Electromechanical Behavior And Device Design Of Dielectric Elastomer

Distinguished from primates by using tools, human civilization has gone through the Stone Age, the Bronze Age, the Iron Age and those periods characterized by the chief hard materials in tools manufacture. Until today, the hard materials are the most widely used materials in engineering, and well studied in research. However, the main structure and organisms of creatures in nature such as the tree leaves, the animal muscles are soft materials. Soft materials have gone through the evolution of life on earth with hundreds of millions of years. Compared to metals, ceramics and other conventional hard materials, soft materials have many features such as large deformation, multi-function and multi-physics behaviors. The behaviors of soft materials are complex, and result more challenges in modeling and analysis. Many features of soft material become key technologies of engineering solutions in many fields. Recently, the research and practical applications of soft materials arises general concern in both academia and industry. Researchers are dedicating to develop various soft materials with the performances that cannot be realized by conventional hard materials.In response to a stimulus, a soft material deforms, and/or provides functions. We call such a material a soft active material (SAM). Dielectric elastomer (DE) is a typical soft active material. It exhibits large deformation (over100%strain) when subjected to an electric field. DEs are promising as active materials in the fields of intelligent bionics, aerospace, mechanical engineering and clean energy. DEs possess the merits of light mass, quick response, and high energy density, etc. DEs have been primarily used as actuators, soft robotics, energy harvesters and braille display equipments, and shows great potential.Electromechanical coupling effects and large deformation make mechanics study dominant in analyzing the behaviors and enhancing the performances of DEs. While the mechanical modeling, material and structural optimizations are of main challenges. This dissertation adopts the theory of DEs within continuum mechanics and thermodynamics, and motivated by molecular pictures and empirical observations. Large deformation, electric fields, nonlinear and non-equilibrium behaviors, electromechanical instability and viscoelasticity are considered in the analysis. DE transducers in various modes (actuators, generators, resonators) are analyzed. Suppressing or harnessing the featured electromechanical behaviors enhances the performances of DEs. Theoretical guidelines of high performance DE transducer are proposed, such as giant voltage-induced deformation, high efficiency energy harvesting and active tuning vibration. Optimization and practical experiments of DE transducers in various modes are conducted with high performance.Based on continuum mechanics and thermodynamics, the material discriptions based on Gent, Arruda-Boyce, Neo-Hookean models and the assumption of ideal dielectric elastomer are adopted in the analyses. This dissertation focuses on the following electromechanical behaviors of DEs: First, the equilibrium slate of DEs under static loads, electromechanical stability, electrical breakdown and loss of tension is explored that incorporates the effects of material and struactural parameters. Then, the non-equilibrium process and dynamic behavior of DEs considering viscoelasticity, current leakage and inertial effects is studied. Improved simulation methods are developed, which are capable of modeling the multi-stable states, inhomogeneous fields and dynamics of DEs.Practical DE transducer devices, including: circular actuator, dead load actuator, membrane inflation actuator, generator and active tuning resonator, are analyzed. Performances enhancement of DE transducers are conducted with the consideration of voltage-induced deformation, energy harvesting density, energy conversion efficiency and electromechanical dissipation. In the actuation mode, with suitable values of the parameters, we obtain giant voltage-induced expansion of area of488%for a dielectric elastomer under equalbiaxial dead load, and of1692%for a membrane inflation DE actuator, far beyond the largest values reported in the literature. In the generator mode, high specific electrical energy generated per cycle of102mJ/g is demonstrated in the membrane inflation DE generator. The modeling based designs and experiments may guide the specifical designing of DE transducers and other soft active materials with high performances.