Instabilities in multilayered soft dielectrics

Experimental observations clearly show that the performance of dielectric elastomeric-based devices can be considerably improved using composite materials. A critical issue in the development of composite dielectric materials toward applications is the prediction of their failure mechanisms due to the applied electromechanical loads. In this paper we investigate analytically the influence of electromechanical finite deformations on the stability of multilayered soft dielectrics under plane-strain conditions. Four different criteria are considered: i.) loss of positive definiteness of the tangent electroelastic constitutive operator, ii.) existence of diffuse modes of bifurcation (microscopic modes), iii.) loss of strong ellipticity of the homogenized continuum (localized or macroscopic modes), and iv.) electric breakdown. While the formulation is developed for generic isotropic hyperelastic dielectrics, results are presented for the special class of ideal dielectrics incorporating a neo-Hookean elastic response. The effect of material properties and loading conditions is investigated, providing a detailed picture of the different possible failure modes.