Monitoring the evolution of fatigue in corrugated paperboard under random loads

During the transportation phase of the distribution cycle, packaging systems are subjected to random dynamic compressive loads that arise from vibrations generated by the vehicle. The level and severity of these dynamic compressive loads are generally a function of the vibration levels, the stack configuration and stack weight. The container's ability to withstand these compressive loads for sufficiently long periods depends on the material's characteristics as well as the container design. The research presented herein tests the hypothesis that cumulative damage in the material under random dynamic compression will result in a reduction in the overall stiffness as well as an increase in the overall damping of the element. These are expected to be manifested, respectively, as a shift in the fundamental resonant frequency as well as an increase in the bandwidth of the frequency response function of the material at resonance when configured as a single degree of freedom system. The paper presents the results of preliminary experiments in which a number of corrugated paperboard samples were subjected to dynamic compressive loads by means of broadband random base excitation with a vibration table coupled with a guided dead-weight arrangement. The level of cumulative damage in the sample was continuously evaluated by monitoring the stiffness and overall damping of the sample which were extracted from the Frequency Response Function (FRF) of the system. This was obtained from continuous acceleration measurements of the vibration table and the guided dead weight.