## 3 Results and Discussion
### Active Thermographic Inspection and Computer Tomography  
An active thermographic inspection of the specimens before loading revealed damage to the electrical contacts of the sensors made of pitch carbon fiber tow 95 A. The temperature profile along the sensor with the damaged contact area is shown in Figure 12. In Figure 13. The temperature profile of a sensor without any pre-damage is depicted. Six out of 9 specimens with implemented sensors made of material 95 A were definitely damaged during manufacturing or during implementation. Two specimens were indeterminate regarding damage to the sensor, and no data were provided for one specimen. This demonstrates the sensitivity for the structural integration of carbon fiber sensors made of brittle ex-pitch filaments.  
Specimens T300-16, T300-17, 95 A-11, 95 A-12, 70 A-8, 70 A-7 were investigated after 200 cycles of flexural loading and before impact loading. No signs of damage caused by flexural cyclic loading were observed for specimens with a T300 sensor. Damage to the electrical contacts could be detected for specimens 95 A-11, 95 A-12. The temperature profile along the sensor changed slightly after cyclic loading in the case of sensors 70 A-7 and 70 A-8.  
Figure 11: Electrical resistance of integrated sensors as a percentage of the value of a pristine sensor after implementation-results for specimens with CFős made of material 95 A.  
Figure 12: Active thermographic inspection: (**a**) 95 A-11 before loading, (**b**) 95 A-11 after 200 cycles of cyclic flexural loading, (**c**) 95 A-11 after impact.  
Sensors made of pitch 70 A carbon fiber tow and sensors made of pan T300 carbon fiber tow showed no signs of damage before loading.  
The specimens were thermographically inspected again after impact loading. The results of this observation are given in Table 5. Based on our measurements, T300 has the greatest potential for use as a heating element for active thermography. It was possible to detect the impact if the sensor was on the impacted site, and if the sensor was on the opposite side of the specimen to the impact. Based on observations with CFSs made of material 95A, the impact can also be detected by a sensor with damaged electrical contacts. In the case of specimens with an integrated CFS made of material 70 A, damage to the electrical contacts was observed for specimens 70 A-1, 70 A-3, and 70 A-9 after cyclic loading and impact loading. Unfortunately, only two specimens for each type of CFS were observed.  
Figure 13: Thermographic inspection: (**a**) 70 A-8 before loading, (**b**) 70 A-8 after 200 cycles of 3 PB, (c) 70 A-8 after impact, (**d**)–T300-30 after impact.  
material were inspected thermographically after 200 cycles, and before impact loading, for material type 70 A, specimens 70 A-7 and 70-8 were checked. Therefore, based on data from active thermography, it is not possible to determine whether the damage to the electrical contacts was caused by impact loading or by cyclic loading.  
Three specimens of each type of carbon fiber tow underwent CT, see Table 1. No signs of damages were detected using CT. Different sizes of the inserted carbon fiber tow are illustrated in pictures made by CT, see Figure 14.