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Dissertations / Theses on the topic 'Material Transformations'
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Douglass, Ian Michael. "A Computational Study of Material Transformations in Glass Forming Systems." Thesis, The University of Sydney, 2018. http://hdl.handle.net/2123/19729.
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Amorphous solids (glasses) are a class of materials that lack the traditional long-range order found in crystals, and are primarily formed by rapid cooling of a liquid to bypass crystal nucleation. Their lack of crystallinity and associated defects gives them useful electromagnetic and mechanical properties. However, the affinity of a material to vitrification is only loosely understood, and structural detail is difficult to obtain via traditional methods. This thesis firstly investigates the promotion of glass formation via crystal inhibition. Molecular dynamics simulations of binary alloys are used to show crystal frustration via specific interactions of interaction range and particle softness, resulting in a lower enthalpic drive and complex crystal structures. Secondly, a facilitated kinetic Ising model is used to investigate the dynamics of organic glasses in solution. Glass dissolution is shown to have a non-linear dependence on the effective temperature of the solute, switching between a front-like dissolution at low temperatures, and a diffuse interface at higher temperatures. Also shown is a method of preparing an enhanced glass via precipitation from a solution, capable of creating a much lower energy glass than simple bulk cooling.
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Murphy, Celine. "Reconciling materials, artefacts and images : an examination of the material transformations undergone by the Philioremos anthropomorphic figurines." Thesis, University of Kent, 2016. https://kar.kent.ac.uk/57949/.
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Visually-compelling small finds have traditionally been examined for their appearances. These artefacts, consisting of figurines, ornaments and body adornments, for example, have been primarily studied for the meanings that the images they project might have held. Strikingly fewer are analyses of these objects' material qualities. Frequently ignored are their composition, the sourcing and working of their materials, or their materiality. The aim of this thesis is to reconcile considerations of the visual and material aspects of visually compelling small finds. It is here argued that examinations of the material aspects of artefacts can reveal important information about the course of their production and consumption, and about the nature of the relationships involved therein. The volume's reconciliatory endeavour is thus undertaken with the creation of a new materially-inclusive, biographically-orientated, methodologically-holistic and multi-scalar framework. Bolstered by theories drawn from philosophy and the social sciences, this methodology allows for closer investigations into the web of closely-knit inter-nodal relationships maintained between humans, materials and the environment during the making and the use of material culture. The following chapters present the results of the framework's application to the clay anthropomorphic figurines from the Minoan peak sanctuary of Philioremos. The various ways in which clay was engaged with during the different stages of the figurines' becoming and unbecoming are explored. The types of relationships that the artefacts' production and consumption depended upon and engendered, alongside the types of knowledge these dynamics were rooted in, are then discussed. Subsequently, broader considerations of the use of the human body as a representational theme are undertaken. In reconciling examinations of the visual and material qualities of the Philioremos figurines, this thesis demonstrates the utility of a materially-integrative approach. Ultimately, this study contributes to two main areas of current archaeological interest simultaneously: the analysis of prehistoric material culture and the examination of Minoan peak sanctuary anthropomorphic figurines more specifically.
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Grimes, Jodi Elisabeth. "Rhetorical Transformations of Trees in Medieval England: From Material Culture to Literary Representation." Thesis, University of North Texas, 2008. https://digital.library.unt.edu/ark:/67531/metadc12130/.
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Literary texts of medieval England feature trees as essential to the individual and communal identity as it intersects with nature, and the compelling qualities and organic processes associated with trees help vernacular writers interrogate the changing nature of this character. The early depiction of trees demonstrates an intimacy with nature that wanes after the tenth-century monastic revival, when the representation of trees as living, physical entities shifts toward their portrayal as allegorical vehicles for the Church's didactic use. With the emergence of new social categories in the late Middle Ages, the rhetoric of trees moves beyond what it means to forge a Christian identity to consider the role of a ruler and his subjects, the relationship between humans and nature, and the place of women in society. Taking as its fundamental premise that people in wooded regions develop a deep-rooted connection to trees, this dissertation connects medieval culture and the physical world to consider the variety of ways in which Anglo-Saxon and post-Norman vernacular manuscripts depict trees. A personal identification with trees, a desire for harmony between society and the environment, and a sympathy for the work of trees lead to the narrator's transformation in the Dream of the Rood. The Tree of Knowledge of Good and Evil in the Junius 11 manuscript, illustrated in Genesis A, Genesis B, and manuscript images, scrutinizes the Anglo-Saxon Christian's relationship and responsibility to God in the aftermath of the Fall. As writers transform trees into allegories in works like Genesis B and Geoffrey Chaucer's Parson's Tale, the symbolic representations retain their spontaneous, organic processes to offer readers a visual picture of the Christian interior-the heart. Whereas the Parson's Tale promotes personal and radical change through a horticultural narrative starring the Tree of Penitence and Tree of Vices, Chaucer's Knight's Tale appraises the role of autonomous subjects in a tyrannical system. Forest laws of the post-Norman period engender a bitter polemic about the extent of royal power to appropriate nature, and the royal grove of the Knight's Tale exposes the limitations of monarchical structures and masculine control and shapes a pragmatic response to human failures.
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Grimes, Jodi Elisabeth Upchurch Robert K. "Rhetorical transformations of trees in medieval England from material culture to literary representation /." [Denton, Tex.] : University of North Texas, 2008. http://digital.library.unt.edu/ark:/67531/metadc12130.
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Horacek, Ivana. "Alchemy of the gift : things and material transformations at the court of Rudolf II." Thesis, University of British Columbia, 2015. http://hdl.handle.net/2429/52830.
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The full abstract for this thesis is available in the body of the thesis, and will be available when the embargo expires.Arts, Faculty of
Art History, Visual Art and Theory, Department of
Graduate
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McDonald, F. P. "Charting material memories : an ethnography of visual and material transformations of woollen blankets in Canada, Aotearoa New Zealand, and the United States." Thesis, University College London (University of London), 2014. http://discovery.ucl.ac.uk/1447476/.
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Taking one thing—the industrially produced woollen blanket—as an object of investigation, this thesis sets out to bring together a study of aesthetics, materiality, and locality in relation to the woollen blanket to consider it as a possible “technology of enchantment” (Gell 1998) in both its original and transformed states. This dissertation investigates the aesthetic transformations of the woollen blanket into art, craft, and Indigenous cultural property within our current historical moment and within specific abstract and concrete localities. Two distinct locations, Aotearoa New Zealand and North America, where such acts of transformation upon woollen blankets have had a sustained presence, are examined and compared. This project attempts to address how focusing upon the acts of transformation of materials makes visible a gap in the literature where more consideration into the movement and consumption of materials simultaneously in multiple locations is needed. The dynamism of multi-vocal and, yet, intensely local uses and transformations of woollen blankets reveal that movement and consumption are together a single transformative act. What results from these acts of transformation are both tangible and intangible values that will be described through case studies of use in order to draw out the imagined futurity of woollen blankets in their ‘renewed’ forms against their historical and colonial legacies. The varied values that emerge from distinct aesthetic transformations enable a new reading of the importance of aesthetic and creative manipulations of materials and matter that informs the local take-up of an industrial product. This thesis pushes beyond a current analytical framework that has considered how objects come to be entangled in local and global meanings through either their social life or biography. Instead this thesis focuses on the intentional transformations of materials that inform larger critical arguments around how both Indigenous and non-Indigenous individuals and communities fashion cultural knowledge and identity through soft materials that are themselves manifestations of the hard-edged, imperial, colonial, and industrial projects.
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Choudhary, Muhammad Ajmal [Verfasser], and Heike [Akademischer Betreuer] Emmerich. "Modeling microstructural evolution and phase transformations in material science / Muhammad Ajmal Choudhary. Betreuer: Heike Emmerich." Bayreuth : Universität Bayreuth, 2016. http://d-nb.info/1113107294/34.
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Sun, Xinxing. "Phase Transformations and Switching of Chalcogenide Phase-change Material Films Prepared by Pulsed Laser Deposition." Doctoral thesis, Universitätsbibliothek Leipzig, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-224762.
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The thesis deals with the preparation, characterization and, in particular, with the switching properties of phase-change material (PCM) thin films. The films were deposited using the Pulsed Laser Deposition (PLD) technique. Phase transformations in these films were triggered by means of thermal annealing, laser pulses, and electrical pulses. The five major physical aspects structure transformation, crystallization kinetics, topography, optical properties, and electrical properties have been investigated using XRD, TEM, SEM, AFM, DSC, UV-Vis spectroscopy, a custom-made nanosecond UV laser pump-probe system, in situ resistance measurements, and conductive-AFM.
