High-field deformation of elastomeric dielectrics for actuators (original) (raw)
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The strain response of silicone dielectric elastomer actuators
Proceedings of SPIE - The International Society for Optical Engineering, 2005
Dielectric elastomers are known to produce large transverse strains in response to electrically induced Maxwell stresses and thus provide a useful form of electromechanical actuation. The transverse strain response of silicone (Dow Corning HS III RTV) based Maxwell stress actuators have been measured earlier as a function of driving electric field, frequency and pre-load. Experimental results show that a pre-load initially causes an increase in the strain. However, this increase appears to be a function of the relative geometries of the electroded area and of the specimen itself. The transverse strains in these materials decrease when larger values of pre-load are applied. Models of hyperelasticity that are capable of describing the large deformation of polymer materials have been used to interpret our results. Numerical finite element simulations of the material's behavior using a hyperelastic model provides good agreement with most of our observations on the electric field and pre-strain dependencies of the transverse strain.
On the nature of dielectric elastomer actuators and its implications for their design
Proceedings of SPIE, 2006
Dielectric Elastomer (DE) actuators have been studied extensively under laboratory conditions where they have shown promising performance. However, in practical applications, they have not achieved their full potential. Here, the results of detailed analytical and experimental studies of the failure modes and performance boundaries of DE actuators are presented. The objective is to establish fundamental design principles for DE actuators. Analytical models suggest that DE actuators made with highly viscoelastic films are capable of reliably achieving large extensions when used at high speeds (high stretch rates). Experiments show that DE actuators used in low speed applications, such as slow continuous actuation, are subject to failure at substantially lower extensions and also have lower efficiencies. This creates an important reliability/performance trade-off because, due to their viscoelastic nature, highest DE actuators forces are obtained at low speeds. Hence, DE actuator design requires careful reliability/performance trade-offs because actuator speeds and extensions for optimal performance can significantly reduce actuator life.
Sensors and Actuators A-physical, 2003
This work intends to extend the electromechanical characterisation of dielectric elastomer actuators. Planar actuators were realised with a 50 m-thick film of an acrylic elastomer coated with compliant electrodes. The isotonic transverse strain, the isometric transverse stress and the driving current, due to a 2 s high voltage impulse, were measured for four electrode materials (thickened electrolyte solution, graphite spray, carbon grease and graphite powder), four transverse prestress values (19.6, 29.4, 39.2 and 49.0 kPa) and different driving voltages (up to the dielectric breakdown voltage). Results showed that the electrode material and prestress strongly influence the electromechanical performances of the devices. Actuators with graphite spray electrodes and transverse prestress of 39.2 kPa exhibited an isotonic transverse strain of 6% at 49 V/m, with a driving current per unit electrode area of 3.5 A/cm 2 , and an isometric transverse stress of 49 kPa at 42 V/m. An electromechanical coupling efficiency of 10% at 21 V/m was calculated for actuators with thickened electrolyte solution electrodes and a transverse prestress of 29.4 kPa. The presented data permits to choose the best electrode material and the best prestress value (among those tested), to obtain the maximum isotonic transverse strain, the maximum isometric transverse stress or the maximum efficiency for different ranges of applied electric field.
Comparative study of electromechanical response in some dielectric elastomers
JOURNAL OF …, 2011
Dielectric elastomers, a subclass of electroactive polymers (EAP) materials, are very promising for actuator and sensor applications due to their interesting properties such as high energy density, high strain levels from 10 to 380 % and fast response in order of milliseconds. Polymer films were sandwich between two rigid electrodes and subjected to high DC electric fields. We investigate the transverse strain responses of some dielectric elastomer actuators (DEA) using an eddy current displacement sensor. Electric-field-induced thickness strains in order of micrometers were measured at different high DC step voltage and a quadratic dependence was observed. A comparison has been made between three categories of elastomers. The preliminary results show that performance of the actuators not only depends on the material properties but it is also a function of the actuator structure and electrode materials. We also concluded that these materials may be candidates for actuator materials in micro-actuation mechatronic systems.
High-Speed Electrically Actuated Elastomers with Strain Greater Than 100%
Science, 2000
Electrical actuators were made from films of dielectric elastomers (such as silicones) coated on both sides with compliant electrode material. When voltage was applied, the resulting electrostatic forces compressed the film in thickness and expanded it in area, producing strains up to 30 to 40%. It is now shown that prestraining the film further improves the performance of these devices. Actuated strains up to 117% were demonstrated with silicone elastomers, and up to 215% with acrylic elastomers using biaxially and uniaxially prestrained films. The strain, pressure, and response time of silicone exceeded those of natural muscle; specific energy densities greatly exceeded those of other field-actuated materials. Because the actuation mechanism is faster than in other high-strain electroactive polymers, this technology may be suitable for diverse applications.
