Modeling the effect of oxidation on fatigue life of carbon fiber-reinforced ceramic-matrix composites at elevated temperature

An analytical method has been developed to investigate the effect of oxidation on fatigue life of fiber-reinforced ceramic-matrix composites (CMCs) at elevated temperature under air. The Budiansky-Hutchinson-Evans shear-lag model was used to describe the micro-stress field of the damaged composite considering fibers failure. The statistical matrix multicracking model and fracture mechanics interface debonding criterion were used to determine the matrix crack spacing and interface debonded length. The interface shear stress and fiber strength degradation model and oxidation region propagation model have been adopted to analyze the fatigue and oxidation effects on fatigue life of the composite, which is controlled by interface frictional slip and diffusion of oxygen gas through matrix multicrackings. Under fatigue loading, the fibers failure probabilities were determined by combining the oxidation model, interface wear model and fiber statistical failure model based on the assumption that the fiber strength is subjected to two-parameter Weibull distribution and the loads carried by broken and intact fibers satisfy the global load sharing criterion. The fatigue life S-N curves of unidirectional, cross-ply and 2.5D C/SiC composites at 800 °C under air have been predicted.