Stability Of Dielectric Elastomers Research Articles

Modulation of the dynamic response and stability of dielectric balloon by stretch-dependent dielectric permittivity

The dynamic response of dielectric elastomers is widely used in many functional devices, but current research has neglected the effect of varying dielectric permittivity on their dynamic oscillations and stability. This paper studies the thin-walled dielectric balloon in which the stretch-dependent dielectric permittivity is considered. We obtain the dynamic equation of motion by Hamilton’s principle. Based on the principle of no energy dissipation in conservative systems, we establish energy conservation at the maximum stretching position and at the initial moment, then we investigate the stability in the dynamic case. It is found that a stretch-related dielectric permittivity can increase the critical electric field of the balloon and can also change the mode of electric field instability and modulate the critical stretch value. In the dynamic case, the stretch-dependent permittivity increases the critical electric field by 4% when the balloon is only subjected to electric force; moreover, it increases the critical stretch value by 316.68% by changing the unstable mode from pull-in instability to snap-through instability. It is hoped that this work will provide new thinking in designing functional devices by using the dynamical response and stability of dielectric elastomers.

Theory analysis method for the effect of temperature and electrostrictive on the actuation stability of dielectric elastomers

Dielectric elastomer (DE) as an electroactive soft material can produce large deformation induced by voltage. Usually, the deformation is limited by various failure modes, which affect the stability of the DE electrical actuation. The previous researches have demonstrated temperature affection on the dielectric constant of DE. In this paper, the mathematical calculation theory for the various unstable DE failure is deduced with the thermoelastic model. The numerical model and analysis result discussed the effects of temperature and electrostriction coefficient on the instability phenomena of DE. The nominal stress deformation changes with the nominal electric displacement on the DE material at different temperatures. The stable working range area encircles by the curves of electromechanical instability (EMI), tension loss ( s = 0), electrical breakdown (EB), and tension rupture (λ = λR). The results show that the increase of temperature can improve the nominal stress and the nominal electric field of the actuator, which consequently enhances the stability of DE. Simultaneously, the stability of DE can also be improved when the electrostriction coefficient becomes smaller within a certain range. These conclusions have implications for improving the stability of DE electro-deformation.

Effects of pre-stretch on the oscillation and stability of dielectric elastomers

Pre-stretch affects the dynamic performance of the dielectric elastomers (DEs). In this paper, the effects of pre-stretch on the nonlinear viscoelastic oscillation and stability of the DE membrane actuator are investigated. Analytical model based on Euler-Lagrange method and homogeneity assumption is developed to describe the complex dynamic behaviour of the viscoelastic DE membrane actuator under equibiaxial and non-equibiaxial pre-stretches, respectively. Numerical calculations are applied to predict dynamic responses of the DE membrane actuator with different initial stretch ratios. The results indicate that the viscoelastic creep of the DE membrane actuator can be eliminated by specific initial stretch ratio. The phase paths and Poincaré maps reveal that proper pre-stretch helps to improve the stability of the DE membrane actuator. This work provides guidance for the structure design, stability control, and optimization of soft actuators and soft robots.

Theoretical Estimation of Stability of Dielectric Elastomers

When dielectric elastomers sandwiched between compliant electrodes and high electric voltage is applied to the dielectric elastomers. Then due to the electrostatic force between the electrodes the elastomers expands in plane and contract out of plane so that it becomes thinner. As the thickness decreases we observe the increase in the applied electric voltage with the positive feedback effect. This positive feedback leads the electrical as well as mechanical breakdown of elastomer. By applying a mechanical pre-stretch the mechanical stability of dielectric elastomers gets also increased. In this paper, a new generalized set of strain/stretch variables qrN has been introduced to get the expression for second order elastic moduli for the ideal electro elastic material deformed to orthorhombic structure. The strength of a loaded crystal determined from the new moduli has been compared with the strength of classical (Green, Stretch) moduli. It has been observed that the use of incorrect formula by ignoring shear strain leads to incorrect estimation of stability. This problem has been resolved by considering stretch variable in tensor form as generally observed in the process of electrostriction in the elastomers.

Effect of mechanical force field on the electromechanical stability of dielectric elastomers

To study the electromechanical stability of dielectric elastomer subjected to a mechanical force field, we use free energy functions of variable forms to analyze the mechanical performance of dielectric elastomer. The relation among critical nominal electric field, critical true electric field, nominal stress and mechanical force field is derived. These calculations agree well with the experimental results. The results can help us better understand the stability conditions of dielectric elastomers and furthermore guide the design and manufacture of sensors and actuators based on dielectric elastomers.

Effect of temperature on the stability of dielectric elastomers

Dielectric elastomer (DE) is a kind of electroactive polymer material, capable of large deformation up to 380%. However, under conservative operating conditions, DE is susceptible to instability with a small deformation due to various modes of failure, including electrical breakdown, electromechanical instability (EMI), loss of tension and rupture by stretch. This paper proposes a free energy model in the thermodynamic system of DE involving thermoelastic strain energy, electric energy and purely thermal contribution energy to obtain the stability conditions of all failure modes. The numerical results indicate that the increase in temperature can markedly contribute to improving the entropy production, the actuation stress and the critical nominal electric field of the DE. The increase in temperature could modify the failure modes of loss of tension and the EMI, which consequently enhances the stability of DE. Simultaneously, estimations on the maximal energy to be converted can be made from the theoretical formulation of the stability states. These conclusions may guide the exploration for high-performance DE materials under thermo, mechanical and electrical loads.

RECENT PROGRESSES IN POLYMERIC SMART MATERIALS

Smart materials can be defined as materials that sense and react to environmental conditions or stimuli. In recent years, a wide range of novel smart materials have been developed in biomaterials, sensors, actuators, etc. Their applications cover aerospace, automobile, telecommunications, etc. This paper presents some recent progresses in polymeric smart materials. Special emphasis is laid upon electroactive polymer (EAP), shape memory polymer (SMP) and their composites. For the electroactive polymer, an analysis of stability of dielectric elastomer using strain energy function is derived, and one type of electroactive polymer actuator is presented. For the shape memory polymer, a new method is developed to use infrared laser to actuate the SMP through the optical fiber embedded within the SMP. Electrically conductive nanocarbon powders are utilized as the fillers to improve the electrical conductivity of polymer. A series of fundamental investigations of electroactive SMP are performed and the shape recovery is demonstrated.