关键词: 硅橡胶, 防热涂层, 烧蚀, 裂纹, 热/力耦合, 数值模型

Abstract: The silicone rubber-based thermal protective coating may undergo ablation-coupled cracking in aerothermodynamic environments, which affects its thermal protection effectiveness and mechanical properties. The coatings’ mechanical properties at room and high temperatures were studied using a high-temperature thermomechanical analyzer and a universal testing machine. The dynamic ablation and cracking processes were investigated using high-temperature gas flow experiments. A thermo/mechanical coupling finite element model was established to consider the above phenomena, and crack propagation calculations were performed. The deformation curve shows that the material undergoes linear thermal expansion at low temperatures (below 600 K), before beginning to contract significantly at higher temperatures. The material properties show as “reinforced elastomer”, “organically softened polymer”, and “inorganic, porous and brittle ceramic” under different temperature conditions. Ablation experiment results indicate that cracks almost occur in the char layer, with the maximum crack depth being near the interface between the char and pyrolysis layers. The numerical results indicate that the early deformation of the coating occurs primarily in the surface layer and the bottom constrained region. As ablation and heat transfer progress deeper into the material, the range and magnitude of deformation and shrinkage gradually increase, resulting in expansion on both sides of the material. After considering the cracking effects, the principal stresses and strains of the material increase. During the initial stage (0~12 seconds), the temperature gradient and thermal stress on the surface layer are relatively high, resulting in crack initiation at these locations. The effects of intense thermal expansion and contraction amplify the driving force for crack propagation, causing rapid crack development. In the middle-to-late stage (12~30 seconds), the temperature gradient decreases, the energy at the crack tip reaches equilibrium, and the rate of crack propagation slows down and stops.

Key words: silicon rubber, thermal protection coating, ablation, cracking, thermal/mechanical coupling, numerical model