Optimization of slenderness ratio and visco-elastic material properties in a 2D hybrid auxetic lattice for enhanced impact mitigation

Armor is known to protect underlying targets by reducing force transmission during impact events. However, the kinetic energy associated with an impact, often underappreciated, can be as destructive as the force, causing relative motion in the target and consequent damage. Therefore, efficient protective gear and packaging should be lightweight and effective at both force reduction and energy mitigation. Although auxetic lattices have been studied as lightweight alternatives for force reduction, the simultaneous optimization of force reduction and energy dissipation in impact mitigation, through geometric configurations and material selection, has not been addressed. In the present study, we demonstrate that a 2D auxetic lattice, optimized for the slenderness ratio of its struts and for elastic and viscoelastic material properties, can not only reduce the transmitted peak force but also significantly mitigate energy. By employing a multi-step optimization method integrated with Finite Element (FE) analysis, we achieve an optimal auxetic lattice design that simultaneously considers both peak force and energy mitigation. Our results are further validated through theoretical analyses from existing literature.