Axial compressive breaking strain of carbon fiber.

Abstract

Efforts were made to estimate the axial compressive breaking strain of PAN- and pitch-based carbon fibers by bending a rectangular epoxy beam in which a single carbon filament was embedded near the surface. The compressive breaking strain of carbon fibers increases gradually with increasing temperature in a temperature range from room temperature to about 60°C and it decreases with increasing temperature above 60°C. The low compressive breaking strain obtained at room temperature may be attributable to the high mold shrinkage. There is a linear relationship between the compressive breaking strain estimated by considering the mold shrinkage and radial compressing force owing to residual thermal stress in a temperature range from room temperature to 60°C. The true compressive breaking strain of carbonized fibers, determined by extrapolating the straight line to the radial compressive force is zero, is approximately 3 times that of graphitized fibers. The ratio of the compressive breaking strain to the tensile breaking strain is approximately 2-2.5 for carbonized fibers and 1.3 for graphitized fibers. The compressive breaking strain of fibers agrees roughly with that of unidirectional composites reinforced with the fibers.