## 5 Results and Discussion
### Unit Load Segment Results and Discussion  
Using the support test setup that has already been validated and the methods previously described, experimental trials were conducted by loading the board with different box sizes. Small (254 \(\times\) 254 \(\times\) 318 mm), medium (338 \(\times\) 254 \(\times\) 318 mm), and large (508 \(\times\) 254 \(\times\) 318 mm) boxes were tested. The initial deflections recorded at the end of the simulation at the board midspan are shown in Table 9 for the seven different unit load combinations of columns and layers of boxes. Parallel to this, the finite element model was adjusted to the same box sizes and number of layers combinations. Table 9 shows the results for each of the analyses. The mean absolute percent error (MAPE) of the model is 22%. The greatest error with 59% MAPE was observed for the unit loads with the largest boxes (two columns). By limiting the prediction scope of the model to those unit loads with three or four columns, model accuracy improves to a MAPE of 7.8%, which is considered an acceptable accuracy for such a general unit load bending model. Unit loads with three columns presented a MAPE of 12% and those with four columns a MAPE of 1.3%, suggesting an increased accuracy with smaller boxes. The scenario of unit loads of two columns presented a special case that needs to be formulated as a different model in order to accurately predict pallet deflection. The assumptions and simplifications in this project do not properly represent the actual unit load behavior. The boxes in the designed experiment present a large 'rotation' movement when they are under load. This movement is accurately predicted by the model, as seen in Figure 10a. The absolute value predicted, on the other hand, diverges by 29% from the measured experimental value for the 2 \(\times\) 2 unit. A similar case occurs for the unit load of 2 \(\times\) 3. For this scenario, the model underpredicted the overall pallet deflection, with an error of 88%. This specific two-column scenario presented significant differences from the rest of the unit loads studied. When using the friction values obtained by evaluating the linerboard contact properties, as conducted for this study, the actual properties of the contact might not have been properly represented. Corrugated boxes have imperfections. One example could be that there was compression of the flutes or of the linerboard between the fluting structure, albeit small, but that could affect the characteristics of the horizontal box frictions or the pallet frictions. Additional variations could come from the use of packaging tape for the closures and any other environmental impurities when testing, such as dust, that could affect more directly the horizontal surfaces. When measuring the friction with the slide angle method, only the actual contact properties between the linerboards are evaluated, with low weight and perfect samples. Figure 9: Two-dimensional FE model result for the simulated pallet segment and weight box, deformed. Figure values shown in inches. Another reason for the deviation of the model with the two-column unit load can be attributed to the use of non-deformable boxes in the simulations. Unit loads with smaller boxes, such as three and four-column units, presented no deformation and therefore, they are more accurate in their prediction. The larger boxes could have slight deformations in the experimental tests, changing the contact interactions; therefore, changing how the load is transferred to the pallet and ultimately affecting the pallet's deflection. Additionally, the use of no containment force in these experiments allowed the boxes to be freely displaced during the rotation generated through bending. This movement will be much more constrained in an actual unit load, given the use of containment mechanisms. By constraining the contact interactions, the contact interactions are more accurate in their prediction.