BMW is leading the way, with its innovative i3 runabout, showing that it is possible to build a compact city car using a high-tech material like carbon fibre without sending production costs through the roof. Admittedly the i3 is not a bargain-basement minicar. The extra-light, ultra-strong carbon fibre it employs has seldom found its way into regular production models. Widespread use of the material has so far been confined to Formula One or to exclusive sports cars. Experts believe that carbon fibre has a great future, although the quantity of the material used in a given car will depend on the model’s prestige or the need to save weight - in search of enhanced fuel economy. The carbon fibre used is Carbon Fibre Reinforced Plastic (CFRP). The material is heat-treated to provide a tough, high-impact-resistant surface. In the case of the i3, the use of carbon fibre offsets the weight of the car’s heavy battery pack. The manufacturer believes carbon fibre is the only material capable of satisfying enhanced vehicle safety requirements without incurring a weight penalty. Experts say CFRP is 20 per cent lighter than aluminium, a metal that has been at the core of competitor Audi’s weight-saving efforts for decades; it is half as heavy as steel. Other carbon fibre advantages are the ‘secondary effects’, as explained by Klaus Drechsler, a professor for carbon composites at Munich’s Technical University. “The lower mass of such a vehicle means that the brakes can be downsized, while smaller engines can still provide the same performance.” One carbon fibre disadvantage is that it is harder to repair than steel, which can be welded or panel-beaten - even if the result does not turn out to be completely factory-grade. While damaged carbon composites can be patched and re-bonded to eliminate dents, the process is expensive. That may be another reason why CFRPs have seen little use is mass-production vehicles. Drechsler expects that the cost of using carbon fibre will be halved in five years. The drop in overall production costs, including logistics aspects, is likely to amount to more than 90 per cent, says the specialist. BMW says it has already cut carbon fibre costs by half over the past five years. Until costs come down further, ‘mundane’ cars are likely to be made largely of steel. “We have to ensure that we can produce a marketable product,” said VW technology spokesman Harthmut Hoffmann. In order to shave off weight the company is testing high-tensile steels, which permit thinner panels to be pressed at higher temperatures. “This makes the components both lighter and stronger,” says Hoffmann. Safety requirements dictate that future cars will never be made entirely out of carbon fibre. “The B pillar of a car is supposed to deform in a crash,” says Eckstein. “So CFRP would not be suitable for making the pillar. On the other hand, making some other front vehicle sections out of carbon fibre makes sense, since CFRP absorbs more crash energy than steel
or aluminium.”
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