Bibliografias temáticas / Dislocation discrète

Literatura científica selecionada sobre o tema "Dislocation discrète"

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Publicado: 25 de maio de 2024

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Artigos de revistas sobre o assunto "Dislocation discrète"

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Huang, C. C., C. C. Yu e Sanboh Lee. "The behavior of screw dislocations dynamically emitted from the tip of a surface crack during loading and unloading". Journal of Materials Research 10, n.º 1 (janeiro de 1995): 183–89. http://dx.doi.org/10.1557/jmr.1995.0183.

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The behavior of screw dislocations dynamically emitted from the tip of a surface crack during loading and unloading has been investigated using a discrete dislocation model. The critical stress intensity factor at the crack tip for dislocation emission is a function of friction stress, core radius of dislocation, and dislocations near the crack tip. During motion, the velocity of dislocation is assumed to be proportional to the effective shear stress to the third power. The effect of crack length and friction stress on dislocation distributions, plastic zone, and dislocation-free zone during loading and unloading was examined.
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Holec, David, e Antonín Dlouhý. "Stability and Motion of Low Angle Dislocation Boundaries in Precipitation Hardened Crystals". Materials Science Forum 482 (abril de 2005): 159–62. http://dx.doi.org/10.4028/www.scientific.net/msf.482.159.

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The present study investigates stability and motion of low angle dislocation boundaries in an array of precipitates. The model considers discrete dislocations and precipitates that are treated as impenetrable particles. Peach-Koehler forces, which originate due to the combined effect of dislocation-dislocation interactions and the applied stress, act the individual dislocations on. Both, the dislocation glide and the dislocation climb at elevated temperatures are taken into account. Results of the numerical study suggest that a critical applied shear stress (CASS) always exists which separates stable and unstable low angle boundary configurations. Varying particle size, interparticle spacing and density of dislocations in the boundary cause changes of the CASS that are systematically investigated. It is shown that the CASSs can considerably differ from the standard Orowan stress controlling the equilibrium of an isolated dislocation in a given microstructure. This result underlines the importance of long-range dislocation interactions that influence the high temperature strength of the precipitation-hardened alloys.
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Gurrutxaga-Lerma, Beñat, Daniel S. Balint, Daniele Dini, Daniel E. Eakins e Adrian P. Sutton. "A dynamic discrete dislocation plasticity method for the simulation of plastic relaxation under shock loading". Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 469, n.º 2156 (8 de agosto de 2013): 20130141. http://dx.doi.org/10.1098/rspa.2013.0141.

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In this article, it is demonstrated that current methods of modelling plasticity as the collective motion of discrete dislocations, such as two-dimensional discrete dislocation plasticity (DDP), are unsuitable for the simulation of very high strain rate processes (10 6 s −1 or more) such as plastic relaxation during shock loading. Current DDP models treat dislocations quasi-statically, ignoring the time-dependent nature of the elastic fields of dislocations. It is shown that this assumption introduces unphysical artefacts into the system when simulating plasticity resulting from shock loading. This deficiency can be overcome only by formulating a fully time-dependent elastodynamic description of the elastic fields of discrete dislocations. Building on the work of Markenscoff & Clifton, the fundamental time-dependent solutions for the injection and non-uniform motion of straight edge dislocations are presented. The numerical implementation of these solutions for a single moving dislocation and for two annihilating dislocations in an infinite plane are presented. The application of these solutions in a two-dimensional model of time-dependent plasticity during shock loading is outlined here and will be presented in detail elsewhere.
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Diop, Mouhamadou, Hai Hao, Han Wei Dong e Xing Guo Zhang. "Simulation of Discrete Dislocation Statics and Dynamics of Magnesium Foam". Materials Science Forum 675-677 (fevereiro de 2011): 929–32. http://dx.doi.org/10.4028/www.scientific.net/msf.675-677.929.

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The simulation of magnesium plasticity at the microscopic and mesoscopic scale using space and time-discretized statics and dynamics dislocation was carried out. The complexity of discrete dislocation models dues to the fact that the mechanical interaction of ensembles of such defects is with an elastic nature, and therefore involves long-range interactions. The motion of dislocations or dislocation segments in their respective glide planes are usually described by assuming simple phenomenological viscous flows laws. The formulation of the dislocation dynamics is obtained by the Newton’s Second Law of motion for each dislocation or dislocation segment. The evolution of the dislocation position is obtained by simple difference algorithms.
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Li, Luo, e Tariq Khraishi. "An Investigation of Spiral Dislocation Sources Using Discrete Dislocation Dynamics (DDD) Simulations". Metals 13, n.º 8 (6 de agosto de 2023): 1408. http://dx.doi.org/10.3390/met13081408.

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Discrete Dislocation Dynamics (DDD) simulations are a powerful simulation methodology that can predict a crystalline material’s constitutive behavior based on its loading conditions and micro-constituent population/distribution. In this paper, a 3D DDD model with spiral dislocation sources is developed to study size-dependent plasticity in a pure metal material (taken here as Aluminum). It also shows, for the first time, multipole simulations of spirals and how they interact with one another. In addition, this paper also discusses how the free surface of a crystalline material affects the plasticity generation of the spiral dislocation. The surface effect is implemented using the Distributed Dislocation Method. One of the main results from this work, shown here for the first time, is that spiral dislocations can result in traditional Frank–Read sources (edge or screw character) in a crystal. Another important result from this paper is that with more dislocation sources, the plastic flow inside the material is more continuous, which results in a lowering of the flow stress. Lastly, the multipole interaction of the spiral dislocations resulted in a steady-state fan-shaped action for these dislocation sources.
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Mastorakos, Ioannis N., Firas E. Akasheh e Hussein M. Zbib. "Treating internal surfaces and interfaces in discrete dislocation dynamics". Journal of the Mechanical Behaviour of Materials 20, n.º 1-3 (1 de dezembro de 2011): 13–20. http://dx.doi.org/10.1515/jmbm.2011.002.

