A Finite Element Method for Inhomogeneous Deformation of Viscoelastic Dielectric Elastomers

Viscoelasticity is known to adversely affect the performance of a dielectric elastomer actuator and limit its application. In this paper, we present a finite element method for dielectric elastomers based on a nonlinear field theory that couples viscoelasticity and electrostatics. This method is implemented in a commercial finite element software. We use the method to solve electromechanical coupling problems of viscoelastic dielectric elastomers under inhomogeneous deformation in various configurations.

Field Driven Stiffness Control of Legged Robotic Structures Using Dielectric Elastomers

Dielectric elastomers are known for their electro-mechanically coupled constitutive behavior which has demonstrated the potential for developing a number of novel adaptive structures. Despite the advances in understanding these materials using nonlinear field theory and experimental characterization, several questions remain regarding how to effectively integrate these materials in adaptive robotic structures. Here, a new design is proposed to integrate these materials into legged robotic structures that can achieve relatively large and rapid stiffness changes for enhanced mobility and agility of a field demonstrated hexapod robot. A set of resonance test are performed to quantify changes in effective stiffness as a function of the applied electric field. The results are incorporated into a bi-layer beam model to estimate changes in the effective stiffness of a robotic C-shaped leg. The results show promise for developing adaptive robotics legs for multi-terrain mobility.

Nonlinear Field Theory of Fracture Mechanics for Paramagnetic and Ferromagnetic Materials

A nonlinear field theory of fracture mechanics is developed for crack propagation in paramagnetic and ferromagnetic materials from the global energy balance equation and the non-negative global dissipation requirement. The crack-front generalized J̃-integral is equivalent to the generalized energy release rate serving as the thermodynamic driving force for crack propagation and also related to the generalized energy-momentum tensor in a way similar to the material force method. On the basis of the developed theory, the generalized energy release rate method, the generalized J̃-integral method, and the extended essential work of fracture method are proposed for quasistatic and dynamic fracture characterization of magnetosensitive materials in the presence of magnetothermomechanical coupling and dissipative effects. The present work overcomes the drawbacks and limitations of conventional fracture mechanics and resolves the controversial issues on magnetoelastic fracture criterion. Especially, the crack-front generalized J̃-integral has an odd dependence on the magnetic induction intensity factor for a Griffith-type crack in a magnetoelastic solid.