Slenderness Ratio and Material Optimization of an Impact-Resistant 2d Auxetic Lattice

Abstract

It is well known that armor prevents failures of behind-armor targets by reducing the force in an impact event and thereby providing protection under certain impact events. However, the kinetic energy associated with an impact, often underappreciated in impact events, can be as fatal as the force by causing relative motion in the target and destructive damage as a consequence. Therefore, efficient protection gear and packaging should be lightweight and good at force reduction as well as energy mitigation. Although auxetic lattices have been studied as lightweight alternatives for force reduction, simultaneous optimization of force reduction and energy dissipation in impact mitigation via geometric and material choices for auxetic lattices has not been addressed. In the present study, we show that a 2D auxetic lattice with an optimized slenderness ratio of the struts that comprise the lattice and optimized elastic and visco-elastic material properties can not only reduce the transmitted peak force but also mitigate the energy significantly. A multi-step optimization method using Finite Element (FE) analysis and a verification procedure via impact experiments are described by which an optimal design of the auxetic lattice can be achieved by simultaneously considering both peak force and energy mitigation.

Keywords: Material optimization, Slenderness ratio, Auxetic lattice, Visco-elastic material, Impact mitigation.