Thermal-mechanical-chemical Multi-physical Coupling Analysis Of Silica/Phenolic Composites Under Volume Ablation Condition

In recent years, with the rapid development of national aviation and aerospaceindustry, a higher requirement has been put forward for space vehicles’ thermalprotective materials and structural design. As a kind of thermal protective and thermalinsulation material, silica/phenolic composites have many advantages, such as goodthermal protective, thermal insulation and ablation resistant performance, as well aslow-cost and sample preparation process. Thus, silica/phenolic composites have beenwidely used as a thermal protective material for hypersonic space vehicles. Thevolume ablation of silica/phenolic composites is a complicated mass transfer and heattransfer process when it is exposed to unilateral thermal flux. This process generallyconsists of pyrolysis reaction of phenolic resin, heat conduction inside the material,diffusion of decomposition gases, thermal deformation of material, thermal blockadeeffect and radiation cooling effect. Therefore, the volume ablation of silica/phenoliccomposites should be considered as a thermal-mechanical-chemical coupling problem.Due to the difference of thermal expansion coefficient about fiber and matrix, thethermal stress is produced and non-uniformly distributed in the local region. The localstress analysis is directly related to evaluate the high temperature strength behavior.Therefore, it is essential to analyze the local thermal deformation and thermal stresswhen the material is exposed to high temperature. However, there are few literaturesreport about the complicated3D multi-physical coupling calculation. At present, it isurgent to establish a3D multi-physical coupling calculation model aboutsilica/phenolic composites to satisfy the requirement in the engineering.Firstly, the endothermic/exothermic mechanism and thermal blockade effectabout silica/phenolic composites under volume ablation condition are introduced. Avolume ablation model considering char layer, pyrolysis layer and virgin materiallayer has been established based on the heat protection and insulation mechanisms ofthe composite material. And the three-dimensional multi-physical field governingequation of the transverse isotropic silica/phenolic composites are deduced.Secondly, the oxyacetylene radiation flux system combining with digital imagecorrelation system and thermocouple temperature measurement system are used tomeasure the temperature history and high temperature deformation of Silica/Phenoliccomposites. The surface morphology and the products of the heating surface ofsamples after volume ablation experiment are analyzed by SEM. The different timetemperature distribution at specific points and the full-field high temperaturedeformation of the specimen have been provided.Finally, based on the thermal-mechanical-chemical coupling governing equation of the composites, a3D thermal and mechanical response model of the compositesunder unilateral thermal flux is established by using commercial finite elementsoftware COMSOL. The temperature field, displacement field, pore pressure, resinresidual ratio and stress-strain of the composites are obtained. In comparison of thepredicted results with the high temperature deformation experimental data, it is foundthat the predicted temperature and displacement are in good agreement with theexperimental results.