The systematic investigation of the ex situ thermally induced crystallization process of pure stoichiometric GeTe films and O-incorporating GeTe films provides detailed information on structure transformation, topography, crystallization kinetics, optical reflectivity and electrical resistivity. The results reveal a significant improvement of the thermal stability in PCM application for data storage. With the aim of reducing the switching energy consumption and to enhance the optical reflectivity contrast by improving the quality of the produced films, the growth of the GeTe films with simultaneous in situ thermal treatment was investigated with respect to optimizing the film growth conditions, e.g. growth temperature, substrate type.
For the investigation of the fast phase transformation process, GeTe films were irradiated by ns UV laser pulses, tailoring various parameters such as pulse number, laser fluence, pulse repetition rate, and film thickness. Additionally, the investigation focused on the comparison of crystallization of GST thin films induced by either nano- or femtosecond single laser pulse irradiation, used to attain a high data transfer rate and to improve the understanding of the mechanisms of fast phase transformation.
Non-volatile optical multilevel switching in GeTe phase-change films was identified to be feasible and accurately controllable at a timescale of nanoseconds, which is promising for high speed and high storage density of optical memory devices. Moreover, correlating the dynamics of the optical switching process and the structural information demonstrated not only exactly how fast phase change processes take place, but also, importantly, allowed the determination of the rapid kinetics of phase transformation on the microscopic scale.
In the next step, a new general concept for the combination of PCRAM and ReRAM was developed. Bipolar electrical switching of PCM memory cells at the nanoscale can be achieved and improvements of the performance in terms of RESET/SET operation voltage, On/Off resistance ratio and cycling endurance are demonstrated. The original underlying mechanism was verified by the Poole-Frenkel conduction model. The polarity-dependent resistance switching processes can be visualized simultaneously by topography and current images. The local microstructure on the nanoscale of such memory cells and the corresponding local chemical composition were correlated.
The gained results contribute to meeting the key challenges of the current understanding and of the development of PCMs for data storage applications, covering thin film preparation, thermal stability, signal-to-noise ratio, switching energy, data transfer rate, storage density, and scalability.
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Della, Porta Francesco M. G. "Selection mechanisms for microstructures and reversible martensitic transformations." Thesis, University of Oxford, 2018. http://ora.ox.ac.uk/objects/uuid:085f0e90-6d07-4cb6-9bb9-13517de1b65e.
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The work in this thesis is inspired by the fabrication of Zn45Au30Cu25. This is the first alloy undergoing ultra-reversible martensitic transformations and closely satisfying the cofactor conditions, particular conditions of geometric compatibility between phases, which were conjectured to influence reversibility. With the aim of better understanding reversibility, in this thesis we study the martensitic microstructures arising during thermal cycling in Zn45Au30Cu25, which are complex and different in every phase transformation cycle. Our study is developed in the context of continuum mechanics and nonlinear elasticity, and we use tools from nonlinear analysis. The first aim of this thesis is to advance our understanding of conditions of geometric compatibility between phases. To this end, first, we further investigate cofactor conditions and introduce a physically-based metric to measure how closely these are satisfied in real materials. Secondly, we introduce further conditions of compatibility and show that these are nearly satisfied by some twins in Zn45Au30Cu25. These might influence reversibility as they improve compatibility between high and low temperature phases. Martensitic phase transitions in Zn45Au30Cu25 are a complex phenomenon, especially because the crystalline structure of the material changes from a cubic to a monoclinic symmetry, and hence the energy of the system has twelve wells. There exist infinitely many energy-minimising microstructures, limiting our understanding of the phenomenon as well as our ability to predict it. Therefore, the second aim of this thesis is to find criteria to select physically-relevant energy minimisers. We introduce two criteria or selection mechanisms. The first involves a moving mask approximation, which allows one to describe some experimental observations on the dynamics, while the second is based on using vanishing interface energy. The moving mask approximation reflects the idea of a moving curtain covering and uncovering microstructures during the phase transition, as appears to be the case for Zn45Au30Cu25, and many other materials during thermally induced transformations. We show that the moving mask approximation can be framed in the context of a model for the dynamics of nonlinear elastic bodies. We prove that every macroscopic deformation gradient satisfying the moving mask approximation must be of the form 1 + a(x) ⊗ n(x), for a.e. x. With regards to vanishing interface energy, we consider a one-dimensional energy functional with three wells, which simplifies the physically relevant model for martensitic transformations, but at the same time highlights some key issues. Our energy functional admits infinitely many minimising gradient Young measures, representing energy-minimising microstructures. In order to select the physically relevant ones, we show that minimisers of a regularised energy, where the second derivatives are penalised, generate a unique minimising gradient Young measure as the perturbation vanishes. The results developed in this thesis are motivated by the study of Zn45Au30Cu25, but their relevance is not limited to this material. The results on the cofactor conditions developed here can help for the understanding of new alloys undergoing ultra-reversible transformations, and as a guideline for the fabrication of future materials. Furthermore, the selection mechanisms studied in this work can be useful in selecting physically relevant microstructures not only in Zn45Au30Cu25, but also in other materials undergoing martensitic transformations, and other phenomena where pattern formation is observed.
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Oueslati, Jamel. "Contribution à l'étude numérique des grandes transformations élastoplastiques." Paris 6, 1986. http://www.theses.fr/1986PA066132.
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On cherche à étudier aux grandes transformations des moyens de calcul permettant de traiter des problèmes généraux d'équilibre élastoplastiques de structures planes ou axosymétriques; ces structures peuvent subir de grands déplacements, de grandes rotations et de grandes déformations plastiques, les déformations élastiques étant supposées petites. On se limite au cas du matériau initialement isotrope, avec écrouissage isotrope ou cinématique.
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Lyubina, Julia. "Nanocrystalline Fe-Pt alloys: phase transformations, structure and magnetism." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2007. http://nbn-resolving.de/urn:nbn:de:swb:14-1179487984718-30186.
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This work has been devoted to the study of phase transformations involving chemical ordering and magnetic properties evolution in bulk Fe-Pt alloys composed of nanometer-sized grains. A comprehensive study of phase transformations and ordering in Fe-Pt alloys is performed by a combination of in-situ neutron powder diffraction and thermal analysis. The dependence of ordering processes on the alloy composition and initial microstructure (homogeneous A1 phase or multilayer-type) is established. Through the use of mechanical alloying and subsequent heat treatment it has been possible to achieve the formation of chemically highly ordered L10 FePt and, in the case of the Fe-rich and Pt-rich compositions, L12 Fe3Pt and FePt3 phases, respectively. Whereas in Pt-rich alloys the decoupling effect of the FePt3 phase leads to coercivity improvement, in Fe-rich nanocomposites a peculiar nanometer scale multilayer structure gives rise to remanence enhancement due to large effects of exchange interactions between the crystallites of the phases. The structure, magnetic properties and magnetisation reversal processes of these alloys are investigated. Experimentally observed phenomena are understood on the basis of a simple two-particle interaction model. Neutron diffraction has also been used for the investigation of the magnetic structure of ordered and partially ordered nanocrystalline Fe-Pt alloys. It has been shown that the magnetic moment of Fe atoms in L10-type Fe Pt alloys is sensitive to the compositional order. The results are compared to density functional calculations.
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Anomasiri, Namkhang. "The Final Cut : Transformations of laser-cut textile surfaces for placemaking." Thesis, Konstfack, Inredningsarkitektur & Möbeldesign, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:konstfack:diva-7844.
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My project explores the possibilities of shaping space using lightweight textile-based elements. The focus is on the transformation of surface patterns into three-dimensional forms, using analogue parametric design with laser-cut beds as a main testbed. The result is a smorgasbord of prototypes: spatial configurations that divide and define space. Each design is a permeable three-dimensional form that projects a unique pattern of shadow and light. The basis of my project comes from an initial investigation of Uppsala public libraries’ needs for flexible solutions. The libraries have housed many civic activities that I have experienced in recent years since moving to Uppsala in 2018. With their requirement of multiple types of use, I propose using fabric infrastructure as configurable room dividers. I use discarded textile (used carpets, fabric remnants) as the starting point for each prototype. The material itself imposes certain restrictions on the work. Each new piece of fabric acquired a problem waiting for a solution. In this sense, the finished prototype constitutes a solved puzzle. One key objective is to create designs that are flexible while still being robust enough to be portable. Another key objective is to create inviting and organic designs. While I used laser cutters to cut the fabric into precise patterns, I allowed gravity and light to create an imperfect and organic end-result. However, the outcome of my experimental exploration is a system and a technique for making use of discarded textile materials to create atmospheres and spaces.
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Lyubina, Julia. "Nanocrystalline Fe-Pt alloys: phase transformations, structure and magnetism." Doctoral thesis, Technische Universität Dresden, 2006. https://tud.qucosa.de/id/qucosa%3A24990.
