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1
Patra, Anirban. "Modeling the mechanical behavior and deformed microstructure of irradiated BCC materials using continuum crystal plasticity." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/50366.
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The mechanical behavior of structural materials used in nuclear applications is significantly degraded as a result of irradiation, typically characterized by an increase in yield stress, localization of inelastic deformation along narrow dislocation channels, and considerably reduced strains to failure. Further, creep rates are accelerated under irradiation. These changes in mechanical properties can be traced back to the irradiated microstructure which shows the formation of a large number of material defects, e.g., point defect clusters, dislocation loops, and complex dislocation networks. Interaction of dislocations with the irradiation-induced defects governs the mechanical behavior of irradiated metals. However, the mechanical properties are seldom systematically correlated to the underlying irradiated microstructure. Further, the current state of modeling of deformation behavior is mostly phenomenological and typically does not incorporate the effects of microstructure or defect densities.
The present research develops a continuum constitutive crystal plasticity framework to model the mechanical behavior and deformed microstructure of bcc ferritic/martensitic steels exposed to irradiation. Physically-based constitutive models for various plasticity-induced dislocation migration processes such as climb and cross-slip are developed. We have also developed models for the interaction of dislocations with the irradiation-induced defects. A rate theory based approach is used to model the evolution of point defects generated due to irradiation, and coupled to the mechanical behavior. A void nucleation and growth based damage framework is also developed to model failure initiation in these irradiated materials. The framework is used to simulate the following major features of inelastic deformation in bcc ferritic/martensitic steels: irradiation hardening, flow localization due to dislocation channel formation, failure initiation at the interfaces of these dislocation channels and grain boundaries, irradiation creep deformation, and temperature-dependent non-Schmid yield behavior. Model results are compared to available experimental data.
This framework represents the state-of-the-art in constitutive modeling of the deformation behavior of irradiated materials.
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Raja, Daniel Selvakumar. "Dependence of Initial Grain Orientation on the Evolution of Anisotropy in FCC and BCC Metals Using Crystal Plasticity and Texture Analysis." Thesis, Southern Illinois University at Edwardsville, 2015. http://pqdtopen.proquest.com/#viewpdf?dispub=1597933.
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<p>Abundant experimental analyses and theoretical computational analyses that had been performed on metals to understand anisotropy and its evolution and its dependence on initial orientation of grains have failed to provide theories that can be used in macro-scale plasticity. Ductile metals fracture after going through a large amount of plastic deformation, during which the anisotropy of the material changes significantly. Processed metal sheets or slabs possess anisotropy due to textures produced by metal forming processes (such as drawing, bending and press braking). Metals that were initially isotropic possess anisotropy after undergoing forming processes, <i>i.e</i>., through texture formation due to large amount of plastic deformation before fracture. It is therefore essential to consider the effect of anisotropy to predict the characteristics of fracture and plastic flow performances in the simulation of ductile fracture and plastic flow of materials. Crystal plasticity simulations carried out on grains at the meso-scale level with different initial orientations (ensembles) help to derive the evolution of anisotropy at the macro-scale level and its dependence on initial orientation of grains. This paper investigates the evolution of anisotropy in BCC and FCC metals and its dependence on grain orientation using crystal plasticity simulations and texture analysis to reveal the mechanics behind the evolution of anisotropy. A comparison of anisotropy evolution between BCC and FCC metals is made through the simulation, which can be used to propose the theory of anisotropy evolution in macro-scale plasticity. </p><p> <i>Keywords</i>: ensembles; grains; initial orientation; anisotropy; evolution of anisotropy; crystal plasticity; textures; homogeneity; isotropy; inelastic; equivalent strain </p>
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Gaspard, Vincent. "Interactions Hydrogène – Plasticité dans les Alliages Ferritiques." Thesis, Saint-Etienne, EMSE, 2014. http://www.theses.fr/2014EMSE0730/document.
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Le développement à grande échelle des projets de véhicules électriques à pile àcombustible nécessite le déploiement d’infrastructures de transport et de stockaged’Hydrogène gazeux. La conception de ces structures et la sélection des matériaux nécessitede s’affranchir des risques liés à la fragilisation par l’Hydrogène des alliages métalliques. Cephénomène est bien décrit depuis plusieurs décennies, mais les mécanismes élémentaires àl’origine de ce mode d’endommagement restent controversés, notamment par manque demodèles quantitatifs. Plus précisément, le rôle de la déformation (micro-)plastique en pointede défaut sur le piégeage et l’endommagement par l’hydrogène, s’il est bien démontréexpérimentalement dans de nombreux systèmes, reste mal pris en compte dans les modèlesmicro-mécaniques. Le centre SMS de l’ENSM.SE a proposé des approches originales demodélisation des interactions hydrogène – dislocations, qui ont pu être validéesexpérimentalement dans des matériaux modèles de structure cubique à faces centrées. Cette thèsese propose d’appliquer une démarche semblable dans des alliages de structure cubiquecentrée. On mettra en oeuvre des essais de déformation sur des matériaux modèles pré-chargésen hydrogène, des modèles semi-analytiques et des observations des structures de déformationen microscopie électronique à transmission<br>The development of electrical vehicles powered by hydrogen fuel cells requires the large scaledeployment of hydrogen storage and transport infrastructures. This in turn requires theassessment of the sensitivity of structural materials to hydrogen embrittlement phenomena.These damage modes, while being well described experimentally for since several decades,are still highly debated when it comes to elementary physical processes, mainly because of thelack of quantitative models for these elementary processes. More precisely, the role of the(micro-)plasticity developing at the tip of structural defects, while being well establishedexperimentally, is still poorly accounted for in the available micro-mechanical models. TheScience of Materials and Structures division of ENSM.SE already proposed originalmodelling approaches for hydrogen – dislocation interactions, that have been experimentallyvalidated in face-centred cubic materials. This project aims at applying the same type ofapproach to body-centred cubic metals. This will be achieved by means ofdeformation tests on hydrogen-charged model body centred cubic alloys, investigations of thedislocation microstructures by transmission electron microscopy and the development ofsemi-analytical models of hydrogen-dislocation interactions
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Tsai, Joshua Jr-Syan. "Micromechanisms of Near-Yield Deformation in BCC Tantalum." BYU ScholarsArchive, 2021. https://scholarsarchive.byu.edu/etd/8906.