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AbstractThe treatment of coherent interfaces and cracks is discussed in the framework of dislocation dynamics (DD). In the case of interfaces, we use DD to study dislocation interactions in nanoscale bimetallic laminates, and to predict their structure after relaxation and during loading. In agreement with experimental observations, our discrete dynamics simulations show that dislocation structure develops only at the interface between coherent layers leaving layers’ interior dislocation-free. The main dislocation mechanism at this length scale is Oworan bowing of threading dislocations confined to their respective layers by the sign-alternating coherency stress field in the layers. Slip transmission across the interfaces marks the end of the confined slip regime, hence, the breakdown of the interfaces and macroscopic yielding of these structures. In the case of crack, its long-range and singular stress field is determined by modeling the crack as continuous distribution of dislocation loops. The traction boundary condition to be satisfied at the crack surface, results into a singular integral equation of the first kind that is solved numerically. The model is integrated with the DD technique to investigate the behavior of a specimen containing cracks of different shapes under fatigue. The results are compared with the behavior of an uncracked specimen and conclusions are extracted. Extension of this crack treatment methodology to account for their presence at interfaces, all within the frame dislocations dynamics, opens the door for a more realistic approach to a wide range of interfaces-related problems.
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Záležák, Tomáš, e Antonín Dlouhý. "3D Discrete Dislocation Modelling of High Temperature Plasticity". Key Engineering Materials 465 (janeiro de 2011): 115–18. http://dx.doi.org/10.4028/www.scientific.net/kem.465.115.

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A 3D model is presented that addresses an evolution of flexible dislocation lines at high temperatures. The model is based on the linear theory of elasticity. A smooth dislocation line is approximated by a piecewise curve composed of short straight dislocation segments. Each dislocation segment is acted upon by a Peach-Koehler force due to a local stress field. All segment-segment interactions as well as an externally applied stress are considered. A segment mobility is proportional to the Peach-Koehler force, temperature-dependent factors control climb and glide motion of the segments. The potential of the model is demonstrated in simulations of simple high temperature processes including interactions of dislocations with secondary particles.
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Stricker, Markus, Michael Ziemann, Mario Walter, Sabine M. Weygand, Patric Gruber e Daniel Weygand. "Dislocation structure analysis in the strain gradient of torsion loading: a comparison between modelling and experiment". Modelling and Simulation in Materials Science and Engineering 30, n.º 3 (8 de fevereiro de 2022): 035007. http://dx.doi.org/10.1088/1361-651x/ac4d77.

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Abstract Complex stress states due to torsion lead to dislocation structures characteristic for the chosen torsion axis. The formation mechanism of these structures and the link to the overall plastic deformation are unclear. Experiments allow the analysis of cross sections only ex situ or are limited in spacial resolution which prohibits the identification of the substructures which form within the volume. Discrete dislocation dynamics simulations give full access to the dislocation structure and their evolution in time. By combining both approaches and comparing similar measures the dislocation structure formation in torsion loading of micro wires is explained. For the ⟨100⟩ torsion axis, slip traces spanning the entire sample in both simulation and experiment are observed. They are caused by collective motion of dislocations on adjacent slip planes. Thus these slip traces are not atomically sharp. Torsion loading around a ⟨111⟩ axis favors plasticity on the primary slip planes perpendicular to the torsion axis and dislocation storage through cross-slip and subsequent collinear junction formation. Resulting hexagonal dislocation networks patches are small angle grain boundaries. Both, experiments and discrete dislocation simulations show that dislocations cross the neutral fiber. This feature is discussed in light of the limits of continuum descriptions of plasticity.
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liu, F. X., A. C. F. Cocks e E. Tarleton. "Dislocation dynamics modelling of the creep behaviour of particle-strengthened materials". Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 477, n.º 2250 (junho de 2021): 20210083. http://dx.doi.org/10.1098/rspa.2021.0083.

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Plastic deformation in crystalline materials occurs through dislocation slip and strengthening is achieved with obstacles that hinder the motion of dislocations. At relatively low temperatures, dislocations bypass the particles by Orowan looping, particle shearing, cross-slip or a combination of these mechanisms. At elevated temperatures, atomic diffusivity becomes appreciable, so that dislocations can bypass the particles by climb processes. Climb plays a crucial role in the long-term durability or creep resistance of many structural materials, particularly under extreme conditions of load, temperature and radiation. Here we systematically examine dislocation-particle interaction mechanisms. The analysis is based on three-dimensional discrete dislocation dynamics simulations incorporating impenetrable particles, elastic interactions, dislocation self-climb, cross-slip and glide. The core diffusion dominated dislocation self-climb process is modelled based on a variational principle for the evolution of microstructures, and is coupled with dislocation glide and cross-slip by an adaptive time-stepping scheme to bridge the time scale separation. The stress field caused by particles is implemented based on the particle–matrix mismatch. This model is helpful for understanding the fundamental particle bypass mechanisms and clarifying the effects of dislocation glide, climb and cross-slip on creep deformation.
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Mesarovic, Sinisa. "Plasticity of crystals and interfaces: From discrete dislocations to size-dependent continuum theory". Theoretical and Applied Mechanics 37, n.º 4 (2010): 289–332. http://dx.doi.org/10.2298/tam1004289m.

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In this communication, we summarize the current advances in size-dependent continuum plasticity of crystals, specifically, the rate-independent (quasistatic) formulation, on the basis of dislocation mechanics. A particular emphasis is placed on relaxation of slip at interfaces. This unsolved problem is the current frontier of research in plasticity of crystalline materials. We outline a framework for further investigation, based on the developed theory for the bulk crystal. The bulk theory is based on the concept of geometrically necessary dislocations, specifically, on configurations where dislocations pile-up against interfaces. The average spacing of slip planes provides a characteristic length for the theory. The physical interpretation of the free energy includes the error in elastic interaction energies resulting from coarse representation of dislocation density fields. Continuum kinematics is determined by the fact that dislocation pile-ups have singular distribution, which allows us to represent the dense dislocation field at the boundary as a superdislocation, i.e., the jump in the slip filed. Associated with this jump is a slip-dependent interface energy, which in turn, makes this formulation suitable for analysis of interface relaxation mechanisms.
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Mais fontes

Teses / dissertações sobre o assunto "Dislocation discrète"

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Gonzalez, Joa Javier Antonio. "Mesoscale dislocation simulation accounting for surfaces using the superposition method : Application to nanomechanics". Electronic Thesis or Diss., Lyon, INSA, 2022. http://www.theses.fr/2022ISAL0129.