Dielectric elastomer film actuators: characterization, experiment and analysis
Smart Materials & Structures, 2009
Silicone is a common dielectric elastomer material. Actuators made from it show excellent activation properties including large strains (up to 380%), high energy densities (up to 3.4 J g-1), high efficiency, high responsive speed, good reliability and durability, etc. When a voltage is applied on the compliant electrodes of the dielectric elastomers, the polymer shrinks along the electric field and expands in the transverse plane. In this paper, a silicone dielectric elastomer is synthesized and the area strains are tested under different electric fields. Pre-strain and a certain driving electric field are applied to the film and the induced large strain by the Maxwell stress is measured. Barium titanate (BaTiO3) was incorporated into the silicone to fabricate a new dielectric elastomer: the experimental results show that the elastic modulus and dielectric constant were significantly improved. The experimental results coincide well with those of finite element analysis at a large deformation. Also, a theoretical analysis is performed on the coupling effects of the mechanical and electric fields. A nonlinear field theory of deformable dielectrics and hyperelastic theory are adopted to analyze the electromechanical field behavior of these actuators. Also the mechanical behavior of the dielectric elastomer undergoing large free deformation is studied. Finally, the constitutive model of a dielectric elastomer composite under free deformation and restrained deformation is derived. This article was originally submitted for the special section 'Smart Composite Materials: Selected Papers from the International Conference on Multifunctional Materials and Structures (MFMS 08) (Hong Kong, 28-31 July 2008)', Smart Materials and Structures, volume 18, issue 7.
Mechanisms of large actuation strain in dielectric elastomers
2011
Abstract Subject to a voltage, a dielectric elastomer (DE) deforms. Voltage-induced strains of above 100% have been observed when DEs are prestretched, and for DEs of certain network structures. Understanding mechanisms of large actuation strains is an active area of research. We propose that the voltage-stretch response of DEs may be modified by prestretch, or by using polymers with “short” chains. This modification results in suppression or elimination of electromechanical instability, leading to large actuation strains.
On the performance mechanisms of Dielectric Elastomer Actuators
Sensors and Actuators A: Physical, 2007
Dielectric Elastomer Actuators (DEAs) show promise for robotics and mechatronics applications. They are lightweight, low costs, and have shown good performance in laboratory demonstration. However, these actuators have not been widely applied commercially after more than ten years of development. One reason is that the mechanisms governing their performance are not completely understood. Hence designing practical actuators is difficult. This paper has the objective of understanding the dominant performance mechanisms of DEAs. To do so, an experimental characterization of actuator performance is conducted in terms of force, power, current consumption, work output, and efficiency. Key performance mechanisms of viscoelasticity and current leakage are identified from experimental observations and analytical models are developed. The models explain well the experimental observations and should aid designers in selecting applications that are appropriate for DEAs as well as designing effective DEAs.
Theory of dielectric elastomers capable of giant deformation of actuation
2010
The deformation of a dielectric induced by voltage is limited by electrical breakdown if the dielectric is stiff, and by electromechanical instability if the dielectric is compliant. The interplay of the two modes of instability is analyzed for a dielectric elastomer, which is compliant at a small stretch, but stiffens steeply. The theory is illustrated with recent experiments of interpenetrating networks, and with a model of swollen elastomers.
IOP Conference Series: Materials Science and Engineering, 2018
A dielectric elastomer is capable of large deformation under three basic modes of deformation: equi-biaxial, pure shear and uniaxial. Pre-stretching of dielectric elastomer improves the actuation strain appreciably. Experimental results shows that pre-stretching using equal biaxial mode can result to higher actuation strain compared to other two modes of stretching, i.e., uniaxial and pure shear. However, analysis of the experimental results shows that the actuation strain is independent of the modes of pre-stretching rather it is dependent upon the thickness stretch. For same thickness stretch at a particular voltage, the actuation strain is almost similar for all pre-stretching modes. Power trend lines are obtained to predict the actuation strain at any thickness stretch for a particular voltage. The present analysis opens the door to easily design the actuators, sensors and energy harvesting devices.