## 2 Materials and Methods
### Numerical Simulation  
The 3D modeling and simulation were performed using ABAQUS finite element code to develop a layered (PLA) model that is subjected to compressive loading. The experimental sample was in an open-top cylinder form of \(D=11.42\) mm (diameter) and \(H=10\) mm (height) built with MEX technology. The MEX process parameters used in the sample production are defined in [35]. It was determined that it is not possible to print a 100% infill sample with that technology (Figure 4). In order to decrease computational costs and save time, the numerical model used in this study was one-twenty-fourth of the entire open-top cylinder. Therefore, first, the cross-section of the sample was divided into twelve equal and symmetrical parts, and the height was halved (Figure 5). The influence of model shape on numerical simulation results was examined. Therefore, a simplified geometrical model (Figure 6) and a layered model, following the shape of the printed sample and the cross-section of the real shape (Figure 7), were created. Figure 4: (**A**) Microscopic cross-section image of MEX-produced specimen with 100% infill. (**B**) The microscopic image from the top view of the MEX-produced specimen sample with 100% infill. Figure 5: (**A**) Dividing the cross-section of the sample into twelve equal symmetrical parts; (**B**) halving the height of one of the symmetrical parts. The mechanical properties of the PLA used in this simulation are provided in Table 1 and Figure 8 [1]. \begin{table}
\begin{tabular}{c c c} \hline
**Property** & **Unit** & **Value** \\ \hline Density (\(\rho\)) & kg/m\({}^{3}\) & 1240 [5] \\ Initial [PERSON]’s modulus (\(E\)) (altered with PEEQ & MPa & 2800 [35] \\ during the simulation) & [PERSON]’s ratio (\(v\)) & - & 0.36 \\ Yield strength (\(\sigma_{y}\)) & MPa & 59 \\ \hline \end{tabular}
\end{table} 
Table 1: Mechanical properties of the PLA applied in the numerical simulation. Figure 6: Three-dimensional model of the MEX-produced specimen (geometrical simplified model). Figure 7: Three-dimensional model of the MEX-produced specimen with boundary conditions assigned to the middle cross-section of the model, the amount of layers of the model, and tool (orange points represent the boundary conditions that applied to the model). Therefore, to achieve the plastic properties of the PLA used in the numerical simulation, the plastic properties of [PERSON] [1] were chosen as a reference. After analyzing the results of numerical simulation, the stress and strain values of the plastic properties used by [PERSON] [1] were shifted together to some different percentages in different steps. By examining the results of numerical simulation after each step of making changes according to Figure 8, the data of diagram 5 (simultaneous 22% decrease of the stress and strain values) in this numerical simulation were used. It was not possible to print the sample with one hundred percent infill using MEX technology; therefore, references for the material (PLA) data were sought for use in the numerical simulation. The \(Z\)-direction fixed boundary condition (normal direction displacement = 0) was applied at the middle cross-section, and the normal direction fixed boundary condition (normal direction displacement = 0) was applied at both side cross-sections of the model in the local coordinate system, as shown in Figure 7. The numerical model of the specimen is composed of 308,734 C3D8R elements (linear 8 node hexahedra with reduced integration) (Figure 9). The model consists of 26 parts, of which 25 are PLA layers (each separate object) stacked on top of each other; the other part is the tool (Figure 5). The Poisson's ratio was 0.36 [44]. In this model, Young's modulus changes with the equivalent plastic strain, which was performed using the USDFLD subroutine. In this way, by changing the equivalent plastic strain in the model, a new Young's modulus was assigned to the material. To validate with laboratory results, loading was applied in two conditions of three and five cycles.