Experimental investigations on tensile mechanical behavior and real-time thermal damage analysis of granite subjected to high temperature

Understanding the tensile mechanical characteristics and damage mechanisms of granite suffering thermal loading is of vital significance to the construction and safe operation of various deep underground engineering projects. In this study, a series of laboratory experiments were conducted to acquire the tensile mechanical properties and fracture characteristics of granite after high-temperature. Based on thermal expansion behavior and real-time thermoacoustic emission signals, the thermal damage mechanism of granite was revealed. The results indicate that the tensile mechanical properties of granite exhibit a thermal strengthening effect, with the tensile strength reaching its peak at about 200 °C. Both the thermal strain and thermal expansion coefficient of granite increase linearly with rising temperature, which may contribute to densification of the rock matrix at relatively low heating temperatures. With further increases in temperature, the evolution shifts to a nonlinear pattern, driven by the differential thermal expansion of mineral grains and the initiation and propagation of microcracks. Thermal damage primarily occurs during the heating stage, while damage in the cooling phase is concentrated within a short initial period of cooling. The degree of damage in both stages increases with the target temperature, implying that the target temperature is one of the primary factors governing the degree of damage in granite. The proposed thermal damage variable equation enables quantitative characterization of damage during both heating ( D h ) and cooling ( D c ) stages. Furthermore, an improved empirical thermal damage variable equation for granite was proposed. This study is expected to provide insights into the analysis of thermal damage in granite.