A framework to investigate instabilities of homogeneous andcomposite dielectric elastomer actuators

Predictive models for Dielectric Elastomer Actuators require the nonlinear solid mechanics theory of soft dielectrics. This is certainly true for homogeneous systems, but also for devices made of composite materials, where the insertion of stiff conductive particles in the soft matrix may help to improve the overall actuation performance. In this note, we present a theoretical framework to investigate a wide range of instabilities in both homogeneous and composite-manufactured actuators: pull-in/electromechanical instability, buckling-like modes and band-localization failure, that can be analyzed taking into account all the geometric and electromechanical properties of the device such as i) nonlinearities associated with large strains and the employed material model; ii) initial prestretch applied to the system; iii) dependency of the permittivity on the deformation (electrostriction). In particular, we focus on the general expression which gives the condition for pull-in instability, also valid for anisotropic composite soft dielectrics. In the second part, we show that in a layered composite an electromechanical/snap through instability can be designed and possibly exploited to conceive release-actuated systems.