## 3 Results and Discussion
### Evaluation of the Degree of Recovery of Carbon Plastics during Delamination of a Macrosample  
Figure 10 shows the load curves for CFRP based on a thermoreversible binder before and after heat treatment. The CFRP samples that are delaminated for the first time (Figure 10a), before reaching the critical force or the maximum load at which the crack grows, are deformed elastically. After reaching the maximum force, the crack grows, which is accompanied by load fluctuations. Load fluctuations indicate that the rate of crack propagation is not constant. After the crack had grown to a predetermined length, the sample was unloaded. Then, the cycle of loading--crack growth--unloading was repeated several times. For secondarily layered CFRP, i.e., after crack propagation and heat treatment, the load diagrams do not change. At the same time, the character of crack propagation remains unchanged. It should be noted that the level of critical load peaks in \"recovered\" CFRP is lower. Preservation of the form of loading diagrams for macrosamples of carbon plastics before and after the recovery cycle indicates that the \"healing\" process in damaged materials is possible [37; 38].  
In Figure 11, for both samples with the effect of self-healing, the values of crack resistance are shown separately from the length of the crack before and after heat treatment. The G\({}_{\text{IR}}\) values noticeably decrease with increasing crack length. Such a change in the crack resistance parameter as a function of the crack length is not typical for fibrous reinforced plastics based on matrices without the self-healing effect. Typically, crack resistance remains virtually unchanged with crack lengthening or may increase. An increase in crack resistance parameters is associated with the formation and development of strands during crack growth [39]. In this case, the formation of strands was not observed during CFRP delamination. Probably, such a mechanism of CFRP delamination is associated with the elastic-strength properties of the matrix.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Relative Crack** & \multicolumn{3}{c}{**Heat Treatment Time at 80 \({}^{\circ}\)C, h**} \\ \cline{2-4}
**Length** & **24** & **48** & **72** \\ \hline
0.25 & 91 & 118 & 91 \\
0.5 & 114 & 96 & 82 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Degree of self-healing \(\alpha\) (%) CFRP with different relative crack length and heat treatment time.  
Figure 10: Loading diagram of CFRP samples before (**a**) and after (**b**) self-healing.  
The average values of the \(\mathrm{G_{IR}}\) crack resistance of CFRP before and after the self-healing process are given in Table 3. For comparison, the table shows the crack resistance of CFRP based on an anhydride-cured epoxy matrix. It should be noted that the value of \(\mathrm{G_{IR}}\) CFRP obtained on the basis of the synthesized FuEp oligomer (80 wt.%) is higher by 70% than the crack resistance values of the reference sample. Such a high crack resistance is characteristic of CFRP based on epoxy matrices modified with thermoplastics (polysulfone, polyethersulfone, polyetherimide, etc.) and can reach 0.6 kJ/m\({}^{2}\)[38,40].  
After carrying out the CFRP recovery mode with a germinated macrocrack, the \(\mathrm{G_{IR}}\) values decrease by an order of magnitude compared to the reference sample. The degree of self-healing of crack resistance values for macro-samples was about 7%.  
It can be concluded that the restoration of crack resistance values on massive samples is less effective than on samples with smaller dimensions. This may also be due to the fact that when splitting the samples, the matrix can break off from the reinforcing material, and when the surfaces come into contact, the existing volume of the matrix will not be enough to fully restore the material.