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This work has been devoted to the study of phase transformations involving chemical ordering and magnetic properties evolution in bulk Fe-Pt alloys composed of nanometer-sized grains. A comprehensive study of phase transformations and ordering in Fe-Pt alloys is performed by a combination of in-situ neutron powder diffraction and thermal analysis. The dependence of ordering processes on the alloy composition and initial microstructure (homogeneous A1 phase or multilayer-type) is established. Through the use of mechanical alloying and subsequent heat treatment it has been possible to achieve the formation of chemically highly ordered L10 FePt and, in the case of the Fe-rich and Pt-rich compositions, L12 Fe3Pt and FePt3 phases, respectively. Whereas in Pt-rich alloys the decoupling effect of the FePt3 phase leads to coercivity improvement, in Fe-rich nanocomposites a peculiar nanometer scale multilayer structure gives rise to remanence enhancement due to large effects of exchange interactions between the crystallites of the phases. The structure, magnetic properties and magnetisation reversal processes of these alloys are investigated. Experimentally observed phenomena are understood on the basis of a simple two-particle interaction model. Neutron diffraction has also been used for the investigation of the magnetic structure of ordered and partially ordered nanocrystalline Fe-Pt alloys. It has been shown that the magnetic moment of Fe atoms in L10-type Fe Pt alloys is sensitive to the compositional order. The results are compared to density functional calculations.
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Amalraj, Julian Joyce. "Effect of variable material properties on purely thermal phase transformations in shape memory alloy wires, modeling and experiments." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0020/MQ47001.pdf.
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Vink, Luke (Luke Alexander Jozef). "Materiality in suspense : exploring radical interfaces capable of representing multiple physical property transformations to enable computational, physical material perception." Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/107548.
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Thesis: S.M., Massachusetts Institute of Technology, School of Architecture and Planning, Program in Media Arts and Sciences, September 2016.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 86-89).
Years after the inception of the Radical Atoms vision, significant advances in technology have seen to dynamic tangible interfaces that bridge the biological and micromechanical to enable radical physical interaction with computation. With an increasing multi-modal complexity in such interfaces, this thesis explores a new methodologies and frameworks to designing input/output coincident and physically embodied computers. New types of Shape Changing Interfaces introduce physical perception of material properties to dynamic shape with physically accurate force feedback and introduce Radical Materiality as a way to afford physical interactions with a rendered object. Finally, the Radical Reality Test is proposed as an objective for such interfaces to eventually become indistinguishable from the physical entity or behavior they are computationally and dynamically imitating.
by Luke Vink.
S.M.
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Boisly, Martin. "Modellierung des Materialverhaltens Magnetorheologischer Fluide unter Verwendung der Fourier-Transformations Rheologie." Doctoral thesis, Logos Verlag Berlin GmbH, 2017. https://tud.qucosa.de/id/qucosa%3A32282.
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In dieser Dissertation wird das viskoplastische Schubverhalten eines magnetorheologischen Fluids (MRF) modelliert. Mithilfe eines phänomenologischen Modellierungsansatzes auf Basis nichtlinearer rheologischer Elemente können die gemessenen Fließkurven sowie Speicher- und Verlustmoduli abgebildet werden. Ein MRF ist ein Material mit fest-flüssig Übergang. Es besitzt von einem Magnetfeld abhängige Materialeigenschaften. Um diese beschreiben zu können, wird zunächst eine phänomenologische Stoffklassifizierung eingeführt. Auf deren Grundlage teilen sich Stoffe allgemein in Flüssigkeiten, Festkörper und Materialien mit fest-flüssig Übergang auf. Zur Beschreibung des Materialverhaltens von MRF werden drei viskoplastische Modelle formuliert und gegenübergestellt. Zur Identifikation der Materialparameter wird eine Identifikationsstrategie auf der Grundlage charakteristischer Punkte entwickelt. Charakteristische Punkte sind exklusive Punkte von Materialfunktionen, die analytisch beschrieben und ohne Weiteres experimentell ermittelt werden können. Analytische Ausdrücke für charakteristische Punkte der Speicher- und Verlustmoduli werden über das Analogieprinzip unter Verwendung von Lissajous Diagrammen abgeleitet. Infolgedessen können die Materialparameter durch das Auswerten algebraischer Zusammenhänge identifiziert werden, ohne nichtlineare Optimierungsverfahren anwenden zu müssen. Hierbei stellt die Fließspannung einen signifikanten Materialparameter dar. Deswegen werden die Standardverfahren zur Bestimmung der Fließspannung auf rheologische
Modelle angewendet und bewertet.
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Queiroz, Claudia Moreira. "Chácara Xavier : um estudo de caso em arqueologia histórica." Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/71/71131/tde-06022007-095412/.
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Durante o século XIX as chácaras tornaram-se uma opção de morar entre as classes dominantes. Resultante de um período próspero devido à riqueza ocasionada pela cultura do café, esse novo estilo de moradia passa a representar em determinados locais sinônimo de luxo e status. Em Jacareí, não foi diferente. É a partir dessa premissa que tomou-se objeto de estudo a Chácara Xavier, uma das poucas propriedades desse padrão que ainda conserva várias de suas características enquanto exemplar daquele período. Tendo testemunhado vários acontecimentos, esse local tinha ainda muito a mostrar. Dessa forma, a cultura material recuperada através dos métodos e técnicas utilizados pela arqueologia, aliada a uma série de opções oferecidas pela Arqueologia Histórica como estudos documentais, levantamentos arquitetônicos, história oral, entre outras, acabou revelando parte desta história, bem como algumas transformações ocorridas não só no espaço, mas principalmente no modo de vida de uma sociedade que começava a se esboçarDuring XIX century, the rural residences became a living option among dominant classes. Result of a prosper age caused by the coffee culture\'s richness, this new life style was going to represent, in some places, splendour and status. In Jacareí, it was not different. Starting from this premise, Chácara Xavier was taken as object of study: being one of the few properties with such standart wich conserves several self-characteristics while a sample of that age. Confirming several events, this local still had a lot to show. In that way, the material culture that was recovered by methods and technics used by archaeology, plus series of options offered by Historical Archaeology, like documental studies, architetonical risings, oral history, among other things, was about to reveal part of this history, including some transformations that occours not only in this place, but mainly in the way of living of a society that begans to plot out
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Gao, Yipeng. "Transformation Pathway Network Analysis for Martensitic Transformations." The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1385978073.
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Renaud, Adrien. "The Discontinuous Galerkin Material Point Method : Application to hyperbolic problems in solid mechanics." Thesis, Ecole centrale de Nantes, 2018. http://www.theses.fr/2018ECDN0058/document.
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Dans cette thèse, la Méthode des Points Matériels (MPM) est étendue à l’approximation de Galerkin Discontinue (DG) et appliquée aux problèmes hyperboliques en mécanique des solides. La méthode résultante (DGMPM) a pour objectif de suivre précisément les ondes dans des solides subissant de fortes déformations et dont les modèles constitutifs dépendent de l’histoire du chargement. A la croisée des méthodes de types éléments finis et volumes finis, la DGMPM s’appuie sur une grille de calcul arbitraire dans laquelle des flux sont calculés au moyen de solveurs de Riemann approximés sur les arêtes entre les éléments. L’intérêt de ce type de solveurs est qu’ils permettent l’introduction de la structure caractéristique des solutions des équations aux dérivées partielles hyperboliques directement dans le schéma numérique. Les analyses de stabilité et de convergence ainsi que l’illustration de la méthode sur des simulations de problèmes unidimensionnels et bidimensionnels montrent que le schéma numérique permet d’améliorer le suivi des ondes par rapport à la MPM. Par ailleurs, un deuxième objectif poursuivi dans cette thèse consiste à caractériser la réponse des solides élastoplastiques à des sollicitations dynamiques en deux dimensions en vue d’améliorer la résolution numérique de ces problèmes. Bien qu’un certain nombre de travaux aient déjà été menés dans cette direction, les problèmes étudiés se limitent à des cas particuliers. Un cadre unifié pour l’étude de la propagation d’ondes simples dans les solides élastoplastiques en déformations et contraintes plane est proposé dans cette thèse. Les trajets de chargement suivis à l’intérieur de ces ondes simples sont de plus analysésIn this thesis, the material point method (MPM) is extended to the discontinuous Galerkin approximation (DG) and applied to hyperbolic problems in solid mechanics. The resulting method (DGMPM) aims at accurately following waves in finite-deforming solids whose constitutive models may depend on the loading history. Merging finite volumes and finite elements methods, the DGMPM takes advantage of an arbitrary computational grid in which fluxes are evaluated at element faces by means of approximate Riemann solvers. This class of solvers enables the introduction of the characteristic structure of the solutions of hyperbolic partial differential equations within the numerical scheme. Convergence and stability analyses, along with one and two-dimensional numerical simulations,demonstrate that this approach enhances the MPM ability to track waves. On the other hand, a second purpose has been followed: it consists in identifying the response of two-dimensional elastoplastic solids to dynamic step-loadings in order to improve numerical results on these problems. Although some studies investigated similar questions, only particular cases have been treated. Thus,a generic framework for the study of the propagation of simple waves in elastic-plastic solids under plane stress and plane strain problems is proposed in this thesis. The loading paths followed inside those simple waves are further analyzed
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Sun, Xinxing [Verfasser], Bernd [Akademischer Betreuer] Rauschenbach, Bernd [Gutachter] Rauschenbach, and Petr [Gutachter] Němec. "Phase Transformations and Switching of Chalcogenide Phase-change Material Films Prepared by Pulsed Laser Deposition / Xinxing Sun ; Gutachter: Bernd Rauschenbach, Petr Němec ; Betreuer: Bernd Rauschenbach." Leipzig : Universitätsbibliothek Leipzig, 2017. http://d-nb.info/1240847815/34.
