Effect Of Temperature And Viscoelasticity On The Static And Dynamic Electromechanical Coupling Performance Of Dielectric Elastomer

Dielectric elastomers(DEs)are emerging electro-active polymer(EAP)used in high-performance applications as actuators.Subject to a voltage,a DE reduces its thickness and generates large expansion in its area of a maxmum area strain of 1600%.However,few reports have been released on the effect of temperature and viscoelasticity on nonlinear electromechanical performance of DEs,futhermore,even fewer are capable of making reliable predictions under dynamic performance.In this paper,we investigate the influence of temperature and viscoelasticity on the static and dynamic electromechanical coupling characteristics of the most widely used DE(VHB 4910).Fist,the mechanical and dielectric properties,the glass transition temperature and thermal stability of DE were studied by dynamic mechanical analysis(DMA),broadband dielectric spectroscopy(BDS)analyzer,differential scanning calorimetry(DSC),and thermal gravimetric analysis(TGA),respectively.Based on the experimental results of the mechanical and dielectric properties,the actuation factor,mechanical,electrical efficiency and electromechanical coupling efficiency of DE were analyzed.It is demonstrated that the actuation performance was dominated by the mechanical properties of DE,and was less influenced by the frequency and temperature dependence of dielectric properties;the electromechanical coupling efficiency decreased with increasing frequency and increased with the increase of the electric field and temperature.Subsequently,this paper proposed a free energy model in the thermodynamic system of DE by involving thermoelastic strain energy,electric energy and purely thermal contribution energy to obtain the influence of temperature on electromechnical instability(EMI),electrical breakdown(EB),loss of tension and rupture.The performance of DE was affected by temperature and pre-stretch,based on the thermodynamic model,the electrostriction induced by large deformation and temperature was studied.The model predicts the stability criteria with physical interpretation of its dependence on dielectric constant and electrostrictive coefficient.The numerical simulation indicated that the stress due to electrostriction relies on temperature and deformation dependent dielectric constant partially removed the Maxwell stress and contributed to enhance the stability of the dielectric elastomer.The increase in temperature can markedly contribute to improving the deformation of the DE and the decrease of temperature could modify the EMI,which consequently enhanced the stability of DE.The effect of temperature on the deformation of DE was mesured by experiments,which agreed well with the numerical results.Viscoelasticity of DE can significantly influence the electromechanical transduction and its application.Combining with the rheological model of viscoelastic relaxation,the effect of voltage waveform and temperature on deformation was analyzed.The results indicated that DE could attain a big deformation under a small constant voltage with a long time or under a big voltage with a short time.The model also showed that a higher critical stretch could be achieved by applying ramping voltage with a lower rate.Moreover,the stretch of DE increased with increasing temperature.Subsequently,the in-plane deformation of DE due to viscoelasticity was performed experimentally,which verified the numerical results.And then,we used the Euler-Lagrange equation and the viscoelastic relaxation model to characterize the influence of temperature and excitation frequency on the dynamic electromechanical deformation and stability of DE actuator by considering viscoelasticity.It was observed that the natural frequency of the DE actuator decreased with increasing temperature and the maximal amplitude increased at higher temperatures.At relative low frequencies,the amplitude was very small and the viscoelasticity had a significant effect on the oscillation of the system.Finally,this paper presented a nonlinear dynamic model to study the dynamic characteristics of a DE actuator undergoing in-plane deformation,subjected to combined loads of the electric field and mechanical press.The nonlinear dynamic behaviors under periodic electric loading were analyzed.The numerical results,such as displacement response,phase diagrams and amplitude-frequency response were analyzed.Poincaré maps were presented to show the influence of damping on the nonlinear dynamic stability of DE actuator.Numerical results indicated that pre-stresses,damping effects and applied voltages could tune the natural frequency and modify the dynamic behavior of DE actuator.It is hoped that the approach presented in this paper could guide the design of dynamic and static applications in dielectric elastomers actuators.