Computational study of electromechanical instabilities in dielectric elastomers
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Dielectric elastomers (DEs) have attracted significant attention in recent years and have been found to provide excellent overall performance in actuation-based application. This thesis will introduce the fundamentals of DEs, derive the field and finite element equations for simulating its deformation, and then focus on numerically studying electromechanical instabilities, in particular electrostatically driven creep and the effect of pre-stretch on surface (creasing) instabilities. First, a nonlinear, dynamic finite element model coupled with a finite deformation viscoelastic constitutive law is utilized to study the inhomogeneous deformation and instabilities resulting from the application of a constant voltage to dielectric elastomers. Theoretical studies are performed of two problems that have been experimentally observed, i.e. electromechanical snap-through instability and bursting drops in a dielectric elastomer. In general, increasing the viscoelastic relaxation time leads to an increase in time needed to nucleate the electromechanical instability. However, it is found that the time needed to nucleate the instability of these two cases scales with the relaxation time. Second, the effect of pre-stretch on the performance of dielectric elastomers is studied. Two cases are studied, the electromechanical snap-through instability under equibiaxial pre-stress, and a strip under uniaxial pre-stretch. It is found that prestress markedly increases the stability of the elastomers, while pre-stretch increases the critical field for electro-creasing instability.