NONEQUILIBRIUM THERMODYNAMICS OF DIELECTRIC ELASTOMERS

2011 ◽  
Vol 03 (02) ◽  
pp. 203-217 ◽  
Author(s):  
XUANHE ZHAO ◽  
SOO JIN ADRIAN KOH ◽  
ZHIGANG SUO
Keyword(s):  
Nonequilibrium Thermodynamics ◽  
Dielectric Elastomer ◽  
Specific Model ◽  
Critical Voltage ◽  
Dielectric Elastomers ◽  
Internal Variables ◽  
Strain Rates ◽  
Dissipative Processes ◽  
Electromechanical Instability ◽  
External Loads

This paper describes an approach to construct models of dielectric elastomers undergoing dissipative processes, such as viscoelastic, dielectric and conductive relaxation. This approach is guided by nonequilibrium thermodynamics, characterizing the state of a dielectric elastomer with kinematic variables through which external loads do work, as well as internal variables that describe the dissipative processes. Within this approach, a method is developed to calculate the critical condition for electromechanical instability. This approach is illustrated with a specific model of a viscoelastic dielectric elastomer, which is fitted to stress-strain curves of a dielectric elastomer (VHB tape), measured at various strain rates. The model shows that a higher critical voltage can be achieved by applying a constant voltage for a shorter time, or by applying ramping voltage with a higher rate. A viscoelastic dielectric elastomer can attain a larger strain of actuation than an elastic dielectric elastomer.

scholarly journals Delayed electromechanical instability of a viscoelastic dielectric elastomer balloon

2019 ◽  
Vol 475 (2229) ◽  
pp. 20190316 ◽  
Author(s):  
Xiongfei Lv ◽  
Liwu Liu ◽  
Jinsong Leng ◽  
Yanju Liu ◽  
Shengqiang Cai
Keyword(s):  
Hoop Stress ◽  
Mechanical Load ◽  
Viscoelastic Model ◽  
Dielectric Elastomer ◽  
Time Dependent ◽  
Convex Shape ◽  
Nonlinear Viscoelastic ◽  
Electromechanical Instability ◽  
Electromechanical Loading ◽  
Nonlinear Viscoelastic Model

When a dielectric elastomer (DE) balloon is subjected to electromechanical loading, instability may happen. In recent experiments, it has been shown that the instability configuration of a DE balloon under electromechanical loading can be very different from that only subjected to mechanical load. It has also been observed in the experiments that the electromechanical instability phenomena of a DE balloon can be highly time-dependent. In this article, we adopt a nonlinear viscoelastic model for the DE membrane to investigate the time-dependent electromechanical instability of a DE balloon. Using the model, we show that under a constant electromechanical loading, a DE balloon may gradually evolve from a convex shape to a non-convex shape with bulging out in the centre, and compressive hoop stress can also gradually develop the balloon, resulting in wrinkles as observed in the experiments. We have further shown that the snap-through instability phenomenon of the DE balloon also greatly depends on the ramping rate of the applied voltage.

Electrostatically Driven Creep in Viscoelastic Dielectric Elastomers

2013 ◽  
Vol 81 (5) ◽  
Author(s):  
Jin Wang ◽  
Thao D. Nguyen ◽  
Harold S. Park
Keyword(s):  
Finite Element ◽  
Relaxation Time ◽  
Element Model ◽  
Constitutive Law ◽  
Dielectric Elastomers ◽  
Inhomogeneous Deformation ◽  
Viscoelastic Relaxation ◽  
Constant Voltage ◽  
Dynamic Finite Element ◽  
Electromechanical Instability

We utilize a nonlinear, dynamic finite element model coupled with a finite deformation viscoelastic constitutive law to study the inhomogeneous deformation and instabilities resulting from the application of a constant voltage to dielectric elastomers. The constant voltage loading is used to study electrostatically driven creep and the resulting electromechanical instabilities for two different cases that have all been experimentally observed, i.e., electromechanical snap-through instability and bursting drops in a dielectric elastomer. We find that in general, increasing the viscoelastic relaxation time leads to an increase in time needed to nucleate the electromechanical instability. However, we find for these two cases that the time needed to nucleate the instability scales with the relaxation time.

