Research On The Electromechanical Coupling Characteristics Of Dielectric Electoactive Polymer (EAP) Transducer

As a new kind of emerging smart material, dielectric electroactive polymer (EAP) hasdemonstrated low weight, large strain rate (up to380%), high energy density (3.4J/g), good efficiency,fast response and excellent environmental adaptability. The overall performance of dielectric EAP issimilar to that of biological muscle tissue. Nowdays, research on dielectric EAP has been becomingthe focus of intelligent material field wordwidely. It has two working modes including actuator modeand generator mode, which can transform electrical energy directly into mechanical work and viceversa. The common problem of two working modes is the relationship between force and deformationof dielectric EAP in the presence of electric field, named the electromechanical couplingcharacteristic of dielectric EAP. Thus the same method can be used to model dielectric EAPtransducer. Supported by National Natural Science Foundation of China (No.50975139), research onelectromechanical coupling characteristic of dielectric EAP transducer is performed based thematerial and geometrical nonlinearities in this dissertation. Theoretical modeling and experimentalanalysis on dielectric EAP transducer can contribute to the design of dielectric EAP transducer.Using a continuum mechanics theory, the stress, strain description and equations of equilibriumof dielectric EAP are deduced. The stress analysis of dielectric EAP activated by electrical field isexecuted. The constitutive equation of the dielectric EAP is determined by a superposition of themechanical stress due to the nonlinear elastic theory and the Maxwell stress due to the electrostaticfield.Based on the proposed electromechanical constitutive equations of dielectric EAP, themechanical behavior of circular dielectric EAP actuator under electrical field is analyzed. With thedeveloped analytical model of circular actuator, the impacting of pre-stretch ratio and area of activeregion to the circular actuator’s deformation under different applied voltages has been achieved bysolving the differential equations with boundary value problem by Matlab. The theoretical results arevalidated by experiments, which verify the of electromechanical constitutive equations of dielectricEAP.Using elastic theory of membrane, a model that describing conically-shaped dielectric EAPactuator is founded. Combing the working principle and process of dielectric EAP actuator, a methodof designing actuator is proposed by using the force-displacement curve of actuator. The force outputand displacement output of actuator with positive stiffness preload mechanism (compressive spring) are determined and validated by the experiments. To improve the displacement output, a negativestiffness preload mechanism with half diamond is presented. Actuation characteristics and efficiencyof conically-shaped dielectric EAP actuator with negative stiffness preload mechanism are analyzedin detail. Moreover, the electrical model of dielectric EAP actuator is discussed.Several failure mechanisms of dielectric EAP actuator including mechanical strength, dielectricbreakdown, pull-in phenomena (electromechanical instability), wrinkling phenomena and systeminstability are investigated, and the safe working area of ideal dielectric EAP actuator is determined.In addition, the failure behavior of conically-shaped actuator is discussed in detail.The energy harvesting mechanisms and working cycles of dielectric EAP transducer areinvestigated. Three different cycles including constant charges, constant electric voltage and constantelectrical field are compared. Based on the working cycles, the energy conversion betweenmechanical energy inputted and electrical energy generated have been studied. With the proposedmodel of dielectric EAP transducer, the force-stroke of generator unit in the stretching process withvoltage on and the retracting process with voltage off are determined. With the force-stroke ofgenerator unit, the energy generated and energy conversion efficiency are calculated. It isdemonstrated that the stretch displacement of dielectric EAP generator and bias voltage are the mainfactors influencing the amount of electrical energy generated and the efficiency of energy conversion.In addition, the theoretical analysis results are validated by the experiments. To improve theefficiency of energy conversion, a scheme of a generator with multiple dielectric EAP units isdeveloped.