Nonlinear dynamics of thermal shock in graphite

https://doi.org/10.3221/IGF-ESIS.79.13

The transition to combustion of carbon materials in components of rocket and space technology is preceded by intensive heating from the surface, which can be accompanied by the initiation of a stress wave (thermal shock) with subsequent ablation, delamination, or spalling. The heating rate and the nonlinear dependence of thermal diffusivity on temperature, which depends on the porosity of the carbon material, determine the possibility of the effect of heat localization in the blow-up mode. The research is devoted to the analysis of the patterns of heat localization and its connection with the mechanisms of thermal shock in graphite under intense thermal exposure. Assessing the thermal strength of the material under conditions of heat localization generally requires solving a wave problem as the defect development time approach acoustic times using specific criteria. An approach to the numerical modeling of the nonlinear heat conduction problem is presented, taking into account the dependence of thermophysical and physicomechanical properties on temperature. The boundary conditions for the emergence of blow-up modes are defined, and the dynamics of heat localization are investigated. A comparison of numerical results with an analytical solution is carried out, which confirms the transition between two modes of heat propagation: a blow-up mode and a wave mode. The numerical estimate of the damage depth under a single thermal pulse is consistent with known experimental data.