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Статті в журналах з теми "Dislocation field mechanics"
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Beyerlein, I. J., and A. Hunter. "Understanding dislocation mechanics at the mesoscale using phase field dislocation dynamics." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 374, no. 2066 (April 28, 2016): 20150166. http://dx.doi.org/10.1098/rsta.2015.0166.
Повний текст джерелаАнотація:
In this paper, we discuss the formulation, recent developments and findings obtained from a mesoscale mechanics technique called phase field dislocation dynamics (PFDD). We begin by presenting recent advancements made in modelling face-centred cubic materials, such as integration with atomic-scale simulations to account for partial dislocations. We discuss calculations that help in understanding grain size effects on transitions from full to partial dislocation-mediated slip behaviour and deformation twinning. Finally, we present recent extensions of the PFDD framework to alternative crystal structures, such as body-centred cubic metals, and two-phase materials, including free surfaces, voids and bi-metallic crystals. With several examples we demonstrate that the PFDD model is a powerful and versatile method that can bridge the length and time scales between atomistic and continuum-scale methods, providing a much needed understanding of deformation mechanisms in the mesoscale regime.
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Fressengeas, Claude, and Vincent Taupin. "Revisiting the Application of Field Dislocation and Disclination Mechanics to Grain Boundaries." Metals 10, no. 11 (November 16, 2020): 1517. http://dx.doi.org/10.3390/met10111517.
Повний текст джерелаАнотація:
We review the mechanical theory of dislocation and disclination density fields and its application to grain boundary modeling. The theory accounts for the incompatibility of the elastic strain and curvature tensors due to the presence of dislocations and disclinations. The free energy density is assumed to be quadratic in elastic strain and curvature and has nonlocal character. The balance of loads in the body is described by higher-order equations using the work-conjugates of the strain and curvature tensors, i.e., the stress and couple-stress tensors. Conservation statements for the translational and rotational discontinuities provide a dynamic framework for dislocation and disclination motion in terms of transport relationships. Plasticity of the body is therefore viewed as being mediated by both dislocation and disclination motion. The driving forces for these motions are identified from the mechanical dissipation, which provides guidelines for the admissible constitutive relations. On this basis, the theory is expressed as a set of partial differential equations where the unknowns are the material displacement and the dislocation and disclination density fields. The theory is applied in cases where rotational defects matter in the structure and deformation of the body, such as grain boundaries in polycrystals and grain boundary-mediated plasticity. Characteristic examples are provided for the grain boundary structure in terms of periodic arrays of disclination dipoles and for grain boundary migration under applied shear.
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ROY, A. "Finite element approximation of field dislocation mechanics." Journal of the Mechanics and Physics of Solids 53, no. 1 (January 2005): 143–70. http://dx.doi.org/10.1016/j.jmps.2004.05.007.
Повний текст джерела
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Mironova, M., V. Selvamanickam, D. F. Lee, and K. Salama. "TEM studies of dislocations in deformed melt-textured YBa2Cu3Ox superconductors." Journal of Materials Research 8, no. 11 (November 1993): 2767–73. http://dx.doi.org/10.1557/jmr.1993.2767.
Повний текст джерелаАнотація:
TEM studies have been conducted on melt-textured YBa2Cu3Ox samples that were uniaxially and isostatically deformed at high temperatures and compared with those of undeformed samples. Dislocation pile-ups along [100] and [010] are found to be the common feature between undeformed samples with the best Jc and the uniaxially deformed samples, and are suggested to be responsible for enhanced pinning when the magnetic field (H) is applied parallel to the a-b plane. Dislocation loops, tangles, and arrays are also observed, and are considered to contribute to pinning in field orientations other than H ‖ a-b. In addition to these dislocations, 〈301〉 type partial dislocations are found to be present in isostatically deformed samples. The strain field around these dislocations is considered to be an additional source of pinning in the intermediate field orientations.
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Mesarovic, Sinisa. "Plasticity of crystals and interfaces: From discrete dislocations to size-dependent continuum theory." Theoretical and Applied Mechanics 37, no. 4 (2010): 289–332. http://dx.doi.org/10.2298/tam1004289m.
Повний текст джерелаАнотація:
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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Puri, Saurabh, Amit Das, and Amit Acharya. "Mechanical response of multicrystalline thin films in mesoscale field dislocation mechanics." Journal of the Mechanics and Physics of Solids 59, no. 11 (November 2011): 2400–2417. http://dx.doi.org/10.1016/j.jmps.2011.06.009.
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Acharya, Amit. "Constitutive analysis of finite deformation field dislocation mechanics." Journal of the Mechanics and Physics of Solids 52, no. 2 (February 2004): 301–16. http://dx.doi.org/10.1016/s0022-5096(03)00093-0.
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Weertman, J. "Mode III Crack Tip Plastic Zone Solution for Work Hardening Solid Using Dislocation Motion." Journal of Applied Mechanics 56, no. 4 (December 1, 1989): 976–77. http://dx.doi.org/10.1115/1.3176200.
Повний текст джерелаАнотація:
The stress and strain field solutions for the stationary mode III crack in small-scale yielding is obtained from a direct physical picture in which the plastic strain is produced by the motion of infinitesimal dislocations. The analysis is based on a shifting center, cylindrical coordinate system. The nonredundant dislocation density is determined. The ratio of nonredundant to redundant dislocation density within the plastic zone may be a useful measure for placing cracks into a brittle class, a ductile class and semibrittle to semiductile classes.
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Luo, H. A., and Y. Chen. "An Edge Dislocation in a Three-Phase Composite Cylinder Model." Journal of Applied Mechanics 58, no. 1 (March 1, 1991): 75–86. http://dx.doi.org/10.1115/1.2897182.
Повний текст джерелаАнотація:
An exact solution is given for the stress field due to an edge dislocation embedded in a three-phase composite cylinder. The force on the dislocation is then derived, from which a set of simple approximate formulae is also suggested. It is shown that, in comparison with the two-phase model adopted by Dundurs and Mura (1964), the three-phase model allows the dislocation to have a stable equilibrium position under much less stringent combinations of the material constants. As a result, the so-called trapping mechanism of dislocations is more likely to take place in the three-phase model. Also, the analysis and calculation show that in the three-phase model the orientation of Burgers vector has only limited influence on the stability of dislocation. This behavior is pronouncedly different from that predicted by the two-phase model.
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Vivekanandan, Vignesh, Joseph Pierre Anderson, Yash Pachaury, Mamdouh S. Mohamed, and Anter El-Azab. "Statistics of internal stress fluctuations in dislocated crystals and relevance to density-based dislocation dynamics models." Modelling and Simulation in Materials Science and Engineering 30, no. 4 (April 11, 2022): 045007. http://dx.doi.org/10.1088/1361-651x/ac5dcf.
Повний текст джерелаАнотація:
Abstract A statistical analysis of internal stress fluctuations, defined as the difference between the local mean stress and stress on dislocations, is presented for deforming crystals with 3D discrete dislocation systems. Dislocation realizations are generated using dislocation dynamics simulations and the associated stress field is computed as a superposition of a regularized stress field of dislocation lines within the domain of the solution and a complementary stress field computed via a finite-element boundary value problem. The internal stress fluctuations of interest are defined by an ensemble of the difference between the stress on dislocation lines and the local mean field stress in the crystal. The latter is established in a piecewise fashion over small voxels in the crystal thus allowing the difference between the local average stress and stress on segments to be easily estimated. The results show that the Schmid stress (resolved shear stress) and Escaig stress fluctuations on various slip systems sampled over a random set of points follow a Cauchy (Lorentz) distribution at all strain levels, with the amplitude and width of the distribution being dependent on the strain. The implications of the Schmid and Escaig internal stress fluctuations are discussed from the points of view of dislocation cross-slip and the dislocation motion in continuum dislocation dynamics.
