## 3 Results and Discussion  
### Shear Load-Displacement Curves  
As demonstrated in Figures 6-9, the shear load-displacement curves of coarse and fine granite under different high-temperature cold impact modes can be categorized into five stages [34].The first stage is the compression-density stage, during which the existence of pores and microcracks within the granite results in compression. When the specimen is subjected to compression-shear loading, the pores and microcracks will be gradually closed, resulting in the load curve showing a 'concave' shape in the initial stage of the test. The second stage is the linear elasticity stage, during which the load increases linearly with the increase in displacement, and the load-displacement curve is basically a straight  
Figure 4: Appearance of high-temperature granite specimens subjected to different cooling methods.  
Figure 5: Schematic diagram of variable-angle shear apparatus.  
line. This stage is characterized by the emergence and stable expansion of cracks within the specimen, resulting in a transition of the load-displacement curve from a linear to a non-linear trajectory. The third stage is marked by the non-stable expansion of these cracks, leading to their rapid propagation and penetration within the granite. The fourth stage, known as the post-peak stress softening stage, is characterized by a sudden drop in load following the peak, resulting in a sudden rupture of the specimen and the manifestation of typical brittle damage characteristics.  
The load-displacement curves demonstrate that, for a given cold-shock method, both coarse-grained and fine-grained granite exhibit shortened compaction and linear elastic stages with increasing shear angle, with peak load and peak displacement decreasing continuously. This phenomenon is primarily attributable to the reduced normal stress on the granite, which reduces friction between internal particles and weakens its ability to resist shear loads [35]. Furthermore, as illustrated in Figure 10, at identical treatment temperatures and shear angles, high-temperature liquid nitrogen cold shock exhibited a greater effect on the peak displacement of fine-grained granite, with a smaller total displacement compared to high-temperature water-cooled shock. This phenomenon was less pronounced in coarse granite. The analysis suggests that fine-grained granite experiences greater thermal stresses under high-temperature liquid nitrogen cold shock, resulting in an increased number of thermally induced cracks. When shear loading is applied, these cracks propagate rapidly, significantly reducing the peak displacement. Furthermore, when the treatment temperature reaches 600 \({}^{\circ}\)C, both the peak load and peak displacement show a significant reduction, probably due to the \(\alpha\)-\(\beta\) phase transition of quartz (\(\geq\)573 \({}^{\circ}\)C), which causes crystal volume expansion and an increase in interparticle cracking, significantly degrading its mechanical properties [36].  
Figure 10: _Cont._  
Figure 9: Shear load–displacement curve of fine-grained granite subjected to liquid nitrogen cooling, (**a**) 45\({}^{\circ}\), (**b**) 55\({}^{\circ}\), (**c**) 65\({}^{\circ}\).