## 4 Results and Discussion
### Experimental Results of CTRC
These results align with the description of stages provided in the literature on the material behavior of CTRC [1; 41; 42; 43]. Regarding the material behavior of the electrically heated specimens, the crack development stage was thus not adversely affected by the electrical current flow. The stress-strain curves depicted in Figure 14 are provided as examples and correspond to the trends observed in the subsequent experiments. For the crack analysis, the number of cracks at failure and their respective average crack widths for each test temperature were examined. The results showed that CTRC-EP-Sand exhibits more and smaller cracks compared to CTRC-P. This suggests positive bonding behavior of CTR-EP-Sand, correlated with its higher tensile strength. As discussed, this can be ascribed to the additional sanding of the CTR. With increasing temperature, a decrease from nine to seven cracks was observed for CTRC-EP-Sand in AH. In contrast,  
Figure 14: Representative stress–strain curves for uniaxial tensile loading with crack width opening of CTR-EP-Sand. Figure 13: Mean values of the ultimate strain of CTRC with standard deviation at increasing testing temperatures. this tendency was less pronounced for CTRC-P, reducing from five to four cracks. The overall reduced crack formation at higher temperatures, compared to 20 \({}^{\circ}\)C, is attributed to the softening of the coating and impregnation material of CTR, resulting in reduced bond behavior [1,44]. Additionally, it is noticeable that for CTRC-EP-Sand, electrical heating increased the number of cracks compared to AH, as seen in Figure 15, while reducing the average crack width. Therefore, the authors assume that EH has a positive effect on crack distribution by promoting the occurrence of numerous small cracks. However, this effect is more pronounced in CTRC-EP-Sand. The authors assume that the flow of the electric current induces post-curing of the epoxy resin impregnation material. In a thermosetting plastic, re-crosslinking is an inherent possibility, which could enhance bond behavior and explain the positive effect on the number of cracks. Conversely, for polystyrene, an amorphous thermoplastic, this phenomenon cannot occur. For further investigation, Figure 16 shows representative crack patterns immediately before failure for the CTRC uniaxial tensile specimens sorted by EH and AH at rising test temperatures. Additionally, the weft fiber strands are shown schematically. The increased number of cracks for CTR-EP-Sand is depicted in Figure 16. However, no influence on the crack pattern, such as an irregular width across the entire cross-section or a bulging trajectory, can be observed with EH. Therefore, in the event of a crack occurring in the composite structure and being influenced by electrical heating, it can be assumed that the crack distribution will be typical. Figure 15: Crack analysis of CTRC—mean values with standard deviation: (**a**) number of cracks at failure; (**b**) average crack width at failure. Additionally, the ratio of crack count in the failure state was analyzed to characterize crack formation. Comparing the ratio of crack count in the failure state to the available number of wet rovings in the measurement range, no discernible trend was observed with increasing temperature for the examined materials and testing methods, cf. Figure 12.0  
Figure 12.1 Exemplary crack pattern of the investigated materials immediately before failure. The textile reinforcement grid is symbolized by the dashed lines: (**a**) CTRC-EP-Sand-EH; (**b**) CTRC-EP-Sand-AH; (**c**) CTRC-P-EH; (**d**) CTRC-P-AH. Moreover, for CTRC-EP-Sand, the ratio of crack count to weft rovings is greater, attributed to additional sanding, than for CTRC-P. Furthermore, an increase in crack numbers was noted for the tested materials with EH. This can be attributed to the discussed post-curing of the epoxy resin impregnation material.