Дисертації з теми "Dislocation field mechanics"
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Zhang, Xiaohan. "Field Dislocation Mechanics with Applications in Atomic, Mesoscopic and Tectonic Scale Problems." Research Showcase @ CMU, 2015. http://repository.cmu.edu/dissertations/649.
Повний текст джерелаАнотація:
This thesis consists of two parts. The first part explores a 2-d edge dislocation model to demonstrate characteristics of Field Dislocation Mechanics (FDM) in modeling single and collective behavior of individual dislocations. The second work explores the possibility of modelling adiabatic shear bands propagation within the timespace averaged framework of Mesoscopic Field Dislocation Mechanics (MFDM). It is demonstrated that FDM reduces the study of a significant class of problems of discrete dislocation dynamics to questions of the modern theory of continuum plasticity. The explored questions include the existence of a Peierls stress in translationally-invariant media, dislocation annihilation, dislocation dissociation, finite-speed-of-propagation effects of elastic waves vis-a-vis dynamic dislocation fields, supersonic dislocation motion, and short-slip duration in rupture dynamics. A variety of dislocation pile-up problems are studied, primarily complementary to what can be dealt by existing classical pile-up models. In addition, the model suggests the possibility that the tip of a shear band can be modelled as a localized spatial gradient of elastic distortion with the dislocation density tensor in continuum dislocation mechanics; It is demonstrated that the localization can be moved by its theoretical driving force and forms a diffuse traveling band tip, thereby extending the thin layer of the deformation band. A 3-d, parallel finite element framework of MFDM is developed in a geometrically nonlinear context for the purpose of modelling shear bands. The numerical formulations and algorithm are presented in detail. Constitutive models appropriate for single crystal plasticity response and J2 plasticity with thermal softening are implemented.
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Lima, chaves Gabriel. "On the thermomechanics of field dislocations." Electronic Thesis or Diss., Institut polytechnique de Paris, 2024. http://www.theses.fr/2024IPPAX058.
Повний текст джерелаАнотація:
Cette thèse explore le couplage entre l'évolution des dislocations et la conduction thermique dans les corps continus à travers une approche théorique et numérique. Les principaux objectifs sont : (i) développer une théorie de la thermomécanique des champs de dislocation en grandes déformations qui tient compte de l'interaction mutuelle entre l'activité des dislocations et l'évolution de la température, tout en considérant uniquement des champs observables ; (ii) proposer une linéarisation géométrique de cette théorie en montrant qu'elle revient à la théorie thermomécanique des champs de dislocations (TFDM) en petites déformations proposée par Upadhyay, J. Mech. Phys. Solids, 145 (2020) 104150, et implémenter numériquement cette dernière en utilisant la méthode des éléments finis (EF) pour étudier l'évolution de la température pendant le transport des dislocations.Les aspects fondamentaux de la modélisation des dislocations sont passés en revue, mettant en évidence les différentes approches couramment utilisées. Après avoir identifié les limitations actuelles de l'état de l'art, une théorie avec une nouvelle cinématique basée sur la mécanique des dislocations dans un cadre de grandes déformations considérant un champ de température hétérogène transitoire est proposée. La théorie ne nécessite pas la spécification d'une configuration de référence globale, d'où l'absence de décomposition multiplicative du gradient de déformation en parties élastique, plastique et thermique. Au lieu de cela, en ne considérant que des variables d'état observables, il est montré que la cinématique basée sur la conservation du vecteur de Burgers est suffisante pour obtenir la décomposition additive couramment acceptée du gradient de vitesse en taux de distorsion élastique, plastique et thermique. En prenant en compte la densité de dislocations polaires comme variable d'état dans l'énergie libre de Helmholtz du système, et en utilisant les première et deuxième lois de la thermodynamique, une nouvelle structure de l'équation d'évolution de la température est obtenue, permettant des solutions sous forme d'ondes dispersives avec une vitesse de propagation finie, sans dérivée seconde du champ de température dans le temps.La théorie développée est montrée se réduire, sous linéarisation géométrique, à la théorie TFDM en petites déformations précédemment proposée. Ensuite, l'accent est mis sur cette dernière, et les formes variationnelles de ses équations aux dérivées partielles (EDP) sont présentées. En utilisant une bibliothèque open-source conçue pour résoudre les EDP avec la méthode des EF, les formes variationnelles sont implémentées dans un algorithme échelonné. L'implémentation est vérifiée par rapport à une solution analytique pour le champ de température généré par une dislocation en mouvement, et un excellent accord est obtenu. Certaines des capacités de TFDM sont ensuite explorées dans des exemples de chaleur générée par le mouvement d’une dislocation coin/vis, l'annihilation des dislocations et l'expansion des boucles de dislocations, fournissant une compréhension en profondeur des sources de chaleur thermoélastiques et plastiques transitoires impliquées dans chaque cas.La présente recherche fait progresser le domaine de la modélisation des champs de dislocations en proposant un nouveau cadre théorique, ainsi que l'implémentation numérique de sa version linéarisée. Ce travail sert de base à la compréhension de l'évolution des structures de dislocations lors de différents processus thermomécaniques, tels que la fabrication additive de métaux, le soudage, la trempe, etc., ce qui pourrait contribuer à un meilleur contrôle des propriétés mécaniques des pièces fabriquées. Les travaux futurs incluraient une extension de l'implémentation numérique à la théorie proposée en grandes déformations, ainsi qu'un échelonnement de cette dernière pour tenir compte du rôle des dislocations statistiquement stockées dans les problèmes classiques de plasticitéThis thesis investigates the coupling between dislocation evolution and heat conduction in continuum bodies through a theoretical and numerical approach. The main objectives are twofold: (i) to develop a finite deformation theory of thermomechanics of field (i.e. continuously represented) dislocations that account for the interplay between dislocation activity and temperature evolution, while considering only observable fields; (ii) to propose a geometrical linearisation of the finite deformation theory showing that it is similar to the small deformation thermal field dislocation mechanics (TFDM) theory proposed in Upadhyay,J. Mech. Phys. Solids, 145 (2020) 104150, and numerically implement the latter using the finite element (FE) approach to study temperature evolution during dislocation transport.The fundamental aspects of dislocation modelling are reviewed, highlighting the different approaches that have commonly been used to study dislocation-based plasticity in crystals. After identifying the current limitations of the state of the art, a theory with a novel kinematics for thermo-elastoplastic problems based on dislocation mechanics in a finite deformation framework within a transient heterogeneous temperature field is proposed. The theory does not require the specification of a global reference configuration, whence we do not make use of a multiplicative decomposition of the deformation gradient into elastic, plastic, and thermal parts. Instead, considering only observable state variables, we show that the kinematics based on the conservation of Burgers vector is sufficient to yield the commonly-accepted additive decomposition of the velocity gradient into elastic, plastic, and thermal distortion rates. Accounting for the polar dislocation density as a state variable in the Helmholtz free energy of the system, using the first and second laws of thermodynamics, we obtain a new structure of the temperature evolution equation, which allows for solutions in the form of dispersive waves with finite propagation speed without a second derivative of the temperature field in time.The developed theory is shown to reduce, when geometrically linearised, to the small-strain TFDM theory previously proposed. Then, the focus is turned to the latter, and the variational forms of its partial differential equations (PDEs) are presented. Using an open-source library designed to solve PDEs with the FE method, the variational forms are implemented in a staggered algorithm. The implementation is verified against an analytical solution for the temperature field generated by a moving dislocation, and excellent agreement is obtained. Some of the TFDM capabilities are then explored in examples of the heat generated by single edge/screw dislocation, dislocation annihilation, and dislocation loop expansion, which provide a clear understanding of the transient thermoelastic and plastic heat sources involved in each case.The present research advances the field of continuum dislocation modelling by proposing a novel theoretical framework, as well as the numerical implementation of its linearised version. This work serves as a basis for understanding the evolution of dislocation structures during different thermomechanical processes, such as metal additive manufacturing, welding, quenching, etc., which would ultimately contribute to better controlling the mechanical properties of manufactured parts. Future work would include an extension of the numerical implementation to the general finite-deformation theory proposed, as well as an upscaling of the latter to account for the role of statistically stored dislocations in classical problems of plasticity
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Kharouji, Houssam. "Modélisation micromécanique des défauts cristallins informée par simulation atomistique." Electronic Thesis or Diss., Université de Lorraine, 2024. http://www.theses.fr/2024LORR0146.
