Optimization and experimental validation of 3D near-isotropic auxetic structures

Abstract

The maturation of additive manufacturing has caused an explosion in lattice metamaterials. One of the most promising metamaterial families are auxetics, but these structures often exhibit anisotropy which limits their use. In this study, novel polygon celled 3D star structures were investigated and engineered to counteract design deficiencies. A new lattice design ontology was developed and used to carry out low cost optimisation with curved links. The resulting cells opened new forms of symmetry which were shown to reduce the anisotropy of the lattices by between 75% and 90%. The cubic and rhombic dodecahedral cells performed promisingly with Poisson’s ratios of −0.449 and −0.401 and anisotropic range of 0.022 and 0.085 respectively. Link thickness was parameterised and used to aid cell scaling and balance stiffness and metamaterial behaviour while ensuring cell manufacturability. The experiments demonstrated that the geometrical simplicity was beneficial to the cell properties and the success probability of the manufacturing process. The new optimisation method described in this study has been demonstrated to be sufficiently low cost to be applied at the cell level. It will pave the way to practical strain based design of graded structures which are vital for the practical growth of metamaterials.