Mathematical modeling of static long-term storage of corrugated boxes

The compression strength of a corrugated container is used to indicate the amount of top load that the corrugated container can withstand. This can be done by performing the standard test procedure, ASTM D 642. During long-term storage, the strength of a corrugated box will be substantially reduced over time. The corrugated container life can be determined by applying empirical strength retention factors obtained from published data. However, most published data is from decades ago and is questionable since the board making process and the content of paper has been changed significantly since then, especially due to the increased use of recycled paper. The accuracy of strength retention factors from published data was checked by placing dead loads on top of corrugated boxes. The time it took for the boxes to collapse was investigated. The results show that these published strength retention factors greatly overestimate box endurance. A new method for predicting failure times based on a mathematical model is presented here. The new test method uses a compression tester to compress a test box at a constant load level equal to a fraction of the ASTM D 642 compression strength. The deflection due to creep was recorded over a 12-hour time period, which is a realistic limit for industry practice. A mathematical model was built based on engineering failure analysis. The results show a marked improvement in predictability using this method. The results also support the fact that corrugated boxes collapse during long-term storage when they absorb a critical amount of energy.