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New materials, optimized for increased strength, ductility, and other desirable properties, have the potential to improve every aspect of modern living. To achieve these optimums, the necessary technological advancements are impeded mainly by the limits of available material models. Innovations in this field rely on research into the nature of material behavior. While a typical model of material behavior in the region near yield involves the initial linear elastic response, followed by yield and isotropic hardening, this fails to explain various important phenomena that manifest in a range of materials, such as pre-yield nonlinearity, anelasticity, yield point phenomena, hardening stagnation, and the Bauschinger effect. These effects have been explained over the past century with the theories of Cottrell atmospheres, the Orowan by-pass mechanism, and back stress. This manuscript compares data from experimental observation in tantalum to these theories to better understand the micromechanisms occurring near yield. Understanding deformation in this region has significant implications in structural and mechanical engineering, as well has having direct applications in the forming of metals. Forty-four dogbone-shaped samples were cut from 99.99% pure tantalum and pulled in load-unload-load and multi-cycle loop tensile tests at room temperature. The specimens were either single crystal, whose orientations were chosen based on desired active slip mode determined by Schmid factors, or bicrystal, based on the orientation of the single grain boundary. Sample behavior was simulated in both crystal plasticity and General Mesoscale finite element models to assist in interpreting results and in suggesting plausible micromechanisms. The experimental results and crystal plasticity simulations suggest alternate explanations to some of the discussed mechanical theories of near-yield deformation. The combined experimental / modeling approach indicates that other slip systems, besides the conventionally assumed {110}, are activated upon yield; particularly the {112} system. The breakaway model traditionally associated with the yield point phenomenon may also be better explained through a different mechanism; back stress development during deformation is shown to result in the observed behavior. Lastly, as is well-known, the Taylor formulation, upon which most crystal plasticity models are based, does not adequately predict yield stress behavior in the presence of grain boundaries; once again, an internal stress mechanism matches much better with the experimental results on single and bicrystals. While not all observations could be fully explained by simply adding internal stress generation to a standard crystal plasticity model, this work anticipates further studies to enable more accurate predictive modeling capabilities and increase understanding of the mechanisms driving the fundamental material properties necessary for future progress.
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Wang, Guofeng Goddard William A. Johnson W. L. "First principles based multiscale modeling of single crystal plasticity application to BCC tantalum /." Diss., Pasadena, Calif. : California Institute of Technology, 2002. http://resolver.caltech.edu/CaltechTHESIS:11132009-112545862.
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Thesis (Ph. D.)--California Institute of Technology, 2010. PQ #3052851.<br>Advisor names found in the Acknowledgements pages of the thesis. Title from home page. Viewed 01/13/2010. Includes bibliographical references.
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Howie, Philip Robert. "Measuring plasticity in brittle materials." Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610682.
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Varillas, Javier. "A molecular dynamics study of nanocontact plasticity and dislocation avalanches in FCC and BCC crystals." Doctoral thesis, Universitat Politècnica de Catalunya, 2019. http://hdl.handle.net/10803/667172.
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This study aims to investigate the underlying mechanisms which govern the development of dense defect networks in nanoscale crystal plasticity, either under contact and uniaxial loading conditions, with emphasis on the onset of intermittent avalanche phenomena. The investigation is based on a comprehensive set of massive molecular dynamics (MD) simulations performed with embedded-atom method potentials in face-centered cubic (FCC) and body-centered cubic (BCC) crystals.
The first part of the thesis concerns the combined role of elasticity and plasticity in nanocontact loadings, where attention is given to the mechanisms leading to the formation of a permanent nanoimprint as well as to the onset of material pile-up at the contact vicinity. It is found that the topographical arrangement of the slip traces emitted at the surface into specific deformation patterns is a distinctive feature of the underlying dislocation glide and twinning processes occurring in FCC and BCC crystals as a function of temperature and surface orientation. A mechanistic analysis is made on the influence of the defect nucleation events in conjunction with the development of entangled defect networks upon the material hardness and its evolution towards a plateau level with increasing indenter-tip penetration. Complementary MD simulations of the uniaxial stress-strain curve of the plastically deformed region are carried out with the purpose of establishing a direct correlation between nanoscale material responses attaining under uniaxial and contact loading conditions. The results of this comparison illustrate on the key role played by defect nucleation processes on the formation of permanent nanoimprints, which differs from the conventional view in that in micro and macroscopic scales imprint formation is essentially governed by the evolutionary character of a preexisting (entangled) defect network: the greater the dislocation density, the larger the measured hardness. In overall, this work provides a fundamental insight into the understanding of why BCC surfaces are harder than FCC surfaces at the nanoscale.
A statistical physics background is devised to investigate the influence of the dislocation mechanisms on the onset of avalanche events that are inherent to crystal plasticity. The analysis is predicated upon the notion in that the size distribution of such avalanches follows power-law scaling. To investigate the avalanche size distributions in cubic crystals, a group of novel MD simulations are performed where the computational cells containing a periodic arrangement of a preexisting dislocation network are subjected to uniaxial straining under displacement control at different strain rates and temperatures. Under sufficiently slow driving, the dislocation networks evolve through the emission of dislocation avalanches which do not overlap in time. This illustrates that the mobilized entangled dislocation arrangements exhibit quiescent periods during each plastic (dissipative) event, enabling comparison with experimental results which are also performed under strict displacement controlled conditions. The results illustrate on the attainment of a transitional slip size separating two power-law avalanche regimes as a function of the fundamental dislocation glide processes at the crossroads of self-organized and tuned criticality models. Detailed analyses of the MD simulations furnish specific mechanisms characterizing dislocation avalanche emission and propagation in FCC and BCC metals throughout a wide temperature range, which is central in supporting the onset of the aforementioned two power-law regimes.<br>En este estudio se investigan los mecanismos fundamentales para el desarrollo de las densas redes de defectos que se producen durante la deformación plástica de metales mediante ensayos uniaxiales y de indentación en escalas nanométricas. Estos procesos de deformación plástica se caracterizan por la producción de eventos intermitentes o avalanchas de dislocaciones. La investigación se basa en un extenso grupo de simulaciones de dinámica molecular en las que se emplean potenciales interatómicos del tipo embedded-atom method en cristales cúbicos centrados en las caras (CCC) y cúbicos centrados en el cuerpo (CC). La primera parte de esta tesis discute el papel combinado de la elasticidad y plasticidad en los nanocontactos. Se presta una especial atención a los mecanismos que llevan a la formación de nanohuellas plásticas así como al desarrollo de apilamiento de material alrededor del nanocontacto. Se encuentra que los arreglos topográficos de trazas de deslizamiento (emitidas a la superficie) muestran patrones específicos de deformación, los cuales son a su vez un rasgo distintivo de los mecanismos de deslizamiento de dislocaciones y procesos de nanomaclado que ocurren en los materiales CCC y CC en función de la temperatura y la orientación de la superficie. Se presenta un estudio mecanístico sobre la influencia de los eventos de nucleación de defectos, que llevan al desarrollo de una compleja red de defectos, sobre la nanodureza y su convergencia hacia un valor relativamente constante a medida que el indentador penetra en la superficie La modelización del comportamiento uniaxial de la zona deformada debajo de las nanoindentaciones permite la correlación entre ambos tipos de ensayos. Los resultados de esta comparación ilustran el importante papel que juegan los procesos de nucleación de dislocaciones sobre la formación de nanohuellas plásticas, lo que difiere (en términos mecanísticos) del comportamiento plástico convencional encontrado en escales micro y macroscópicas, donde el carácter evolutivo de una red de defectos preexistente gobierna la formación de huella, cumpliéndose así que cuanto mayor es la densidad de defectos, mayores son también las macro y microdurezas. En general, este trabajo aporta un trasfondo fundamental para comprender la razón por la que las superficies CC son más duras que las CCC en la nano escala. En la última parte de esta investigación se utilizan modelos de física estadística para investigar la influencia de los mecanismos de propagación de dislocaciones sobre la emisión de avalanchas plásticas. El análisis se basa en la noción de que la distribución del tamaño de las avalanchas sigue una ley potencial universal. Para investigar esta distribución en cristales cúbicos, se realizan un grupo de simulaciones novedosas donde las celdas computaciones, que contienen arreglos periódicos de las redes de dislocaciones, son sometidas a cargas uniaxiales a diferentes temperaturas y velocidades de deformación. A velocidades de deformación suficientemente lentas, las redes de dislocaciones evolucionan a través de la emisión de avalanchas que no se sobreponen en el tiempo, lo que ilustra que la movilización de las redes ocurre de tal manera que se garantiza una alternancia entre periodos de inactividad y cada evento plástico. La comparación entre resultados experimentales y computacionales lleva a encontrar la existencia de una magnitud de deslizamiento crítico que separa a dos regímenes de avalanchas cuya distribución de tamaños obedece leyes potenciales. Este resultado demuestra que los procesos de avalanchas son claramente dependientes de los mecanismos de deslizamiento e interacción de dislocaciones presentes en el material; aspecto que describe la transición entre el modelo de criticalidad gobernada por la tensión y el de criticalidad auto-organizada. Las simulaciones muestran los mecanismos específicos que caracterizan la emisión y propagación de avalanchas en metales CC y CCC en un amplio rango de temperatura, lo que es de gran importancia para justificar la utilización de estos modelos de criticalidad.
