# Experimental Study on Dynamic Mechanical Properties of Sandstone Under Different Damage Degrees
## 5 Dynamic Uniaxial Compression Experiment and Result Analysis
### Analysis of Uniaxial Compression Experimental Results  
From the stress-strain curves of each group of rock specimens shown in Figure 11, The stress-strain curve is clearly divided into the elastic stage, plastic stage, and post-peak stage. In the initial stage of the experiment, the curves do not exhibit a concave form, contrasting with the initial stage of static loading conditions, where the elastic modulus is relatively high. This phenomenon indicates that under impact loading, the period during which the stress wave acts on the rock is short and insufficient, and the rock crack expands and propagates, resulting in the absence of a compaction stage in the stress-strain curves. The first half of each curve is approximately linear, indicating the elastic deformation stage. This indicates that during the dynamic impact experiment, the rock is subjected to a load at a nearly constant strain rate. During the plastic stage, the compressive modulus  
Figure 10: Trend chart of variations in wave velocity for different specimen types. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Specimen** & \begin{tabular}{c} **Impact** \\ **Pressure** \\ **(MPa)** \\ \end{tabular} & \begin{tabular}{c} **Strain Rate** \\ **(s\({}^{-1}\))** \\ \end{tabular} & \
\begin{tabular}{c} **Compressive** \\ **Strength** \\ **(MPa)** \\ \end{tabular} &
\begin{tabular}{c} **Cumulative Specific** \\ **Energy Absorption** \\ **Value (j/cm\({}^{3}\))** \\ \end{tabular} \\ \hline NS-13 & 0.5 & 138 & 113.3 & 1.25 \\ NS-14 & 0.6 & 166.9 & 128.8 & 1.46 \\ NS-15 & 0.7 & 226 & 138.0 & 2.15 \\ NS-16 & 0.8 & 247.9 & 140.3 & 2.55 \\ LS-13 & 0.5 & 171.2 & 109.8 & 1.77 \\ LS-14 & 0.6 & 194.4 & 119.2 & 1.87 \\ LS-15 & 0.7 & 195.5 & 136.8 & 2.28 \\ LS-16 & 0.8 & 216.8 & 138.4 & 2.60 \\ HS-13 & 0.5 & 145.6 & 105.2 & 1.82 \\ HS-14 & 0.6 & 187.7 & 115.5 & 1.92 \\ HS-15 & 0.7 & 226 & 128.8 & 2.55 \\ HS-16 & 0.8 & 279 & 131.6 & 3.09 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Dynamic uniaxial experimental parameters of rock specimens. starts to decline, indicating that the internal microcracks begin to rapidly expand and propagate under dynamic loading, causing macroscopic fractures within the rock specimen when the stress wave reaches its peak. When the stress wave generated by the impact of the spindle-shaped striker on the incident bar arrives at the contact surface between the incident bar and the rock, after a period of constant strain loading (approximately 100\(\upmu\)s), the rock strength reaches its limit and begins to fail. When the stress wave reaches the contact surface between the rock and the transmission bar, a portion of the stress wave is transmitted into the transmission bar and another portion returns to the incident bar. Subsequently, the rock enters the unloading phase. When the stress-strain curve is at the stage of post-peak, due to the occurrence of a macroscopic fracture surface within the specimen, its load-bearing capacity decreases. However, during the stress reduction process, the bars remain in contact with the rock specimen, and the compression strain continues to increase at a slower rate. This suggests that the impact load-induced damage does not disrupt the stress equilibrium state at either end of the specimen, and it also confirms that the experimental procedure adheres to the fundamental requirements of the SHPB test. According to Figure 12, there is a positive correlation between the compressive strength and strain rate of the three groups of rock specimens. This indicates that the rock material exhibits a significant strain rate effect. Meanwhile, the axial compressive strain of each group of rock specimens also showed a positive correlation with the impact load. Compared with rock specimens drilled with non-impact load, the compressive strength of rock specimens drilled with impact load is lower at various impact pressures.