Ablation Properties, Thermal Insulation Properties, and Finite Element Analysis of Gradient Ceramifiable Composites Based on Boron Phenolic Resin, MoSi ₂ , and Vitreous Silica Fabric

ABSTRACT Ceramifiable polymer composites have the potential as thermal protection material. In this work, four kinds of ceramifiable functionally gradient materials (CFGMs) composed of boron phenolic resin (BPR) composites with MoSi ₂ particles as ceramifiable fillers and reinforced by vitreous silica fabric were prepared by prepreg and molding process. CFGMs consist of three parts, including a ceramifiable thermal protection part (CTPP), a gradient transition part (GTP), and a carbonizable thermal insulation part (CTIP). Moreover, the CFGMs with different structures were designed by varying the thickness of CTPP and CTIP. Density, thermal insulation properties, ablation properties, and microscopic morphology of the CFGMs were studied, and the temperature and thermal stress fields of CFGMs during oxyacetylene ablation were simulated by ABAQUS. This study presents a novel approach by optimizing the gradient structure to enhance both ablation and thermal insulation properties, which has not been previously explored. The experimental results show that the optimal gradient structure based on integrated performance is CFGM‐3. During the 60 s oxyacetylene ablation test, the back surface temperature of CFGM‐3 decreased from 294°C to 203°C in comparison with the neat ceramifiable composite. ABAQUS simulations showed the GTP could effectively disperse thermal stress. Furthermore, the linear ablation rate of CFGM‐4 (0.0032 mm s ⁻¹ ) was lower than that of neat ceramifiable composites (0.0035 mm s ⁻¹ ). SEM showed that the ablation surface of CFGMs was covered with a dense eutectic film, which could delay thermal oxygen into the inner glassy carbon and avoid oxidation crack.