High-temperature fracture toughness of C/C–ZrC–SiC composites

This study investigates the high-temperature fracture behavior of C/C–ZrC–SiC composites, focusing on the evolution of R-curve parameters, including initiation and steady-state fracture toughness. High-temperature compact tension (CT) experiments up to 1600 °C were conducted to obtain load–displacement responses at various temperatures, and initiation fracture toughness was obtained in accordance with ASTM E399. The steady-state fracture toughness was subsequently identified using a Bayesian optimization framework integrating a trilinear bridging law into the element-based peridynamic (EBPD) model. The results show initiation fracture toughness exhibits non-monotonic temperature dependence, increasing to a maximum at approximately 1000 °C before declining at higher temperatures. The steady-state fracture toughness decreases from room temperature (RT) to 800 °C, recovers between 800 °C and 1000 °C, and then rapidly deteriorates up to 1600 °C, exhibiting a transition from toughened fracture to brittle instability. Fractographic analyses reveal that fiber pullout and crack bridging dominate crack propagation at low and intermediate temperatures, significantly enhancing crack growth resistance. At elevated temperatures, particularly at 1600 °C, enhanced interfacial bonding and matrix evolution suppress fiber pullout, leading to rapid brittle crack propagation. These findings elucidate the distinct temperature sensitivities of initiation and steady-state fracture toughness to reveal high-temperature fracture behavior of C/C–ZrC–SiC composites.