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Lin, Peter Keng-Yu. "Evolution of grain boundary character distributions in FCC and BCC materials." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ27994.pdf.
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Sinclair, Chad. "Co-deformation of a two-phase FCC/BCC material /." *McMaster only, 2001.
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Douat, Benjamin. "Étude de surfaces sous contrainte à l'échelle atomique : application au cas du niobium." Thesis, Poitiers, 2018. http://www.theses.fr/2018POIT2274/document.
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Les mécanismes de déformation plastique des matériaux cubiques à corps centré sont étudiés depuis plus d’un demi-siècle. Il est maintenant bien établi que les dislocations vis contrôlent la plasticité de ces matériaux. Ceci est dû à une structure non-plane du cœur de ces dislocations, qui induit une forte friction de réseau communément appelée ‘pseudo-Peierls’. Le mécanisme supposé est la nucléation thermiquement activée de paires de décrochements. Cette structure de cœur particulière limite également les plans de glissement possibles. Les traces de glissement aux échelles méso et microscopiques apparaissent ‘ondulées’, ce qui a amené à proposer toute une variété de plans de glissement.Dans ce contexte, nous avons analysé à une échelle plus fine, i .e. à l’échelle atomique, les traces de glissement obtenues par déformation en compression de monocristaux de niobium à des températures situées dans le régime de température thermiquement activé: 293 K, 200 K et 90 K. L’analyse par microscopie à effet tunnel sous environnement ultra vide indique qu’à la résolution atomique chaque trace de glissement peut être décomposée en segments associés à des plans de type {112} et {110}. De manière surprenante, il est mis en évidence qu’à 293 K et 200 K du glissement se produit à la fois dans le sens maclage et antimaclage. De plus, toutes les traces de glissement impliquent du glissement sur des plans de type {110}, étayant ainsi la structure de cœur compact prévue par simulations atomistiques ab initio.L’étude in situ de la surface sous contrainte, à T = 293 K et 200 K, a aussi mis en évidence des réorganisations, voire des disparitions, de terrasses atomiques au voisinage de dislocations émergentes. Le calcul des forces d’interaction en élasticité linéaire isotrope montre que les dislocations proches de ces terrasses ne jouent pas de rôle prépondérant sur la position d’équilibre des terrasses. En revanche, celles-ci modifient localement le potentiel chimique de surface, favorisant la diffusion atomique à l’origine des réorganisations de surface constatées expérimentalement<br>The plastic deformation of body-centred cubic metals is the subject of extensive studies since more than half a century. It is now well established that the screw dislocations control the plasticity of these metallic metals. The reason for this is attributed to a non-planar configuration of the core of these dislocations, which induces a high friction force usually referred to as ‘pseudo-Peierls’. The underlying elementary mechanism is the thermally activated nucleation of kink pairs. While perfect screw dislocations do not have specific glide plane, the non-planar core configuration limits the number of possible slip planes. The slip traces observed at the meso and microscopic scales are wavy, which has leaded to the proposal of several possible slip planes.In this context, we propose an analysis at a finer scale, i.e. the atomic scale, of the slip traces produced by compressive stress on niobium single crystals at three temperatures in the thermally activated temperature regime, namely: 293 K, 200 K and 90 K. The analyses were carried out using a scanning tunnelling microscope under ultra-high vacuum environment. At this scale of observation, the slip traces are made up of crystallographic segments that can be associated with {011} and {112} planes. It is also noticeable that at 200 K and 293 K dislocation glide is observed in both the twinning and the anti-twinning directions. More importantly, all slip traces include segments that belong to {011} planes strongly supporting the latest ab initio atomistic simulations predicting a compact core configuration for screw dislocation.In this study, we also established that, at T = 293 K and 200 K, the sample surface may undergo drastic changes of its vicinal terraces, when they are close to emerging dislocations. The calculation of interaction forces, in the frame of isotropic linear elasticity, indicates that dislocations close to vicinal terraces do not play a major role regarding the stable positions of the vicinal terraces. However, they locally modify the chemical potential of the surface, thus enhancing atomic diffusion which is at the origin of the surface reorganisations experimentally observed
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Oloyede, Vincent Olayinka Adekunle. "Computational studies of materials under cyclic plasticity." Thesis, Imperial College London, 1986. http://hdl.handle.net/10044/1/38123.
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Kashinath, Abishek. "Helium behavior at fcc-bcc semicoherent interfaces: trapping, clustering, nucleation, and growth of cavities." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/88276.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2013.<br>This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.<br>Cataloged from student-submitted PDF version of thesis.<br>Includes bibliographical references (pages 153-171).<br>He implanted into metals precipitates into nanoscale bubbles that grow into voids, degrading the properties of engineering alloys in nuclear energy applications. In this thesis, multi-scale modeling techniques and neutron reflectometry measurements are used to study the He trapping, clustering and growth of clusters at fcc-bcc interfaces. Choosing Cu-Nb as a model fcc-bcc interface, a predictive Cu-Nb-He interatomic potential is constructed using density functional theory. These calculations show that two-body radial forces are sucient to describe interactions of He with fcc Cu and bcc Nb. Atomistic simulations reveal that He is initially trapped in the form of stable, sub-nanometer platelet-shaped clusters and not bubbles at the Cu-Nb interface. This behavior occurs due to the spatial heterogeneity of interface energy: He wets high energy, heliophilic regions while avoiding low energy, heliophobic ones. Using these insights, the maximum He concentration that can be stored without forming bubbles at any interface in terms of its location-dependent energy distribution may be predicted. The modeling predictions are validated by neutron reflectometry measurements, which show that interfacial He bubbles form only above a critical He concentration and provide evidence for the presence of stable He platelets below a critical He concentration. This work paves the way for the design of composite structural materials with increased resistance to He-induced degradation by tailoring the types of interfaces they contain.<br>by Abishek Kashinath.<br>Ph. D.
