Bi-layer dielectric elastomer beams: Theory and applications

Dielectric elastomers (DEs) are soft polymeric materials that deform in response to electric excitation. In this work, we investigate the behavior of bi-layer DE beams comprising layers with different electro-mechanical properties. Due to the mismatch in the properties of the layers, such beams bend when subjected to an electric field. We begin by deriving a model based on moderate rotations theory, which is an extension of linear elasticity that accounts for moderate-to-large rotations and deflections, for beams subjected to an electromechanical loading. The model reveals the dependency of the electro-mechanical properties of the layers on the overall response. To validate the model, we focus on free-standing beams that are subjected to two types of boundary conditions: (1) the application of an electric field across both layers and (2) imposing an electric field on one layer, while the second remains passive and serves as an elastic constraint. The model predictions show good quantitative agreement with finite element simulations. To demonstrate the practicality of using DE bi-layers, we consider the properties of commonly-employed DEs and study their performance in two types of applications — weight lifting actuators and grippers. We show that activation of a single layer enables the designs to perform a larger mechanical work. The proposed framework provides a fundamental understanding that enables efficient design of electrically activated systems, including actuators and soft robotics.