scholarly journals A Derivation of the Main Relations of Nonequilibrium Thermodynamics

2013 ◽  
Vol 2013 ◽  
pp. 1-9 ◽  
Author(s):  
Vladimir N. Pokrovskii
Keyword(s):  
Nonequilibrium Thermodynamics ◽  
Second Law Of Thermodynamics ◽  
Thermodynamic System ◽  
Internal Variables ◽  
Second Law ◽  
Basic Principles ◽  
First Law Of Thermodynamics ◽  
Sum Of Products ◽  
Thermodynamic Forces ◽  
Production Of Entropy

The principles of nonequilibrium thermodynamics are discussed, using the concept of internal variables that describe deviations of a thermodynamic system from the equilibrium state. While considering the first law of thermodynamics, work of internal variables is taken into account. It is shown that the requirement that the thermodynamic system cannot fulfil any work via internal variables is equivalent to the conventional formulation of the second law of thermodynamics. These statements, in line with the axioms introducing internal variables can be considered as basic principles of nonequilibrium thermodynamics. While considering stationary nonequilibrium situations close to equilibrium, it is shown that known linear parities between thermodynamic forces and fluxes and also the production of entropy, as a sum of products of thermodynamic forces and fluxes, are consequences of fundamental principles of thermodynamics.

Temperature Influence on the Viscoelastic Electromechanical Deformation of Dielectric Elastomer

2014 ◽  
Vol 1052 ◽  
pp. 137-142
Author(s):  
Jun Jie Sheng ◽  
Yu Qing Zhang ◽  
Shu Yong Li ◽  
Hua Ling Chen
Keyword(s):  
Dielectric Elastomer ◽  
Electric Load ◽  
Temperature Influence ◽  
Temperature Dependent ◽  
Influence Of Temperature ◽  
Dielectric Elastomer Actuators ◽  
Influence Of Temperature On ◽  
Electromechanical Instability ◽  
Increasing Temperature ◽  
Electromechanical Deformation

Temperature can significantly affect the performance of a viscoelastic dielectric elastomer (DE). In the current study, we use a thermodynamic model to characterize the influence of temperature on the viscoelastic electromechanical response undergoing a constant electric load by taking into account the temperature dependent elastic modus and dielectric constant. Due to the significant viscoelasticity in the dielectric elastomer, DE membrane creeps in time and the inelastic stretch of DE is smaller than that of the total stretch. The results show that the total stretch of the viscoelastic electromechanical deformation increases with the increasing temperature until suffering electromechanical instability at a high temperature; the actuation performance is dominated by the moduli of the elastomer. This may be used to guide the design of dielectric elastomer actuators undergoing temperature variation.

Lumped Parameter Modeling and Snap-Through Stability Analysis of Planar Hydraulically Amplified Dielectric Elastomer Actuators

2020 ◽  
Vol 1 (1) ◽  
Author(s):  
Amir Hosein Zamanian ◽  
David Y. Son ◽  
Paul S. Krueger ◽  
Edmond Richer
Keyword(s):  
Finite Element ◽  
Analytical Model ◽  
Central Area ◽  
Dielectric Elastomer ◽  
Lumped Parameter Model ◽  
Critical Voltage ◽  
Average Error ◽  
Dielectric Fluid ◽  
Functional Region ◽  
Lumped Parameter

Abstract In this paper, we established an analytical model that avoids extensive numerical computation for the analysis of a hydraulically amplified dielectric elastomer actuator. This actuator comprises a thin elastomer shell filled with an incompressible dielectric fluid coupled with a pair of electrodes placed in the central area. Application of high voltage on the electrodes inflates the actuator due to the induced Maxwell stress that pressurizes the incompressible dielectric fluid. The lumped parameter model predicts the stable functional region and the snap-through instability in the actuator. The model was compared with multi-physics finite element models that considered both linear elastic and nonlinear Mooney–Rivlin materials. The proposed model showed good agreement in the estimation of the actuation strain and the hydrostatic pressure as a function of voltage when compared to the finite element results. The average error in the axial and radial actuation using the proposed analytical model and nonlinear finite element method models was 1.62% and 3.42%, respectively. This shows the model strength in the estimation of the actuator states and the critical voltage to avoid snap-through instability, required in applications such as control algorithms.