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Les nano-objets (fils, particules, films minces) sont connus pour leurs propriétés mécaniques exceptionnelles au regard de leurs homologues massifs. Diverses techniques expérimentales (microscopie électronique à transmission ou à balayage, diffraction des rayons X) sont utilisées pour étudier les nano-objets, complétées par des approches numériques telle que la dynamique moléculaire. Bien que fournissant des détails à l'échelle atomique, la dynamique moléculaire reste limitée en termes de taille et de vitesse de déformation, ouvrant la porte à d'autres méthodes comme la dynamique des dislocations discrète. La dynamique des dislocations discrète permet de décrire l'évolution d'une population de dislocations à l’échelle du grain mais est généralement utilisée dans des ensembles quasi-infinis en utilisant des cellules de simulation particulièrement grandes ou des conditions limites périodiques. Par conséquent, la dynamique des dislocations discrète seule ne peut fournir une description physique des surfaces d’un échantillon, surfaces à l'origine de nombreux processus à l'échelle nanométrique. Cette étude vise à modéliser mieux et plus fidèlement la mécanique des nano-objets en tenant compte des interactions complexes entre les dislocations et les surfaces. Pour ce faire, un nouvel outil appelé El-Numodis a été développé. El-Numodis repose sur le couplage du code de dynamique des dislocations discrète Numodis avec le code d'éléments finis Elmer en utilisant la méthode de superposition. Nous présentons ici les étapes de développement d'El-Numodis (pilotes de couplage, forces d'image des dislocations, algorithme de nucléation, etc.) ainsi que plusieurs applications incluant des problèmes d'élasticité classiques dans lesquels des surfaces sont impliquées. A titre d'exemple, la modélisation de films minces métalliques fcc montre l'influence majeure des surfaces sur la mécanique des nano-objets. Enfin, El-Numodis est utilisé pour modéliser la mécanique de nanoparticules céramiques où la nucléation de dislocation informée de manière atomistique, combinée à la théorie de l'état de transition, permet d'étudier le rôle de la taille, température et de la vitesse de déformation sur la déformation de nanocubes de MgO
Nano-objects (wires, particles, thin films) are known for their outstanding mechanical properties when compared to their bulk counterparts. Various experimental techniques (transmission and scanning electron microscopy, X-ray diffraction) are used to investigate nano-objects, all complemented by computational approaches such as molecular dynamics. While modelling atomic-scale processes in the details, molecular dynamics is limited in terms of sample size and strain rates opening doors to other methods such as the discrete dislocation dynamics. Discrete dislocation dynamics is able to describe the evolution of a dislocation population at the mesoscale but is mostly used to describe quasi-infinite ensembles using either particularly large simulation cells or relying on periodic boundary conditions. Consequently, standalone discrete dislocation dynamics cannot provide a complete description of sample surfaces that are known to be at the roots of several nanoscale processes. This study aims at better and faithfully model the mechanics of nano-objects accounting for the complex interactions between dislocations and surfaces. For this purpose, a new tool called El-Numodis was developed. El-Numodis relies on the coupling of the discrete dislocation dynamics code Numodis with the finite elements code Elmer using the superposition method in which the stress field generated by a dislocation population is corrected at the virtual surfaces of a finite-size sample using a finite-element elastic solver. In this work, we present the main development stages of El-Numodis (coupling drivers, dislocation image forces, nucleation algorithm, etc.) as well as several applications including analytically soluble elasticity problems in which surfaces are involved. As an example, the modelling of face-centered cubic metal thin films practically demonstrates the influence of surfaces on nano-objects mechanics. Finally, El-Numodis is used to model the mechanics of ceramics nanoparticles for which atomistically-informed dislocation nucleation as combined to the transition state theory allow to investigate the role of size, temperature and strain rate on the mechanical properties of MgO nanoparticles
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Siska, Filip. "Simulation numérique du comportement mécanique des films minces métalliques par la théorie continue et la dynamique discrète des dislocations". Phd thesis, École Nationale Supérieure des Mines de Paris, 2007. http://tel.archives-ouvertes.fr/tel-00204422.

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Le sujet de la thèse contenue l'étude de propriétés mécaniques des couches minces à base de cuivre. Ces propriétés sont étudiées à aide de la méthode élément finis dans le cadre de la plasticité cristalline classique et dans le cadre de dynamique discrète des dislocations. Les simulations élasto-plastiques montrent que la présence des grains avec une orientation (001) et aléatoire augmentent les contraintes dans les grains adjacents d'orientation (111). La comparaison avec les résultats expérimentaux montre que le modele n'est pas capable de prévoir des contraintes aussi élevées que l'écrouissage quel sont mesurés dans les expériences.L'évolution de l'écrouissage, de la microdéformation plastique, de la rugosité locale et globale de la surface sont étudiées par les simulations de chargement cyclique d'agrégats polycristallins de cuivre. L'écrouissage et la rugosité saturent pendant le chargement. Il existe des régions où la déformation résiduelle cumulée et la rugosité locale évoluent pendant le chargement cyclique. Ces régions favorisent par l'amorçage de l'endommagement. L'autre approche dans les simulations des agrégats polycristallins est représentée par la théorie de la dynamique discrète des dislocations. Les simulations montrent que la plus grande influence est due à la longueur initiale des sources. Par contre, l'épaisseur des films a peu d'influence sur la comportement du film. Les dislocations sont le plus actives dans les grains avec une orientation (001) et l'activité minimale est observée dans les grains avec une orientation (111).
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Shin, Chansun. "3D discrete dislocation dynamics applied to dislocation-precipitate interactions". Grenoble INPG, 2004. http://www.theses.fr/2004INPG0116.

