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Modeling of dielectric elastomer as electromechanical resonator

Dielectric elastomers (DEs) feature nonlinear dynamics resulting from an electromechanical coupling.

Under alternating voltage, the DE resonates with tunable performances. We present an

analysis of the nonlinear dynamics of a DE as electromechanical resonator (DEER) configured as a

pure shear actuator. A theoretical model is developed to characterize the complex performance

under different boundary conditions. Physical mechanisms are presented and discussed. Chaotic

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Electromechanical deformation of dielectric elastomer in two types of pre-stretch

A pre-stretched dielectric elastomer is capable of large deformation, when subject to voltage. This paper investigates the effect of two types of pre-stretch: by strain and by stress. The difference is compared and discussed using thermodynamics models. The significance of the pre-stretch in actuation is explained by examining the true stress in actuation. Under both pre-stretch strategies, during the actuation, the dielectric elastomer exhibits hysteresis loops due to snap-through but differs in shape and physical quantity.

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Modeling of the muscle-like actuation in soft dielectrics: deformation mode and electromechanical stability

Soft dielectric elastomer is able to generate an
electromechanical response in terms of reversible shape
changing, which is a muscle-like behavior. The deformation
and electromechanical stability of dielectric elastomers,
classified by their deformation modes, uniaxial extension,
equal biaxial expansion and pure shear, are investigated.
Pull-in instability occurs in equal biaxial and uniaxial modes
at a small stretch ratio, while the pure shear mode features
wrinkling instability after a large stable deformation. The

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Temperature dependence of the dielectric constant of acrylic dielectric elastomer

The dielectric constant is an essential electrical parameter to the
achievable voltage-induced deformation of the dielectric
elastomer. This paper primarily focuses on the temperature
dependence of the dielectric constant (within the range of 173 K
to 373 K) for the most widely used acrylic dielectric
elastomer (VHB 4910). First the dielectric constant was investigated
experimentally with the broadband dielectric spectrometer
(BDS). Results showed that the dielectric constant first increased
with temperature up to a peak value and then dropped to a
relative small value. Then by analyzing the fitted curves, the Cole–Cole
dispersion equation was found better to characterize the
rising process before the peak values than the Debye dispersion

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Dynamic model of ion and water transport in ionic polymer-metal composites

In the process of electro-mechanical transduction of
ionic polymer-metal composites (IPMCs), the transport of ion and water molecule
plays an important role. In this paper, the theoretical transport models of
IPMCs are critically reviewed, with particular emphasis on the recent
developments in the latest decade. The models can be divided into three classes,
thermodynamics of irreversible process model, frictional model and Nernst-Planck
(NP) equation model. To some extent the three models can be transformed into
each other, but their differences are also obvious arising from the various
mechanisms that considered in different models. The transport of ion and water
molecule in IPMCs is compared with that in membrane electrode assembly and

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Experimental study on the dielectric properties of polyacrylate dielectric elastomer

The dielectric constant of elastomeric dielectric material is an
essential physical parameter, whose value may affect the
electromechanical deformation of a dielectric elastomer actuator. Since
the dielectric constant is influenced by several external factors as
reported before, and no certain value has been confirmed to our
knowledge, in the present paper, on the basis of systematical comparison
of recent past literature, we conducted extensive works on the
measurement of dielectric properties of VHB films, involving five
influencing factors: prestretch (both equal and unequal biaxial),
electrical frequency, electrode material, stress relaxation time and
temperature. Experimental results directly show that the dielectric

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Theoretical investigation on polar dielectric with large electrocaloric effect as cooling devices

Polar dielectric based cooling devices are
modeled as a system with two degrees of freedom and represented by either an
entropy-temperature or electric displacement-electric field plane. A typical
thermodynamic energy cyclic path is proposed for polar dielectric as cooling
devices to experience. With the influence of temperature taken into
consideration, the free energy of a thermal electrical coupling system of polar
dielectrics is formulated, and the variation of temperature and entropy, the
absorption of heat, and the work under different electric fields are calculated
for BaTiO3, Pb(ZrxTi1-x)O3, P(VDF-TrFE), and water. And the simulation results
obtained agree well with the recently published experimental data [B. Neese, et

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Effect of temperature on the stability of dielectric elastomers

Dielectric elastomer (DE) is a kind of electroactive polymer material,
capable of large deformation up to 380%. However, under conservative
operating conditions, DE is susceptible to instability with a small
deformation due to various modes of failure, including electrical
breakdown, electromechanical instability (EMI), loss of tension and
rupture by stretch. This paper proposes a free energy model in the
thermodynamic system of DE involving thermoelastic strain energy,
electric energy and purely thermal contribution energy to obtain the
stability conditions of all failure modes. The numerical results
indicate that the increase in temperature can markedly contribute to
improving the entropy production, the actuation stress and the critical

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Effect of mechanical pre-stretch on the stabilization of dielectric elastomer actuation

A dielectric elastomer is capable of giant electromechanical actuation but fails at breakdown due to instability under certain conditions with a small deformation. By applying a mechanical pre-stretch, one obtains a stabilized large actuation.

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Extension limit, polarization saturation, and snap-through instability of dielectric elastomers

A dielectric elastomer is capable of largevoltage-induced deformation, particularly when the voltage is applied on theverge of snap-through instability.  Thispaper describes a model to show that the snap-through instability is markedlyaffected by both the extension limit of polymer chains and the polarizationsaturation of dipoles.  The model mayguide the search for high-performance dielectric elastomer transducers.

 

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Capillary origami controlled by an electric field

Article citation: Miguel Piñeirua, Soft Matter, 2010, DOI: 10.1039/c0sm00004c

 

Capillary origami controlled by an electric field

Miguel Piñeirua, José Bico and Benoît Roman

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The 23rd issue of the WW-EAP Newsletter is now available

From: Bar-Cohen, Yoseph (355N) <yoseph.bar-cohen@jpl.nasa.gov>

 


Dear Colleague,

I am very pleased to inform you that the 23rd issue of the WW-EAP Newsletter is now available at: 

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Dielectric strength: dependent or independent of stretch?

 Dielectric elastomer can undergo giant deformation, but are susceptive to various failure modes. i.e electrical breakdown.

Some experimental papers (Kofod, Plante, Chen, see the attachment) reported the dielectric strength of VHB material (a kind of dielectric elastomer) under difference pre-stretch, equal bi-axially or unequal bi-axially. And the strength (maximum voltage can be applied before breakdown) has be greatly improved by these mechanical stretches.

 So here comes the question: is the dielectric strength dependent or independent of stretch?

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How is the entropy of polarization in dielectric material

In the study of thermoelastic actuation of dielectric elastomer, we can write the Helmholtz free-energy as a function of stretch ratio, nominal electric displacement and temperature (T).

The entropy (S) is the negative partial differential coefficient of W with respect of temperature (T). And we can see the change of S is due to three components: deformation, heat conduction and polarization. In an isothermal state, the deformation part has been fully investigated by Arruda and Boyce in 1993, but the polarization-induced entropy (Sp) has not been clearly stated.

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