Carbon fiber composite is a strong, light and very expensive material. Technically the term "carbon fiber" is used to refer to carbon filament thread, or to felt or woven cloth made from carbon filaments. The fiber-polymer composite made with carbon filament is more properly termed carbon fiber reinforced plastic (CFRP or CRP). It has many applications in aerospace and automotive fields, and notably in modern bicycles, where these qualities are of importance. It is becoming increasingly common in small consumer goods as well, such as laptops, tripods, and fishing rods.
Each carbon filament is made out of long, thin sheets of carbon similar to graphite. A common method of making carbon filaments is the oxidation and thermal pyrolysis of polyacrylonitrile (PAN), a polymer used in the creation of many synthetic materials. Like all polymers, polyacrylonitrile molecules are long chains, which are aligned in the process of drawing fibers. When heated in the correct fashion, these chains bond side-to-side, forming narrow graphene sheets which eventually merge to form a single, jelly roll-shaped filament. The result is usually 93-95% carbon. Lower-quality fiber can be manufactured using pitch or rayon as the precursor instead of the PAN.
These filaments are stranded into a thread. Carbon fiber thread is rated by the number of filaments per thread, in thousands. 3K (3,000 filament) carbon fiber is 3 times as strong as 1K carbon fiber, but is also 3 times as heavy. This thread can then be used to weave a carbon fiber cloth. The appearance of this cloth generally depends on the size of thread and the weave chosen. Carbon fiber is naturally a glossy black, but recently colored carbon fiber has become available.
The resulting cloth is usually made into carbon fiber reinforced plastic. One common plastic of this type is graphite epoxy, and materials produced with this methodology are generically referred to as composites. The material is produced by layering sheets of carbon fiber cloth into a mold in the shape of the final product. The alignment and weave of the cloth fibers is important for the strength of the resulting material. In professional applications all air is evacuated from the mold, however in applications where cost is more important than structural rigidity, this step is skipped. The mold is then filled with epoxy and is heated or air cured. The resulting stiff panel will not corrode in water and is very strong, especially for its weight. If the mold contains air, small air bubbles will be present in the material, reducing strength. For hobby or custom applications the cloth can instead be draped over a mold, and the epoxy is "painted" over it, however because of the resulting lack of strength, this is usually only used for cosmetic details.
The high amount of (often manual) work required to manufacture composites has hitherto limited their use in applications where a high number of complicated parts is required.
BMW has begun studying and creating methods of producing carbon fiber reinforced plastics in its Landshut plant. To make the roof of the BMW M3 CSL, 5 layers of carbon fiber cloth are placed in an 1,800 ton press, where epoxy is resin transfer molded and heat-cured in a robot-automated process. The resulting roof is half the weight of the equivalent steel roof.
The chemistry and manufacturing techniques for thermosetting plastics like epoxy are often poorly-suited to mass-production. One potentially cost-saving and performance-enhancing measure involves replacing the epoxy matrix with a thermoplastic material such as Nylon or polyketone . Boeing's entry in the Joint Strike Fighter competition included a Delta-shaped carbon fiber reinforced thermoplastic wing, but difficulties in fabrication of this part contributed to Lockheed Martin winning the competition.
Other materials can be used as the matrix for carbon fibers, as well. Due to the formation of metal carbides (i.e., water-soluble AlC) and corrosion considerations, carbon has seen limited success in metal matrix composite applications. Reinforced Carbon-Carbon (RCC) consists of carbon fiber-reinforced graphite, and is used structurally in high-temperature applications, such as the nose cone and leading edges of the space shuttle.
Carbon fiber cloth can also be used in air filtration.
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Last updated: 10-19-2005 05:50:32
