# Tensile Properties of Granite Under Cyclic Thermal Shock and Loading
## 1 Introduction
[19] conducted Brazilian splitting tests on granite after water-cooling shock and liquid nitrogen cooling and found that when the temperature is below 200 \({}^{\circ}\)C, water-cooling shock causes greater damage to the granite, whereas above 200 \({}^{\circ}\)C, granite cooled with liquid nitrogen exhibits lower tensile strength. In addition, considering that rocks in rock mass engineering are frequently subjected to cyclic loading, numerous studies have been conducted both domestically and internationally to address this issue. [PERSON] et al. [20; 21] performed Brazilian splitting tests on tuff under cyclic loading-unloading and found that rock failure initiates at the contact points between strong grains and a weak matrix. They also observed that when the preset load upper limit is below 65%, the rock is less prone to failure. [PERSON] et al. [22] employed CT techniques to investigate the effects of cyclic loading-unloading on the pore structure of granite and observed that the increase in porosity is primarily concentrated within the first 20 loading cycles. Similarly, [PERSON] et al. [23] conducted three-point bending tests on granite under cyclic loading-unloading at real-time high temperatures. Their results indicated that as the temperature increases, the fatigue failure threshold of granite gradually decreases. [PERSON] et al. [24] conducted triaxial cyclic loading-unloading tests on granite under hydro-mechanical coupling and found that higher confining pressure results in reduced fatigue damage from cyclic loading-unloading while also exhibiting a compaction effect. Likewise, [PERSON] et al. [25] performed triaxial cyclic loading-unloading tests on granite and reported that as the confining pressure and stress upper limit increase, the elastic modulus of granite increases while the damping ratio decreases. [PERSON] et al. [26] conducted uniaxial cyclic loading-unloading tests on granite at real-time high temperatures. Their findings indicated that at temperatures above 200 \({}^{\circ}\)C, both the elastic strain energy density and input energy density increase with rising temperature. The energy accumulation was predominantly observed during the loading phase. In summary, with regard to the safety issues encountered during the fracturing and cyclic injection-production processes of hot dry rock reservoirs, the specific process is shown in Figure 1. Existing research mainly focuses on the impact of high temperatures on the physical and mechanical properties of rocks or solely considers the effects of cyclic loading and unloading. However, there is still a lack of systematic research on the evolution of rock tensile behavior under the combined effects of high temperatures and cyclic loading and unloading. To address this knowledge gap, the present study utilized Brazilian splitting tests on granite subjected to cyclic water-cooling shock at 400 \({}^{\circ}\)C (for 1, 3, 5, and 7 cycles) under varying preset load upper limits (65%, 70%, 75%, and 80% of the peak load). Furthermore, scanning electron microscope (SEM) analysis was performed to investigate the effects of the combined action of cyclic water-cooling shock and cyclic loading and unloading on the tensile properties of granite. The findings of this study provide a theoretical basis for the hydraulic fracturing modification of hot dry rock reservoirs.