Volume 33, Issue 4 (July 2005)
Predicting Collapse Times for Corrugated Boxes Under Constant Top Load Using Short-Term Creep Tests
The ability of a corrugated box to withstand the weight of other packages on top of it is determined by its compression strength. The compression strength of a box is measured by squeezing it in a compression test machine following the standard procedure, ASTM D 642. The loss of strength over time is substantial and can be estimated by applying empirical strength retention factors. But most published factors came from long-term stacking tests done decades ago, when corrugated board was made from paper that had virtually no recycled content. The use of recycled paper has increased significantly since then, making the accuracy of these data questionable. The accuracy of published strength retention factors was checked by placing weights on top of test boxes and measuring the time it took for the boxes to collapse. The results show that these published factors greatly overestimated failure times. A new method for predicting failure times using creep tests is presented here. Using the compression test machine, a constant load equal to a fraction of the ASTM D 642 compression strength was placed on a test box and the deflection was recorded over a 12 h time period. The failure time in long-term storage under the same load was estimated from a simple extrapolation of the creep data. The results show a marked improvement in predictability using this method.