Instrumented Dynamic Penetration of Sandwich Panels with Auxetic and Non-Auxetic Core using Direct Impact Hopkinson Bar

Abstract

This article deals with the dynamic penetration of 3D-printed panels with auxetic and conventional honeycomb unit cell-based cores. The geometry of the unit cells and their periodic assembly in the resulting lattices are selected to ensure the same relative density and overall weight of the individual sample types. Such a similarity of both specimen types allows for the evaluation of differences between conventional and auxetic lattices in terms of penetration characteristics and deformation energy mitigation properties. Dynamic penetration of the samples is performed using a fully strain-gauge instrumented open Hopkinson pressure bar at three impact velocities resulting in three loading scenarios. All the performed experiments are captured by two optical cameras for detailed observation and to track the impactor movement using digital image correlation. The force-penetration depth relation is used to evaluate the elastic and postyield compression characteristics of the lattices together with their deformation energy mitigation capabilities. The results show that the main differences in the deformation response of the lattices consist of lower overall stiffness and effective yielding of the auxetic lattices at a higher penetration depth. Numerical simulation using an explicit solver is performed to analyze the deformation mechanism of the individual core types.