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Abstract Micro-electromechanical systems (MEMS) are subject to inevitable and inherent uncertainties in their dimensional and material parameters. Those lead to variability in their performance and reliability. Manufacturing processes leave substantial variability in the shape and geometry of the device due to its small dimensions and high feature complexity, while the material properties of a component are inherently subject to scattering. The effects of these variations have to be considered and a modeling methodology is needed in order to ensure required MEMS performance under uncertainties. Furthermore, in the design of high-Q micro-resonators, dissipation mechanisms may have detrimental effects on the quality factor (Q). One of the major dissipation phenomena to consider is thermoelastic damping, so that performances are directly related to the thermoelastic quality factor, which has to be predicted accurately. The purpose of this research is to develop a numerical method to analyze the effects of geometric and material property random variations on the thermoelastic quality factor of micro-resonators. The extension of the Perturbation Stochastic Finite Element Method (PSFEM) to the analysis of strongly coupled multiphysic phenomena allows the quantification of the influence of uncertainties, making available a new efficient numerical tool to MEMS designers. Résumé Dans le domaine des microsystèmes électromécaniques (MEMS), les micro-résonateurs jouent un rôle important pour le développement de micro-capteurs de plus en plus précis (ex : micro-accéléromètres). Dans cette optique daugmentation de la précision, les pertes dénergie qui limitent les performances des micro-résonateurs doivent être identifiées et quantifiées. Le facteur limitant des micro-résonateurs actuels est leur facteur de qualité thermo-élastique, qui doit donc être prédit de manière précise. De plus, suite à la tendance actuelle de miniaturisation et complexification accrues des MEMS, les sources de dispersions sont très nombreuses, à la fois sur les constantes physiques des matériaux utilisés et sur les paramètres géométriques. La mise au point doutils numériques permettant de prendre en compte les incertitudes de manière efficace est donc primordiale afin daméliorer les prestations densemble du microsystème et dassurer un certain niveau de robustesse et de fiabilité. Le but de cette recherche est de développer une méthode numérique pour analyser les effets des variations aléatoires des propriétés matérielles et géométriques sur le facteur de qualité thermo-élastique de micro-résonateurs. Pour ce faire, lapproche dite perturbative de la méthode des éléments finis stochastiques (PSFEM) est étendue à lanalyse de phénomènes multiphysiques fortement couplés, fournissant ainsi aux acteurs de lindustrie des MEMS un nouvel outil de conception efficace.

Shape memory alloys (SMAs) are multifunctional materials with thermoelastic phase transformation behavior capable of recovering the designed geometry after deformation. These alloys can undergo a solid-to-solid phase transformation in response to external stimuli, such as pressure or temperature, to accommodate or alleviate strain. Such a response can be utilized to design solid-state actuators by converting thermal energy into mechanical energy. Interest in these unique alloys is expanding to conserve energy and reduce weight and mechanical complexity in various engineering fields such as the medical, aerospace, automotive, and refrigeration industries. Aerospace and energy applications need high temperature operating SMAs due to the commercially available binary NiTi SMAs having a limited maximum austenite start temperature of 115 °C, thus encouraging research towards high temperature SMAs (HTSMAs). The challenge with designing HTSMAs is maintaining the functional and actuation response throughout the service life of high cycle fatigue SMA components in aerospace applications. Actuation cycles consequently lead to transformation-induced plasticity (TRIP) and microcracking, effectively evolving after every thermal cycle. The primary focus of this dissertation is linking macroscopic damage evaluation to microscopic mechanisms to improve the thermomechanical response and actuation fatigue. This was achieved by examining a variety of NiTiHf compositions using in situ synchrotron radiation X-ray diffraction, microscopy, tomography, and novel processing techniques after evaluating the fatigue response. Through this research, several paths to improving actuation response and fatigue life are revealed by utilizing temperature to control damage mechanisms and resist functional and structural fatigue through processing and microstructure.

Thesis (M.S.)--Rochester Institute of Technology, 1991. / Typescript. References: leaves 139-147.

Thesis (M.S.)--West Virginia University, 2005. / Title from document title page. Document formatted into pages; contains ix, 138 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 90-94).

Thesis (M. S.)--Civil and Environmental Engineering, Georgia Institute of Technology, 2007. / White, Donald, Committee Member ; Haj-Ali, Rami, Committee Chair ; Will, Kenneth, Committee Member.

Thesis (Ph.D.)--University of Nebraska-Lincoln, 2007. / Title from title screen (site viewed July 9, 2007). PDF text: 118 p. : ill. UMI publication number: AAT 3252834. Includes bibliographical references. Also available in microfilm and microfiche formats.

Rigidizable/Inflatable space structures have been the focus of renewed interest in recent years due to efficient packaging for transport. In this work, we examine new mathematical systems used to model small-scale joint dynamics for inflatable space truss structures. We investigate the regularity and asymptotic behavior of systems resulting from various damping models, including Kelvin-Voigt, Boltzmann, and thermoelastic damping. Approximation schemes will also be introduced. Finally, we look at optimal control for the Kelvin-Voigt model using a linear feedback regulator. / Ph. D.