Density-Dependent Impact Resilience and Auxeticity of Elastomeric Polyurea Foams

Abstract

This research investigates the dynamic response of a novel polyurea foam with different densities by separately submitting samples to single and multiple impacts at different energies ranging from 1.77 to 7.09 J. The impact and transmitted force-time histories are acquired during the impact events. Deformation of the samples is also recorded using high-speed photography and analyzed using digital image correlation (DIC) to characterize density-dependent strain rate and Poisson's ratio. The analyses of the force-time histories highlight the interrelationship between the incoming impact energy and force characteristics, including amplitude and durations. The experimental results reveal that polyurea foams can absorb nearly 50% of the incoming impact energy irrespective of their density. The dynamic impact efficacy of the foam persists even after sequential impact events are imparted on the same samples, with only a 20% drop in the load-bearing capacity after seven consecutive impacts. Furthermore, as verified via electron microscopy observations, the higher-density foam does not exhibit any permanent damage. This high-density polyurea foam shows reversible auxetic transition at all impact energies considered herein. The outcomes of this research indicate the suitability of polyurea foams for cushioning and impact mitigation applications, especially in repeated biomechanical impact scenarios.