## 3 Numerical Research
### Comparison of Experimental and Numerical Research  
The results of the conducted experimental and numerical research were compared based on the diameters and depth of penetration of cavities formed after impact of the strikers. Figure 10 shows the comparison of the diameters of the cavities formed after the impact.  
The damage caused by the blunt striker in the experiment (Figure 4c) is limited to the matrix cracking. The diameter of the resulted crack corresponds to the diameter of the edge of the impacting striker. The resulting damage did not damage the reinforcing layer in any way. Performing numerical research in the selected scale makes it impossible to capture phenomena like matrix cracking, but proper analysis of the stress map could bring valuable conclusions. As discussed in the numerical research results, the obtained Tresca stress value suggests that the matrix was damaged, as in the case of the experimental research. The measured diameter of damaged area was almost the same as in the case of the experimental research. Another discrepancy between the experimental and numerical research is in the case of hitting the composite by the conical striker. During the experimental research, the pointed tip of the cone stuck between the individual fibers, pushing them sideways. Fibers pushed sideways constituted resistance for the striker, and tightened on it, thus reducing damage caused in subsequent layers. In the case of numerical research, individual fibers were not considered. Each reinforcing layer was modeled as a single part with directionally assigned properties. The indicated directions  
Figure 10: Comparison of cavity diameter formed after impact.  
Figure 9: Kinetic energy of strikers during impact depending on their geometry.  
corresponded to the directions of the fibers in the used reinforcing fabric, however, the modeling of the reinforcement in this way makes it impossible to imitate the mechanism of deformation of individual fibers. Finite elements hit directly by the tip of the cone were quickly removed. When an element was removed, it stopped absorbing the energy, so material did not resist as much energy as in the case of the experiment. This fact could have an effect for the larger amount of destruction in the case of the numerical research. The same remark applies to the discrepancy between the results obtained for the ogival striker.  
Figure 11 shows the comparison of the depths of penetration obtained as a result of the provided experimental and numerical research. For conical and hemispherical strikers, the depths of penetration obtained as a result of numerical research were larger than in the experimental research. In the case of the experimental research, depths were determined indirectly based on the diameter of the formed cavity and the striker geometry. This method could be subject to a large error, resulting from the lack of information about the damaged fibers under the visible layer of damaged reinforcement. Additionally, in the case of the numerical research, elements removed during calculations do not constitute any resistance for the strikers' movement at a later stage. In real conditions, the damaged fibers were still in the forming cavity, clamping on the striker, or accumulating in front of its forehead, thus affecting the formation of further damage. Figure 12 shows the percentage variation between the results obtained from the experimental and numerical research.  
Figure 11: Comparison of depth of penetration after impact.  
Figure 12: Percentage variation between the results obtained from experimental and numerical research.