Two types of transitions to wrinkles in dielectric elastomers (original) (raw)
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Dynamic pattern of wrinkles in a dielectric elastomer
Soft matter, 2017
A membrane of a dielectric elastomer may undergo electromechanical phase transition from the flat to wrinkled state, when the applied voltage reaches a critical value. The wrinkled region is observed to expand at the expense of the flat region during the phase transition. In this paper, we report on a dynamic pattern of wrinkles in a circular membrane of a dielectric elastomer. During phase transition, both the flat and wrinkled regions move interchangeably in the membrane. The radial prestretch is found to significantly affect electromechanical phase transition. For example, a membrane with a small prestretch can exhibit a dynamic pattern of wrinkles, which is essentially related to snap-through instability. However, a membrane with a large prestretch undergoes continuous phase transition, without exhibiting a dynamic pattern. An analytical model is developed to interpret these experimental phenomena. Finite element simulations are performed to predict the wrinkle morphology, espec...
Voltage-Induced Wrinkling in a Constrained Annular Dielectric Elastomer Film
Journal of Applied Mechanics, 2017
Wrinkles can be often observed in dielectric elastomer (DE) films when they are subjected to electrical voltage and mechanical forces. In the applications of DEs, wrinkle formation is often regarded as an indication of system failure. However, in some scenarios, wrinkling in DE does not necessarily result in material failure and can be even controllable. Although tremendous efforts have been made to analyze and calculate a variety of deformation modes in DE structures and devices, a model which is capable of analyzing wrinkling phenomena including the critical electromechanical conditions for the onset of wrinkles and wrinkle morphology in DE structures is currently unavailable. In this paper, we experimentally demonstrate controllable wrinkling in annular DE films with the central part being mechanically constrained. By changing the ratio between the inner radius and outer radius of the annular films, wrinkles with different wavelength can be induced in the films when externally ap...
Taut states of dielectric elastomer membranes
Actuation devices based on dielectric elastomers, typically exhibit various kinds of instability which may determine a decrease of performances and, eventually, the device failure. In this work we focus on wrinkling instabilities for polymer films subjected to an electric field. The main result is the definition of a domain of taut states in the plane of principal stretches strongly dependent on the applied voltage and on the constitutive properties of the polymer film. We discuss these features, crucial in the perspective of electroactive materials design, through simple boundary value problems for Neo-Hookean and Ogden materials.
Dielectric elastomer membranes undergoing inhomogeneous deformation
2009
Abstract Dielectric elastomers are capable of large deformation subject to an electric voltage and are promising for use as actuators, sensors, and generators. Because of large deformation, nonlinear equations of states, and diverse modes of failure, modeling the process of electromechanical transduction has been challenging.
Complex interplay of nonlinear processes in dielectric elastomers
2012
An elastomeric membrane can be readily stretched to many times its initial area by mechanical forces, but inducing such a large deformation by voltage is difficult. An important discovery was made about a decade ago that voltage-induced deformation can be greatly enhanced by prestretch [1, 2], which also increases the apparent electric breakdown field more than ten times [3, 4].
Electromechanical phase transition in dielectric elastomers
2012
Abstract Subject to forces and voltage, a dielectric elastomer may undergo electromechanical phase transition. A phase diagram is constructed for an ideal dielectric elastomer membrane under uniaxial force and voltage, reminiscent of the phase diagram for liquid–vapour transition of a pure substance. We identify a critical point for the electromechanical phase transition.
Journal of the Mechanics and Physics of Solids, 2019
Voltage controlled dielectric membranes exhibit two fundamental types of instability, strongly affecting their performances: the occurrence of wrinkling, which is due to membranal compressive stresses, and the onset of pull-in, a catastrophic thinning localisation that preludes electrical breakdown. In this manuscript we provide a unifying energetic description of both instabilities for large, out-of-plane and inhomogeneous deformations. By using the ideas of relaxation and regularisation of the energy, originally proposed by Pipkin (IMA J. Appl. Math. 36, 85-99, 1986) and Hilgers and Pipkin (Quart. Appl. Math. 50, 389-400, 1992) for purely elastic membranes, we show that the onset and development of wrinkling can be effectively described by the relaxed electroelastic energy. For axially symmetric membranes and neo-Hookean materials, we show that pull-in corresponds to failure of the strong ellipticity condition of the regularised electroelastic energy, thus extending to out-of-plane deformations the validity of a previous estimate for planar systems (Phys. Rev. Lett., 118(7) 078001, 2017). In agreement with ubiquitous experimental evidence, we also show that wrinkled states are always stable below the pull-in voltage. Our theoretical findings are assessed by the comparison with experiments on out-of-plane, voltage-actuated annular membranes, showing good agreement both in terms of description of wrinkled states, and for the prediction of the pull-in instability.
Theory of dielectric elastomers
2010
Abstract: In response to a stimulus, a soft material deforms, and the deformation provides a function. We call such a material a soft active material (SAM). This review focuses on one class of soft active materials: dielectric elastomers. Subject to a voltage, a membrane of a dielectric elastomer reduces thickness and expands area, possibly straining over 100%. The phenomenon is being developed as transducers for broad applications, including soft robots, adaptive optics, Braille displays, and electric generators.