## 3 Results  
### Results of the Hopkinson Test  
The data measured by [PERSON]'s test are shown in Table 1, and the stress-strain curve is shown in Figure 6.  
From Table 1, it can be seen that when the initial damage state of the rock samples is certain, both the strain rate and the peak stress keep increasing with the increase in the confining pressure. When the rock samples are in the no-damage state, the change in strain rate is the largest, increasing from 153 s\({}^{-1}\) to 188 s\({}^{-1}\). The increase in the confining pressure also increases the peak stress of the rock samples. However, the effect of initial damage on  
Figure 5: Flowchart of 3D model reconstruction. the strain rate and peak stress was opposite, and a decrease in both the strain rate and peak stress occurred with increasing damage. The stress-strain curve under no damage and confining pressure of 5 MPa is taken as a typical stress-strain curve for analysis, as shown in Figure 6a. The stress-strain curve can be roughly divided into four stages: compaction stage (OA segment), elastic deformation stage (AB segment), plastic deformation stage (BC segment), and post-peak stage (CD segment). \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Damage Degree** & **Impact Air Pressure** & **Confining Pressure/MPa** & **Average Strain Rate /s\({}^{-1}\)** & **Peak Stress /MPa** \\ \hline \multirow{4}{*}{No damage} & & 5 & 153 & 270.10 \\  & & 10 & 165 & 328.49 \\  & & 15 & 173 & 397.13 \\  & & 20 & 188 & 450.12 \\  & & 5 & 150 & 263.67 \\  & & 10 & 164 & 321.01 \\  & & 15 & 165 & 390.77 \\  & & 20 & 176 & 447.45 \\  & & 5 & 152 & 250.72 \\  & & 10 & 160 & 309.78 \\  & & 15 & 167 & 382.87 \\  & & 20 & 170 & 444.72 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Test results of granite under different states. Figure 6: Stress–strain curves of granite under different states. Compaction stage (OA segment): From the stress-strain curve, the slope of the curve in this stage is smaller than that of the elastic stage. During this stage, the minor fissures and cracks within the rock sample are compacted [29]. As confining pressure increases, this stage becomes more pronounced. But the initial damage has the opposite effect. The reason for this is that the increase in initial damage leads to an increase in the number of fissures in the rock sample, which causes changes that delay the microcracks from closing before the impact load begins to develop, and the sample directly enters the next stage, showing a decrease in peak stress in mechanical properties. Elastic deformation stage (AB segment): In this stage, the stress-strain curve is close to a straight line, and the slope can be used as the dynamic elastic modulus of the rock sample. After the compaction stage, the internal components of the rock sample are in more thorough contact, and the sample undergoes elastic deformation under load. It can be seen from Figure 6b-d that the slope of this stage increases with the increase in confining pressure, while the duration of the elastic deformation stage decreases. Plastic deformation stage (BC segment): After entering this stage, the tangent slope of the stress-strain curve decreases continuously, and the stress exhibits certain fluctuations and reaches a peak. The reason for this is that the independent pores and microcracks in the rock sample begin to expand first; when they expand to a certain extent, relatively independent pores and microcracks gradually connect to form larger interconnected fissures. When the confining pressure increases to 15 MPa, the stress-strain curve in this stage shows a smoother trend. The existence of confining pressure makes the development of microcracks in rock samples more stable. Post-peak stage (CD segment): As the deformation continues, the stress of the rock sample gradually declines after reaching its peak. Although strain continues to increase, the rate of increase becomes progressively smaller. This indicates that a few microcracks within the rock sample are still expanding during this stage.