## 3 Results and Discussion
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \multirow{2}{*}{**Material**} & \multirow{2}{*}{**Relative Density**} & \multicolumn{3}{c}{**Elastic Modulus 1 (GPa)**} & \multicolumn{3}{c}{**Yield Strength 1 (MPa)**} & \multicolumn{1}{c}{**Ultimate Strength 1 (MPa)**} \\ \cline{3-8}  & & **Experimental Study** & **Analytical Method [17]** & **Analytical Method [19]** & **Experimental Study** & **Analytical Method [17]** & **Experimental Study** \\ \hline \multirow{3}{*}{316L} & 50.48 & 44.18 (1.89) & 42.95 & 43.52 & 47.31 (0.34) & 41.78 & 100.83 (1.29) \\  & 61.87 & 54.89 (4.43) & 50.34 & 51.43 & 63.68 (2.26) & 48.98 & 124.91 (0.28) \\  & 72.94 & 76.07 (5.60) & 57.73 & 59.59 & 78.54 (2.57) & 56.17 & 164.02 (2.66) \\ \hline \multirow{3}{*}{17-4 PH} & 50.68 & 42.51 (2.77) & 41.31 & 41.86 & - & - & 155.05 (5.37) \\  & 62.19 & 53.28 (2.60) & 48.42 & 49.47 & - & - & 198.36 (6.60) \\ \cline{1-1}  & 73.60 & 74.73 (3.18) & 55.53 & 57.32 & - & - & 271.97 (5.11) \\ \hline \end{tabular} \({}^{1}\) Standard deviation is depicted in the brackets (SD).  
\end{table} 
Table 4: The mechanical properties of the infill specimens obtained from the tensile tests and analytical methods. Figure 12: S–N curves of the 316L full-solid specimens in a linear–log plot and linear fitting in a log–log plot. Figure 13: S–N curves of 316L infill specimens with different densities in a linear–log plot and linear fitting in a log–log plot. To estimate the lifetime of the specimens with different stress levels, a relationship between the maximum stress \(S_{max}\) and lifecycle \(N_{f}\) can be expressed as  
\[S_{max}=A\Big{(}N_{f}\Big{)}^{B} \tag{9}\]  
where \(A\) and \(B\) are constant parameters obtained from curve fitting using linear regression, as shown in Figures 12 and 13, in which the relationship between \(\log(S_{max})\) and \(\log\Big{(}N_{f}\Big{)}\) is linear. The \(A\) and \(B\) parameters for each relative density of the infill specimens and the fatigue limit at \(10^{6}\) cycles are presented in Table 5. In linear regression, the determination (\(R^{2}\)) is used to measure how well the data fit the regression model or the goodness of fit. The fatigue test results show a good fitting, with \(R^{2}\) close to 1. As expected, the specimens with a higher relative density show a greater fatigue limit and \(A\) parameters, while \(B\) yields similar constant values. The weight efficiency, defined as the relationship between a considered mechanical property and the relative density, can be computed using Equation (8). The elastic modulus and ultimate tensile strength were the mechanical properties considered for calculating the weight efficiency, i.e., \(e_{E}\) and \(e_{UTS}\). Table 6 shows the values of the weight efficiency with different relative densities. The weight efficiency is used to assess the efficiency of the infill specimens with different densities by concerning the mechanical properties and weight of the specimens. In fact, the greater the relative density, the more weight efficiency of the specimens. Nevertheless, this behavior is not linear because the weight efficiency rapidly increases when an infill specimen is denser, closer to being a full-solid one. Thus, selecting an appropriate relative density for the infill specimens could be taken into account to minimize the weight. It can be seen from Table 6 that the values of \(e_{E}\) of the 316L and 17-4 PH infill specimens are similar, while the values of \(e_{UTS}\) are slightly different. The \(e_{E}\) and \(e_{UTS}\) show little difference between the 316L and 17-4 PH specimens, with 16% and 20% infill densities. In contrast, the \(e_{E}\) and \(e_{UTS}\) of the specimens with 24% infill density show a noticeable increase. It is implied that, if the weight is a major consideration, the specimens with 16% and 20% infill densities yielding similar performance per weight can be used. However, when strength is the main requirement, the specimens with 24% infill density may be a better choice.