ELECTROMECHANICAL ANALYSIS OF DIELECTRIC ELASTOMER MINIMUM ENERGY STRUCTURES (DEMES)

Abstract

In the current scenario, dielectric elastomer minimum energy structures (DEMES) with an ability to achieve unique shape morphing behavior have gained increasing attention toward smart materials-based system designs. Because of highly nonlinear electromechanical coupling behavior, the design and development of DEMES-based actuators demand accurate and efficient modeling approaches. In general, the DEMES-based actuators exhibit both material and geometrical nonlinearities. Hence, the modeling and design of DEMES actuators become more complicated, primarily due to the addition of the geometrical nonlinearity. Such concerns established a new research direction, which has enough potential to provide more advanced structures to our industrial society. Herein, the present thesis deals with the study of deformation problems concerning the constitutive modeling of nonlinear behavior of the DEMES-based actuators within the framework of the classical continuum mechanics-based approach. Primarily, four broad topics are covered: (i) theoretical modeling of dielectric visco-elastomer minimum energy structures, (ii) modeling of anisotropic behavior in dielectric visco-elastomer minimum energy structures, (iii) alleviation of warping by employing 3-D stiffeners based anisotropy in DEMES actuator, and (iv) finite element-based framework for modelinginhomogeneouslydeforming DEMES actuators. Each topic plays a vital role in the theoretical, experimental, and computational advancement of smart structure modeling in soft actuation technology. The first problem explores the development of an energy-based analytical model pertaining to the electromechanical response of the dielectric visco-elastomer minimum energy structures. This is accomplished by applying a Zener rheological model alongside the neo-Hookean hyperelasticity model for the polymer film and the linear elastic constitutive model for the frame. The proposed analytical framework and the material models are implemented into an in-house MATLABprogram and utilized to predict the attained equilibrium states, DC and AC response, and the DEMES actuator periodicity over feasible viscosity range parameters. The second problem explores an energy-based analytical model by imparting anisotropy to the material behavior of the DE membrane to enhance the electromechanical response of dielectric visco-elastomer minimum energy structures. This is accomplished by applying a Polignone transversely isotropic model alongside the neo-Hookean hyperelasticity model for the polymer film. The proposed model investigates the effect of material anisotropy on the equilibrium configuration, DC and AC response, and the periodicity of the DEMES actuator over a feasible range of anisotropy parameters. In addition, the formulated model based on the proposed method is compared and validated with an experimental study existing in the literature. The third problem explores the effect of anisotropy, imparted by finitely spaced reinforce ments in controlling the warping and subsequently the actuation performance of DEMES when driven electrically. The proposed framework uses the neo-Hookean hyperelasticity model for the polymer film and the linear elastic constitutive model for both the frame and the stiffeners. The predictive capability of the proposed analytical model is established through comparisons with experimental observations. At last, we propose a finite element-based numerical framework for inhomogeneously deforming dielectric elastomer minimum energy structure actuators in the fourth problem. User element subroutines (UELs) are written to implement a family of finite elements, particularly an eight-noded continuum brick element, in the commercial finite-element Abaqus/Standard program. The proposed framework capability is evaluated by validating with experimental investigations, simulating the effect of various geometrical parameters, and incorporating stiffeners’ influence on the electromechanical behavior of the DEMES actuator. Conclusively, the modeling frameworks and the inferences drawn from the studies presented in this thesis can find their potential applications in the analysis and design of dielectric elastomer minimum energy structure-based soft actuators. Keywords: Electro-active polymers (EAPs), Dielectric elastomer actuators (DEAs), Di electric elastomer minimum energy structures (DEMES), Hyperelasticity, Viscoelasticity, Aniso visco-hyperelasticity, Nonlinear dynamics, Poincar´e map, Phase diagram, Quasiperiodicity