Master of Engineering Science
Mechanical and Materials Engineering
Dielectric elastomers (DEs) are capable of producing large deformation under electric stimuli, which makes them desirable materials for a variety of applications including biomimetics, dynamics, robotics, energy harvesting, and waveguide devices. In general, DEs possess intrinsic hyperelasticity and viscosity. Such material properties may significantly affect the dynamic performance of DE-based devices. The delicate interplay among electromechanical coupling, large deformation, material viscosity and dynamics makes modeling of the performance of DE-based devices more challenging. Therefore, in order to provide guidelines for the optimal design of DE waveguide devices, it is essential to develop appropriate and reliable models, and efficient numerical methods to examine their performance first.
In this thesis, by integrating the state-of-art finite-deformation viscoelasticity theory into the framework of small-amplitude wave propagation superposed on a finitely deformed medium, the Rayleigh-Lamb wave propagation in a viscoelastic DE medium is investigated. Simulation results have demonstrated the effects of material viscosity, status of relaxation, external electric load, and mechanical pre-stretch on the dispersion behavior of the wave. For both pure elastic and viscoelastic DE media, waves with certain frequencies could be filtered by actively tuning electric loads. Moreover, some interesting findings conclude that the material viscoelasticity may cause some significant changes in the wave dispersion behavior. Therefore, incorporating the material viscosity in modeling DE waveguide is expected to provide more accurate prediction on their performance. This thesis will help to better understand the fundamentals of wave propagation in DE media and trigger more innovative and optimal design for DE waveguide applications.
Summary for Lay Audience
Electroactive polymers (EAPs) are smart materials that exhibit unique mechanical response to an external electric field, which enables engineering designs to have more innovative features and functions. As one family of EAPs, dielectric elastomers (DEs) have received growing interest in soft material-based transduction technologies recently due to their large deformation capability, high energy density, softness and flexibility. In addition to the well-studied large-actuation and high-power applications for artificial muscles, soft robotics, biomimetics and energy harvesters, DE structures have also received attention for the dynamics applications as waveguide in recent years. The electromechanical coupling property of the material enables the DE waveguide to actively filter waves in the prescribed range of frequencies by adjusting the applied voltage.
In the literature, dynamic analysis on finitely deformed DEs is still very limited, particularly when involving material’s intrinsic viscoelasticity. The lack of understanding the fundamentals underlying the electromechanical dynamics is certainly a major barrier for the full potential applications of DE waveguide. In order to overcome this obstacle, this thesis aims to establish a rigorous modeling and simulation framework to investigate the characteristics of wave propagation in dielectric media by adopting the finite-deformation viscoelasticity model for DEs. Simulation results will help to quantitatively understand the effects of material properties and electromechanical loads upon the wave propagation through DE media and how the waveguide can be tuned by the applied electrical stimuli. Thus, the fulfilment of this thesis is expected to provide better understanding of the fundamentals of wave propagation in DE media and be helpful for optimal design of DE waveguide.
Sheikh Bagher Mohajer, Mohammad Mahdi, "Wave Propagation in Viscoelastic Dielectric Elastomer Media" (2020). Electronic Thesis and Dissertation Repository. 6847.