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 A degrees C), fracture toughness increases slowly, with a total increase of approximately 11%. At the medium-temperature stage (100-500 A degrees C), fracture toughness decreases slowly, at a rate of approximately 18%. During the high-temperature stage (500-800 A degrees C), fracture toughness was reduced by approximately 44%. The mode I fracture toughness has a clear temperature threshold (500-600 A degrees 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 A degrees C, the mechanisms include transgranular fracturing, intergranular fracturing, thermal cracking, and mutual coupling fracturing. When the temperature exceeds 500 A degrees 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.