Exploring the anisotropic damage behaviour during the scratching process of SiCf/SiC composites

SiCf/SiC composites are ideally suited for demanding high-temperature applications, such as high thrust-weight ratio aeroengines, and accident-tolerant fuel claddings. However, their anisotropic damage behaviour causes the significant challenge in high-quality machining. To explore this difficulty, linear loading nanoindentation and scratch tests were conducted. The results indicated significant variations in mechanical property and damage resistance across different structural locations. The damage behaviour in fibre bundle region was observed to differ from matrix-rich region, depending on the fibre-related scratch direction phi. Except for phi = 0 degrees and 90 degrees, the two sides of scratch exhibited an asymmetric damage feature. At phi = 90 degrees, the largest lateral damage was observed. Fibre-matrix interface debonding was crucial, accompanied by complex force fluctuations. Based on beam bending theory and fracture mechanics, a microstructure-based model was developed to explain the mechanisms of debonding and fibre fracture at different fibre orientations, showed consistency with the evaluated results.