Modeling of Impact Properties of Auxetic Materials: Phase 1

Abstract : The report describes a recent investigation on the impact properties of auxetic materials which are special materials with a negative Poissons ratio. These materials have been demonstrated to have some unique characteristics and may provide advantages over the conventional engineering materials in certain applications. The objective of the present study was to gain a better understanding of the behaviour of the auxetic materials subjected to impact loads and to determine the influence of the various geometric parameters associated with the material on its performance as protective layer of military structures through a parametric study. A simplified model was utilized, which included conventional and re-entrant honeycomb foam structures resting on a rigid surface and impacted by a rigid mass. The time histories of the internal energy absorption, the impact force and the velocity reduction of the impacter were predicted and used to compare the relative performance of the honeycombs with different geometries. The numerical analyses were first carried out based on shell elements in LS-DYNA and the finite element models were verified for linear and nonlinear static analyses. However, the numerical results of impact simulations indicated some issues with the treatment of the internal contacts between the deformed ribs. Further analyses are underway at the present time to use solid elements which can deal with the contact conditions more reliably.