Bistability in popper-like shells programmed by geometric defects

Abstract

Bistable structures that can switch between two stable shapes are ubiquitous and have found applications in deployable structures, actuators, energy harvesters, etc. Among these, a bistable, spherical shell can stay stable in either the natural or “everted” shape. Previous works concentrate on the bistability of an intact shell, yet few efforts have been put into shells that feature a toy popper – a spherical shell with a circular hole located at its apex. To expand the existing design space of bistable shells, it is necessary to identify the quantitative relationship between the shell’s bistability and the size of this geometric and topological defect. In this paper, through experiments, theory, and finite element analysis (FEA), we demonstrate that the bistability of a popper-like shell is mainly controlled by its geometric parameters and gets weakened initially and then enhanced as the relative size of the defect increases, indicating that a properly introduced defect can shift an intact shell from bistability to monostability or vice versa. Therefore, our research not only identifies the enriched design space of bistable shells, but also may advance the development of intelligent structures and devices such as smart switches and soft robotics, where the bistable shells can be employed.