| New technology and advanced materials are developing rapidly in the 21st century. With the development of computer, communication, biology and microelectronic technology, people now expect a common system and structure with moderate activity or intelligence to adapt itself to the changes of its surroundings. This is known as "Smart or Intelligent Material and Structure". Ferroelectric materials are not only vital electronic functional materials, but are thought of as the most interesting and promising intelligent materials of the future. Though ferro-electricity was recognized in the early 1920's, people still do not clearly understand even its basic characteristics and microstructure because descriptions of the behavior of ferro-electric ceramics remain in their infancy. The mechanism of damage, fatigue, crack and fracture of ferro-electrics should be studied more concretely not only in theory but also in application. The purpose behind this thesis is to study the nonlinear electro-mechanical coupling performance, and to have relatively simple yet substantial constitutive relations of ferro-electrics, that can eventually provide guidance for material design, sensor or actuator structural analysis and life expectancy for ferro-electric structure and system. The main work and result of this dissertation include the following aspects: (1) A new mechanical-electric model of ferro-electric materials is proposed to describe the complicated electromechanical coupling phenomena._Based on the domain switching behavior of ferroelectrics, a model of "SuccessiveSwitching" for ferroelectric domains is introduced. This may help to avoid some of the intrinsic limitations of the "Complete Switching" hypothesis, and be a more physical representation._Incremental form of evolution law of domain switching is developed by taking thevolume fraction of domains as key intrinsic factors. The main factors that have great influence on domain switching are material parameters, domain wall motion, domain volume fraction and the interaction energy between inclusion and matrix. Inclusion and its neighbors could be addressed in the description as well._The phenomenon of saturation or "lock up" when all of the grains have transformed,is described in a rattier simple form through domain volume fractions by the proposed model, in which domain switching in ferro-electrics is analogous to that of dislocation movement on crystal slip planes in metals.(2) A primary multi-scale method for the electromechanical coupling analysis of ceramics is developed and show good agreement between the calculated results and the related experiments.The equivalent inclusion method is modified to include the geometrical and physical parameters of the ferroelectric inclusion units, and be expanded into piezo/ferro-electric media. The inclusion cell is the bridge of macro and micro mechanical-electrical responses, but also provides a direct relationship between meso/micro grain characteristic parameters and between globe macro performance, which could become a great help for the study on damage, fatigue and fracture mechanism of ferro-electrics.The self-consistent method based on Hill's theory is extended to be applicable to ferroelectrics. The introduction of global iteration and local iteration under loading of electric and/or stress fields calculate the nonlinear electromechanical coupling behavior.(3) The electro-mechanical coupling behavior of layer-structured ferroelectric composites is investigated and predicted.The electrical and mechanical boundary conditions are obtained considering the characteristics of layered ferroelectrics; the local electric-mechanical response equations of each structural layer of units are derived under the coupling of electric and mechanical loads.Various calculations are conducted when the volume fraction of each layer differs, as well as when the ratio of Yang's modular between layers changes. The influence of these factors to material performance is studied.The distributi...
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