Chirality-induced Normal-Shear Coupling Effects of Auxetic Chiral Mechanical Metamaterial

Mechanical metamaterials with chiral geometry often have auxetic effects. Different from auxetic materials with symmetric geometry, such as the reentrant honeycomb, chiral mechanical metamaterials are observed to have strong normal-shear coupling effects. For example, under uni-axial load, the chiral mechanical metamaterial will experience noticeable shearing deformation, and vice versa. This is because that chiral geometry is asymmetric which would induce local rotation. It is not well understood what the relationships between the chiral geometry and the coupling effects are, and how the coupling effects influence auxeticity and other effective mechanical properties.
In this investigation, two specific periodic material systems are chosen, one is periodic chiral mechanical metamaterial with four-fold symmetry; the other is periodic square lattice with introduced chirality. Finite element simulations of the two types of FE models under various boundary conditions are performed in ABAQUS. The effective mechanical properties and the constitutive relationships of them are quantified. Design guidelines for desired properties related to the coupling effects, auxeticity, and effective stiffness will be provided.