Abstract
This paper presents a numerical study on the effects of microwave irradiation on the mechanical properties of hard rock. More specifically, the weakening effect of microwave heating induced damage on the uniaxial compressive and tensile strength of granite-like rock is numerically evaluated. Rock fracture is modelled by means of a damage-viscoplasticity model with separate damage variables for tensile and compressive failure types. We develop a global solution strategy where the electromagnetic problem is solved first separately in COMSOL multiphysics software, and then provided into a staggered implicit solution method for the thermo-mechanical problem. The thermal and mechanical parts of the problem are considered as uncoupled due to the dominance of the microwave-induced heat source. The model performance is tested in 2D finite element simulations of heterogeneous numerical rock specimens subjected first to heating in a microwave oven and then to uniaxial compression and tension tests. According to the results, the compressive and tensile strength of rock can be significantly reduced by microwave heating pretreatment.
Highlights
In the mineral processing industry, the comminution of hard rock such as granite is a process that demands a considerable amount of time and energy (Ek 1986) and accounts for a large percentage of the total energy consumption in the whole mineral recovery process
The aim of this paper is to evaluate numerically, by 2D simulations, the weakening effect of microwave irradiation on the uniaxial compressive and tensile strength of polycrystalline rock specimens inserted in a multimode oven
The mechanical part is solved as a quasi-static problem, which is justified by the negligible inertia effects during microwave heating
Summary
In the mineral processing industry, the comminution of hard rock such as granite is a process that demands a considerable amount of time and energy (Ek 1986) and accounts for a large percentage of the total energy consumption in the whole mineral recovery process. New energy-efficient comminution methods, where rocks and ores are weakened by a. Non-mechanical pre-treatment, have been developed in the last decades. These methods include magnetic, electrical and thermal agents (Somani et al 2017; Klein et al 2018). Microwave heating applications of rock have been developed since the 1960s (Ford and Pei 1967; Maurer 1968) within the mineral processing industry, with the scope of reducing energy demand during comminution of ores (Teimoori and Hassani 2021). The energy absorbed by rock through the exposure to microwave radiation is converted to heat. Microwave radiation conditions such as power level, exposure time and distance from rock have an influence on temperature intensity and distribution (Wang and Forssberg 2005)
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