Nonlinear Response And Parametric Optimization Design Of Universal Muscle Actuators

When subject to a voltage or an electric field, a class of polymers will change theirshape or volume and they are known as electroactive polymers. The electroactivepolymer is a class of smart material which undegoes large deformation under anelectric field. It consists of soft dielectric material which covered by soft electrodesand the electrodes are made of conductive material. Under the action of an electricfield, the electroactive polymer will change its shape by reducing its thickness whileexpanding its area. Conversely, when subjected to mechanical loads, nature of theelectrical aspects will be changed. Therefore, the electroactive polymer is a promisingnew material with strong electromechanical coupling.In the second section of this thesis, a class of soft active materials: dielectricelastomer, is introduced and the nonlinear theory of deformbale dielectrics proposedby Zhigang Suo is cited.In the third section, some material models are introduced, and three of them:Neo-Hookean model,Mooney-Rivlin model,Ogden model are choosen to investigatethe out-of plane axisymmetric nonlinear deformation of such actuator made ofelectroactive polymers membrane subject to electromechanical loads. The equationsof equilibrium state of three models characterizing the large deformation of theannular membrane subject to a concentrated force and a voltage are derived. Thederived state equations are solved by using shooting method and the obtainednumerical results show that the deformation field in the membrane is highlyinhomogeneous. The deformation near the central part of the membrane is large whilethe deformation near the edge of the membrane is small, which leads to the inducedelectric field in the membrane increases monotonically from the edge to the centralpart and reaches maximum at the central part of the membrane. This results in theconsequence that the membrane near the central part risks the possibility of electricbreakdown while the major part of the membrane can still function normally. Theinhomogeneity of deformation field leads to the consequence that the membrane doesnot function efficiently, which results in material waste.The fourth section focuses on investigating the optimization design of the universalmuscle actuator of electroactive polymers membrane and three specific ratios a/A, b/Band b/a, called as the initial pre-streteches, are considered as design parameters. Theperformance of the actuator can be optimized by altering the values of the design parameters. The effect of initial prestretches on the thickness of the membrane,stretches, stresses and electric field are obtained and illustrated graphically. Theresults show that the electric field in the membrane tends to be uniform under certainset of design parameters. The method proposed here provides basic analysis patternsfor optimization design for such actuators.