## 3 Experimental Results and Discussion
### Flexural Experimental Results
#### 3.2.1 Knitted 3D TRC  
In bending, four specimens were tested for each orientation of the knitted 3D TRC. The experimental force-displacement curves for both orientations are given in Figure 13. Similar to the tensile results, no influence of the orientation on the mechanical response was observed for this layup, while the observed failure was by means of fiber pull-out. Table 6 summarizes all averaged flexural experimental parameters for this layup, which were taken as the average of both orientations. The Ks in the table represent the stiffness of the load-displacement curves.  
Figure 14 compares the averaged flexural experimental curves of the knitted 3D TRC with the equivalent 2D TRC (properties given in Table 7, according to [21]). Table 8 summarizes the flexural stiffness in the three stages for the different layups.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multicolumn{2}{c}{**Woven 3D TRC, Along x, V\({}_{\rm f}\) = 1.49\%**} & \multicolumn{3}{c}{**Woven 3D TRC, Along y, V\({}_{\rm f}\) = 1.49\%**} \\ \hline \(\varepsilon_{0}\) (\%) & 0 & \(\sigma_{0}\) (MPa) & 0 & \(\varepsilon_{0}\) (\%) & 0 & \(\sigma_{0}\) (MPa) & 0 \\ \(\varepsilon_{\rm c}\) (\%) & 0.022 & \(\sigma_{\rm c}\) (MPa) & 2.40 & \(\varepsilon_{\rm c}\) (\%) & 0.021 & \(\sigma_{\rm c}\) (MPa) & 2.31 \\  & & \(\sigma_{\rm mc}\) & & & & \(\sigma_{\rm mc}\) & \\ \(\varepsilon_{\rm mc}\) (\%) & 0.225 & (MPa) & 3.14 & \(\varepsilon_{\rm mc}\) (\%) & 0.301 & (MPa) & 2.95 \\ \(\varepsilon_{\rm f}\) (\%) & 0.464 & \(\sigma_{\rm f}\) (MPa) & 4.96 & \(\varepsilon_{\rm f}\) (\%) & 0.719 & \(\sigma_{\rm f}\) (MPa) & 4.82 \\ E\({}_{1}\) (MPa) & & 10,903 \(\pm\) 705 & E\({}_{1}\) (MPa) & & 10,957 \(\pm\) 812 \\ E\({}_{2}\) (MPa) & & 365 \(\pm\) 64 & E\({}_{2}\) (MPa) & & 229 \(\pm\) 38 \\ E\({}_{3}\) (MPa) & & 761 \(\pm\) 44 & E\({}_{3}\) (MPa) & & 446 \(\pm\) 35 \\ \hline \hline \end{tabular}
\end{table}
Table 5: Averaged tensile experimental parameters for the woven 3D TRC layup.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Knitted 3D TRC, All Specimens, Vf = 1.49\%** \\ \hline d\({}_{0}\) (mm) & 0 & F\({}_{0}\) (N) & 0 \\ d\({}_{\rm c}\) (mm) & 0.562 & F\({}_{\rm c}\) (N) & 310 \\ d\({}_{\rm mc}\) (mm) & 2.711 & F\({}_{\rm mc}\) (N) & 460 \\ d\({}_{\rm f}\) (mm) & 14.045 & F\({}_{\rm f}\) (N) & 1503 \\ K\({}_{1}\) (N/mm) & & 551 \(\pm\) 48 \\ K\({}_{2}\) (N/mm) & & 70 \(\pm\) 12 \\ K\({}_{3}\) (N/mm) & & 92 \(\pm\) 7 \\ \hline \hline \end{tabular}
\end{table}
Table 6: Averaged flexural experimental parameters for the knitted 3D TRC layup.  
Figure 14: Flexural comparison of averaged curves of all layups.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Equivalent 2D TRC, All Specimens, Vf = 1.49\%** \\ \hline d\({}_{0}\) (mm) & 0 & F\({}_{0}\) (N) & 0 \\ d\({}_{\rm c}\) (mm) & 0.555 & F\({}_{\rm c}\) (N) & 306 \\ d\({}_{\rm mc}\) (mm) & 1.848 & F\({}_{\rm mc}\) (N) & 395 \\ d\({}_{\rm f}\) (mm) & 16.503 & F\({}_{\rm f}\) (N) & 1456 \\ K\({}_{1}\) (N/mm) & & 552 \(\pm\) 42 \\ K\({}_{2}\) (N/mm) & & 68 \(\pm\) 19 \\ K\({}_{3}\) (N/mm) & & 72 \(\pm\) 3 \\ \hline \hline \end{tabular}
\end{table}
Table 7: Averaged flexural experimental parameters for the equivalent 2D TRC layup.  
Figure 13: All flexural experimental curves in x- and y-direction for the knitted 3D TRC layup, as well as averaged curve.  
Contrary to the tensile behavior, the post-cracking stiffness of the 3D TRC layups showed a clear improvement compared to the equivalent 2D layup.  
The knitted 3D TRC layup showed a clearly higher post-cracking stiffness compared to the reference equivalent 2D TRC (92 N/mm compared to 72 N/mm, Table 8), while having the same in-plane fiber volume fraction. These results highlighted the increased flexural anchorage and therefore higher fiber efficiency provided by the transversal connections in the 3D TRC layups.