Application of Multirank Lamination Theory to the Modeling of Ferroelectric and Martensitic Materials
Date Issued
2008
Date
2008
Author(s)
Yen, Jui-Hen
Abstract
Ferroelectrics and shape-memory alloys are two major families of smart materials, and are both key units for several advanced devices. Their unique features and nonlinear behaviors, however, originate from the arrangements and evolution of the underlying microstructures. Therefore, to take full advantage of these materials, it is essential to study the microscopic and mesoscopic physics of them. This thesis addresses these topics via developing novel models based on energy arguments and verifying them. mesoscopic electromechanical switching model is developed to investigate the switching behavior of ferroelectric single crystals. The theoretical model makes an assumption that switching follows the evolution of a particular domain pattern. The construction of this pattern is achieved using multirank laminates, which guarantee that domains remain compatible during evolution. This in turn provides a low-energy path for the overall switching. It offers an advantage of specifying different types of domain wall movements, leading to a distinction for the switching types.he required input parameters, 180◦ and 90◦ coercive fields, are taken from measured data. Simulation results show good agreement with the measured strains in experiments. It is found that depolarization has a non-trivial influence on attainable actuation strains.ext, to investigate the formation and evolution of microscopic domain patterns in ferroelectrics, a non-conventional phase-field model is developed through competing energetics to describe the coarsening, refinement, selection, and alignment of microstructure. It employs a set of field variables motivated by multirank laminates to represent energy-minimizing domain configurations. As a result, the energy-well structure can be expressed explicitly in a unified fashion. The framework is applied to domain simulation in both the tetragonal and rhombohedral phases assuming that polarization is close to one of their ground states. Several electromechanical self-accommodation patterns and an engineered domain configuration are predicted and found in good agreement with those observed in experiment.inally, we build a phase-field model for martensitic materials. The main feature of this novel model is also built on the ideas of multirank lamination. The model is applied to the investigation of pattern formation in martensitic thin films with trigonal symmetry. Various intriguing and fascinating patterns are predicted and are found in good agreement with those observed in experiments. In addition, the film orientations and patterns to achieve large actuation strains are suggested for dome-shaped and tunnel-shaped microactuators. It is found that the resultingorphologies evolve with coherent interfaces under various loading conditions. This suggests that compatible walls provide a low-energy path during evolution, and thenderstanding of them leads to novel strategies of large strain actuation.
Subjects
Ferroelectric single crystal
Multirank lamination
Electromechanical processes
Depolarization
Phase-field models
Pattern formation
Martensite
Thin films
Type
thesis
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