## 4 Conclusions  
EPS is widely used in various industrial fields; in particular, when used as a packaging cushioning material, its greatest advantage is the ability to mass-produce uniform-quality cushioning materials. This study was conducted as a part of the CAE prediction technology development of inclinations for unitized loads of packaged appliances applied to EPS-based cushioning systems. More specifically, the EPS creep properties were validated for ensuring the reliability of the FEA results for creep behavior of EPS-based cushioning systems. The results of this study can be summarized as follows:  
1. The EPS elastic modulus and Poisson's ratio were analyzed as its elastic properties. Because the proportional limit and 10% strain strength of EPS did not exhibit temperature trends for temperatures in the 0-60 \({}^{\circ}\)C range, the elastic modulus and Poisson's ratio were analyzed only for density dependence. Both mechanical properties were significantly affected by the EPS density and increased with increasing density. Compared with the initial tangent modulus (Young's modulus) of the initial proportional portion, the secant modulus was approximately 35-38%, and the tangent modulus was approximately 5-9%. With increasing density, the EPS Poisson's ratio increased almost linearly, and it was approximately 0.095-0.175 for densities in the 16-30 kg/m\({}^{3}\) range. 2. After describing the measured 12-h-long creep data using the Burgers model, the characteristics were qualitatively analyzed using the model's constant values. The instantaneous elastic strain, creep amount, and rate of the transient and steady-state creep phases increased with increasing applied stress. In addition, along with these values, the retardation time significantly differed, depending on whether the applied stress was below or above the proportional limit. However, the effect of density on \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Division**} & \multicolumn{2}{c}{\(\boldsymbol{\rho=16\) kg/m\({}^{3}\)}} & \multicolumn{2}{c}{\(\boldsymbol{\rho=20\) kg/m\({}^{3}\)}} & \multicolumn{2}{c}{\(\boldsymbol{\rho=25\) kg/m\({}^{3}\)}} & \multicolumn{2}{c}{\(\boldsymbol{\rho=30\) kg/m\({}^{3}\)}} \\ \cline{2-9}  & **Step 1** & **Step 2** & **Step 1** & **Step 2** & **Step 1** & **Step 2** & **Step 1** & **Step 2** \\ \hline Experiment (_a_) & 0.76 & 3.47 & 0.64 & 1.11 & 0.62 & 1.55 & 0.72 & 1.88 \\ \hline FEA (_b_) & 0.68 & 3.55 & 0.58 & 1.16 & 0.59 & 1.37 & 0.67 & 1.70 \\ \hline \multirow{2}{*}{Conformity \({}^{(1)}\)} & 89.5\% & 97.7\% & 90.6\% & 95.7\% & 95.2\% & 88.4\% & 93.1\% & 90.4\% \\ \cline{2-9}  & 100\% & & 99.4\% & & 90.3\% & & 91.2\% \\ \hline \hline \end{tabular} Note: \({}^{(1)}\) (upper) \((b)/(a)\) or \((a)/(b)\), (lower) \((b)\) of step \(1+\text{step}\ 2\)\(/(|a)\) of step 1 + step 2\(|\).  
\end{table} 
Table 6: Concordance of experimental and FEA results. Figure 12: Comparison of experimental and FEA results. these properties could not be analyzed because the applied stress levels were different for different densities. 3. As a result of performing two-step FEA on the EPS creep behavior using the measured elastic modulus, Poisson's ratio, and 7-day-long creep data, the concordance between the experimental and FEA results was 89.5-95.2% for step 1 and 88.4-97.7% for step 2; the overall concordance was very high, in the 90.3-100% range. 4. The values of the elastic and viscoelastic properties measured in this study were captured well by FEA. Therefore, by applying the validation results for creep behavior to the material properties in FEA, it is believed that the reliability of the FEA prediction for the inclination amount of unitized loads owing to the displacement of EPS-based cushioning systems in multiple stages of actual packaged appliances can be improved. Data curation, J.M.P. and H.M.J. ; Formal analysis, J.M.P. ; Funding acquisition, H.M.J. ; Investigation, G.Y.L. and D.H.K. ; Software, J.M.P. and H.M.J. ; Validation, J.M.P. ; Visualization, J.M.P.