Повний текст джерелаАнотація:
Cette thèse propose un cadre multiéchelle pour modéliser de manière continue les structures de cœur des défauts cristallins, tels que les dislocations et les joints de grains, ainsi que leurs interactions élastiques et les énergies de cœur associées, en combinant des approches atomistiques et de mécanique des milieux continus. L'idée centrale de cette étude est de transformer les structures atomiques de coeurs des défauts en champs continus de densités de dislocations, tout en préservant les détails atomistiques essentiels. L'approche développée repose sur un modèle micromécanique récent basé sur la mécanique des champs de dislocations qui utilise le tenseur de densité de dislocation de Nye, dérivé des données atomistiques, pour modéliser les champs mécaniques à courte et longue portée associés à ces défauts. La méthode a été appliquée avec succès à des dislocations vis compactes dans le tungstène, issues de simulations extit{ab initio}, ainsi que sur des joints de grains dans le cuivre, simulés par statique moléculaire. Cette approche s'est révélée capable de reproduire remarquablement les vecteurs de Burgers et les champs mécaniques des défaut, démontrant l'absence de perte significative d'information au niveau des cœurs des défauts. Il a été possible de reproduire des joints de grains de tout angle de désorientation en utilisant une densité équivalente de dislocations, tout en capturant les champs élastiques continus. Par ailleurs, cette étude a permis d'intégrer les champs élastiques et les densités de dislocations dans des fonctionnelles énergétiques basées sur le tenseur de Nye, typiquement utilisées au sein de modèles de plasticité à gradient, afin d'évaluer leur contribution respective à l'énergie totale des joints de grains. Nous avons ainsi analysé et discuté les formes de fonctionnelles pertinentes pour ces modèles énergétiques, en explorant l'origine physique du paramètre de longueur interne inhérent à ces fonctionnelles, et sa dépendance aux types de joints de grains, aux structures atomistiques, et à l'échelle de résolution spatiale. Cette formulation nous a permis d'établir des corrélations entre les structures atomiques des joints de grains et les énergies de cœur, apportant des perspectives nouvelles pour la compréhension et la modélisation des défauts cristallins dans les matériaux polycristallinsThis thesis proposes a multiscale framework aimed at providing a continuous representation of the core structures of crystalline defects, such as dislocations and grain boundaries, as well as their elastic interactions and associated core energies, by combining atomistic and continuum mechanics approaches. The central idea of this study is to transform the atomic core structures of defects into continuous fields of dislocation densities, while preserving the essential atomistic details. The approach developed relies on a recent micromechanical model based on field dislocation mechanics, , which uses the Nye dislocation density tensor, derived from atomistic data, to reproduce the short and long-range mechanical fields associated with these defects. The method has been successfully applied to compact screw dislocations in tungsten, derived from extit{ab initio} simulations, as well as to grain boundaries in copper, simulated by molecular statics. This approach is capable of remarkably reproducing Burgers vectors and defect mechanical fields, demonstrating the lack of any significant loss of information at defect cores. It was possible to reproduce grain boundaries of any misorientation angle using an equivalent density of dislocations, while capturing the continuous elastic fields. Furthermore, this study enables to integrate elastic fields and dislocation densities into Nye tensor-based energy functionals, typically used within strain gradient plasticity models, in order to assess their respective contribution to the total energy of grain boundaries. We analyzed and discussed the relevant forms of energy functionals, explored the physical origin of the internal length parameter inherent to these functionals, and its dependence on grain boundary types, atomistic structures, and spatial resolution scale. This formulation enables to establish correlations between grain boundary atomistic structures and core energies, providing new insights into the understanding and modeling of crystal defects in polycrystalline materials
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Lv, Duchao. "A Multi-Scale Simulation Approach to Deformation Mechanism Prediction in Superalloys." The Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1469009668.
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Kerisit, Christophe. "Analyse des mécanismes de recristallisation statique du tantale déformé à froid pour une modélisation en champ moyen." Phd thesis, Ecole Nationale Supérieure des Mines de Paris, 2012. http://pastel.archives-ouvertes.fr/pastel-00873188.
Повний текст джерелаАнотація:
L'objectif de ce travail est de prédire les évolutions microstructurales se produisant dans le tantale pur lors d'un traitement thermique en fonction de son état microstructural initial. La restauration, la recristallisation et la croissance de grains sont décrites à l'aide d'un modèle en champ moyen qui nécessite une description adéquate de la microstructure, en termes de distributions de tailles de grains et de densités de dislocations équivalentes. La densité de dislocation équivalente moyenne peut être évaluée par une simple mesure de dureté Vickers. L'établissement de la relation dureté-densité de dislocations nécessite l'utilisation d'une loi de comportement basée sur la densité de dislocations équivalente. Les évolutions microstructurales au cours d'un traitement thermique ont été observées et les paramètres pilotant ces phénomènes ont été identifiés à l'aide d'essais originaux comme l'observation in situ de la recristallisation ou l'utilisation d'essais à gradient de déformation pour déterminer le seuil de densité de dislocations équivalente pour déclencher la recristallisation. Des essais plus classiques ont permis d'obtenir des cinétiques de recristallisation dans la gamme 1000°C-1100°C pour différentes microstructures initiales. Les simulations des différents traitements thermiques à l'aide du modèle à champ moyen rendent bien compte des évolutions microstructurales en termes de fraction recristallisée et de taille des grains recristallisés pour des microstructures faiblement déformées ou fortement déformées et fragmentées, en utilisant une description adéquate du type de microstructure initiale. Le modèle devra en revanche être adapté pour traiter le cas de microstructures intermédiaires, en enrichissant non seulement la description de la microstructure initiale mais également celle de l'étape de germination des grains recristallisés. Il deviendra alors capable de prédire les évolutions de microstructures pour tout type de microstructure initiale de tantale.
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Djaka, Komlan Sénam. "Développement et applications d’une technique de modélisation micromécanique de type "FFT" couplée à la mécanique des champs de dislocations." Thesis, Université de Lorraine, 2016. http://www.theses.fr/2016LORR0250/document.
