Damage and Failure Analysis of Fiber-Reinforced Ceramic-Matrix Composites with Different Fiber Preforms Under Stochastic Fatigue Load Spectrum

Under cyclic fatigue loading, the stochastic stress occurs and affects the fatigue damage and failure of fiber-reinforced ceramic-matrix composites (CMCs). In this paper, combining the stress and cyclic-dependent fatigue damage mechanisms and models, the damage parameter of fiber’s breakage probability is adopted to characterize fatigue damage and failure in fiber-reinforced CMCs. Two stochastic load spectrums with increasing or decreasing stochastic stress level occurring at different applied cycle number are considered. Relationships between the composite’s fatigue life, stochastic load spectrum, fiber’s breakage probability, and fatigue life degradation rate are established. Experimental fatigue life of 1D unidirectional, 2D cross-ply, 2D plain-woven, 2.5D woven, and 3D braided C/SiC composites subjected to different stochastic load spectrums are predicted. The fatigue damage and failure of CMCs under stochastic load spectrum are affected by the fiber’s volume fraction along the loading direction (i.e., the high fiber’s volume fraction along the loading directional indicating the high resistance of fatigue damage and failure subjected to stochastic loading), the strength degradation caused by fabrication process (i.e., hot pressing, chemical vapor infiltration, etc.), and also the fiber’s preform. Among different fiber’s preforms, the fatigue life degradation rate is the highest for 2D cross-ply C/SiC composite and is the lowest for 2.5D woven C/SiC composite. The fatigue life degradation rate under stochastic load spectrum of increasing stochastic stress level is much higher than that under stochastic load spectrum with decreasing stochastic stress level except for 2D cross-ply C/SiC composite.