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1
Thompson, Robert Peter. "Plastic deformation in complex crystal structures." Thesis, University of Cambridge, 2019. https://www.repository.cam.ac.uk/handle/1810/286335.
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Many materials with complex crystal structures have attractive properties, including high specific strength, good creep resistance, oxidation resistance, often through high silicon or aluminium content. This makes them of interest for high temperature structural applications, but the use of many such phases is limited by low toughness. Even outside structural applications, brittle failure is a primary cause of failure in coatings and device materials and, therefore, improved toughness is desirable. In complex crystals plasticity, and hence toughness, is limited by the energy increases that occur as linear defects, dislocations, move. This is known as the lattice resistance. By understanding the factors controlling the lattice resistance in complex crystal structures, it is hoped that a general method for tailoring the flow stress of a material might be found. Present ductile-brittle criteria are based on simple ratios of polycrystalline elastic constants and are too limited to accurately capture flow behaviour. There are complex materials which, despite such criteria predicting brittle behaviour, exhibit low flow stresses, though on a limited number of slip systems: MAX phases, Mo$_2$BC, Nb$_2$Co$_7$ and Ta$_4$C$_{3-x}$ are examples of this. Where plastic flow is limited by the lattice resistance we must consider the effect of crystal structure on dislocation motion more directly. Aspects which are lost by considering bulk polycrystalline properties are elastic heterogeneity, elastic anisotropy and contributions to the energy changes by other interactions, such as electrostatic interactions. In this work examples of each of these are presented and modelled using an adapted version of the Peierls model. A Peierls model generalised to use the entire stiffness tensor has been implemented in Python; this allows the investigation of the effect of varying anisotropy on the yield stress of materials that would not be picked up by the use of polycrystalline elastic constants. Calculations using the changing elastic tensor during hydrogen loading of cementite suggest that hydrogen loading causes a dramatic reduction in the flow stress, consistent with experiments and associated with hydrogen embrittlement of steel. Materials for which empirical potentials can provide more insight than linear elasticity are explored with the example of ionic materials. This is done with a Peierls dislocation configuration and a molecular statics energy calculation. A simple model built electrostatic and Lennard-Jones interactions was used for the rocksalt structure, this model was found to describe the hard slip system well, but was insufficient to describe the softer slip system. Local heterogeneity in elastic properties is explored in the MAX phases where local variation in chemical environment, characterised by electronegativity, produces pronounced variation in the local stiffness within the unit cell. These local variations have been modelled with density functional theory and have been shown to be consistent with the macroscopic elastic properties while also explaining the apparent scatter in the elastic properties. These non-uniform strains are shown to have a dramatic effect on the flow stress of the MAX phases. The face-centred cubic Ti$_2$Ni structure has been used to experimentally demonstrate this effect of heterogeneity softening. The slip system was characterised by micropillar compression and the slip planes were found to be the {1 1 1} planes. The hardness of a range of alloys with the Ti$_2$Ni structure was characterised by nanoindentation of the {1 1 1} faces of single crystals. The hardness was found to decrease as the chemical, and thus elastic, heterogeneity of the unit cell increased, as expected. This effect of heterogeneity softening presents a potential route to tailoring the yield stress of crystals.
2
Cumbest, Randolph J. "Crystal-plastic deformation and chemical evolution of clinoamphibole." Diss., Virginia Polytechnic Institute and State University, 1988. http://hdl.handle.net/10919/54322.
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Clinoamphibole from a mylonitic amphibolite, located on Senja, Norway, exhibits microstructures characteristic of dynamic recrystallization, including larger host grains in a finer grained matrix of needle shaped amphibole. The matrix amphibole defines an LS fabric and host grains have core and mantle structures with a core containing undulose to patchy extinction and (100) deformation twinning surrounded by a mantle of recrystallized grains. In addition intragranular grains also occur within the cores.
TEM analysis of the host grains revealed high densities of dislocations, dislocation arrays/subgrain boundaries parallel to (hk0), stacking faults, and (100) deformation micro-twins. Dark field, weak beam images show that the dislocations are commonly dissociated. Diffraction contrast experiments compared with computer simulation of dislocation images indicate the primary unit Burgers vector is [001]. This information in conjunction with trace analysis of glide loops and dislocation line direction shows that the following glide systems were operative: [001]{110}, [001](100), and possibly [001](010), in order of relative occurrence. These data along with dislocation energies are considered in order to propose a possible model for the [001] unit Burgers vector in the clinoamphibole structure. TEM also showed that matrix grains and intragranular grains have relatively low defect densities, and that the intergranular new grains occur at localities in the host grains characterized by high densities of dislocations. These observations along with the chemical and orientation relationships between the recrystallized grains and their host indicate that the new grains may have formed by heterogeneous nucleation and that further growth probably occurred by both strain assisted and chemically induced grain boundary migration or liquid film migration. This recrystallization event is interpreted to be synkinematic based on the fact that no recrystallization textures are present in the matrix grains and that the matrix grains define an LS fabric. However, the low defect densities in the matrix grains and the lack of intracrystalline strain in other phases indicate that post-kinematic recovery processes were active.Ph. D.
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Sherry, A. H. "The deformation and fracture of a single crystal superalloy." Thesis, University of Manchester, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.384116.
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Hillier, Graham Stewart. "The defect energies and deformation mechanisms of single crystal superalloys." Thesis, University of Cambridge, 1985. https://www.repository.cam.ac.uk/handle/1810/221896.
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Chen, Tzung-Ming. "Synthesis of compliant single crystal silicon mechanisms with large deformation." Tönning Lübeck Marburg Der Andere Verl, 2009. http://d-nb.info/995862664/04.
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Rowell, D. K. "Point defect calculations in ionic crystals." Thesis, University of Reading, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.370129.
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Milligan, Walter W. Jr. "Yielding and deformation behavior of the single crystal superalloy PWA 1480." Thesis, Georgia Institute of Technology, 1986. http://hdl.handle.net/1853/20152.
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Liang, Hong. "Crystal plasticity modelling of lengthscale effects in deformation and nano-indentation." Thesis, University of Oxford, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.496995.
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Westbrooke, Eboni F. "Effect of crystallographic orientation on plastic deformation of single crystal nickel-base superalloys." [Gainesville, Fla.] : University of Florida, 2005. http://purl.fcla.edu/fcla/etd/UFE0011466.
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Chaloupka, Ondrej. "Modelling evolution of anisotropy in metals using crystal plasticity." Thesis, Cranfield University, 2013. http://dspace.lib.cranfield.ac.uk/handle/1826/8435.
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Many metals used in modern engineering exhibit anisotropy. A common
assumption when modelling anisotropic metals is that the level of anisotropy is
fixed throughout the calculation. As it is well understood that processes such as
cold rolling, forging or shock loading change the level of anisotropy, it is clear
that this assumption is not accurate when dealing with large deformations.
The aim of this project was to develop a tool capable to predict large
deformations of a single crystal or crystalline aggregate of a metal of interest
and able to trace an evolution of anisotropy within the material.
The outcome of this project is a verified computational tool capable of predicting
large deformations in metals. This computational tool is built on the Crystal
Plasticity Finite Element Method (CPFEM). The CPFEM in this project is an
implementation of an existing constitutive model, based on the crystal plasticity
theory (the single crystal strength model), into the framework of the FEA
software DYNA3D® .
