Study on the effect of geometrical parameters on energy absorption capability of two auxetic materials

Abstract

Auxetic cellular structures have attracted considerable attention for impact energy-absorption applications because their negative Poisson’s ratio (NPR) promotes deformation-induced densification and improved energy dissipation. However, the coupled influence of loading velocity and unit-cell geometry on the dynamic crushing behaviour of auxetic lattices remains insufficiently understood, particularly for hybrid re-entrant–chiral configurations. In this study, the dynamic compression behaviour of a re-entrant auxetic (REA) structure and a re-entrant chiral auxetic (RCA) structure is investigated using analytical modelling and finite element simulations. Both lattices are modelled as a 6 × 4 unit-cell assembly and compressed between rigid platens at impact velocities ranging from 5 to 200 m/s. The analytical model is developed to estimate the Poisson’s ratio and energy absorption capacity of the unit cells based on ligament bending and rotational deformation mechanisms. The numerical model is validated at both unit-cell and multi-cell levels by comparing deformation modes, Poisson’s ratio, and energy absorption with analytical predictions and published studies. A parametric investigation is then conducted to evaluate the influence of key geometric parameters, including internal angle, horizontal strut length, inclined strut length, and ring radius. The results show that deformation in the REA structure is primarily governed by ligament bending, which leads to localised collapse bands under dynamic loading. In contrast, the RCA structure exhibits a combined ligament-bending and node-rotation mechanism that promotes more distributed deformation. Increasing impact velocity increases plateau stress and specific energy absorption by inertia-induced stabilisation of ligament deformation. Geometric parameters strongly influence both auxetic response and specific energy absorption by controlling ligament slenderness and rotational kinematics. In particular, horizontal strut length significantly increases the energy absorption capacity, while inclined strut length and ring radius exhibit non-monotonic behaviour, suggesting the existence of favourable geometric configurations. These findings provide mechanistic insights and design guidelines for tailoring auxetic lattice geometries for impact-energy-absorption applications.