# Tensile Properties of Granite Under Cyclic Thermal Shock and Loading
## 3 Test Results and Analysis
### Load-Displacement Curve  
Figure 9 presents the load-displacement curves obtained from the Brazilian splitting tests on granite after 400 \({}^{\circ}\)C cyclic water-cooling quenching. It can be observed that, following cyclic quenching, the load-displacement curves of granite exhibit a compaction stage, an elastic linear stage, a crack propagation stage, and an instability failure stage. Figure 8: Variation curves of physical parameters with the number of circulating water cold shocks. (**a**) mass loss rate; (**b**) volumetric expansion rate; (**c**) density attenuation rate; (**d**) longitudinal wave velocity reduction rate. With an increasing number of cyclic water-cooling shocks, the peak load shows a gradual decline. The peak loads of granite for 0, 1, 3, 5, and 7 quenching cycles are 26.37 kN, 14.29 kN, 12.82 kN, 11.31 kN, and 9.57 kN, respectively. This indicates that cyclic quenching imparts significant thermal damage to the granite, with thermal damage accumulating progressively as the number of quenching cycles increases; compared with the peak load of granite in its natural state, the peak load decreases by 45.81%, 51.38%, 57.11%, and 63.71% after 1, 3, 5, and 7 quenching cycles, respectively. Moreover, as observed in Figure 7, the deformation characteristics of granite are influenced by the 400 \({}^{\circ}\)C cyclic quenching, with the slope of the load-displacement curve gradually decreasing as the number of quenching cycles increases. Figure 10 shows the load-displacement curves from the cyclic loading-unloading Brazilian splitting tests on granite after 400 \({}^{\circ}\)C cyclic water-cooling shock. It can be seen that the stages experienced by the load-displacement curves after a cyclic water-cooling shock are similar to those in conventional Brazilian splitting tests. After the first cyclic loading-unloading, the granite exhibits obvious plastic deformation, where the magnitude of plastic deformation is defined as the displacement from the starting point of the hysteresis loop during loading to the endpoint during unloading. For instance, under a 70% load upper limit, when cyclic water-cooling shocks are applied in 0, 1, 3, 5, and 7 cycles, the corresponding plastic deformation displacements after the first cyclic loading-unloading are 0.003 mm, 0.018 mm, 0.042 mm, 0.054 mm, and 0.071 mm, respectively. This indicates that, under the same preset load upper limit, the plastic deformation displacement of granite increases gradually with the number of cyclic water-cooling shocks. Moreover, after seven cyclic water-cooling shocks (Figure 10e), when the preset load upper limits are 65%, 70%, 75%, and 80%, the plastic deformation displacements are 0.056 mm, 0.071 mm, 0.057 mm, and 0.074 mm, respectively. This demonstrates that, under the same number of water-cooling shocks, the plastic deformation displacement of granite generally increases with the rise in the preset load upper limit. Figure 9: Load–displacement curves for conventional Brazilian splitting of granite after cyclic water-cooling impact at 400 \({}^{\circ}\)C.  
As observed in Figure 10, following a 400 \({}^{\circ}\)C cyclic water-cooling shock, the slope of the hysteresis loop in the load-displacement curves of granite during cyclic loading-unloading progressively increases. This phenomenon is attributed to the gradual propagation of microcracks within the granite induced by the cyclic water-cooling shock, while the cyclic loading-unloading process compacts and closes these microcracks, thereby enhancing the resistance of granite to deformation [24]. When granite is subjected to a small number of water-cooling shocks, such as under one cycle (Figure 10b), the hysteresis loops in the load-displacement curves obtained from the cyclic loading-unloading Brazilian splitting test are relatively compact.