Stiffer, Stronger and Centrosymmetrical Class of Pentamodal Mechanical Metamaterials.

Yan Huang,Muamer Kadic,Gongying Liang,Xiaozhe Zhang

doi:10.3390/ma12213470

Abstract

Pentamode metamaterials have been used as a crucial element to achieve elastical unfeelability cloaking devices. They are seen as potentially fragile and not simple for integration in anisotropic structures due to a non-centrosymmetric crystalline structure. Here, we introduce a new class of pentamode metamaterial with centrosymmetry, which shows better performances regarding stiffness, toughness, stability and size dependence. The phonon band structure is calculated based on the finite element method, and the pentamodal properties are evaluated by analyzing the single band gap and the ratio of bulk and shear modulus. The Poisson’s ratio becomes isotropic and close to 0.5 in the limit of small double-cone connections. Stability and scalability analysis results show that the critical load factor of this structure is obviously higher than the classical pentamode structure under the same static elastic properties, and the Young’s modulus gradually converges to a stable value (the infinite case) with an increasing number of unit cells.

Highlights

Metamaterials are rationally designed composite structures made of building blocks, which are composed of one or more constituent bulk materials
The constituent material of the pentamode structure we consider here is a polymer with mass density ρ0 = 1190 kg/m3, Poisson’s ratio ν = 0.4 and Young’s modulus E = 3 GPa
The phonon band structure was calculated with COMSOL Multiphysics using the structural mechanics module

Summary

Introduction

Metamaterials are rationally designed composite structures made of building blocks (or unit cells or even meta-atoms), which are composed of one or more constituent bulk materials. They are said to have effective properties beyond the standard material [1,2]. Kadic et al [12] fabricated the polymer pentamode structure using state-of-the-art dip-in direct-laser-writing (DLW) optical lithography They took advantage of the scalability of continuum mechanics and fabricated a much larger macroscopic version of the pentamode structure to directly perform elastic measurements [14]. In this paper we propose a new class of pentamodal metamaterials with centrosymmetry that show better stability, better performances (stiffness and toughness) and for which effective properties depend much less on the number of unit cells than the previous proposals [12,13,14,15,16,17,18,19,20,21,22,25,26,27]

Modeling and Method

Results and Discussion

Conclusions