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Máca, Tomáš. "Modifikace hydroxidu nikelnatého pro zlepšení jeho elektrochemických vlastností v alkalických akumulátorech." Doctoral thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2015. http://www.nusl.cz/ntk/nusl-233682.
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Commercial alkaline accumulators with positive electrode based on nickel hydroxide generally comprise beta modification of the active material at present due to its excellent stabilization of performance during electrochemical cycling. This dissertation refers to a research work accomplished by author, which has been aimed to utilization of alpha nickel hydroxide in alkaline batteries including exploration of possibilities to attain its stability in strong alkali medium of the electrolyte. I have focused my effort to elucidate reasons for its transformation tendency and to find way of their suppression.
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Chang, Liang. "Sustainable Transformations of Methyl Coumalate : efficient Preparations of Unsaturated Carboxylic Acids, 2HPyrans, Trifluoromethyl Benzenes and Fluorescents Molecules." Thesis, Sorbonne université, 2018. http://www.theses.fr/2018SORUS109.
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Dans ce travail, nous décrivons le développement de nouvelles transformations utilisant le coumalate de méthyle, composé renouvelable biosourcé. Un couplage double séquentiel d'alkyl-alkyle ou d'alkyl-hydrure one-pot conduit à des acides insaturés d’intérêt. Nous décrivons une synthèse efficace de 2H-pyranes tétrasubstitués dans des conditions douces, puis nous décrivons une réaction efficace et sans solvant avec des dicétones trifluorométhylées, pour conduire à des benzènes trifluorométhylés. Enfin, nous avons rapporté une nouvelle stratégie générale de réaction de désaromatisation de composés hétérocycliques de type pyrido [1, 2-a] bicycliquesIn this work, we have described the development of new transformations using bio-based renewable methyl coumalate as feedstock. An iron and copper catalyzed one-pot sequential double alkyl-alkyl or alkyl-hydride 1,6-addition with methyl coumalate was described. We then described an efficient synthesis of tetrasubstituted 2H-pyrans under mild condition. Later we reported a solvent-free reaction of methyl coumalate with trifluoromethyl-β-diketones, in a tBuOK-catalyzed domino sequence. A novel reaction, for efficient C-C bond formation between the bio-based methyl coumalate and a variety of imines and aldehydes via MBH pathway was reported. Finally, we reported a novel, general dearomatization strategy with an unprecedented pyrido[1, 2-a] fused heterocyclic scope
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Boozula, Aravind Reddy. "Use of Bio-Product/Phase Change Material Composites in the Building Envelope for Building Thermal Control and Energy Savings." Thesis, University of North Texas, 2008. https://digital.library.unt.edu/ark:/67531/metadc1248391/.
Full textAbstract:
This research investigates the bio-products/phase change material (PCM) composites for the building envelope application. Bio-products, such as wood and herb, are porous medium, which can be applied in the building envelope for thermal insulation purpose. PCM is infiltrated into the bio-product (porous medium) to form a composite material. The PCM can absorb/release large amount of latent heat of fusion from/to the building environment during the melting/solidification process. Hence, the PCM-based composite material in the building envelope can efficiently adjust the building interior temperature by utilizing the phase change process, which improves the thermal insulation, and therefore, reduces the load on the HVAC system. Paraffin wax was considered as the PCM in the current studies. The building energy savings were investigated by comparing the composite building envelope material with the conventional material in a unique Zero-Energy (ZØE) Research Lab building at University of North Texas (UNT) through building energy simulation programs (i.e., eQUEST and EnergyPlus). The exact climatic conditions of the local area (Denton, Texas) were used as the input values in the simulations. It was found that the EnergyPlus building simulation program was more suitable for the PCM based building envelope using the latent heat property. Therefore, based on the EnergyPlus simulations, when the conventional structure insulated panel (SIP) in the roof and wall structures were replaced by the herb panel or herb/PCM composite, it was found that around 16.0% of energy savings in heating load and 11.0% in cooling load were obtained by using PCM in the bio-product porous medium.
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Boozula, Aravind Reddy. "Use of Bio-Product/Phase Change Material Composite in the Building Envelope for Building Thermal Control and Energy Savings." Thesis, University of North Texas, 2018. https://digital.library.unt.edu/ark:/67531/metadc1248391/.
Full textAbstract:
This research investigates the bio-products/phase change material (PCM) composites for the building envelope application. Bio-products, such as wood and herb, are porous medium, which can be applied in the building envelope for thermal insulation purpose. PCM is infiltrated into the bio-product (porous medium) to form a composite material. The PCM can absorb/release large amount of latent heat of fusion from/to the building environment during the melting/solidification process. Hence, the PCM-based composite material in the building envelope can efficiently adjust the building interior temperature by utilizing the phase change process, which improves the thermal insulation, and therefore, reduces the load on the HVAC system. Paraffin wax was considered as the PCM in the current studies. The building energy savings were investigated by comparing the composite building envelope material with the conventional material in a unique Zero-Energy (ZØE) Research Lab building at University of North Texas (UNT) through building energy simulation programs (i.e., eQUEST and EnergyPlus). The exact climatic conditions of the local area (Denton, Texas) were used as the input values in the simulations. It was found that the EnergyPlus building simulation program was more suitable for the PCM based building envelope using the latent heat property. Therefore, based on the EnergyPlus simulations, when the conventional structure insulated panel (SIP) in the roof and wall structures were replaced by the herb panel or herb/PCM composite, it was found that around 16.0% of energy savings in heating load and 11.0% in cooling load were obtained by using PCM in the bio-product porous medium.
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Lainé, Christian. "Étude numérique et expérimentale du comportement mécanique de plaques et coques sandwich : développement d'un élément non-linéaire, grandes transformations et application au flambement de plaques raidies en construction navale." Université Joseph Fourier (Grenoble ; 1971-2015), 1998. http://www.theses.fr/1998GRE10037.
Full textAbstract:
Cette etude s'interesse au comportement mecanique des structures en materiaux composites epais, utilisees en construction navale (monolithiques epais et sandwichs). Une attention particuliere est apportee au comportement en flambement. La premiere etape consiste a identifier les caracteristiques materiaux. Des essais permettant de determiner la contrainte de compression, les modules de cisaillement transverse ainsi que le comportement non-lineaires sont examines. Une procedure de caracterisation en vue du calcul est proposee. La seconde etape aboutit au developpement de deux elements coques, non lineaires, grands deplacements et grandes deformations. Le champs de cisaillement transverse est decrit soit par une formulation variationnelle, soit par une evolution quadratique dans l'epaisseur. Une ecriture de la loi de comportement en reperage materiel est proposee. Lors de la troisieme etape deux essais sont proposes : plaque sous pression hydrostatique pour la validation du logiciel, flambement de plaques raidies par cisaillement afin de mettre au point une procedure de calcul.
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Ou, Jifei. "Material transformation designing shape changing interfaces enabled by programmable material anisotropy." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/91304.
Full textAbstract:
Thesis: S.M., Massachusetts Institute of Technology, School of Architecture and Planning, Program in Media Arts and Sciences, 2014.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 91-93).
This thesis takes a material perspective on designing transformable interfaces. The structure of material and mechanical properties such as stiffness, can determine not only its static performances, but also, with the help of external forces, support dynamic shape change. By encoding structural or stiffness distribution in the actuated materials, we can partially offload the shape-changing control from actuators (digital) to the material itself (analogue), in order to achieve expressive transformations that current modularized actuation system cannot easily provide. The implementation of this thesis will be three series of material primitives and three application prototypes that demonstrate the real world potential of this research.
by Jifei Ou.
S.M.
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Wehrenberg, Christopher. "Phase transformations in shock compacted magnetic materials." Diss., Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/43595.
