## 4 Results and Discussion
### Design Phase Results
#### 4.1.2 Material Properties Optimization: 3D FE Model  
The final lamination sequences of the upper blade and the middle blade were obtained after varying the types, the orientations and the numbers of layers of CFRP prepregs and are reported in Table 8.  
This prototype was made with the aim of validating the two 2D and 3D models of the _design phase_. For the present application, no fiber orientation other than 0\({}^{\circ}\) and 45\({}^{\circ}\) was used, to simplify the manufacturing of the prototype. Other orientations, such as 30 degrees, may also be considered for further optimization. As can be seen in Table 8, 45\({}^{\circ}\) oriented fibers were only found in the upper blade, while, in the middle blade, they were absent. Based on the result from the point of view of stress/strength, fibers woven oriented at 45\({}^{\circ}\) led to too-high stress values when the prosthesis was subjected to operating loads and this can be justified by the shape of the middle blade, shown in Figure 23. The two parts into which the middle blade was divided into its fork shape were dimensionally too narrow; further, 45\({}^{\circ}\) oriented fibers reduced the strength of the entire laminate. The stiffness in dorsiflexion and plantarflexion of the foot prosthesis (modeled with the final lamination sequences) are presented as _foot rotation-reaction force_ in Figure 24 and as _platform displacement-reaction force_ in Figure 25.  
Considering the strength properties of the materials used to realize the elastic components (Table 9), the stress-strength ratio analysis for these components was carried out. The Tsai-Wu criterion was used as the assessment criterion of the composite parts (the upper blade and the middle blade). When the foot was loaded with the 220% of the weight \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Part** & **Type** & **Orientation (deg)** & **No. of Layers** & **Total Thickness (mm)** \\ \hline \multirow{4}{*}{Upper blade} & Woven 200 g/m\({}^{2}\) & 0 & 3 & 0.702 \\  & Woven 200 g/m\({}^{2}\) & 45 & 2 & 0.468 \\  & Unidir. 250 g/m\({}^{2}\) & 0 & 18 & 4.518 \\  & Woven 200 g/m\({}^{2}\) & 45 & 2 & 0.468 \\  & Woven 200 g/m\({}^{2}\) & 0 & 3 & 0.702 \\ \hline \multirow{4}{*}{Middle blade} & \multicolumn{4}{c}{total =} & 6.858 \\ \cline{2-5}  & Woven 200 g/m\({}^{2}\) & 0 & 3 & 0.702 \\  & Unidir. 250 g/m\({}^{2}\) & 0 & 5 & 1.255 \\  & Unidir. 150 g/m\({}^{2}\) & 0 & 10 & 1.510 \\  & Woven 200 g/m\({}^{2}\) & 0 & 3 & 0.702 \\  & Unidir. 150 g/m\({}^{2}\) & 0 & 10 & 1.510 \\  & Unidir. 250 g/m\({}^{2}\) & 0 & 5 & 1.255 \\  & Woven 200 g/m\({}^{2}\) & 0 & 3 & 0.702 \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Final lamination sequences of the upper blade and the middle blade. The properties of the three types of CFRP prepregs are listed in Table 5. The directions of the fibers and the stack up for the upper blade and middle blade are depicted in Figure 14.  
Figure 23: Shape of the middle blade of MyFlex-\(\gamma\). category, the _inverse reserve factor_ was under 0.5 (Figure 26) in the most critical area. An _inverse reserve factor_ of 0.5 corresponded to a _safety factor_ of 2. Figure 24: Comparisons among the static plantarflexion and dorsiflexion 2D FEAs and 3D FEAs and the mechanical tests on the physical prototype with stiffness curves gives as _reaction force–rotation_. Again, the vertical shadow is the rotation range that the foot must have (values defined and specified in Section 2.4, “Biomechanical Requirements”, i.e., between \(-5\) degrees and \(-8\) degrees in the plantarflexion and between 14 degrees and 18 degrees in the dorsiflexion). The horizontal shadow is the range of the ground reaction force (between 95% and 130% in plantarflexion and between 95% and 108% in dorsiflexion of the body weight of the user). The intersection area between the two shadows is the optimal area in which the curve of stiffness of the foot must fall, so that the foot rotates up to the degrees desired when subjected to ground reaction forces.