Intrinsically polar elastic metamaterials

TL;DR

This paper introduces a novel design principle for creating intrinsically polar elastic metamaterials with stable inhomogeneous properties, using topological band theory to achieve damage-resistant, directionally dependent stiffness.

Contribution

It presents a new approach to designing elastic materials with stable, topologically protected inhomogeneity and intrinsic polarity, resistant to damage and wear.

Findings

Created a periodic elastic material with topological properties.

Demonstrated stable inhomogeneity resistant to damage and cutting.

Achieved intrinsically polar behavior with direction-dependent stiffness.

Abstract

The ability to design and fabricate materials with tailored mechanical properties, combined with immunity to damage, is a frontier of materials engineering. For example, materials which are characterized by elastic properties that depend on the position inside a medium are required in applications where structural stability has to be combined with a soft and compliant surface, like in impact protection and cushioning. A gradient in the elastic properties can be built from a single material, varying gradually the bulk porosity of the material or its geometrical structure. However, if such a gradient is built into the material at production, damage or wearing over time might expose unwanted elastic properties. Here, we implement a design principle for a spatially inhomogeneous material based on topological band-theory for mechanical systems. The resulting inhomogeneity is stable against wearing and even cutting the material in half. We show how, by creating a periodic elastic material with topological properties, one can create an intrinsically polar behavior, where a face with a given surface normal is stiff while its opposing face is soft.