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3d Discrete Dislocation Dynamics Applied To Dislocation Precipitate Interactions
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Book Synopsis 3D Discrete Dislocation Dynamics Applied to Dislocation-precipitate Interactions by : Chansun Shin
Download or read book 3D Discrete Dislocation Dynamics Applied to Dislocation-precipitate Interactions written by Chansun Shin and published by . This book was released on 2004 with total page 160 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Book Synopsis Evolution, Interaction, and Intrinsic Properties of Dislocations in Intermetallics by :
Download or read book Evolution, Interaction, and Intrinsic Properties of Dislocations in Intermetallics written by and published by . This book was released on 2008 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The generation, motion, and interaction of dislocations play key roles during the plastic deformation process of crystalline solids. 3D Dislocation Dynamics has been employed as a mesoscale simulation algorithm to investigate the collective and cooperative behavior of dislocations. Most current research on 3D Dislocation Dynamics is based on the solutions available in the framework of classical isotropic elasticity. However, due to some degree of elastic anisotropy in almost all crystalline solids, it is very necessary to extend 3D Dislocation Dynamics into anisotropic elasticity. In this study, first, the details of efficient and accurate incorporation of the fully anisotropic elasticity into 3D discrete Dislocation Dynamics by numerically evaluating the derivatives of Green's functions are described. Then the intrinsic properties of perfect dislocations, including their stability, their core properties and disassociation characteristics, in newly discovered rare earth-based intermetallics and in conventional intermetallics are investigated, within the framework of fully anisotropic elasticity supplemented with the atomistic information obtained from the ab initio calculations. Moreover, the evolution and interaction of dislocations in these intermetallics as well as the role of solute segregation are presented by utilizing fully anisotropic 3D dislocation dynamics. The results from this work clearly indicate the role and the importance of elastic anisotropy on the evolution of dislocation microstructures, the overall ductility and the hardening behavior in these systems.
Book Synopsis Dislocation Dynamics and Plasticity by : Taira Suzuki
Download or read book Dislocation Dynamics and Plasticity written by Taira Suzuki and published by Springer Science & Business Media. This book was released on 2013-03-07 with total page 237 pages. Available in PDF, EPUB and Kindle. Book excerpt: In the 1950s the direct observation of dislocations became possible, stimulat ing the interest of many research workers in the dynamics of dislocations. This led to major contributions to the understanding of the plasticity of various crys talline materials. During this time the study of metals and alloys of fcc and hcp structures developed remarkably. In particular, the discovery of the so-called in ertial effect caused by the electron and phonon frictional forces greatly influenced the quantitative understanding of the strength of these metallic materials. Statis tical studies of dislocations moving through random arrays of point obstacles played an important role in the above advances. These topics are described in Chaps. 2-4. Metals and alloys with bcc structure have large Peierls forces compared to those with fcc structure. The reasons for the delay in studying substances with bcc structure were mostly difficulties connected with the purification techniques and with microscopic studies of the dislocation core. In the 1970s, these difficulties were largely overcome by developments in experimental techniques and computer physics. Studies of dislocations in ionic and covalent bonding materials with large Peierls forces provided infonnation about the core structures of dislocations and their electronic interactions with charged particles. These are the main subjects in Chaps. 5-7.
Book Synopsis Discrete Dislocation Dynamics Simulations of Dislocation - Low Angle Grain Boundary Interactions by : Liu Bing
Download or read book Discrete Dislocation Dynamics Simulations of Dislocation - Low Angle Grain Boundary Interactions written by Liu Bing and published by . This book was released on 2012 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Dislocation Dynamics by : Alan R. Rosenfield
Download or read book Dislocation Dynamics written by Alan R. Rosenfield and published by . This book was released on 1968 with total page 806 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Creep and High Temperature Deformation of Metals and Alloys by : Stefano Spigarelli
Download or read book Creep and High Temperature Deformation of Metals and Alloys written by Stefano Spigarelli and published by MDPI. This book was released on 2019-12-12 with total page 212 pages. Available in PDF, EPUB and Kindle. Book excerpt: By the late 1940s, and since then, the continuous development of dislocation theories have provided the basis for correlating the macroscopic time-dependent deformation of metals and alloys—known as creep—to the time-dependent processes taking place within the metals and alloys. High-temperature deformation and stress relaxation effects have also been explained and modeled on similar bases. The knowledge of high-temperature deformation as well as its modeling in conventional or unconventional situations is becoming clearer year by year, with new contemporary and better performing high-temperature materials being constantly produced and investigated. This book includes recent contributions covering relevant topics and materials in the field in an innovative way. In the first section, contributions are related to the general description of creep deformation, damage, and ductility, while in the second section, innovative testing techniques of creep deformation are presented. The third section deals with creep in the presence of complex loading/temperature changes and environmental effects, while the last section focuses on material microstructure–creep correlations for specific material classes. The quality and potential of specific materials and microstructures, testing conditions, and modeling as addressed by specific contributions will surely inspire scientists and technicians in their own innovative approaches and studies on creep and high-temperature deformation.
