## 3 Results and Discussion
### EPS Box Strength Study  
#### Stacking Strength Test  
Load-deformation curves obtained from the stacking strength test and simulation results of three models corresponding to EPS boxes in test groups were plotted in a single graph, as shown in Figure 8a. Load values at 10 mm displacement from simulation and experiments were extracted, together with the maximum load values from experiments, as shown in Figure 8b and Table 6. The stacking strength of a box herein is defined as the maximum load the box withstands. In compression and flexure tests, EPS23 exhibited higher strength than EPS22. Consequently, the stacking strength of EPS-B23 was 2.7% higher than EPS-B22 and slightly brittle. In the simulation, it was 7.9% higher. The difference in stacking strength test results was not as large as in mechanical properties tests since more factors affect the whole box's strength. Unexpectedly, the stacking strength of EPS-B23X was 10.5% higher than EPS-B23, and the load pattern was slightly different; there was a visible rise in load after experiencing a considerable plateau region for some time, which was not observed in EPS-B23. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Reference** & **Standard** & **Density (kg/m\({}^{3}\))** & **Specimen Size (mm)** &
\begin{tabular}{c} **Compressive** \\ **Strength (kPa)** \\ \end{tabular} \\ \hline [PERSON] [18] (2022) & ASTM D 1621 & 20 & Cubical 50 \(\times\) 50 \(\times\) 50 & 126 \\ [PERSON] [19] (2020) & ISO 844 1 & 20, 25 & Cubical 50 \(\times\) 50 \(\times\) 25 & 112, 138 \\ [PERSON] and [PERSON] [7] (2017) & ASTM D 1621 & 20 & Cubical 50 \(\times\) 50 \(\times\) 50 & 112 \\ [PERSON] and [PERSON] [32] (2016) & ASTM D 1621 & 19 & Cubical 50 \(\times\) 50 \(\times\) 50 & 105 \\ [PERSON] and [PERSON] [6] (2014) & ASTM D 1621 & 20 & Cylindrical D63.5 \(\times\) 127 & 101 \\ [PERSON] and [PERSON] [8] (2014) & ASTM D 1621 & 21.6 & Cubical 50 \(\times\) 50 \(\times\) 50 & 160 \\ This study & ASTM D 1621 & 22, 23 & Cubical 50\(\times\)50\(\times\)22 & 165, 177 \\ \hline \hline \end{tabular} \({}^{1}\) Equivalent to ASTM D 1621.  
\end{table} 
Table 5: Comparison of EPS compressive strength with previous studies. The simulation results were always slightly higher in comparison between simulation results and experiment results. Considering the load at 10 mm deformation, Sim22 was 0.1% higher than EPS-B22, and Sim23 was 5.8% higher than EPS-B23; the difference between Sim23X and EPS-B23X was 2.2%. Buckling was observed in both experimental and simulation results; the instability that occurred on the walls could be the principal cause of the failure of the boxes. Equivalent stress distribution and locations of plastic strain across the body, under the same stacking load of 4.5 kN, are shown in Figure 9. Sim22 was observed to be the one \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & \multicolumn{4}{c}{**Stacking Strength Test**} & \multicolumn{4}{c}{**Bottom Strength Test**} \\ \cline{2-7}
**Test Group** & **Simulation (kN)** & **Load@10 mm** & **Maximum Load (kN)** & **Deformation (mm)** & **Breaking Load (kN)** & **Deformation (mm)** \\ \hline EPS-B22 & 4.5 & 4.5 (0.017) & 4.8 (0.034) & 22.7 (0.8) & 3.1 (0.14) & 6.5 (0.6) \\ EPS-B23 & 4.9 & 4.6 (0.026) & 4.9 (0.036) & 21.6 (0.8) & 2.8 (0.12) & 5.6 (0.6) \\ EPS-B23X & 5.1 & 5.0 (0.061) & 5.5 (0.044) & 31.3 (2.0) & 2.2 (0.16) & 4.5 (0.3) \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Results of stacking and bottom strength tests of EPS boxes. Figure 8: Stacking strength test and bottom strength test results of EPS boxes. (**a**) Load-deformation curve from the stacking strength test. (**b**) Comparison of stacking loads. Sim: simulated stacking load at 10 mm deformation; Exp10: tested stacking load at 10 mm deformation; ExpMax: tested maximum stacking load. (**c**) Load-deformation curve from the bottom strength test. (**d**) Breaking load in the bottom strength test. with the largest equivalent stress and had the most plastic strains, while Sim23X was the smallest and least.