## 4 Conclusions  
In this study, a simulation of a PLA model under cyclic compressive loading-unloading was performed, and the results were compared to the experimental results. At first, the effect of shape on the results and whether the modeling method is important were examined. In this regard, two simulations were performed; in the first one, the model was layered, which follows better the contour of the MEX-produced sample and the cross-section of the real shape; in the second one, the model was geometrically simplified. The results show that the model's shape is also effective in the results, and the results of the layered models were different from the geometrically simplified ones. The elastic stiffness obtained in the full solid model from Cycle 1 to Cycle 5 was 2818.2 MPa, 2943.9 MPa, 2989.1 MPa, 3018.2 MPa, and 3039.8 MPa, respectively, while in the layer model, these numbers were 2732.8 MPa, 2936.8 MPa, 3005 MPa, 3036.5 MPa, and 3057.5 MPa, respectively. Therefore, a layer-by-layer model was used according to the experimental sample shape.  
In contrast, by comparing the results of the layered model with the experimental results, it was observed that the percentage differences of changing elastic stiffness in experimental work and simulation during five cycles of loading-unloading were really low. The percentages of difference in elastic stiffness between the experimental results and numerical simulation results from cycle to cycle were 1.4, 2.9, 3.8, and 4.2 percent, respectively. The numerical simulation outcomes show that the elastic stiffness significantly increases during the first cycle, but in the following cycles, the amount of increase in elastic stiffness decreases, which is in agreement with the experimental results. The force-displacement diagrams are also in acceptable agreement with the experimental results. It is evident that plastic deformations in the sample increase from cycle to cycle and influences its elastic stiffness, which also increases. Plastic deformations developed in narrow transitions between layers. This is why the geometrical model of the sample, used in mechanical analysis, should also take into account the approximation of the real layer's cross-section shape.  
Finally, some of the results that were not obtained in experimental work were achieved in the numerical simulation, such as the Mises stress, elastic strain, and PEEQ diagrams alongside the two paths. It was observed that the Mises stress has the lowest value in the first layers (from the tool side), and the stress values increase from top to bottom of the model alongside the paths on the primitive layers, and then it will start to decrease. The  
Figure 18: Elastic strain contour at the end of loading–unloading.  
maximum amount of stress is almost at the middle layers of Path 1 and Path 2. In addition, the full amount of the Mises stress was observed between the layers. The results of all observations on the numerical simulation are for investigation in future works.  
Conceptualization: A.K., N.M. and T.P.; software: A.K. and N.M.; validation: A.K., T.P. and N.M.; formal analysis: A.K.; data curation: A.K., N.M. and T.P.; writing--original draft preparation: A.K.; writing--review and editing: T.P. and N.M.; supervision: N.M. and T.P.; project administration: T.P.; funding acquisition: N.M. and T.P. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the Slovenian Research Agency, research core programs No. P2-0248 and P2-0263. The APC was equally funded by both research core programs.  
Not applicable.  
The authors declare no conflict of interest.