Mechanics of Bi-Chiral Mechanical Metamaterials: Design, Modelling and Experiments

A family of bi-chiral mechanical metamaterials with both regular and random handedness distribution patterns are designed. The mechanical properties of them are explored via systematic finite element simulations. The effects of handedness distributions, handedness ratio, and domain size and length aspect ratios are investigated. Furthermore, the anisotropic properties of bi-chiral mechanical metamaterials are studied. Specimens with various material orientations are fabricated via 3D printing. Mechanical experiments are performed to measure the effective mechanical properties in the corresponding material orientations. Experimental results show bi-chiral mechanical metamaterial has strong anisotropic behavior in stiffness, Poisson's ratio and coupling coefficients which agrees well with FE simulations. To further predict these anisotropic properties, micropolar continuum theory are used and micropolar parameters are obtained from FE simulations. The influences of these parameters on the anisotropy are systematically quantified. Finally, the effect of handedness, hinge rigidity, lattice topology and lattice tessellation on the anisotropic properties are studied. The results provide design guidelines for bi-chiral mechanical metamaterials with enhanced mechanical performance and widely tuned mechanical properties for broad engineering and biomedical applications.