## 4 Method Validation
### Experiments  
Static tests were carried out to validate the structural simulation and the complete process of mapping the material model from the stamping to the structural simulations. These tests were based on the AFNOR NF F 31-119 standard. The experimental setup, shown in Figure 11, included two dial indicators with 0.01 mm precision and an up to 80 mm range, another dial indicator with 0.001 mm precision and an up to 80 mm range, a pneumatic cylinder, and a load cell with 0.1 kg precision and an up to 200 kg range. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Load Step**} & \multicolumn{2}{c}{**NL PARAM**} & \multicolumn{2}{c}{**NL ADAPT**} & \multicolumn{1}{c}{**NL OUT**} \\ \cline{2-5}  & **NINC** & **DT** & **DTMAX** & **NINT** \\ \hline Loading & 20 & 0 & 0.05 & 20 \\ Unloading & 10 & 0 & 0.1 & 10 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Numerical control details of loading and unloading steps. Figure 10: Visualization of the (a) standard and the (b) nonlinear By-Prop models. +++ ==ERROR: No output for this page==
The setup was organized as follows. The sheet-metal seat was fixed to the platform by the base, which was also virtually modeled, and lifted by two additional 10 mm thick plates to prevent the lower edge from touching the floor during loading. The body was tightened between the base and the L-Plates using six bolts, which provided the main anchorage. To anchor the pneumatic piston and the comparator, two beams were used, which were positioned transversely to the direction of the load. First, several tests were carried out in the linear field before the destructive ones:  
++  
avoid shocks, and sufficient resting time was allowed before reading the numbers from the dial comparators. After each step, the force was removed, and the setup was inspected to confirm its complete return to the zero position, ensuring the reliability of the instruments and the procedure. A similar procedure was implemented for the destructive test, gradually increasing the load until the sheet-metal seat reached its breaking point. Deformations at important points were recorded as a function of the load cell values and then were compared with FEM simulation results for validation. For conciseness, only the results of the initial tests are included in this paper. The validation was conducted at three primary measurement points: Point A, situated at the application point of the pneumatic cylinder at a height of 652 mm from the floor; Point B, positioned approximately halfway up the backrest at a 204 mm height; and Point C, located at the folding junction between the backrest and the seat, representing the lowest part of the backrest. Points A and B measured deformations along the \(X\)-axis, while Point C captured deformation along the \(Z\)-axis, as shown in Figure 12.  
As previously described, several tests were conducted, exceeding those strictly required to validate the structural simulation. The first subtest (backrest push along the X-positive direction) is identical to the test described in previous subchapters, except for the opposite direction of the load application. The workstation setup remained unchanged; the body was simply rotated 180\({}^{\circ}\), and the instrumentation was repositioned while maintaining the comparator heights. The first loading is always regarded as \"invalid\" as it allows the body to settle into position. Following this initial step, the comparators are reset, and the official measurements commence. The test results are presented in Table 7.  
In this test, the loads were kept lower than those applied along the negative X direction, as the body exhibited greater compliance. The observed residual deformations were relatively \"high,\" potentially indicating a failure risk. However, in the elastic range, residual deformations should theoretically return to zero after the spring back phase. According to the AFNOR NF F 31-119 standard, the residual deformations must remain below 5% of the maximum deformation under load.