## 3 Results and Discussions
### Porosity Analysis of the Multi-Material Composite
The pores are distributed between the constituent material volumes (volumes 1 and 2) based on the sorting procedure of the proposed methodology. The pore characteristics (radius, diameter, center X/Y/Z, volume, and surface) for each constituent (composite 1 and composite 2) were saved in distinct sheets of a Microsoft Excel file and subsequently analyzed. * Based on the numerical CT results, the following parameters were calculated (Table 2):  
Figure 11: Visualization of the 3D stereolithography (STL) model for the multi-material composite (left column), composite 2 (middle column), and composite 1 (right column). Figure 10: Splitting procedure of the multi-material volume into constituent materials volumes for sample S1. A local coordinate system is represented within the figure. * Total volume of the multi-material composite (\(V_{\rm mat}\));
* Volume of composites 1 and 2 (\(V_{\rm mat\,1}\) and \(V_{\rm mat\,2}\));
* Pores volume (\(V_{\rm pore1}\) and \(V_{\rm pore2}\)) within composites 1 and 2;
* Porosity of composites 1 (\(P_{\rm mat1}\)) and 2 (\(P_{\rm mat2}\)). The mass of the multi-material (\(M_{\rm multi-mat}\)) was determined using a scale for all the samples. Following this, the multi-material density (\(\varrho_{\rm multi-mat}\)) was then calculated for all samples. Detailed results related to the porosity and the density of panel 1 are shown in Table 2. This procedure was then repeated for panels 2 and 3, the results for which are shown in Table 3.  
The porosity of all five samples for three panels was determined based on the proposed methodology. An interval plot to examine the distributions was subsequently created. The confidence level for each interval is 95%. The means and confidence intervals appear to be consistent for all the panels (Figure 12). The interval plot of the multi-material density for all the panels is shown in Figure 12c. Finally, it may be concluded that the variance of the porosity assures the manufacturing reproducibility of the panels. The results of the confirmatory experiments (Table 3) show that the mean porosity of the composite panel (Figure 12a,b) is confirmed with an error of 0.004% for composite 1 and 0.54% for composite 2. \begin{table}
\begin{tabular}{l c c c c c c c} \hline \hline \multicolumn{1}{c}{**Panel 1**} & & & & & \\ \hline \multicolumn{1}{c}{**Sample**} & **S1** & **S2** & **S3** & **S4** & **S5** & **Mean** & **SD 1** \\ \hline \multicolumn{1}{c}{V\({}_{\rm multi\_mat}\) [mm\({}^{3}\)]} & 7770 & 8350 & 7250 & 7180 & 7480 & 7606 & - \\ \multicolumn{1}{c}{V\({}_{\rm mat\,1}\) [mm\({}^{3}\)]} & 2206 & 3156 & 2283 & 2445 & 2897 & 2597.4 & - \\ \multicolumn{1}{c}{V\({}_{\rm mat\,2}\) [mm\({}^{3}\)]} & 5564 & 5194 & 4967 & 4735 & 4583 & 5008.6 & - \\ \multicolumn{1}{c}{V\({}_{\rm pore\,1}\) [mm\({}^{3}\)]} & 3.93 & 4.01 & 2.67 & 2.85 & 5.39 & 3.77 & \\ \multicolumn{1}{c}{V\({}_{\rm pore\,2}\) [mm\({}^{3}\)]} & 1890 & 1485 & 1443 & 1561 & 1494 & 1581.8 & - \\ \multicolumn{1}{c}{P\({}_{\rm mat\,1}\) [\%]} & 0.178\% & 0.127\% & 0.117\% & 0.117\% & 0.186\% & 0.145\% & 0.0003 \\ \multicolumn{1}{c}{P\({}_{\rm mat\,2}\) [\%]} & 33.97\% & 28.59\% & 29.05\% & 32.97\% & 32.60\% & 31.44\% & 0.024 \\ \multicolumn{1}{c}{M\({}_{\rm multi\_mat}\) [g]} & 13.335 & 15.031 & 12.536 & 12.216 & 12.041 & 13.032 & - \\ \multicolumn{1}{c}{\(\rho_{\rm multi\_mat}\) [g/cm\({}^{3}\)]} & 1.716 & 1.8 & 1.729 & 1.701 & 1.730 & 1.735 & 0.038 \\ \hline \hline \end{tabular} \({}^{1}\) SD—standard deviation.  
\end{table} 
Table 2: Material characterization for the first experiment (panel 1).