Hybrid anisotropic pentamode mechanical metamaterial produced by additive manufacturing technique

Pentamode metamaterials are a type of extremal designer metamaterials, which are able to demonstrate extremely high rigidity in one direction and extremely high compliance in other directions. Pentamodes can, therefore, be considered as building blocks of exotic materials with any arbitrarily selected thermodynamically admissible elasticity tensor. The pentamode lattices can then be envisioned to be combined to construct intermediate extremal materials, such as quadramodes, trimodes, and bimodes. In this study, we constructed several primary types of anisotropic pentamode lattices (with midpoint positioning of 10%, 15%, 20%, 25%, 30%, 35%, and 42% of the main unit cell diagonal) and then combined them mutually to explore the dependence of elastic properties of hybrid pentamodes on those of individual constructing lattices. Several anisotropic individual and hybrid pentamode lattice structures were produced using the MultiJet Additive Manufacturing technique and then mechanically tested under compression. Finite element models were also created using the COMSOL Multiphysics package. Two-component hybrid pentamode lattices composed of individual lattices with extensively different (as large as two orders of magnitudes) B/G ratios were constructed and analyzed. It was demonstrated that it is possible to design and construct composite intermediate extremal materials with arbitrary eigenvalues in the elastic tensor. It is concluded that the elastic E, shear G, and bulk moduli B of the hybrid structure are the superpositions of the corresponding moduli of the individual lattice structures. Poisson's ratio ν of the hybrid pentamode structure equals that of individual structure with higher Poisson's ratio. The yield stress σy of the hybrid pentamode lattice structure depends on the elastic moduli of the constructing lattice structures, as well as the yield stress of the weaker lattice structure.