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Shock compaction experiments were performed on soft magnetic phases Fe₄N and Fe₁₆N₂, and hard magnetic phases Nd₂Fe₁₄B and Sm₂Fe₁₇N₃ in order to determine their thermo-mechanical stability during shock loading and explore the possibility of fabricating a textured nanocomposite magnet. Gas gun experiments performed on powders pressed in a three capsule fixture showed phase transformations occurring in Fe₄N, Fe₁₆N₂, and Nd₂Fe₁₄B, while Sm₂Fe₁₇N₃ was observed to be relatively stable. Shock compaction of FCC Fe₄N resulted in a partial transformation to HCP Fe₃N, consistent with previous reports of the transition occurring at a static pressure of ~3 GPa. Shock compaction of Fe₁₆N₂ produced decomposition products alpha-Fe, Fe₄N, and FeN due to a combination of thermal effects associated with dynamic void collapse and plastic deformation. Decomposition of Nd-Fe-B, producing alpha-Fe and amorphous Nd-Fe-B, was observed in several shock consolidated samples and is attributed to deformation associated with shock compaction, similar to decomposition reported in ball milled Nd-Fe-B. No decomposition was observed in shock compacted samples of Sm-Fe-N, which is consistent with literature reports showing decomposition occurring only in samples compacted at a pressure above ~15 GPa. Nd-Fe-B and Sm-Fe-N were shown to accommodate deformation primarily by grain size reduction, especially in large grained materials. Hard/Soft composite magnetic materials were formed by mixing single crystal particles of Nd-Fe-B with iron nanoparticles, and the alignment-by-magnetic-field technique was able to introduce significant texture into green compacts of this mixture. While problems with decomposition of the Nd₂Fe₁₄B phase prevented fabricating bulk magnets from the aligned green compacts, retention of the nanoscale morphology of the alpha-Fe particles and the high alignment of the green compacts shows promise for future development of textured nanocomposite magnets through shock compaction.
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Kuritsky, Orit. "Transformational tales : media, makeovers, and material culture." Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/46660.
Full textAbstract:
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Comparative Media Studies, 2009."February 2009."
Includes bibliographical references (p. 94-101).
This thesis probes into current American makeover culture, thorough three detailed case studies that represent an increasing confluence of commerce, entertainment, and, at times, spirituality. Each of the chapters is devoted to a niche media property, or genre, dedicated to the domestic sphere. The first chapter focuses on the genre of home decorating TV shows and practices of their consumption. The second centers on a single television program - TLC's What Not to Wear, and the interpretative activities it provokes among viewers. The third chapter examines the FlyLady - a transmedia property with a strong internet base, described by its founder as a "behavior modification system" that coaches its subscribers in getting their houses in order. This study was driven, among other things, by the following questions: as the 'commodity frontier' gets increasingly intermingled with our daily lives, with the help of increasingly pervasive media, how do certain communities respond, and with what methods of meaning-making? What draws audiences to engage with media properties so intermingled with commerce in the first place? And, what constitutes these properties' entertainment value as well as the other values audiences find in them? The answers vary with each case study, yet, there are many commonalities pertaining to meanings associated with consumer goods in late capitalism. The media properties described here capitalize on the movement of meaning from culture through consumer goods to individuals. At the same time these three chapters exemplify many cases of redirecting, filtering, and damming up the flow of meaning on the part of viewers and subscribers.
by Orit Kuritsky.
S.M.
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Loh, Angeline M. "The recovery of 3-D structure using visual texture patterns." University of Western Australia, 2006. http://theses.library.uwa.edu.au/adt-WU2006.0101.
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[Truncated abstract] One common task in Computer Vision is the estimation of three-dimensional surface shape from two-dimensional images. This task is important as a precursor to higher level tasks such as object recognition - since shape of an object gives clues to what the object is - and object modelling for graphics. Many visual cues have been suggested in the literature to provide shape information, including the shading of an object, its occluding contours (the outline of the object that slants away from the viewer) and its appearance from two or more views. If the image exhibits a significant amount of texture, then this too may be used as a shape cue. Here, ‘texture’ is taken to mean the pattern on the surface of the object, such as the dots on a pear, or the tartan pattern on a tablecloth. This problem of estimating the shape of an object based on its texture is referred to as shape-form-texture and it is the subject of this thesis . . . The work in this thesis is likely to impact in a number of ways. The second shape-form-texture algorithm provides one of the most general solutions to the problem. On the other hand, if the assumptions of the first shape-form-texture algorithm are met, this algorithm provides an extremely usable method, in that users should be able to input images of textured objects and click on the frontal texture to quickly reconstruct a fairly good estimation of the surface. And lastly, the algorithm for estimating the transformation between textures can be used as a part of many shape-form-texture algorithms, as well as being useful in other areas of Computer Vision. This thesis gives two examples of other applications for the method: re-texturing an object and placing objects in a scene.
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Ma, Xiao. "Topological modelling of martensitic transformations in crystalline materials." Thesis, University of Liverpool, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.440851.
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Juliano, Thomas Frank Gogot︠s︡i I︠U︡ G. "Inducing phase transformations using depth-sensing indentation /." Philadelphia, Pa. : Drexel University, 2004. http://dspace.library.drexel.edu/handle/1860/334.
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Choudhry, Mohammad Arshad. "Crystallography of phase transformations and interphase boundaries in materials." Thesis, University of Surrey, 1985. http://epubs.surrey.ac.uk/847304/.
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The main purposes of this study were; (i) to apply the theory of martensite crystallography to martensitic transformations in low-symmetry materials, (ii) to investigate, using the computer simulation method, the microscopic structure of complex interphase boundaries which are not yet fully understood in terms of the martensitic mechanism. Although the unique symmetry of a twin boundary makes it a rather exceptional kind of interface, it is clearly a particularly appropriate starting point especially due to the role which twinning plays in martensitic transformations. The accuracy of twinning modes is vital for their use as lattice-invariant shears in theories of martensite crystallography. Potential twinning modes for zirconia were determined using the analysis due to Bilby and Crocker (1965) and the associated atomic shuffling was also considered. Twinning orientation relationships involving a screw axis and a glide plane have been established. The theory of martensite crystallography (Acton et al. 1970) was then applied to the tetragonal to monoclinic martensitic transformation in zirconia. The predictions for the habit plane, shape strain and the direction of the shape deformation were obtained and compared with available experimental observations. The application of the theory was also extended to the face-centred cubic to monocline martensitic transformation in plutonium alloys. The predictions of the crystallographic features for this transformation are reported. The computer simulation method was applied to investigate the relaxed atomic structure and energies of the complex interphase boundaries. The (100)b//(100)f and the (011)b /(111)f interphase boundaries were investigated using interatomic potential. Special consideration was given to the misfit dislocations at the interface which can accomplish the lattice-invariant shear of the phenomenological theories of martensite crystallography. A new equilibrium interatomic potential for iron was developed to study the relaxed structure of the (225)f b. c. c. /f. c. c. interphase boundary. These results are also compared with experimental information. Finally the general results of the thesis are discussed and main conclusions summarized.
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Schmidt, Iver. "Design of nanoporous materials for light alkane transformation." Thesis, University of Liverpool, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.369114.
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Blander, Alexandre Joel. "Transformation phenomena in superplastic aluminum 7475." Thesis, McGill University, 2004. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=81529.
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The process of superplastic forming in 7475 aluminum alloy was analyzed using orientation imaging microscopy (OIM), x-ray diffraction and scanning electron microscopy (SEM). These techniques were used to determine the effect of the superplastic forming on texture, grain boundary character distribution (GBCD), grain size, residual stress and microstructure at different stages of the deformation of specimens deformed in tension. Results indicate that a microstructure is transformed mainly by the grain boundary sliding process that is responsible for rapid randomization of texture. There is also much evidence for crystallographic slip occurring in conjunction with grain boundary sliding. Accommodation of superplastic flow is linked to increased dislocations density in the lattice. At a threshold level, the dislocation density reaches certain saturation level and the nucleation of voids starts. At this threshold strain, the deformation mechanism is altered and superplastic flow proceeds, however, cavities continue to be produced and coalesce due to the grain boundary sliding process. A precipitate free zone is observed during deformation. This zone is more plastic and presents an orientational difference when compared to the grain interior. It is theorized that this precipitate free zone aids in the accommodation of GBS and plays a role in the cavitation process. The Kernel average misorientation function of OIM was used to indicate the level of strain within the grains to explain the formation of cavities.
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Toumar, Alexandra Jeanne. "Phase transformations in layered electrode materials for sodium ion batteries." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/111255.
Full textAbstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2017.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 118-130).