scholarly journals Variational principles and nonequilibrium thermodynamics

2020 ◽  
Vol 378 (2170) ◽  
pp. 20190178 ◽  
Author(s):  
P. Ván ◽  
R. Kovács
Keyword(s):  
Symplectic Structure ◽  
Evolution Equations ◽  
Nonequilibrium Thermodynamics ◽  
Variational Principles ◽  
Dissipative Systems ◽  
Second Law ◽  
Theme Issue ◽  
Dissipative Processes ◽  
Variational Techniques ◽  
Lagrange Form

Variational principles play a fundamental role in deriving the evolution equations of physics. They work well in the case of non-dissipative evolution, but for dissipative systems, the variational principles are not unique and not constructive. With the methods of modern nonequilibrium thermodynamics, one can derive evolution equations for dissipative phenomena and, surprisingly, in several cases, one can also reproduce the Euler–Lagrange form and symplectic structure of the evolution equations for non-dissipative processes. In this work, we examine some demonstrative examples and compare thermodynamic and variational techniques. Then, we argue that, instead of searching for variational principles for dissipative systems, there is another viable programme: the second law alone can be an effective tool to construct evolution equations for both dissipative and non-dissipative processes. This article is part of the theme issue ‘Fundamental aspects of nonequilibrium thermodynamics’.

Development, manufacturing, and validation of a dielectric elastomer membrane actuator–driven contactor

2018 ◽  
Vol 30 (4) ◽  
pp. 636-648 ◽  
Author(s):  
Philipp Linnebach ◽  
Filomena Simone ◽  
Gianluca Rizzello ◽  
Stefan Seelecke
Keyword(s):  
New Technology ◽  
Dynamic Performance ◽  
Dielectric Elastomer ◽  
Dielectric Elastomers ◽  
Mechatronic Systems ◽  
Additional Advantage ◽  
Out Of Plane ◽  
Actuator System ◽  
Dielectric Elastomer Membrane

Dielectric elastomers represent a relatively new technology with high potentials for actuators’ applications. Thanks to their lightweight, fast operations, energy efficiency, low power consumption, large deformations, and high scalability, dielectric elastomers permit to develop novel mechatronic systems capable of overperforming standard actuation technologies, such as solenoid valves, in several applications. This article presents a novel design for a dielectric elastomer–driven actuator system which enables closing and opening of a contactor. The design is based on a combination between circular out-of-plane dielectric elastomer membranes and a bi-stable biasing system which allows to increase the out-of-plane stroke. Characterization of the contactor is initially performed in order to establish the actuator requirements in terms of force and stroke. Then, systematic design and manufacturing are carried out for both dielectric elastomer membranes and biasing mechanism. Finally, the effectiveness of the actuator in closing and opening the contactor is validated experimentally. The results show comparable dynamic performance to a conventional electromagnetic drive, with the additional advantage of a significantly lower energy consumption.

On the Design of Driver Electronics for Dielectric Elastomer Applications

2011 ◽  
Author(s):  
Mitja Babicˇ ◽  
Jadran Lenarcˇicˇ
Keyword(s):  
Mechanical Response ◽  
Design Procedure ◽  
Dielectric Elastomer ◽  
Dielectric Elastomers ◽  
Design And Optimization ◽  
Converter Topology ◽  
Protection Circuit ◽  
Circuit Components ◽  
Safety Operation ◽  
Driver Electronics

