Inverted and programmable Poynting effects in metamaterials

TL;DR

This paper presents a metamaterial engineered to exhibit inverted and programmable Poynting effects, allowing control over its deformation responses under torsion and compression for diverse practical applications.

Contribution

The authors design a metamaterial that can be programmed to invert and tune its Poynting effect, enabling customizable nonlinear elastic responses.

Findings

Demonstration of a novel inverted Poynting effect where compression induces torsion.

Programmable Poynting modulus from negative to positive via pre-compression.

Potential applications in soft robotics, actuators, and biomedical devices.

Abstract

The Poynting effect generically manifests itself as the extension of the material in the direction perpendicular to an applied shear deformation (torsion) and is a material parameter hard to design. Unlike isotropic solids, in designed structures, peculiar couplings between shear and normal deformations can be achieved and exploited for practical applications. Here, we engineer a metamaterial that can be programmed to contract or extend under torsion and undergo nonlinear twist under compression. First, we show that our system exhibits a novel type of inverted Poynting effect, where axial compression induces a nonlinear torsion. Then the Poynting modulus of the structure is programmed from initial negative values to zero and positive values via a pre-compression applied prior to torsion. Our work opens avenues for programming nonlinear elastic moduli of materials and tuning the couplings between shear and normal responses by rational design. Obtaining inverted and programmable Poynting effects in metamaterials inspires diverse applications from designing machine materials, soft robots and actuators to engineering biological tissues, implants and prosthetic devices functioning under compression and torsion.