# Impact of Soil on the Penetration of Prefabricated Spherical Fragments and Its Protective Effect
## 2 Experiments on Fragment Penetration into Soil
### Experimental Results  
From Table 1, it can be seen that 8 tests were conducted using 6 mm and 11 mm prefabricated tungsten alloy fragments in this experiment, with speeds ranging from 689 m/s to 1761 m/s (6 mm diameter) and 596 m/s to 1325 m/s (11 mm diameter). Fragments with a diameter of 6 mm cannot penetrate soil media with a thickness of 300 mm, while fragments with a diameter of 11 mm can penetrate that soil media. Figure 4 shows the front target and behind target results of fragments penetrating the soil medium in the experiment. From Figure 4, it can be seen that on the front and rear target papers, in addition to large holes created when the fragments passed through, there is also a dense grouping of small holes left by sand splashing in the target box. Due to the looseness of soil as a medium, the trajectory left by fragments penetrating the soil medium under the influence of soil gravity is quickly buried. Therefore, the next main focus is on studying the velocity changes in prefabricated fragments. Figure 3: Six channel tachometer. Figure 2: Physical diagram of the experimental set-up. (**a**) is the launched projectile structure; (**b**) is the experimental testing equipment. Study on the Effect of Prefabricated Fragments Penetrating into the Soil Based on Numerical Simulation  
In this part, in order to further study the mechanism of fragments penetrating into soil medium, firstly, the simulation model parameters of tungsten alloy and soil are obtained by using numerical modeling software based on the experimental results, so as to carry out the next part of the research and calculations. In practice, the motion parameters and initial conditions of fragments are relatively random, so it is necessary to simulate the penetration of fragments into soil at different speeds and angles. Combined with the common soil fortification forms in engineering, it is necessary to study under what conditions the protection conditions are effective, so a soil boundary condition analysis method is designed below, and the fragment motion parameters and protection parameters under this condition are obtained based on the simulation results. In order to study the penetration effect of fragments penetrating soil under various conditions, the authors used LS-DYNA software to numerically simulate the penetration process of spherical tungsten alloy fragments. By comparing the residual velocity of fragments under the same initial conditions, the soil medium model parameters were modified. In the numerical simulation, the JC model [18; 19; 20] was used for tungsten alloy spherical \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**No.**} & **Fragment** & **Type of** & **Speed Measurement in** & **Speed Measurement** & **Ability to** \\  & **Diameter (mm)** & **Target Plate** & **Front of Target (m/s)** & **Behind Target (m/s)** & **Penetrate** \\ \hline
1 & 6 & Soil & 1269.05 & 0 & Unable \\
2 & 6 & Soil & 1144 & 0 & Unable \\
3 & 6 & Soil & 1761 & 15.67 & Able \\
4 & 6 & Soil & 1533.58 & 0 & Unable \\
5 & 6 & Soil & 985.03 & 0 & Unable \\
6 & 6 & Soil & 885.44 & 0 & Unable \\
7 & 6 & Soil & 763.28 & 0 & Unable \\
8 & 6 & Soil & 689.55 & 0 & Unable \\
9 & 11 & Soil & 1060.85 & 157.69 & Able \\
10 & 11 & Soil & 721.46 & 87.35 & Able \\
11 & 11 & Soil & 1154.10 & 121.31 & Able \\
12 & 11 & Soil & 1178.23 & 173.18 & Able \\
13 & 11 & Soil & 902.86 & 75.04 & Able \\
14 & 11 & Soil & 755.62 & 83.96 & Able \\
15 & 11 & Soil & 596.23 & 121.94 & Able \\
16 & 11 & Soil & 1325.50 & 398.68 & Able \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Experimental conditions and results of prefabricated fragments penetrating soil. Figure 4: Results of fragment penetration into the soil medium in front of and behind the target. fragments, and the \"Soil_and_Foam\" (keyword name) model [4; 6] was used for soil media. The detailed parameters of both models are shown in Tables 2 and 3, respectively.