Rock fracturing through microwave irradiation has received significant attention recently as a viable pretreatment for improving the energy efficiency of comminution processes. This study presents a numerical analysis on the effects of microwave heating on the mechanical properties of hard rock. In particular, the reduction of the uniaxial compressive and tensile strength of granite-like rock due to microwave irradiation induced damage is numerically assessed. Rock fracture is modelled by a damage-viscoplasticity model, with separate damage variables for tension and compression types of failure. A global solution strategy is developed where first the electromagnetic problem is solved in COMSOL multiphysics software, then its solution is used as an input for the thermomechanical problem, which is finally solved by means of a staggered explicit solution method. Due to the preeminence of the thermal radiation, the thermal and the mechanical parts of the problem are considered as uncoupled. The model behaviour is tested in 3D finite element simulations of three-mineral numerical rock specimens, with mesostructures explicitly defined, pretreated first in a microwave oven and then subjected to uniaxial compression and tension tests. The results show that the compressive and tensile strength of rock can be considerably reduced by the microwave irradiation pretreatment.
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