In this thesis, I investigate sodium ion intercalation in layered electrode materials for sodium ion batteries. Layered metal oxides have been at the forefront of rechargeable lithium ion battery technology for decades, and are currently the state of the art materials for sodium ion battery cathodes in line for commercialization. Sodium ion intercalated layered oxides exist in several different host phases depending on sodium content and temperature at synthesis. Unlike their lithium ion counterparts, seven first row layered TM oxides can intercalate Na ions reversibly. Their voltage curves indicate significant and numerous reversible phase transformations during electrochemical cycling. These transformations arise from Na-ion vacancy ordering and metal oxide slab glide but are not well understood and difficult to characterize experimentally. In this thesis, I explain the nature of these lattice differences and phase transformations for O and P-type single-transition-metal layered systems with regards to the active ion and transition metal at hand. This thesis first investigates the nature of vacancy ordering within the O3 host lattice framework, which is currently the most widely synthesized framework for sodium ion intercalating oxides. I generate predicted electrochemical voltage curves for each of the Na-ion intercalating layered TM oxides using a high-throughput framework of density functional theory (DFT) calculations and determine a set of vacancy ordered phases appearing as ground states in all NaxMO₂ systems, and investigate the energy effect of stacking of adjacent layers. I also examine the influence of transition metal mixing and transition metal migration on the materials' thermodynamic properties. Recent work has established the P2 framework as a better electrode candidate structure type than O3, because its slightly larger interlayer spacing allows for faster sodium ion diffusion due to lower diffusion barriers. However, little has been resolved in explaining what stabilizing mechanisms allow for the formation of P-type materials and their synthesis. This work therefore also investigates what stabilizes P2, P3 and O3 materials and what makes them synthesizable at given synthesis conditions, both for the optimization of synthesis techniques and for better-guided material design. It is of further interest to understand why some transition metal oxide systems readily form P2 or P3 compounds while others do not. I investigate several possible stabilizing mechanisms that allow P-type layered sodium metal oxides to by synthesized, and relate these to the choice of transition metal in the metal oxide structure. Finally, this work examines the difficulty of sodium ion intercalation into graphite, which is a commonly used anode material for lithium ion batteries, proposing possible reasons for why graphite does not reversibly intercalate sodium ions and why cointercalation with other compounds is unlikely. This thesis concludes that complex stabilizing mechanisms that go beyond simple electrostatics govern the intercalation of sodium ions into layered systems, giving it advantages and disadvantages over lithium ion batteries and outlining design principles to improve full-cell sodium ion battery materials.
by Alexandra Jeanne Toumar.
Ph. D.
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Fan, Frank Yongzhen. "Kinetics of phase transformations in lithium-sulfur batteries." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/111247.
Full textAbstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2017.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 139-150).
Sulfur is a promising positive electrode for lithium batteries with the potential to create the step-change improvement in energy density and cost needed for the widespread adoption of electric vehicles and renewable energy. However, lithium-sulfur batteries suffer from a number of challenges, among them poor rate capability resulting in part from a complex dissolution-precipitation mechanism which produces electronically insulating end members S₈ and Li₂S. Few studies have heretofore been performed on rate-limiting mechanisms in Li-S batteries, which must be elucidated in order to inform rational design of electrodes with high capacity and rate capability. Polysulfide solutions, intermediates in the electrochemical reduction of sulfur, are used for the first time to make an efficient, high energy density flow battery, enabled by a novel flow battery architecture using a percolating network of nanoscale conductive carbon. An extensive experimental study of exchange current density for redox of higher order polysulfide solutions and their ionic conductivity has been conducted. The type and amount of electrolyte solvent has been found to influence both of these. The second portion of this thesis characterizes the kinetics of Li₂S electrodeposition, which is responsible for three-quarters of the theoretical capacity of the sulfur cathode. Kinetics are found to be highly dependent on solvent choice in a manner similar to exchange current density. Furthermore, electrodeposition kinetics are found to slow considerably at the low electrolyte/sulfur ratios which are needed for high energy density and low cost. Materials such as conductive oxides can serve as nucleation promoters and help solve this challenge. The morphology of precipitates is found to be dependent on discharge rate, with large, discrete particles forming at low rates. A model was for describing 3-D electrodeposition of Li₂S under the influence of a soluble redox mediator which enables efficient utilization of conductive surface area and prevents passivation of conductive carbon with insulating Li₂S.
by Frank Yongzhen Fan.
Ph. D.
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Christensson, Jesper. "Relation Between the Material in Press Hardening Dies and Fully Martensitic Transformation : Sheet properties of thick 3D-sheets in small series production." Thesis, Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-79015.
Full textAbstract:
This report evaluates the influence of the die material on the cooling rate and martensitic transformation of press hardened sheets. The goal was to increase the thicknesses of sheets that can form fully martensitic microstructure when press hardened. To achieve this, a numerical- and an experimental method was used and results were compared to assess the impact of die material change. The tests were conducted with two die materials, a ductile cast iron according to standard EN‑GJS‑700‑2 and a casted steel according to standard EN 1.6220. Two sheet materials, Hardox400 and Hardox450, were press hardened and two different thicknesses were evaluated. Simulations have been designed with temperature dependent material properties based on data gathered from the literature survey. All simulations indicated an improved cooling rate over the entire temperature spectrum when changing from the iron die to the steel die. An experimental procedure has been performed using two different dies, both planar and of approximately the same thickness. Thermocouples were used to obtain cooling curves of all sheets during quenching. Samples were taken from each sheet and the hardness, microstructure and the present phases were investigated. The experiments concluded that the thinner sheets, when quenched, experienced an overall increase in cooling rate in the steel die compared with the iron die. A total reduction in cooling time by 37.5%-43,7% was observed over the entire temperature span. However, only the Hardox400 sheet fully formed martensite, as the cooling of the Hardox450 sheets still was not fast enough in either of the dies. For the thicker sheets, the experiments also indicated a reduction in total cooling time. The total cooling time was reduced by 23% when pressed in the steel die compared to the iron die. This improvement, however, was not observed at higher temperatures. At the critical temperature span between 800˚C and 500˚C, the sheet showed no improvements in cooling rate with the die material change. Both the hardness measurements and the microstructure evaluation of the thicker sheets indicated a pearlitic-martensitic microstructure. As both the simulations and experiments indicated similar improvements, the increase in cooling rate could be accredited to the die material change. This concludes that the heat transfer properties of the die material affected the cooling characteristics of the process. It was also concluded that the thinner sheets experienced a reduced cooling time over the entire temperature spectrum with the die material change. The thicker sheet, however, only experienced a reduced cooling time in the lower temperature span. Thus, changing the die material did not affect the hardening of the thicker sheets. This ultimately resulted in an unsuccessful attempt to increase the possible thickness of sheets with fully martensite microstructure. The improvements observed for the thinner sheets, are however promising and could be further evaluated for another sheet material.I denna avhandling har relationen mellan ett verktygmaterials kylningseffekt och genomhärdningsförmåga under presshärdning utvärderats, med målet att öka tjockleken på plåtmaterial som genomhärdar. För att åstadkomma detta har en numerisk undersökning och en experimentell undersökning utförts för att bedöma effekten av ett byte av verktygsmaterial. Undersökningarna utfördes med två verktygsmaterial, ett segt gjutjärn enligt standard EN‑GJS‑700‑2 och ett gjutet stål enligt standard EN 1.6220. Under testerna användes även två olika plåtmaterial, Hardox400 och Hardox450, i två olika tjocklekar. Simuleringen har utformats med relevanta temperaturberoende materialparametrar erhållna från teorin. Resultaten från simuleringarna påvisade att ett byte av verktygsmaterial gav snabbare kylning av all plåtar över hela det undersökta temperaturspannet. Den experimentella undersökningen har utförts med två olika pressverktyg, båda plana med likartad tjocklek. Temperaturgivare användes för att erhålla kylkurvor för plåtarna när de kyldes i verktygen. Hårdhet, mikrostruktur och erhållna faser undersöktes för varje plåt. Experimenten påvisade att de tunnare plåtarna kyldes snabbare i stålverktyget än i järnverktyget över hela temperaturspannet, och resulterade i 37,5%-43,7% kortare kyltider. Trots detta, var det endast Hardox400-plåten som genomhärdades, då kylningen av Hardox450-plåten inte var tillräckligt snabb i något av verktygen. Även de tjockare plåtarna uppvisade en totalt kortare kyltid. Kyltiden minskade med 23% i stålverktyget jämfört med järnverktyget. Denna förbättring observerades dock inte över hela temperaturspannet. Vid höga temperaturer kylde stålverktyget långsammare än järnverktyget. De släckta plåtarna erhöll en perlitisk/martensitisk struktur vid komplett svalning, oberoende av verktygsmaterial. Eftersom både simuleringarna och experimenten påvisade liknande förbättringar, kan den ökade kylhastigheten härledas till bytet av verktygsmaterial. Detta fastställer att värmetransportegenskaperna hos verktygsmaterialet hade en inverkan på kylningen i processen. Studien påvisade också att de tunnare plåtarna kyldes fortare över hela temperaturspannet vid materialbytet. De tjockare plåtarna uppvisade dock endast en kortare kyltid i det lägre temperaturspannet. Därmed förblev härdningen av de tjockare plåtarna opåverkad av materialbytet. Detta resulterade i att presshärdning av ökad plåttjocklek för det undersökta materialet inte lyckades. De observerade förbättringarna hos de tunnare plåtarna är dock mycket lovande och bör studeras vidare.
