## 4 Model Validation
### Methods
#### 4.2.1 Validation of the FE Simulation of a Warehouse Packing Support Analogue  
In order to measure pallet deflection while under each unit load configuration, a simulated pallet rack was built. The objective of this was to validate the support model without including boxes. Two square, 50.8 mm \(\times\) 50.8 mm, hollow aluminum beams acted as direct supports and the pallet simulator rested on them. A free span of 914 mm between the inside ends of the aluminum beams simulated the common warehouse cracking condition where the pallet is racked across its width. The aluminum beams were placed on top of two I-beams (101 mm wide flange, 101 mm high), which were secured to a rigid, flat platen on the floor.  
To record board deflection, string potentiometers were attached to the center of each side of the pallet simulator (i.e., the PMMA board). Two additional string potentiometers were connected to the racking setup in order to measure and adjust the effects of the test setup when compressed downward from loading. This method assured measurement of only the board's deflection while eliminating any influence from external loading on the test setup.  
While the pallet simulator was being loaded, it was supported from underneath using two car jacks. This was done to avoid any additional bending of the pallet during the loading of the payload. The removal of the car jack supports was done at a slow rate, manually lowering the supports until they had no further contact with the board. Maximum deflection at board midspan was recorded one minute after the supports were removed. All measurements were conducted under standard laboratory conditions (50 \(\pm\) 2% Relative Humidity and 23 \(\pm\) 1 \({}^{\circ}\)C), and every material that was used had been acclimated to those conditions for at least 72 h. Figure 7 shows the experimental test setup for the warehouse racking support simulator.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Property** & **Standard** & **Mean** & **Std. Dev.** & **No. of** \\  & & & & **Samples** \\ \hline ECT (kN m\({}^{-1}\)) & ISO 3037:2013 & 7.20 & 0.21 & 10 \\ FCT (kPa) & ISO 3035:2011 & 154.22 & 24.94 & 10 \\ Thickness (mm) & ISO 3034:2011 & 4.17 & 0.03 & 10 \\ Combined Board & ISO 536:2019 & 654.7 & 5.4 & 5 \\ Weight (g m\({}^{-2}\)) & ISO 536:2019 & 601.4 & 5.4 & 5 \\  & & Inside liner: 203.18 & 2.81 & 5 \\  & & Medium: 182.55 & 3.71 & 5 \\  & & Outside liner: 207.14 & 7.01 & 5 \\ \hline \hline \end{tabular}
\end{table}
Table 7: Material properties of the corrugated board.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Box** & **Dimensions (mm)** & **Weight per Box (kg)** \\ \hline Small & \(254\times 254\times 318\) & 9.07 \\ Medium & \(338\times 254\times 318\) & 12.11 \\ Large & \(508\times 254\times 318\) & 18.14 \\ \hline \hline \end{tabular}
\end{table}
Table 8: Weight and dimensions of boxes used for model validation.  
To evaluate board bending under a specific loading condition and subsequently simulate it, the PMMA pallet analogue was loaded with a steel box, as shown in Figure 7, and the absolute deflection at the center of the board was measured and recorded. Weight box dimensions were 318 mm \(\times\) 114 mm \(\times\) 89 mm, with a weight of 22.7 kg. The experiment was conducted five times.