Book Synopsis Crystal Plasticity Finite Element Methods by : Franz Roters
Download or read book Crystal Plasticity Finite Element Methods written by Franz Roters and published by John Wiley & Sons. This book was released on 2011-08-04 with total page 188 pages. Available in PDF, EPUB and Kindle. Book excerpt: Written by the leading experts in computational materials science, this handy reference concisely reviews the most important aspects of plasticity modeling: constitutive laws, phase transformations, texture methods, continuum approaches and damage mechanisms. As a result, it provides the knowledge needed to avoid failures in critical systems udner mechanical load. With its various application examples to micro- and macrostructure mechanics, this is an invaluable resource for mechanical engineers as well as for researchers wanting to improve on this method and extend its outreach.
Book Synopsis Fundamental Aspects of Dislocation Interactions by : G. Kostorz
Download or read book Fundamental Aspects of Dislocation Interactions written by G. Kostorz and published by Elsevier. This book was released on 2013-09-03 with total page 471 pages. Available in PDF, EPUB and Kindle. Book excerpt: Fundamental Aspects of Dislocation Interactions: Low-Energy Dislocation Structures III covers the papers presented at a European Research Conference on Plasticity of Materials-Fundamental Aspects of Dislocation Interactions: Low-Energy Dislocation Structures III, held on August 30-September 4, 1992 in Ascona, Switzerland. The book focuses on the processes, technologies, reactions, transformations, and approaches involved in dislocation interactions. The selection first offers information on work softening and Hall-Petch hardening in extruded mechanically alloyed alloys and dynamic origin of dislocation structures in deformed solids. Discussions focus on stress-strain behavior in relation to composition, structure, and annealing; comparison of stress-strain curves with work softening theory; sweeping and trapping mechanism; and model of dipolar wall structure formation. The text then ponders on plastic instabilities and their relation to fracture and dislocation and kink dynamics in f.c.c. metals studied by mechanical spectroscopy. The book takes a look at misfit dislocation generation mechanisms in heterostructures and evolution of dislocation structure on the interfaces associated with diffusionless phase transitions. Discussions focus on dislocation representation of a wall of elastic domains; equation of equilibrium of an elastic domain; transformation of dislocations; and theoretical and experimental background. The selection is a valuable reference for readers interested in dislocation interactions.
Book Synopsis Discrete Dislocation Dynamics Simulations of Dislocation-low Angle Grain Boundary Interaction by : Bing Liu
Download or read book Discrete Dislocation Dynamics Simulations of Dislocation-low Angle Grain Boundary Interaction written by Bing Liu and published by . This book was released on 2012 with total page 97 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Dislocations and Strength in Thin Films by : Ray Stuart Fertig
Download or read book Dislocations and Strength in Thin Films written by Ray Stuart Fertig and published by . This book was released on 2010 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Single-crystal films were simulated using three-dimensional discrete dislocation dynamics simulations, where an initial distribution of dislocation loops was allowed to move naturally in response to successive applied strains. The types of interactions that stopped threading dislocations (threads) were identified and the relative fraction of threads stopped in each interaction was determined. An inhomogeneous stress field in the film evolved as the dislocation structure evolved. Threads were observed to interact primarily in regions of low stress. The simulations were used as a virtual test bed for understanding dislocation behavior in thin films. The intuition gained from the simulations led to the construction of three models, which are discussed in detail. First, a model was developed to determine the capture cross-section of a thread, such that if another thread was within its capture cross-section the two threads would interact. Second, a statistical model was constructed to evaluate the effect of stress inhomogeneity on the local concentration of threads. Finally, results from the simulations and analytical models were used to construct a model of strain hardening in thin films based on fundamental behavior of dislocations in thin films.
Book Synopsis Evolution, Interaction, and Intrinsic Properties of Dislocations in Intermetallics by : Qian Chen (Ph.D.)
Download or read book Evolution, Interaction, and Intrinsic Properties of Dislocations in Intermetallics written by Qian Chen (Ph.D.) and published by . This book was released on 2008 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Discrete Dislocation Dynamics Simulations of Dislocation by : Bing Liu
Download or read book Discrete Dislocation Dynamics Simulations of Dislocation written by Bing Liu and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Dislocation Dynamics During Plastic Deformation by : Ulrich Messerschmidt
Download or read book Dislocation Dynamics During Plastic Deformation written by Ulrich Messerschmidt and published by Springer Science & Business Media. This book was released on 2010-04-19 with total page 509 pages. Available in PDF, EPUB and Kindle. Book excerpt: Along with numerous illustrative examples, this text provides an overview of the dynamic behavior of dislocations and its relation to plastic deformation. It introduces the general properties of dislocations and treats the dislocation dynamics in some detail.
