Pyrolysis-driven progressive microstructural degradation in carbon/phenolic needle-punched composites

Carbon fiber-reinforced needle-punched composites are widely used in thermal protection systems; however, the elucidation of the structural damage mechanism caused by their heterogeneous materials and nonlinear thermodynamic behavior under extreme conditions remains unclear. To reveal the failure mechanisms of materials in high-temperature environments, this study systematically investigates pyrolysis-driven progressive microstructural degradation in carbon/phenolic needle-punched composites. Oxidation-kerosene ablation experiments were conducted at various temperatures, with the residual bending mechanical properties of the materials assessed through three-point bending tests combined with digital image correlation techniques. To track microstructural evolution, we performed X-ray computed tomography and scanning electron microscopy on the needle-punched composites. Complementary to experimental characterization, we developed a microstructural model of the needle-punched composite and simulated its damage under thermo-mechanical coupled degradation using Abaqus user-defined subroutines (UMAT and UMATHT), thereby elucidating pyrolysis-driven microstructural evolution. The results indicate that the degradation of the composites’ mechanical properties due to ablation pyrolysis is primarily attributed to the alteration of microstructural morphology, including fiber fracture, crack propagation, pore coalescence, and cavity formation induced by pyrolytic oxidation.