Deformation and stress concentration behavior of two-dimensional mechanical metamaterials

Abstract

Mechanical metamaterials are materials or structures that are intentionally designed to exhibit abnormal mechanical properties, such as negative Poisson’s ratio, negative stiffness, compression-twisting coupling, etc. It is suggested that mechanical metamaterials with negative Poisson’s ratio (called auxetic materials) can reduce stress concentration at a crack tip and it becomes tough. However, to our knowledge, there is no experimental evidence for the toughening. Here, we introduced a defect in a hexachiral lattice and investigated the effects of the defect on deformation and stress concentration behavior by applying Finite Element Method (FEM). We found that the introduction of the defect induces internal rotation that lead to suppression or enhancement of tensile stress in the rib of the hexachiral structure. We believe that this is the starting point for stress concentration free design using mechanical metamaterials. The results obtained indicate that there is stress transmission between ribs via the rotation of disks. If the disk rotation can be controlled in some way, stress on ribs can be reduced or increased intentionally.