Transformable topological mechanical metamaterials

TL;DR

This paper introduces a design principle for topological mechanical metamaterials that can be reversibly transformed between states with different properties using uniform soft deformation, with properties protected by topological phonon band structures.

Contribution

It proposes a new design approach based on soft deformation for creating transformable topological mechanical metamaterials with robust properties.

Findings

Metamaterials can be reversibly transformed between states with contrasting properties.

Topological phonon band structures protect the properties against disorder.

Examples demonstrate significant property changes through soft deformation.

Abstract

Mechanical metamaterials are engineered materials that gain their remarkable mechanical properties, such as negative Poisson's ratios, negative compressibility, phononic bandgaps, and topological phonon modes, from their structure rather than composition. Here we propose a new design principle, based on a uniform soft deformation of the whole structure, to allow metamaterials to be immediately and reversibly transformed between states with contrasting mechanical and acoustic properties. These properties are protected by the topological structure of the phonon band of the whole structure and are thus highly robust against disorder and noise. We discuss the general classification of all structures that exhibit such soft deformations, and provide specific examples to demonstrate how to utilize soft deformations to transform a system between different regimes such that remarkable changes in their properties, including edge stiffness and speed of sound, can be achieved.