Temperature dependent fatigue damage evolution of SiCf/SiC composites captured using in-situ X-ray imaging and strain analysis

Continuous SiCf/SiC composites are promising for high-temperature applications, but inherent structural defects compromise their mechanical performance under extreme conditions. This study investigates the fatigue damage mechanisms of SiCf/SiC composites at room temperature (RT) and 1200 degrees C using in-situ X-ray computed tomography (X-CT). A deep learning-based image enhancement and segmentation approach was employed to achieve fast and precise reconstruction of internal crack morphology. Additionally, the 3D deformation field under fatigue was monitored by digital volume correlation, revealing stress concentrations linked to crack propagation. Results show temperature-dependent fatigue and damage accumulation behaviour due to both initial defects and high-temperature induced compositional changes. At RT, damage occurs through multiple matrix cracking, bypassing bridging fibres and connecting with longitudinal cracks promoted by initial interfacial defects, leading to failure with a relatively flat fracture surface. At 1200 degrees C, fibre fractures tend to occur at early stages, and extensive fibre pull-out leads to a rough fracture surface. Notably, fibre-matrix debonding occurs along the PyC-SiCf interface at RT, while along the PyC-SiC coating interface at 1200 degrees C. Furthermore, decomposition of SiCxOy impurities at 1200 degrees C increases the crystallinity of beta-SiC, which further enhances hightemperature properties of the matrix.