## 4 Results and Discussion
### Design Phase Results  
#### 4.1.1 Geometry Optimization: 2D FE Model Results  
Several combinations of the parameters listed in Table 3 and depicted in Figure 5 were used to carry out more than 1000 simulations. From these 1000+ simulations, the final and pre-optimized values of the parameters were obtained and are listed in Table 7. The tabulated values are the final values from the 2D model for the weight category that was chosen to be developed (60 kg), while they are not the final values for the 3D model. In fact, of these values, the values of the thickness of the two blades in the 3D model change based on their stack-up sequence (which is defined in the 3D model, during the optimization of the properties of the materials). The choice of the final parameters was based on the _rotation-reaction force_. However, different configurations of the geometry could give similar results in terms of stiffness. Thus, stress and approximated final weight of the device were also used as evaluation parameters. However, among the 1000+ simulations, a configuration was considered optimal if the curve _foot rotation-reaction force_ fell into the optimal area, highlighted in \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Final Value** \\ \hline upper blade thickness UB\({}_{\text{f}}\) (mm) & 6.80 \\ upper blade curvature 1 UB \(\text{c}_{1}\) (deg) & 2.00 \\ upper blade curvature 2 UB \(\text{c}_{2}\) (deg) & 2.00 \\ upper blade curvature 3 UB \(\text{c}_{3}\) (deg) & 2.20 \\ upper blade curvature 4 UB \(\text{c}_{4}\) (deg) & 2.50 \\ upper blade curvature 5 UB \(\text{c}_{5}\) (deg) & 4.20 \\ middle blade length MB\({}_{L}\) (mm) & 163 \\ middle blade thickness MB\({}_{\text{f}}\) (mm) & 7.60 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Final geometric parameters that define the profile shape of MyFlex-\(\gamma\) elastic elements, for the 60 kg weight category. See Figure 5.  
Figure 20: ISO–22675: the tilting table simulates the relative rotation between the ground and the thigh. The force F depends on the weight category and the maximum value was 130% of the body weight (BW). For the 60 kg weight category, the maximum value of the force F was 764 N. The tilting table ranged from \(-20^{\circ}\) to \(40^{\circ}\). the graphs in dark grey, as the intersection of the two lighter grey areas in Figure 21. These areas, both for the dorsiflexion and for the plantarflexion, were defined considering the biomechanical requirements previously reported in Section 2.4. Among the 1000+ combinations, the results from one of the non-optimal combination were taken into account to be compared with the results coming from the final combination of parameters that was considered pre-optimized. The dashed curve falls only partially into the optimal plantarflexion area (Figure 21), although the same combination of parameters already gives a curve that falls into the optimal dorsiflexion area. On the other hand, the black straight line is the curve that describes the stiffness of the combination of parameters considered pre-optimized. By varying the combinations of the parameters, similar stiffness curves can be obtained in dorsiflexion and different stiffness curves in plantarflexion or vice versa. This situation depends on the configuration of the elastic elements of each foot prosthesis to be optimized. In this application, one or more combinations of geometric parameters were considered to be those sought for biomechanical objectives if the stiffness curves fell within the ranges of rotations and loads defined in Section 2.4. However, for future works, exploiting the proposed methodology, optimization functions can be implemented in such a way that the choice of the final configuration is not based only on the evaluation of the stiffness curves. The stiffness curves, plotted as _foot rotation-reaction force_ in Figure 21, are also provided as _platform displacement-reaction force_, as shown in Figure 22.  
Figure 21: Results from the first stage of the _design phase_.