Mid-plane forces during stress wave propagation through 1D granular chains of closed-cell PVC foams

This study presents the first experimental investigation of stress wave propagation in 1D granular chains of closed-cell PVC foam disks. Average impact velocities for H130 and H250 foams ranged from 17.6 to 38.1 m/s. The analysis focuses solely on the incident stress wave, excluding the reflected wave. The mid-planes of the disks were chosen for analysis due to their uniaxial force components along the chain's length. The results show that the stress wave speed is faster in the H250 foam chain due to its higher stiffness. Wave speed increases with impact velocity but decreases as it travels along the chain, with a more pronounced reduction in the H130 foam compared to the H250 foam. The peak normal forces in the H250 foam chain disks are approximately three times greater than those observed in the H130 foam chain disks at comparable impact velocities. The peak normal forces in both foam chains decrease rapidly with increasing impact velocity, especially over the first few disks. As the wave propagates further from the impact source, the attenuation rate slows, with a more gradual force reduction in the H250 foam due to its higher density and stiffness. Energy loss is governed by viscoelastic and plastic dissipation at disk contacts, which becomes more significant at higher impact velocities. This study provides new insight into dissipative wave phenomena in granular systems of deformable elements and offers experimental data for future modeling of strongly nonlinear, dissipative granular media.