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Gilbert, Mark R. "BCC metals in extreme environments : modelling the structure and evolution of defects." Thesis, University of Oxford, 2010. http://ora.ox.ac.uk/objects/uuid:d972d28d-5d2d-4392-8cf5-fc5728dc74f6.
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Designing materials for fusion applications is a very challenging problem, requiring detailed understanding of the behaviour of materials under the kinds of extreme conditions expected in a fusion environment. During the lifetime of fusion-reactor components, materials will be subjected to high levels of neutron irradiation, but must still perform effectively at high operating temperatures and under significant loading conditions. Body-centred cubic (bcc) transition metals are some of the most promising candidates for structural materials in fusion because of their relatively high density, which allows for effective neutron-shielding with the minimum volume and mass of material. In this work we perform atomistic simulations on two of the most important of these, Fe and W. In this thesis we describe atomic-scale simulations of defects found in bcc systems. In part I we consider the vacancy and interstitial loop defects that are produced and accumulated as a result of irradiation-induced displacement cascades. We show that vacancy dislocation loops have a critical size below which they are highly unstable relative to planar void defects, and thus offer an explanation as to why they are so rarely seen in TEM observations of irradiated bcc metals. Additionally, we compare the diffusion rates of these vacancy loops to their interstitial counterparts and find that, while interstitial loops are more mobile, the difference in mobility is not as significant as might have been expected. In part II we study screw dislocations, which, as the rate limiting carriers of plastic deformation, are significantly responsible for the strength of materials. We present results from large-scale finite temperature molecular dynamics simulations of screw dislocations under stress and observe the thermally-activated kink-pair formation regime at low stress, which appears to be superseded by a frictional regime at higher stresses. The mobility functions fitted to the results are vital components in simulations of dislocation networks and other large-scale phenomena. Lastly, we develop a multi-string Frenkel-Kontorova model that allows us to study the core structure of screw dislocations. Subtle changes in the form of the interaction laws used in this model demonstrate the difference between the non-degenerate and degenerate core structures. We provide simple criteria to guarantee the correct structure when developing interatomic potentials for bcc metals.
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Escobedo, Juan Pablo. "Measurement of shear strength and texture evolution in BCC materials subjected to high pressures." Online access for everyone, 2007. http://www.dissertations.wsu.edu/Dissertations/Fall2007/j_escobedo_120507.pdf.
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Saad, Abdullah Aziz. "Cyclic plasticity and creep of power plant materials." Thesis, University of Nottingham, 2012. http://eprints.nottingham.ac.uk/12538/.
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The thermo-mechanical fatigue (TMF) of power plant components is caused by the cyclic operation of power plant due to startup and shutdown processes and due to the fluctuation of demand in daily operation. Thus, a time-dependent plasticity model is required in order to simulate the component response under cyclic thermo-mechanical loading. The overall aim behind this study is to develop a material constitutive model, which can predict the creep and cyclic loading behaviour at high temperature environment, based on the cyclic loading test data of the P91 and the P92 steels. The tests on all specimens in the study were performed using the Instron 8862 TMF machine system with a temperature uniformity of less than ±10°C within the gauge section of the specimen. For the isothermal tests on the P91 steel, fully-reversed, strain-controlled tests were conducted on a parent material of the steel at 400, 500 and 600˚C. For the P92 steel, the same loading parameters in the isothermal tests were performed on a parent material and a weld metal of the steels at 500, 600 and 675°C. Strain-controlled thermo-mechanical fatigue tests were conducted on the parent materials of the P91 and the P92 steels under temperature ranges of 400-600°C and 500-675°C, respectively, with in-phase (IP) and out-of-phase (OP) loading. In general, the steels exhibit cyclic softening behaviour throughout the cyclic test duration under both isothermal and anisothermal conditions. The cyclic softening behaviour of the P91 steel was further studied by analyzing stress-strain data at 600°C and by performing microstructural investigations. Scanning electron microscope (SEM) and transmission electron microscope (TEM) images were used to investigate microstructural evolution and the crack initiation of the steel at different life fractions of the tests. The TEM images of the interrupted test specimens revealed subgrain coarsening during the cyclic tests. On the other hand, the SEM images showed the initiation of microcracks at the end of the stabilisation period and the cracks were propagated in the third stage of cyclic softening. A unified, Chaboche, viscoplasticity model, which includes combined isotropic softening and kinematic hardening with a viscoplastic flow rule for time-dependent effects, was used to model the TMF behaviour of the steels The constants in the viscoplasticity model were initially determined from the first cycle stress-strain data, the maximum stress evolution during tests and the stress relaxation data. Then, the initial constants were optimized using a least-squares optimization algorithm in order to improve the general fit of the model to experimental data. The prediction of the model was further improved by including the linear nonlinear isotropic hardening in order to obtain better stress-strain behaviour in the stabilisation period. The developed viscoplasticity model was subsequently used in the finite element simulations using the ABAQUS software. The focus of the simulation is to validate the performance of the model under various types of loading. Simulation results have been compared with the isothermal test data with different strain ranges and also the anisothermal cyclic testing data, for both in-phase and out-of-phase loadings. The model’s performance under 3-dimensional stress conditions was investigated by testing and simulating the P91 steel using a notched specimen under stress-controlled conditions. The simulation results show a good comparison to the experimental data.
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Zamiri, Amir Reza. "Computationally efficient crystal plasticity models for polycrystalline materials." Diss., Connect to online resource - MSU authorized users, 2008.
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Belnoue, Jonathan Pierre-Henri. "Local-nonlocal coupled damage-plasticity modelling of ductile materials." Thesis, University of Oxford, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.540154.
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Martinez, Irene Suarez. "Theory of diffusion and plasticity in layered carbon materials." Thesis, University of Sussex, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.439023.
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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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Picallo, González Clara Beatriz. "A Mesoscopic Study of Plasticity and Fracture in Disordered Materials." Doctoral thesis, Universidad de Cantabria, 2010. http://hdl.handle.net/10803/10648.
