Effect of temperature on pure mode Ⅲ fracture behavior and fracture morphology of granite after thermal shock

Abstract

To investigate the effect of temperature on the pure mode III fracture behavior and fracture morphology of granite after thermal shock, edge-notched disc bend granite specimens are selected for heat treatment and a series of fracture tests. Firstly, the effect of temperature on the macroscopic fracture behavior of the rock is analyzed regarding the physical and mechanical properties and fracture toughness. Then, the impact of temperature on the microscopic fracture morphology of the rocks is discussed based on a fractal theory using 3D laser scanning techniques. The results show that temperature affects the fracture behavior of rock by changing its physical parameters and mechanical properties. High temperatures can change the fracture mode of rocks and have a softening effect on rocks. The heat treatment temperature of 325 °C above can convert rocks from brittle to ductile failure. When the heat treatment temperature is above 525 °C can evolve rocks from pure mode III fracture to mixed mode I/III fracture. The fracture toughness of the rock and the joint roughness coefficient are highly linearly correlated with temperature. The fracture toughness of the rock decreases by 0.5 MPa∙m0.5, and the joint roughness coefficient increases by 1.7 for every 100 °C increase in temperature in the range of 25 °C to 625 °C. The asperity height and slope angle of the rock obey a normal distribution. The higher the temperature, the larger the fracture surface area, the larger the fractal dimension, the stronger the anisotropy of the surface protrusions, and the rougher the rock surface.