## 2 Experimental Research
### Results  
The impact striker geometry assessment on the composite panels' destruction was made on the basis of microscopic tests. The tests allowed the authors of this article to measure the diameter of the panel damages after impact. Because of the plastic character of aramid fiber destruction, the damages in the panel reflected the striker geometry, and the depth of the penetration could be calculated based on the cavity diameter and the geometry of the used striker. The results are shown in Table 3.  
The microscope images of the damage in composite panels presented in Figure 4 show the significant influence of the striker geometry. During the same impact, the same values of impact kinetic energy and destruction level in composite panels were limited from the matrix cracking in the blunt striker case to the almost complete penetration in the conical striker case. For the blunt striker, fibers absorbed almost all impact energy--there was no fiber damage. The cracked matri  
Figure 3: Test stand used in experiment. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Striker Geometry** & \begin{tabular}{c} **Average Striker** \\ **Velocity [m/s]** \\ \end{tabular} & \begin{tabular}{c} **Average Kinetic** \\ **Energy [J]** \\ \end{tabular} & \
\begin{tabular}{c} **Average Cavity** \\ **Diameter [mm]** \\ \end{tabular} &
\begin{tabular}{c} **Average Depth of** \\ **Penetration [mm]** \\ \end{tabular} \\ \hline Conical & 30.99 & 23.5 & 5.9 & 5.1 \\ Hemispherical & 30.98 & 23.5 & 6.2 & 1.5 \\ Blunt & 30.92 & 23.4 & 7.0 & 0.1 \\ Ogival & 31.05 & 23.6 & 4.7 & 4.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Average experimental results, depending on striker geometry. sign after impact in this case. That fact proved the high resistance of fiber reinforced composites on the impact of blunt elements. Cross sections of the samples after impact of the strikers are presented in Figure 10.  
The destruction caused by a hemispherical striker was characterized by a high amount of compressed fibers. Around a newly created cavity, the characteristic bulge was formed. Fibers that were initially in the first layer of the impact area (in the center of panel) were then ripped out from the matrix. The broken and compressed fibers in this formed cavity were also visible. However, their amount was low, which proved that only fibers from the first layers were damaged, and fibers in the next layers were in good shape. There were no carbon fibers in the cavity, which suggests that the panel penetration is limited to the first four layers of the reinforced material. This was also confirmed by the calculated depth of penetration. It was circa 1.5 mm, which corresponds to the thickness of approximately of three layers of used aramid fabric. The cross section of the sample (Figure 10) also confirms that the penetration of the composite stops before the reinforcing layer made from carbon fibers was damaged. The destruction caused by an ogival striker suggests much more sensitivity of the hybrid composite to the impact of such elements. The penetration depth was much higher compared with the penetration depth in the case of a hemispherical striker. The analysis of the microscopic images shows a lot of broken fibers in the created cavity. The broken fibers were visible as sticking out parts of the reinforcing fabric directed towards to the cavity. These fibers were also compressed at the boundary of the cavity. Like in the previous case, the first layer damage around the impact zone was also visible. The penetration  
Figure 4: Selected samples after impact of the striker: (**a**) conical, (**b**) hemispherical, (**c**) blunt, (**d**) ogival. depth in this case was 4.5 mm, which corresponds to the depth of the second reinforcing layer made from carbon fibers. At the bottom of the created cavity, there were no carbon fibers, which suggests that the second carbon reinforced layer was not penetrated.