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Understanding how materials deform and break is a subject of critical importance in industry. At the same time, it requires from the knowledge of the basic processes governing the phenomenon and hence, fundamental physics research is a must. The presence of power law distributions in both temporal and spatial properties and the universality of the behavior seem to suggest that fracture and plasticity could be explained as some type of critical phenomena. This means that there should be some general principles that rule the process and that are more important than a detailed description of the interactions and atomic structure of the media. Hence, simplified theoretical approaches based on fundamental concepts can help to capture the essential ingredients in the system. This Thesis is devoted to the study of the deformation and failure of materials in the presence of disorder with the help of statistical mechanics tools and models.
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Courte, Luca [Verfasser], and Patrick W. [Akademischer Betreuer] Dondl. "Scaling laws and emergent effects for plasticity in heterogeneous materials." Freiburg : Universität, 2021. http://d-nb.info/1237220939/34.
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Bystrický, Pavel. "Plasticity of metal matrix composites reinforced with continuous alumina fibers." Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/44488.
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Vadlakonda, Suman. "Indentation induced deformation in metallic materials." Thesis, University of North Texas, 2005. https://digital.library.unt.edu/ark:/67531/metadc4904/.
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Nanoindentation has brought in many features of research over the past decade. This novel technique is capable of producing insights into the small ranges of deformation. This special point has brought a lot of focus in understanding the deformation behavior under the indenter. Nickel, iron, tungsten and copper-niobium alloy system were considered for a surface deformation study. All the samples exhibited a spectrum of residual deformation. The change in behavior with indentation and the materials responses to deformation at low and high loads is addressed in this study. A study on indenter geometry, which has a huge influence on the contact area and subsequently the hardness and modulus value, has been attempted. Deformation mechanisms that govern the plastic flow in materials at low loads of indentation and their sensitivity to the rate of strain imparted has been studied. A transition to elastic, plastic kind of a tendency to an elasto-plastic tendency was seen with an increase in the strain rate. All samples exhibited the same kind of behavior and a special focus is drawn in comparing the FCC nickel with BCC tungsten and iron where the persistence of the elastic, plastic response was addressed. However there is no absolute reason for the inconsistencies in the mechanical properties observed in preliminary testing, more insights can be provided with advanced microscopy techniques where the study can be focused more to understand the deformation behavior under the indenter. These experiments demonstrate that there is a wealth of information in the initial stages of indentation and has led to much more insights into the incipient stages of plasticity.
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Zhu, Tingting. "Micrometre-scale plasticity size effects in metals and ceramics : theory and experiment." Thesis, Queen Mary, University of London, 2009. http://qmro.qmul.ac.uk/xmlui/handle/123456789/1648.
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This thesis comprises studies of size effects in the plasticity of metals and ceramics at length scales of the order of micrometres and includes both experimental work and theoretical development. Experimental results are presented for foil flexure (nickel and copper)and nanoindentation (ceramics and hard metals).These studies were conducted because existing data does not cover a range broad enough or with sufficient precision to test various theories. With the developed bending technique more accurate data is obtained covering a wide range of strain, especially around the key region of the elastic-plastic transition. Moreover, the interaction between grain and thickness size effect is successfully studied by varying the ratio of grain size over thickness of the foils. After carefully calibrating the indenters, the macroscopic indentation yield strength for ceramics and high strength metals is determined in a direct way by using spherical nanoindentation. The magnitude of size effect is significantly different between metals and ceramics. By comparing the Berkovich and spherical indentation size effect, the results implies that the contact size, a, is the most fundamental length scale in the indentation size effect, independent of the indenter shape. The indentation strength is found to be inversely scaled with the square root of a. The slip-distance theory (based on (Conrad et al, 1967)) with an effective length scale reconciling intrinsic and extrinsic size effects appears able to account for the size effects in all contexts, without requiring strain gradient plasticity theory or an implicit characteristic length.
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Hosseinzadeh, Delandar Arash. "Numerical Modeling of Plasticity in FCC Crystalline Materials Using Discrete Dislocation Dynamics." Licentiate thesis, KTH, Materialteknologi, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-175424.
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Plasticity in crystalline solids is controlled by the microscopic line defects known as “dislocations”. Decisive role of dislocations in crystal plasticity in addition to fundamentals of plastic deformation are presented in the current thesis work. Moreover, major features of numerical modeling method “Discrete Dislocation Dynamics (DDD)” technique are described to elucidate a powerful computational method used in simulation of crystal plasticity. First part of the work is focused on the investigation of strain rate effect on the dynamic deformation of crystalline solids. Single crystal copper is chosen as a model crystal and discrete dislocation dynamics method is used to perform numerical uniaxial tensile test on the single crystal at various high strain rates. Twenty four straight dislocations of mixed character are randomly distributed inside a model crystal with an edge length of 1 µm subjected to periodic boundary conditions. Loading of the model crystal with the considered initial dislocation microstructure at constant strain rates ranging from 103 to 105s1 leads to a significant strain rate sensitivity of the plastic flow. In addition to the flow stress, microstructure evolution of the sample crystal demonstrates a considerable strain rate dependency. Furthermore, strain rate affects the strain induce microstructure heterogeneity such that more heterogeneous microstructure emerges as strain rate increases. Anisotropic characteristic of plasticity in single crystals is investigated in the second part of the study. Copper single crystal is selected to perform numerical tensile tests on the model crystal along two different loading directions of [001] and [111] at two high strain rates. Effect of loading orientation on the macroscopic behavior along with microstructure evolution of the model crystal is examined using DDD method. Investigation of dynamic response of single crystal to the mechanical loading demonstrates a substantial effect of loading orientation on the flow stress. Furthermore, plastic anisotropy is observed in dislocation density evolution such that more dislocations are generated as straining direction of single crystal is changed from [001] to [111] axis. Likewise, strain induced microstructure heterogeneity displays the effect of loading direction such that more heterogeneous microstructure evolve as single crystal is loaded along [111] direction. Formation of slip bands and consequently localization of plastic deformation are detected as model crystal is loaded along both directions.<br><p>QC 20151015</p>
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Knezevic, Marko Kalidindi Surya. "A new spectral framework for crystal plasticity modeling of cubic and hexagonal /." Philadelphia, Pa. : Drexel University, 2009. http://hdl.handle.net/1860/3018.
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HASHMI, QUAZI SARWAR EHSAN. "NONASSOCIATIVE PLASTICITY MODEL FOR COHESIONLESS MATERIALS AND ITS IMPLEMENTATION IN SOIL-STRUCTURE INTERACTION." Diss., The University of Arizona, 1987. http://hdl.handle.net/10150/184024.
