## 4 Results
### Microcrack Evolution  
Figure 10 illustrates the distribution of local microcracks in the granite samples after failure at different temperatures. It is observed that when the temperature does not exceed 200 \({}^{\circ}\)C, microcracks are randomly distributed within the sample, with little apparent connection between them. Intragranular cracks mainly occur within the feldspar and mica crystals, with few occurring within the quartz. After 300 \({}^{\circ}\)C, cracks at the boundaries of mineral crystals significantly increase, with a small number of cracks beginning to propagate and combine. At 400 \({}^{\circ}\)C, as shown in Figure 10d at points 1 and 2, numerous cracks appear within and at the boundaries of the mica crystals. This is because the thermal expansion coefficient of mica is smaller than that of other minerals, making it easier for tensile stress to concentrate near mica under high-temperature conditions. After 500 \({}^{\circ}\)C, as shown in Figure 10e at point 3, tensile cracks begin to aggregate at the boundaries of quartz crystals. When the temperature reaches 600 \({}^{\circ}\)C, Figure 10f at point 4 displays a large number of intragranular tensile cracks within the quartz crystals. Additionally, from Figure 10f at points 5 and 6, it can be observed that cracks at the grain boundaries increase, forming a network of interconnected cracks. Overall, the main areas where microcracks gather at different temperatures are within the mica and feldspar, indicating that the compression failure of granite under real-time high-temperature conditions is mainly controlled by these minerals. This observation aligns with the experimental and simulation results of [PERSON] et al. and [PERSON] et al. [43; 44]. On the other hand, high temperature significantly affects crack evolution. As the temperature increases, the aggregation of tensile cracks within and between various types of crystals gradually intensifies, leading to a more severe failure of granite due to the formation of a crack network. Figure 11 presents scanning electron microscope images of the fracture surfaces of the granite samples after real-time high-temperature uniaxial compression tests. The development of microcracks in the samples at different temperatures varies significantly,  
Figure 10: Evolution of granite microcracking with temperature. indicating a significant influence of high temperature on the microcrack evolution in granite. At 25 \({}^{\circ}\)C, the fracture surface of the granite sample contains only a few native microcracks, indicating that the internal structure of the granite is nearly intact, with mineral particles arranged relatively closely. At 200 \({}^{\circ}\)C, the effect of high temperature causes some initial microcracks to begin closing, and the expansion of mineral particles improves the microstructure of the granite. When the temperature rises to 300 \({}^{\circ}\)C, internal stress between particles increases, resulting in the deformation and delamination of mica, leading to a continuous increase in intergranular cracks [45]. With the temperature further increasing, thermal damage becomes more severe. Between 400 \({}^{\circ}\)C and 500 \({}^{\circ}\)C, the fracture surface becomes rougher, with a significant increase in the number of dense cracks. The widths and lengths of the cracks also increase, and the damaged zones along the crack edges are more prone to initiate new cracks under the interaction of frictional forces. This also leads to the connection and propagation of some intergranular and intragranular cracks, forming distinct crack aggregation zones [46]. After 600 \({}^{\circ}\)C, due to the \(\alpha\)-\(\beta\) phase transition of quartz at 573 \({}^{\circ}\)C, transgranular cracks appear abundantly on the fracture surface, with a wider distribution and deeper aggregation. Many crystals are divided into small pieces, forming a honeycomb-like structure, accompanied by a large amount of debris generation [47].