Assessment of thermal effect on the fracture toughness of granite

The effect of temperature on rock properties has attacked wide attention with the development of deep earth engineering. The change of temperature results in brittle-ductile transformation and makes the fracture toughness different. In the current study, a modified elastic–plastic damage model is proposed to predict the constitutive relation of granite in tension at different temperatures. The model is applied to predict the J-integral of a double-edge-notched plate. Unloading at the point where slope of the secant line is 0.95 times of the initial linear segment slope, the elastic and plastic part of the J-integral can be distinguished. It is noted that the J-integral decreases with elevated temperature and the downward trend changes obviously at around 600 °C. The plastic part takes 57–73 % of the total J-integral for quasi-brittle materials at different temperatures. The fracture toughness predicted based on different methods is compared, it shows that the fracture toughness predicted by the J-integral method is about 1.43 times of the ASTM load-based method.