Fracture of carbon fibers

Abstract

Carbon fibers are made from many different feedstocks, and the most important commercial fiber is made from polyacrylonitrile (PAN). PAN fibers are made by a variety of methods. This polymer is made by free-radical polymerization either in solution or in a solvent-water suspension. The polymer is then dried and re-dissolved in another solvent for spinning, either by wet-spinning or by dry-spinning. High-performance fibers are made from mesophase pitch, which is a discotic liquid crystalline material. While mesophase pitches can be made from many starting materials, there are only a few that are of commercial interest. These fibers are typically melt spun, and spinning technology is the same for all pitch types. Commercially useful fibers are made from mesophase pitch at heat-treatment temperatures of 1600 °C and above. The modulus of mesophase pitch fibers increases with an increase in heat-treatment temperatures, and modulus values close to the theoretical modulus of graphite (1 TPa) are possible. Most carbon fibers, even those with a modulus above 700 GPa, are mostly made of turbostratic carbon with small graphitic domains.