Rate of strength decrease of fiber-reinforced ceramic-matrix composites during fatigue

An experimental investigation was performed to study the rate at which stre ngth-controlling fatigue damage evolves in a ceramic-matrix composite. Tens ile specimens of a unidirectional SiC-fiber-reinforced calcium aluminosilic ate matrix composite were cycled to failure or to a preselected number of c ycles under similar loading histories. The residual strength of the precycl ed specimens was found to be similar to that of virgin specimens. Microstru ctural investigations showed that the Fracture surfaces of the specimens cy cled to failure had a central region where fiber pullout was negligible. It is proposed that frictional heating (due to interfacial sliding) is the ca use of fatigue failure. High interfacial temperatures are assumed to cause the formation of a strong interface bond, leading to internal embrittlement .