Actuators based on dielectric elastomers are a promising technology in robotic and mechatronic applications. Up to now, the practical electro-mechanical response and controllability of actuators based on dielectric elastomers are limited by the inadequacy of the employed driving circuits, which are based on voltage-regulated converters. In order to circumvent the aforementioned activation issues, the design procedure of a novel activation strategy for controlling dielectric elastomer actuators is presented in this article. The proposed electronic driver derives from the flyback converter topology and it is able of delivering to the dielectric elastomer actuator middle-frequency, current-pulse trains dependent on the duty-cycle value. The driver’s transformer, switching and protection circuit components design and optimization are based on an estimation of the dielectric elastomer actuator’s electrical parameters. The design of the transformer is crucial for the actuator’s performance and energy efficiency, meanwhile the driver’s switching and protection circuit components are important for the appropriate driver functioning and safety operation. The reported experimental results show that the proposed electronic driver performances are in accordance with the driver’s design.

scholarly journals Tuning Elastic Waves in Soft Phononic Crystal Cylinders Via Large Deformation and Electromechanical Coupling

2018 ◽  
Vol 85 (3) ◽  
Author(s):  
Bin Wu ◽  
Weijian Zhou ◽  
Ronghao Bao ◽  
Weiqiu Chen
Keyword(s):  
Large Deformation ◽  
Axial Force ◽  
Electromechanical Coupling ◽  
Phononic Crystal ◽  
Electrical Stimulus ◽  
Critical Voltage ◽  
Electric Voltage ◽  
Propagation Behavior ◽  
Electromechanical Instability ◽  
Longitudinal Stretch

Soft electroactive materials can undergo large deformation subjected to either mechanical or electrical stimulus, and hence, they can be excellent candidates for designing extremely flexible and adaptive structures and devices. This paper proposes a simple one-dimensional soft phononic crystal (PC) cylinder made of dielectric elastomer (DE) to show how large deformation and electric field can be used jointly to tune the longitudinal waves propagating in the PC. A series of soft electrodes, which are mechanically negligible, are placed periodically along the DE cylinder, and hence, the material can be regarded as uniform in the undeformed state. This is also the case for the uniformly prestretched state induced by a static axial force only. The effective periodicity of the structure is then achieved through two loading paths, i.e., by maintaining the longitudinal stretch and applying an electric voltage over any two neighboring electrodes or by holding the axial force and applying the voltage. All physical field variables for both configurations can be determined exactly based on the nonlinear theory of electroelasticity. An infinitesimal wave motion is further superimposed on the predeformed configurations, and the corresponding dispersion equations are derived analytically by invoking the linearized theory for incremental motions. Numerical examples are finally considered to show the tunability of wave propagation behavior in the soft PC cylinder. The outstanding performance regarding the band gap (BG) property of the proposed soft dielectric PC is clearly demonstrated by comparing with the conventional design adopting the hard piezoelectric material. One particular point that should be emphasized is that soft dielectric PCs are susceptible to various kinds of failure (buckling, electromechanical instability (EMI), electric breakdown (EB), etc.), imposing corresponding limits on the external stimuli. This has been carefully examined for the present soft PC cylinder such that the applied electric voltage is always assumed to be less than the critical voltage except for one case, in which we illustrate that the snap-through instability of the axially free PC cylinder made of a generalized Gent material may be used to efficiently trigger a sharp transition in the BGs.

Maximum Energy that can be Harvested from a Dielectric Elastomer Generator

2009 ◽  
Vol 1218 ◽  
Author(s):  
Adrian Koh
Keyword(s):  
Electrical Breakdown ◽  
Mechanical Energy ◽  
Electrical Energy ◽  
Dielectric Elastomer ◽  
Maximum Energy ◽  
Maximum Amount ◽  
Biaxial Stretching ◽  
Modes Of Failure ◽  
Electromechanical Instability

AbstractMechanical energy can be converted to electrical energy using a dielectric elastomer generator (DEG). The maximum amount of energy that can be harvested from a DEG is constrained by various modes of failure and operational limits. Known limiting mechanisms include electrical breakdown, electromechanical instability, loss of tension and rupture by stretch. These limits define a cycle where maximum energy can be harvested. The cycle was represented on work-conjugate planes, which can be used as a guide for the design of practical cycles. The amount of energy harvested is larger when a DEG is subject to equal-biaxial stretching.

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