Accuracy of the new tool was validated for a large deformation of a single
crystal of an annealed OFHC copper at room temperature. The implementation
was also tested for a large deformation of a polycrystalline aggregate comprised
of 512 crystals of an annealed anisotropic OFHC copper in a uniaxial
compression and tension test. Here sufficient agreement with the experimental
data was not achieved and further investigation was proposed in order to find
out the cause of the discrepancy. Moreover, the behaviour of anisotropic metals
during a large deformation was modelled and it was demonstrated that this tool
is able to trace the evolution of anisotropy.
The main benefit of having this computational tool lies in virtual material testing.
This testing has the advantage over experiments in time and cost expenses.
This tool and its future improvements, which were proposed, will allow studying
evolution of anisotropy in FCC and BCC materials during dynamic finite
deformations, which can lead to current material models improvement.
11
Vempati, Vamsi Krishna. "Texture Evolution In Materials With Layered Crystal Structures." Wright State University / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=wright1621942851365157.
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Thistlethwaite, T. "Crystal deformation and structure of oriented poly(ethylene terephthalate), poly(pentamethylene terephthalate) and polyethylene." Thesis, University of Leeds, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.355475.
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Han, Songlin. "High temperature deformation modelling and finite element implementation for single crystal turbine blade materials." Thesis, University of Bristol, 2000. http://hdl.handle.net/1983/943aaa75-6406-4a06-9250-9b0ae85a5eae.
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Wu, Xianping Kalidindi Surya Doherty R. D. "Prediction of crystallographic texture evolution and anisotropic stress-strain response during large plastic deformation in alpha-titanium alloys /." Philadelphia, Pa. : Drexel University, 2006. http://hdl.handle.net/1860/1122.
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Husser, Edgar [Verfasser], and Swantje [Akademischer Betreuer] Bargmann. "Micromechanical modeling of size-dependent crystal plasticity and deformation twinning / Edgar Husser ; Betreuer: Swantje Bargmann." Hamburg : Universitätsbibliothek der Technischen Universität Hamburg-Harburg, 2019. http://d-nb.info/1193575192/34.
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Karamched, Phani Shashanka. "Deformation studies near hard particles in a superalloy." Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:e740592d-8d82-4c12-9bfe-99901d132b60.
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Superalloys have performed well as blade and disc materials in turbine engines due to their exceptional elevated temperature strength, high resistance to creep, oxidation and corrosion as well as good fracture toughness. This study explores the use of a relatively new technique of strain measurement, high resolution electron backscatter diffraction (HR-EBSD) to measure local deformation fields. The heart of the HR-EBSD technique lies in comparing regions in EBSD patterns from a strained region of a sample to those in a pattern from an unstrained region. This method was applied to study the elastic strain fields and geometrically necessary dislocation density (GND density) distribution near hard carbide particles in a nickel-based superalloy MAR-M-002. Significant thermal strains were initially induced by thermal treatment, which included a final cooling from the ageing temperature of 870°C. Elastic strains were consistent with a compressive radial strain and tensile hoop strain that was expected as the matrix contracts around the carbide. The mismatch in thermal expansion coefficient of the carbide particles compared to that of the matrix was sufficient to have induced localized plastic deformation in the matrix leading to a GND density of 3 x 1013 m–2 in regions around the carbide. These measured elastic strain and GND densities have been used to help develop a crystal plasticity finite element model in another research group and some comparisons under thermal loading have also been examined. Three-point bending was then used to impose strain levels within the range ±12% across the height of a bend bar sample. GND measurements were then made at both carbide-containing and carbide-free regions at different heights across the bar. The average GND density increases with the magnitude of the imposed strain (both in tension and compression), and is markedly higher near the carbide particles. The higher GND densities near the carbides (order of 1014 per m2) are generated by the large strain gradients produced around the plastically rigid inclusion during monotonic mechanical deformation with some minor contribution from the pre-existing residual deformation from thermal loading. A method was developed of combining the local EBSD measurements with FE modelling to set the average residual strains within the mapped region even when a good strain free reference point was unavailable. Cyclic loading was then performed under four point loading to impose strain levels of about ±8% across the height of bend bar samples. Similar measurements as in the case of monotonic deformation were made at several interruptions to fatigue loading. Observations from the cyclic loading such as slip features, carbide cracking, GND density accumulation have been explored around carbide particles, at regions away from them and near a grain boundary.
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Zhou, Ning. "Simulation Study Of Directional Coarsening (Rafting) Of γ' In Single Crystal Ni-Al." The Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1228152557.
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Al-Harbi, Hamad F. "Crystal plasticity finite element simulations using discrete Fourier transforms." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/51788.
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Crystallographic texture and its evolution are known to be major sources of anisotropy in polycrystalline metals. Highly simplified phenomenological models cannot usually provide reliable predictions of the materials anisotropy under complex deformation paths, and lack the fidelity needed to optimize the microstructure and mechanical properties during the production process. On the other hand, physics-based models such as crystal plasticity theories have demonstrated remarkable success in predicting the anisotropic mechanical response in polycrystalline metals and the evolution of underlying texture in finite plastic deformation. However, the integration of crystal plasticity models with finite element (FE) simulations tools (called CPFEM) is extremely computationally expensive, and has not been adopted broadly by the advanced materials development community. The current dissertation has mainly focused on addressing the challenges associated with integrating the recently developed spectral database approach with a commercial FE tool to permit computationally efficient simulations of heterogeneous deformations using crystal plasticity theories. More specifically, the spectral database approach to crystal plasticity solutions was successfully integrated with the implicit version of the FE package ABAQUS through a user materials subroutine, UMAT, to conduct more efficient CPFEM simulations on both fcc and bcc polycrystalline materials. It is observed that implementing the crystal plasticity spectral database in a FE code produced excellent predictions similar to the classical CPFEM, but at a significantly faster computational speed. Furthermore, an important application of the CPFEM for the extraction of crystal level plasticity parameters in multiphase materials has been demonstrated in this dissertation. More specifically, CPFEM along with a recently developed data analysis approach for spherical nanoindentation and Orientation Imaging Microscopy (OIM) have been used to extract the critical resolved shear stress of the ferrite phase in dual phase steels. This new methodology offers a novel efficient tool for the extraction of crystal level hardening parameters in any single or multiphase materials.
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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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Shyue, Jein. "The effects of alloying on the crystal structure and plastic deformation of the intermetallic compound Nb?Al /." The Ohio State University, 1992. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487779439844711.
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Shepherd, James Ellison. "Multiscale Modeling of the Deformation of Semi-Crystalline Polymers." Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/10479.
