Acrylic Display Box Failures

Rapperport Associates was engaged to determine why one shipment of boxes arrived completely intact while the contents of the other shipment were so badly damaged. It was initially suspected that the damage was the result of mishandling during shipping but the display boxes were well packed and no damage was observed in the packaging materials or with the shipping container.

We traced the failures to the difference in elevation change between the rail routes between the two shipments. The shipment that arrived intact experienced a maximum altitude of 4,612 ft during rail transit and the shipment that was badly damaged was subject to a maximum elevation of 7,355 ft during rail transit. The boxes were hermetically sealed which prevented the interior box pressure from equilibrating with the decrease in atmospheric pressure from elevation gain during transit. The higher elevation resulted in a greater pressure differential from inside to outside the box (3.48 psi versus 2.26 psi) which caused the boxes to burst.

This failure mechanism was confirmed by a finite element stress analysis which predicted box failure at the higher elevation but not at the lower elevation and was also remarkably consistent with exemplar pressure testing.

The plot of finite element stress analysis results on the left shows the von Mises stress contours for a 16x16x16 inch acrylic display box subjected to a uniform 2.62 psi internal pressure. Areas shaded in reds, oranges, and yellows indicate areas of high stress.

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