## 3 Experimental Results and Discussion
### Tensile Experimental Results
#### 3.1.1 Knitted 3D TRC  
Six specimens of the knitted 3D TRC were tested in tension along both the x- and the y-direction of the 3D textile (Figure 8a,b). Figure 10 shows all of the experimental results in combination with a tri-linear average experimental curve obtained as described in the previous section. The experimental results of the knitted 3D TRC layup did not present a difference between both orientations; similar values of the average first and third stage stiffness (E\({}_{1}\) and E\({}_{3}\)), and the average stress and strain at matrix cracking (\(\sigma_{\rm c}\) and \(\epsilon_{\rm c}\)), end of multiple cracking (\(\sigma_{\rm mc}\) and \(\epsilon_{\rm mc}\)) and failure (\(\sigma_{\rm f}\) and \(\epsilon_{\rm f}\)) (see Table 3) were observed for both orientations. Therefore, the mechanical response in tension was considered as independent from the loading orientation for the knitted 3D TRC layup and the averaged curve was constructed using the experimental data from both orientations. Figure 10: All tensile experimental curves in x- and y-direction for the knitted 3D TRC layup, as well as averaged curve. Figure 9: Schematic representation of loading in (a) x-direction, (b) y-direction for the woven 3D TRC system. The observed experimental scatter on the experimental curves (Figure 10) was attributed to the relatively low amount of unidirectional fiber reinforcement (V\({}_{\text{f}}\) = 1.49%) inherent to the open 3D textile architecture. Consequently, individual cracks led to noticeable load drops and a subsequent stochastic scatter between the individual specimens. In opposition to the high scatter on the multiple cracking stage, the uncracked and post-cracking stiffness showed low standard deviations values (Table 3). The observed specimen failure was fiber pull-out for both orientations at an average pull-out stress of 7.02 MPa. Figure 11 compares the averaged curves of the knitted 3D with the equivalent 2D layup. The global macroscopic behavior of the equivalent 2D TRC layup in tension was similar to the knitted 3D TRC layup, as concluded in [21]. At the level of the post-cracking stiffness, no influence was observed from the layups containing transversal connections, as can be seen in Table 4. This means that the presence of transversal connections did not activate any further anchorage of the in-plane textiles under tensile loading conditions when compared to a layup without transversal connections. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multicolumn{4}{c}{**Knitted 3D TRC, along x, V\({}_{\text{f}}\) = 1.49\%**} \\ \hline \(\varepsilon_{0}\) (\%) & 0 & \(\sigma_{0}\) (MPa) & 0 \\ \(\varepsilon_{\text{c}}\) (\%) & 0.022 & \(\sigma_{\text{c}}\) (MPa) & 2.47 \\ \(\varepsilon_{\text{mc}}\) (\%) & 0.365 & \(\sigma_{\text{mc}}\) (MPa) & 3.40 \\ \(\varepsilon_{\text{f}}\) (\%) & 0.880 & \(\sigma_{\text{f}}\) (MPa) & 7.03 \\ E\({}_{1}\) (MPa) & & 11,027 \(\pm\) 541 \\ E\({}_{2}\) (MPa) & & 271 \(\pm\) 73 \\ E\({}_{3}\) (MPa) & & 710 \(\pm\) 45 \\ \hline \multicolumn{4}{c}{Knitted 3D TRC, along y, V\({}_{\text{f}}\) = 1.49\%} \\ \hline \(\varepsilon_{0}\) (\%) & 0 & \(\sigma_{0}\) (MPa) & 0 \\ \(\varepsilon_{\text{c}}\) (\%) & 0.022 & \(\sigma_{\text{c}}\) (MPa) & 2.41 \\ \(\varepsilon_{\text{mc}}\) (\%) & 0.369 & \(\sigma_{\text{mc}}\) (MPa) & 3.36 \\ \(\varepsilon_{\text{f}}\) (\%) & 0.840 & \(\sigma_{\text{f}}\) (MPa) & 7.01 \\ E\({}_{1}\) (MPa) & & 10,919 \(\pm\) 532 \\ E\({}_{2}\) (MPa) & & 275 \(\pm\) 77 \\ E\({}_{3}\) (MPa) & & 738 \(\pm\) 48 \\ \hline \hline \multicolumn{4}{c}{Knitted 3D TRC, all, Vf = 1.49\%} \\ \hline \(\varepsilon_{0}\) (\%) & 0 & \(\sigma_{0}\) (MPa) & 0 \\ \(\varepsilon_{\text{c}}\) (\%) & 0.022 & \(\sigma_{\text{c}}\) (MPa) & 2.44 \\ \(\varepsilon_{\text{mc}}\) (\%) & 0.367 & \(\sigma_{\text{mc}}\) (MPa) & 3.38 \\ \(\varepsilon_{\text{f}}\) (\%) & 0.860 & \(\sigma_{\text{f}}\) (MPa) & 7.02 \\ E\({}_{1}\) (MPa) & & 10,973 \(\pm\) 534 \\ E\({}_{2}\) (MPa) & & 273 \(\pm\) 74 \\ E\({}_{3}\) (MPa) & & 724 \(\pm\) 46 \\ \hline \hline \end{tabular}
\end{table}