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The mechanical and physical properties of polymers are determined primarily by the underlying nano-scale structures and characteristics such as entanglements, crystallites, and molecular orientation. These structures evolve in complex manners during the processing of polymers into useful articles. Limitations of available and foreseeable computational capabilities prevent the direct determination of macroscopic properties directly from atomistic computations. As a result, computational tools and methods to bridge the length and time scale gaps between atomistic and continuum models are required. In this research, an internal state variable continuum model has been developed whose internal state variables (ISVs) and evolution equations are related to the nano-scale structures. Specifically, the ISVs represent entanglement number density, crystal number density, percent crystallinity, and crystalline and amorphous orientation distributions. Atomistic models and methods have been developed to investigate these structures, particularly the evolution of entanglements during thermo-mechanical deformations. A new method has been created to generate atomistic initial conformations of the polymer systems to be studied. The use of the hyperdynamics method to accelerate molecular dynamics simulations was found to not be able to investigate processes orders of magnitude slower that are typically measurable with traditional molecular dynamics simulations of polymer systems. Molecular dynamics simulations were performed on these polymer systems to determine the evolution of entanglements during uniaxial deformation at various strain rates, temperatures, and molecular weights. Two methods were evaluated. In the first method, the forces between bonded atoms along the backbone are used to qualitatively determine entanglement density. The second method utilizes rubber elasticity theory to quantitatively determine entanglement evolution. The results of the second method are used to gain a clearer understanding of the mechanisms involved to enhance the physical basis of the evolution equations in the continuum model and to derive the models material parameters. The end result is a continuum model that incorporates the atomistic structure and behavior of the polymer and accurately represents experimental evidence of mechanical behavior and the evolution of crystallinity and orientation.
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Jensen, Katharine Estelle. "Structure and Defects of Hard-Sphere Colloidal Crystals and Glasses." Thesis, Harvard University, 2013. http://dissertations.umi.com/gsas.harvard:11052.
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Colloidal particles provide convenient and useful building blocks for creating ordered and disordered structures with length scales on the order of a micrometer. These structures are useful materials in their own right, and also serve as excellent scale models for exploring properties of atomic materials that would otherwise be inaccessible to direct experiment. In this dissertation, we explore structure formation in hard-sphere colloidal systems using templated sedimentation techniques, and then use colloidal crystals and glasses formed in this way to study the development of extended defects in single crystals and shear defects in glasses. We find that it is possible to form large, defect-free colloidal single crystals extremely rapidly by centrifugation onto a deterministic template. On non-deterministic templates, we find a critical deposition flux above which the material always crosses over to forming a glass. With this understanding of the effects of template and deposition flux, we designed and tested amorphous templates that allow us to make colloidal glasses by sedimentation under gravity, as well as more complex structures. In face-centered cubic colloidal single crystals grown on (100) templates, extended defects (dislocations and stacking faults) can nucleate and grow if the crystal exceeds a critical thickness that depends on the lattice misfit with the template spacing. We account for the experimental observations of the density of misfit dislocations using the Frank-van der Merwe theory, adapted for the depth-dependent variation of lattice spacing and elastic constants that results from the gravitational pressure. In the second part of the thesis, we report the first results of a detailed study of reversible and irreversible deformation of colloidal glasses. We show that shear defects exist and are active in both sheared and quiescent colloidal glasses and that these defects behave as Eshelby inclusions. We observe a decrease in the shear modulus of the glass, which corresponds to a small dilatation, which, in turn, lowers the activation barrier for shear.Physics
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Ilin, Dmitrii. "Simulation of hydrogen diffusion in fcc polycrystals. Effect of deformation and grain boundaries : effect of deformation and grain boundaries." Thesis, Bordeaux, 2014. http://www.theses.fr/2014BORD0157/document.
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Une approche couplée prenant en compte l’interaction de la plasticité cristalline et de la diffusion d’hydrogène a été établie et utilisée pour étudier le transport de l’hydrogène dans les agrégats polycristallins synthétiques de l’acier 316L avec des géométries de grains and des orientations cristallographiques différentes. Les champs mécaniques calculés à l’aide du code ZeBuLoN sont transférés dans un code de diffusion développé dans le cadre de ce travail. Une nouvelle formulation associée à un nouveau schéma numérique permet un calcul qui présente une bonne convergence. Les résultats des simulations montrent la redistribution de l’hydrogène dans les polycristaux due à la présence des hétérogénéités des contraintes hydrostatiques à l’échelle intragranulaire. L’effet de la vitesse de déformation a été quantitativement obtenu. Afin d’enrichir l’approche continue, un intérêt particulier est porté sur le rôle des joints de grains. Des simulations numériques d’un modèle atomique plan par plan ont été développées et appliquées aux bicristaux et aux structures de type ”bambou”. Les effets de puits ou de barrière induits par la présence des joints de grains sont clairement démontrés dans le cas du nickel pur. Pour reproduire ces effets dans les simulations de diffusion avec le modèle continue, une approche originale de simulation”multi-échelles” de la diffusion au joint de grain a été développée, et un nouveau régime de diffusion au joint de grain a été modéliséIn the present work, we establish a one-way coupled crystal plasticity – hydrogen diffusion analysis and use this approach to study the hydrogen transport in artificial polycrystalline aggregates of 316L steel with different grain geometries and crystallographic orientation. The data about stress/strain fields computed at the microstructure scaleutilizing the crystal plasticity concept are transferred to the in-house diffusion code which was developed using a new numerical scheme for solving parabolic equations. In the case of initial uniform hydrogen content, the heterogeneity of the mechanical fields is shownto induce a redistribution of hydrogen in the microstructure. The effect of strain rate is clearly revealed. In the second part, hydrogen transport across grain boundaries is investigatedconsidering the specific diffusivity and segregation properties of these interfaces. Using a discrete atomic layer model, the retarding impact of grain boundaries is demonstrated on bicrystals and bamboo type membranes with and without external mechanical loading. To reproduce the effects observed in the atomistic simulations into the crystal plasticity – hydrogen diffusion model, a new physically based multi-scale method is proposed. Using this new approach we study the effect of grain boundary trapping kinetics on hydrogen diffusion and reveal a new grain boundary diffusion regime which has notbeen reported before
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CUNHA, CECILIO A. da. "Desenvolvimento de revestimentos nanostruturados de Crsub(2)Crsub(2)-25(Ni20Cr)." reponame:Repositório Institucional do IPEN, 2012. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10125.
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Made available in DSpace on 2014-10-09T12:35:01Z (GMT). No. of bitstreams: 0Made available in DSpace on 2014-10-09T14:00:02Z (GMT). No. of bitstreams: 0
Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
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Bönisch, Matthias. "Structural properties, deformation behavior and thermal stability of martensitic Ti-Nb alloys." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-207914.
