# Double-Bend and Semi-Spherical Energy Deflectors' Blast Load Efficiency--A Comparative Study
## 4 Results and Discussion
### Numerical Analyses of the Double-Bend Deflector  
As mentioned earlier, in the case of double-bend deflectors, the effect of changing two characteristic dimensions on their ability to dissipate energy from the detonation of an explosive charge was considered. This ability was determined by recording the deflection of the ballistic pendulum and determining its maximum value. Analyses were carried out for three distances of the explosive charge from the pendulum mounting plate: 30, 40, and 50 cm. The recorded deflections for all considered cases are presented in Figure 15. Analyzing the graphs below, we can see that the curves for the cases wherein the B-dimension (the distance in the vertical plane from the edge of the deflector to the second bend) was constant, while the A-dimension (the distance in the horizontal plane from the edge of the deflector to the second bend) was differentiated, are relatively close. For all three distances analyzed, the difference between the extreme deflections (the best and worst cases) did not exceed 10% and was 7.4%, 6.4%, and 8.9% for stand-offs of 30, 40, and 50 cm, respectively. In the case of deflectors in which the A-dimension was constant and the B-dimension was differentiated, we observe a much wider distribution of curves (Figure 16). In this case, the difference between the smallest and largest pendulum deflection values obtained is 15.6%, 10.6%, and 10.5%, respectively, for the considered stand-offs. For a distance of 30 cm, the scatter of these values expressed as a percentage is more than double that of the constant B-size variant. For larger distances, the difference is reduced, but it is still significant. This distribution of curves suggests that for double-bend deflectors, the change in the B-dimension is more critical for the energy dissipation capacity than the A-dimension. Figure 14: Swing of the ballistic pendulum for 50 g explosive charge and 30 cm stand-off (solid line—experiment, dashed line—FEM results). \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Deflector Type**} & **Pendulum** & **Pendulum** & \multirow{2}{*}{**Difference [\%]**} \\  & **Swing—Experiment** & **Swing—Numerical** & & \\  & **[mm]** & **[mm]** & \\ \hline Double-bend 100-15 & 62.79 & 58.62 & 6.64 \\ Semi-spherical 50 & 57.91 & 54.66 & 5.61 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Comparison of experimental and numerical results. Figure 15: Swing of the pendulum—double-bend deflector with constant B-dimension. (**a**) Stand-off of 30 cm; (**b**) Stand-off of 40 cm; (**c**) Stand-off of 50 cm. The change in the value of the maximum tilt is well illustrated by the curves presented in Figure 17. The first one shows the variant when the A-dimension is constant (Figure 17a). The change in deflection with increasing distance of the explosive charge has a linear character in most cases. The only clearer bend in the curve can be observed only for deflectors 60-15 (solid red line) and 80-15 (solid black line). Here, too, it is clear that the smallest deflection value was obtained for the variant when the A-dimension equaled 60. Figure 16: Swing of the pendulum—double-bend deflector with constant A-dimension. (**a**) Stand-off of 30 cm; (**b**) Stand-off of 40 cm; (**c**) Stand-off of 50 cm. Subsequent increases in this dimension only resulted in a deterioration of the deflector's ability to dissipate energy. For a fixed B-dimension (Figure 17b), the distribution of the curves is similar. Again, the vast majority show a linear character. Against this background, the 80-45 (black dashed line), 80-40 (green dashed line), and 80-30 (solid blue line) deflectors stand out, where we can observe an evident bend for a distance of 40 cm. Such a change means a sharp increase in energy dissipation efficiency for distances greater than 40 cm in their cases.