# Tensile Properties of Granite Under Cyclic Thermal Shock and Loading
## 6 Conclusions  
This study investigates the effects of cyclic water-cooling shock at 400 \({}^{\circ}\)C and cyclic loading-unloading on the tensile properties of granite through Brazilian splitting tests and scanning electron microscopy (SEM) analysis. The main conclusions are as follows:  
1. For granite subjected to cyclic water-cooling shock at 400 \({}^{\circ}\)C, an increase in shock cycles leads to mass loss, volume expansion, density reduction, and a decrease in P-wave velocity. The most significant changes occur after the first quenching, after which the variation trends gradually stabilize. With the increasing number of water-cooling shock cycles, the tensile strength gradually decreases, while the rate of decrease diminishes progressively.
2. The tensile strength of granite in cyclic loading-unloading Brazilian splitting tests decreases progressively with increasing water-cooling shock cycles. Additionally, the tensile strength under cyclic loading-unloading conditions is significantly lower than that in conventional Brazilian splitting tests. As the preset load upper limit decreases, the tensile strength also exhibits a declining trend.  
Figure 16: Schematic of the damage mechanism of granite under 400 \({}^{\circ}\)C cyclic water-cooling shock and cyclic loading-unloading. (**a**) natural state; (**b**) cyclic loading-unloading effect; (**c**) cyclic water-cooling shock; (**d**) combined effect of 400\({}^{\circ}\)C water-cooling shock and cyclic loading-unloading.  
Under cyclic loading-unloading, the initial peak displacement increases with the preset load upper limit. However, at five shock cycles, no clear trend is observed due to the transition of granite from brittle to ductile behavior. As the preset load upper limit increases, the number of cycles required for failure decreases. The elastic stiffness of granite initially increases with the number of loading-unloading cycles, then stabilizes before eventually decreasing. Moreover, with increasing water-cooling shock cycles, the overall elastic stiffness shows a decreasing trend. In the early stages of cyclic loading and unloading during the Brazilian splitting test, a competitive mechanism exists between damage accumulation and compaction effects in granite. When the number of water-cooling shock cycles is low, damage accumulation dominates; however, after five cycles, the compaction effect becomes the prevailing mechanism.
4. With an increasing number of cyclic water-cooling shocks, macro-fracture patterns in granite transition from straight to curved cracks. SEM observations reveal that microcracks become more numerous and wider with additional shock cycles. Under cyclic loading-unloading, the microcrack width further increases, and the fracture surface becomes rougher.  
Conceptualization, Y.Z. and F.Z.; formal analysis, S.L., C.L. and S.X.; data curation, Y.Z.; writing--original draft preparation, Y.Z.; writing--review and editing, Y.Z.; supervision, F.Z. The results were discussed and conclusions were drafted jointly by all authors. All authors have read and agreed to the published version of the manuscript.  
This work was jointly supported by the National Natural Science Foundation of China (Grant No. 51979100).  
Not applicable.  
The raw data supporting the conclusions of this article will be made available by the authors on request.  
The authors declare no conflict of interest.