Повний текст джерелаАнотація:
Dans ce mémoire, des méthodes spectrales basées sur la transformée de Fourier rapide ("fast Fourier transform" en anglais notée "FFT") sont développées pour résoudre les équations de champs et d’évolution des densités de dislocations polarisées ou géométriquement nécessaires dans la théorie de la mécanique des champs de dislocations ("Field Dislocations Mechanics" en anglais et notée "FDM") et de son extension phénoménologique et mésoscopique ("Phenomenological Mesoscopic Field Dislocations Mechanics" en anglais et notée "PMFDM"). Dans un premier temps, une approche spectrale a été développée pour résoudre les équations élasto-statiques de la FDM pour la détermination des champs mécaniques locaux provenant des densités de dislocations polarisées et des hétérogénéités élastiques présentes dans les matériaux de microstructure supposée périodique et au comportement élastique linéaire. Les champs élastiques sont calculés de façon précise et sans oscillation numérique même lorsque les densités de dislocations sont concentrées sur un seul pixel (pour les problèmes à deux dimensions) ou sur un seul voxel (pour les problèmes à trois dimensions). Ces résultats sont obtenus grâce à l’application de formules de différenciation spatiale pour les dérivées premières et secondes dans l’espace de Fourier basées sur des schémas à différences finies combinées à la transformée de Fourier discrète. Les résultats obtenus portent sur la détermination précise des champs élastiques des dislocations individuelles de types vis et coin, et des champs élastiques d’interaction entre des inclusions de géométries variées et différentes distributions de densités de dislocations telles que les dipôles ou les boucles de dislocations dans un matériau composite biphasé et des microstructures tridimensionnelles. Dans un second temps, une approche spectrale a été développée pour résoudre de façon rapide et stable l’équation d’évolution spatio-temporelle des densités de dislocations dans la théorie FDM. Cette équation aux dérivées partielles, de nature hyperbolique, requiert une méthode spectrale avec des filtres passe-bas afin de contrôler à la fois les fortes oscillations inhérentes aux approches FFT et les instabilités numériques liées à la nature hyperbolique de l’équation de transport. La validation de cette approche a été effectuée par des comparaisons avec les solutions exactes et les méthodes éléments finis dans le cadre de la simulation des phénomènes physiques d’annihilation ou d’extension/annihilation de boucles de dislocations. En dernier lieu, une technique numérique pour la résolution des équations de la PMFDM est développée dans le cadre d’une formulation FFT pour un comportement élasto-visco-plastique avec la prise en compte de la contribution des dislocations géométriquement nécessaires et statistiquement stockées ainsi que des conditions de saut de la distorsion plastique aux interfaces de type joint de grains ou joint de phases. Cette technique est par la suite appliquée à la simulation de la déformation plastique de structures modèles telles que des microstructures périodiques à canaux et des polycristaux métalliquesFast Fourier transform (FFT)-based methods are developed to solve both the elasto-static equations of the Field Dislocation Mechanics (FDM) theory and the dislocation density transport equation of polarized or geometrically necessary dislocation (GND) densities for FDM and its mesoscopic extension, i.e. the Phenomenological Mesoscopic Field Dislocations Mechanics (PMFDM). First, a numerical spectral approach is developed to solve the elasto-static FDM equations in periodic media for the determination of local mechanical fields arising from the presence of both polarized dislocation densities and elastic heterogeneities for linear elastic materials. The elastic fields are calculated in an accurate fashion and without numerical oscillation, even when the dislocation density is restricted to a single pixel (for two-dimensional problems) or a single voxel (for three-dimensional problems). These results are obtained by applying the differentiation rules for first and second derivatives based on finite difference schemes together with the discrete Fourier transform. The results show that the calculated elastic fields with the present spectral method are accurate for different cases considering individual screw and edge dislocations, the interactions between inhomogeneities of various geometries/elastic properties and different distributions of dislocation densities (dislocation dipoles, polygonal loops in two-phase composite materials). Second, a numerical spectral approach is developed to solve in a fast, stable and accurate fashion, the hyperbolic-type dislocation density transport equation governing the spatial-temporal evolution of dislocations in the FDM theory. Low-pass spectral filters are employed to control both the high frequency oscillations inherent to the Fourier method and the fast-growing numerical instabilities resulting from the hyperbolic nature of the equation. The method is assessed with numerical comparisons with exact solutions and finite element simulations in the case of the simulation of annihilation of dislocation dipoles and the expansion/annihilation of dislocation loops. Finally, a numerical technique for solving the PMFDM equations in a crystal plasticity elasto-viscoplastic FFT formulation is proposed by taking into account both the time evolutions of GND and SSD (statistically stored dislocations) densities as well as the jump condition for plastic distortion at material discontinuity interfaces such as grain or phase boundaries. Then, this numerical technique is applied to the simulation of the plastic deformation of model microstructures like channel-type two-phase composite materials and of polycrystalline metals
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Borges, Gomes Lima Yuri. "Μοdélisatiοn atοmistique de la transfοrmatiοn de phase austénite-ferrite dans les aciers". Electronic Thesis or Diss., Normandie, 2024. http://www.theses.fr/2024NORMR086.
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Cette thèse applique l'approche des Quasiparticles (QA) pour étudier les mécanismes à l'échelle atomique qui conduisent à la transformation de phase CFC à CC dans le fer. Dans un premier temps, cette étude se concentre sur le fer pur, fournissant des résulats détaillés sur la nature et le rôle des dislocations à l'interface CFC-CC. Il a été montré que l'interface CFC-CC est semi-cohérente, avec des marches, et contient deux réseaux de dislocations de transformations. L'approche des Quasiparticles a permis de révéler l'influence de la relation d'orientation sur les caractéristiques de l'interface. Bien que les relations d'orientation étudiées ont montré diférentes structures d'interface, il a été démontré que toutes suivent le même chemin de transformation atomique, dû au glissement des dislocations de transformation à l'interface. Il a été conclu que la transformation complète de CFC à CC implique le mécanisme de transformation de Kurdjumov-Sachs (KS) en deux variantes le long des lignes de dislocations, avec le mécanisme de transformation de Kurdjumov-Sachs-Nishiyama (KSN) qui émerge comme la moyenne de l'action des deux mécanismes KS. Cette description détaillée a servi de base pour l'étude des systèmes Fe-C, où la ségrégation du carbone à l'interface a été observée. De plus, il a été montré que les profils de concentration de carbone sont cohérents avec des conditions d'équilibre local à l'interfaceThis thesis applies the Quasiparticle Approach (QA) to investigate the atomic scale mechanisms driving the phase transformation from FCC to BCC structures in iron. Initially, the study focuses on pure iron, providing detailed results into the nature and role of dislocations, at the FCC-BCC interface. It was shown that the FCC-BCC interface is semi-coherent and stepped, with two sets of transformations dislocations at the interface. The QA framework reveals how each orientation relationship (OR) influences the interface characteristics. Although the ORs displayed different interface structures, all were ultimately found to follow the same atomic transformation path, driven by the glide of transformation dislocations at the interface. It was concluded that the complete FCC to BCC phase transformation involves the action of the Kurdjumov-Sachs (KS) transformation mechanism in two variants along the two sets of dislocations, with the Kurdjumov-Sachs-Nishiyama (KSN) mechanism emerging as the average of the two KS mechanisms. This detailed description served as a basis for the study of Fe-C systems, where carbon segregation at the interface was observed. Moreover, it was shown that the carbon concentration profiles were consistent with local equilibrium conditions at the interface
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Oztop, Muin S. "Multiscale Experimental Analysis in Plasticity: Linking Dislocation Structures to Continuum Fields." Thesis, 2011. https://doi.org/10.7916/D8NP2BS1.