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Ti-Nb alloys are characterized by a diverse metallurgy which allows obtaining a wide palette of microstructural configurations and physical properties via careful selection of chemical composition, heat treatment and mechanical processing routes. The present work aims to expand the current state of knowledge about martensite forming Ti-Nb alloys by studying 15 binary Ti-c_{Nb}Nb (9wt.% ≤ c_{Nb} ≤ 44.5wt.%) alloy formulations in terms of their structural and mechanical properties, as well as their thermal stability. The crystal structures of the martensitic phases, α´ and α´´, and the influence of the Nb content on the lattice (Bain) strain and on the volume change related to the β → α´/α´´ martensitic transformations are analyzed on the basis of Rietveld-refinements. The magnitude of the shuffle component of the β → α´/α´´ martensitic transformations is quantified in relation to the chemical composition. The largest transformation lattice strains are operative in Nb-lean alloys. Depending on the composition, both a volume dilatation and contraction are encountered and the volume change may influence whether hexagonal martensite α´ or orthorhombic martensite α´´ forms from β upon quenching. The mechanical properties and the deformation behavior of martensitic Ti-Nb alloys are studied by complementary methods including monotonic and cyclic uniaxial compression, nanoindentation, microhardness and impulse excitation technique. The results show that the Nb content strongly influences the mechanical properties of martensitic Ti-Nb alloys. The elastic moduli, hardness and strength are minimal in the vicinity of the limiting compositions bounding the interval in which orthorhombic martensite α´´ forms by quenching. Uniaxial cyclic compressive testing demonstrates that the elastic properties of strained samples are different than those of unstrained ones. Also, experimental evidence indicates a deformation-induced martensite to austenite (α´´ → β) conversion. The influence of Nb content on the thermal stability and on the occurrence of decomposition reactions in martensitic Ti-Nb alloys is examined by isochronal differential scanning calorimetry, dilatometry and in-situ synchrotron X-ray diffraction complemented by transmission electron microscopy. The thermal decomposition and transformation behavior exhibits various phase transformation sequences during heating into the β-phase field in dependence of composition. Eventually, the transformation temperatures, interval, hysteresis and heat of the β ↔ α´´ martensitic transformation are investigated in relation to the Nb content. The results obtained in this study are useful for the development and optimization of β-stabilized Ti-based alloys for structural, Ni-free shape memory and/or superelastic, as well as for biomedical applicationsTi-Nb Legierungen zeichnen sich durch eine vielfältige Metallurgie aus, die es nach sorgfältiger Auswahl der chemischen Zusammensetzung sowie der thermischen und mechanischen Prozessierungsroute ermöglicht eine große Bandbreite mikrostruktureller Konfigurationen und physikalischer Eigenschaften zu erhalten. Das Ziel der vorliegenden Arbeit ist es den gegenwärtigen Wissensstand über martensitbildende Ti-Nb Legierungen zu erweitern. Zu diesem Zweck werden 15 binäre Ti-c_{Nb} Nb (9 Gew.% ≤ c_{Nb} ≤ 44.5 Gew.%) Legierungen hinsichtlich ihrer strukturellen und mechanischen Eigenschaften sowie ihrer thermischen Stabilität untersucht. Die Kristallstrukturen der martensitischen Phasen, α´ und α´´, sowie der Einfluss des Nb-Gehalts auf die Gitterverzerrung (Bain-Verzerrung), auf die Verschiebungswellenkomponente (Shuffle-Komponente) und auf die Volumenänderung der martensitischen β → α´/α´´ Transformationen werden anhand von Rietveld-Verfeinerungen analysiert. In Abhängigkeit des Nb-Gehalts tritt entweder eine Volumendilatation oder -kontraktion auf, die bestimmen könnte ob hexagonaler Martensit α´ oder orthorhombischer Martensit α´´ aus β bei Abkühlung gebildet wird. Die mechanischen Eigenschaften und das Verformungsverhalten martensitischer Ti-Nb Legierungen werden mit einer Reihe komplementärer Methoden (monotone und zyklische einachsige Druckversuche, Nanoindentation, Mikrohärte, Impulserregungstechnik) untersucht. Die Ergebnisse zeigen durchgehend, dass die mechanischen Eigenschaften martensitischer Ti-Nb Legierungen stark vom Nb-Gehalt beeinflusst werden. Die mechanischen Kennwerte sind minimal in der Nähe der Zusammensetzungen, innerhalb derer β → α´´ bei Abkühlung auftritt. Aus Druckversuchen geht hervor, dass die elastischen Eigenschaften verformter Proben verschieden zu denen unverformter sind. Die experimentellen Ergebnisse weisen außerdem auf eine verformungsinduzierte Umwandlung von Martensit in Austenit (α´´ → β) hin. Der Einfluss des Nb-Gehalts auf die thermische Stabilität und das Auftreten von Zerfallsreaktionen in martensitischen Ti-Nb Legierungen wird anhand von dynamischer Differenzkalorimetrie, Dilatometrie, und in-situ Synchrotronröntgenbeugung in Kombination mit Transmissionselektronenmikroskopie untersucht. Das thermische Zerfalls- und Umwandlungsverhalten ist durch das Auftreten einer Vielzahl von in Abhängigkeit des Nb-Gehalts unterschiedlichen Phasentransformationssequenzen gekennzeichnet. Abschließend werden die Transformationstemperaturen und -wärmen, das Transformationsinterval und die thermische Hysterese der martensitischen β ↔ α´´ Umwandlung untersucht. Die Ergebnisse dieser Arbeit sind für die Entwicklung und Optimierung β-stabilisierter Ti-Legierungen für strukturelle und biomedizinische Anwendungen sowie Ni-freier Komponenten, die Formgedächtniseffekt und/oder Superelastizität aufweisen, von Nutzen
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Rose, Kelly Kathleen. "Identification of Fold Hinge Migration in Natural Deformation: A New Technique Using Grain Shape Fabric Analysis." Thesis, Virginia Tech, 1999. http://hdl.handle.net/10919/43205.
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Partitioning of finite strains in different domains within the limb and hinge regions of a fold can be used to understand the deformation processes operative during fold formation. Samples taken from the limb and hinge regions of a gently plunging, asymmetric, tight, mesoscale fold in the Erwin formation of the Blue Ridge in North Carolina were analyzed to determine the deformation mechanisms and strains associated with the folding event. Rf/phi grain shape fabric analysis was conducted for each sample and used to calculate the orientation and magnitude of the final grain shape fabric ellipsoids. Flexural folding and passive-shear folding models predict that the highest finite strains will be recorded in the hinge of a fold. The highest grain shape magnitudes recorded in the North Carolina fold, however, lie along the overturned fold limb.
The final geometry of many folds indicates that hinge plane migration processes are active during compressive deformation events. Numeric, conceptual, and analogue based studies have demonstrated the migration of fold hinges during deformation. However, documentation of these processes in field based studies is rare and limited to techniques that are frequently site specific. Methods proven successful in natural studies include the analysis of superposed folding; the migration of earlier hinge-related features such as fractures, cleavage planes, and boudinaged bedding planes; and the kinematic analysis of syntectonic pressure shadows. The magnitude and orientation of the grain shape ellipsoids calculated for the North Carolina fold indicate that rocks in the overturned limb were once located in the hinge of the fold. Subsequent noncoaxial deformation processes operative during folding resulted in the migration of the hinge to its present orientation and position. This relationship indicates that it is possible to use strain/shape fabric analysis as a test for hinge migration in folds, and that this technique may be more generally applicable in natural settings than previously proposed tests.Master of Science
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Begau, Christoph [Verfasser], Alexander [Gutachter] Hartmaier, and Dierk [Gutachter] Raabe. "Characterization of crystal defects during molecular dynamics simulations of mechanical deformation / Christoph Begau ; Gutachter: Alexander Hartmaier, Dierk Raabe ; Fakultät für Maschinenbau." Bochum : Ruhr-Universität Bochum, 2012. http://d-nb.info/1199608017/34.
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Hu, Jianan. "A theoretical study of creep deformation mechanisms of Type 316H stainless steel at elevated temperatures." Thesis, University of Oxford, 2015. http://ora.ox.ac.uk/objects/uuid:d956b7ff-9748-408e-a68f-31d4c1d492b5.
