Mechanical Metamaterials with Negative Compressibility Transitions

TL;DR

This paper introduces novel mechanical metamaterials that exhibit negative compressibility transitions, contracting when tensioned due to destabilized stable states, enabling applications like actuators and force amplifiers.

Contribution

It presents a new design concept for metamaterials that undergo stress-induced phase transitions, resulting in negative compressibility, which was not previously demonstrated.

Findings

Demonstration of negative compressibility transitions in designed metamaterials

Identification of destabilization of stable equilibria as the mechanism

Potential applications in actuators and force amplification devices

Abstract

When tensioned, ordinary materials expand along the direction of the applied force. Here, we explore network concepts to design metamaterials exhibiting negative compressibility transitions, during which a material undergoes contraction when tensioned (or expansion when pressured). Continuous contraction of a material in the same direction of an applied tension, and in response to this tension, is inherently unstable. The conceptually similar effect we demonstrate can be achieved, however, through destabilisations of (meta)stable equilibria of the constituents. These destabilisations give rise to a stress-induced solid-solid phase transition associated with a twisted hysteresis curve for the stress-strain relationship. The strain-driven counterpart of negative compressibility transitions is a force amplification phenomenon, where an increase in deformation induces a discontinuous increase in response force. We suggest that the proposed materials could be useful for the design of actuators, force amplifiers, micro-mechanical controls, and protective devices.