The Influence of Temperature on Mode I Fracture Toughness and Fracture Characteristics of Sandstone

This study investigated the influence of temperature on the mode I fracture toughness of sandstone using semicircular bend specimens. Fracture characteristics were studied using scanning electron microscopy and other means. The results showed that temperature influenced fracturing in three stages along a temperature gradient. In the low-temperature stage (20–100 °C), fracture toughness increases slowly, with a total increase of approximately 11%. At the medium-temperature stage (100–500 °C), fracture toughness decreases slowly, at a rate of approximately 18%. During the high-temperature stage (500–800 °C), fracture toughness was reduced by approximately 44%. The mode I fracture toughness has a clear temperature threshold (500–600 °C). Below this threshold, the fracture toughness decreases slowly. When the temperature threshold is reached, the fracture toughness decreases sharply. The sharp decrease is mainly caused by the creation of a fragmentation structure. The sandstone experiences more transgranular fracture mechanics in the low-temperature stage compared to the high-temperature stage. Above 100 °C, the mechanisms include transgranular fracturing, intergranular fracturing, thermal cracking, and mutual coupling fracturing. When the temperature exceeds 500 °C, several different fragmentation structures are seen. This research study provides significant data to evaluate fracture characteristics and rock safety and stability after heat treatment.