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Plastic deformation in metals is a complex phenomenon and is result of competition between different complicated mechanisms, and among all, dislocation nucleation and motion are the most dominant ones. Dislocation evolution is known to be a multiscale phenomenon, and has been incorporated to crystal plasticity theories to analyze the size effect in metals for almost a decade ago. Although the theories suffice to predict the size effect in metals, they are largely phenomenological. Here a novel experimental method is developed to resolve the complexity in plastic deformation due to dislocations and to extract new material length scales that can be incorporated to numerical models. A continuum-based quantity: the geometrically necessary dislocation density (GND) that describes the signed part of the overall dislocations is measured on a nickel single crystal sample using recently developed high resolution electron backscatter diffraction (HR-EBSD) over different field of view, 90 μm^2 − 1mm^2 with various step sizes, 50 nm to 2, 500 nm . The net Burgers vector density, which includes the information of the direction of the overall dislocation motion and also quantifies the flux of atoms changing positions due to dislocations, is measured for the first time using continuum methods. A new parameter, β, that is extracted from the net Burger vector density to monitor dislocation activity on crystallographic slip planes is measured. Measurements reveals patterning in GND densities and a distribution of length scales rather than a single length scale as assumed. The length scales, such as dislocation spacing, and dislocation cell sizes are quantified. The linear relationship between dislocation spacing and dislocation cell size is obtained, where the slope of the linear fit varies with different crystallographic slip systems and the number of the active slip systems. The slope ranges between 23-29 for dominantly single slip regions, whereas it ranges between 13-16 for multislip regions, which agrees with the findings from TEM analysis in the literature showing how a continuum based method can be used to obtain same material parameters. The experimental measurements and the assumptions are elaborated in a detailed analysis. The effect of step size in EBSD results is presented, and the information loss with increasing the step size is shown. The uncertainty in GND density from the HR-EBSD measurements is found to be 10^13, which is two order of magnitude less than results from traditional diffraction methods. The effect of dislocation mobility on microstructure evolution has been also investigated, specifically tantalum single crystal specimens tested at 77 K and 293 K. The results unraveled occurrences of different deformation mechanisms: kink shear, and twinning at low temperatures. Interactions between dislocations and twin formations are observed and striking microstructure differences are examined. The dislocations density measurement results on tantalum are unique in the experimental sense and data can be used to extract length scale information. The experimental observations have been exploited to build the foundations of a numerical model. The effect of microstructure evolution on mechanical response has been investigated numerically based upon experimental observations. One of the main outcome of the experimental analysis -the variation of GND densities in cell walls- has been incorporated into a strain gradient plasticity framework. The proposed model is demonstrated with constrained shear and pure bending problems. The results presented show patterning in the GND density profile depending on the prescribed initial variation of the saturation value of GND densities and also change in overall mechanical response depending on the complexity of the prescribed profile.
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(9312344), Xiaorong Cai. "PHASE FIELD MODELING OF MICROSTRUCTURE EVOLUTION IN CRYSTALLINE MATERIALS." Thesis, 2020.
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The material responses and the deformation pattern of crystals are strongly influ- enced by their microstructure, crystallographic texture and the presence of defects of various types.
In electronics, Sn coatings are widely used in circuits to protect conductors, reduce oxidation and improve solderability. However, the spontaneous growth of whiskers in Sn films causes severe system failures. Based on extensive experimental results, whiskers are observed to grow from surface grains with shallow grain boundaries. The underlying mechanism for these surface grains formation is crucial to predict potential whisker sites. A phase field model is coupled with a single crystal plasticity model and applied to simulate the grain boundary migration as well as the grain rotation process in Sn thin film, which are two possible mechanisms for surface grain formation. The grain boundary migration of three columnar grains is modeled and no surface grain is formed due to large plastic dissipation. In polycrystal Sn thin film, the nucleation of subgrains with shallow grain boundaries is observed for certain grain orientations on the film surface and the location of which corresponds to the regions with high strain energy density. From these simulations, it can be concluded that the grain rotation is the mechanism for whisker grain formation and the nucleated subgrains may be the potential whisker sites.
Sn-based solders are also widely used in electronics packaging. The reliability and the performance of SAC (Sn-Ag-Cu) solders are of key importance for the miniaturiza- tion of electronics. The interfacial reaction between Cu substrates and Sn-based sol- ders forms two types of brittle intermetallic compounds (IMCs), Cu6Sn5 and Cu3Sn.
During the operation, the interconnecting solders usually experience thermal loading
and electric currents. These environmental conditions result in the nucleation of voids
in Cu3Sn layer and the growth of the IMCs. A phase field damage model is applied
to model the fracture behavior in Cu/Sn system with different initial void densities
and different Cu3Sn thickness. The simulation results show the fracture location is
dependent on the Cu3Sn thickness and the critical stress for fracture can be increased
by lowering the void density and Cu3Sn thickness.
In alloys, the stacking fault energy varies with the local chemical composition. The effects of the stacking fault energy fluctuation on the strengthening of alloys are studied using phase field dislocation method (PFDM) simulations that model the evolution of partial dislocations in materials at zero temperature. Some examples are shown to study the dependency of the yield stress on the stacking fault energy, the decorrelation of partial dislocations in the presence of impenetrable and penetrable particles. Simulations of the evolution of partial dislocations in a stacking fault energy landscape with local fluctuations are presented to model the responses of high entropy alloys. A strong size dependency is observed with a maximum strength when the mean region size approaches the average equilibrium stacking fault width. The strength of high entropy alloys could be improved by controlling the disorder in the chemical misfit.
Книги з теми "Dislocation field mechanics"
1
Fressengeas, Claude. Mechanics of Dislocation Fields. Hoboken, NJ, USA: John Wiley & Sons, Inc., 2017. http://dx.doi.org/10.1002/9781118578285.
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Fressengeas, Claude. Mechanics of Dislocation Fields. Wiley & Sons, Incorporated, John, 2017.
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3
Fressengeas, Claude. Mechanics of Dislocation Fields. Wiley & Sons, Incorporated, John, 2017.
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4
Fressengeas, Claude. Mechanics of Dislocation Fields. Wiley & Sons, Incorporated, John, 2017.
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5
Fressengeas, Claude. Mechanics of Dislocation Fields. Wiley & Sons, Limited, John, 2017.
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Fressengeas, Claude. Mechanics of Dislocation Fields. Wiley & Sons, Incorporated, John, 2017.
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Sutton, Adrian P. Physics of Elasticity and Crystal Defects. Oxford University Press, 2020. http://dx.doi.org/10.1093/oso/9780198860785.001.0001.
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Mechanical properties of crystalline materials are almost always dominated by the defects within them. The ability to shape metals into pipes, girders and furniture stems from the generation, motion and interaction of these defects. Defects are also the agents of chemical changes within crystals, enabling mass transport by atomic diffusion and changes of phase. Defects distort the crystal and these distortions enable defects to interact over large distances. The theory of elasticity is used to describe these interactions. Assuming no familiarity with the theory, this book introduces the reader to linear elasticity and its application to point defects, dislocations and cracks. A unique feature of the book is the attention given to the atomic structure of defects and its influence on their properties and their elastic fields. Where it is available brief biographical information is provided about prominent contributors to the field. This textbook is written for postgraduate students in physics, engineering and materials science. It is very likely that even those students with some knowledge of elasticity and defects will find much that is new to them in this book.There are exercises to help the student check their understanding as they work through each chapter. The student is guided through more advanced problems at the end of each chapter. Worked solutions to all exercises and problems are available to course instructors from the OUP website. The last chapter describes four technologically important areas requiring fundamental research, with suggestions for possible PhD projects.
Частини книг з теми "Dislocation field mechanics"
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Luo, J. "On the Stress Field and Dislocation Emission of an Elliptically Blunted Mode III Crack with Surface Stress Effect." In IUTAM Symposium on Surface Effects in the Mechanics of Nanomaterials and Heterostructures, 277–87. Dordrecht: Springer Netherlands, 2012. http://dx.doi.org/10.1007/978-94-007-4911-5_24.
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Koyama, Motomichi, Hiroshi Noguchi, and Kaneaki Tsuzaki. "Microstructural Crack Tip Plasticity Controlling Small Fatigue Crack Growth." In The Plaston Concept, 213–34. Singapore: Springer Nature Singapore, 2022. http://dx.doi.org/10.1007/978-981-16-7715-1_10.
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AbstractIn this chapter, we present a metallurgical–mechanical mechanism-based strategy for the design of fatigue-resistant metals. Specifically, we elucidate the importance of the metallurgical microstructure in a mechanical singular field (crack tip). The fatigue crack growth resistance is controlled through the crack tip “plasticity”, and the effect of the associated microstructure becomes significant when the crack is “small (or short)”. More importantly, the resistance to small crack growth determines a major portion of fatigue life and strength. Therefore, the microstructural crack tip plasticity is a key breakthrough to the development of fatigue-resistant metals. As successful examples of this concept, we introduce the effects of grain refinement, martensitic transformation, strain aging, dislocation planarity enhancement, and microstructure heterogeneity on small fatigue crack growths.