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La dynamique des dislocations discrètes (DDD) a été appliquée pour examiner les effets des précipités sur la plasticité des monocristaux de structure CFC. Les précipités sont modélisés par un assemblage de facettes franchissable pour une contrainte donnée. Afin de tenir compte des interactions élastiques entre les dislocations et les particules, un couplage avec la méthode des éléments finis (MEF) a été utilisé. Afin d'accélérer les temps de calculs, la 'méthode des boites' a été revisitée et une version parallèle du code a été développée en utilisant le standard du programmation 'Message Passing Interface (MPI)'. Dans un premier temps, les contraintes images créées par une particule 3D ont été calculées grâce un couplage entre la MEF et le code de DDD. Les résultats numériques ont été comparés aux solutions analytiques correspondantes. L'effet de la différence des modules d'Young sur la limite élastique et le comportement durcissant qui en découle ont ensuite été étudiés numériquement. Nous avons montré que les contraintes image ont un effet significatif sur le durcissement et les événements locaux tels que le glissement dévié et la montée. Finalement, la fatigue des matériaux durcis par des précipités cisaillables et non-cisaillables a été simulée avec le nouveau code parallèle de DDD. Les résultats obtenus grâce à nos simulations sont en accord avec nos observations experimentales et les données de la littérature. Un mécanisme de formation des bandes de glissement intense a été proposé à partir de l'observation des microstructures obtenues par simulation
The 3D Discrete Dislocation Dynamics (DDD) method has been applied to investigate the effects of precipitates on the plasticity of FCC single crystals. A method to represent the internal interfaces by a series of facets with a pre-defined strength has been proposed. For a full account of the mutual elastic interactions between dislocations and second-phase particles, the coupling method with a finite element method is extended. In order to accelerate the computing time, the serial 3D DDD algorithm has been improved by revisiting the 'box method' and a new parallel code has been developed using the standard Message passing Interface (MPI). The image stresses due to a three-dimensional particle were computed using the FEM/DDD coupling code. The numerical results have been compared to the corresponding analytical solutions. The effect of the elastic modulus mismatch on the flow stress and the subsequent hardening behavior has then been analyzed. The image stresses were found to affect significantly the work hardening and the local events such as cross slip and climb. Finally, the fatigue of precipitate-hardened materials was simulated using the new parallel DDD code. The effects of shearable and non-shearable particles on the fatigue properties were well reproduced by the simulations, and the numerical results showed good agreements with the available experimental observations in a qualitative way. The mechanism of the intense slip band formation is proposed from the observation of the simulated dislocation microstructure
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Liu, Bing [Verfasser]. "Discrete dislocation dynamics simulations of dislocation : low angle grain boundary interactions / Bing Liu". Aachen : Hochschulbibliothek der Rheinisch-Westfälischen Technischen Hochschule Aachen, 2012. http://d-nb.info/1027743900/34.

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Mohammad, Davoudi Kamyar. "Plastic Behavior of Polycrytalline Thin Films: Discrete Dislocation Study". Thesis, Harvard University, 2014. http://dissertations.umi.com/gsas.harvard:11634.

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Explaining the work-hardening behavior of crystalline materials and the size dependent plasticity has been a long lasting problem. Plastic deformation mainly arises from the collective motion of dislocations. Although individual dislocation processes are well studied, the study of the overall effects of these processes was challenging before the emergence of computer modeling. Of the computer simulation techniques, discrete dislocation dynamics (DDD) is the most suitable method to model thin films at the micron scale and below. This method allows us to study the quantitative effects of certain mechanisms.
Engineering and Applied Sciences
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Bizet, Laurent. "Caractérisation et modélisation du comportement thermomécanique des matériaux métalliques : vers la prise en compte des hétérogénéités micro-structurales intrinsèques". Thesis, Université Grenoble Alpes (ComUE), 2016. http://www.theses.fr/2016GREAA001/document.

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La prédiction de la géométrie d'une pièce mise en forme par déformation plastique grâce à un logiciel de calcul par éléments finis (EF) s'effectue en suivant séquentiellement différentes étapes : la caractérisation thermo-mécanique du matériau, la modélisation de son comportement et son intégration dans un logiciel EF, puis la mise en données et la simulation de l'opération de formage. La phase de modélisation consiste entre autre à identifier quel type de modèle de comportement est le plus approprié pour prédire les réactions du matériau lors de l'opération de formage. Ces modèles sont essentiellement développés dans le cadre de la mécanique des milieux continus (MMC). L'hypothèse forte, si ce n'est centrale, de la MMC consiste à considérer que les variables qui servent à déterminer le comportement du matériau sont continues et dérivables. Cependant, les connaissances les plus élémentaires de métallurgie indiquent que les grandeurs locales dans les matériaux métalliques sont discontinues. La majorité des modèles de comportement mécanique des matériaux métalliques repose sur la définition d'un volume élémentaire représentatif dont la taille est assez grande pour permettre une homogénéisation de la description du comportement en gommant l'influence des hétérogénéités localesL'objet de ces travaux est de montrer que la prise en compte des hétérogénéités locales dans la modélisation du comportement des matériaux métalliques est pertinente et contribue à l'amélioration de la prédiction des simulations d'opérations de mise en forme en élargissant le potentiel prédictif des modèles ainsi construits. Un modèle élasto-plastique prenant en compte les hétérogénéités locales est alors proposé
To obtain a relevant shape of a formed part during its finite element simulation, several steps are needed: thermo-mechanical caracterization of the material, definition of the most relevant model and integration of this model in the FE software and finally after data converting and computing processes. The modelling step include, among other things, the identification of the most appropriate model to fit the experimental material behaviour. Those models are essentially developped within the framework of continuum mechanics (CM). A strong, if not the main assumption of the CM consists in considering that mechanical description variables are continuous and differentiable. However, the basic knowledge of metallurgy indicates that local data in metallic materials are discontinuous. For metallic materials, the majority of constitutive models are based on the definition of a representative elementary volume (REV). This REV is supposed to be large enough to erase the incidence of local heterogeneities. Then those constitutive models are assumed to be homogeneous.The aim of this work is to show that introducing local heterogeneities in the description of constitutive models is relevant and contribute to improve the simulation accuracy. Those models also provide an enlargement of the simulation predictive potential. Then an elasto-plastic model, based on local heterogeneities description, is proposed
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Korzeczek, Laurent. "Modélisation mésoscopique en 3D par le modèle Discret-Continu de la stabilité des fissures courtes dans les métaux CFC". Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLC049/document.

