Hierarchical hexachiral auxetics for large elasto-plastic deformation

To improve the auxeticity and isotropy behavior of standard hexachiral structures at large elasto-plastic deformation, the authors have earlier proposed a modified hexachiral structure with wavy ligaments (Zhu et al 2018 Smart Material Structures 27 055001). While a significant improvement was achieved with the proposed modified chiral structure, it was reported therewith that its auxeticity and isotropy degrade rapidly at large tensile deformation, in contrast to the excellent performance in compression. The present work builds upon the basic structure proposed in (Zhu et al 2018 Smart Material Structures 27 055001), to further improve the mechanical behavior in tension, without compromising the already excellent performance achieved at large compressive deformation. To reduce the distortion of the central ring in a hexachiral structure—the deformation mechanism that degrades its mechanical performance in tension—a hierarchical hexachiral structure is proposed, where a standard hexachiral structure reinforces the central ring of the basic hexachiral structure in (Zhu et al 2018 Smart Material Structures 27 055001). A significant improvement in mechanical behavior over the basic structure is demonstrated, with potential applications in a protective system.