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Makhetha, William Motsoko. "An investigation of phase transformations in Pt-V coating systems." Master's thesis, University of Cape Town, 2012. http://hdl.handle.net/11427/17104.
Full textAbstract:
Includes bibliographical references.Phase transformations in Pt-V coatings after heat treatment have been investigated. Five Pt- V ordered phases (PtV, PtV 3 , Pt 2 V, Pt 3 V and Pt 8 V) have been previously observed in bulk platinum-vanadium alloys. Phase formation in coatings is expected to be sequential and controlled by the lowest temperature eutectic (liquidus) composition; this allows control of experimental parameters for formation of desired ordered phases. This investigation included fabrication of coatings, heat treatments, morphology characterization and phase analysis. Single and multilayer coatings ranging between 0.07 μm and 0.5 μm were deposited on vanadium and platinum substrates using E-beam deposition. The kinetics of phase transformation were studied by subjecting the coated layers to a variety of heat treatments in the temperature range 600°C to 900°C for 4 and 8 hours. Composition and morphology characterization was carried out using EDS and SEM respectively. XRD was used for phase analysis. Four (PtV, PtV 3 , Pt 2 V, Pt 3 V) out of the five Pt-V ordered phases exhibited in bulk alloys, were successfully formed from the coating system investigated in this project. The first phase formed, and the sequence of phase formation, was found to be different depending on which metal formed the substrate. The vanadium-rich ordered phase (PtV 3 ) was preferentially formed first on vanadium substrates and the sequence of phase formation progressed through ordered phases richer in platinum. The platinum-rich ordered phase (Pt 3 V) was preferentially formed first on platinum substrates and the sequence continued towards formation of ordered phases richer in vanadium. An increase in heat treatment temperature from 600°C to 900°C resulted in rapid kinetics of phase transformation but affected the morphology of the coatings. An increase in coating thickness, number of coating layers, heat treatment time, and temperature resulted in an increase in overall total number of ordered phases and volume of ordered phases.
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Behrens, Gesa. "The martensitic transformation in zirconia." Case Western Reserve University School of Graduate Studies / OhioLINK, 1993. http://rave.ohiolink.edu/etdc/view?acc_num=case1057156303.
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Shottenkirk, B. A. "Improvise, adapt, and overcome : the archaeology of material transformation in conflict." Thesis, University College London (University of London), 2013. http://discovery.ucl.ac.uk/1396233/.
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Evidence of individual decision-making and how the subsequently implemented actions may contribute to long-term material change are largely absent from the archaeological record. Indeed, due to a paucity of clearly associated artefacts, few archaeological studies attempt to explore the role, or even the reality, of how individual decisions and actions may impact macro-scale change. This dissertation addresses this deficiency and examines specific artefacts created within the context of a historical conflict to investigate both the practical implications and theoretical considerations of micro-scale action. Framed within the historical context of the First World War, this research offers both practical implications and theoretical considerations. Although the archaeological study of conflict has traditionally focused on varied aspects of martial artefacts - to include architecture, battlefield surveys, and weapon and armour typology - the chaotic nature of warfare nonetheless provides a unique resource to consider both the role of the individual and the transmission of new cultural knowledge and skill-sets. The data-set is composed of exigent matériel fabricated by soldiers of the British Empire who sought to supplement non-existent or otherwise unsuitable martial resources that were already a part of their inventory. By examining these selected artefacts and their associated background information in detail, this research provides clear evidence on how individuals adapt and transform material to affect their immediate environment through innovative, self-directed, and purposeful action. This practical micro-scale insight of Agency theory integrates with an assessment of how different mechanisms of transmission combine with real world factors to influence the macro-scale propagation of new knowledge and designs in a pragmatic analysis of Cultural Transmission theory. In conclusion, this research promotes a unique approach to conflict archaeology while raising awareness of the wider call for Agency and Cultural Transmission theory to provide micro-scale to macro-scale interaction in real world situations and contexts.
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SANTANA, Flávio Carreiro de. "Recriando espaços, inventando lugares: Memória e oralidade sobre as transformações urbanas em Pombal (1930-1950)." Universidade Federal de Campina Grande, 2007. http://dspace.sti.ufcg.edu.br:8080/jspui/handle/riufcg/1787.
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Cidade, memória, passado, representações, transformações materiais e suas implicações simbólicas, eis algumas das preocupações dessa narrativa escrita que pretende ser, antes de tudo, uma incursão científica pela qual convidamos o leitor a percorrer conosco. Motivados por tais interesses, esta incursão pretende apresentar os resultados de nossa pesquisa referente às representações criadas para as transformações materiais e simbólicas vividas em Pombal - Pb, entre 1930 e 1950. Enquanto problematizações, procuramos entender se estas transformações sofridas no espaço urbano pombalenses foram vividas e lembradas de forma coletiva, quais as alterações mais representativas e que ficaram presentes na memória dos nossos narradores, e quais as lembranças e sentimentos dessas pessoas pata com o acontecimento pesquisado. Paia tanto, buscamos explorar tais significações a partir das falas de seus antigos (re)memoradores, possibilitadas peio emprego metodológico da história orai Consoante às evidências orais também foi possível perceber outras representações criadas para o mesmo acontecimento e diversas daquelas, através de evidencias escritas enunciadas peio discurso oficial da Câmara Municipal, bem como pelas representações agenciadas peia historiografia local. Neste sentido, nossos narradores enunciaram representações sobre tais transformações ocorridas em Pombal menos como uma experiência marcada peia pessoalidade e idealizações de progresso, e mais como significações envoltas em estranheza e exclusão social provocadas por essas transformações materiais. Para tanto, as narrativas da memória dos nossos antigos (re)memoradores puderam reconstruir e reinventar no presente, práticas culturais compartilhadas socialmente. São representações criadas para a cidade naquele instante de suas transformações materiais e simbólicas, compondo pela oralidade outros cenários, personagens, tramas e apropriação dos espaços pombalenses.
City, memory, past, representations, materiai transformations and its symbolic questions arc some concerns of me written narrative presented here, ft intends to be a scientifical path through which we invite the reader to walk with us. Moved by these interests, this path intends to present the results of our research related to representations generated by symbolic and material transformations experienced in the municipality of Pombal, State of Paraíba between 1930 and 1950. As analytical issues, we seek to understand if those transformations happened in the urban space in the municipality of Pombal were experienced and are recalled collectively, what are the more significant changes which we kept in the memories of our narrators and which are the memories and feelings of those people related to the events under study. By using the methodology of oral history, we explored the meanings constructed in the memories of old people. According to oral evidence, it was also possible to observe other representations created about the same event than those in the written document constructed by official discourse of the Munieipiialy Board and the local historiography, in this sense, our narrators told representations about transformations happened in Pombal which were less a personal experience and idealizations of progress and more meanings attached to the íèeiing of social exclusion. The memories of old people reconstruct in the present some cultural practices shared in the past. They are representations about the city in that historical moment and its material and symbolic transformations, construction through oraliry other sceneries, people, stories and uses of space.
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Annie, Lundberg. "Environmental transformations of Manganese and Manganese oxide nanoparticles." Thesis, KTH, Materialvetenskap, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-289637.
