Numerical Analysis Of IPMC Electro-Mechanical Properties And Its Structure Simulation

Ionic polymer-metal composite (IPMC) is a potential emerging class of electro-active polymer material (EAP) exhibiting prominent electro-mechanical behaviors with inherent actuating properties. As the current research works are mainly on experimental basis and domestic works are still in an early stage, the mechanisms for the electromechanical coupling are not yet fully understood and the theoretical studies remain limited. The good quantificational predictions can not be given and some visual experiment phenomena can not be explained reasonably.The fundamental goal of this research work is to present a dynamic model for IPMC and suitable engineering structures. To this end, a physicochemical model is built with consideration of electric field,the movement of hydrated ions and characterization of bending motion based on Tadokoro theory. This study will improve the accuracy of prediction and is helpful to the characteristics analysis and products design of the IPMC materials. The main works have completed as follows:(1) Based on the mechanism of Tadokoro theory, the governing equations were deduced and solved with an explicit finite difference technique. The partial differential equations were transformed into ordinary differential equations by employing general finite difference for space derivatives and Runger-Kutta method for time derivatives. Compared with general finite difference method, the proposed technique can improve the stability of solution distinctly.(2) The dynamic electro-mechanical response of IPMC was simulated, used a finite element program ANSYS by coding user-defined subroutines. A multi-field finite element computational scheme was developed and the mechanical bending resulting from the water molecules redistribution is simulated by building equivalent thermal expansion model. Using the proposed method, the ion movement and the electro-mechanical deformation behavior have been predicted.Generally, the water molecule diffusion force is neglected in the most of the former numerical simulation works. In the present paper, the influence of water diffusion resistance force in the process of the movement of sodium ion has been emphatically explored and compared by building two different governing equations: with and without consideration of water diffusion resistance force. The water diffusion resistance force is described as a non-linear term and the corresponding governing equation is solved by iteration. The simulation results show that the water diffusion force has no obvious effect on the displacement, but has significant effect on the sodium ion concentration, effective moisture distribution and internal balance force. The predicting accuracy will be improved by involving this nonlinear component within the governing equation. Furthermore, the migration speed of the hydrated sodium ions, electric field intensity and the determination of driving force distribution across the thickness have also been studied.The numerical results compared with those available from open literatures show the validity of the present method. Since the whole simulation is carried out based on ANSYS platform, the proposed technique is convenient and effective, paving the way for modeling and designing more sophistic IPMC-based products.(3) An improved Tadokoro model was proposed in this paper. The relationship between voltage and current within an EPMC film for computation of electric field intensity was established by using an equivalent RC circuit. Moreover, a modified Kelvin-Voigt model was incorporated into the model to represent the viscoelastic property of the IPMC (Nafion) film and the non-uniform bending characteristics were discussed. Hence, the dynamic electro-mechanical response of IPMC was simulated using finite element (FE) method based on the Tadokoro model as previous proposed. When alternating voltage is applied, the IPMC undergoes back-and-forth bending movement and vibration with large amplitude at the frequency of the applied voltage. This character was also been simulated successfully under the frame of Tadokoro theory.By introducing the linear viscoelastic property of the Nafion film and considering the non-uniform bending behaviour into proposed model, the numerical results agreed well with the experimental measurement. The influences of the equivalent values of RC circuit on the predicted electro-mechanical response given by the model were investigated. Result implies that the current intensity and its distribution across the film membrane are dominant factors for controlling the deformation ability of IPMC. The function of young's modulus E was determined by curve fit with experiment data. The dynamic response of under square and sine waveform voltage input was also discussed. The simulation demonstrated that the behaviour of the IPMC device is frequency dependent.(4) IPMC micro-gripper and artificial urinary sphincter (AUS) were analyzed as the potential application in micro-electro-mechanical system (MEMS) and biomedical field. An IPMC micro-gripper system was proposed. The behaviour of motion and the exerting clamping force was determined. The dynamic response of the gripper under square waveform voltage input was also discussed. The simulation demonstrates that IPMC is a potential candidate for use in the design and manufacture of micro-grippers. The governing equation of IPMC curve beam was also developed to design the artificial urinary sphincter using IPMC. The simulation results show that under a driving voltage of 4.5 V, the maximum open displacement is about 0.7mm and the actuating pressure is about 14 cmH₂O under a humid work condition. Compared to the traditional empirical means, the proposed method provides a more scientific route for design and development of new IPMC structures.(5) The methods to improve the characters of generative displacement and force were discussed by numerical modeling. The optimal coating thickness for IPMC electrode was determined using the proposed FE model by varying the electric resistance in the RC circuit. The stacking technique was used to enhance the output of block force of IPMC actuators. The results show that the technique is feasible and the force if the reduction of displacement was acceptable simultaneously. Finally, the enormous displacement of IPMC was preliminarily explored by incorporating ionic cluster-network structure of Nemat-Nasser theory into the model.