Compressive strength and compressive failure mechanism of high-modulus carbon fibers from polyacrylonitrile and mesophase pitch

Abstract

Compressive strength of high-modulus carbon fibers from polyacrylonitrile (PAN) and mesophase pitch (MPP) was measured by single fiber compression tests. In addition, in-situ void structure analysis was conducted during the compression process to clarify the difference in compressive fracture behavior between the PAN- and MPP-based carbon fibers. The compressive strength tends to decrease with increasing the crystallites layer extent parallel to the fiber axis. In addition, compressive strength of MPP-based carbon fiber was significantly lower than that of PAN-based carbon fiber. The void structure of MPP-based carbon fiber began to change from the initial stage of compression, whereas that of PAN-based carbon fiber kept constant during the compression and was expected to deform just before failure. The existence of amorphous regions between crystallites may allow for stress homogenization in PAN-based carbon fibers, which results in relatively higher compressive strength than that of MPP-based carbon fibers.