# Mechanical Properties of Metasandstone under Uniaxial Graded Cyclic Loading and Unloading
## 2 Materials and Test Methods
### Test Methods  
Uniaxial compression tests were first conducted on metasandstone samples A01, A02 and A03, which were loaded by the force-controlled method with a loading rate of 0.5 MPa/s. The average natural uniaxial compressive strength (UCS)and elastic modulus (E) of the rock samples were measured, and recorded as R0 and E0, respectively. Uniaxial cyclic loading and unloading tests were carried out on rock samples B01, B02, B03, B04, B05, and B06, with each 20% R0 incrementing one level. A total of 5 levels of 0-20% R0, 0-40% R0, 0-60% R0, 0-80% R0, and 0-100% R0 were set, and the same rock samples were loaded and unloaded sequentially, with each level being loaded and unloaded only once (Figure 3). If the rock sample was still not damaged after the unloading of 0-100% R0, the rock sample was loaded at a rate of 0.5 MPa/s until it was damaged, which was recorded as the 6 th one-way loading.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Test Items** & **Rock Samples** & **Height/mm** & **Diameter/mm** &
\begin{tabular}{c} **Average Wave** \\ **Velocity/m s\({}^{-1}\)** \\ \end{tabular} \\ \hline \multirow{3}{*}{Uniaxial compression} & A01 & 99.85 & 50.11 & 5247 \\  & A02 & 100.29 & 49.89 & 5305 \\  & A03 & 100.18 & 50.23 & 5266 \\ \hline \multirow{3}{*}{Uniaxial staged cyclic loading and unloading} & B01 & 99.92 & 49.90 & 5282 \\  & B02 & 100.04 & 49.96 & 5255 \\ \cline{1-1}  & B03 & 100.11 & 49.83 & 5141 \\ \cline{1-1}  & B04 & 100.15 & 49.97 & 5149 \\ \cline{1-1}  & B05 & 100.12 & 50.03 & 5115 \\ \cline{1-1}  & B06 & 100.21 & 49.99 & 5182 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Basic parameters of test rock samples.  
Figure 3: Rock sample for uniaxial graded cyclic loading and unloading test.  
The test steps are as follows:  
1. Place the prepared rock sample under the working platform of the material testing machine, start the material testing machine, and make the loading end of the material testing machine slowly approach the upper end of the rock sample.
2. Start loading, use the force control mode to load the rock sample at the loading rate of 0.50 MPa/s to the preset upper limit value of the level stress, and reach the upper limit value of the level stress. Immediately, the rock sample is unloaded at the unloading rate of 0.50 MPa/s until the axial force is zero, and a complete loading and unloading cycle is completed. In this process, the data recording system and acoustic emission acquisition system of the material testing machine maintain synchronous acquisition throughout the whole process.
3. After a loading and unloading cycle, measure and record the longitudinal wave data of 5 points (0, 1, 2, 3 and 4) of the rock sample with an ultrasonic collector (Figure 4). If the test piece is macroscopically damaged, this step is terminated.
4. After the wave velocity measurement at five points of the rock sample is completed, place the metasandstone rock sample back on the working platform of the material testing machine, and prepare to start the loading and unloading test at the next level until the macro instability failure of the rock sample occurs. At this point, the test of a single rock sample is completed, and the test of the next rock sample is started.