Carbon fiber (sometimes called graphite fiber) possesses both high fiber modulus (>33 to 120+ Msi), and high fiber strength (>200 to 1000+ Ksi). Carbon fiber can be made from a variety of organic or petroleum polymer fibers. Most commonly, it is made from either of two precursor materials: pitch or polyacrylonitrile (PAN). Most standard intermediate modulus fiber is made from PAN, while pitch is used for the production of high modulus fibers. The precursor material is spun into fibers and processed in three steps: oxidation, carbonization, and graphitization. This processing forms a turbostratic graphitic structure in which graphitic crystallites are aligned with the fiber axis and intermingled with each other. The processing of carbon fibers produces three types of fiber:
- •High Modulus fibers have marginal strength and marginal elongation to failure.
- •Intermediate Modulus/Intermediate Strength fibers have higher elongation to failure.
- •High Strength fibers have standard modulus and elongation to failure.