## 2 Materials and Methods
The compliances of the bulk and cohesive interfaces are \(1/E_{m}\) and \(1/Lk\), respectively, resulting in the overall compliance,  
\[\frac{1}{E_{\text{eff}}}=\frac{1}{E_{m}}+\frac{1}{Lk} \tag{1}\]  
where \(E_{\text{eff}}\) is the effective elastic modulus of the material. Clearly, \(1/E_{\text{eff}}\) and \(1/E_{\text{m}}\) are effective and bulk compliances. To relate this simple 1D model to the microstructure shown in Figures 2a and 5a, \(L\) is set to the average spacing of the melt pools in the vertical direction. Subsequently, \(E_{m}\) can be considered to be the elastic modulus of the bulk material within the melt pools. Finally, \(E_{\text{eff}}\) corresponds to the vertical stiffness of SLM from Table 1 (160.80 GPa). We note that Equation (1) will be exact for the vertical stiffness of material only if in Figure 2a, the melt pool lines are horizontal lines separated by distance \(L\). However, this equation still provides a good starting point for choosing the combinations of the bulk material stiffness, \(E_{\text{m}}\), and cohesive model stiffness, \(k\), that result in a vertical stiffness close to the experimental value of 160 GPa in Table 1.  
Interestingly, the 1D equation relating \(k\), \(E_{m}\) has worked well in the calibration process by varying \(k\), calculating \(E_{m}\) from (1), and assigning reasonable values for \(\sigma_{max}\) and \(\phi\), the other two parameters of the TSR in Figure 6. Specifically, we choose a value of \(\sigma_{max}\) equal to the macroscopic vertical strength of the bulk material equal to 1.08 GPa in Table 1. Unfortunately, no energy measure was provided in the experimental results of [38]; thus, there is no direct means to assign the value of \(\phi\). However, computational results provided some guidance on choosing a reasonable value for \(\phi\); in Figure 6, the area under the unloading line represents the energy reserve past the maximum strength of the interface; the smaller \(\beta\) is defined as the ratio of the unloading to loading energies, the more brittle the behavior of the TSR is. From the simulation of SVEs of different sizes, we encountered nonconvergence problems when \(\beta\lesssim 2\). \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \multicolumn{2}{c}{**Experimental**[38]} & \multicolumn{2}{c}{**Calibration Domain**} \\ \cline{2-5}  & **Horizontal** & **Vertical** & **Horizontal** & **Vertical** \\ \hline Young’s Modulus (GPa) & 172 & 160 & 171.75 & 160.80 \\ \hline Yield (max) Strength (GPa) & 1.09 & 1.08 & 1.27 & 1.07 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Experimental results compared to simulation results for vertical and horizontal load cases. In short, in the calibration process, we only varied the value of \(k\), with the corresponding value of \(E_{m}\) obtained from Equation (1), \(\sigma_{max}=1.08\) GPa and \(\phi\) obtained from \(\beta=2\). Figure 7a,b show the computed vertical stiffness, \(E_{v}\), and strength, \(\sigma_{v,\max}\), as a function of \(k\). Interestingly, for the same value of \(k\approx 72\) GPa/\(\upmu\)m, the vertical \(E_{v}\) and \(\sigma_{v,\max}\) from Table 1 are matched simultaneously. Having chosen \(k=72\) GPa/\(\upmu\)m, other parameters are obtained from the process explained earlier and are reported in Table 2, noting that \(\phi=0.025\) GPa-\(\upmu\)m is the rounded-up fracture energy corresponding to \(\beta=2\), and a Poisson ratio of \(\
u=0.3\) is a typical value chosen for steel. Figure 8a shows the VE geometry and boundary conditions used to calibrate the material properties discussed above. Displacement boundary conditions were applied to the top of the domain with a fixed BC at the bottom. Traction-free BCs are used on the left and right sides to match the experimental setup. The corresponding vertical stress vs. strain response is depicted in Figure 8b for the final calibrated parameters. The slope of the linear part matches \(E_{v}=160.80\) GPa and the maximum strength matches \(\sigma_{v,max}=1.08\) GPa in Table 1 from [38] (see the last two columns).