Fatigue behavior of continuous fiber-reinforced ceramic-matrix composites (CFCCs) at room and elevated temperatures

Fabric orientation effects on the fatigue behavior of Nicalon*/Al₂O₃ and Nicalon/SiC composites were investigated by performing the mechanical tests at room temperature (RT) in air, and at 1,000 °C in an argon environment. It was observed that the flexural-fatigue behavior of the Nicalon/Al₂O₃ composite at ambient and elevated temperatures was significantly affected by the orientation of the loading direction to the fabric plies. Also, there was a significant reduction in the fatigue life of the Nicalon/Al₂O₃ composite at 1,000 °C, relative to that at RT. In contrast, the fatigue behavior of the Nicalon/SiC composite was not noticeably influenced by either the fabric orientation or the test temperature. The micromechanisms responsible for the differences in the fatigue behavior of the Nicalon/Al₂O₃ and Nicalon/SiC composites are elucidated in this paper.