Download or read book 3D Dislocation Dynamics written by and published by . This book was released on 1999 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: A dislocation dynamics (DD) model for plastic deformation, connecting the macroscopic mechanical properties to basic physical laws governing dislocation mobility and related interaction mechanisms, has been under development. In this model there is a set of critical reactions that determine the overall results of the simulations, such as the stress-strain curve. These reactions are, annihilation, formation of jogs, junctions, and dipoles, and cross-slip. In this paper we discuss these reactions and the manner in which they influence the simulated stress- strain behavior in fcc and bcc metals. In particular, we examine the formation (zipping) and strength of dipoles and junctions, and effect of jogs, using the dislocation dynamics model. We show that the strengths (unzipping) of these reactions for various configurations can be determined by direct evaluation of the elastic interactions. Next, we investigate the phenomenon of hardening in metals subjected to cascade damage dislocations. The microstructure investigated consists of small dislocation loops decorating the mobile dislocations. Preliminary results reveal that these loops act as hardening agents, trapping the dislocations and resulting in increased hardening.
Book Synopsis Statistical Analysis and Constitutive Modeling of Crystal Plasticity Using Dislocation Dynamics Simulation Database by : Shamseddin Akhondzadeh
Download or read book Statistical Analysis and Constitutive Modeling of Crystal Plasticity Using Dislocation Dynamics Simulation Database written by Shamseddin Akhondzadeh and published by . This book was released on 2021 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Most metals are crystalline materials that can undergo significant plastic (permanent) deformation when subjected to applied loading. Plastic deformation is usually accompanied by an increase in the flow stress of the material. This phenomenon is called strain hardening and is of vital importance in many engineering applications, including aerospace, automotive, and power generation industries. Developing accurate material models to predict the plastic response and hardening behavior of metals during deformation is a prerequisite to the engineering design processes, which requires a physical understanding of the underlying deformation mechanisms. In single crystals, plastic deformation of the crystal is governed by the evolution of dislocations--line defects inside the crystalline materials which marks the boundary between the slipped and unslipped regions--moving and interacting in response to the applied loading. Dislocation dynamics (DD) simulations, which track the time-space trajectories of individual dislocation lines, provide a promising tool to establish a physical link between the dislocation microstructure evolution and the strain hardening phenomenon. However, the high computational cost of DD simulations renders the accessible length and time scales to well below those which are relevant to most engineering applications. Due to this challenge, instead of directly using DD simulations for engineering applications, we have utilized DD simulations to delineate how constitutive relations of crystal plasticity (CP) can be constructed for FCC copper, based on coarse-graining of high-throughput DD simulations. This thesis consists of three main components, and we show how they fit together into a complete, physical model like three pieces of a puzzle. The first piece is a massive DD simulation database that we were able to generate thanks to recent computational advances in DD, including the subcycling time-integration algorithm and its implementation on Graphics Processing Units (GPUs). By systematically coarse-graining the database we present a strain hardening model which consists of two components: 1) a dislocation multiplication model, which accounts for slip-free multiplication, and 2) an exponential flow-rule connecting slip system shear rate to the resolved shear stress through an exponential function. These components can be thought of as the second and third puzzle pieces. By analyzing the data, it was discovered that dislocation multiplication frequently occurs on slip systems which experience zero applied shear stress (i.e., zero Schmid factor) and have a plastic strain rate of zero; we termed such multiplication slip-free multiplication and it serves as the second puzzle piece. This finding questions the assumption of the existing phenomenological expression that multiplication is proportional to the shear rate. We propose to add a correction term to the generalized Kocks-Mecking expression to account for slip-free multiplication, whose mechanistic explanation is provided. A major finding of this thesis is that DD results suggest an exponential flow-rule, in contrast to the commonly used power-law flow-rule, even in the cases where thermal fluctuations are not present. The exponential flow-rule is the third piece in the puzzle of the presented strain hardening model. We demonstrate that the observed exponential flow-rule, despite the common notion that thermal fluctuations are the responsible mechanism, can be explained by statistical properties of the dislocation links. Hence, by statistically analyzing the number density and plastic activity of links in terms of their length, we formulate a physically justified link length based flow rule which can numerically capture the exponential dependence of shear rate on shear stress. The proposed link length based flow-rule has two key components: 1) the number density of links on each slip system, which was observed to follow the sum of two exponentials distribution, and 2) an average velocity of links as a function of resolved shear stress and link length, whose fitting coefficients are independent of the loading orientation. The exponential dependence of on resolved shear stress is traced to the spatial fluctuation of the internal stress field, which can be approximated by a Laplace distribution. The proposed average velocity function incorporates the Laplace distribution in its form. This thesis shows that discrete dislocation dynamics simulations can be used to inform higher length scale models of non-phenomenological constitutive relations. The presented model captures the strain hardening as a result of slip system interactions in FCC single crystals. It works as an example for developing similar coarse-grained models based on DDD which includes additional strain hardening mechanisms such as cross-slip, or precipitate hardening. We hope that the present thesis motivates more researchers to use DDD simulations for constructing constitutive relations.
