  Pentamode metamaterials are a type of extremal designer metamaterials which
are able to demonstrate 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 MultiJet Additive Manufacturing technique and then mechanically tested
under compression. Finite element models were also created using COMSOL
Multiphysics package. Two-component hybrid pentamode lattices composed of
individual lattices with extensively different (as large as of 2 order of
magnitudes) FOM ratios were constructed and analysed. It was demonstrated that
it is possible to design and construct composite intermediate extremal
materials with arbitrary eigen values 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. The Poisson's ratio of the hybrid pentamode structure equals that
of individual structure with higher Poisson's ratio. The yield stress of the
hybrid pentamode lattice structure depends on the elastic moduli of the
constructing lattice structures as well as yield stress of the weaker lattice
structure.
