On the dynamic compression of cellular materials with local structural softening

Abstract

Analytical and numerical analyses are carried out in order to reveal the importance of the cellular materials topology for their dynamic compaction. The aim is to distinguish between the deformation and energy absorption mechanisms of materials which exhibit local structural softening, such as out-of-plane loaded honeycomb, and materials with local structural hardening (foam). It is shown that the dynamic out-of-plane compaction of honeycombs does not obey the law of shock wave propagation and a new phenomenological model of the velocity attenuation is proposed. It is revealed that the absorbed energy by the honeycomb is proportional to the area under the dynamic stress-strain curve, which is defined by the foil material properties, in contrast to the shock-wave propagation model where the absorbed energy is proportional to the area under the shock chord. Comparisons with the predictions of the Rigid Perfectly-Plastic Locking (RPPL) model, which approximates well the average quasi-static stress-strain characteristic of a honeycomb, are discussed. Special attention is given to the effects of neglecting the honeycomb topology on their response to impact loading.Finite element simulations are carried out to verify the proposed theoretical model revealing the major factors which influence the dynamic response of out-of-plane loaded honeycombs to high velocity impact.