Highly-stretchable 3D-architected Mechanical Metamaterials.

Yanhui Jiang,Qiming Wang

doi:10.1038/srep34147

Abstract

Soft materials featuring both 3D free-form architectures and high stretchability are highly desirable for a number of engineering applications ranging from cushion modulators, soft robots to stretchable electronics; however, both the manufacturing and fundamental mechanics are largely elusive. Here, we overcome the manufacturing difficulties and report a class of mechanical metamaterials that not only features 3D free-form lattice architectures but also poses ultrahigh reversible stretchability (strain > 414%), 4 times higher than that of the existing counterparts with the similar complexity of 3D architectures. The microarchitected metamaterials, made of highly stretchable elastomers, are realized through an additive manufacturing technique, projection microstereolithography, and its postprocessing. With the fabricated metamaterials, we reveal their exotic mechanical behaviors: Under large-strain tension, their moduli follow a linear scaling relationship with their densities regardless of architecture types, in sharp contrast to the architecture-dependent modulus power-law of the existing engineering materials; under large-strain compression, they present tunable negative-stiffness that enables ultrahigh energy absorption efficiencies. To harness their extraordinary stretchability and microstructures, we demonstrate that the metamaterials open a number of application avenues in lightweight and flexible structure connectors, ultraefficient dampers, 3D meshed rehabilitation structures and stretchable electronics with designed 3D anisotropic conductivity.

Highlights

We propose a simple manufacturing strategy and create a class of mechanical metamaterials in nearly arbitrary 3D architectures of highly-stretchable elastomer lattices
The method enables us to fabricate a variety of elastomer lattices with nearly arbitrary 3D architectures, such as Octet-truss (Fig. 1B), Kelvin (Fig. 1C), Kagome (Fig. 1D), Octahedron (Fig. 1E) and Dodecahedron lattices (Fig. 1F), which are orderly assembled from a number of corresponding unit cells (Supplementary Fig. 3)[26,30,36]
Since the elastomer modulus is in a range of 20–400 kPa (Supplementary Fig. 6), once the relative density is lower than 6%, achieving freestanding elastomer lattices is challenging because the surface tension plays a significant role in deforming the elastomer lattices into crumpled geometries[37]

Summary

Introduction

We propose a simple manufacturing strategy and create a class of mechanical metamaterials in nearly arbitrary 3D architectures of highly-stretchable elastomer lattices. The manufactured metamaterials are highly architected to enable density as low as 60 kg/m3 (6% of bulk elastomer), and ultra-stretchable with reversible strain as large as 414%, 4 times larger than that of the existing counterparts with the similar complexity of 3D architectures[32]. We show that the metamaterials can be tailored into customized geometries for lightweight connectors to flexibly bridge various 3D printed components, highly-efficient dampers that are better than the existing elastomer foams, rehabilitation structures that can conformally support organs with prescribed rigidity distribution and lightweight stretchable electronics with designed 3D conductivity pathways

Methods

Results

Conclusion