In Situ Testing of C/C Composites under Thermal Ablation and Biaxial Tensile Coupling

Carbon/carbon composites serve as critical thermal protection materials in aerospace applications due to their exceptional high‐temperature mechanical properties. Conventional performance evaluations inadequately replicate the coupled thermo‐mechanical loading inherent to operational environments. Consequently, this study introduces a test system designed to simultaneously apply thermal ablation and biaxial tensile loading. Building on this, the study conducted biaxial tensile tests at 1500 °C ablation, revealing that the specimens’ tensile strength is 59.3 MPa. The damaged specimens are analyzed using in situ observation devices, which calculated the average linear and volumetric ablation rates of the C/C composites to be 0.0274 mm s −1 and 0.0288 g s −1 , respectively. Scanning electron microscopy shows grooves and oxides on the specimen surface, along with distinct features like matrix disappearance, exposed fiber tips, and sheath structures. Mechanistic analysis demonstrates that the synergistic effect of thermal–chemical ablation and biaxial stress accelerated interfacial degradation between fibers and matrix, leading to localized stress concentration and brittle fracture. The integrated methodology enables accurate performance assessment of thermal protection systems under realistic coupled‐field conditions.