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A constitutive model based on rate-independent elastoplasticity concepts is developed and used to simulate the behavior of geologic materials under arbitrary three-dimensional stress paths. The model accounts for various factors such as friction, stress path and stress history that influence the behavior of geologic materials. A hierarchical approach is adopted whereby models of progressively increasing sophistication are developed from a basic isotropic-hardening associative model. Nonassociativeness is introduced as correction or perturbation to the basic model. Deviation of normality of the plastic strain increments to the yield surface F is captured through nonassociativeness. The plastic potential Q is obtained by applying a correction to F. This simplified approach restricts the number of extra parameters required to define the plastic potential Q. The material constants associated with the model are identified, and they are evaluated for three different sands (Leighton Buzzard, Munich and McCormick Ranch). The model is then verified by comparing predictions with laboratory tests from which the constants were found, and typical tests not used for finding the constants. The effect of varying initial density of a material on the stress-strain and volumetric response is investigated. An empirical relation is proposed, whereby one parameter is modified based on the initial density, such that improved predictions can be obtained without increasing the total number of parameters. Implementation of the nonassociative model in a finite element program to solve boundary value problems leads to a nonsymmetric stiffness matrix. Besides, using a nonsymmetric solver, three numerical schemes are investigated. The idea of the schemes is to modify the stiffness matrix such that a symmetric equation solver can be used. Prediction of stress-strain, volumetric response and CPU time for different schemes are compared with the predictions obtained using the nonsymmetric solver. The nonsymmetric equation solver used less CPU time and the solutions were more accurate. Based on the above findings, a soil-footing system is analyzed using the finite element techniques. The associative and nonassociative models are used to predict the behavior. For the nonassociative model, solution is obtained by using a nonsymmetric solver. Results obtained from both models are compared with a model footing test performed in the laboratory.
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Daniel, Robert David. "The influence of nitrogen on the plasticity of diamond." Thesis, University of Hull, 2000. http://hydra.hull.ac.uk/resources/hull:5900.
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The aim of this work has been to use the soft impressor technique to investigate the plastic deformation of single crystal diamond and in particular to determine the effect that single substitutional nitrogen has on plasticity. Traditionally hardness tests in the form of Vickers or Knoop rigid indenters have been used to investigate the mechanical properties of materials which cannot be fabricated into tensile or three point bend test specimens. The high stress concentrations created by these types of test introduce a large degree of brittle failure in ultra-hard, covalently bonded materials. The soft impressor technique, on the other hand, allows large pressures to be applied without large stress concentrations. The result is that plastic deformation can be more readily induced into super hard materials such as diamond. This work has shown that not only can diamond be readily plastically deformed but that traces of nitrogen impurities within the lattice have a significant effect on the conditions necessary to produce dislocations. For this work, several different soft impressors were used to produce a range of pressures in the temperature range 800° to 1400°C. A selection of synthetic (HPHT) diamonds with various nitrogen concentrations were impressed and compared with impressions placed in natural type IIa specimens containing no nitrogen but heavily dislocated. Numerous analytical techniques were used to determine the level of deformation produced and gain a better understanding of the effect of nitrogen related defects. The first two chapters of this thesis review, first plasticity and then diamond, with reference to those properties/characteristics relevant to this topic. The third chapter discusses the principle of the soft impressor technique and the methodologies used. In the fourth chapter, models by which single crystal diamond plastically deforms are introduced, together with results that have extended the brittle-ductile transition schematic produced by Brookes, EJ. (1992). Results on the effect of dwell time and the phenomenon of impression creep are also presented. The fifth chapter identifies the predominant defects associated with substitutional nitrogen in HPHT diamond and presents profiles of impressions for diamonds with different 'grown-in' defect levels. The results are discussed and conclusions are made, in conjunction with suggestions for further work in chapter 6.
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Thompson, Gregory B. "Predicting Polymorphic Phase Stability in Multilayered Thin Films." The Ohio State University, 2003. http://rave.ohiolink.edu/etdc/view?acc_num=osu1046469309.
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陳增源 and Chang-yuen Chan. "The initiation of catastrophic tensile instability in Niobium crystalsat 77K." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1995. http://hub.hku.hk/bib/B31234069.
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Chan, Chang-yuen. "The initiation of catastrophic tensile instability in Niobium crystals at 77K /." Hong Kong : University of Hong Kong, 1995. http://sunzi.lib.hku.hk/hkuto/record.jsp?B19668910.
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Bai, Jie. "A homogenization based continuum plasticity-damage model for ductile fracture of materials containing heterogeneities." Columbus, Ohio : Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1211910660.
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Osa, Aitor Arriaga. "Plasticity and impact test studies on thermoplastic materials, finite element analysis and experimental correlation." Thesis, London Metropolitan University, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.573377.
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The primary aim of the study was to evaluate the validity of the elasto-plastic constitutive models implemented in the Finite Element Analysis (FEA) software ANSYS~. This was carried out comparing experimental tensile, bending and puncture or plate penetration test results with the corresponding FEA calculations. The studies were carried out in concern to the slow rate testing and finite element analysis of two thermoplastic materials. The selected materials were a blend of Polycarbonate (PC) and Acrylonitrile-Butadiene-Styrene (ABS), Bavblend" T45 from Bayer Material Science, as an amorphous polymer and a Polypropylene (PP) copolymer, BE677AI from Borealis, as a semi-crystalline polymer. The uniaxial tensile behavior of both materials was used to generate material data input for the simulation software. Due to post yield uncertainties when measuring true values of stress and strain with conventional extensometric devices, an iterative approach was presented here as a solution for measuring large local plastic strains in tensile specimens. The experimental three point bend test and the plate perforation test with hemispherical darts, were used as correlation tests with simulations in order to validate not only the used constitutive elasto-plastic models based on the Von Mises yield criteria, but also to check the influence of different simulation variables. The parameters studied were the element type, mesh density, friction and contact conditions between different parts. Additionally, another yielding criteria, the hydrostatic pressure sensitive Drucker-Prager model, was analysed. It was observed that for both materials, the use of a classical approach for obtaining true values of stress and strain in conjunction with a Von Mises yielding criteria gave acceptable results for the studied testing modes. However, the input curves did not closely correlate with the tensile test results. This was overcome to using an iterative method to correct the input curves to match then to the experimental tensile tests. Being a precise procedure for uniaxial cases, it was observed that for bending or puncture problems this method offered stiffer responses than using the classical approach of stress-strain conversions. Finally, the Drucker-Prager criterion was able to capture in a more precise way bending dominated problems than the usual Von Mises yielding criteria.
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Bai, Jie. "A Homogenization based Continuum Plasticity-Damage Model for Ductile Frature of Materials Containing Heterogeneities." The Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1211910660.
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Mayeur, Jason R. "Generalized continuum modeling of scale-dependent crystalline plasticity." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/39635.
