2 - Introduction to Carbon Composites

Abstract

Continuous carbon fibers are dominant among reinforcements used for high-performance composite materials, particularly polymer-matrix composites, which are attractive for aircraft, satellites, automobile, and sporting goods, due to their combination of low density, high strength, and high elastic modulus. The fibers are also attractive for their low thermal expansion coefficient, thermal stability, and chemical resistance. For high-temperature applications (such as aircraft brakes and reentry space vehicles), carbon fibers are used in carbon-matrix composites, which are known as carbon–carbon composites. The small diameter of carbon nanofibers and nanotubes results in a large area of the interface between reinforcement and matrix in a composite, and this interface is a weak link in relation to both mechanical properties and electrical conduction. On the other hand, the large surface area is attractive for applications in electrochemical electrodes and electromagnetic interference shielding. Carbon fiber/nanofiber/nanotube assemblies in the absence of a matrix material are mainly in the form of mats (also known as papers and films) and yarns. With the CNTs well-aligned in a mat or yarn, high values of the tensile strength, modulus, and ductility are obtained, with the strength and modulus values being comparable to those of continuous carbon fibers and the ductility being greater than that of the continuous carbon fibers. However, the gage factor for tensile testing is lower for the CNT mat/yarn testing than the continuous carbon fiber testing, so that the validity of the tensile strength comparison is questionable. Twisting enhances the yarn properties. The processing, structure, properties, and applications of carbon fibers, carbon nanofibers, carbon nanotubes, and their assemblies and their composites are introduced.