromthe fuel cell stack, which is by definitiontwice as efficient as the best internal-combustion engine, is lost in liquefyingthe hydrogen. To counteract that, we aredeveloping a hybrid approach that we callcryopressure, which is a combination ofliquid storage and compressed storage.

The best solution ultimately may lie infinding a solid-state material for hydrogenstorage. Recently, a number of materialssystems have been discovered that areincreasing, by a factor of two, the amountof hydrogen storage density over existingsolid-state storage materials. A break-through has already been achieved in thatwe now have materials with close to theright storage density. The conundrum weface is that we cannot release and chargethose materials quickly enough. In addi-tion, the materials systems that have goodthermokinetics have poor thermodynamics.Figure 5. GM’s fuel cell vehicles.



Finding a breakthrough class of mate-rials that circumvents these problems maybe just a matter of time. Given today’s im-pressive breakthroughs in combinatorialexperimental techniques, the world’s re-search infrastructure has the capability toaccomplish this fairly quickly. In the “goodold days,” the ability to successfully ana-lyze 10 alloys in a year meant that aresearcher was doing productive break-through work. Today, our researchers cansputter-deposit an entire phase diagramfor a ternary alloy and perform sub-millimeter site characterization in a week.Right now, they are limited not by theexperiment, but by their data analysistechniques and the quantum mechanicsthat guide the selection. Based on theseadvances, the materials community isnow able to develop the kinds of materialsthat will solve our energy storage mediaproblems.

Advanced MaterialsSo far, this discussion has centered on

the materials challenges associated withengine efficiency—how fuel economy canbe achieved through hybridization or byfully electrifying the vehicle. Now I wouldlike to discuss what impact the weight ofthe vehicle has on fuel economy, and whatmaterials challenges are posed by weight.

For every 10% reduction in vehicle mass,fuel economy is improved by 6%, which il-lustrates the significant leverage of vehicleweight. Over the past 30 years, the indus-try has reduced the weight of its vehicles byabout 30%. That weight reduction camefrom smarter design and materials substi-tutions. Currently, the improvements fromgood mechanical engineering design arecontinuing, while the advantages to begained from materials substitutions havejust begun to gather momentum. A largerange of materials is now being developedthat will significantly change the nature ofmaterials usage in vehicles.

Steel versus Lighter-WeightMaterials

Since 1920, the composition of vehicleshas been three-quarters low-carbon steel.Except for the substitution of plastic forwood, this basic materials distribution ofvehicles remained the same until 1975,when the entire equation changed. Today,high-strength steel represents about one-third of the steel on the vehicle (Figure 6).According to GM’s agenda, in five to sevenyears, high-strength steel will represent80% of the steel on the vehicle. Metallurgistswill recognize the challenges inherent inthat goal, including the fact that high-strength steel is stronger and more diffi-cult to form, heat-treat, repair, and weld.

AluminumToday, other lighter-weight materials, in

particular, aluminum, magnesium, andhigh-strength plastics, are increasinglyreplacing steel in cars. GM is the most ag-gressive user of aluminum and magne-sium in the industry, measured by thenumber of pounds of these materials wehave on each vehicle. We use these mate-rials because they provide better perform-ance for the cost in terms of fuel economy.Many of our closures—for example,hoods—are now made from aluminum.

This use of aluminum has posed diffi-culties. Aluminum conducts heat moreeasily than steel, but it also has lower elec-trical resistivity and thus requires a lot morecurrent for welding. For example, whenwe started the changeover to aluminum inthe early 1990s, had we decided to convertjust half of our plants from steel to alu-minum, we would have had to change theelectric capacity of the plants to accom-plish it. We therefore developed alterna-tive joining approaches. Indeed, we havelearned how to weld, form, and paint alu-minum, and we have learned about itscorrosion and durability characteristics.

Aluminum in general has lower ductil-ity and therefore lower formability thansteel. The black dots in Figure 7a representthe simulated major and minor strainsthat occur in various parts of the sheetwhen it is formed (in this case, we are look-ing at an inner panel of the lift gate for oneof our Malibu MAXX cars; see Figure 7b).We faced the issue that some parts thatcould be made in steel could not be madein aluminum. On the other hand, someautomotive parts were so difficult to formthat they could not be fabricated even insteel. Sometimes the only solution was to

break the part into two pieces, a move thatdispleased our designers.

Quick Plastic-Forming of AluminumTo find a viable parts-fabrication method

that would not destroy the integrity of thedesign, we sought help from the aerospaceindustry. We borrowed a technique calledsuperplastic forming, which lends itselfwell to manufacturing a small number ofparts, for example, 50–100 fuselages a year.At GM, we tend not to think about anythingbelow 10,000 units a year, and we preferruns of about 100,000 units. We discovered,however, that without going into the fullsuperplastic regime, we could make partsusing some conventional aluminum alloysthat did not need high-cost processing. Weidentified a “quick plastic-forming range”(QPF range) that now allows us to formparts in aluminum that cannot be formedin steel.