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The use of metallic material systems (e.g. pure metals, alloys, metal matrix composites) in a wide range of engineering applications from medical devices to electronic components to automobiles continues to motivate the development of improved constitutive models to meet increased performance demands while minimizing cost. Emerging technologies often incorporate materials in which the dominant microstructural features have characteristic dimensions reaching into the submicron and nanometer regime. Metals comprised of such fine microstructures often exhibit unique and size-dependent mechanical response, and classical approaches to constitutive model development at engineering (continuum) scales, being local in nature, are inadequate for describing such behavior. Therefore, traditional modeling frameworks must be augmented or reformulated to account for such phenomena. Crystal plasticity constitutive models have proven quite capable of capturing first-order microstructural effects such as grain orientation, grain morphology, phase distribution, etc. on the deformation behavior of both single and polycrystals, yet suffer from the same limitations as other local continuum theories with regard to modeling scale-dependent mechanical response. This research is focused on the development, numerical implementation, and application of a novel, physics-based generalized (nonlocal) theory of single crystal plasticity. Two distinct versions of a dislocation-based micropolar single crystal plasticity theory are developed and discussed within the context of more prominent nonlocal crystal plasticity theories. The constitutive models have been implemented in the commercial finite element code Abaqus, and the size-dependent deformation of both single and polycrystalline metals have been studied via direct numerical simulation. A comparison of results obtained from the solution of several equivalent initial-boundary value problems using the developed models and a model of discrete dislocation dynamics has demonstrated the predictive capabilities of the micropolar theory and also highlighted areas for potential model refinement.
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Kim, Hyun Sung. "Experimental and Numerical Analysis of Hydroformed Tubular Materials for Superconducting Radio Frequency (SRF) Cavities." The Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1462533811.
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Manchiraju, Sivom. "Modeling the Coupling Between Martensitic Phase Transformation and Plasticity in Shape Memory Alloys." The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1291993965.
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Ying, Siqi. "On the mesoscale plasticity of nickel-base superalloy single crystals." Thesis, University of Oxford, 2017. http://ora.ox.ac.uk/objects/uuid:9d636959-b59d-4e00-adf4-357b6b6c88af.
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Experimental micromechanics of materials is a branch of science that seeks to build tight connections between composition, structure, processing and performance of materials under specific operating conditions required for particular technology applications. The present project is focused on the development of techniques that use the combination of electron, ion and X-ray microscopies to study the deformation behaviour of a particularly important class of metallic alloys used in the manufacture of aeroengines, namely, the so-called Ni-base superalloys. The complex hierarchical structure of these materials means that their macroscopic response is controlled to a great extent by the phenomena that play out on very fine scales, from angstroms (lattice spacing dimension) to nanometres (precipitates, phase boundaries, dislocations, chemical inhomogeneities) to microns (grains and their boundaries, defects and their clusters, dislocation pileups) to millimetres (component scale). Understanding the fine structure and deformation behaviour requires the development of specially configured experimental setup that allow the observation and quantification of deformation to external loading. In this study, FIB-SEM methods for sample characterization and fabrication were combined with synchrotron-based X-ray diffraction and imaging techniques, and backed up by theoretical analysis and numerical simulation, to elucidate the origins of the strength of these alloys. Micropillar compression tests using in-SEM nanoindentation were used to reveal the size dependence of the apparent strength, and connection was made with the dislocation-mediated crystal slip to provide an explanation of the observed Hall-Petch type dependence with a modified Hall-Petch equation considering both intrinsic and extrinsic characteristic lengths introduced. X-ray scattering was used in the polychromatic micro-Laue mode and using Bragg coherent diffractive imaging to reveal the crystal distortion arising due to plastic deformation. A Discrete dislocation dynamics in the 2.5D formulation was used to obtain a model description of the observed phenomena. The key outcome of the work presented in this thesis lies in the successful development of advanced observational tools and relevant theoretical or computational models for mesoscale plasticity problems for crystal with complex microstructure.
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Rosić, Bojana [Verfasser], and Hermann [Akademischer Betreuer] Matthies. "Variational Formulations and Functional Approximation Algorithms in Stochastic Plasticity of Materials / Bojana Rosic ; Betreuer: Hermann Matthies." Braunschweig : Technische Universität Braunschweig, 2012. http://d-nb.info/1175822434/34.
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Kuzmenkov, Konstantin. "Etude de l'effet du temps de maintien sur le comportement et la rupture de l'alliage Ti-6242." Phd thesis, Ecole Nationale Supérieure des Mines de Paris, 2012. http://pastel.archives-ouvertes.fr/pastel-00745834.
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L'application d'un temps de maintien, même de faible durée, lors d'un chargement cyclique, modifie de façon très sensible à la fois le comportement contrainte-déformation et le nombre de cycles à amorçage dans l'alliage base titane TI-6242. Ceci est lié à un régime de fluage cyclique, conduisant à de la déformation progressive d'une part, et à une forte interaction fatigue-temps de maintien pour ce qui concerne le nombre de cycles à amorçage. Les différents phénomènes sont pour le moment assez mal analysés, si bien qu'il n'est pas possible d'effectuer une conception optimale des pièces, de larges marges de sécurité étant nécessaires. Le but du travail est de mieux comprendre les mécanismes locaux qui régissent le comportement et l'amorçage des fissures, dans le but de suggérer des microstructures optimales, et de calibrer des modèles macroscopiques utilisables en bureau d'études. En s'appuyant sur une base expérimentale fournie par Snecma et l'ENSMA, une approche multiéchelles a été mise en place pour représenter les hétérogénéités locales qui ont un rôle significatif sur les comportements observés. Dans les calculs des microstructures, faisant intervenir une étape d'évaluation statistique, on se focalise sur la représentation explicite des "plumes", grains de taille exceptionnelle, qui sont à l'origine des premières microfissures en raison du contraste cristallin qu'ils introduisent avec l'environnement. Une revue des différentes configurations de plumes, afin de retenir celles qui sont le plus critique, a été établie. Cette analyse a permis de mettre en évidence la présence de plumes simples, doubles ou triples, les domaines se présentant sous formes de bandes. Les configurations à étudier comportent comme paramètres critiques l'orientation géométrique de la bande par rapport à la direction du chargement macroscopique, mais surtout l'orientation cristallographique au sein de cette (ces) bande(s). Des calculs systématiques ont été effectués afin de mener une étude statistique et de déterminer les configurations les plus sensibles.
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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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Li, Lin. "A Quantized Crystal Plasticity Model for Nanocrystalline Metals: Connecting Atomistic Simulations and Physical Experiments." The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1299605340.
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Pradeau, Adrien. "Anisotropic behaviour and fracture for sheet metals under associated and non-associated flow plasticity." Thesis, Lorient, 2018. http://www.theses.fr/2018LORIS507/document.
