## 6 Results and Discussion
Figure 10: The setup for tensile testing: (**a**) unloaded test tube and (**b**) loaded test tube. All the values of the mechanical parameters required for the simulation and FEA are determined by examining the data collected from the performed tensile test. The entire set of mechanical parameters for the 3D-printed Taulman Nylon 230 material is presented in Table 4. As can be observed, the acquired Young's modulus is nearly 4.5 times greater than the manufacturer's Young's modulus (manufacturer's Young's modulus--73 MPa; Young's modulus obtained by tensile test--325 MPa), while ultimate tensile strength is not that different. With the experimentally acquired mechanical characteristics, FEA of the compliant fingers was carried out. The FEA setup was the same as that described in Section 3, with a few additional improvements. A mesh is now defined as a size of 0.2 mm for rigid segments of compliant mechanisms and 0.05 mm for elastic segments (flexure hinge). This was implemented in order to ensure the repeatability of the FEA results, which has a stress convergence test tolerance below 1%. A compliant mechanism with a curved flexure hinge with a 21-degree bend now has the resulting mesh of the FE model, which contains 32,615 elements and 33,425 nodes, while a compliant mechanism with a 90-degree bend contained 34,552 elements and 34,552 nodes. The force with which the compliant fingers were loaded in the simulation corresponds to the product of the mass of the weights (from the initial 10 g to 60 g) with which the experiments were performed and the gravitational acceleration obtained at the site where the experiment was performed (the value of the gravitational acceleration for the city of Nis, Serbia, is 9.80408 m/s\({}^{2}\)). Adding forces corresponding to weights of 50 and 60 g was necessary so that in FEA, we could obtain results of maximum bending angles that correspond to the theoretical range of motion for the PIP joint of 100 degrees. The resulting forces and deflection angles obtained by FEA can be seen in Figure 12. The difference between bending angles for the two types of compliant fingers can be clearly seen. Better angle results are produced by a compliant finger with a 90-degree bend curved flexure hinge (red line), which is visible even at modest load levels. \begin{table}
\begin{tabular}{c c} \hline \hline
**Material Property** & **Taulman Nylon 230** \\ \hline Young’s modulus, E & 325 MPa \\ Poisson’s ratio, \(\
u\) & 0.39 \\ Ultimate tensile strength, \(\sigma_{\max}\) & 38.8 MPa \\ Yield strength, \(\sigma_{y}\) & 7.9 MPa \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Mechanical properties of the 3D-printed Taulman Nylon 230 obtained by tensile testing. Figure 11: The stress–strain curve obtained from tensile testing data. (**blue**) True stress–strain curve. (**orange**) Hypothetical straight line of pure elastic behavior of the material. The above results should be seen as results in terms of internal stress and strain. In Figure 13, it can be seen that the compliant finger with a 90-degree bend curved flexure hinge has minor stress through the entire range of angular deformations. The maximal stress in the end position at the highest load force for a 90-degree bend curved flexure hinge is 17.324 MPa for bending angle \(\theta\) = 102.721\({}^{\circ}\), and for a 21-degree bend curved flexure hinge, it is 17.406 MPa for bending angle \(\theta\) = 93.789\({}^{\circ}\). As a result of all the above, it was necessary to repeat the experimental measurement in order to provide the values of the angles for the weights of 50 and 60 g so that we could perform a comparison with the FEA. Therefore, two new prototypes of compliant fingers were 3D-printed, which served us for the desired experimentation. This opportunity was used to repeat the already conducted experiment once more, ensuring the outcome results of the earlier experiment (Figure 14). Figure 12: Angle–force diagram for compliant fingers obtained by FEA. Figure 13: Stress–angle diagram for compliant fingers obtained by FEA.