## 4 Results  
### Stress-Strain and Crack Propagation  
To visually illustrate the entire process of crack initiation and propagation within granite, the crack evolution during the compression process of granite at room temperature is divided into four stages, as shown in Figure 8. (1) Initial densification stage (curve ab): The stress-strain relationship is linear, indicating that cracks have not yet initiated due to the relatively small load. (2) Elastic stage (curve bc): The number of cracks gradually increases with the increase in load. Compared to intragranular contacts, the intergranular contacts are weaker. When the tensile stress on the sample exceeds the tensile strength between mineral crystals, dispersed intergranular tensile cracks rapidly form. (3) Plastic strengthening stage (curve cd): The rate of crack development further increases, with a significant increase in the number of intragranular tensile cracks compared to the elastic stage. Additionally, shear failure cracks begin to appear during this stage. At point d, where the peak stress is reached, crack development becomes concentrated, and the failure mode of the sample becomes foreseeable. (4) Post-peak failure stage (curve de): The slope of both intergranular and intragranular tensile crack curves significantly increases compared to the previous stage. Although a certain number of intergranular shear cracks have formed, tensile failure cracks still dominate. At this stage, crack propagation weakens the overall strength of the material, leading to a gradual decrease in stress and the eventual macroscopic fracture of the sample. Figure 7: Comparison results of failure modes: (**a**) experimental results; (**b**) numerical results. To investigate the influence of high temperature on the damage and failure of granite under uniaxial compression, Figure 9 presents a statistical analysis of the total number of microcracks and the proportions of different types of cracks observed in the samples at different temperatures. It is observed that at 200 \({}^{\circ}\)C, the effect of high temperature on the mechanical properties of the granite samples is minimal, with the number of microcracks remaining relatively unchanged compared to that at room temperature (20 \({}^{\circ}\)C). Due to the lowest intergranular tensile strength, intergranular tensile cracks constitute the majority of cracks, accounting for 92.8% of the total microcracks. This result is consistent with the viewpoint proposed by [PERSON] [41] that shear strength exceeds tensile strength in brittle materials. At 300 \({}^{\circ}\)C, the differential coefficients of thermal expansion of the mineral crystals result in the uneven expansion of the sample, accelerating the development of microcracks, albeit with a slight decrease in the proportion of intergranular tensile cracks. Between 400 \({}^{\circ}\)C and 500 \({}^{\circ}\)C, the continued weakening of intergranular bonding leads to a further increase in the rate of microcrack formation due to structural damage to the mineral crystals. During this period, the rate of intragranular crack expansion remains lower than that of intergranular cracks. Upon reaching 600 \({}^{\circ}\)C, there is a sharp increase in the number of microcracks, nearly doubling compared to that at 20 \({}^{\circ}\)C.  
In summary, the crack development in granite during uniaxial compression mainly undergoes four stages: initial compression, elasticity, plastic strengthening, and post-peak failure. Intergranular tensile cracks dominate the initiation process, followed by intragranular tensile cracks, with only a few shear cracks starting to propagate in the later stages. This result is also consistent with the experimental and simulation findings of [PERSON]  
Figure 8: Stress–strain versus crack derivation curves. Figure 9: Total number of microcracks and the proportion of each type of crack at different temperatures. et al. [42]. With the increase in temperature, the number of microcracks gradually increases.