Wrinkles and waves in soft dielectric plates
Conroy Broderick, Hannah
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This article-based thesis comprises a collection of three articles, each of which constitutes a separate chapter, written and formatted in pre-print manuscript form. The general aim of the thesis is to model instabilities and waves in soft dielectric elastomer plates, with a particular focus on wrinkle formation and wave propagation modes. Soft dielectric materials are smart materials that deform in the presence of an electric field. They have potential promising applications in devices such as artificial muscles and soft robotics, where there is great demand for materials that can undergo repeated large deformations. In principle, large deformations can be obtained by exploiting the so-called snap-through instability. However, this phenomenon is difficult to achieve and control in practice, as the material often fails due to electric breakdown, or due to wrinkles appearing on the surface of the material. Here we study in turn the stability of voltage and charge-controlled soft dielectric plates. We investigate Hessian and geometric instability modes. We find that voltage-controlled dielectrics can wrinkle in compression and extension, whereas charge-controlled dielectrics can only wrinkle in compression. We find that charge-controlled actuation is more stable than voltage-controlled actuation. Studies on waves in dielectric materials suggest the possibility of controlling the wave velocity by applying an appropriate electric field. This paves the way for applying acoustic non-destructive evaluation techniques to dielectric plates, a technique already used in purely elastic materials. Here we study Lamb wave propagation in dielectric plates subject to electrical and mechanical loadings. We look at the effects of the pre-stress, the electric field and the strain-stiffening on the wave characteristics. This work relies on theoretical and numerical treatments, using the multiphysics theory of nonlinear electro-elasticity, the incremental theory of small deformations and motions superposed on a large actuation, the Stroh formalism, the numerical resolution of boundary-value problems, and Finite Element simulations.
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