## 3 Analysis of Dynamic Performance and Energy Consumption
### Analysis of Cyclic Impact Stress and Strain  
In this paper, under the same impact load, sandstone specimen is subjected to the equal-amplitude cyclic impact until a complete destruction. In the test, the original data obtained by the ultra-dynamic strain gauge were processed, and the stress and strain were calculated using a 'two-wave method' formula [38]. The stress-strain curves of  
Figure 10: Stress–strain curves of sandstone in the first impact. (**a**) At room temperature. (**b**) At different temperatures.  
Figure 9: Relationship between first impact dynamic peak stress, peak strain, average strain rate, and temperature of sandstone. (**a**) Relationship between peak stress and temperature. (**b**) Relationship between peak strain and temperature. (**c**) Relationship between average strain rate and temperature.  
the sandstone under cyclic impact at different temperatures were obtained, as shown in Figure 11.  
The cyclic impact stress-strain curves of sandstone specimens after different high-temperature treatments are plotted in Figure 11. From Table 2 and Figure 11, it is observed that when the impact pressure is set to 0.6 MPa, the sandstone specimens are completely destroyed after two to three cycles of impact. It can be concluded from Figure 11 that, at different temperatures, the stress-strain curves of sandstone specimens after the second impact show obvious brittle characteristics compared with those after the first impact. In the second impact, the compaction and elastic stages are significantly shortened, and the initial elastic modulus significantly increases. It shows that the internal pores are compressed under the first impact, and the initial deformation is small under impact loading,  
Figure 11: Cyclic impact stress–strain curves of sandstone after different temperatures.  
but the stress increases rapidly. At 800 \({}^{\circ}\)C, the sandstone curve presents different variation laws. This is perhaps because large cracks appear in the sandstone under the first impact and the sandstone specimen is already in a failure state. Therefore, under the second impact, cracks in the sandstone develop rapidly and the deformation increases, showing an obvious plastic property. In addition, at 25 \({}^{\circ}\)C, the sandstone specimen is damaged three times by cyclic impact. Due to a development of cracks, the compaction and elastic stages of sandstone under the third impact are significantly larger than those of the second impact, which indicates that the sandstone has experienced the stages of pore compaction, crack development, and failure under cyclic loading. The results show obvious plastic characteristics. In addition, for the sandstone specimen after 200 \({}^{\circ}\)C, as analyzed earlier, the sandstone loses water, the ductility increases, and the high temperature causes a certain heat loss, resulting in a decrease in the strength. The thermal stress produces fewer cracks in the sandstone. Therefore, the dynamic characteristics under cyclic loading are similar to those under 25 \({}^{\circ}\)C, which shows a certain plasticity. Moreover, for the sandstone specimens with high temperatures of 400 \({}^{\circ}\)C and 600 \({}^{\circ}\)C, with an increase in heat treatment temperature, the brittleness of sandstone increases under repeated loads, indicating that the number and length of micro-cracks increase with the temperature. Therefore, the cracks generated by high temperature at the first impact are developed. In the subsequent impact, when temperature increases, the plasticity of sandstone decreases and the brittleness increases, resulting in an impact failure of the sandstone. When the temperature increases from 800 \({}^{\circ}\)C to 1000 \({}^{\circ}\)C, the thermal expansion of particles, thermal cracking, and clay mineral morphology of the sandstone change, leading to a cohesive failure and a development of micro-cracks in the sandstone. Thus, the strength decreases sharply and brittle failure occurs.