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

Abstract

Single-fiber compression tests were conducted to measure the compressive strength of high-modulus carbon fibers produced from polyacrylonitrile (PAN) and mesophase pitch (MPP). The difference in the compressive fracture behaviors of PAN- and MPP-based carbon fibers was clarified by performing an in-situ void structure analysis during the compression process. The compressive strength decreased with an increase in the extent of the crystallite layers parallel to the fiber axis. In addition, the compressive strength of the MPP-based carbon fibers was significantly lower than that of the PAN-based carbon fibers. The void structure of the MPP-based carbon fibers began to change during the initial stage of compression, whereas that of the PAN-based carbon fibers remained constant during compression and was expected to deform only immediately before failure. Stress homogenization in PAN-based carbon fibers may be caused by the existence of amorphous regions between crystallites, which results in a higher compressive strength than that of MPP-based carbon fibers.