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Tsuji, Nobuhiro, Shigenobu Ogata, Haruyuki Inui, Isao Tanaka, and Kyosuke Kishida. "Proposing the Concept of Plaston and Strategy to Manage Both High Strength and Large Ductility in Advanced Structural Materials, on the Basis of Unique Mechanical Properties of Bulk Nanostructured Metals." In The Plaston Concept, 3–34. Singapore: Springer Nature Singapore, 2022. http://dx.doi.org/10.1007/978-981-16-7715-1_1.
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AbstractAdvanced structural materials are required to show both high strength and large ductility/toughness, but we have not yet acquired the guiding principle for that. The bulk nanostructured metals are polycrystalline metallic materials having bulky dimensions and average grain sizes smaller than 1 μm. Bulk nanostructured metals show very high strength compared with that of the coarse-grained counterparts, but usually exhibit limited tensile ductility, especially small uniform elongation below a few %, due to the early plastic instability. On the other hand, we have recently found that particular bulk nanostructured metals can manage high strength and large tensile ductility. In such bulk nanostructured metals, unusual deformation modes different from normal dislocation slips were unexpectedly activated. Unusual <c+a> dislocations, deformation twins with nano-scale thickness, and deformation-induced martensite nucleated from grain boundaries in the bulk nanostructured Mg alloy, high-Mn austenitic steel, and Ni-C metastable austenitic steel, respectively. Those unexpected deformation modes enhanced strain hardening of the materials, leading to high strength and large tensile ductility. It was considered that the nucleation of such unusual deformation modes was attributed to the scarcity of dislocations and dislocation sources in each recrystallized ultrafine grain, which also induced discontinuous yielding with clear yield drop universally recognized in bulk nanostructured metals having recrystallized structures. For discussing the nucleation of different deformation modes in atomistic scales, the new concept of plaston which considered local excitation of atoms under singular dynamic fields was proposed. Based on the findings in bulk nanostructured metals and the concept of plaston, we proposed a strategy for overcoming the strength-ductility trade-off in structural metallic materials. Sequential nucleation of different deformation modes would regenerate the strain-hardening ability of the material, leading to high strength and large tensile ductility. The strategy could be a guiding principle for realizing advanced structural materials that manage both high strength and large tensile ductility.
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Bykovtsev, A. S., and Zh S. Tavbaev. "Studies on Wave Fields Caused by a Star-Like System of Propagating Dislocation Ruptures." In Computational Mechanics ’88, 381–82. Berlin, Heidelberg: Springer Berlin Heidelberg, 1988. http://dx.doi.org/10.1007/978-3-642-61381-4_92.
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Li, Xiangyu, Baoji Ma, Bin Liu, Jinkui Cao, and Liangliang Li. "Microstructure of AZ31B Alloy Induced by Laser Shock." In Lecture Notes in Mechanical Engineering, 727–34. Singapore: Springer Nature Singapore, 2025. https://doi.org/10.1007/978-981-97-7887-4_63.
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Abstract Magnesium alloys have great potential in the field of biomedical degradable materials. However, their poor mechanical and corrosion resistance properties limit their applications. In this study, the AZ31B alloy with a compact hexagonal close-packed (HCP) crystal structure was selected as the material, as it tends to undergo twinning deformation rather than dislocation slip during plastic deformation due to its low stacking fault energy. The microstructures before and after LSP treatment were characterized using optical microscopy (OM), electron backscatter diffraction (EBSD), and X-ray diffraction (XRD). The results showed that the grain size was refined and exhibited a gradient distribution after LSP treatment. Electron backscatter diffraction (EBSD) was used to characterize the microstructure of LSP before and after treatment. The results showed that the grain size was refined after LSP treatment, and showed a gradient distribution trend.
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Ekanem, Jemimah Timothy, and Idongesit Michael Umoh. "Social Vulnerability of Rural Dwellers to Climate Variability: Akwa Ibom State, Nigeria." In African Handbook of Climate Change Adaptation, 2269–91. Cham: Springer International Publishing, 2021. http://dx.doi.org/10.1007/978-3-030-45106-6_232.
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AbstractFor their livelihood activities, rural farming communities depend more on extractive capital. Their capacity to cultivate sufficiently for their family maintenance is greatly impeded by the absence of either temperature or rainfall quantity pattern or uniformity. The divergent effects of recent extreme weather events around the world, including within relatively small geographical areas, exemplify the unequal impacts of climate change on populations. Akwa Ibom State has been found vulnerable to extreme weather events, such as flooding, severe storms, and rising sea levels, leading to homelessness, poverty, conflicts, and war for millions of people. All of these have resulted in social disturbances and dislocations among rural populations, especially in coastal communities, making them more vulnerable to climate variability. In the field of social vulnerability in the state, not much has been achieved. This chapter analyzes the vulnerability of the rural population to climate variability; the socio-economic characteristics of the rural population; the index of social vulnerability of rural dwellers to climate variability; social vulnerability factors; and the rural population’s social vulnerability mitigation initiatives in Akwa Ibom State, Nigeria. Social science approaches to human vulnerability draw critical attention to the root causes and factors why people are forced to respond to risks from climate change. A complex social approach to vulnerability is most likely to enhance mitigation and adaptation preparation efforts, given that vulnerability is a multidimensional mechanism rather than an invariable state.
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Ekanem, Jemimah Timothy, and Idongesit Michael Umoh. "Social Vulnerability of Rural Dwellers to Climate Variability: Akwa Ibom State, Nigeria." In African Handbook of Climate Change Adaptation, 1–23. Cham: Springer International Publishing, 2021. http://dx.doi.org/10.1007/978-3-030-42091-8_232-1.
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AbstractFor their livelihood activities, rural farming communities depend more on extractive capital. Their capacity to cultivate sufficiently for their family maintenance is greatly impeded by the absence of either temperature or rainfall quantity pattern or uniformity. The divergent effects of recent extreme weather events around the world, including within relatively small geographical areas, exemplify the unequal impacts of climate change on populations. Akwa Ibom State has been found vulnerable to extreme weather events, such as flooding, severe storms, and rising sea levels, leading to homelessness, poverty, conflicts, and war for millions of people. All of these have resulted in social disturbances and dislocations among rural populations, especially in coastal communities, making them more vulnerable to climate variability. In the field of social vulnerability in the state, not much has been achieved. This chapter analyzes the vulnerability of the rural population to climate variability; the socio-economic characteristics of the rural population; the index of social vulnerability of rural dwellers to climate variability; social vulnerability factors; and the rural population’s social vulnerability mitigation initiatives in Akwa Ibom State, Nigeria. Social science approaches to human vulnerability draw critical attention to the root causes and factors why people are forced to respond to risks from climate change. A complex social approach to vulnerability is most likely to enhance mitigation and adaptation preparation efforts, given that vulnerability is a multidimensional mechanism rather than an invariable state.
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"Elasto-static Field Equations." In Mechanics of Dislocation Fields, 31–48. Hoboken, NJ, USA: John Wiley & Sons, Inc., 2017. http://dx.doi.org/10.1002/9781118578285.ch2.
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"Elasto-plastic Field Equations." In Mechanics of Dislocation Fields, 99–119. Hoboken, NJ, USA: John Wiley & Sons, Inc., 2017. http://dx.doi.org/10.1002/9781118578285.ch5.
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Sutton, Adrian P. "The force on a defect." In Physics of Elasticity and Crystal Defects, 163–78. Oxford University Press, 2020. http://dx.doi.org/10.1093/oso/9780198860785.003.0008.
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This chapter is based on Eshelby’s static energy-momentum tensor which results in an integral expression for the configurational force on a defect. After elucidating the concepts of a configurational force and an elastic singularity the mechanical pressure on an interface, such as a twin boundary or a martensitic interface, is derived. Eshelby’s force on a defect is derived using both physical arguments and more formally using classical field theory. It is equivalent to the J-integral in fracture mechanics. The Peach–Koehler force on a dislocation is rederived using the static energy-momentum tensor. An expression for an image force is derived, where a defect interacts with a free surface.