We went into QPF production quietlyfive years ago, and then announced it twoyears ago when we started using it to formparts on the Malibu, one of our highest-volume cars. QPF allows us to make a liftgate in a single piece, in aluminum, with asignificant weight savings compared withmaking the part from two pieces of steel.More importantly, the QPF technique pro-vides an intersection of art and science thatworks well from a technology standpointand can produce an “edgy” look that sat-isfies our designers. A good example is thetrunk lid on our Cadillac STS (Figure 8).With QPF, we can fabricate the trunk lid ina single piece without sacrificing the clean,sharp edge. QPF is the kind of technologi-cal breakthrough we need to build on sothat we can apply it to other parts of thevehicle.

Figure 6.The use of lighter-weight materials in a typical automobile has doubled between1977 (left) and today (right).The “other” category includes glass, rubber, and ceramic materials.



Magnesium CastingsI mentioned earlier that GM is one of

the most aggressive users of magnesiumin the automotive industry. In 2004, weproduced more than two million units inthe form of magnesium instrument panels.Like aluminum, magnesium posed prob-lems that we were able to solve. As a resultof another technological breakthrough,we learned how to make the largest mag-nesium castings in the world, producinginstrument panels 5 feet long, 4 mm thick,and weighing 27 pounds. Because our pan-els are covered by plastic, you can’t seethat they are composed of an integratedsingle casting of magnesium, which ulti-

mately yields higher performance at alower weight with better packaging.

Thermoplastic OlefinOne class of materials whose use is ac-

celerating for automotive applications isthermoplastic olefin (TPO). GM is usingTPO in increasing amounts because it en-ables us to differentiate the styling of thefascia we put on external parts of our ve-hicles, and to do it with a low-cost invest-ment. Like other lighter-weight materials,TPO poses challenges, in terms of proc-essing quality, cost, and strength.

GM has found a way to use nanocom-posites to overcome these problems. For the

past five years, we have been the largestuser of nanomaterials in the world (Fig-ure 9). Our technology is based on takinga naturally occurring smectite clay andchemically treating it so that it actually ex-foliates down to single molecular sheets.We learned how to process the clay with-out agglomerating the sheets, which meansthat we now have a reinforcement that isat the nanometer scale.

TPO nanocomposites constitute anothercase of science lagging behind engineer-ing. We were able to make these materialswork quickly by creating partnerships withseveral suppliers—a molder, a resin sup-plier, and a particulate supplier.

Figure 7. (a) Strain data from (b) the inner panel of the lift gate for the Malibu MAXX. Data on the graph in (a) demonstrate that a conventionallystamped steel or aluminum sheet could not have been used to produce the inner panel design because of the strains, represented by the blackdots, that would occur in fabrication; the part could only be stamped using GM’s quick plastic-forming (QPF) aluminum process.

Figure 8. Quick plastic-forming (QPF) technology provides an intersection of art and science that can produce an “edgy” look that satisfies GM’sdesigners. A good example is the trunk lid on the Cadillac STS. With QPF, the trunk lid can be fabricated in a single piece without sacrificing theclean, sharp edge.



Even today, however, we still do not fullyunderstand why our nanomaterials workso well. We do know that one of the resultsis anomalous strengthening—the modulusis greater than what we expect from calcu-lations using current theories. In addition,we are achieving lower weight, lower costs,and higher quality, with a larger processingwindow.

At this point, some high-quality researchis needed to tell us why we are gettinganomalous strengthening. We could usethat information to guide some materialssubstitutions and to help us tailor theinterfaces so we can reduce costs evenfurther. The anomalous strengthening ofnanometer-sized particulate for structuralapplications is just one more automotivematerials area that is ripe for development.

Although we utilize lighter-weight ma-terials in many of our vehicles, our mate-rials flagship vehicle is the ChevroletCorvette. It contains multiple aluminumand magnesium parts, including hydro-formed aluminum frame rails and roof bow,magnesium roof frame and engine cradle,carbon-fiber floor pan, and titanium valvesand connecting rods. We have even usedbalsa wood in a Corvette floor, in the Z05model.

Smart MaterialsThe real paradigm-changer for our in-

dustry, outside of the propulsion system,

is the introduction of smart materials. Thesematerials have historically been the domainof the aerospace industry, where typicallyone can spend $100 per pound for certainparts, or $1000 per pound on a satellite.

When it comes to vehicles, however,one is able to spend only about $1.50 perpound. Fortunately for the automotive industry, certain smart materials applica-tions are approaching volume productionat costs that we can afford.

We have accomplished that by inte-grating smart materials with certainmechanical–electrical solutions. Considerthe concept of mechatronics, where me-chanical and electrical engineers combinetheir areas of expertise to devise new typesof solutions. An example of that would beGeneral Motors’ variable valve timingengine technology. We have taken thisidea a step further with a solution that wecall “mechamatronics,” which integratesmechatronics with smart materials.

