Interlaminar Shear Strength of C/C Composites at Elevated Temperature

Abstract

Interlaminar shear strength (ILSS) measurements were performed on two kinds of C/C composites (sample A and B) to study the effect of fiber orientation on the shear strength. Sample A (C/C-501, Ohwada Carbon Co.) is reinforced with plain-woven cloths (2D-C/C), and sample B (BN-M, Nippon Steel Chemical Co.) is reinforced with random chopped fibers. ILSS was measured at elevated temperatures by a double notched compression method. Sample A was found to be one half of sample B in value of ILSS at room temperature. The ILSS of both types of composites increased with increasing measurement temperature. The typical fractured surfaces of sample A tested at room temperature showed flat planes and the shear failure was caused by the delamination between CF cloths and matrices. As for sample B, the boundaries of the fiber preforms were not observed clearly, and the shear failure seemed to initiate not from the special portions but from the randomly distributed microcracks within the preforms. At high temperatures, the fractured surfaces of all samples were found to be rough. The results suggest that the values of ILSS measured at high temperatures became higher than those measured at room temperature because of release of the internal residual stress and closure of preexisting cracks.