## 3 Results
### Comparison of FEM and Experimental Results

Table 5: Numerical results for a compression load of 200 N and a callus stiffness of 220 Nmm\({}^{-1}\). Figure 7: Experimental and numerical cell loads in the AC configuration for the three different distances between axes. Although Figure 10 does not show significant differences among variables of the two configurations, the average y-displacement of the contact surface at the free clamps is about 1.9% smaller in the BC pin configuration than it is in the AB pin configuration, and the y-contact force is about 0.4% higher. Note that the values of y-displacement of the free clamp are not constant in the z-axes direction, which is due to the clamp rotation around the x-axes. Moreover, in the case of a free clamp rotation about its geometric center, the absolute values of y-displacement of two points geometrically positioned should be equal, but with opposite direction, leading to a null average value of the y-displacement. In the case of a non-free rotation, the tangent trigonometric function and the values of y-displacement of two points symmetrically positioned is used to estimate the rotation angle of the free clamp contact surface or even of the pins. Using this approximation, it was possible to verify that the angle of rotation of the pins and the free clamp was 1.6% higher in the BC pin alignment than in the AB configuration. Higher rotations of pins lead to higher values of contact pressure in the interface of the cell load. The distribution of the contact pressure, and the vector representation of the distributed contact pressure, on the cell load of both AB and BC pin configurations are presented in Figure 11.  
The distributions of the contact pressure of both pin configurations are quite similar, but the maximum value is about 1.96% higher in the BC pin alignment. The numerical von Mises stresses were obtained at all configurations, but Table 6 contains only the results for the distance between axes of 70 mm in the upper pins and the nylon components. Figure 8: Predicted and measured forces in the artificial callus: (**a**) Symmetrical pin configurations and (**b**) nonsymmetrical pin configurations. The values of Table 6 show that the ABC pin configuration leads to a more homogeneous distribution of stresses than any other pin alignments, especially in the pin holes of both nylon components. The higher level of von Mises stress in the pin A of the AB configuration seems to indicate that the locking moment in this configuration is also higher than in any other configuration. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Configuration**} & \multicolumn{3}{c}{**Upper Pins [MPa]**} & \multicolumn{3}{c}{**Upper-Nylon [MPa]**} & \multicolumn{3}{c}{**Bottom-Nylon [MPa]**} \\ \cline{2-11}  & **A** & **B** & **C** & **A** & **B** & **C** & **A** & **B** & **C** \\ \hline AB & 76.29 & 66.12 & - & 3.95 & 3.53 & - & 5.59 & 4.87 & - \\ AC & 66.68 & - & 70 & 3.75 & - & 3.47 & 5.28 & - & 4.92 \\ BC & - & 63.77 & 72.97 & - & 3.83 & 3.67 & - & 5.66 & 2.21 \\ ABC & 43.07 & 35.07 & 46.26 & 2.73 & 1.39 & 1.39 & 3.84 & 1.39 & 1.39 \\ ACAB & 69.82 & - & 66.48 & 3.74 & - & 3.46 & 5.60 & 4.88 & - \\ BCAB & - & 63.87 & 73.08 & - & 3.83 & 3.68 & 5.59 & 4.87 & - \\ ABCAB & 39.57 & 34.73 & 45.84 & 2.72 & 2.4 & 2.46 & 5.63 & 4.91 & - \\ ABCAC & 39.69 & 34.63 & 45.97 & 2.71 & 2.4 & 2.46 & 5.31 & - & 4.94 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Numerical von Mises stresses in the upper pins and in the nylon components for a distance between axes of 70 mm. Figure 9: Predicted and measured locking stiffness: (**a**) symmetrical pin configurations; (**b**) nonsymmetrical pin configurations. Figure 10: Finite element results for the pin configurations: (**a**) AB and (**b**) BC. Figure 11: Distributed contact pressure in the cell load for the pin configurations: (**a**) AB and (**b**) BC.