Homogenization-based analysis of pyrolysis and mechanical degradation of ablative silica fiber-reinforced phenolic resin composites

Silica fiber-reinforced phenolic resin composites (SiFPRCs), characterized by exceptional insulative properties and ablation resistance, are widely utilized in thermal protection systems (TPS) and structural materials for hypersonic vehicles. Under extreme thermal conditions, the physicochemical ablative processes, including severe local thermal conduction, decomposition, and structural failure, lead to complex variations in thermomechanical properties. This study developed a homogenization-based thermomechanical model to investigate the micro-ablation characteristics of SiFPRCs and the resultant overall mechanical degradation. The ablation rate and porosity evolution were experimentally analyzed firstly, through oxyacetylene ablation experiments and mechanical property tests coupled with high-precision CT technology. Within the framework of non-equilibrium dissipative thermodynamics, a cross-scale consistent thermomechanical model integrating heat conduction and pyrolysis reaction characteristics of SiFPRCs was developed and implemented through a nonlinear finite element algorithm. After calibration and validation through comparison with experimental results, the developed model was applied to examine multiple thermal dissipation mechanisms, including thermal decomposition of phenolic resin, heat blocking effects, phase transitions in silica fibers, carbo-silicon reactions, and mechanical degradation. This research provides robust theoretical support and a design foundation for the development and application of high-performance TPS materials.