# Experimental Study on Dynamic Mechanical Properties of Sandstone Under Different Damage Degrees
## 5 Dynamic Uniaxial Compression Experiment and Result Analysis
### Energy Consumption Analysis During Dynamic Uniaxial Loading  
According to the basic principles of dynamic uniaxial experiments and one-dimensional wave theory, when the spindle-shaped striker hits the incident bar, some of the energy is absorbed by the rock as the stress waves propagate from the incident bar to the transmission bar. Now, defining the energy absorbed by the rock per unit volume in the uniaxial compression experiment as \(E_{a}\), we have:  
\[E_{a}=\frac{E_{s}}{V_{s}} \tag{6}\]  
Figure 12: Variation relationship of compressive strength with strain rate for each group of rock specimens. (**a**) Variation relationship of compressive strength with strain rate for NS rock specimens. (**b**) Variation relationship of compressive strength with strain rate for LS rock specimens. (**c**) Variation relationship of compressive strength with strain rate for HS rock specimens. Figure 13: Compressive strength of each group of rock specimens under different impact pressures. where \(V_{s}\) represents the volume of the rock. According to Equations (4) and (5), we obtain:  
\[E_{s}=\frac{A_{e}}{\rho_{e}C_{e}}\int_{0}^{t}{(\sigma_{I}^{2}-\sigma_{R}^{2}- \sigma_{T}^{2})dt} \tag{7}\]  
After the rock absorbs this portion of energy, the microcracks within it will expand. The more energy absorbed per unit time, the greater the speed and extent of crack propagation. When more and more microcracks within the rock participate in the propagation and connect into macroscopic cracks, damage and fracture occur in the rock. Figure 14 shows the energy absorption of each group of rock specimens under different impact pressures. It demonstrates that the energy absorbed by each group of rock specimens increases with the increase in impact load. What differs is that the rock specimens drilled with high-impact power absorb more energy than the other groups. This is because, after drilling with a high-impact load, a certain range of rock surrounding the borehole will generate more microcracks under the radial component of the impact load. These microcracks will accelerate their propagation under the action of the incident stress wave, and the propagation of cracks requires energy consumption. The more microcracks there are, the more energy from the impact wave will be consumed. In contrast, rock specimens drilled with non-impact loads have fewer internal microcracks compared to those drilled with impact loads. Therefore, when the incident stress wave propagates through rock specimens with fewer microcracks, the energy absorbed will be relatively less. The energy absorption characteristics of each group of rock specimens can be observed through the failure modes of the rock specimens after the dynamic uniaxial compression experiment, as shown in Figure 15. According to Figure 15a, when the impact pressure value is 0.5 MPa, the sandstone is fragmented into small chunks, and when the impact pressure value reaches 0.8 MPa, most of the sandstone will be crushed into powder. This occurs because higher impact pressure leads to greater energy absorption by the rock, which in turn encourages the growth of internal microcracks. The more energy absorbed, the smaller the fragment size after failure. By comparing Figure 15a,b, it can be seen that when the impact pressure value is the same, the fragment size of HS rock specimens is smaller than that of NS rock specimens. This is because, after drilling with a high-impact load, more microcracks are generated in the surrounding rock of the borehole. More microcracks will also absorb more energy and further expand, creating more new surfaces, and resulting in smaller fragment sizes after failure. Figure 14: Energy absorption of each group of rock specimens under different impact pressures. The results of the uniaxial experiment indicate that in open-pit mining engineering, drilling blast holes with higher impact loads can cause greater damage to the zone of surrounding rock.