## 3 Results and Discussion
### Impedance Analysis, 3D SHM Damage Localization  
Damage mapping was also performed for the 3D composite. Reference IS scans were taken for each of the 27 loci at the junction points of the carbon fabric strips, at three different levels (Figures 8-13, black curves). As aforementioned, the projectile impacted the centre of the laminate. The impedance magnitude Bode plots before (black curves), and after the damage (red curves) of the front side of the composite are presented in Figure 8. As can be observed, the impact affected the laminate between locations (1,2,1) and (2,2,1). A minor increase in the measure of the impedance was also detected at the locus (3,2,1). The rest of the area of the top three laminas of the composite remained intact, as shown by the Bode plots of the impedance magnitude. Figure 8: Impedance results for SHM mapping of the front group of laminas in the smart composite with 3D mapping capabilities (Bode plots). Figure 7: Impedance results for SHM mapping (Nyquist plots). Figure 9: Impedance results for SHM mapping of the front group of laminas in the smart composite with 3D mapping capabilities. (**a**) Phase delay Bode plots and (**b**) Nyquist plots. Figure 11: Impedance results for SHM mapping of the intermediate group of laminas in the smart composite with 3D mapping capabilities. (**a**)Phase delay Bode plots and (**b**) Nyquist plots. Figure 10: Impedance results for SHM mapping of the intermediate group of laminas in the smart composite with 3D mapping capabilities (Bode plots). Figure 9a illustrates the Bode plots of the phase delay of the front group of laminas. As can be observed, the changes in the phase delay after the impact test are almost negligible. As seen in Figure 9b in the relevant Nyquist diagrams, smaller changes were observed after the introduction of damage compared to the laminate with 2D SHM tomography illustrated in Section 3.1 Damage was more distinct only for locations (1,2,1) and (2,2,1). This probably occurred due to the thickness of the scanning area. Regarding the laminate with 2D SHM tomography, the scan took place through the entire thickness of the 8-ply laminate, in contrary to the laminate with 3D SHM tomography, in which every scanning level consisted of only three plies, resulting in a greater crack and microcrack accumulation. This damage accumulation was reflected in both real and imaginary parts of the impedance. Figure 10 depicts the magnitude of the impedance versus frequency plots of the IS scans which were performed on plies 4-6. The projectile inflicted the same pattern of damage on the intermediate group of laminas as the laminas at the front side of the composite. IS measurements revealed that the area most damaged by the impact was in locations (1,2,2) and (2,2,2). Simultaneously, a slight increase in the magnitude of the impedance occurred in location (3,2,2), pinpointing less significant damage. In Figure 11a the phase delay Bode plots before and after the impact test of the intermediate group of laminas are presented. As in the case of the plots of the front group, differences after the introduction of the damage were insignificant. According to the Nyquist plots (Figure 11b), the damage was indicated in the junction points of the carbon fibre strips with coordinates (1,2,2), (2,2,2) and (3,2,2). It should be noted that in the locus (3,2,2) damage is more manifested by the Nyquist plot, and not by the Bode plot of the impedance magnitude. The rear side of the laminate is analysed in Figure 12, which illustrates the IS measurements for laminas 7-9 before and after the impact test. In this case, more extensive damage was detected than in the front and the intermediate group of laminas. The highest increase of the magnitude of the impedance can be observed in loci (1,2,3) and (2,2,3), which was the area where the most intense damage occurred.