The observed values of the mechanical parameters are given in
Section 3.1.1 (
Table 4,
Table 5,
Table 6,
Table 7,
Table 8 and
Table 9). A comparison of these values can be seen in the following graphs (
Figure 7 and
Figure 8). It can be seen in the graph that the highest compressive strengths (f
c) after 28 days were reached by mixture A, which contained only microparticles, with a value of 146.9 MPa. On the other hand, the lowest value of 104.7 MPa was achieved by mixture B, which contained a substitute in the form of an aggregate fraction of 0/2 mm and microsand with a fraction of 0.3 to 0.8 mm. A similar compressive strength was achieved by substituting C, 109.8 MPa, which contained, in addition to aggregates of the 0/2 fraction, 0.1 to 0.6 mm. In contrast, mixes D, E, and F, which contained more types of fractions, recorded compressive strengths of 121.9 MPa, 136.3 MPa, and 129.8 MPa, respectively. The results show the dependence of compressive strength on the grain size curve, with a more optimal and uniform distribution of fractions, i.e., limiting the use of one type of microsand or one fraction results in an increase in the compressive strength by up to 23%. The lowest flexural tensile strength values were achieved by mixes B and C, at 22.7 MPa and 23.5 MPa, respectively. However, the highest values were 33.9 MPa for substitute F and 29.1 MPa for reference substitute A, which can be attributed to the high degree of homogeneity and cohesion of the matrix with fibre reinforcement.
The damage sizes of the samples according to the individual dimensions are given in
Table 10. Considering the standard deviations, the observed depth of penetration (DOP) did not show a significant increasing or decreasing trend, with all measured values ranging from 22.6 to 25.5 mm (
Figure 9). The difference in these values of 2.9 mm corresponded to less than 6% of the total thickness of the tested samples. On the contrary, an increasing linear trend can be seen in the case of the dependence of the entrance crater diameter on the compressive strength (
Figure 10). With increasing strength, the diameter of the entrance crater increased from 52.6 mm at 104.7 MPa to 63.0 mm at 146.9 MPa. The difference between these two extreme values was 10.4 mm at 42.2 MPa, which means a difference of 16.5% in the diameter of the crater and 28.7% in compressive strength. In this case, it is necessary to consider the relatively small standard deviations, which, although they did not exceed more than 5% of the overall average, amounted to almost 27% in terms of the difference between the highest and lowest values. A similar increasing trend is evident in the case of the size of the area of the entrance crater (
Figure 11). Here, the linear increase in the crater surface area with increasing compressive strength is clearly seen. The size of the entrance crater areas ranged from 4011 mm
2 at a compressive strength of 104.7 MPa to a value of 5072 mm
2 at 146.9 MPa. In terms of growth, the difference between the two extreme intrusions was 1061 mm
2 at 42.2 MPa or an increase in the area of 21% with an increase in strength of less than 29%. This trend only confirms the effect of the compressive strength on the magnitude of the damage and, in general, the resistance of the composite to projectile impact [
5,
19,
20]. The increased size of the crater with increasing compressive strength can be attributed to the composite’s higher mechanical energy absorption capacity. For similar material compositions, a composite with higher compressive strength can absorb a greater amount of projectile energy, resulting in more significant damage in the form of a larger entry crater [
21]. A relatively similar increasing trend is evident in the exit crater area and flexural tensile strength (
Figure 12 and
Figure 13). In the interval of up to 25 MPa, the increase in area size was significantly higher, from 6712 mm
2 at 22.7 MPa to 7828 mm
2 at 24.0 MPa. Therefore, this was an increase of 1116 mm
2 with an increase in flexural strength of 1.3 MPa. The growth in the other three mixes was only 900 mm
2 with an increase of 9.9 MPa. This phenomenon can again be attributed to the higher energy absorption in the rear of the specimen, resulting in a larger exit crater after the projectile passes through. The behaviour described above on the entrance and exit sides of the crater corresponds to deformation models of thin-walled structures [
6,
7,
8,
9].