Viscoelastic Behaviors Of Dielectric Elastomer Actuators Under Out-of-plane Deformation

Compared with hard materials widely used in engineering, many flexible structures exist in nature, such as octopus legs, mimosa with touch reactions and so on. It has been an important target to develop new materials, to mimic the significant and excellent characteristics of the life. Dielectric elastomers gradually come into people’s perspective with their superior characteristics. For example, they can produce more than 100% strain under an external electric field. In addition to large voltage-induced strains, they have some other advantages such as fast response, low noise, light and cheap, high fatigue life and outstanding performance in bionics, therefore, they have been used more and more in many kinds of intelligent drives such as intelligent robots, Braille displays, optical lenses, energy harvester et al. They also have great potential applications in artificial muscles, intelligent bionic, aerospace, machinery and other fields.It is found that the dielectric elastomers are usually stretch-rate dependent, which not only affects the efficiency of converters, but also has a huge impact on the output and response speed of the devices. In fact, the stretch-rate dependent behaviors are usually interpreted as the consequence of the viscoelasticity of the polymers. More and more studies show that the viscoelasticity is a significant feature of dielectric elastomers and cannot be ignored. So the investigation on viscoelasticity of dielectric elastomer is necessary.This paper describes the nonlinear, non-equilibrium and dynamic behaviors of dielectric elastomers when coupled with large deformation and electro-mechanical load, based on the model of continuum mechanics and thermodynamics framework. Based on this model, we study the viscoelastic properties of round film and circular ring actuator under different mechanical loads and voltages. The main works are as following:(1) Considering the viscoelastic effects, we derived the thermodynamic equations by introducing the spring-damper model and provided a theoretical basis and solving method for the viscoelastic problem; (2) Considering the coupling effect of the mechanical and voltage, we obtained the distribution and evolution of the physical field based on the viscoelastic model and round film, and presented a good description of the electromechanical instability behavior of this model; (3) We established the analytical model of viscoelastic ring actuator, analyzed the mechanical behavior of the actuators, and studied the effect of different parameters on the output. We provided a theoretical basis for the prediction of electromechanical instability and the deformation behaviors when considering the viscoelastic effect. It also provides a practical reference or guidance for the product design optimization when the viscoelastic effect is considered.