## 4 Conclusions  
Impact damage detection using sensors made of different types of carbon fiber tows has been demonstrated on rectangular coupons made of a prepreg glass fabric composite. According to obtained results, it is possible to detect barely visible impact damage of glass fabric composite using integrated CFS. Different ways of positioning the sensors in the lay-up were investigated. According to our investigation, it is better to place the CFSs on the side opposite to an impact, rather than on the impacted side. If a CFS is positioned on the side opposite to the impact, there is a bigger probability that the impact can be detected. Integrating the sensor in the middle of the lay-up is not convenient for impact damage detection. The Pan type of fiber tow used for integrated CFS showed stable cyclic loading behavior. Sensors made of pitch carbon fiber tows were more sensitive to cyclic loading. For industrial applications with a lot of cyclic loading, a more extensive experimental campaign on the influence of cyclic loading on the measured signal need to be done. It is not advisable to manufacture CFSs using extremely brittle pitch carbon fiber tows (Pitch 95 A), because the contact quality cannot be guaranteed, and there are difficulties when manufacturing the sensor and during handling (during integration into the structure). The difficulties came from the brittleness of the Pitch 95 A fiber itself. It is assumed that failure occurred in the contact zone between the filaments and the solder. The handling of the CFS made of 70 A and T300 material is problem-free for the manufacturing operator. Moreover, no damage after manufacturing was observed using active thermography for specimens with sensors made of 70 A and T300 material. Figure 14: Non-destructive testing using CT: (**a**) specimen T300-18 (zoom = 150%), (**b**) specimen 70A-8 (zoom = 150%), (**c**) specimen 95A-12 (zoom = 150%). \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**CFS between Layers** & **T300** & \multicolumn{3}{c}{**95A**} & \multicolumn{2}{c}{**70A**} \\ \hline \multirow{4}{*}{1–2} & 30 & IV 1  & 1 & 1 & IV & 1 & DEC \\  & 31 & IV & 2 & IV & 2 & CH \\  & 32 & IV & 4 & ND & 3 & DEC, CH \\  & 33 & INV & & & & \\ \hline \multirow{4}{*}{4–5} & 34 & ND & 5 & INV & \(\frac{4}{5}\) & IV \\  & 35 & ND & 7 & INV & 5 & INV \\  & 36 & INV & 8 & INV & 6 & INV \\  & 37 & INV & & & & \\ \hline \multirow{4}{*}{7–8} & 16 & IV & 9 & INV & 7 & ND \\  & 17 & IV & 11 & IV & \(\frac{8}{5}\) & IV, DEC \\ \cline{1-1}  & 18 & IV & 12 & INV & 9 & DEC \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Results of a thermographic inspection after impact loading. The influence of the mechanical loading on the change in the electrical resistance of the integrated Pan T300 CFS and Pitch 70 A CFS is small in comparison with the effect of barely visible impact damage. It has been shown that it is possible to distinguish the change in the electrical resistance of all types of CFSs resulting from mechanical loading. The response to the temperature of the CFSs has been described, and the temperature effect can be eliminated during the measurements. Active thermography inspection using the CFS as a heating element can be applied for inspection and also for impact damage detection in combination with CFSs. Conceptualization, N.S. ; methodology, N.S. and J.M. ; formal analysis, N.S. and J.M. ; investigation, N.S., J.M., R.S., T.K. and J.S. ; resources, N.S. and J.M. ; data curation, N.S. and J.M. ; writing--original draft preparation, N.S. ; writing--review and editing, R.S., T.K., M.R. and A.H.; visualization, N.S. and J.M. ; supervision, M.R. and A.H.; project administration, N.S. ; funding acquisition, M.R and A.H. All authors have read and agreed to the published version of the manuscript. This research was funded by Bayerisch-Tschechische Hochschulagentur, grant number BTHA-AP-2019-16.