## 4 Conclusions  
This article investigated the capabilities of linear elastic material models when modeling a nonlinear elastic material under quasi-static loading. First, a tensile test was performed by the ISO 527-2 standard to ensure that the defined material models were as accurate as possible. During the evaluation of the standard measurement results, the Young's modulus calculated in the ISO 527-2 standard's recommended 0.05-0.25% strain interval showed higher than 10% error values. Thus, the Young's modulus for the material was determined at the 0.25-0.45% strain interval with a 3% error. Based on the material testing results, a linear elastic material model defined by the standard Young's modulus, a linear elastic material model with Young's modulus calculated until the limit stress, and a multilinear material model was chosen for the finite element simulations. The models were then simulated using three different specimen geometries. After the simulations, the laboratory measurements were performed using the GOM Aramis full-field optical measurement system. The results of the comparison showed that the specimen geometries and the method of comparing the optical measurements are accurate and usable for the validation of material models.  
The comparison between the three material models and the optical measurements showed that the linear elastic material models with the standard Young's modulus can be used for the modeling of the small strain behavior of nonlinearly elastic materials. In the case of the PA6 material, the limit of modeling is 0.96% strain. It is interesting to note that during comparison, this material model showed the same 3% error that was seen when calculating the standard Young's modulus of the material, meaning that the 3% error could exist in the production of the sheet material and not in the modeling itself. When evaluating the deformations, on the other hand, the linear elastic material models never provided accurate results. This could be due to the fact that near the grips, increased strain values occur, which exceed the modeling limit of 0.96% strain. This results in increased local deformations, which the material model is not able to account for.  
Overall, the linear elastic material model with standard Young's modulus could be used in the industry to model any polymeric materials' small strain behavior when the product is under quasi-static loading, and the goal is to find the average strain or stress values of a part. In these cases, the usage of this material model can shorten the design process because setting up such a model is a shorter process than creating a multilinear material model, and the data required for this model is vastly available. In contrast, the stress-strain curves required to create the multilinear material models must be obtained via standardized material testing, which is a costly and time-consuming process. Although, to evaluate deformations, the multilinear material models are still the more accurate choice.  
Figure 15: The four deformation images of the middle-weakened plate.  
**Author Contributions:** Conceptualization, D.H. and T.M.; methodology, M.F. and D.H.; software, M.F.; validation, D.H.; formal analysis, M.F.; investigation, D.H. and M.F.; resources, T.M.; data curation, M.F.; writing--original draft preparation, M.F.; writing--review and editing, D.H. and T.M.; visualization, M.F.; supervision, T.M.; project administration, T.M.; funding acquisition, T.M. All authors have read and agreed to the published version of the manuscript.  
**Funding:** The research was supported by the Thematic Excellence Programme (TKP2020-NKA-04) of the Ministry for Innovation and Technology in Hungary, within the framework of the (Automotive Industry) thematic program of the University of Debrecen.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Conflicts of Interest:** The authors declare no conflict of interest associated with this publication.