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The currently operating Generation II Advanced Gas-Cooled Reactors (AGR) in the nuclear power stations in the UK, mainly built in the 1960s and 1970s, are approaching their designed life. Besides the development of the new generation of reactors, the government is also seeking to extend the life of some AGRs. Creep and failure properties of Type 316H austenitic stainless steels used in some components of AGR at elevated temperature are under investigation in EDF Energy Ltd. However, the current empirical creep models used and examined in EDF Energy have deficiency and demonstrate poor agreement with the experimental data in the operational complex thermal/mechanical conditions. The overall objective of the present research is to improve our general understanding of the creep behaviour of Type 316H stainless steels under various conditions by undertaking theoretical studies and developing a physically based multiscale state variable model taking into account the evolution of different microstructural elements and a range of different internal mechanisms in order to make realistic life prediction. A detailed review shows that different microstructural elements are responsible for the internal deformation mechanisms for engineering alloys such as 316H stainless steels. These include the strengthening effects, associated with forest dislocation junctions, solute atoms and precipitates, and softening effects, associated with recovery of dislocation structure and coarsening of precipitates. All the mechanisms involve interactions between dislocations and different types of obstacles. Thus change in the microstructural state will lead to the change in materials' internal state and influence the mechanical/creep property. Based on these understandings, a multiscale self-consistent model for a polycrystalline material is established, consisting of continuum, crystal plasticity framework and dislocation link length model that allows the detailed dislocation distribution structure and its evolution during deformation to be incorporated. The model captures the interaction between individual slip planes (self- and latent hardening) and between individual grains and the surrounding matrix (plastic mismatch, leading to the residual stress). The state variables associated with all the microstructure elements are identified as the mean spacing between each type of obstacles. The evolution of these state variables are described in a number of physical processes, including the dislocation multiplication and climb-controlled network coarsening and the phase transformation (nucleation, growth and coarsening of different phases). The enhancements to the deformation kinetics at elevated temperature are also presented. Further, several simulations are carried out to validate the established model and further evaluate and interpret various available data measured for 316H stainless steels. Specimens are divided into two groups, respectively ex-service plus laboratory aged (EXLA) with a considerable population of precipitates and solution treated (ST) where precipitates are not present. For the EXLA specimens, the model is used to evaluate the microscopic lattice response, either parallel or perpendicular to the loading direction, subjected to uniaxial tensile and/or compressive loading at ambient temperature, and macroscopic Bauschinger effect, taking into account the effect of pre-loading and pre-crept history. For the ST specimens, the model is used to evaluate the phase transformation in the specimen head volume subjected to pure thermal ageing, and multiple secondary stages observed during uniaxial tensile creep in the specimen gauge volume at various temperatures and stresses. The results and analysis in this thesis improve the fundamental understanding of the relationship between the evolution of microstructure and the creep behaviour of the material. They are also beneficial to the assessment of materials' internal state and further investigation of deformation mechanism for a broader range of temperature and stress.
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Allen, Robert. "Exploratory simulations of multiscale effects of deformation twinning on the mechanical behavior of FCC and HCP metals." Thesis, Université de Lorraine, 2018. http://www.theses.fr/2018LORR0167.
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Les méthodes conçues pour être incorporées dans des polycristaux de modélisation multi-échelles sont présentées dans ce travail en deux tâches. Ce travail contient des méthodes à moyenne échelle pour capturer les effets des interactions de dislocations de glissement rencontrant des joints de grains maclage et la croissance simultanée de plusieurs fractions de volume de grains maclage sur le durcissement mécanique et l’évolution de la texture. Celles-ci sont mises en œuvre dans un cadre de plasticité cristalline utilisant le code visco-plastic-self consistent de Los Alamos, VPSC-7. Présentés ici, les effets de la croissance simultanée de multiples variantes maclage sur l’évolution de la texture sont suivis à l’aide d’un schéma de transfert de volume double de type Kalidindi. Dans la tâche 1, la mise en œuvre de ce schéma afin de simuler la texture des aciers à plasticité induite par maclage (TWIP) soumis au pressage angulaire à canal égal (ECAP) est résumée. Dans la tâche 2, les effets de durcissement de deux types d’interaction entre les dislocations de glissement et les joints de grain maclage rencontrés, à savoir la transmutation et la dissociation de dislocation, sont capturés au moyen de la modification du modèle de durcissement basé sur la densité de dislocation de [11]. Les interactions du premier type sont présentées dans une relation constitutive calculant la quantité de densité de dislocations attribuée à un système de glissement donné contenu dans la fraction de volume maclage rencontrée à partir de chaque système de glissement en interaction dans la fraction de volume mère. La quantité transmutée à partir de chaque système de glissement en interaction décrit à l’aide de la méthode de correspondance, sur la cartographie des systèmes de glisse- ment d’un grain parent à des systèmes de glissement dans des grains maclage considérés. Des interactions du second type sont ensuite introduites dans cette relation constitutive en tant que paramètre de dissociation, dont la valeur est établie par les observations tirées des résultats des simulations de dynamique moléculaire de [8] et [53]. Ces méthodes sont implantées pour simuler le comportement de durcissement anisotrope du magnésium HCP sous plusieurs chemins de chargeMethods designed for incorporation into multiscale modeling polycrystals are presented in this work in two tasks. This work contains mesoscale methods for capturing the effects of both the interactions of slip dislocations encountering twin grain boundaries and the simultaneous growth of multiple twin grain volume fractions on mechanical hardening and texture evolution. These are implemented in a crystal plasticity framework using the Los Alamos viscoplastic self-consistent code, VPSC-7. Presented here, the effects of simultaneous growth in multiple twin variants on textural evolution is tracked using a Kalidindi-type twin volume transfer scheme. In Task 1, the implementation of this scheme in order to simulate the texture of Twinning Induced Plasticity steels (TWIP) subjected to Equal Channel Angular Pressing (ECAP) are summarized. In Task 2, the hardening effects of two types of interactions between slip dislocations and encountered twin grain boundaries, namely dislocation transmutation and dissociation, are captured by way of modifying the dislocation density based hardening model of [11]. Interactions of the first type are presented in a constitutive relation calculating the amount of dislocation density apportioned to a given slip system contained within the encountered twin volume fraction from each interacting slip system in the parent volume fraction. The amount transmuted from each interacting slip system described using the Correspondence Method, an on to mapping of slip systems in a parent grain to slip systems in considered twin grains. Interactions of the second type are then introduced into this constitutive relation as a disassociation parameter, the value of which is established by observations gleaned from the results of the molecular dynamics simulations of [8] and [53]. These methods are implanted to simulate the anisotropic hardening behavior of HCP magnesium under multiple load paths
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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.QC 20151015
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Wu, Xiaoxiang Verfasser], Gunther [Gutachter] Eggeler, and Dierk [Gutachter] [Raabe. "Elementary deformation processes during low temperature and high stress creep of Ni-base single crystal superalloys / Xiaoxiang Wu ; Gutachter: Gunther Eggeler, Dierk Raabe." Bochum : Ruhr-Universität Bochum, 2017. http://d-nb.info/1129451925/34.
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Wu, Xiaoxiang [Verfasser], Gunther Gutachter] Eggeler, and Dierk [Gutachter] [Raabe. "Elementary deformation processes during low temperature and high stress creep of Ni-base single crystal superalloys / Xiaoxiang Wu ; Gutachter: Gunther Eggeler, Dierk Raabe." Bochum : Ruhr-Universität Bochum, 2017. http://d-nb.info/1129451925/34.
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Rossiter, Angelina Jane. "Solubility and crystal growth of sodium nitrate from mixed alcohol – water solvents." Thesis, Curtin University, 2009. http://hdl.handle.net/20.500.11937/505.
