# Space Node Topology Optimization Design Considering Anisotropy of Additive Manufacturing
## 2 Materials and Methods
### 316L Stainless-Steel Anisotropy and Microscopic Research  
To obtain the anisotropic mechanical properties of 316L stainless-steel components manufactured using SLM technology, this paper printed small-sized samples based on the ASTM-E8 specification, conducted tensile tests, and studied the mechanical properties in each molding direction. The morphological changes of the samples before and after stretching were analyzed by SEM, and the failure mechanism was explored. The tensile properties of the specimen were determined according to the ASTM-E8 metal tensile test specification, which is a dumbbell-shaped specimen, as shown in Figure 3, and the specific dimensions are shown in Table 1.  
In order to compare the influence of the mechanical properties of the 316L stainless-steel printed parts in all directions, the test pieces in this paper were printed in three \begin{table}
\begin{tabular}{c c} \hline \hline
**Name** & **Length (mm)** \\ \hline Gauge length G & 25 \\ Clamping section width C & 10 \\ Clamping part length B & 30 \\ Total length L & 100 \\ Width W & 6 \\ Thickness T & 6 \\ Radius R & 6 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Parameters of 316L stainless-steel sample. Figure 3: Schematic diagram of SLM 316L stainless-steel metal specimen. orientations: vertical, side, and flat. The scanning path direction and printing direction of the samples manufactured in this paper are shown in Figure 4.  
The coding of the sample in Figure 4 indicates the plane on which the largest surface of the sample is located. For example, the largest surface of the vertically printed sample is in the ZX plane in Figure 4; hence, ZX is used to represent vertical printing. There was a difference between vertical and flat printing. When the vertically printed sample was stressed, the bonding of each layer of the printed surface was relatively weak, which affected the tensile properties. For the flat-printed style, the performance in this direction was best since the direction of the tensile test was the direction of the scanning path and stretched along the grain. Side-printed samples also performed better in tensile tests than those printed vertically. However, the side-printed samples did not stretch according to the scanning path during the tensile test; hence, the mechanical properties were weak. In general, the mechanical properties of the flat-printed samples should be the strongest, and the vertical-printed samples should be the weakest. The parameters of 316L stainless-steel material are shown in Table 2, and the sample printing process parameters are shown in Table 3.  
In order to ensure that the performance comparison of the specimens was valid, all printed specimens were manufactured and printed under the same process parameters. In this paper, the failure of the sample before and after the tensile test was observed, and the difference in the internal structure of the sample was observed through SEM analysis. The results are compared in Section 3.3. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Physical properties**} & \multirow{2}{*}{\begin{tabular}{c} Particle size (\(\mu\)m) \\ 15–53 \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} Shape \\ Ball type \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} Hall flowmeter (s) \\ 40 \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} Loose packing density (cm\({}^{3}\)) \\ 3.9 \\ \end{tabular} } \\ \hline \multirow{4}{*}{\
\begin{tabular}{c} **Elemental composition** \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} Fe \\ margin \\ \end{tabular} } & S & Cr & P \\  & & \(\leq\)0.03\% & 16–18\% & \(\leq\)0.0045\% \\ \cline{2-5}  & Ni & Mo & Mn & C \\  & 10–14\% & 2–3\% & \(\leq\)2\% & 0.03\% \\ \hline \hline \end{tabular}
\end{table} 
Table 2: The stainless-steel metal powder parameters. Figure 4: Schematic diagram of sample printing: (**a**) printing direction; (**b**) finished product.