Ultrahigh compression-shear ratio of sandwich pentamode metamaterials

Abstract

Pentamode metamaterials (PMs) are a novel class of mechanical metamaterials showing the unusual decoupling relationship between compression and shear moduli. This study originates from the contradictory question of how to improve the compression-shear ratio without sacrificing the crucial size as much as possible. Here, novel sandwich PMs with ultrahigh compression-shear ratios are proposed. For example, under the same crucial size like d/a = 1 % (ratio of diameter of intersections d to lattice constant a, which dominates the mechanical properties of PMs and the smallest size limiting the fabrication), the compression-shear ratio of new PMs can be up to 1877, whereas the classical diamond-like lattice is 4.7, corresponding to a 391-fold increase. The finite element results by COMSOL Multiphysics and experimental results match well, mutually verifying the validity. The influence of single-layer and multi-layer sandwich lattices is further investigated, which shows that stiffening plates tip the scales. This study escapes the current limitations of limited compression-shear ratio, extreme crucial size, and high-cost fabrication, which promotes the concept of PMs towards practical applications.