# Assessment of Crash Performance of an Automotive Component Made through Additive Manufacturing
## 2 FEM (Finite Element Method) Modeling  
The numerical activity was carried out with the LS-DYNA solver [15], using Hypermesh [16] and ANSA [17] as the pre-processors and Hyperview [18] as the post-processor. The system that was subjected to a knee impact was the front interior of the vehicle, specifically the dashboard glove box. The vehicle used was the Fiat 500 currently in production. To reduce calculation times, only the dashboard body was modeled, rather than the entire vehicle. This operation did not lead to significant errors because the eliminated components (belonging to the rear part of the vehicle) were not directly influenced by the knee impact test.  
The FEM modeling involved three phases:  
1. The CAD (Computer Aided Design) model is imported into a pre-processor. The current box and the additive box are imported, and both geometries are meshed using mainly shell linear elements with an average size of 5 mm. This setting was used as a compromise between the calculation time and the convergence analysis (the mesh is refined until a satisfactory convergence of the results is reached).
2. Properties and materials were defined.
3. Both meshes were exported to create the dashboard body (Figure 2).  
Figure 1: Sections of the actual (realized through molding) and the additive glove box.  
PA + 5%B and PP + 5%B (Table 1) were characterized according to the analytical methodology described below.  
The number of shell elements (2D) was nearly \(3.40\times 10^{5}\). The model was constrained in all directions. The chosen nodes were located in the center of the wheels. These nodes were connected by rigid elements to the adjacent structure.  
The smallest elements were approximately 2 mm in size. The largest elements, about 10 mm in size, were in components far from the impact zone. It was not necessary to have an accurate mesh in this zone because these components will not deform excessively. Both geometric and material nonlinearities (to simulate yielding of the components) were properly enforced.  
To characterize the materials, the same tensile stress test carried out experimentally was reproduced numerically using a test piece with dimensions prescribed by ISO 527-2 [19]. The adopted plastic constitutive law, which characterized an isotropic hardening, was obtained using an analytical procedure based on the engineering curves of stresses vs. strains \(\sigma-\varepsilon\) that were obtained experimentally. Subsequently, such input curves were calibrated by correlating the calculation model with the physical stress test. When the process was complete, the \(\sigma-\varepsilon\) curves showed an adequate level of correlation (Figure 3). The descendent part of the curve is generally not relevant to the analysis considered.  
\begin{table}
\begin{tabular}{c c c c} \hline
**Parameter** & **Actual** & **PA + 5\%B** & **PP + 5\%B** \\ \hline Young’s modulus E & 164 GPa & 157 GPa & 125 GPa \\ Poisson’ ratio \(\upsilon\) & 0.3 & 0.3 & 0.3 \\ Mass density \(\varrho\) & 1030 kg/m\({}^{3}\) & 1230 kg/m\({}^{3}\) & 1040 kg/m\({}^{3}\) \\ Mass \(m\) & 871 g & 810 g & 685 g \\ \hline \end{tabular}
\end{table}
Table 1: Main mechanical properties of the materials considered in the numerical models.  
Figure 3: Constitutive law (stress vs. strain) for PA + 5%B and PP + 5%B.  
Figure 2: The FEM model considered in the analyses.