Prediction of mesoscopic volumetric ablation of 3D quartz-polysulfonamide charring composite in thermal protection systems enabled by geometric reconstruction

Low-density, charring composites for thermal protection systems exhibit multi-scale and multi-physics high-temperature responses due to complex mesoscopic structures. A quartz-polysulfonamide/phenolic (QPP) charring composite with organic and inorganic fiber interpenetrating network was proposed, which possesses both excellent ablative resistance and thermal insulation performances. The 3D mesoscopic geometrical structure of this innovative composite was reconstructed. The mechanisms of mass conversion and energy transfer during ablation was revealed by using thermal exposure experimental test and microscopic observation methods. Considering both the true mesoscopic structures and different temperature-dependent thermal-physical properties of the fiber bundles and matrix, a volumetric ablation model on mesoscopic scale was proposed and validated. Effects of pyrolysis reaction, generation of decomposition gases and its flow in porous charred structure on ablation and thermal responses were fully studied. The fiber interpenetrating network makes the innovative, charring composite intact in shape and porous inside after exposed to a moderate heat flux, which in turn provides better thermal protection and insulation capacities. The comprehensive study on mesoscopic volumetric ablation model can be instrumental in precisely predicting the ablation and thermal response of the charring composite, which offers a fundamental understanding and new composite design guidelines applicable to low-density thermal protection systems.