Monitoring the Evolution of Damage in Packaging Systems under Sustained Random Loads

摘要

The ability of protective packaging systems to withstand dynamic loads during transportation is an important consideration when it comes to selecting a suitable material. The performance characteristics of packaging systems are best determined by subjecting the systems (such as cushioning materials and containers) to sustained random loads under controlled conditions. It is during these fatigue endurance tests that the loss of structural integrity of a material or an element needs to be quantified. The research presented herein uses two recently developed continuous structural integrity assessment techniques to evaluate variations in the mechanical properties (namely stiffness) of typical packaging elements. The first technique is based on the short-time Fourier transform, and the other uses an adaptive digital finite impulse response (FIR) filter technique developed by the authors. The effectiveness and the limitations of the techniques were evaluated by undertaking selected controlled experiments during which damage was simulated by varying the length of a single degree-of-freedom vibratory system subjected to random base excitation. The materials used for the controlled experiments include steel, aluminium, acrylic and carbon fibre. Results show that, although both methods are capable of identifying the level of damage and the time at which it occurs, the FIR technique is generally more sensitive and better able to detect small changes in stiffness. Finally, the ability of integrity assessment techniques to monitor the progression of damage in real packaging elements, such as biodegradable air cushions and corrugated paperboard containers, was established. The analysis of real protective packaging elements subjected to random loads using both structural integrity assessment techniques yielded positive results. Generally, the adaptive FIR technique was found to be more sensitive in detecting small changes in system characteristics, even when the estimates were obtained with relatively coarse temporal resolution. Overall, the results presented in this study indicate that the adaptive FIR technique can be a practical and effective tool for establishing the ability of materials and structures to withstand sustained random loads.