Damage evolution of carbon fiber-reinforced ceramic-matrix composites with different fiber preforms using the fatigue hysteresis loop area

The damage evolution of C/SiC ceramic-matrix composites with different fiber preforms, that is, unidirectional, cross-ply and 2.5D woven, under cyclic fatigue loading at room and elevated temperatures in air and inert atmosphere has been investigated. The experimental fatigue hysteresis modulus and hysteresis loop area versus cycle numbers have been analyzed. The relationships between the fatigue hysteresis loop area, interface slip and interface shear stress have been established. The evolution of the fatigue hysteresis loop area and interface shear stress as a function of applied cycles has been analyzed for different peak stresses, fiber preforms and test conditions. For different fiber preforms and test conditions, the fatigue hysteresis loop area degrades the fastest for unidirectional C/SiC at 800? in air, and the slowest for 2.5D C/SiC at 600? in an inert atmosphere, due to the different degradation rates of interface shear stress.