Fracture strength model of C/SiC composites considering temperatures, oxidation times, applied stresses, and residual thermal stresses

C/SiC composites are widely used in the aerospace field, yet they suffer severe strength degradation when exposed to high-temperature stress oxidation environments. Under applied stress, needle-like oxidation occurs in the C/SiC composite, and existing strength models cannot accurately characterize the strength degradation considering the stress oxidation. In this work, a physics-based fracture strength model for C/SiC composites is developed, considering temperature, oxidation time, and applied stress. The contributions of the longitudinal and transverse fiber tow, matrix, and residual thermal stress on the fracture strength are included in the proposed model. Based on the oxidation experiments and residual strength tests conducted, oxidation kinetic models for the oxidation depth and equivalent oxidation length of the fiber tows are established, and the empirical formula for the strength degradation factor of the matrix is developed. The high accuracy of the model is verified by predicting the residual strength after various high-temperature stress oxidation. The influencing factors analysis is performed, regarding the evolution of fracture strength with temperature, oxidation time, applied stress, and porosity. This study provides a reliable theoretical model for predicting the residual strength of C/SiC composites under high-temperature stress oxidation environments, offering a theoretical basis for their reusability assessment.