Ph.D Student | Kushnir Uri |
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Subject | Physical Nonlinearity in Piezoelectric Smart Structures - from Micromechanics to Engineering |

Department | Department of Civil and Environmental Engineering |

Supervisor | Professor Oded Rabinovitch |

Full Thesis text |

The dissertation deals with the use of ferro-electro-elasticity as a mean to improve the performance of piezoelectric structures in terms of induced force and displacement range. The literature review shows that the knowledge regarding smart structures operated in the ferroelectric range is very limited. Hence, the goals of the research are to characterize the behavior and to draw the guidelines for the design and operation of ferroelectric structures in the nonlinear range. As a first step, a computationally efficient constitutive model is developed by adopting a micromechanical approach. The material point is represented by a deterministic set of grains with different lattice directions. The domain state and the corresponding properties are determined for each grain individually. The material point properties are determined by averaging over the grains. Next, a principle of virtual work is developed. The external virtual work is formulated on a ferro-electro-elastic volume. The internal virtual work is developed through conservation laws and integral transformations. The equivalence of the internal and external virtual works defines the principle of virtual work. A general solution procedure that combines the variational formulation with the constitutive model is developed. A structural model for ferroelectric rod-like structures is derived from the 3D theory. The model is used for the analysis of an active layer in a stack actuator. The analysis shows that actuation in the ferroelectric range increases the displacement by 300%. Next, an electrically first order quasi-static theory for ferro-electro-elastic beams is developed. The theory is formulated in terms of generalized electromechanical stiffnesses. This model is used for the analysis of a ferroelectric beam. The results demonstrate the potential of the ferroelectric range to increase the actuation capabilities of beam-like actuators. Finally, design and actuation guidelines of advanced ferroelectric stack actuators are developed. The advanced actuator enables separate control of the active layers and combines a prestressing device. The control algorithm for the stack is based on predetermined data. Hence, it is suited for fast response applications. The special features of the actuator and the control algorithm enable a controllable continuous and extended travel range. The dissertation throws light on the behavior of ferroelectric structures operated in the nonlinear range and draws the guidelines for the design, operation and control of advanced ferroelectric actuators that overcome the travel range limitations of existing piezoelectric actuators. In that, sense, the dissertation opens the path for a new generation of ferroelectric smart structures and devices.