## 4 Results and Discussion  
In this section, the results of the experimental investigations are presented and discussed. Figure 5 shows the median of the corresponding force and strength each with standard deviation of the multi-material test specimens classified by load type. As both material transition zones failed separately--suggesting a difference in the interface zones--the result of the compression-shear test is divided into two values. This is probably caused by a difference in printing order and glass transition temperatures. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Material**} & \multirow{2}{*}{**Color**} & \multirow{2}{*}{\begin{tabular}{c} **Class** \\ **Transion** \\ \end{tabular} } & \multicolumn{3}{c}{**Temperature**} & \multirow{2}{*}{**Nozzle**} & \multirow{2}{*}{\begin{tabular}{c} **Layer** \\ **Thickness** \\ \end{tabular} } & \multirow{2}{*}{\
\begin{tabular}{c} **Raster** \\ **Angle** \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} **Perimeter** \\ **Shells** \\ \end{tabular} } \\ \hline PLA [9] & white & 55–60 \({}^{\circ}\)C & 60 \({}^{\circ}\)C & 215 \({}^{\circ}\)C & 0.2 mm & \(\pm\)45\({}^{\circ}\) & 2 \\ ABS [10] & blue & 105 \({}^{\circ}\)C & 245 \({}^{\circ}\)C & 0.2 mm & \(\pm\)45\({}^{\circ}\) & 2 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Selective material properties and utilized process parameters for the manufacturing of the multi-material test specimens separated between acrylonitrile butadiene styrene (ABS) and polylactic acid (PLA) material. Figure 4: Geometry and dimensions of the developed test specimens, dimensions in millimeters for: (a) tensile, (b) lap-shear, and (c) compression-shear (scale-factor: 2). It can be seen that the standard deviation validates the developed geometry of test specimens for testing multi-material parts manufactured by ME. However, because of comparatively low interface strength of the representatively chosen material combination PLA and ABS, uncertainties regarding the printing process (e.g., machine calibration or fluctuations in filament diameter) or testing procedure (e.g., tipping because of fixation) have a strong impact on the mean variation of the maximum strength. All specimens failed in the material transition zone because of interface fracture. The tensile and lap-shear test specimens show the lowest standard deviation of about 6.5%. The corresponding values are 39.70 N/0.24 MPa (tensile tests) and 65.49 N/0.53 MPa (lap-shear tests), respectively. On the contrary, the results of compression-shear tests show a standard deviation of about 10%, which equates to a deviation of 248.18 N in force and 0.79 MPa in strength. As a result of a lower layer bonding on the upside, where PLA is deposited on ABS, the transmittable force and resultant strength is about 2.5 times lower and the standard deviation is about three times higher relative to applied forces. The lower layer bonding most likely corresponds to abnormalities in machine calibration; it could be identified that the PLA processing nozzle had a larger distance to the ABS surface, which resulted in pores and a weaker initial bonding. In addition, because of the lower extrusion temperature of PLA and higher glass transition temperature of ABS, the diffusion at the upside interface is probably lower than on the downside. The experimental set-up and the force-displacement curve for the conducted tensile tests are shown in Figure 6. All specimens are clamped with a clamping length of 60 mm. The result indicates a regular increase of the force and a brittle fracture behavior with a low deformation. Apart from specimen 5, the transmittable forces are close together--between 0.62 kN and 0.68 kN. Figure 5: Bar plots of force (**a**) and strength (**b**) each with standard deviation of tensile, lap-shear, and compression-shear multi-material test specimens with fracture pattern.