Phase transition and optimal actuation of active bilayer structures

Abstract

Active bilayer structures have great potential applications in the fields of drug delivery, soft robots and actuators. In this paper, we have investigated the phase transition and optimal actuation of bilayer structures under biaxial active strains. A theoretical model is developed to predict the bending curvature of the bilayer in the large deformation regime, instead of the traditional Timoshenko’s buckling solution. A Riks path-following procedure in the finite element method is utilized to trace the active-strain induced snap-through instability to identify the phase boundaries of bistability in the bilayer. The phase transition diagram from bistability to monostability and the general requisites to generate a snap-through instability by varying active strains are thoroughly discussed based on the bending curvature and energy landscape from simulations. Using the average curvature to characterize the actuation efficiency, we find that the anisotropy of active strains can be utilized to tune the bending angle and configuration of bilayer structures. The presented model and the obtained phase diagram provide a potential guidance for future design of high-performance bilayer-based actuators and machines in a broad range of applications.