## 3 Results and Discussion
### X-ray Tomography of CFRP  
Table 4 shows the porosity of GFRP based on the control matrix and matrix with the effect of recovery. It can be seen that the porosities of GFRP with the reduction effect and control samples have similar values (2.5 and 3.1 vol.%, respectively). After crack healing in self-healing CFRP samples, the porosity tends to decrease and is almost equal to that of the control samples.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**CFRP Type**} & **CFRP without** & **CFRP with** & **CFRP with** \\  & **Self-Healing Effect** & **Self-Healing Effect** & **Self-Healing Effect** \\  & & & **after Crack Healing** \\ \hline Porosity, vol.\% & 2.5 & 3.1 & 2.7 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Porosity of CFRP based on a binder for comparison and a binder with a self-healing effect.  
Figure 11: Crack resistance of \(\mathrm{G_{IR}}\) CFRP based on a binder with thermally reversible bonds depending on the length of the crack \(\mathrm{L_{c}}\) before (**a**) and after (**b**) self-healing. 1—sample No. 1; 2—sample No. 2.  
Figures 12 and 13 show X-ray tomograms of compact CFRP samples before and after a reduction process of several hours at 80 \({}^{\circ}\)C. On samples with relative crack lengths of 0.25 and 0.5 before recovery (Figures 12a and 13a), delamination is visible along the entire length of the sections in the XY and ZY planes (a). The bundles (a) extend between and through the layers (b) of the fabric. The thickness of the matrix (c) between the layers of the reinforcing filler (b) is 15-40 microns. The opening of a crack is the distance between its surfaces in the investigated section of about 20-50 microns. Pores (d) with sizes of 150-220 \(\upmu\)m are also visible. The pores are arranged randomly throughout the volume of the samples.  
Figure 12: Tomograms of samples of CFRP with a relative crack length of 0.25 before (**a**) and after (**b**) recovery for an 24 h (I), 48 h (II) and 72 h (III) at 80 \({}^{\circ}\)C. a—crack, b—layer of reinforcing fibers, c—matrix, d—pores, e—defect region.  
From Figures 12b and 13b, it can be seen that for samples heat-treated for 24 h (I) and 48 h (II), the specified defects are not identified (region (e)). However, a decrease in the size of large pores (d) was observed after heat treatment of the samples. Characteristic pores were used to identify the corresponding cross sections after CFRP heat treatment.  
Thus, it can be concluded that the selected heat treatment mode and the applied contact pressure provide a high degree of recovery of the CFRP properties (see Table 2). In addition, the number and size of pores in the material decreases, which ultimately contributes to an increase in the physical and mechanical characteristics of the material. The decrease in defectiveness can explain the values of the degree of recovery of more than 100%.  
Microcracks (a) and pores (d) in region (e) were found in the volume of CFRP samples heat-treated for 72 h. For the CFRP sample, with a relative length of the initial crack of 0.25, extended closed pores 300-500 \(\upmu\)m long and 50-70 \(\upmu\)m wide are observed along the fracture surfaces that were in the crack volume before repair (Figure 12b). In a CFRP sample  
Figure 13: Tomograms of samples of CFRP with a relative crack length of 0.5 before (a) and after (b) recovery for an 24 h (I), 48 h (II) \(n\) 72 h (III) at 80 \({}^{\circ}\)C. a—crack, b—layer of reinforcing fibers, c—matrix, d—pores, e—defect region.  
with a relative length of the initial crack of 0.5, areas with an unhealed crack (a) 20-30 \(\upmu\)m wide and pores (d) 30-60 \(\upmu\)m in size were found (Figure 13b). Apparently, the presence of remaining defects resulted in lower values of the modulus of elasticity E' at the maximum heat treatment time (see Figure 9).