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Le mode de propagation complexe des fissures courtes observé dans les métaux ductiles sous chargement cyclique est généralement attribué à différents mécanismes de stabilisation intervenant à l’échelle de la microstructure, l’échelle mésoscopique. Parmi ces mécanismes, l’interaction de la fissure avec la microstructure de dislocation semble jouer un rôle majeur. La dynamique des dislocations contrôle la déformation plastique et le transfert de chaleur qui lui est associé et réduit ainsi la quantité d’énergie élastique stockée dans le matériau. De plus, la microstructure de dislocations peut « écranter » le champ élastique induit par la fissure par son propre champ de contraintes et modifier la géométrie de la fissure par l’émoussement des surfaces en pointe. Pour la première fois, ces mécanismes sont étudiés avec des simulations 3D de Dynamique des Dislocation avec le modèle Discrete-Continu. Trois orientations de fissure sont testées sous un chargement monotone en traction, promouvant une ouverture en fond de fissure en mode I. De manière surprenante, les simulations montrent que les effets d’écrantage et d’émoussement n’ont pas un rôle clé dans la stabilisation des fissures testées en mode I. Le mécanisme principal se trouve être la capacité du matériau à se déformer plastiquement sans mettre en oeuvre un durcissement important par le mécanisme de la forêt. Des recherches supplémentaires sur deux effets de taille confirment ces résultats et montrent également la contribution mineure d’une densité de dislocations polarisées et du durcissement cinématique associé à la stabilisation des fissures
The erratic behaviour of short cracks propagation under low cyclic loading in ductile metals is commonly attributed to a complex interplay between stabilisation mechanisms that occur at the mescopic scale. Among these mechanisms, the interaction with the existing dislocation microstructure play a major role. The dislocation microstructure is source of plastic deformation and heat transfer that reduce the specimen stored elastic energy, screen the crack field due to its self generated stress field or change the crack geometry through blunting mechanisms. For the first time, these mechanisms are investigated with 3D-DD simulations using the Discrete- Continuous Model, modelling three different crack orientations under monotonic traction loading promoting mode I crack opening.Surprisingly, screening and blunting effects do not seem to have a key role on mode I crack stabilisation. Rather, the capability of the specimen to deform plastically without strong forest hardening is found to be the leading mechanism. Additional investigations of two different size effects confirm those results and show the minor contribution of a polarised dislocations density and the associated kinematic hardening on crack stabilisation
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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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Perrin, Camille. "Etude expérimentale et modélisation des microstructures de déformation plastique intragranulaires discrètes". Thesis, Metz, 2010. http://www.theses.fr/2010METZ030S/document.

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L’amélioration des techniques de caractérisation (EBSD, MET, AFM) permet actuellement une meilleure compréhension des mécanismes plastiques intra-granulaires pour des poly-cristallin déformé. Les observations expérimentales montrent que les processus de plastification sont fortement hétérogènes et intermittent à l’intérieur des grains. Les modèles micromécaniques à champs moyens développés ces dernières décennies ne considèrent pas proprement les hétérogénéités intra-granulaires du glissement plastique. Or il est aujourd’hui démontré (simulations de Dynamique des Dislocations Discrètes par exemple) que la prise en compte de l’auto-organisation des dislocations à l’intérieur des grains est fondamentale pour mieux comprendre et expliquer les effets de taille de grains sur le comportement mécanique des polycristaux. Dans cette étude, deux approches complémentaires ont été développées : Une approche théorique qui consiste aux calculs des champs élastiques (contrainte interne et rotation de réseau) dus à une distribution discrète de boucles de dislocations contraintes par le joint de grains, et une approche expérimentale dont le but est de caractériser quantitativement les longueurs caractéristiques (espacements inter-bandes, et niveau de plasticification dans les bandes) pour des polycristaux à plusieurs tailles de grains se déformant plastiquement et de mesurer les rotations de réseau locales associées (mesure EBSD de désorientation de réseau cristallin) en vue de les comparer au champs de rotations élastiques calculés par le modèle. Le modèle a également été étendu pour permettre l’étude à des microstructures plus complexes, comme par exemple, les cellules de dislocations
The improvement of the materials characterization techniques in the last years has given access to new important information about the microstructure of polycrystalline metals. From experimental studies of deformed polycrystals, plastic strain within grains is known to be strongly heterogeneous and intermittent. As a consequence of the collective motion of dislocations, sample surfaces are indeed characterized by the presence of slip lines and slip bands (as slip traces). In the present study, a new micromechanical approach is developed to derive the mechanical fields (stresses, distortion, lattice curvature, elastic energy) arising from the presence of an inelastic strain field representing a typical internal "microstructure" as the one observed during the plastification of metallic polycrystals. This "microstructure" is due to the formation of discrete (spatial-temporal) intra-granular plastic slip heterogeneities which are modelled using discrete distributions of circular glide dislocation loops for a grain embedded in an infinite elastic matrix. Then, field equations have been solved using the method of Fourier Transforms. In contrast with the mean field approach based on the Eshelby formalism, it is then found that stress and lattice curvature fields are not more uniform inside the grain. A grain boundary layer actually appears where strong gradients occur and whose thickness depends on the introduced internal lengths. These results are compared with experimental measurements of local lattice rotation fields obtained by orientation imaging mapping (OIM). The model is able to capture different behaviours between near grain boundary regions and grain interior. The model was also develop to allow the study of more complex microstructures like the dislocation cells
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Al, Haj Mohammad. "Modèles discrets de dislocations : ondes progressives et dynamique de particules". Thesis, Paris Est, 2014. http://www.theses.fr/2014PEST1001/document.

