A thermo-chemo-mechanical damage model for carbon/carbon composites under ablative conditions: application to short fiber reinforced microstructures

The ablation behavior and mechanical performance of carbon/carbon (C/C) composites are critical for the safe and reliable operation of thermal protection systems under extreme thermochemical environments. In this study, a coupled computational framework is proposed to characterize the degradation of C/C composites by linking carbon concentration–dependent damage with local stress evolution. The model incorporates thermochemical ablation theory and a wall energy balance equation to describe the coupling between thermal and chemical processes, while mechanical degradation is captured through a reaction–diffusion equation and stress–carbon concentration-dependent damage constitutive laws. A finite element implementation of the model is developed using the standard Galerkin method and a Newton–Raphson iterative scheme. A thermo-chemo-mechanical damage element (TCMDEL) subroutine is constructed to simulate the coupled failure process. The model is applied to short fiber reinforced C/C composites (C_sf/C), where a microscale model is used to investigate the effects of fiber volume fraction and arrangement on ablation resistance and residual mechanical properties. The results provide insight into the microstructural influence on coupled degradation mechanisms in C_sf/C composites under ablative conditions.