Тези доповідей конференцій з теми "Dislocation field mechanics"
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EricksonKirk, Marjorie A., and Matthew Wagenhofer. "A Theoretically-Based Statistical Model of Transition Toughness." In ASME 2007 Pressure Vessels and Piping Conference. ASMEDC, 2007. http://dx.doi.org/10.1115/pvp2007-26303.
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A program was undertaken to develop a fully predictive model of the scatter in toughness across a wide range of transition temperatures based on a physical understanding of deformation and fracture behavior. The temperature dependence of the proposed model is taken from previous work in which the local mechanisms of cleavage fracture were used to define the plastic work to fracture. The local to global stress transference is achieved by a dislocation-mechanics based examination of the interaction between the globally applied stresses, a macroscopic crack and a nearby accumulation of dislocations blocked by a second phase particle, i.e. slip band, whose position relative to the macroscopic crack tip is variable. The scatter of toughness values at each temperature is captured through variation of this macro-crack / micro-crack geometry, and of the particle size. Once the local stress field is determined using the dislocation-based transference equations, an energy balance criterion for fracture is applied that incorporates the temperature-dependent fracture work term and the local stresses determined from the transference equations. This paper summarizes this multiscale fracture model, which serves as a foundation for more detailed descriptions of the mathematics of the quantitative model, its temperature dependence and scatter characteristics and coding efforts. These latter topics will be addressed in greater detail in subsequent papers.
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Zhu, Haiyan, Xinru He, Yang Li, Xuanhe Tang, Chuhao Huang, Bo Zeng, and Yi Song. "Investigation to Integrated Geomechanics of Casing Deformation and a New Technique: A Case in Deep Gas Shale of Sichuan Basin, China." In 57th U.S. Rock Mechanics/Geomechanics Symposium. ARMA, 2023. http://dx.doi.org/10.56952/arma-2023-0371.
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ABSTRACT To investigate the mechanism of casing deformation and failure during volumetric fracturing of deep gas shale in Sichuan Basin, we put forward targeted comprehensive prevention and control measures. Based on the idea of geological-engineering integration, a three-dimensional geo-mechanical model is established, which coupled the formation - cementing sheath - casing during hydraulic fracturing of deep shale reservoir. Taking TB01 well as an example, the correlation between induced stress, cementing quality, fault or natural fracture dislocation and other factors in the process of hydraulic fracturing was analyzed. The main cause of fault or natural fracture dislocation under the influence of multiple factors is determined firstly. Then, the effectiveness of fracturing scale controlling, casing and cementing quality improvement and other process measures are investigated. Finally, based on the above study, a novel process and supporting tools for fault pre-slip are proposed in this paper. The feasibility of the process is demonstrated, and the structural parameters of the supporting tools are optimized. Taking Luzhou as an example, it provides theoretical and technical support of deep shale gas in safety and high efficiency. INTRODUCTION China has abundant reserves of shale gas with great development potential. Speeding up the development of shale gas is of great significance for relieving the pressure on natural gas supplies and adjusting energy structure. Shale gas is developed according to the causes of casing deformation, many of those who learn to conduct the research, puts forward the effect of thermal stress[1-3], asymmetric fracturing[4-9], the cementing quality [10-15] and fault slip[16-30], etc. At present, most scholars have recognized that fault activation in the process of hydraulic fracturing may be the main controlling factor leading to casing deformation[17-29], which has been verified by more and more field data. These research understandings provide theoretical guidance for the field, however, casing deformation still occurs from time to time, and there is still a lack of specific measures to solve the problem, which needs further research.
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Banerjee, Sauvik, Mutasem Shehadeh, Gang Lu, Nicholas Kioussis, and Nasr Ghoniem. "A Multiscale Approach for the Determination of Nonsingular Elastic Fields of Dislocations in Bulk and Nano-Layered Materials." In ASME 2007 International Mechanical Engineering Congress and Exposition. ASMEDC, 2007. http://dx.doi.org/10.1115/imece2007-42058.
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The traditional description of elastic field and energies of dislocations is based on continuum theory of linear elasticity that suffers from the long-standing problem of singularities at the dislocation core. Singular solutions are often circumvented by introducing an artificial core-cutoff radius. This limits the applicability of the theory to describe situations where it is important to know the strained state and nanoscopic details within a few atomic spacings surrounding the dislocation center, known as the dislocation core. In this paper, a computationally tractable multiscale approach is developed to calculate the nonsingular elastic fields of dislocations in both bulk and nano-layered materials. The approach is an extension of Peierls-Nabarro (PN) model, with the following features: (1) all three components of the displacement vector for atoms within the dislocation core are included; (2) the entire generalized stacking fault energy (GSFE or gamma-γ) surface obtained from ab initio calculations is utilized; and (3) the method can be generalized to treat curved dislocations. We combine the parametric dislocation dynamics (DD) approach for the interaction and motion of dislocations with the ab initio calculations of the lattice restoring forces, which are extracted from the γ surface. The method is used to study two important problems: (a) dislocation dissociation in bulk crystals (b) dislocation transmission across interfaces in elastic bimaterials. Dislocation core structures in bulk aluminum and silver are determined. The results from the model are shown to be in excellent agreement with experiments for both Al and Ag. For bi-materials system, the effects of the mismatch in the elastic properties, γ surface and lattice parameters on the spreading of the dislocation onto the interface(s) and the transmission across the interface(s) are studied in detail.
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Liu, Yingjun, Chenggang Xian, Hui Zhang, Guoqing Yin, Ke Xu, Zhimin Wang, Shujun Lai, Jingrui Liang, and Ziwei Qian. "Development and Validation of a New Wellbore Stability Prediction Model for Complex Reservoirs: Application to the Keshen Gas Field in the Tarim Basin." In 58th U.S. Rock Mechanics/Geomechanics Symposium. ARMA, 2024. http://dx.doi.org/10.56952/arma-2024-0105.
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ABSTRACT: The objective of this paper is to propose a new method for predicting the safe mud density window of drilling fluid in the Keshen gas field, located in the Tarim Basin. The study focuses on applying this method to analyze wellbore stability in the complex and high-pressure environment of the field. The new method incorporates the Mogi-Coulomb criterion, which considers intermediate stress as the shear failure criterion of the wellbore. Additionally, the method accounts for the shear breakdown of rock when calculating the fracture pressure. It predicts the shear slip of the reservoir's weak surface using the Jaeger criterion. Furthermore, it takes into account the weak surface of drilling fluid invasion when calculating the tensile failure of the wellbore. The application of wellbore stability analysis in Well A reveals that the dislocation of natural fractures and the tensile fracture after the invasion of drilling fluid are significant factors contributing to wellbore instability, such as chipping and lost circulation, particularly in formations with developed natural fractures. In the case of a strike-slip stress field, shear sliding is more likely to occur when the fluid invades the crack or weak surface, as opposed to tensile failure. Based on the prediction results of the new method, the mechanism of wellbore instability is interpreted, and engineering countermeasures are proposed to mitigate the risk of wellbore instability. 1. INTRODUCTION The Keshen gas field in Tarim Basin poses significant challenges due to its complex structure, high temperature, high pressure, complicated stress state, and developed natural fractures. These factors contribute to issues such as wellbore instability, a high accident rate, and prolonged drilling periods (Zhang et al., 2015; Cai et al., 2019; Zhu et al., 2014). The primary cause of wellbore instability lies in the disruption of the original mechanical equilibrium near the wellbore, leading to the redistribution and concentration of stress that exceeds the rock's strength once the drill bit penetrates the formation (Nelson et al., 2005; Abbas et al., 2019). The most common manifestations of wellbore instability are collapse and leakage. However, proactive determination of critical mud weights can often mitigate these drilling issues. To achieve this, a constitutive model is employed to estimate the stresses surrounding the wellbore and is complemented by failure criterions. Thus, establishing an accurate and reliable safe mud weights window is of utmost importance.
