  Designing smart devices with tunable shapes has important applications in
industrial manufacture. In this paper, we investigate the nonlinear deformation
and the morphological transitions between buckling, necking, and snap-through
instabilities of layered DE balloons in response to an applied radial voltage
and an inner pressure. We propose a general mathematical theory of nonlinear
electro-elasticity able to account for finite inhomogeneous strains provoked by
the electro-mechanical coupling. We investigate the onsets of morphological
transitions of the spherically symmetric balloons using the surface impedance
matrix method. Moreover, we study the nonlinear evolution of the bifurcated
branches through finite element numerical simulations. Our analysis
demonstrates the possibility to design tunable DE spheres, where the onset of
buckling and necking can be controlled by geometrical and mechanical properties
of the passive elastic layers. Relevant applications include soft robotics and
mechanical actuators.
