## 2 Materials and Methods
### Numerical Simulations  
To simulate the behavior of the IGU tested in the experimental campaign, an FE reference model was developed in the ABAQUS CEA software [39]. It consists of two parallel planar shells representing glass panes, and one extruded rectangular shell referring to an aluminum spacer and secondary sealing (Figure 4). The components are connected by hinged tie constraint elements and create a closed volume representing the air gap. The glass plates are rectangular 500 mm \(\times\) 500 mm with a thickness of 6 mm. For the spacer, a 10 mm shell was applied. For all shells, five integration points across the cross-section of the shell were applied. The axial gap between the glass plates equals 16 mm, resulting in the same gas volume entrapped between the panes. Figure 4b displays the mechanical boundary conditions. The model was supported at the bottom edge to simulate the simply supported setup. The panes were supported laterally along the edges to represent the real boundary conditions in the experiments.  
\begin{table}
\begin{tabular}{c c c c} \hline
**Series** & **Volume of Injected/Sucked** & **Equivalent Change of Gas** & **Equivalent Change in** \\  & **Gas [mL]** & **Temperature in Gap \(\Delta T_{\rm sim}\) [\({}^{\circ}\)C]** & **Atmospheric Pressure \(\Delta p_{\rm sim}\) [kPa]** \\ \hline
1 & +50 & 3.977 & \(-\)1.334 \\
2 & +100 & 7.954 & \(-\)2.652 \\
3 & +150 & 11.934 & \(-\)3.953 \\
4 & +200 & 15.908 & \(-\)5.236 \\
5 & \(-\)50 & \(-\)3.950 & +1.342 \\
6 & \(-\)100 & \(-\)7.845 & +2.684 \\
7 & \(-\)150 & \(-\)11.685 & +4.023 \\
8 & \(-\)200 & \(-\)15.471 & +5.364 \\ \hline \end{tabular}
\end{table}
Table 1: Overview of experiments.  
The analyses used 20 mm square finite elements (4-node elements, known as S4R from ABAQUS library [39]), which divided the glass plate into 25 elements in each direction. The authors provided the mesh convergence tests in the previous study [9].  
The air inside the IGU is represented by the 'fluid cavity' interaction component from the ABAQUS library [39]. The initial temperature of the panes and the air entrapped in the gap was assumed to be 20 \({}^{\circ}\)C, and ambient pressure before loading was set to 100 kPa. In the analyses, the following constants were used: the universal gas constant \(R_{\text{u}}=8.314\,J/(K\cdot\text{mol})\)[40] and the molecular weight of dry air: \(M_{\text{air}}=28.97\times 10^{-3}\) kg/mol [41]. The initial volume of the cavity is constant and equal to \(4\times 10^{-3}\) m\({}^{3}\), which corresponds to a cubic volume of 500 mm \(\times\) 500 mm \(\times\) 16 mm.  
To simulate the behavior of the air entrapped inside the IGU, a fluid cavity component was applied inside the closed space of the model [18; 39]. The Gas Flux internal property feature was used to simulate the additional gas exchange volume in the experiments. The analyses used the Explicit solver, a dynamic method with a constant load increment.  
The mechanical properties of the materials assumed for the analyses are shown in Table 2. The properties of glass are based on [42]. Because the main aim of the spacer was to create the closed volume between the panes, a relatively high Young's modulus was arbitrarily used.