One of the primary results of this smartmaterials research will be an explosion ofopportunities—the development of dif-ferent materials systems that can give usactuation not by motors or gears, but byheat, magnetic field, or electricity. Whenwe can change the shape of something withheat, magnetic field, or current, we canchange the way we do our fundamentaldesigns.

We have already commercialized two ofthe applications to come out of this smartmaterials research. The first application is magnetorheological fluid (MRF) (Fig-ure 10). Basically, we developed a way totake iron particles, put them into suspen-sion, build magnetic yokes around them,and then change the viscosity by orders of

Figure 9. GM nanocomposite applications.The image at upper left is a transmissionelectron micrograph of smectite clay filler dispersed in thermoplastic olefin; the schematicbeside it shows the atomic structure of smectite clay (blue � sodium ions, red � oxygenatoms, gold � silicon atoms, magenta � aluminum atoms, and white � hydrogen atoms).SUT stands for “sport utility truck.”

Figure 10. GM mechamatronic application to shock absorbers: magnetorheological fluid(MRF). MRF is a suspension of fine magnetizable particles in a synthetic oil. (a) In the offstate, MRF is a random dispersion of magnetizable particles exhibiting Newtonianrheological behavior (shear stress � viscosity � shear rate). (b) In the on state, the appliedmagnetic field aligns the metal particles into fibrous structures, and the MRF rheologychanges from Newtonian to Bingham plastic (shear stress � yield stress � viscosity �shear rate).The yield stress is controlled by the applied magnetic field. P is pressure.



magnitude by turning the magnetic fieldon and off. As a result, we can replace asingle-state hydraulic system with an ad-vanced system that allows us to makereal-time changes in the damping charac-teristics of clutches and shock absorbersby the application of a magnetic field.

We have applied this concept to ourtruck fan clutch as a way to achieve fueleconomy. We are also proud of the way weused magnetorheological fluid in ourshock absorbers (Figure 10). In GM’s Mag-netic Selective Ride Control system, MRFis used as a working medium within afluid-based shock absorber. By controllingthe current to an electromagnetic coil in-side the piston of the shock, the MRF al-lows for any damping state between thelow forces of “off” and the high forces of“on.” The result is continuously variablereal-time damping for enhanced vehicleride and handling performance. This tech-nology allows us to make real-time adjust-ments to the viscosity of the shock absorbermaterial. Vehicles with these shock ab-sorbers offer a smoother ride than thosewith conventional shocks. Improved dy-namic damping can also help maintaincorrect vehicle ride height in preparationfor collisions and thereby help reduce therisk of under-ride, where a vehicle slidespartially or completely under a higher ve-hicle in a crash. These examples representthe introduction of mechamatronic systemsinto our vehicles.

ConclusionThe issues I have discussed, from

sustainability to safety to lower costs, are

the ones driving the agendas for automo-tive technologies. There is a role for thematerials community in each of theseagendas.

The automotive industry is, after all, nolonger built around bending steel. We needto have the best minds working on the latestsolutions to reach our goals of improvingfuel economy and reducing emissions. Theautomotive field represents a major areaof opportunity for materials researchers, aconcept I have been promoting for morethan 20 years. This particular MRS meet-ing, with about one-third of its sessionsrelevant to our industry, has borne thatout. I hope that all of you will take advan-tage of this opportunity and help us de-velop the next generation of automotivematerials.

Alan I. Taub isexecutive director ofGeneral Motors Researchand Development inWarren, Mich., where heis responsible for GM’sseven science laboratoriesin Michigan and India.These laboratories focuson a wide range of

technologies, including advanced powertrainsystems, computer-based design and analysissystems for vehicle engineering, electronicsand information-based vehicle systems, newmaterials and fabrication processes, moreenvironmentally friendly fuels and lubricants,and more efficient emission control systems.Taub was named to his current position in2004.

Before joining GM in 2001, Taub workedfor Ford Motor Company. In his tenure withFord, he managed the materials sciencedepartment, where he was responsible foradvanced automotive body, chassis, andpowertrain materials. He later managedNorth American vehicle crash safety for Fordand vehicle engineering for the Lincoln brand.Taub joined Ford from General Electric, wherehe had worked for nearly 15 years in researchand development and ultimately managedGE’s materials properties and processeslaboratory.

Taub was elected to membership in theNational Academy of Engineering in 2006.He holds a BS degree in materials engineeringfrom Brown University and master’s andPhD degrees in applied physics from HarvardUniversity. He was a member of the USCARAutomotive Composites Consortium(1993–1997) and served on the MaterialsTechnical Team for the Partnership for a NewGeneration of Vehicles (1995–1997). He hasbeen an active member of MRS and serves onthe advisory boards of several institutions,including Harvard, Brown, theMassachusetts Institute of Technology,Northwestern University, and the NationalScience Foundation. He holds 26 patents andhas authored more than 60 papers.

Taub can be reached at General MotorsR&D Center, MC480-106-EX1, 30500Mound Rd., Warren, MI 48090-9055, USA;tel. 586-986-6347, fax 586-986-8312, and e-mail [email protected].

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