Axial compressive fracture of carbon fibers

The axial compressive strength was measured on single-filaments of polyacrylonitrile and pitch-based carbon fibers. The compressive fracture mechanism of carbon fibers was investigated based on the crystallite and the microvoid structures characterized with X-ray scattering. The distribution of the compressive strength at a fixed fiber length, and the length dependence of the average compressive strength were much smaller than those of the tensile strength. The compressive strength is proposed to be limited by the buckling stress of individual carbon layers in the transversely unsupported regions of the crystallites, the length of the unsupported regions being determined by the axial length of the microvoids. This model represents the variation in the compressive strength of carbon fibers with different microstructures very well. (C) 1999 Elsevier Science Ltd. All rights reserved.