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Engineered nanoparticles (NPs) are produced in increased quantities. Due to this increase, itis vital to understand the full lifecycle and fate of these NPs to prevent any possible environmental stress. As a result of their size, NPs may interact differently with their environment compared to bulk materials with the same composition, this both gives NPs their usage as well as risks. The risks often include unwanted interaction with biological systems which may lead to generation of toxicity. This study focused on environmental transformations of manganese and manganese oxide (Mn3O4) NPs. Applications these nanoparticles are often in battery technology and catalysis. A solution intended to mimic the composition of freshwater was used as the environmental media to study these transformations. Exposure of NPs was performed both with and without added natural organic matter (NOM). Several experiments were preformed such as Atomic absorption spectroscopy (AAS) for dissolution of the NPs, Nanoparticle Tracking Analysis (NTA) for particle size, and Attenuated total reflection Fourier transform infrared spectroscopy (ATR- FTIR) for adsorption studies. The production of reactive oxygen species (ROS) was also investigated, and simulations of metal speciation using Visual MINTEQ were also performed. The results from NTA and AAS (for Mn3O4) were not very reliable due to inconsistencies in the results which were probably caused by problems with preparation. However, for both, the results point towards that the dissolution rates of the particles are slightly slowed down when NOM is added. From ATR-FTIR and the simulations it was confirmed that NOM, carbonate, and sulfur will adsorb onto both particles, possibly in multiple layers. As for increased ROS development, no evidence of such an increase was found. However, the method used does not test for increased hydrogen peroxide development so this would in interesting test as well. Other studies which also would contribute to a more nuanced picture of this system is studies regarding zeta potential and studies which furtherinvestigates the type of adsorption mechanism which occurs at the particles surface.Industriella nanopartiklar används i allt större utsträckning. Därför är det av stor vikt attundersöka hela livscykeln som dessa produkter går igenom for att säkerhetsställa att de inte utgör någon fara för miljön och ekosystemen som de kan komma att hamna i. Som ett resultat av deras storlek interagerar nanopartiklar annorlunda med sin omgivning om man jämför med bulkmaterial av samma sammansättning, detta nanopartiklar både sina unika fördelar och risker. Riskerna innefattar ofta oönskade interaktioner med biologiska kretslopp som kan resultera i toxicitet. I den här rapporten läggs fokus på just denna typ av kemiska omvandlingar som nanopartiklar av mangan och manganoxid kan tänkas genomgå i det naturliga kretsloppet. Applikationer man ofta ser dessa partiklar i är batteriteknologi och katalys. De medium som används för att studera omvandlingarna är en lösning som efterliknar ytvatten från en klar sjö. Exponeringar gjordes både med denna lösning så som den är och med tillsatt naturligt organiskt material, NOM.En rad olika experiment gjordes så som analyser med AAS för att undersöka partiklarnas upplösning, NTA för partikelstorlekar och ATR-FTIR som undersökte adsorption på partiklarna. Även en studie med en DCFH metod där ökat ROS aktivitet undersöktes och en rad med SHM simuleringar gjorda i Visual MINTEQ utfördes. Resultaten från NTA och AAS analysen visade sig inte vara särskilt tillförlitliga på grund av tvetydliga resultat som troligen orsakats av problem med provpreparationen. Men resultaten från båda dessa pekar mot att upplösningshastigheten blir något hämmad då man tillsätter naturligt organiskt material, för båda partiklarna. Från ART-FTIR och simuleringarna kunde de säkerhetsställas att adsorption av NOM, karbonat och svavel sker på båda partiklarna, möjligen i fler än ett lager. När det kommer till ROS studien kunde inga bevis på ökad ROS aktivitet hittas med den använda metoden. Dock så kunde inte ökat väteperoxid aktivitet mätas med den metod som användes så detta hade varit av intresse att testa i framtiden. Andra studier som också skulle vara hjälpsamma för att ge en mer nyanserad bild av detta system är en studie om partiklarnas zeta potential och merundersökningar om vilken typ av adsorptions mekanism som sker vid partiklarnas yta.
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Lo, Cynthia Tsien. "Geometric and optical transformations of supramolecular host-guest amphiphiles." Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/119027.
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Thesis: S.B., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2018.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 30-31).
Molecular self-assembly has been an area of recent interest due to its application in a variety of important contexts including drug delivery, regenerative medicine, energy applications, and others. Simultaneously, host-guest chemistry provides a robust and powerful mechanism for inducing switching on the molecular level. In this research, we demonstrate a new platform that combines molecular self-assembly of an amphiphilic chromophore guest molecule with its host molecule counterpart, CB[8] in water. We find that upon addition of CB[8] to a solution of the amphiphilic guest molecule, host-guest complexation occurs and a transition in the morphology of the observed self-assembled nanostructures occurs. Here we present the synthetic route to our amphiphilic guest molecule, in addition to the nanostructural characterization of the supramolecular nanostructures and the host-guest nanostructure by TEM, UV-Vis, and fluorescence spectra.
by Cynthia Tsien Lo.
S.B.
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Whitney, Michael J. (Michael John). "Transformation-mismatch plasticity in zirconia ceramic composites." Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/43447.
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Young, Chune-Ching. "Transformation toughening in phosphocarbide-strengthened austenitic steels." Thesis, Massachusetts Institute of Technology, 1988. http://hdl.handle.net/1721.1/77693.
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Zhong, Yuan. "Nanomechanics of plasticity in ultra-strength metals and shape memory alloys." Diss., Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/45795.
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We study the plasticity mechanisms of diffusionless martensite phase transformation in Nickel-Titanium, one of the most widely used shape memory alloys. The research here involves four thrusts focusing on different length and time scales: (I) Molecular statics and dynamics simulations are applied to study the nanotwin structures and temperature-driven B2 → B19′ phase transitions. (II) Molecular dynamics simulations are performed to explore the stress-driven martensitic phase transformation governing the pseudoelasticity and shape memory effects in NiTi nanopillars. (III) Monte Carlo simulations are conducted to characterize the temperature- driven B2 → B19 phase transition and the patterning of martensitic nanotwins in NiTi thin films. (IV) Phase field simulations are performed to predict the formation and evolution of complex martensitic microstructures, including the detailed analysis of twin compatibility under complex loading conditions.
We also study the nucleation-controlled plasticity mechanisms in different metals of Cu, Al and Ni. Our work focuses on understanding how dislocations nucleate in single crystals. Interatomic potential finite element method is applied to determine when, where and how dislocations nucleate during nanoindentation in metals such as Cu, Al and Ni.
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Abbas, Naseeba. "Analysis of phase transformations in hydrogenated titanium metals by non-isothermal dilatometry." Master's thesis, University of Cape Town, 2011. http://hdl.handle.net/11427/12339.
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Includes bibliographical references (leaves 124-127).Hydrogen was used as a temporary alloying element in CP Ti and Ti-6AI-4V. The microstructural evolution and phase transformations were monitored, before, during and after hydrogenation with in-situ dilatometric testing. Wrought CP Ti and Ti-6AI-4V specimens were pre-annealed and experienced four consecutive thermal cycles (Cycles 1-4) i.e. hydrogenation, post-hydrogenation, dehydrogenation and post-dehydrogenation, during dilatometric testing. The specimen in each thermal cycle was heated to 1000°C, heating rate 1°C/min (with an isothermal hold at 1000°C for three hours for hydrogenation and dehydrogenation cycles) and then cooled to room temperature at cooling rate of 1°C/min.
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Nxumalo, Silethelwe. "The Pt₈V ordering transformation in Pt 11 at. % V." Doctoral thesis, University of Cape Town, 2006. http://hdl.handle.net/11427/4958.
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Includes bibliographical references (leaves 121-125).The Pt₈V ordering transformation in Pt 11 qt.% V alloys has been studied. The study included determining the thermodynamic stability of Pt₈V, the kinetics of Pt₈V ordering transformation and the strengthening due to the presence of the ordered phase. Transmission electron microscopy, using election diffraction and dark and bright field imaging, and X-ray diffraction were used for structural characterisation. Electrical resistivty was used to investigate the kinetics of Pt₈V ordered phase. Microhardness measurements were used to investigate the Pt₈V ordered phase and its effects on hardness.
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Arvidsson, Viktor. "Digital transformation : the material roles of IT resources and their political uses." Doctoral thesis, Umeå universitet, Institutionen för informatik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-109761.
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As IT became ubiquitous, we recognized that IT was everywhere but in our theories. Despite significant efforts, Information System (IS) research is still in desperate search for the IT artifact. Recent reviews show that IS research first and foremost considers IT resources as a socio-technical and managerial concern. Analyses of inertia are restricted to cognitive limitations or technical challenges of IT development and use as separate activities. Hence, IS research assumes that more development resources, extended training, and better management could turn most failures into success. In this thesis, I posit that IS strategy research often treats normal failure as unexpected to maintain the rational idea that managers are in control and that IT does not matter in and of itself. I argue that planned and convergent views of change work well under stable and unitary conditions but in this way fail to account for the complexity of current IS strategy practice. To substantiate this claim, I demonstrate how IS research routinely neglects the material IT use story in the context of digital transformation (DT) studies and social informatics. Political conflict is a constant theme in IS strategy implementation research, yet few studies provided explanation for the apprehension that managers and workers display during the introduction of new IT resources; even as most managers remain men I found also no study that theorized gender politics as related to IS strategy outcomes. I argue in particular that the IS fields routine adherence to borrowed assumptions about the pace, linearity, and sequence of radical change have limited IS scholars to marginally improve on received DT narratives in which IT plays little or no part as IT appears as an agent mostly before and after DT. Though much is said about how IT triggers and enables organizational change, the actual processes and mechanisms that underlies IS strategy change enactments are thus poorly understood. To examine how the material roles of IT resources and their political use can be captured and explained, I summarize and synthesize insights grounded in empirics from four appended research papers. In this way, I chart avenues for material theorizing of micro-affordances and institutions, and develop an IS strategy-as-practice lens that attends IT use as a material practice. After developing this lens, I discuss how material practice perspectives afford deep understanding of the materialities through which actors create, sustain, and transform organizational practice with digital material, and highlight some opportunities to observe the social consequences of IT use in the context of critical studies on men and masculinities and digital gender.
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Haidemenopoulos, Gregory N. "Dispersed-phase transformation toughening in ultrahigh-strength steels." Thesis, Massachusetts Institute of Technology, 1988. http://hdl.handle.net/1721.1/14564.
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