Author(s)

XIN LI, CHUANQING CHEN

Abstract

Chiral structures, a special type of negative Poisson’s ratio structures, possess excellent energy absorbing capabilities and hold great promise in the field of impact protection. Compared with homogeneous structures, the gradient design of chiral structures can further optimize and enhance their energy absorbing capabilities. In this work, we experimentally and numerically investigated the deformation modes of gradient hexachiral auxetic metamaterials under quasi-static, dynamic and blast loadings. Five gradient design strategies were employed in the test, including uniform (UG), positive (PG), negative (NG), centre positive (CPG), and centre negative gradients (CNG). The effects of gradient distribution on deformation/failure modes under different loading conditions were analysed. Plane impact experimental results revealed that the gradient design can mitigate the shear deformation of hexachiral auxetics, which efficiently remain its negative Poisson’s ratio effect under dynamic loading. Compare with the quasi-static loading, earlier failure of auxetics was observed under dynamic loads due to the strain rate and inertial effect, which diluted their negative Poisson’s ratio effect and energy absorption capability. Among various gradient designs, the auxetics with negative gradient configurations exhibit the best energy absorption capability under dynamic loadings. Under blast loads, the various gradient types of auxetic cores exhibited distinct compression deformation behaviours. The hexachiral cores in sandwich panels with larger radius nodes on the blast surface are more likely to undergo compression deformation. The NG and CNG cores, featuring nodes resistant to flattening deformation, are more effective in generating NPR effect, resulting in a larger impact resistance. In addition, by using finite element method, the deformation mods of gradient hexachiral auxetics are further investigated under higher impact velocities and blast loadings to reveal loading rate effects on their deformation modes. This work offers profound insights into enhanced performance mechanisms and provides avenues for optimizing structural design of auxetic metamaterials.

Keywords

hexachiral, gradient, impact and blast loadings, deformation mode