## 4 Method Validation  
### Simulation  
Based on the seat geometry and material property distribution obtained from the stamping forming in Section 3, a structural FEM model was developed to conduct a virtual verification of structural performance and simulate the static and dynamic tests required by the AFNOR NF F 31-119 and EN 12663-1 standards [24,27]. The AFNOR NF F 31-119 standard defines the test conditions for approving both passenger and driver seats, applying conventional loads at specific points on the seat. Conversely, the EN 12663-1 standard provides guidelines for additional equipment and their fixation, with loads applied at the center of gravity and scaled proportionally to the total weight of the seat, including the occupant. For the tests focusing solely on the sheet-metal part, the AFNOR NF F 31-119 standard was used as the primary reference. The test procedure defined by the AFNOR NF F 31-119 standard involves applying a constant force of 1500 N to the center of the upper backrest in a front-to-back direction, as shown in Figure 8. The yellow sheet-metal seat is bolted to the red base floor of the test room using six virtual screws, while vertical movements are restricted by purple L-plates connected to the base. The load is applied via a blue pad, simulating realistic loading conditions. This setup tests the unreinforced sheet-metal part under particularly high forces, pushing it to the limits of its structural integrity. In the stamping simulation, the holes in the component remain unfilled, as these regions are critical for capturing stress concentrations and serve as interfaces for connections or constraints. Around these holes, elements are thickened to form washers, enhancing local stiffness and accommodating increased stress. The meshing process begins with a two-dimensional (2D) mesh created on one face of the component. Using the Solidmap tool, this mesh is extruded into a 3D hexahedral (brick) element mesh, providing precise geometric representation and ensuring accurate stress and deformation analysis during simulation. Table 3 summarizes the material properties and mathematical models used for different structural components, including steel sheet-metal, solid parts, and M8 screws. Figure 8: Simulation setup with respect to AFNOR NF F 31-119 standard. Figure 9 illustrates the balance of forces and reactions on the seat's sheet-metal. A blocked constraint contact, simulating a welded connection between components, significantly increases stiffness, effectively treating the seat as if it were welded to the base. The base, with a thickness of 20 mm, is modeled as particularly rigid. However, this type of contact overlooks stress hot spots, especially those near the edge of the base and the L-Plate, where constraint reactions occur. In practice, the screws do not create constraint reactions but instead generate significant friction forces through tightening, which induce large reaction forces between the components. In the FEM model, relative translation along the \(X\)-axis between the body and the L-Plate is constrained using a TIE contact. This contact is connected to the base through Beam and RBE2 elements, ensuring that it remains rigidly constrained. The nonlinear modeling captures these behaviors, providing a more realistic representation of stress distributions and yielding in critical regions. The structural analysis involves two primary loads: a force applied along the negative X-direction and the gravitational force. The gravitational force primarily serves to simulate springback behavior in the unloaded state, ensuring that the model reflects real-world relaxation effects post-deformation. Constraints were applied to the plate by selecting all nodes on its lower surface and blocking translations in the X, Y, and Z directions, as detailed in Table 4. This constraint setup accurately represents the physical conditions of the test, allowing the model to simulate the component's response under applied loads while maintaining stability and structural integrity during the analysis.