# Tensile Properties of Granite Under Cyclic Thermal Shock and Loading
## 3 Test Results and Analysis
### Tensile Strength  
Figure 11 depicts the relationship between the tensile strength of granite and the number of cyclic water-cooling shocks under cyclic loading-unloading conditions. The tensile strength of granite gradually decreases with increasing water-cooling shock cycles. In the conventional Brazilian splitting test, under natural conditions (i.e., without water-cooling shocks), the tensile strength of granite is 13.37 MPa. However, after a single water-cooling shock, the tensile strength decreases to 7.92 MPa, representing a 41% reduction relative to the unshocked case. This reduction is attributed to significant thermal damage induced by the steep temperature gradient between the interior and exterior during the 400 \({}^{\circ}\)C water-cooling shock, generating numerous microcracks that reduce the tensile strength of the rock [28]. As the number of water-cooling shock cycles increases, the tensile strength continues to decline, although the rate of reduction becomes less pronounced. For three, five, and seven cycles, the tensile strengths are 6.61 MPa, 5.63 MPa, and 5.11 MPa, corresponding to reductions of 50%, 58%, and 62% relative to the natural condition, respectively. During the 400 \({}^{\circ}\)C water-cooling shock, partial local melting of quartz particles occurs; the molten quartz alters interparticle bonding within the rock, thereby reducing its overall strength [35]. In subsequent cycles, further quartz melting occurs, and due to the differing thermal expansion coefficients of quartz, mica, feldspar, and other minerals, the tensile strength of granite gradually decreases with additional cycles [11]. Some researchers have observed a thermal strengthening effect in granite after a 200 \({}^{\circ}\)C water-cooling shock [6]; however, under the 400 \({}^{\circ}\)C shock applied in this study, the tensile strength of granite decreases directly. This outcome is because the water-cooling shock simultaneously induces thermal strengthening and thermal damage in the granite, and at higher temperatures, the thermal strengthening effect is insufficient to compensate for the degradation of the mechanical properties of the rock caused by thermal damage [28]. In addition, Figure 11 also reveals that under the 400 \({}^{\circ}\)C cyclic water-cooling shock, the variation trend of tensile strength from the cyclic loading-unloading Brazilian splitting test is similar to that from the conventional Brazilian splitting test, both showing a gradual decrease in tensile strength with an increasing number of water-cooling shocks. However, compared with the tensile strength obtained from the conventional Brazilian splitting test, the tensile strength of granite under cyclic loading-unloading is significantly reduced. For instance, when the preset load upper limit is 75% after 0, 1, 3, 5, and 7 water-cooling shocks the tensile strengths of granite are 9.19 MPa, 5.43 MPa, 4.61 MPa, 3.91 MPa, and 3.61 MPa, respectively, which represents an overall decrease of approximately 30% compared to the conventional test. This phenomenon is primarily due to the continuous propagation and coalescence of microcracks under cyclic loading-unloading after the granite has been subjected to water-cooling shocks, eventually leading to a significant reduction in its tensile performance [13]. Similarly, it can be observed that under cyclic loading-unloading, the tensile strength of granite increases with the preset load upper limit. Taking the case of five water-cooling shocks as an example, when the preset load upper limits are 65%, 70%, 75%, and 80%, the corresponding tensile strengths from the cyclic loading-unloading Brazilian splitting test are 3.48 MPa, 3.67 MPa, 3.91 MPa, and 4.04 MPa, respectively, representing decreases of 38%, 35%, 30%, and 28% compared with the conventional Brazilian splitting test.