It's the automotive engineer's dream material. Light, stiff, strong, stable and conformable to virtually any shape, carbon fiber composites provide benefits not achievable with any other structural material. Yet, more than 40 years after commercialization, carbon fiber remains a niche product within the automotive industry. Until recently the widespread use of composites reinforced with carbon fiber has been constrained by two major factors - high prices and slow part production rates - confining its application to race cars and exotic supercars, where price takes a back seat to performance.
Following a trend similar to earlier aerospace and sporting goods markets, applications of carbon fiber in street-legal automobiles are starting to move from the highest priced products into more moderately priced ones. At each price level, the applications are dominated by sports cars, where customers have shown a willingness to pay for improved performance in terms of acceleration and top speed.
Engineers have only two ways to improve vehicle acceleration - increase horsepower or decrease mass. This results in a higher power-to-weight ratio, a key predictor of vehicle performance. While raising horsepower alone improves straight-line acceleration and top speed, lowering weight offers these benefits as well as improving handling characteristics (especially around curves). Less weight also reduces loads on the braking and suspension systems, permitting engineers to take additional weight out of these components.
Among mass-reducing materials, carbon fiber composites rank highly. As an anisotropic material, carbon's properties can be tailored in specific directions, which provides increased stiffness and strength along load paths. In a composite component, the part thickness can be easily increased, in localized high-stress areas - something very difficult to accomplish in the metal-stamping process. Designers can create long, flowing contours and achieve shapes not possible with sheet metal, slicing through wind resistance at the same time as being eye-catching. Optimally designed, the high stiffness-to-weight ratio of carbon fiber composites enables weight savings of 75 to 80 percent versus steel, 30 to 40 percent versus aluminum, and up to 50 percent versus fiberglass SMC. In addition, carbon fiber composites are durable - a fact supported by decades of use in military applications such as helicopters and jet fighters, where the material's infinite fatigue life is invaluable.
Now throw in the X-factor - or sex appeal of carbon fiber - and its associated "high-tech" reputation. Carbon fiber is associated with things that go really fast, like airplanes, rockets and championship racecars, making them a natural fit for production sports cars. Most carbon fiber automotive components produced today employ familiar aerospace and Formula 1 design techniques, and various forms of prepreg material. By early 2004, at least two dozen street legal sports cars with carbon fiber components will be in production. While it helps to be a millionaire to buy some of them, others, offered by the world's largest automakers, can be had for less stratospheric figures.