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Due to the ductile nature of the sodium nitrate crystal which deforms plastically under high levels of strain, most of the crystal growth studies in aqueous solution have focussed on the influence of tensile strain, supersaturation and dislocation, using x-ray surface topography to characterise the dislocation structure of the crystal. Most of the crystal growth studies have also focussed on growth from the melt since single crystals of sodium nitrate find application in optical pumping experiments, are a potential substitute for calcite in the preparation of polarising prisms and are interesting for the study of plastic properties because two types of plastic deformation, glide and twinning, take place in these crystals at room temperature. Its crystal habit is also difficult to modify and many researchers have used dyes to investigate its effect. Sodium nitrate is also a highly soluble substance with 96g of sodium nitrate dissolving in 100g of water at 30.0°C, making aqueous solutions of this salt and its supersaturation extremely unstable. Literature on its solubility in organic solvents, such as methanol, ethanol and isoproponal, are quite outdated and limited to specific conditions.This study involved the determination of the solubility of sodium nitrate in aqueous methanol, ethanol and isopropanol solutions at different temperatures and weight percents of the organic solvents. Splitting into two liquid phases was observed when using isopropanol, however this phase separation does not occur at low and high mass fractions of alcohol, as at lower concentrations of one solvent the two solvents are miscible. Whereas in the presence of methanol and ethanol the solubility of sodium nitrate in water was significantly reduced, with the solubility decreasing with increasing molecular weight of the alcohol. The experimental data for methanol and ethanol was used for the determination of the ion-specific Non random two liquid (NRTL) parameters by correlating with the modified extended NRTL model. It was observed for both methanol and ethanol that the model was found to satisfactorily correlate the data at low to moderate concentrations of alcohol. However, as the concentration of alcohol rises the model prediction was found to be less satisfactory, probably due to the interaction parameters of NRTL between alcohol and the ions not being able to represent the low solubility of electrolytes.The growth rates of individual faces of sodium nitrate crystals grown in situ in a batch cell and observed with an optical microscope were measured at different temperatures (20.0, 30.0 and 40.0°C) and relative supersaturations (0.02, 0.04, 0.06, 0.08 and 0.1) to determine the kinetics of growth for homogeneous nucleation. A combined growth order, of 1, and activation energy of 23,580 J/mol was obtained indicating that crystal growth in these sets of experiments was diffusion controlled. Crystal growth rates were also obtained for sodium nitrate crystal seeds grown at 20.0°C at a supersaturation of 0.02 and 0.04, in a modified growth cell where the saturated solution was circulated at a flow rate of 4mL/min. The crystal growth rates obtained were much lower in comparison to the growth rates obtained by homogeneous nucleation. In both sets of experiments size independent growth was observed.The surface morphology of the crystals was also observed by optical microscopy, scanning electron microscopy (SEM) and atomic force microscopy (AFM) for the crystals grown by homogeneous nucleation to elucidate the mechanism of growth. Liquid inclusions were observed by optical microscopy for crystals that were grown at high temperatures and for a long duration. SEM revealed the presence of pitting on the crystal surface due to the high solubility of sodium nitrate, while AFM images showed the presence of growth hillocks which suggests that crystal growth is surface integration controlled. However, the presence of growth hillocks could have been caused by the formation of some nuclei and surface artefacts when the crystal was taken out from solution. In seeded crystal growth experiments the solute was observed by optical microscopy to deposit onto the crystal surface.The effect of solvent composition on the growth rate and habit modification of sodium nitrate was also investigated with aqueous solutions of methanol and ethanol. Crystal growth rates of sodium nitrate crystals grown in situ in a batch cell by homogeneous nucleation in aqueous ethanol at 30.0°C at 20, 50 and 90 weight percent of ethanol and crystal seeds grown at 20.4°C at a supersaturation of 0.02 and 0.04 at 30, 50 and 90 weight percent of ethanol, in a modified growth cell was measured. It was found that growth rates decrease with increasing amounts of ethanol and the habit of the crystal remains unchanged. The growth rate was also observed to be much lower than the growth rates obtained from pure aqueous solution. For crystals grown by homogeneous nucleation it was observed that with increasing supersaturation, decreasing weight percent of ethanol and with increasing crystal size the number of liquid inclusions observed on the crystal surfaces increased, whereas for seeded crystal growth solute was observed to deposit on to the crystal surface mainly at low alcohol weight percents. Sodium nitrate crystals grown in aqueous methanol was also observed to behave similarly to crystals grown in ethanol, with lower growth rates obtained. For all cases size independent growth was observed.The influence of additives, DOWFAX 3B2 and amaranth was also investigated on the habit modification of sodium nitrate for crystals grown by homogeneous nucleation at 20.0°C at a supersaturation of 0.04. Both additives were observed to be effective in changing the crystal habit of sodium nitrate, with the appearance of triangular truncations or octahedral facets at the corners of the sodium nitrate crystal due to the additive being adsorbed onto the crystal surface. The influence of the additives on the crystal habit modification can be explained due to the presence of the anionic polar group, the sulphonate group. The growth ratio value for DOWFAX 3B2 was also found to decrease with increasing additive concentration.It is believed that the results of this thesis provides up to date data on the solubility of sodium nitrate in aqueous ethanol and for temperatures and weight percents that have not been reported before in literature for the aqueous methanol system. The work reported on crystal growth studies by homogeneous nucleation and using crystal seeds, the effect of solvent and DOWFAX 3B2 on crystal growth rates and habit modification is also new and has not been reported in literature before.
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Si, Xiuhua. "Applications of the thermodynamics of elastic, crystalline materials." Texas A&M University, 2005. http://hdl.handle.net/1969.1/4177.
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The thermodynamic behaviors of multicomponent, elastic, crystalline solids under
stress and electro-magnetic fields are developed, including the extension of EulerâÂÂs
equation, Gibbs equation, Gibbs-Duhem equation, the conditions to be expected at
equilibrium, and an extension of the Gibbs phase rule. The predictions of this new
phase rule are compared with experimental observations.
The stress deformation behaviors of the single martensitic crystal with and without
magnetic fields were studied with the stress deformation equation derived by
Slattery and Si (2005). One coherent interfacial condition between two martensitic
variants was developed and used as one boundary condition of the problem. The
dynamic magnetic actuation process of the single crystal actuator was analyzed. The
extension velocity and the actuation time of the single crystal actuator are predicted.
The relationship between the external stress and the extension velocity and the actuation
time with the presence of a large external magnetic field was studied.
The extended Gibbs-Duhem equation and Slattery-Lagoudas stress-deformation
expression for crystalline solids was used. Interfacial constraints on the elastic portion
of stress for crystalline-crystalline interfaces and crystalline-fluids or crystallineamorphous
solids interfaces were derived and tested by the oxidation on the exterior
of a circular cylinder, one-sided and two-sided oxidation of a plate. An experiment
for measuring solid-solid interface surface energies was designed and the silicon-silicon dioxide surface energy was estimated.
A new generalized Clausius-Clapeyron equation has been derived for elastic crystalline
solids as well as fluids and amorphous solids. Special cases are pertinent to
coherent interfaces as well as the latent heat of transformation.
