Bistable Auxetic Mechanical Metamaterials Inspired by Ancient Geometric Motifs

TL;DR

This paper introduces a novel class of bistable auxetic metamaterials inspired by ancient geometric motifs, combining negative Poisson's ratio with the ability to maintain shape after deformation, realized through perforated rubber sheets.

Contribution

The work presents a new design of switchable, bistable auxetic metamaterials based on ancient geometric motifs, with experimental realization and predictive finite element modeling.

Findings

Demonstrated bistable auxetic behavior through perforated rubber sheets.

Validated mechanical performance with finite element simulations.

Provided insights into design principles for bistable auxetics.

Abstract

Auxetic materials become thicker rather than thinner when stretched, exhibiting an unusual negative Poisson's ratio well suited for designing shape transforming metamaterials. Current auxetic designs, however, are often monostable and cannot maintain the transformed shape upon load removal. Here, inspired by ancient geometric motifs arranged in square and triangular grids, we introduce a class of switchable architected materials exhibiting simultaneous auxeticity and structural bistability. The material concept is experimentally realized by perforating various cut motifs into a sheet of rubber, thus creating a network of rotating units connected with compliant hinges. The metamaterial performance is assessed through mechanical testing and accurately predicted by a coherent set of finite element simulations. A discussion on a rich set of mechanical phenomena follows to shed light on the main design principles governing bistable auxetics.