Mechanics of novel asymmetrical re-entrant metamaterials and metastructures

In this work, we evaluate the mechanical performance of an innovative asymmetrical re-entrant metamaterial configuration via finite element (FEM) models. The cell topologies described here consist of asymmetric re-entrant and anti-tetrachiral configurations described by equi-dimensional representative unit cells (RUCs). The asymmetric geometry provides a stiffer in-plane mechanical response and widely tunable auxetic behavior compared to a coventional anti-tetrachiral model. We also describe two sets of metastructures composed by the asymmetrical re-entrant RUCs distributed along the Cartesian x and y directions and subjected to compressive loading. The metastructure made of cells along the y direction exhibits a larger negative Poisson’s ratio and stronger load-bearing capacity compared to the metastructure with the cells aligned along the x direction. Two cylindrical metastructure tubes with asymmetrical re-entrant and anti-tetrachiral RUCs with equal dimensions and generated along the y direction have been built. The elastoplastic mechanical performance of the two series of cylindrical metastructure tubes under quasi-static compression have been identified via experiments and numerical simulations. The new asymmetrical re-entrant metamaterial shows an excellent mechanical performance also as a platform for tubular configurations.