Multifunctional mechanical metamaterials with tunable double-negative isotropic properties

Abstract

This research was focused on innovative design of lattice metamaterials that can exhibit tunable double-negative mechanical properties and elastic isotropy simultaneously. A discrete topology optimization method using a multi-material ground structure was developed to create microlattices exhibiting both negative thermal expansion coefficient and negative Poisson’s ratio in a single integrated design, while maintaining elastic isotropy. First, the numerical homogenization method with beam elements was used to estimate the effective thermal and elastic properties of a microlattice. Second, the topological design, subject to required geometric constraints, was formulated as a mixed integer programming problem to discover a series of multi-material microlattices that present customized isotropic values of negative thermal expansion coefficient and negative Poisson’s ratio. Finally, several three-dimensional multi-material microstructures were produced by altering either the cross-sections or constituent materials of struts to demonstrate their tunable mechanical properties.