## 3 Results and Analysis
### Fatigue Test  
#### 3.3.1 S-N Curve  
During the loading process, any misalignment of the reinforcement to the loading direction significantly affects the stiffness and strength, which was observed during tensile tests. Furthermore, during repetitive loading, fibers tend to align to the loading direction in each loading cycle, accelerating the permanent damage process and even drastically reducing the fatigue limit (endurance limit). On the other hand, performing the fatigue test to build stress-number of cycles (S-N) curves for six groups of samples is time-consuming and technically not feasible; moreover, in composites with reinforcement alignment off-axis, it is complex to determine the fatigue limit since the S-N curve keeps reducing (over \(10^{6}\) cycles). Therefore, only for [0\({}^{\circ}\)]s and [0\({}^{\circ}\)/90\({}^{\circ}\)]s were tests performed in order to build S-N curves; on the rest of the samples, the tests were stopped after 6000 cycles, which is the number of cycles to reach the stabilization temperature and maximum strain. Figure 5 shows the experimental S-N data and fitted curves using the Basquin (\(\sigma_{max}=\sigma_{f}N_{f}^{\mathrm{b}}\)) and Weibull (\((\sigma_{max}-\sigma_{\infty})/(\sigma_{ult}-\sigma_{\infty})=e^{(-\alpha( \log(N_{f}))^{\beta})}\)) models [22; 28]. The fitting parameters for [0\({}^{\circ}\)]s are \(\alpha=0.00216\), \(\beta=4.10\), and \(\sigma_{\infty}=105.20\) MPa, with R\({}^{2}=0.82\) for the Weibull model and \(\sigma_{\mathrm{f}}=390.33\) MPa, b \(=-0.0947\) with R\({}^{2}=0.841\) for the Basquin model. For [0\({}^{\circ}\)/90\({}^{\circ}\)]s, the parameters are \(\alpha=0.00159\), \(\beta=1.706\), and \(\sigma_{\infty}=-2709.3\) MPa with R\({}^{2}=0.92\) for the Weibull model and \(\sigma_{\mathrm{f}}=223.18\) MPa, b \(=-0.1072\) with R\({}^{2}=0.911\) for the Basquin model. An advantage of the Weibull model is the ability to determine the \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Laminate**} & **Initial Modulus** & **Tensile Strength** & **Strain to Failure** \\  & **(GPa)** & **(MPa)** & **(mm/mm)** \\ \hline
[0\({}^{\circ}\)]s & 20.99 \(\pm\) 0.60 & 218.02 \(\pm\) 8.20 & 0.0162 \(\pm\) 0.0007 \\
[0\({}^{\circ}\)/90\({}^{\circ}\)]s & 14.24 \(\pm\) 1.714 & 134.31 \(\pm\) 11.55 & 0.0163 \(\pm\) 0.0026 \\ Basket weave warp & 9.01 \(\pm\) 0.337 & 88.05 \(\pm\) 4.28 & 0.0333 \(\pm\) 0.0036 \\ Basket weave weft & 10.56 \(\pm\) 0.54 & 100.40 \(\pm\) 6.31 & 0.0206 \(\pm\) 0.0011 \\
[+45\({}^{\circ}\)/\(-\)45\({}^{\circ}\)]s & 6.37 \(\pm\) 1.108 & 74.90 \(\pm\) 11.50 & 0.0847 \(\pm\) 0.0276 \\
[90\({}^{\circ}\)]s & 6.49 \(\pm\) 1.655 & 34.70 \(\pm\) 3.77 & 0.0077 \(\pm\) 0.00151 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Summary of the mechanical properties obtained from the static tests. Figure 4: Representative stress–strain curves for studied laminates. fatigue limit (\(\sigma_{\infty}\)); this works only if there is a clear trend, which happens in the case of unidirectional fiber composites loaded in the fiber direction; this is corroborated for the [0\({}^{\circ}\)]\({}_{8}\) laminates with \(\sigma_{\infty}\) = 105.20 MPa. On the contrary, for [0\({}^{\circ}\)/90\({}^{\circ}\)]\({}_{8}\), the \(\sigma_{\infty}\) value is inconsistent (negative value), which means that the fatigue limit is more complex to establish and the Weibull model is inadequate in this case. However, using the Basquin model and considering that the fatigue limit occurs at 2 \(\times\) 10\({}^{6}\) cycles [2; 29], the limit for [0\({}^{\circ}\)/90\({}^{\circ}\)]\({}_{8}\) is 47.11 MPa. During the fatigue process, the damage rate is stable in the second stage, with microcrack nucleation at the interface, followed by crack development along the matrix; however, this mechanism is typically for UD lamina loaded axially.