Computational modelling of microwave-induced fractures in igneous rocks using phase field method

Abstract

This study introduced a simplified thermodynamic model based on the regularized phase field method for simulating the thermally induced fractures of rocks pretreated by microwave. A thermo-mechanical model comprises three main parts developed to evaluate the fractures: the heat generation of the rock specimen is determined via the heat balance equation; the calculation of thermally induced stress is performed in the second part by taking into account the thermal stress due to temperature change; the third part calculates the fracture induced by microwave heating using the phase field equation. Combining these three parts enables simulations of rock fractures due to thermally induced stress. The first simulation is the quenching test of ceramics to validate the robustness of the phase field method in modelling the thermo-mechanical fracture. Then, examples of microwave-induced fracture are presented and discussed in comparison with microwave test results. A good agreement is achieved from the results of numerical analysis and experiments, which proves the feasibility of the proposed thermo-mechanical coupling fracture (phase field) model for the simulation of thermal-mechanical fractures. It is further found that the power level is crucial in influencing the fractures given the same energy input. More specifically, a higher power level leads to an increased non-uniformity of a thermal gradient, which, as a result, leads to a higher stress gradient and more fractures generated eventually. Furthermore, the energy utilization ratio also benefits under a more intensive microwave power level. The developed model quantitatively enriches the understanding of fractures produced by microwave irradiation and advances the application of the microwave-assisted rock breakage technique in industry and academics.