LAUSR

Abstract In this paper, the fatigue damage development and lifetime of C/SiC and SiC/SiC ceramic-matrix composites (CMCs) under cyclic loading at an elevated temperature of 1300 °C in vacuum, in inert, in air and in steam atmospheres are investigated. The damage evolution versus applied cycles of C/SiC and SiC/SiC composites are analyzed through fatigue hysteresis-based damage parameters and fiber/matrix interface shear stress. The Global Load Sharing (GLS) criterion is used to determine the stress distribution between intact and broken fibers. The fibers failure probability of oxidized and unoxidized fibers in the oxidation region, fibers in the interface debonded region and interface bonded region are determined considering the damage mechanisms of interface wear, interface oxidation and fiber oxidation. The effects of fatigue peak stress, testing condition and fiber preforms on the damage evolution and lifetime are discussed. The fatigue life S–N curves and fatigue limit stresses of C/SiC and SiC/SiC composites at 1300 °C under different testing conditions are predicted. In the inert atmosphere, the fatigue limit stress is about 92% tensile strength for 3D C/SiC in vacuum atmosphere, 82% tensile strength for 2D C/SiC in argon atmosphere, 37% tensile strength for 2D SiC/SiC in N2 atmosphere, and 32% tensile strength for 2D SiC/SiC in argon atmosphere, the fatigue limit stress of C/SiC is much higher than that of SiC/SiC; however, in air and in steam atmospheres, the fatigue limit stress of SiC/SiC composite is higher than that of C/SiC.