High Strain Rate Behaviour of Auxetic Cellular Structures

Abstract

Auxetic cellular structures are modern metamaterials with negative Poisson’s ratio. The auxetic cellular structures build from inverted tetrapods were fabricated and experimentally tested under dynamic loading conditions to evaluate the effect of strain rate on their deformation mode. The Split-Hopkinson Pressure Bar (SHPB) apparatus was used for testing at strain rates up to 1,250 s-1, while a powder gun was used for testing at strain rates up to 5,000 s-1. The homogeneous deformation mode was observed at lower strain rates, while shock deformation mode was predominant at higher rates. The results have shown that the strain rate hardening of analysed auxetic specimens is prominent at higher strain rates when the shock deformation mode is observed, i.e. when most of deformation occurs at the impact front. Relevant computational models in LS-DYNA were developed and validated. A very good correlation between the computational and experimental data was observed.