Acousto-elasticity is concerned with the propagation of small-amplitude waves in deformed solids. Results previously established for the incremental elastodynamics of exact non-linear elasticity are useful for the determination of third- and fourth-o
rder elastic constants, especially in the case of incompressible isotropic soft solids, where the expressions are particularly simple. Specifically, it is simply a matter of expanding the expression for $rho v^2$, where $rho$ is the mass density and v the wave speed, in terms of the elongation $e$ of a block subject to a uniaxial tension. The analysis shows that in the resulting expression: $rho v^2 = a + be + ce^2$, say, $a$ depends linearly on $mu$; $b$ on $mu$ and $A$; and $c$ on $mu$, $A$, and $D$, the respective second-, third, and fourth-order constants of incompressible elasticity, for bulk shear waves and for surface waves.
We propose a model to analyze the insurgence of pull-in and wrinkling failures in electroactive thin films. We take in consideration both cases of voltage and charge control, and study the role of prestretch and size of activated regions, which are e
ssential in the analysis of realistic applications of EAPs. Based on simple geometrical and material assumptions we deduce an explicit analytical description of these phenomena, allowing a clear physical interpretation. Despite our simplifying assumptions, the comparison with experiments shows a satisfying qualitative and, interestingly, quantitative agreement. In particular our model shows, in accordance with experiments, the existence of different optimal prestretch values, depending on the choice of the actuating parameter of the EAP.
