Carbon fiber is a polymer constructed from carbon, as the name suggests, and nitrogen, and arranged into crystals (as are all fibers.) Typically, through a repeated heating process, organic polymers such as polyacrylonitrile ("PAN") are converted into strips of aromatic rings of carbon and nitrogen. Repeated heating causes the strips to link together (expelling nitrogen gas) until fibers are formed of almost pure carbon in the form of graphite.

Due to the nature of its hexagonal carbon structure, carbon fiber is extremely strong while retaining flexibility. It is commonly woven into a cloth and used to build composite structures in a fashion similar to fiberglass, but it can also be used to make solid spars, tubes, and essentially any other formed shape.

Carbon fiber is extremely tough and special tools must be used to cut and shape it. It is stronger (though larger) per gram than steel and more resistant to deformation though its failure mode is more abrupt in that it tends to bend elastically to a point and then break sharply, where steel will work harden when pushed past its elastic limit.

Like other composites, the most common of which is fiberglass, carbon fiber cloth is commonly used to make monocoque structures in all sorts of industries including automotive, aerospace, and marine applications. Its light weight and ability to distribute force when utilized in this manner make it ideal for these purposes, but its inability to resist abrasion and side impact, plus the fact that carbon fiber composites cannot effectively be repaired, coupled with the impressive cost of the stuff means that their use is usually limited to high-performance products. The software used to model stress in carbon fiber is some of the most highly and jealously guarded software in existence.

Carbon fiber composites are typically made in a fashion similar to fiberglass in which a mold is coated with a mold release compound and then an epoxy, polyester, or vinyl ester resin, and the carbon fiber cloth is pressed into it to shape with rollers and squeegees. Successive layers are used where necessary to build up to the appropriate thickness and thus load-bearing capability, and the resulting structure is heat cured in an oven, though there are certainly air-cured epoxies used. Some epoxies can handle significant heat and carbon fiber has been used for heat shrouds, exhaust systems, and even engine blocks with steel sleeves for the cylinders. Carbon fiber cloth can be treated like just another layer of fiberglass (with particularly excellent load-bearing characteristics) and is often laid into a fiberglass part to add rigidity, especially in large pieces like hoods. Entire aircraft are being made of carbon fiber including kit-built. Carbon fiber costs about 15 times what fiberglass does, which is why more parts aren't made of 100% carbon fiber.

Carbon fiber is usually supplied as twine, ribbon, cloth sheets, solid rods, or tubes of assorted shapes, especially round or rectangular. The cloth sheets may come impregnated with a heat-cure epoxy in a form known as "pre-preg" carbon fiber which is often used for its attractive cosmetic properties, especially for small decorative automotive parts like gauge mounts.

References:

  1. Department of Polymer Science, Carbon Fiber. University of Southern Mississippi, 1996 (http://www.psrc.usm.edu/macrog/carfib.htm)

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