Abstract: Carbon fiber reinforced silicon carbide matrix composites (C/SiC) have emerged as key materials for thermal protection systems owing to their high strength-to-weight ratio, high-temperature durability, resistance to oxidation, and outstanding reliability. However, manufacturing defects deteriorate the mechanical response of these composites under extreme thermal-force coupling conditions, prompting significant research attention. This study demonstrates a customized in situ loading device compatible with synchrotron radiation facilities, enabling high spatial and temporal resolution recording of internal material damage evolution and failure behavior under thermal-force coupling conditions. Infrared thermal radiation units in a confocal configuration were used to create ultra-high-temperature environments, offering advantages of compactness, rapid heating, and versatility. In situ tensile tests were conducted on C/SiC samples in a nitrogen atmosphere at both room temperature and 1200 °C. The high-resolution image data demonstrate various failure phenomena, such as matrix cracking and pore linkage. Image-based finite element simulations indicate that the temperature-dependent variation of the failure mechanism is attributable to thermal residual stresses and defect-induced stress concentrations. This work seamlessly integrates extreme mechanical testing methods with in situ observation techniques, providing a comprehensive solution for accurately quantifying crack initiation, pore connection, and failure behavior of C/SiC composites.

Key words: Ceramic matrix composites, Extreme environments, X-ray computed tomography, Internal damage evolution, Image-based finite element method