## 3 Numerical Research
### Numerical Results
The diameter of the damaged area in this case was slightly larger than in the case of the impact of the ogival striker. The depth of penetration was based on the number of damaged reinforced layers--0.5 mm of damage for each damaged layer. The largest depth of penetration was observed for the case in which the composite panel was hit by a conical striker. As a result of its impact, 12 layers of reinforcing material were damaged. The impact with an ogival striker resulted in damage to eight layers of reinforcing material. In the case of a hemispherical striker, six layers of reinforcing material were damaged. However, these damages were different. The damage created did not resemble a cone geometry. As it was mentioned, the individual elements were deleted from 5 and 6 damaged layer (damage area was smaller than used striker). Due to that, this two layers were not considered in depth of penetration calculation. For the impact on the composite material with a blunt striker, no damage was observed in the reinforcing material, but small deformation was observed. The graph representing kinetic energy of the striker depending on its geometry is shown in Figure 9. The fastest braking of the striker occurred with a blunted one. This striker was rebounded from the composite panel, obtaining the kinetic energy of about 16 J. This testified that a small amount of energy was absorbed by the composite panel. The hemispherical striker was rebounded from the panel, obtaining a value of the kinetic energy of about 8.5 J. The braking of the striker before it was rebounded proceeded with the same intensity as in the case of a blunt striker, despite the damage caused in the reinforcing layers. A smaller value of the rebounded kinetic energy of the striker is associated with a greater amount of energy absorbed by the composite. Conical and ogival strikers had the lowest kinetic energy after rebounded (approximately 2 J). Despite the differences in the strikers' braking intensity, they were stopped at the same time and had similar kinetic energy after being rebounded. The curve depicting the kinetic energy value of the ogival striker has a distinctive area of braking corresponding to the level of material penetration. The first change in the angle of inclination of this curve at the time t \(\approx\) 0.1 ms is associated with the first damage to the material. Another angle change in the time t \(\approx\) 0.2 ms is associated with the end of damaging of the reinforcement layers. In the next phase, material was deformed without damaging and striker was inhibited and rebounded. Braking of the conical striker was the gentlest, which was probably because of the fact that its pointed end easily damaged the elements in the subsequent layers of the composite. It is interesting that the conical and ogival strikers, despite large differences in the damage caused, were characterized by the same value of the kinetic energy after rebound. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Striker Geometry** & **Cavity Diameter [mm]** & **Depth of Penetration [mm]** \\ \hline Conical & 8 & 6 \\ Hemispherical & 6 & 2 \\ Blunt & 7.5 & 0.07 \\ Ogival & 5.5 & 4 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Numerical results, depending on striker geometry.