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Wen, Wei. "Simulation of large deformation response of polycrystals, deforming by slip and twinning, using the viscoplastic Ø-model." Phd thesis, Université de Strasbourg, 2013. http://tel.archives-ouvertes.fr/tel-00959709.
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The computation of the macroscopic response of polycrystalline aggregates from the properties of their single-crystal is a main problem in materials mechanics. During the mechanical deformation processing, all the grains in the polycrystalline material sample are reoriented. A crystallographic texture may thus be developed which is responsible for the material anisotropy. Therefore, the modeling of the texture evolution is important to predict the anisotropy effects present in industrial processes. The formulation of polycrystals plasticity has been the subject of many studies and different approaches have been proposed. Ahzi and M'Guil developed a viscoplastic phi-model. This model takes into account the grains interaction effects without involving the Eshelby inclusion problems.In this thesis, the phi-model was applied to different crystallographic structures and under different loading conditions. The mechanical twinning has been taken into account in the model. The FCC rolling texture transition from copper-type to brass-type texture is studied. The shear tests in FCC metals are also studied. The predicted results are compared with experimental shear textures for a range of metals having a high SFE to low SFE. For BCC metal, we compare our predicted results with those predicted by the VPSC model. We study the slip activities, texture evolutions and the evolution of yield loci. We also present a comparison with experimental textures from literatures for several BCC metals under cold rolling tests. The model has also been extended to HCP metals. We predict the deformation behavior of the magnesium alloy for different interaction strengths. We also compare our predicted results with experimental data from literatures. We show that the results predicted by the phi-model are in good agreement with the experimental ones.
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Lloyd, Jeffrey T. "Microstructure-sensitive simulation of shock loading in metals." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/51853.
Full textAbstract:
A constitutive model has been developed to model the shock response of single crystal aluminum from peak pressures ranging from 2-110 GPa. This model couples a description of higher-order thermoelasticity with a dislocation-based viscoplastic formulation, both of which are formulated for single crystals. The constitutive model has been implemented using two numerical methods: a plane wave method that tracks the propagating wave front; and an extended one-dimensional, finite-difference method that can be used to model spatio-temporal evolution of wave propagation in anisotropic materials. The constitutive model, as well as these numerical methods, are used to simulate shock wave propagation in single crystals, polycrystals, and pre-textured polycrystals. Model predictions are compared with extensive existing experimental data and are then used to quantify the influence of the initial material state on the subsequent shock response. A coarse-grained model is then proposed to capture orientation-dependent deformation heterogeneity, and is shown to replicate salient features predicted by direct finite-difference simulation of polycrystals in the weak shock regime. The work in this thesis establishes a general framework that can be used to quantify the influence of initial material state on subsequent shock behavior not only for aluminum single crystals, but for other face-centered cubic and lower symmetry crystalline metals as well.
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Murtagian, Gregorio Roberto. "Surface integrity on grinding of gamma titanium aluminide intermetallic compounds." Diss., Available online, Georgia Institute of Technology, 2005, 2004. http://etd.gatech.edu/theses/available/etd-08192004-181021/unrestricted/murtagian%5Fgregorio%5Fr%5F200412%5Fphd.pdf.
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Thesis (Ph. D.)--Mechanical Engineering, Georgia Institute of Technology, 2005.Ashok Saxena, Committee Member ; Carlos Santamarina, Committee Member ; Thomas Kurfess, Committee Member ; Hugo Ernst, Committee Member ; Steven Danyluk, Committee Chair ; David McDowell, Committee Member. Vita. Includes bibliographical references.
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Lin, Chuang-Chia 1968. "Cyclic deformation of FCC crystals." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/37757.
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Kerch, Johanna Katharina [Verfasser], and Olaf [Akademischer Betreuer] Eisen. "Crystal-orientation fabric variations on the cm-scale in cold Alpine ice: Interaction with paleo-climate proxies under deformation and implications for the interpretation of seismic velocities / Johanna Katharina Kerch ; Betreuer: Olaf Eisen." Heidelberg : Universitätsbibliothek Heidelberg, 2016. http://d-nb.info/1180738020/34.
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Utada, Satoshi. "Effect of a Prior Plastic Deformation during Heat Treatments on the Mechanical Properties of Ni-Based Superalloys for Turbine Blade Application Evolution of superalloy for turbine airfoil and development of recycling technology Platinum containing new generation nickel-based superalloy for single crystalline application Tensile, low cycle fatigue and very high cycle fatigue characterizations of advanced single crystal nickel-based superalloys Creep Property and Phase Stability of Sulfur-Doped Ni-Base Single-Crystal Superalloys and Effectiveness of CaO Desulfurization Evaluation and comparison of damage accumulation mechanisms during non-isothermal creep of cast Ni-based superalloys." Thesis, Chasseneuil-du-Poitou, Ecole nationale supérieure de mécanique et d'aérotechnique, 2020. http://www.theses.fr/2020ESMA0019.
Full textAbstract:
Les superalliages monocristallins base Ni sont utilisés pour la conception des aubes de turbines en raison de leur excellente durabilité à haute température. Lors de la production d'une aube de turbine, une déformation plastique (DP)inattendue peut être introduite dans le matériau. Dans cette étude, les matériaux monocristallins ont été pré-déformés entre les traitements thermiques de mise en solution et de revenu pour simuler la DP pouvant être rencontrée lors des étapes de production. Des tests mécaniques sur les matériaux pré-déformés ont été effectués pour comprendre l'effet de cette DP.Au cours des traitements thermiques de revenu du superalliage monocristallin AM1 pré-déformé, un grossissement des précipités γ′ plus rapide et une nucléation accélérée de pores ont été observés à proximité des bandes de glissement introduites lors de la DP à température ambiante. Au cours de la déformation par fluage de l’AM1 pré-déformé dans des conditions de haute température/basse contrainte (≥ 950 °C), les bandes à microstructure grossière sont des sites préférentiels d’accumulation du dommage de fluage induit par diffusion, induisant de la recristallisation et une réduction drastique des propriétés de fluage. Dans des conditions de basse température/haute contrainte (≤ 850 °C), le cisaillement de la microstructure est facilité dans les bandes à microstructure grossière et il réduit également les propriétés de fluage.La recristallisation n'est pas été observée dans des ces conditions de fluage à basse température car les mécanismes diffusifs sont ralentis. Ces résultats ont été confirmés via des essais de fluage sur des matériaux pré-déformés suivant différent chemin de pré-déformation (température, position de la DP dans le cycle thermique…). Le superalliage monocristallin CMSX-4 Plus a été testé de manière similaire à l'AM1 pour comprendre l'effet de la composition chimique. L'effet de la DP sur la microstructure de l'alliage est plus limité pour cet alliage par rapport à celui sur l’AM1. Par conséquent, la pré-déformation n'a pas montré de chute de la durée de vie pour le CMSX-4 Plus à des températures inférieures à 1050 °C. Par contre, pendant le fluage de CMSX-4 Plus à 1150 °C, la pré-déformation a montré un impact spectaculaire sur la durée de vie et la ductilité via les mêmes mécanismes que ceux observés pourl’AM1 à 1050 °C.Afin de régénérer les propriétés des superalliages monocristallins pré-déformés, un traitement thermique de restauration a été ajouté après la DP. Le traitement de restauration a permis de restaurer la microstructure après la DP à température ambiante avec succès, et les propriétés de fluage des matériaux restaurés sont équivalentes à celles de l'AM1 et duCMSX-4 Plus vierges de pré-déformationNi-based single crystal (SX) superalloys are used for turbine blade applications because of their high-temperature durability. During the production of a turbine blade, unexpected plastic deformation (PD) can be introduced to the material. In this study, SX materials were pre-deformed in between solution and aging heat treatments to mimic PD during production. Mechanical tests on the pre-deformed materials have been performed to understand the effect of the prior PD.During aging treatments of pre-deformed AM1 SX superalloy, faster coarsening of γ′ precipitates and enhanced void nucleation were observed in the vicinity of slip bands which were introduced by PD at room-temperature. During creep deformation of pre-deformed AM1 at high temperature/low stress conditions (≥ 950 °C), the microstructure coarsened bands act as diffusion induced creep damage accumulating paths, further triggering recrystallization and resulting in drastic reduction of creep properties. At low temperature/high stress conditions (≤ 850 °C), microstructure shearing was facilitated in the microstructure coarsened band and it decreased creep properties. Recrystallization was not observed at lower temperature creep because the diffusion damage was suppressed. These relationships have been explained by creep tests on pre-deformed materials prepared by different pre-deformation temperatures and heat treatment procedures.CMSX-4 Plus SX superalloy was tested similarly to AM1 to understand the effect of the chemical composition. Effect of pre-deformation on alloy’s microstructure was mild in CMSX-4 Plus compared to that in AM1. Therefore, the predeformation did no exhibit large creep life debit in CMSX-4 Plus at temperatures lower than 1050 °C. However, during creep of CMSX-4 Plus at 1150 °C, pre-deformation presented huge impact on creep life and ductility by the same mechanisms as the ones observed for AM1 at 1050 °C.In order to restore properties of pre-deformed SX superalloys, rejuvenation heat treatment was added after PD.Rejuvenation treatment successfully restored microstructure after PD at room-temperature, and creep properties of rejuvenated specimens were shown to be equivalent to that of original AM1 and CMSX-4 Plus without PD
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Choudhury, Anshuman. "Statistics of dislocations at low temperature in pure metals with body centered cubic symmetry." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLS569/document.
