## 3 Results and Discussion
### Evaluation of the Degree of Recovery of CFRP by the DMA Method  
Figure 6 shows the elastic modulus E' at different frequencies for CFRP samples based on a binder with a self-healing effect (with thermoreversible bonds) and a reference sample. For all the studied samples, the modulus of elasticity practically does not change after 1 Hz. The values of E' for CFRP samples based on binders with thermoreversible bonds (\(\sim\)24 GPa) are two times lower than those for control samples (\(\sim\)53 GPa). Quite often, non-linear dependences of strength or elastic modulus on loading rate are observed when determining mechanical characteristics in a wide range of loading rates, which are associated with changes in the fracture mechanism or the response of the material to external influences [33; 34; 35]. In our case, the change in the elastic modulus with increasing loading rate is associated with the transition from quasi-static loading rates (less than 1 Hz) to dynamic ones. Notches significantly reduce the modulus of elasticity CFRP. When a crack is applied with a length of 0.25 of the total length of the sample, the values of the modulus E' decrease to \(\sim\)41 GPa for control CFRP and to \(\sim\)20 GPa for CFRP based on a binder with thermoreversible bonds. Even more noticeably, the elastic modulus decreases at a notch equal to 0.5 of the sample length: to \(\sim\)17 GPa for the control CFRP and to \(\sim\)13 GPa for CFRP with the self-healing effect. Thus, it can be argued that the chosen parameter (elastic modulus E') is sensitive to the presence of a crack. Figure 7 shows the curves of E' versus f for samples of CFRP based on a binder with a self-healing effect with a relative crack length of 0.25 for different times of the self-healing process at 80 \({}^{\circ}\)C exposure. It can be seen that the values of the modulus of elasticity E' CFRP after heat treatment (curve 3) are higher than the values of E' after cracking (curve 2) and approach the level of the modulus of elasticity for CFRP samples without a notch (curve 1). Figure 6: Elastic modulus E’ of CFRP based on control binder (1, 2, 3) and binder with thermoreversible bonds (4, 5, 6). 1, 4—reference sample; 2, 5—with crack 0.25; 3, 6—with crack 0.5. A similar change in elastic modulus levels for heat-treated CFRP, after a self-healing cycle, is observed for samples with a notch of 0.5 relative to the total length (Figure 8). It should be noted that even with an increase in the length of the notch and the subsequent decrease in the elastic modulus (curve 2), after heat treatment, the values of E' (curve 3) approach the reference level (curve 1). Figure 9 shows the elastic modulus E' versus holding time at 80 \({}^{\circ}\)C. It can be seen that all values of the modulus of elasticity of the samples after heat treatment are higher than the values of E' CFRP without heat treatment of the cracked samples. For both types of samples with a relative crack length of 0.25 and 0.5, a decrease in the elastic modulus is observed after 48 h. The E' values of samples with a crack of 0.25 and 0.5 at 48 h are closest to the E' values of the reference sample. Figure 7: Elastic modulus E’ of samples of CFRP based on a binder with thermoreversible bonds: after 120 \({}^{\circ}\)C for 25 min and at 80 \({}^{\circ}\)C for 24 h (a); 48 h (b) and 72 h (c); 1—reference sample; 2—with crack 0.25, 3—after heat treatment. Thus, it can be assumed that the most optimal exposure time for samples during heat treatment is 48 h. Based on this, heat treatment of CFRP macrosamples for crack resistance was carried out at 120 \({}^{\circ}\)C for 25 min and at 80 \({}^{\circ}\)C for 48 h.  
The generalized data on the self-healing effects of CFRP at different heat treatment times are shown in the Table 2.  
Figure 8: Modulus of elasticity E’ of CFRP samples based on a binder with thermoreversible bonds: after 120 \({}^{\circ}\)C for 25 min and at 80 \({}^{\circ}\)C for 24 h (a); 48 h (b) and 72 h (c); 1—reference sample; 2—with crack 0.5, 3—after heat treatment.