High temperature thermomechanical behavior of silica-phenolic composite exposed to heat flux environments

The thermomechanical behavior of polymer matrix thermoprotective material during chemical decomposition can be recognized as the coupled temperature–diffusion–deformation problem of porous elastomers under high temperatures. A coupled solution model for the problem was developed to analyze the thermal and mechanical responses of a silica-phenolic composite exposed to heat flux environments. In the model, the coupling heat-transfer process, generation of pyrolysis gases and their subsequent diffusion process and thermal deformation were taken into account. The governing equations were established and further modified using the finite element method to obtain the effective element stiffness equation for each triangular element. The decomposition degree, displacement, thermal strain and stress distribution were calculated using the coupled solution model. Additionally, a two-dimensional digital image correlation (2D DIC) method was applied to measure the high-temperature deformation and strain of each specimen. The accuracy of the model was further assessed by comparing predicted and experimental depths of heat affected zones.