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Les observations de microscopie électronique in situ effectuées par Daniel Caillard (CEMES, Toulouse) au cours de la déformation de cristaux de symétrie cubique centrée ont montré que les dislocations vis effectuaient des sauts de plusieurs distances inter-atomiques alors que la théorie standard de Peierls prédit des sauts de une seul distance inter-atomique. Nous avons étudié par simulation atomique le glissement d'une dislocation vis dans un cristal de fer pure. Nous montrons que la propagation de décrochement le long de la dislocation induit un échauffement local qui favorise la nucléation de décrochements supplémentaires. L'accumulation de ces décrochements permet à la dislocation de parcourir plusieurs distances inter-atomiques. Ces simulations nous permettent de proposer une théorie pour l'explication des observations de D. CaillardIn situ straining tests in high purity α-Fe thin-foils at low temperatures have demonstrated that crystalline defects, called dislocations, have a jerky type of motion made of intermittent long jumps of several nanometers. Such an observation is in conflict with the standard Peierls mechanism for plastic deformation in bcc crystals, where the screw dislocation jumps are limited by inter-reticular distances, i.e. of a few Angstroms. Employing atomic-scale simulations, we show that although the short jumps are initially more favorable, their realization requires the propagation of a kinked profile along the dislocation line which yields coherent atomic vibrations acting as traveling thermal spikes. Such local heat bursts favor the thermally assisted nucleation of new kinks in the wake of primary ones. The accumulation of new kinks leads to long dislocation jumps like those observed experimentally. Our study constitutes an important step toward predictive atomic-scale theory for materials deformation
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Smith, Benjamin Daniel. "Microstructure-sensitive plasticity and fatigue of three titanium alloy microstructures." Thesis, Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/49237.
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Titanium alloys are employed in many advanced engineering applications due to their exceptional properties, i.e., a high strength-to-weight ratio, corrosion resistance, and high temperature strength. The performance of titanium alloys is known to be strongly affected by its inherent microstructure, which forms as a result of its thermo-mechanical processing. These microstructures produce compromise relationships between beneficial and detrimental effects on the alloy's performance. To study these structure-property relationships, two distinct crystal plasticity algorithms have been calibrated to data acquired from cyclic deformation experiments performed on three different Ti microstructures: (1) Ti-6Al-4V beta-annealed , (2) Ti-18 solution-treated, age-hardened (STA), and (3) Ti-18 beta-annealed, slow-cooled, age-hardened (BASCA). The calibrated models have been utilized to simulate fatigue loading of variant microstructures to investigate the influence of mean grain size, crystallographic texture, and phase volume fraction. The driving force for fatigue crack nucleation and propagation is quantified through the calculation of relevant fatigue indicator parameters (FIPs) and radial correlation functions are employed to study the correlation between favorably oriented slip systems and the extreme value FIP locations. The computed results are utilized to observe fatigue performance trends associated with changes to key microstructural attributes.
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Dunne, Barry John. "Structural deformations in phosphorus and nitrogen complexes." Thesis, University of Bristol, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.346442.
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Ng, Kwok-sing. "Plastic deformation of aluminium micro-specimens." Click to view the E-thesis via HKUTO, 2008. http://sunzi.lib.hku.hk/hkuto/record/B4175802X.
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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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Chieragatti, Rémy. "Influence de l'orientation cristallographique sur le comportement en fatigue oligocyclique du mar-m200 monocristallin." Paris, ENMP, 1987. http://www.theses.fr/1987ENMP0024.
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Etude experimentale sur le superalliage soumis a une charge cyclique uniaxiale suivant la direction de croissance 001 et les orientations 111, 011 et 123 a 650 c et 900c. Analyse des courbes d'ecrouissage cyclique. Caracterisation des systemes de glisement associes aux grandes deformations plastiques. Description par un modele de l'influence quantitative de l'orientation sur les courbes, d'ecrouissage cyclique. Mise en evidence du role preponderant de la periode de propagation des fissures sur l'endommagement. Prevision theorique de la duree de vie en fatigue en utilisant des donnees de fissuration etablies pour une orientation donnee
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Ng, Kwok-sing, and 吳國勝. "Plastic deformation of aluminium micro-specimens." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2008. http://hub.hku.hk/bib/B4175802X.
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Riss, Joëlle. "Principes de stéréologie des formes en pétrographie quantitative." Orléans, 1988. http://www.theses.fr/1988ORLE2015.
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Les différentes populations de granis des agrégats polycristallins monominéraux déformés et cristallises sont classés suivant leur forme d'après le diagramme de blaschke. On étudie les polyèdres trivalents à 13 et 14 faces grâces a un logiciel de calcul des coordonnées des sommets. On peut aussi déduire les caractéristiques d'un polyèdre a partir de ses coordonnées ainsi que des simulations numériques d'intercepts linéaires et planauss du polyèdre isole et de l'agrégat qu'il engendre s'il est empilable
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Abu-Saman, Awni. "Large plastic deformation and shear localization of crystals." Doctoral thesis, University of Cape Town, 2000. http://hdl.handle.net/11427/4954.
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Poston, Edward J. "Experimental Deformation of O+ Oriented Synthetic Quartz Single Crystals." University of Akron / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=akron1491569717148234.
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