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This paper presents a study of a thermal breakage process used to analyse the thermal stress and crack development that occur when rock is exposed to short-pulse microwave energy. A two-dimensional circular plate, containing two-phase minerals, was used in finite element simulation to calculate thermal stress for the purpose of better understanding thermal fracture behaviour in comminution. It is found that the thermal mismatch between a microwave-absorbing inclusion and a low-absorbing matrix mineral can generate large localized thermal stresses around the inclusion. Fracture initially occurs, not around the grain boundaries between the two minerals, but some distance away, as a result of thermal expansion stress on the matrix mineral. The results also indicate that though grain size is one of the factors causing cracks during heating of granular materials, it is not the only reason. The size and the thermal properties of the matrix mineral can also affect the results of thermal stresses. |
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