MINIMUM SAMPLE SIZE NEEDED TO CONSTRUCT CUSHION CURVES BASED ON THE STRESS-ENERGY METHOD

Cushion curves are graphical tools used by protective package designers to evaluate and choose foamed cushioning materials. Thousands of samples and hundreds of laboratory hours are needed to produce a full set of cushion curves according to the ASTM procedure D 1596. The stress-energy method considerably reduces the number of samples needed to construct cushion curves for closed-cell cushioning materials. Consequently the laboratory and data analysis time are reduced as well. The stress-energy method was used to find the minimum sample size needed to construct cushion curves for closed-cell cushioning materials. A reference set of data collected for ARCEL Resin¨ foam blocks using the stress-energy method was used. Lines fitted to this reference data set were statistically compared against lines fitted to reduced size sample sets. This comparison revealed that 15 samples (5 replicates at 3 energy levels) were sufficient to fit lines without statistical difference. The data analysis also showed a limitation of the stress-energy method associated with densities higher than 2.2 lb/ft3 for the materials used. Cushion curves for two densities of expanded polyethylene were successfully constructed using the reduced sample size of 15. These curves were compared to published data for EPE and were found to vary within expected lab-to-lab tolerance