Shouhua Sun

Electromechanical stability of dielectric elastomer

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.

Analysis and manufacture of an energy harvester based on a Mooney-Rivlin?type dielectric elastomer

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.

An investigation on electromechanical stability of dielectric elastomers undergoing large deformation

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 elastomers typical stability performance. The proposed model offers great help in guiding the design and fabrication of actuators featuring dielectric elastomers.

Comment on “On electromechanical stability of dielectric elastomers” [Appl. Phys. Lett.93, 101902 (2008)]

We would like to thank Diaz-Calleja et al. [Appl. Phys. Lett.93, 101902 (Year: 2008)] for their insight and help on “On electromechanical stability of dielectric elastomers;” unstable domain of electromechanical coupling system of neo-Hookean-type silicone was analyzed by Diaz-Calleja et al. Different from that given in the paper of Diaz-Calleja, in the current work, the elastic strain energy function with two material constants was used to analyze the stable domain of electromechanical coupling system of Mooney–Rivlin-type silicone, and the results seem to support the theory of Diaz-Calleja.

Design and analysis of morphing wing based on SMP composite

A new concept of a morphing wing based on shape memory polymer (SMP) and its reinforced composites is proposed in this paper. SMP used in this study is a thermoset styrene-based resin in contrast to normal thermoplastic SMP. During heating, the wing curled on the aircraft can be deployed, providing main lift for a morphing aircraft to realize the stable flight. Aerodynamic characteristics of the deployed morphing wing are calculated by using CFD software. The static deformation of the wing under the air loads is also analyzed by using the finite element method. The results show that the used SMP material can provide enough strength and stiffness for the application. Finally, preliminary testing is conducted to investigate the recovery performances of SMP and its reinforced composites. During the test, the deployment and the wind-resistant ability of the morphing wing are dramatically improved by adding reinforced phase to the SMP.

Novel deployable morphing wing based on SMP composite

In this paper, a novel kind of deployable morphing wing base on shape memory polymer (SMP) composite is designed and tested. While the deployment of the morphing wing still relies on the mechanisms to ensure the recovery force and the stability performance, the deploying process tends to be more steady and accurate by the application of SMP composite, which overcomes the inherent drawbacks of the traditional one, such as harmful impact to the flight balance, less accuracy during the deployment and complex mechanical masses. On the other hand, SMP composite is also designed as the wings filler. During its shape recovery process, SMP composite stuffed in the wing helps to form an aerofoil for the wing and withstand the aerodynamic loads, leading to the compressed aerofoil recovering its original shape. To demonstrate the feasibility and the controllability of the designed deployable morphing wing, primary tests are also conducted, including the deploying speed of the morphing wing and SMP filler as the main testing aspects. Finally, Wings deformation under the air loads is also analyzed by using the finite element method to validate the flight stability.

Stability analysis of dielectric elastomer using the elastic strain energy function with two material constants

Dielectric elastomers (DE) are the most promising electroactive polymer materials capable of being applied in smart actuators. When the DE film sandwiched between two compliant electrodes is applied high electric field, due to the electrostatic force between two electrodes, the film expands in-plane and contracts out-of-plane such that its thickness becomes thinner. The thinner thickness results in higher electric field which inversely squeezes the film again. This positive feedback induces a mode of instability, known as electromechanical instability or pull-in instability. When the electric field exceeds certain critical value, the DE film collapses. In this paper, the elastic strain energy function with two material constants is applied to analyze the stability of dielectric elastomers, which facilitates to understand fully Suos nonlinear theory. The results verify again the truth of this theory and exploit larger application spectrum. The method is capable of analyzing the stability of different dielectric materials with different values of k and the result can be useful on design of the dielectric elastomer actuator.

Dielectric properties of carbon nanotube/silicone elastomer composites

Dielectric elastomers have received a great deal of attention recently for effectively transforming electrical energy to mechanical work. Their large strains and conformability make them enticing materials which can be applied in many domains: biomimetics, aerospace, mechanics, medicals, etc. In order to maximize actuator performance, the dielectric elastomer actuators should have a high dielectric constant and high dielectric breakdown strength. Here we have investigated the increase in permittivity of a commercial silicone elastomer by the addition of carbon nanotube. The percolation threshold of the composites is obtained to be low. Experimental results suggest that for the case of conductive filler particle-elastomer matrix interaction, actuation strain increases with increasing carbon nanotube content.

Silicone dielectric elastomers filled with carbon nanotubes and actuator

Dielectric elastomers (DEs) are one particular type of electroactive polymers. The excellent features of merit possessed by dielectric elastomers make them the most performing materials which can be applied in many domains: biomimetics, aerospace, mechanics, medicals, etc. In order to maximize actuator performance, the dielectric elastomer actuators should have a high dielectric constant and high dielectric breakdown strength. In this paper, multi-walled carbon nanotube (MWNT) is used to develop a particulate composite based on silicone elastomer matrix, with dielectric permittivity improved. And the composite is designed to a new configuration of dielectric elastomer actuator to show electrically activated linear contractions. Prototype samples of this folded actuator, along with the fabrication and analysis is discussed here.

The area of allowable states in Mooney-Rivlin type dielectric elastomer generators

Dielectric elastomer(DE) could be used in generator design and fabrication, which has been verified by experiments. The function principle of DE generator is contrary to that of DE actuator. By imposing a low voltage to the dielectric elastomer membrane, electric charges are accumulated on the two surfaces. Then we apply mechanical force to the sides of the membrane to produce pre-stretch, and the thickness of the membrane becomes thinner and the capacitance increases, where mechanical energy is converted to elastic energy. After the mechanical force being withdrawn, because of elasticity, the thickness of membrane increases while the capacitance decreases, and elastic energy is converted to electrical energy. This is a work cycle of conversion from elastic to electric energy. Researchers have always been expecting to find a model that can well predict and evaluate the performance of dielectric elastomer generator. Suo et al. proposed the typical failure model of neo-Hooken type dielectric elastomer generator and calculates the maximal energy converted in a mechanical and electrical cycle. In this paper, we demonstrate the area of allowable states of various Mooney-Rivlin type dielectric elastomer generators, which can be employed to direct the design and fabrication of Mooney-Rivlin silicone generator, and the results coincide with Suos theory.