Longitudinal direct compression test of a single carbon fiber in a scanning electron microscope

Longitudinal direct compression testing of a single polyacrylonitrile-based carbon fiber (T800S) is performed with a piezo-actuated testing machine installed in a scanning electron microscope, and the longitudinal compressive behavior of a carbon fiber is observed during loading. The compressive stress–compressive strain relation is linear in the early phase, and then becomes non-linear. The longitudinal tangent modulus in the compression decreases with increasing compressive strain. The failure strain seen in compression is much higher than that in tension. The variability of the compressive strength is evaluated via Weibull analysis, and is found to be smaller than the tensile strength variability. The compressive fracture surface is irregular and possesses a serrated morphology that is different from the tensile fracture surface. The representative strength ratio of the compressive to tensile strengths of the carbon fiber is ≈0.5, which almost matches the compressive to tensile strengths ratio of the unidirectional carbon fiber reinforced plastic.