Characterisation of strain localisation and crack evolution of Cf/SiC-SiC composites by SEM-DIC method

In thermo-mechanical-oxidative coupling service environments, stress-induced microscale damage in ceramic matrix composites (CMCs) governs diffusion kinetics of oxidising media, accelerating degradation of mechanical properties. Therefore, the quantification of microscale damage is a core issue in revealing damage mechanisms. In this study, a low-cost, highly uniform submicron speckle pattern was prepared on the surface of silicon carbide-coated carbon fibre-reinforced silicon carbide matrix (C_f/SiC-SiC) composites and the strain localisation and crack evolution were accurately characterised using scanning electron microscopy combined with digital image correlation. For the first time, this study completely tracked and quantified the dynamic damage evolution process of C_f/SiC-SiC composites at the microscale, including key mechanisms such as strain localisation, interfacial debonding, matrix cracking, fibre slip, and macroscopic failure, further verifying the key contribution of interfacial slip to composite toughening. The experimental results revealed the interaction dynamics of the multicrack system. Further research found that the initial crack widths of the SiC coating follow a log-normal distribution, while the evolution of crack density under tensile load exhibits a strain threshold effect. The crack opening displacement (COD) of the coating has a ‘stress memory’ effect. These findings contribute to deeper understanding of the synergistic effect of stress and oxidation and provide a new perspective for studying the microscale and mesoscale damage behaviour of CMCs.