Damage evolution and resistance response of three-dimensional carbon fiber-reinforced silicon carbide under coupled creep-fatigue stress in different environments

Three-dimensional carbon fiber-reinforced silicon carbide (3D C/SiC) has attracted significant attention due to its excellent mechanical and thermal stability. This study investigates the microstructural evolution, performance degradation, and electrical resistance change of 3D C/SiC under fatigue, creep, and combined fatigue-creep stresses in argon, oxygen, and wet oxygen environments at 1300°C. The results show that under creep stress, a single dominant crack with a large width propagates continuously, accelerating oxidation at the interface and fibers, leading to a high damage rate concentrated around the crack. Meanwhile, the length and electrical resistance increase significantly in parallel. In contrast, under fatigue stress, multiple smaller cracks are evenly distributed, resulting in slower oxidation and a lower damage rate, and the resistance variation remains limited. Under combined fatigue-creep stress, multiple large cracks propagate without fully healing, which accelerates the oxidation at the interface and fibers, and also leads to the rapid rise of electrical resistance. In the wet oxygen environment, the oxidation of the pyrolytic carbon interphase is significantly accelerated, resulting in the highest observed damage rate. This study not only elucidated the damage mechanisms of 3D C/SiC under coupled stresses in different environments, but also indicates that the variation in electrical resistance is consistent with fiber and cross-sectional damage, suggesting that resistance change can serve as a responsive indicator of damage evolution in 3D C/SiC composites, thereby providing a feasible approach for real-time monitoring and damage assessment of the material.