Multiscale investigation on fatigue properties and damage of a 3D braided SiC/SiC + PyC/SiC composites in the full stress range at 1300 °C

Monotonic tensile and fatigue tests of a SiC/SiC composites were conducted at 1300 °C in the full stress range. The macroscopic behaviors were studied based on the strain data. The mesoscopic morphology was observed by X-ray computed tomography, and the microanalysis was conducted using SEM, EDS and XRD. Besides, the interfacial debonding strength (IDS) were measured by nano-indenter. The results reveal that the fatigue behaviors can be divided into three zones. The inelastic strains accumulation and stiffness reduction can be observed in all three zones due to matrix cracking, interface damage, and failure of fibers. The fatigue life is long in the run-out zone because the maximum stress is lower than the proportional limit stress (PLS). In the stress-insensitive zone, the fracture depends on high-temperature and oxidation effects. The failure in the stress-sensitive zone is dominated by the fiber strength. The interface behaviors greatly affect the fatigue life above the PLS.