Effects of prestrain on behavior of dielectric elastomer actuator

Abstract

Among ElectroActive Polymers(EAPs) the dielectric elastomer actuator is regarded as one of the most practically applicable in the near future. So far, its effect on the actuation phenomena has not been discussed sufficiently, although its strong dependency on prestrain is a significant drawback as an actuator. Recent observations clarifies that prestrain has the following pros and cons: prestrain plays an important role in generating large strain, whereas it rather contributes to the reduction of the strain. Prestrain provides the advantages of improving the response speed, increase of the breakdown voltage, and removing the boundary constraint caused by the inactive actuation area of the actuator. On the contrary, the elastic forces by prestrain makes the deformation smaller and the induced stress relaxation is severely detrimental as an actuator. Also, the permittivity decreases as prestrain goes up, which adds an adverse effect because the strain is proportional to the permittivity. In the present work, a comprehensive study on the effects of prestrain is performed. The key parameters affecting the overall performances are extracted and it is experimentally validated how they work on the actuation performance.

Advances in Dielectric Elastomers for Actuators and Artificial Muscles

“…[169] Prestrain has the additional benefits of improving the mechanical efficiency [170] and response speed of most DEs while causing a marginal decrease in the dielectric constant. [171] Prestrain can also be used to achieve preferential actuation in a certain direction by applying high prestrain in the direction perpendicular to the desired actuation direction and low prestrain along the actuation direction. [141] The effects of prestrain on the actuation performance of DEs have been widely studied from both a practical as well as theoretical perspective, [141,163,[166][167][168][169][170][171][172][173][174][175][176][177][178][179][180][181] however the mechanism by which prestrain increases dielectric strength is still not completely understood.…”

Rate-dependent mechanical behavior of VHB 4910 elastomer

“…Hence, reduced thickness due to pre-straining will improve the actuation performance for the same applied voltage or the same actuation performance can be obtained at a lower applied voltage. Since the pre-straining improves the performance of the film, it is therefore desirable that the DE film is pre-strained before applying electrical voltage for actuation [18]. The engineering stress-strain curves of VHB 4910 at different strain rates are shown in Figure 4.…”

The dielectric constant of 3M VHB: a parameter in dispute

“…Some studies suggest that the dielectric constant for VHB4910, a material commonly used in dielectric elastomers, decreases as it is stretched 5-7 , however, a stretch independent value of 4.7 is commonly used for modeling this material 1,8 . Also, values published for the dielectric constant of VHB4910 vary from 4.3 to 6 in an unstretched state [4][5][6][7]9 . With these points in view, a study clearly needs to be carried out to determine the correct approach to determining the dielectric constant and the sources of variation.…”