Research of microcosmic mechanism of brittle-plastic transition for granite under high temperature

The effect of temperature on mechanical characteristics and behaviours of granite was analyzed by using experiments as scanning electron microscope(SEM), X-ray diffraction and acoustic emission(AE) and the micromechanism of brittle-plastic transition of granite under high temperature was discussed as well. SEM result shows that the fracture surface possesses the mixed-rupture characteristics of transcrystalline cracks, cleavage step, slip band and superficial dimple at about 800°C; X-ray diffraction shows crystal form of some crystals of granite has transformed; and AE strength decreases, but the duration increases at about 800°C. The residual plastic deformation of granite still releases serried acoustic emission especially after peak strength, which is uniformly with the variation of macromechanical characteristics of granite. The failure form of granite changes from abruptly brittle fracture to semi-brittle shear fracture gradually with the rise of temperature. The research findings provide valuable basic references for the rock thermodynamics problems in reposition of nuclear waste, practical gasification of coal and oil shale, deep resources mining, exploitation of geothermal resources and safety drilling as well as comprehensive utilization of coal seam gas.