# Study on Dynamic Strain Distribution in Rock Broken by Abrasive Slurry Jet
## 3 Experimental Data and Processing  
Figure 4 is the contour of rock strain calculated by the data analysis system, which can show the static strain distribution on rock surface. To get the rock dynamic strain, the paper chose nine data extraction points of rock strain in an experiment. All of the data extraction points are located on the intersection lines of the rock surface and three spheres, whose center is the intersection of the jet axis and top rock surface and diameters (\(r\)) are 5.4 mm, 6.4 mm, and 7.8 mm. As shown in Figure 2, with \(r_{1}\) set as the constant (5 mm), the three sphere diameters correspond to the fixed values of \(r_{2}\) (2 mm, 4 mm, and 6 mm).  
Figure 5 shows the dynamic rock strain of the three middle data extraction points under 10 MPa ASJ impacting. The dynamic value of rock strain has two characteristics. One of them is that the lower data extraction point is significantly greater than the middle and upper one in the value of rock strain, which is the result that the lower data extraction point locates in the strain concentration area (as shown in Figure 4) caused by the inherent crack in the rock. The other characteristic is that the value of rock dynamic strain fluctuates wildly because there are many influencing factors in the experiment, such as motor vibration, noise vibration, and jet pressure fluctuation.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Parameters**} & **Nozzle** & \multirow{2}{*}{**Nozzle Length**} & **Off-Stand** & \multirow{2}{*}{**Abrasive Type**} & **Abrasive Volume** \\  & **Diameter** & & & **Distance** & **Fraction** \\ \hline Details & 0.8 mm & 38.4 mm & 10 mm & Garnet & 10\% \\ \hline \multirow{2}{*}{**Parameters**} & **High-polymer** & **High-polymer** & **Shooting** & \multirow{2}{*}{**Shooting time**} & \multirow{2}{*}{**\(r_{1}\) (Figure 2)**} \\  & **mass fraction** & & & **frequency** & \\ \hline Details & Polyacrylamide & 1\% & 10,000 Hz & 0.1 s & 5 mm \\ \hline \hline \end{tabular}
\end{table}
Table 2: Details of the parameters.  
Figure 3: Flow diagram of rock process.  
To study the universal distribution law of the dynamic strain, data processing of the rock strain was carried out. Firstly, the dynamic strain values at the data extraction point located in the strain concentration area must be deleted. Then, Fast Fourier Transformation (FFT) was used in filter processing of the rock dynamic strain data.  
Figure 6 shows the filter processing of the rock dynamic strain data. In the first step, initial frequency-domain signal can be obtained by the FFT of the initial time-domain signal. In the second step, filtered frequency-domain signal can be obtained by deleting the high-frequency signal (larger than 50 Hz), which is caused by motor vibration, noise vibration, and jet pressure fluctuation. In the last step, filtered time-domain signal can be obtained by the Inverse Fast Fourier Transformation (IFFT) of the filtered frequency-domain signal.  
Figure 4: Strain distribution of rock impacted by ASJ with various pressures.  
Figure 5: Original data of rock dynamic strain impacted by 10 MPa ASJ.  
Figure 7 shows the data processing results of dynamic strain in rock broken by 10, 15, and 20 MPa ASJ. With rock impacted by ASJ under the same jet pressure, values of the dynamic strain decrease sharply with the increase of sphere diameter. When the sphere diameter keeps constant, values of the dynamic strain increase linearly with the increase of jet pressure. Moreover, the dynamic changes of strain in rock impacted by ASJ with the same pressure are similar, while the dynamic changes of strain in rock impacted by different pressures of ASJ are quite different. It reflects that rock dynamic strain distribution may be related to physical properties and fractures of rock.