A numerical study on the instabilities of viscoelastic dielectric elastomers considering nonlinear material viscosity

Instability has been recognized as one of the major issues restricting the full potential applications of dielectric elastomer (DE)-based devices. While great efforts have been devoted to investigating the instabilities of DE actuators, those studies are limited to using either hyperelastic material models or viscoelastic constitutive models with constant material viscosity. As observed in the experiments, the intrinsic material viscosity of elastomers varies with deformation, which becomes more manifest particularly for DE actuators undergoing large deformation. This work attempts to fill this knowledge gap by developing a finite element (FE) framework that combines the nonlinear field theory with the micro-macro constitutive model incorporating nonlinear material viscosity to investigate the electromechanical responses and the instability of DE actuators. A highly customized user-element subroutine (UEL) in Abaqus is developed for the FE implementation. The effects of the nonlinear material viscosity on a variety of instability modes of DE (VHB 4910) actuators with different configurations are numerically investigated, including electromechanical instability (EMI), buckling, wrinkling, and crumpling. The accuracy and robustness of the FE framework are validated by comparison with existing experimental data and analytical studies. This work provides a general approach for instability analysis of DE actuators with different configurations and can further function as a universal platform for numerical analysis on the electromechanical finite deformation of DE structures with complex configurations, leading to better design and applications of DE-based devices. (C) 2021 Published by Elsevier Ltd.