Investigation of the Initiation of Composite Mode I/II Crack in Gas-Bearing Rock Caused by Nonuniformly Distributed Heat Flux

To investigate the patterns of rock crack initiation caused by the nonuniformly distributed heat flux resulting from fracture air-vapor pressure, the fracture air-vapor pressure control equation was deduced, and five spatial distribution forms of heat flux were established. The crack initiation criterion considering nonuniform heat flux conditions was proposed based on the modified maximum tangential stress criterion, the theory was validated using FEM and FE-FEM numerical methods. The results show that the peak value of nonuniform heat flux determines the maximum value of the crack surface temperature, and the distribution form determines the range of high-temperature and low-temperature regions on the crack surface. Axisymmetric heat flux induces centrosymmetric cracking, and nonaxisymmetric heat flux induces noncentrosymmetric cracking. It was observed that when q_max = 5000 mW/m², there is a mutation line in the critical crack initiation angle, which mutates from −90° to 90°. The position of the mutation line decreases with increasing heat flux.