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Ce travail se concentre sur l'étude de la dynamique des dislocations dans le réseau cristallin et il est découpé en deux parties : la première partie porte sur les mouvements horizontaux d'une chaîne d'atomes en interaction contenant une dislocation. Bien que, la deuxième partie traite de l'accumulation de dislocations formant ce qu'on appelle des murs de dislocations. Dans la première partie, nous considérons une généralisation complètement nonlinéaire des équations de diffusion de réaction discrète également appelée “modèles de Frenkel-Kontorova complètement amortis” qui décrivent la dynamique des défauts cristallins (dislocations) dans un réseau. Nous étudions à la fois : les non-linéarités bistable et monostable. Dans des conditions suffisantes, nous montrons l'existence et l'unicité des ondes progressives pour le cas de non-linéarité bistable. Pour le cas monostable, nous étudions l'existence de la branche des solutions d'ondes progressives pour une non-linéarité Lipschitz général. Nous montrons également que la vitesse minimale est positive et délimitée ci-dessous. Dans cette partie, nous étudions aussi la généralisation du modèle de Frenkel-Kontorova pour laquelle nous pouvons ajouter un paramètre de force motrice. Nous illustrons également, dans ce cas, la variation de la vitesse de propagation des ondes progressives en fonction du paramètre de force. Dans la deuxième partie, nous étudions l'accumulation des dislocations dans les murs de dislocations. Nous montrons en fait la convergence de plusieurs dislocations qui interagissent sur les murs de dislocations. Nous présentons aussi les résultats de quelques expériences numériques qui confirment les résultats théoriques que nous obtenons
This work focuses on the study of the dislocation dynamics in the crystal lattice and it is splitted into two parts : the first part is concerned with the horizontal motion of a chain of interacting atoms containing a dislocation. While, the second part deals with the accumulation of dislocations forming what is known as walls of dislocations. In the first part, we consider a fully nonlinear generalization of the discrete reaction diffusion equations “fully overdamped Frenkel-Kontorova models” that describe the dynamics of crystal defects (dislocations) in a lattice. We study both : the bistable and the monostable non-linearities. Under sufficient conditions, we show the existence and uniqueness of traveling wave solution for the bistable non-linearity case. For the monostable case, we study the existence of branch of traveling waves solutions for general Lipschitz non-linearity. We also prove that the minimal velocity is non-negative and bounded below. In this part, we as well study the generalization of Frenkel-Kontorova model for which we can add a driving force parameter. We also illustrate, in this case, the variation of the velocity of propagation of traveling waves in terms of the parameter force. In the second part, we study the accumulation of dislocations in walls of dislocations. We prove actually the convergence of several interacting dislocations to walls of dislocations. We also present results of some numerical experiments that confirm the theoretical results that we obtain
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Livros sobre o assunto "Dislocation discrète"

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Cui, Yinan. The Investigation of Plastic Behavior by Discrete Dislocation Dynamics for Single Crystal Pillar at Submicron Scale. Singapore: Springer Singapore, 2017. http://dx.doi.org/10.1007/978-981-10-3032-1.

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Davoudi, Kamyar Mohammad. Plastic Behavior of Polycrytalline Thin Films: Discrete Dislocation Study. 2014.

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Cui, Yinan. Investigation of Plastic Behavior by Discrete Dislocation Dynamics for Single Crystal Pillar at Submicron Scale. Springer, 2016.

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Cui, Yinan. The Investigation of Plastic Behavior by Discrete Dislocation Dynamics for Single Crystal Pillar at Submicron Scale. Springer, 2018.

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Cui, Yinan. The Investigation of Plastic Behavior by Discrete Dislocation Dynamics for Single Crystal Pillar at Submicron Scale. Springer, 2016.

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Capítulos de livros sobre o assunto "Dislocation discrète"

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Giessen, E. "Discrete Dislocation Plasticity". In Thermodynamics, Microstructures and Plasticity, 285–300. Dordrecht: Springer Netherlands, 2003. http://dx.doi.org/10.1007/978-94-010-0219-6_18.

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Giessen, E., e A. Needleman. "Discrete Dislocation Plasticity". In Handbook of Materials Modeling, 1115–31. Dordrecht: Springer Netherlands, 2005. http://dx.doi.org/10.1007/1-4020-3286-2_56.

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Giessen, Erik. "Discrete Dislocation Plasticity". In Mechanics of Microstructured Materials, 259–82. Vienna: Springer Vienna, 2004. http://dx.doi.org/10.1007/978-3-7091-2776-6_8.

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Van der Giessen, E., e A. Needleman. "Discrete Dislocation Plasticity". In Handbook of Materials Modeling, 1115–31. Dordrecht: Springer Netherlands, 2005. http://dx.doi.org/10.1007/978-1-4020-3286-8_56.

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Zbib, Hussein M. "Introduction to Discrete Dislocation Dynamics". In Generalized Continua and Dislocation Theory, 289–317. Vienna: Springer Vienna, 2012. http://dx.doi.org/10.1007/978-3-7091-1222-9_4.

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Zbib, Hussein M., Masato Hiratani e Mutasem Shehadeh. "Multiscale Discrete Dislocation Dynamics Plasticity". In Continuum Scale Simulation of Engineering Materials, 201–29. Weinheim, FRG: Wiley-VCH Verlag GmbH & Co. KGaA, 2005. http://dx.doi.org/10.1002/3527603786.ch8.

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Ariza, M. P., A. Ramasubramaniam e M. Ortiz. "Discrete Dislocation Dynamics in Crystals". In Progress in Industrial Mathematics at ECMI 2006, 387–91. Berlin, Heidelberg: Springer Berlin Heidelberg, 2008. http://dx.doi.org/10.1007/978-3-540-71992-2_58.

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El-Achkar, T., e Daniel Weygand. "Discrete dislocation dynamics study of dislocation microstructure during cyclic loading". In Fatigue of Materials at Very High Numbers of Loading Cycles, 395–416. Wiesbaden: Springer Fachmedien Wiesbaden, 2018. http://dx.doi.org/10.1007/978-3-658-24531-3_18.

