## 4 Experimental Validation of the Geometrical Efficiency Calculation
### Metal-Based Cage Armour Systems
#### 4.1.2 Experimental Validation  
The previously developed mathematical expressions can be validated using experimental data. Due to the confidential nature of actual cage armour performance, only limited data are available that can be used to show the validity of the developed expressions. In the following sections, the results of experimental firings on four non-fielded experimental cage armour solutions (two lamellar systems and two net systems) will be compared to the theoretical results. Case A: Lamellar Slat Armour  
Two lamellar cage armour systems were tested against the PG-7 warhead. The two systems were composed of aluminium slats with respective thicknesses D of 6 mm and 8 mm (must be as thin as possible compared to the effective diameter P of the piezoelectrical element) and relative spacing I between the slats of 55 mm and 47 mm (see Table 1 for all relevant properties). These spacings were selected to be sufficiently smaller than the effective diameter \(C_{\mathit{eff}}\) of the PG-7 warhead to avoid non-proper functioning of the cage armour system. A regular RPG-7 lawnucer mounted on a gun carriage was used to fire at the sample targets (consisting of 1.5 m \(\times\) 1.5 m prototype slat armour systems as shown in Figure 12). All impacts were made at 0\({}^{\circ}\) obliquity (NATO impact angle convention) at a shooting distance of 50 m. The impact point in reference to the slat armour was varied randomly in order to obtain a true sample (i.e., statistically independent testing) of the slat armour efficiency. The complete setup is shown in Figure 13.  
Twenty-six shots were done on the 6 mm slat solution, while 25 shots were done on the 8 mm slat solution. The experimental results showed excellent agreement with the theoretically calculated efficiencies, as shown in Table 2. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Case**} & \multicolumn{2}{c}{**Slat Armour Properties**} & \multicolumn{2}{c}{**Projectile Properties**} \\ \cline{2-5}  & \(\mathbf{D}\) **(mm)** & \(\mathbf{I}\) **(mm)** & \(\mathbf{P}\) **(mm)** & **Impact Angle (\({}^{\circ}\))** \\ \hline A & 6 & 55 & 21.5 & 0 \\ B & 8 & 47 & 21.5 & 0 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Relevant slat armour and projectile properties. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Case**} & \multirow{2}{*}{**Number of Shots**} & \begin{tabular}{c} **Short-Circuited** \\ **Fuzes** \\ \end{tabular} & \
\begin{tabular}{c} **Experimental** \\ **Probability (\%)** \\ \end{tabular} &
\begin{tabular}{c} **Theoretical** \\ **Probability (\%)** \\ \end{tabular} \\ \hline A & 26 & 14 & 54 & 55 \\ B & 25 & 11 & 44 & 46 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Experimental results for the two considered slat armour prototype systems and a comparison with their theoretical efficiencies. Case B: Steel Fibre-Based Net Armour System  
Data were also obtained on a steel net armour system against the PG-7 and PG-7L projectiles. The latter is similar in concept to the original PG-7 warhead but is equipped with a shaped charge cone with larger diameter (84 mm, giving a maximum projectile diameter of 93 mm). The net was built out of 4 mm thick high-strength steel wire with a diamond-shaped mesh. The horizontal diagonal of the diamond-shaped measured 192 mm, whereas the vertical diagonal measured 110 mm. Although most data concerns perpendicular impacts, a limited number of shots were also performed with both projectiles for a 45\({}^{\circ}\) azimuth impact angle. However, due to the very limited number of shots, the statistical value of the experimental results is limited. The different considered configurations (cases) are given in Table 3.  
Figure 12: Example of a slat armour prototype (central stiffener removed before testing). Figure 13: Test setup showing the gun carriage with the launcher and the target area.