## 4 Results and Analysis of Impact Tests
### Energy Dissipation Characteristics of Specimens  
Combining Equations (1)-(8), the energy parameters including the incident, reflected energy, transmitted and dissipated energy, and the dissipated energy density of the specimens under dynamic loads could be easily derived. The dissipated energy is applied to prompt the occurrence, development and intersection of fractures in specimens, and the crushing dimension is mainly used to drive the initiation, propagation and coalescence of cracks inside the sample, and the dissipated energy density index could reflect the severity of the damage. The larger the index value, the more energy is absorbed by the specimen, the more violently the specimen is broken and the smaller the fragment of the sample. Table 3 shows the energy index value of each sample suffering from dynamic loads, and we observed that the incident energy of the samples subjected to dynamic loading is between 133.16 J and 145.69 J. Theoretically, the impact velocity and incident energy of each group of specimens at 0.45 MPa nitrogen pressure should be exactly the same. The main causes for the gap in incident energy may be: first, there are some differences in the weight of nitrogen gas filled in the excitation device every time; second, the speed of opening the switch of the excitation device is different, resulting in different speeds of releasing nitrogen; third, the striker was not manually placed in the same position in each experiment.  
According to Table 3, it is calculated that the average dissipated energy densities of the above specimens are: 1.64 J/cm\({}^{3}\), 1.87 J/cm\({}^{3}\), 1.89 J/cm\({}^{3}\), 1.78 J/cm\({}^{3}\), 1.81 J/cm\({}^{3}\), 1.53 J/cm\({}^{3}\) and 1.71 J/cm\({}^{3}\). Apparently, the absorbed energy of the specimen containing three circular holes under impact loads is the smallest, whilst that of the specimen with two circular holes arranged in a horizontal direction is the largest. Compared with the intact specimens, the dissipated energy density of the specimen with holes is basically high. However, for samples with holes, the basic law is that the higher the dynamic compressive strength, the larger the dissipated energy density. Thus, the change law of the dissipated energy density of the rock specimens with holes is completely similar to that of the dynamic compressive strength among the several classes of specimens.  
To figure out the failure features of rock samples under dynamic loads, the fractal geometry method was employed to characterize the fragment distribution of the specimens. Generally, the larger the fractal dimension, the more severe the sample fails and the smaller the fragment. As shown in Figure 4, a rock debris collection box was placed on the pedestal  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Specimen Number** & \(W_{\text{J}}\)**/**J** & \(W_{\text{R}}\)**/**J** & \(W_{\text{T}}\)**/**J** & \(W_{\text{S}}\)**/**J** & \(\rho_{\text{w}}\)**/J**-cm\({}^{-3}\) \\ \hline G1-A & 142.08 & 52.69 & 22.57 & 66.82 & 1.62 \\ G1-B & 136.65 & 44.31 & 28.83 & 63.51 & 1.58 \\ G1-C & 140.35 & 40.89 & 27.32 & 72.14 & 1.71 \\ G2-A & 143.46 & 57.15 & 10.80 & 75.51 & 1.95 \\ G2-B & 144.97 & 62.06 & 9.72 & 73.19 & 1.86 \\ G2-C & 142.35 & 61.41 & 10.45 & 70.50 & 1.80 \\ G3-A & 143.69 & 49.00 & 20.43 & 74.27 & 1.87 \\ G3-B & 144.41 & 55.10 & 13.73 & 75.57 & 1.91 \\ G3-C & 142.85 & 47.65 & 20.52 & 74.67 & 1.89 \\ G4-A & 140.69 & 61.66 & 9.89 & 69.14 & 1.76 \\ G4-B & 141.96 & 62.25 & 9.18 & 70.53 & 1.82 \\ G4-C & 145.51 & 64.89 & 10.08 & 70.55 & 1.76 \\ G5-A & 143.38 & 68.47 & 8.33 & 66.58 & 1.76 \\ G5-B & 145.69 & 65.40 & 9.72 & 70.57 & 1.86 \\ G5-C & 143.47 & 66.20 & 7.74 & 69.53 & 1.81 \\ G6-A & 141.72 & 53.62 & 18.03 & 70.07 & 1.72 \\ G6-B & 150.02 & 69.50 & 14.22 & 66.31 & 1.67 \\ G6-C & 133.16 & 49.25 & 14.76 & 69.14 & 1.73 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Energy index value of the sample under dynamic load.