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La motivation principale de cette thèse est d’être capable de prédire précisément la rupture d’une tôle d’aluminium anisotrope avec un chemin de déformation linéaire et non-linéaire. Dans le cas présent, le matériau utilisé est l’AA6016 et le chemin de déformation considéré est traction uniaxiale suivie de pliage jusqu’à rupture. Deux approches sont appliquées et comparées, l’une utilise la plasticité associée (AFR) et l’autre la plasticité non-associée (NAFR). Dans le but d’obtenir une bonne représentation de l’anisotropie en AFR, un critère de plasticité très flexible est utilisé : Yld2004-18p. L’identification des paramètres est faite avec une approche inverse qui consiste à minimiser itérativement l’écart entre les résultats numériques et expérimentaux. Une fois que l’écart arrête d’évoluer (minimum local) ou atteint une valeur prédéterminé e assez faible, l’optimisation s’arrête et les derniers paramètres mis à jour sont enregistrés. En corrélation avec des travaux de recherche plus récents, un modèle NAFR est utilisé pour modéliser l’anisotropie du matériau. Il combine deux critères de plasticité qui sont utilisés pour la surface d’écrouissage et le potentiel plastique. Leurs paramètres sont identifiés grâce aux ratios de contraintes et aux valeurs r obtenues expérimentalement. Concernant la rupture, des modèles découplés macroscopiques sont étudiés : un critère Hosford-Coulomb modifié et un critère basé sur DF2014. Ces deux critères prennent en compte les trois invariants du tenseur des contraintes pour prédire la déformation équivalente à rupture mais sont identifiés avec différentes méthodes pour prendre en compte l’anisotropie de la rupture. Enfin, des résultats sur des instabilités plastiques obtenus avec un modèle NAFR sont présentés dans le but de prouver les possibilités de cette approche comparée à une approche AFR<br>The main motivation of this thesis is to be able to predict accurately the fracture of an anisotropic aluminium alloy thin sheet under linear and non-linear strain paths. In the studied case, the material used is the AA6016 and the non-linear strain path considered is uniaxial tension followed by free bending until fracture. Two approaches are considered and compared which respectively use the associated flow rule (AFR) and the non-associated flow rule (NAFR). In order to obtain a good representation of the high anisotropy of the material in AFR, a very flexible yield criterion is used: Yld2004-18p. The identification of its parameters is done with an inverse approach consisting of iteratively minimizing the gap between numerical and experimental results. Once this gap stops evolving (local minimum) or reaches a low enough pre-determined value, the optimization stops and the last updated parameters are saved. In correlation with more recent research work, a NAFR model is used to model the anisotropy of the material. It combines two different yield functions that are used for the yield surface and the plastic potential. Their parameters are identified by using stress ratios and rvalues measured experimentally. Concerning the fracture, uncoupled macroscopic models are studied: a modified Hosford-Coulomb and a DF2014 based criteria. Both these criteria take into account the three invariants of the stress tensor to predict the equivalent strain to fracture but their parameters are identified with different methods to take into account the anisotropy of the fracture. Finally, results on plastic instabilities obtained with a NAFR model are presented in order to prove the possibilities of this approach compared to AFR
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Kiwanuka, Robert. "Micro-deformation and texture in engineering materials." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:3c924d01-7501-4d59-bb53-07e6584e50c5.
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This DPhil project is set in the context of single crystal elasticity-plasticity finite element modelling. Its core objective was to develop and implement a methodology for predicting the evolution of texture in single and dual-phase material systems. This core objective has been successfully achieved. Modelling texture evolution entails essentially modelling large deformations (as accurately as possible) and taking account of the deformation mechanisms that cause texture to change. The most important deformation mechanisms are slip and twinning. Slip has been modelled in this project and care has been taken to explore conditions where it is the dominant deformation mechanism for the materials studied. Modelling slip demands that one also models dislocations since slip is assumed to occur by the movement of dislocations. In this project a model for geometrically necessary dislocations has been developed and validated against experimental measurements. A texture homogenisation technique which relies on interpretation of EBSD data in order to allocate orientation frequencies based on representative area fractions has been developed. This has been coupled with a polycrystal plasticity RVE framework allowing for arbitrarily sized RVEs and corresponding allocation of crystallographic orientation. This has enabled input of experimentally measured initial textures into the CPFE model allowing for comparison of predictions against measured post-deformation textures, with good agreement obtained. The effect of texture on polycrystal physical properties has also been studied. It has been confirmed that texture indeed has a significant role in determining the average physical properties of a polycrystal. The thesis contributes to the following areas of micro-mechanics materials research: (i) 3D small deformation crystal plasticity finite element (CPFE) modelling, (ii) geometrically necessary dislocation modelling, (iii) 3D large deformation CPFE modelling, (iv) texture homogenisation methods, (v) single and dual phase texture evolution modelling, (vi) prediction of polycrystal physical properties, (vii) systematic calibration of the power law for slip based on experimental data, and (viii) texture analysis software development (pole figures and Kearns factors).
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Stone, Tonya Williams. "Multiscale friction using a nested internal state variable model for particulate materials." Diss., Mississippi State : Mississippi State University, 2009. http://library.msstate.edu/etd/show.asp?etd=etd-12172008-002750.
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Zhai, Jinyuan. "Modeling Ductile Damage of Metallic Materials." University of Akron / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=akron1466471348.
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McKellar, Dougan Kelk. "A dislocation model of plasticity with particular application to fatigue crack closure." Thesis, University of Oxford, 2001. http://ora.ox.ac.uk/objects/uuid:45183b90-017f-4ac1-9550-94772a0ca88b.
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The ability to predict fatigue crack growth rates is essential in safety critical systems. The discovery of fatigue crack closure in 1970 caused a flourish of research in attempts to simulate this behaviour, which crucially affects crack growth rates. Historically, crack tip plasticity models have been based on one-dimensional rays of plasticity emanating from the crack tip, either co-linear with the crack (for the case of plane stress), or at a chosen angle in the plane of analysis (for plane strain). In this thesis, one such model for plane stress, developed to predict fatigue crack closure, has been refined. It is applied to a study of the relationship between the apparent stress intensity range (easily calculated using linear elastic fracture mechanics), and the true stress intensity range, which includes the effects of plasticity induced fatigue crack closure. Results are presented for all load cases for a finite crack in an infinite plane, and a method is demonstrated which allows the calculation of the true stress intensity range for a growing crack, based only on the apparent stress intensity range for a static crack. Although the yield criterion is satisfied along the plastic ray, these one-dimensional plasticity models violate the yield criterion in the area immediately surrounding the plasticity ray. An area plasticity model is therefore required in order to model the plasticity more accurately. This thesis develops such a model by distributing dislocations over an area. Use of the model reveals that current methods for incremental plasticity algorithms using distributed dislocations produce an over-constrained system, due to misleading assumptions concerning the normality condition. A method is presented which allows the system an extra degree of freedom; this requires the introduction of a parameter, derived using the Prandtl-Reuss flow rule, which relates the magnitude of slip on complementary shear planes. The method is applied to two problems, confirming its validity.
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Boger, Richard K. Jr. "Non-monotonic strain hardening and its constitutive representation." The Ohio State University, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=osu1138979144.
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Zhao, Jingyi Zhao. "Relating Grain Boundaries to the Mechanical Properties of Polycrystalline Material: Gradient Nanocrystalline Material and Electro-Plasticity." University of Akron / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=akron153296020243128.
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Weber, Martin [Verfasser], and Holm [Gutachter] Altenbach. "Material plasticity : evolution of the stiffness tetrad in fiber materials with large plastic strain / Martin Weber ; Gutachter: Holm Altenbach." Magdeburg : Universitätsbibliothek Otto-von-Guericke-Universität, 2020. http://d-nb.info/1226932037/34.
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