Electromechanical instability may occur in dielectric elastomer films due to the coupling between mechanical forces and electric fields. According to Zhao and Suo [Appl. Phys. Lett. 91, 061921 (2007)], free-energy in any form, which consists of elastic strain energy and electric energy, can be used to analyze the electromechanical stability of dielectric elastomer. By taking the permittivity as a variable depending on the deformation in a free energy function, a relationship is established among critical nominal electric field, critical real electric field, nominal stress, and principal stretch ratios. The accurate expressions of these parameters are presented for a special equal biaxial stretch case. All the results obtained by utilizing the single material constant neo-Hookean elastic strain energy model coincide with the conclusions by Zhao and Suo.

We studied a typical failure model of a Mooney-Rivlin-type silicone energy harvester, illustrated the allowable area under equal-biaxial and unequal-biaxial conditions, calculated the energy generated in one cycle of an energy harvester, designed a new harvester, and conducted its primary tests. When the ratio between principal planar stretches p = 1 (λ2 = pλ1) and the material constant ratio k = 0.1 (C2 = kC1), the energy density generated by the harvester is 6.81 J/g. We think that these results can be used to facilitate the design and manufacture of dielectric elastomer energy harvesters.

Shape‐memory polymer (SMP) materials have several drawbacks such as low strength, low stiffness and natural insulating tendencies, which seriously limit their development and applications. Much effort has been made to improve their mechanical properties by adding particle or fiber fillers to reinforce the polymer matrix. However, this often leads to the mechanical properties being enhanced slightly, but the shape‐memory effect of reinforced SMP composites being drastically reduced. The experimental results reported here suggested that the mechanical resistive loading and thermal conductivity of a composite (with hybrid filler content of 7.0 wt%) were improved by 160 and 200%, respectively, in comparison with those of pure bulk SMP. Also, the glass transition temperature of the composite was enhanced to 57.28 °C from the 46.38 °C of a composite filled with 5.5 wt% hybrid filler, as determined from differential scanning calorimetry measurements. Finally, the temperature distribution and recovery behavior of specimens were recorded with infrared video in a recovery test, where a 28 V direct current circuit was applied. The effectiveness of carbon black and short carbon fibers being incorporated into a SMP with shape recovery activated by electricity has been demonstrated. These hybrid fillers were explored to improve the mechanical and conductive properties of bulk SMP. Copyright © 2010 Society of Chemical Industry

Dielectric elastomers are one of the important electroactive polymers used as actuators in adaptive structures due to their outstanding ability to generate very large deformations when subjected to an external electric field. In this paper, the Mooney-Rivlin elastic strain energy function with two material constants is used to analyze the electromechanical stability performance of a dielectric elastomer. This elastic strain energy together with the electric energy incorporating linear permittivity are the main items to construct the free energy of the system. Particular numerical results are also calculated for a further understanding of the dielectric elastomer's typical stability performance. The proposed model offers great help in guiding the design and fabrication of actuators featuring dielectric elastomers.

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The electromechanical stability of a Mooney-Rivlin-type dielectric elastomer undergoing large deformation with nonlinear permittivity is investigated. The stability is analyzed by applying a new kind of free energy model, which couples Ogden elastic strain energy and electric field energy density with nonlinear permittivity. Then, nominal electric field and nominal electric displacement of the dielectric elastomer are introduced. Based on this, the electromechanical stability of the Mooney-Rivlintype dielectric elastomer is analyzed by simplifying the Ogden elastic strain energy. The critical breakdown electric fields under the conditions of two stretching ratios and various material constant ratios k (n = km, where m and n are material constants in the Ogden model, determined experimentally) are also obtained. According to the simulation results, for a larger dimensionless constant k of the dielectric material, the critical nominal electric field is higher, the corresponding dielectric elastomer or structure is more stable and the electromechanical stability of the dielectric elastomer is proved to be markedly enhanced by a pre-stretching process. These results agree well with experimental data and can be used as guidance in the design and fabrication of dielectric elastomer actuators.