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Li, Luo, e Tariq Khraishi. "3D Discrete Dislocation Dynamics Simulations of Multiple Spiral Dislocation Sources". In The Minerals, Metals & Materials Series, 969–77. Cham: Springer Nature Switzerland, 2024. http://dx.doi.org/10.1007/978-3-031-50349-8_83.

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LeSar, Richard, e Laurent Capolungo. "Advances in Discrete Dislocation Dynamics Simulations". In Handbook of Materials Modeling, 1079–110. Cham: Springer International Publishing, 2020. http://dx.doi.org/10.1007/978-3-319-44677-6_85.

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Trabalhos de conferências sobre o assunto "Dislocation discrète"

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Tan, E. H., e L. Z. Sun. "Dislocation Dynamics Modeling for Yield Strength of Nanoscale Film Heterostructures". In ASME 2005 International Mechanical Engineering Congress and Exposition. ASMEDC, 2005. http://dx.doi.org/10.1115/imece2005-79222.

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A novel dislocation dynamics framework is developed to simulate dislocation evolutions in thin film heterostructures at nanoscale. It is based on 3-D dislocation motion together with its physical background by adding the solid viscous effect. As the numerical simulation results demonstrate, this new model completely solves a long-standing paradoxical phenomenon with which the simulation results were dependent on dislocation-segment lengths in the classical discrete dislocation dynamics theory. The proposed model is applied to simulate the effect of dislocations on the mechanical performance of thin films. The interactions among the dislocation loop, free surface and interface are rigorously computed by decomposing this complicated problem into two relatively simple sub-problems. This model is allowed to determine the critical thickness of thin films for a surface loop to nucleate and to simulate how a surface loop evolves into two threading dislocations. Furthermore, the relationship between the film thickness and yield strength is constructed and compared with the conventional Hall-Petch relation.
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Yin, X., e K. Komvopoulos. "A Discrete Dislocation Plasticity Analysis of Plane-Strain Indentation of a Single-Crystal Half-Space by a Smooth and a Rough Rigid Asperity". In STLE/ASME 2010 International Joint Tribology Conference. ASMEDC, 2010. http://dx.doi.org/10.1115/ijtc2010-41155.

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A discrete dislocation plasticity analysis of plane-strain indentation of a single-crystal half-space by a smooth or rough (fractal) rigid asperity is presented. The emission, movement, and annihilation of edge dislocations are incorporated in the analysis through a set of constitutive rules [1,2]. It is shown that the initiation of the first dislocation is controlled by the subsurface Hertzian stress field and occurs in the ±45° direction with respect to the normal of the crystal surface, in agreement with the macroscopic yielding behavior of the indented halfspace. For fixed slip-plane direction, the dislocation density increases with the applied normal load and dislocation source density. The dislocation multiplication behavior at a given load is compared with that generated by a rough indenter with a fractal surface profile. The results of the analysis provide insight into yielding and plastic deformation phenomena in indented single-crystal materials.
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Sandfeld, S., M. Zaiser, T. Hochrainer, Theodore E. Simos, George Psihoyios e Ch Tsitouras. "Expansion of Quasi-Discrete Dislocation Loops in the Context of a 3D Continuum Theory of Curved Dislocations". In NUMERICAL ANALYSIS AND APPLIED MATHEMATICS: International Conference on Numerical Analysis and Applied Mathematics 2009: Volume 1 and Volume 2. AIP, 2009. http://dx.doi.org/10.1063/1.3241264.

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Voskoboinikov, R. E., Anatoly S. Avilov, Sergei L. Dudarev e Laurence D. Marks. "Asymptotics in discrete dislocation pile-up modelling". In ELECTRON MICROSCOPY AND MULTISCALE MODELING- EMMM-2007: An International Conference. AIP, 2008. http://dx.doi.org/10.1063/1.2918102.

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Greer, Julia R., Ju-Young Kim e Steffen Brinckmann. "In-Situ Investigation of Plasticity at Nano-Scale". In ASME 2008 9th Biennial Conference on Engineering Systems Design and Analysis. ASMEDC, 2008. http://dx.doi.org/10.1115/esda2008-59117.

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Mechanical behavior of crystals is dictated by dislocation motion in response to applied force. While it is extremely difficult to directly observe the motion of individual dislocations, several correlations can be made between the microscopic stress-strain behavior and dislocation activity. Here, we present for the first time the differences observed between mechanical behavior in two fundamental types of crystals: face-centered cubic, fcc (Au, Cu, Al, Ni, etc.) and body-centered cubic, bcc (W, Cr, Mo, Nb, etc.) with sub-micron dimensions subjected to in-situ micro-compression in SEM chamber. In a striking deviation from classical mechanics, there is a significant increase in strength as crystal size is reduced to 100nm; however in gold crystals (fcc) the highest strength achieved represents 44% of its theoretical strength while in molybdenum crystals (bcc) it is only 7%. Moreover, unlike in bulk where plasticity commences in a smooth fashion, both nano-crystals exhibit numerous discrete strain bursts during plastic deformation. These remarkable differences in mechanical response of fcc and bcc crystals to uniaxial micro-compression challenge the applicability of conventional strain-hardening to nano-scale crystals. We postulate that they arise from significant differences in dislocation behavior between fcc and bcc crystals at nanoscale and serve as the fundamental reason for the observed differences in their plastic deformation. Namely, dislocation starvation is the predominant mechanism of plasticity in nano-scale fcc crystals while junction formation and subsequent hardening characterize bcc plasticity, as confirmed by the microstructural electron microscopy. Experimentally obtained stress-strain curves together with video frames during deformation and cross-sectional TEM analysis are presented, and a statistical analysis of avalanche-like strain bursts is performed for both crystals and compared with stochastic models.
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Barrera, Olga, e Alan C. F. Cocks. "Computational Modelling of Hydrogen Embrittlement in Weld Joints of Subsea Oil and Gas Components". In ASME 2013 32nd International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/omae2013-10119.

