Starchirals – a novel class of auxetic hierarchal structures

Abstract

A novel class of chiral structures having intersecting ligaments acting as the node is presented in this study. Depending on the geometric parameters, this arrangement may allow both the ligaments connecting the nodes together as well as the ligaments that compose the node itself to bend upon the application of a uniaxial force. Hence, such structures are capable of deforming through two distinct mechanisms, i.e. bending of the ligaments between the nodes and bending of the ligaments in the nodes. The novel six ligament (hexa) arrangement, a structure derived from the hexachiral, was chosen for the purpose of investigating these novel designs. This was studied through the use of finite element simulations and mechanical testing of 3D printed specimens. Analysis of the results supports the suggestion that a hierarchical deformation system exist. The value of the Poisson’s ratio was found to be dependent on the relative thickness of the respective ligaments.