# Al-Foam Compression Tests in Parallel and Serial Concepts
## 9 Conclusions  
In this investigation, the effects of varying the density of the foam arrangement were shown through the compression of closed-cell aluminum foam. The inquiry focused on the energy absorption performance since the test was the first step in a later crash-box optimization. Our hypothesis suggests that the actual arrangement of the foams may have a significant impact on the impact energy-absorbing capability of a crumple structure. The study was divided into three parts. In the first section, a single test was presented to reveal the mechanical parameters of the foams used in the test. Subsequently, the specimens were compressed in serial and parallel arrangements at a rate of 1 mm/s up to 80% deflection, while the force and displacement diagram was recorded to construct the stress-strain diagram. The minimum 80% compression was necessary to allow for the full compression of the foam and to be able to investigate each phase separately. The study provided important and useful results that will be applicable in our future research development. In the study, it was established that the energy absorption capacity of a metal foam structure is not directly proportional to its mass and/or volume, contrary to previous assumptions. The relative position of the foams of different densities with respect to the direction of the compression test could be important. Table 7 summarizes the results of the different compression scenarios. Measurements have shown that the same structure of foams will produce different mechanical properties in parallel and in series as seen in Figure 12. The thesis is that the higher-density material can be considered as the base metal in an alloy and the smaller-density foam as an alloying agent that affects the compressive properties of the structure. However, the effect of this physical alloy can be influenced if used in different arrangements. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Type of Method** & **Labels** & \
\begin{tabular}{c} **SEA\({}_{\text{mass}}\)** \\ **[J/g]** \\ \end{tabular} &
\begin{tabular}{c} **SEA\({}_{\text{volume}}\) [J/cm\({}^{3}\)]** \\ \end{tabular} \\ \hline \multirow{2}{*}{Single test} & SP-LD1 & 0.559 & 0.132 \\ \cline{2-4}  & SP-HD1 & 0.541 & 0.199 \\ \hline \multirow{2}{*}{Parallel test} & SP-LD2 + SP-HD2 & 0.524 & 0.308 \\ \cline{2-4}  & SP-LD3 + SP-HD3 & 0.146 & 0.087 \\ \cline{2-4}  & SP-HD4 + SP-LD4 & 0.213 & 0.128 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: SEA of each scenario (own collaboration of authors). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Label**} & \begin{tabular}{c} **SP-LD1** \\ **(0.22 g/cm\({}^{3}\))** \\ \end{tabular} & \begin{tabular}{c} **SP-HD1** \\ **(0.36 g/cm\({}^{3}\))** \\ \end{tabular} & \begin{tabular}{c} **SP-LD2** \\ **+** \\ **SP-HD2** \\ \end{tabular} & \
\begin{tabular}{c} **SP-LD3** \\ **+** \\ **SP-HD3** \\ \end{tabular} &
\begin{tabular}{c} **SP-DH4** \\ **+** \\ **SP-LD4** \\ **SP-LD4** \\ \end{tabular} \\ \hline \hline Arrangement & single & single & parallel & serial & serial \\ \hline \(\sigma_{\text{max}}\) [MPa] & 1.315 & 2.046 & 2.014 & 0.564 & 1.041 \\ \hline \(\sigma_{\text{pl}}\) [MPa] & 1.062 & 1.445 & 2.764 & 1.908 & 1.991 \\ \hline \(\varepsilon_{\text{D}}\) [\%] & 70 & 73 & 63 & 83 & 81 \\ \hline E\({}_{\text{abs. [M]}}\)/m\({}^{3}\)[J] & 0.76 & 1.25 & 1.55 & 1.299 & 1.34 \\ \hline E\({}_{\text{abs-total}}\) [M]/m\({}^{3}\)[J] & 2.653 & 3.996 & 6.163 & 1.756 & 2.56 \\ \hline SEA\({}_{\text{mass}}\) [J/g] & 0.559 & 0.541 & 0.524 & 0.146 & 0.213 \\ \hline SEA\({}_{\text{volume}}\) [J/cm\({}^{3}\)] & 0.132 & 0.199 & 0.308 & 0.087 & 0.128 \\ \hline \(\eta_{\text{plateau}}\) [\%] & 49.64 & 37.39 & 64.61 & 43.37 & 59.42 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Result summarization (own collaboration of authors). The measurements show that the plateau section, which is important for energy absorption, can be influenced from a design point of view.