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The paper deals with the modelling of the combined hydrogen embrittlement phenomena: hydrogen enhanced local plasticity (HELP) and hydrogen induced decohesion (HID) in subsea dissimilar welds. Fractography analysis of dissimilar welds of 8630 steel / IN625 nickel alloy demonstrate that a cleavage-like fracture path is located through an area called the “featureless zone” characterized by the presence M7C3 carbides. This fracture morphology, which is noticed only in the presence of hydrogen, seems to be consistent with a hydrogen-induced decohesion (HID) mechanism along the M7C3 -matrix interface succeeded by a ductile-type fracture. In light of this the purpose here is to develop constitutive models of the “featureless zone”. We present two types of models: the former (i) is based on a classical continuum mechanics formalism; the latter (ii) is a mescoscopic type of model to represent more accurately the dislocation structure that develops in the vicinity of the carbide-particles. The model (i) describes some of the aspects involved in the failure process of a dissimilar AISI8630/IN625 weld, however continuum models are not appropriate for the scale of the carbide particles in the featureless region. The scale of the particles is such that the interaction of the particles with discrete dislocations and the dislocation structures generated around the particles play an important role in determining the constitutive response.
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Dutta, B. K., P. V. Durgaprasad, A. K. Pawar, H. S. Kushwaha e S. Banerjee. "Modelling of Irradiated Materials". In 14th International Conference on Nuclear Engineering. ASMEDC, 2006. http://dx.doi.org/10.1115/icone14-89685.

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Irradiation of materials by energetic particles causes significant degradation of the mechanical properties, most notably an increased yield stress and decrease ductility, thus limiting lifetime of materials used in nuclear reactors. The microstructure of irradiated materials evolves over a wide range of length and time scales, making radiation damage and inherently multi-scale phenomenon. At atomic length scale, the principal sources of radiation damage are the primary knock-on atoms that recoil under collision from energetic particles such as neutrons or ions. These knock-on atoms in turn produce vacancies and self-interstitial atoms, and stacking fault tetrahedra. At higher length scale, these defect clusters form loops around existing dislocations, leading to their decoration and immobilization, which ultimately leads to radiation hardening in most of the materials. All these defects finally effect the macroscopic mechanical and other properties. An attempt is made to understand these phenomena using molecular dynamics studies and discrete dislocation dynamics modelling.
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Mukherjee, Subhasis, Bite Zhou, Abhijit Dasgupta e Thomas R. Bieler. "Mechanistic Modeling of the Anisotropic Steady State Creep Response of SnAgCu Single Crystal". In ASME 2015 International Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Microsystems collocated with the ASME 2015 13th International Conference on Nanochannels, Microchannels, and Minichannels. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/ipack2015-48710.

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A multiscale modeling framework is proposed in this study to capture the influence of the inherent elastic anisotropy of single crystal Sn and the inherent heterogeneous microstructure of a single crystal SnAgCu (SAC) solder grain on the secondary creep response of the grain. The modeling framework treats the SAC microstructure as having several distinct length scales. The smallest length scale (Tier 0) consists of the Sn BCT lattice. The eutectic Sn-Ag micro-constituent, consisting of nanoscale Ag3Sn IMC particles embedded in the single crystal BCT Sn matrix, is termed Tier 1. The single-crystal SAC microstructure, consisting of Sn dendrites and surrounding eutectic Sn-Ag phase, is termed Tier 2. Dislocation recovery mechanisms, such as Orowan climb and detachment from nanoscale Ag3Sn particles, are found to be the rate controlling mechanisms for creep deformation in the eutectic Sn-Ag phase (Tier 1) of a SAC single crystal. The anisotropic secondary creep rate of eutectic Sn-Ag phase (Tier 1), is then modeled using the above inputs and the saturated dislocation density calculated for dominant glide systems during secondary stage of creep. Saturated dislocation density is estimated as the equilibrium saturation between three competing processes: (1) dislocation generation; (2) dislocation impediment caused by back stress from pinning of dislocations at IMCs; and (3) dislocation recovery due to climb/detachment from IMCs. Secondary creep strain rate of eutectic Sn-Ag phase in three most facile slip systems is calculated and compared against the isotropic prediction. At low stress level secondary steady state creep rate along (110)[001] system is predicted to be ten times the creep rate along (100)[0-11] system. However, at high stress level, secondary steady state creep rate along (110)[001] system is predicted to be ten thousand times the creep rate along (100)[0-11] system. The above predictions are in strong agreement with (1–4) orders of magnitude of anisotropy observed in steady state secondary creep response in SAC305 solder joints tested under identical loading conditions in experiments conducted by several authors. The above model is then combined with Eigen-strain methods and average matrix stress concepts to homogenize the load sharing between the Sn dendrites and the surrounding eutectic Ag-Sn matrix. The resulting steady state creep rates are predicted for a few discrete single crystal SAC305 specimens. Very good agreement is observed between the predicted steady state creep rate and the measured creep rates for two SAC305 single crystal specimens.
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Senger, J., D. Weygand, O. Kraft, P. Gumbsch, Theodore E. Simos, George Psihoyios, Ch Tsitouras e Zacharias Anastassi. "Dislocation Microstructure Evolution in Cyclically Twisted Micrometer-Sized Metallic Samples: A Discrete Dislocation Dynamics Analysis". In NUMERICAL ANALYSIS AND APPLIED MATHEMATICS ICNAAM 2011: International Conference on Numerical Analysis and Applied Mathematics. AIP, 2011. http://dx.doi.org/10.1063/1.3637919.

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Tran, H. S., H. Tummala, L. Duchene, T. Pardoen, M. Fivel e A. M. Habraken. "Quasicontinuum analysis of dislocation-coherent twin boundary interaction to provide local rules to discrete dislocation dynamics". In PROCEEDINGS OF THE INTERNATIONAL CONFERENCE OF GLOBAL NETWORK FOR INNOVATIVE TECHNOLOGY AND AWAM INTERNATIONAL CONFERENCE IN CIVIL ENGINEERING (IGNITE-AICCE’17): Sustainable Technology And Practice For Infrastructure and Community Resilience. Author(s), 2017. http://dx.doi.org/10.1063/1.5008190.

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