Finite bending of a dielectric elastomer actuator and pre-stretch effects

A sandwiched dielectric elastomer actuator consisting of a hyperelastic material layer and two pre-stretched dielectric elastomer layers is introduced in this work, which is bi-directionally bendable when subject to a direct current voltage on the top or bottom layer. By using the pure bending deformation assumption and the nonlinear electroelasticity theory, the voltage-induced finite bending deformation of the actuator is studied theoretically with a focus on the pre-stretch effects. Although pure bending deformation may be not exactly ensured at the free end of the considered structure, according to the well known Saint Venant's principle, the boundary effect will not affect the deformation and stress distribution outside the boundary layers at the free end. Through theoretical modeling and numerical analyses, it is revealed that pre-stretch helps to reduce the drive voltage required to induce a desired bending deformation, and when the pre-stretch is comparatively large, there exists a pre-stretch dependent optimum thickness ratio so that the drive voltage is minimized. This work is expected to provide guide for the design and fabrication of high-performance soft actuators and soft robotics.