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Cochran, Kristine B., Marjorie Erickson, Paul T. Williams, Hilda B. Klasky, and B. Richard Bass. "A Dislocation-Based Cleavage Initiation Model for Pressure Vessel Steels." In ASME 2012 Pressure Vessels and Piping Conference. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/pvp2012-78564.
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Efforts are under way to develop a theoretical, multi-scale model for the prediction of fracture toughness of ferritic steels in the ductile-to-brittle transition temperature (DBTT) region that accounts for temperature, irradiation, strain rate, and material condition (chemistry and heat treatment) effects. This new model is intended to address difficulties associated with existing empirically-derived models of the DBTT region that cannot be extrapolated to conditions for which data are unavailable. Dislocation distribution equations, derived from the theories of Yokobori et al., are incorporated to account for the local stress state prior to and following initiation of a microcrack from a second-phase particle. The new model is the basis for the DISlocation-based FRACture (DISFRAC) computer code being developed at the Oak Ridge National Laboratory (ORNL). The purpose of this code is to permit fracture safety assessments of ferritic structures with only tensile properties required as input. The primary motivation for the code is to assist in the prediction of radiation effects on nuclear reactor pressure vessels, in parallel with the EURATOM PERFORM 60 project. This paper begins with a brief overview of the strategy for implementing the new model into the DISFRAC computer code. The balance of the paper focuses on efforts to model the nucleation of a carbide particle crack near an existing macrocrack under applied load. The carbide microcrack initiation model applies dislocation mechanics to assess the stress intensity exerted on a stiff, elastic carbide particle embedded in an elastic-plastic ferrite matrix near a macrocrack tip. The paper derives and discusses the governing equations for the model; including (1) computation of a slip band dislocation pileup distribution by enforcing equilibrium with the macrocrack-induced elastic-plastic stress field, (2) calculation of the mode I stress intensity on the particle crack plane due to the dislocation pileup and (3) determination of the particle fracture toughness. Together, these calculations provide the basis for determining the applied load required to initiate particle fracture. This paper demonstrates how the prediction of particle fracture depends on various microstructure parameters.
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Sui, Dan, and John E. Huber. "Modelling of Needle Domains in Barium Titanate Single Crystals Using Dislocation Theory." In ASME 2012 Conference on Smart Materials, Adaptive Structures and Intelligent Systems. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/smasis2012-8033.
Повний текст джерелаАнотація:
A model is established to study needle domains in barium titanate single crystals using the theory of dislocations. Considering the mechanical and electrical compatibility in ferroelectrics, the fields produced by a needle domain are represented using the equivalent fields due to an effective edge dislocation coupled with a line charge. Accordingly, the dislocation fields derived by Barnett and Lothe for anisotropic piezoelectric media are used to analyze the stress and electric fields around needle domains. The interaction of the pairs of needle domains in an infinite piezoelectric body is studied by computing the interactive force and the total energy. It is found that the needle tip interactions tend to be dominated by the electrostatic terms. Additionally, comb-like arrays of needle domains are investigated. Stable configurations of needle domains in a herringbone pattern are identified, consistent with experimental evidence. However, comb-like arrays of needles are found to be unstable if perfectly insulating conditions without lattice friction are assumed.
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Korsunsky, Alexander M., and Alexander M. Korsunsky. "Non-Singular Dislocation Elastic Fields and Linear Elastic Fracture Mechanics." In CURRENT THEMES IN ENGINEERING SCIENCE 2009: Selected Presentations at the World Congress on Engineering-2009. AIP, 2010. http://dx.doi.org/10.1063/1.3366503.
Повний текст джерела
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Redko, Roman, Grigorii Milenin, Nadiia Safriuk-Romanenko, and Svitlana Redko. "Modification of dislocation concentration in GaN:Si films by non-thermal microwave radiation treatment." In IXth INTERNATIONAL SAMSONOV CONFERENCE “MATERIALS SCIENCE OF REFRACTORY COMPOUNDS”. Frantsevich Ukrainian Materials Research Society, 2024. http://dx.doi.org/10.62564/m4-rr1233.
Повний текст джерелаАнотація:
Both photoluminescence spectra and X-ray diffraction of GaN:Si were measured during long term (one month) after processing in microwave field (2.45 GHz, 10 s, p=7.5W/cm2). It was obtained non-monotonous changes of detected characteristics of studied samples. Due to small energy obtained in chosen field alternative resonant mechanism was proposed to explain observed features. Transformation of the defect subsystem (impurity-defect complexes destruction and/or detachment and displacement of dislocations) could be realized due to resonant phenomena related with coincidence between the electromagnetic wave frequency and proper frequencies of dislocation oscillations [1] and ion-plasma oscillations of impurity ions [2]. At the resonant frequency with small attenuation, the amplitude and, therefore, the oscillation energy increase sharply. As soon as the oscillation energy becomes higher than the binding energy of defects, the noted changes occur in the state of the latter. The observed features of long-term changes in the PL band intensities and dislocations concentration for the semiconductors under investigation after treatments in microwave field has been well described by the offered physical-statistical model of the behavior of defects, which is based on the idea that the corresponding physical processes can be described as random events. This physical-statistical approach allowed us to estimate the diffusion coefficients of defects in epitaxial films of semiconductor compounds. Obtained information will be value for understanding sensor system natural aging due to presence external microwave fields
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Zhang, Zhen, and Zhigang Suo. "Split Singularities: Applications and Implications." In ASME 2007 International Mechanical Engineering Congress and Exposition. ASMEDC, 2007. http://dx.doi.org/10.1115/imece2007-41213.
Повний текст джерелаАнотація:
In the microelectronic system, many materials are integrated together in complex structures, from the level of transistors to the level of motherboard. These materials are of different thermomechanical properties, and usually meet together to form the sharp features, such as trenches, wedges, corners or junctions. These sharp features can concentrate stresses, which in turn fail the devices in the ways of cracking, debonding, or injecting dislocations, etc. The singular stress field is a linear superposition of two modes, usually of unequal exponents, either a pair of complex conjugates, or two unequal real numbers. In the latter case, a stronger and a weaker singularity coexist, known as split singularities. The weaker singularity can readily affect the outcome of failures. A dimensionless parameter, called the mode mixity, is defined to characterize the proportion of the two modes at the length scale where the processes of fracture occur. If the mode mixity is nearly zero, then the singular stress field can be simplified to a single mode, and be characterized by one stress intensity factor, on which the criteria of avoiding the failure initiated from the sharp features can be established. Otherwise, both modes need to be considered. We apply this theory to crack penetration or debond, and dislocation injection into strained silicon.
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Wu, Bei, Ronghui Ma, and Hui Zhang. "Design and Optimization of an Aluminum Nitride Sublimation Growth System." In ASME 2003 International Mechanical Engineering Congress and Exposition. ASMEDC, 2003. http://dx.doi.org/10.1115/imece2003-41980.
Повний текст джерелаАнотація:
In this paper, an integrated model considering induction heating, heat transfer, growth kinetics and thermo-elastic stress has been developed to study temperature distribution in the growth system, crystal shape and stress distribution in the asgrown aluminum nitride (AIN) crystal. The electromagnetic field and induction heat generation are calculated by the Maxwell equations. Transient temperature distribution in the growth chamber is simulated by energy accounting for conduction/radiation within and between various components. To reduce thermal stress and dislocation, a growth method to enlarge the ingot diameter from a smaller seed and maintain low thermal stress in the crystal has been proposed. The thermo-elastic stress fields have been calculated for several designed temperature profiles along the crucible inner wall and stress distribution has been correlated to dislocation density distribution.