Dekoninck L., Botteldooren D.

On request of an industrial partner, a technique was developed to measure the noise of crumbling packaging materials. According to a study with their costumers, the noise produced when unwrapping the product was a major issue. Thus a technique to quantitatively compare different packaging material with regard to acoustic emission during crumbling was needed. Several questions needed to be answered. How to create a system that allows crumbling the material in a reproducible way? What is the influence of the speed of crumbling? How should a low cost standardized method look like and how could it be calibrated? After testing several alternative methods – that will briefly be discussed –, a tubular specimen, crumbled inside a cavity close to a microphone is used. The specimen is slid over a horizontal bar and is only restricted in its movement by the piercing bar, hereby forcing the sample to crumble in a controlled way. A constant, tunable crumbling speed was obtained using a stepping motor. Both SEL and LAeq during crumbling are found to be useful to discriminate between materials using a single number indicator. Spectral measurements confirm that the acoustic emission is mainly in the kHz frequency range. More interestingly, the temporal fluctuation of sound level during crumbling shows a pattern typical for complex systems for most, but not all of the tested materials. A clear effect of aging of samples that are crumbled several times can be observed.