Analysis To Non-equilibrium Electromechanical Behaviors Of Dielectric Elastomer Membrane Transducers

Dielectric elastomers(DEs)are a class of soft materials.When subjected to an external electric field across the thickness,a membrane of DEs coated with compliant electrodes on top and bottom surfaces reduces its thickness while expands its area,inducing large deformation and converting electrical energy into mechanical energy.This unique attribute plus other excellent material or mechanical features,such as light weight,high efficiency,low cost,high energy density,noise free,easy fabrication etc.,make DEs attract more and more attention in academic field and in industrial field in recent years.DEs can be designed into actuators,sensors and energy harvesters to play significant roles in the fields of artificial muscle,robot,biomedicine,electric product and energy harvesting already or in the future,which would potentially create huge market profits.So far,although a number of theoretical or experimental investigations on the actuation mechanism,modes of failure as well as electromechanical elastic behaviors of DE transducers have been conducted valuably,few works were devoted to exploring the electromechanical viscoelastic behaviors of the DE transducers.In this thesis,the investigations focus on studying the electromechanical viscoelastic behaviors of the DE transducers and the creative researches include:(1)A viscoelastic model for a circular DE membrane actuator,connected centrally to a light rigid disk and subjected to internal pressure and voltage,is established.The actuator undergoes out-of plane large deformation and its electromechanical viscoelastic behaviors are considered.By means of non-equilibrium thermodynamics,the state equations and the governing equations are derived,and the kinetic equations are obtained by a rheological spring-dashpot model.The evolutions of all the considered variables and the profile of the deformed membrane are obtained numerically and illustrated graphically.In calculation,the effects of the internal pressure,voltage and the design parameters on the electromechanical viscoelastic behaviors of the actuator are considered,and the results show that they significantly influence the behaviors of the actuator.(2)A viscoelastic model is formulated for a tubular DE membrane actuator,which is connected to light rigid disks at top and bottom ends respectively and subjected tointernal pressure and voltage,undergoing axisymmetric large deformation.The governing equations describing large deformation and the kinetic equations characterizing the viscoelasticity are obtained and solved numerically by joint use of shooting method and the improved Euler method.The variations of all the considered variables are obtained.In simulation,the emphasis is placed on examining the effects of the internal pressure,voltage and the aspect ratio of the tube membrane on the electromechanical viscoelastic behaviors of the tubular,and the results show that they drastically affect the behaviors the tubular actuator.(3)A viscoelastic model is established for a tubular DE membrane actuator subjected to axial force and voltage,whose top and bottom edges are fixed with light rigid disks respectively.The governing equations for describing the large deformation are derived by quasi-static equilibrium method and the kinetic equations are still given from the rheological model.The variations of the considered variables are obtained numerically.In calculation,the influences of the electromechanical loads,the hoop pre-stretch and the aspect ratio of the membrane to the electromechanical viscoelastic performance of the actuator are found to be significant.(4)The mechanical model of tubular membrane-spring actuator was established.The governing equations for describing the large deformation are derived by quasi-static equilibrium method and the kinetic equations are still given from the rheological model.Through numerical calculation,the viscoelastic behavior under constant electromechanical loads and cyclic electromechanical loads are investigated.From the calculation results,the stiffness of the spring and loading rate play a significant role on the time-dependent behaviors of the membrane.The research presented in this thesis would help to understand the electromechanical viscoelastic performances of such several actuators much better,and provide theoretical guidelines in designing and optimizing such several actuators,which would greatly forward such several actuators into engineering applications.