Effects of temperature on mechanical properties of granite under different fracture modes

Abstract The mechanical properties of rocks are an important basis supporting engineering design and construction. Temperature is one of important factors influencing mechanical properties of rocks. To explore the evolution law of fracture characteristics of rocks at different temperatures, semi-circular three-point bending test was conducted on four groups of granite specimens treated at different temperatures. The research results showed that after treatment at 20 °C–900 °C, the tensile strengths of rocks all declined with increasing temperature. Under different fracture modes, the temperature ranges that influence the tensile strength of rocks are different. With the growth of temperature, the fracture toughnesses (KIC and KIIC) and equivalent fracture toughness Keff of the three groups of rock specimens under different fracture modes all gradually reduced. For rock specimens treated at temperature below 600 °C, the fracture toughness rapidly decreased while it slowly declined after exceeding 600 °C. Under different fracture modes, the temperature-sensitive ranges of granite are different. From low to high, the temperature ranges separately corresponded to those of fracture toughness of granite under mixed mode, mode II and mode I. Compared with conventional maximum tangential stress criterion, the modified maximum tangential stress criterion considered the effect of T stress, so that the resulting theoretical value was more consistent with the test results. Therefore, the modified maximum tangential stress criterion was more suitable for predicting the test results. With the growth of temperature of heat treatment, the damage of rocks was aggravated. The propagation path of main through-wall cracks generated in the specimens containing pre-casted cracks in three different angles became increasingly curved under the effect of external loads, and was deviated from the line between the tip of the pre-casted cracks and loading point at different degrees.