Book Synopsis Dislocation-Density-Function Dynamics Simulation for Crystal Plasticity by : Hing-Shun Leung
Download or read book Dislocation-Density-Function Dynamics Simulation for Crystal Plasticity written by Hing-Shun Leung and published by . This book was released on 2017-01-26 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation, "Dislocation-density-function Dynamics Simulation for Crystal Plasticity: a Full-dynamics, All-dislocation Approach" by Hing-shun, Leung, 梁慶淳, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Current strategies of computational crystal plasticity that focus on individual atoms or dislocations are impractical for real-scale, large-strain problems even with today''s computing power. Dislocation-density based approaches are a way forward but a critical issue to address is a realistic description of the interactions between dislocations. In this thesis, a new scheme for computational dynamics of dislocation-density functions is proposed, which takes full consideration of the mutual elastic interactions between dislocations based on the Hirth-Lothe formulation. Other features considered include (i) continuity nature of the movements of dislocation densities, (ii) forest hardening, (iii) generation according to high spatial gradients in dislocation densities, and (iv) annihilation. Numerical implementation by the finite-volume method, which is well suited for flow problems with high gradients, is discussed. Numerical examples performed for a single-crystal aluminium model show typical strength anisotropy behaviour comparable to experimental observations. Furthermore, this approach has been applied to three engineering problems and discussed in detail: (i) Application on small-scale crystal plasticity successfully captures a number of key experimental features, including power-law relation between strength and size, low dislocation storage and jerky deformation. (ii) Crystal softening and enhanced cell formation are predicted by applying oscillatory loads. The simulations reveal the main mechanism for subcell formation under oscillatory loadings to be the enhanced elimination of statistically stored dislocations by the oscillatory stress, leaving behind geometrically necessary dislocations with low Schmid factors which then form the subgrain walls. This is the first simulation effort to successfully predict the cell formation phenomenon under vibratory loadings. (iii) Tensile deformation of tri-crystals with grain size ranging from 200 to 500 can be divided into three stages. The results indicate different controlling mechanisms of the flow stress at different stages of deformation and grain sizes. Changing the middle grain tilt angle with respect to the outer grains is found to affect the stress-strain relationship and the distribution of plastic strain in the three grains. A refined meso-scale scheme based on the full dynamics of dislocation-density functions is also proposed aiming to bridge across the meso scale. In this scheme, the evolution of the dislocation-density functions is derived from a coarse-graining procedure which clearly defines the relationship between the discrete-line and density representations of the dislocation microstructure. Full dynamics of the dislocation-density functions are considered based on an "all-dislocation" concept in which statistically stored dislocations are preserved and treated in the same way as geometrically necessary dislocations. Elastic interactions between dislocations are treated in accordance with Mura''s formula for eigen-stress. Dislocation generation is considered as a consequence of dislocations to maintain their connectivity, and a special scheme is devised for this purpose. The model is applied to simulate a number of intensive microstructures involving discrete dislocation events, including loop expansion and shrinkage under applied and self-stress, dipole annihilation, and Orowan
Book Synopsis Dislocations, Mesoscale Simulations and Plastic Flow by : L. Kubin
Download or read book Dislocations, Mesoscale Simulations and Plastic Flow written by L. Kubin and published by Oxford University Press (UK). This book was released on 2013-04-18 with total page 320 pages. Available in PDF, EPUB and Kindle. Book excerpt: In the past twenty years, new experimental approaches, improved models and progress in simulation techniques brought new insights into long-standing issues concerning dislocation-based plasticity in crystalline materials. Dislocation dynamics simulations are becoming accessible to a wide range of users. This book presents to students and researchers in materials science and mechanical engineering a comprehensive coverage of the physical body of knowledge on whichthey are based. This includes classical studies, which are too often ignored, recent experimental and theoretical advances, as well as a discussion of selected applications on various topics.
