Dislocation Mechanism-Based Crystal Plasticity

Dislocation Mechanism-Based Crystal Plasticity
Theory and Computation at the Micron and Submicron Scale

by Zhuo Zhuang,Zhanli Liu,Yinan Cui

  • Publisher : Academic Press
  • Release : 2019-04-12
  • Pages : 450
  • ISBN : 0128145927
  • Language : En, Es, Fr & De
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Dislocation Based Crystal Plasticity: Theory and Computation at Micron and Submicron Scale provides a comprehensive introduction to the continuum and discreteness dislocation mechanism-based theories and computational methods of crystal plasticity at the micron and submicron scale. Sections cover the fundamental concept of conventional crystal plasticity theory at the macro-scale without size effect, strain gradient crystal plasticity theory based on Taylar law dislocation, mechanism at the mesoscale, phase-field theory of crystal plasticity, computation at the submicron scale, including single crystal plasticity theory, and the discrete-continuous model of crystal plasticity with three-dimensional discrete dislocation dynamics coupling finite element method (DDD-FEM). Three kinds of plastic deformation mechanisms for submicron pillars are systematically presented. Further sections discuss dislocation nucleation and starvation at high strain rate and temperature effect for dislocation annihilation mechanism. Covers dislocation mechanism-based crystal plasticity theory and computation at the micron and submicron scale Presents crystal plasticity theory without size effect Deals with the 3D discrete-continuous (3D DCM) theoretic and computational model of crystal plasticity with 3D discrete dislocation dynamics (3D DDD) coupling finite element method (FEM) Includes discrete dislocation mechanism-based theory and computation at the submicron scale with single arm source, coating micropillar, lower cyclic loading pillars, and dislocation starvation at the submicron scale

Dislocation Mechanism-Based Crystal Plasticity

Dislocation Mechanism-Based Crystal Plasticity
Theory and Computation at the Micron and Submicron Scale

by Zhuo Zhuang,Yinan Cui

  • Publisher : Academic Press
  • Release : 2019-04-12
  • Pages : 450
  • ISBN : 9780128145913
  • Language : En, Es, Fr & De
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Dislocation Based Crystal Plasticity: Theory and Computation at Micron and Submicron Scale provides a comprehensive introduction to the continuum and discreteness dislocation mechanism-based theories and computational methods of crystal plasticity at the micron and submicron scale. Sections cover the fundamental concept of conventional crystal plasticity theory at the macro-scale without size effect, strain gradient crystal plasticity theory based on Taylar law dislocation, mechanism at the mesoscale, phase-field theory of crystal plasticity, computation at the submicron scale, including single crystal plasticity theory, and the discrete-continuous model of crystal plasticity with three-dimensional discrete dislocation dynamics coupling finite element method (DDD-FEM). Three kinds of plastic deformation mechanisms for submicron pillars are systematically presented. Further sections discuss dislocation nucleation and starvation at high strain rate and temperature effect for dislocation annihilation mechanism. Covers dislocation mechanism-based crystal plasticity theory and computation at the micron and submicron scale Presents crystal plasticity theory without size effect Deals with the 3D discrete-continuous (3D DCM) theoretic and computational model of crystal plasticity with 3D discrete dislocation dynamics (3D DDD) coupling finite element method (FEM) Includes discrete dislocation mechanism-based theory and computation at the submicron scale with single arm source, coating micropillar, lower cyclic loading pillars, and dislocation starvation at the submicron scale

Dislocation Mechanism-based Crystal Plasticity

Dislocation Mechanism-based Crystal Plasticity
Theory and Computation at the Micron and Submicron Scale

by 庄茁,柳占立,崔一南

  • Publisher : Unknown Publisher
  • Release : 2020
  • Pages : 436
  • ISBN : 9787302546368
  • Language : En, Es, Fr & De
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The Investigation of Plastic Behavior by Discrete Dislocation Dynamics for Single Crystal Pillar at Submicron Scale

The Investigation of Plastic Behavior by Discrete Dislocation Dynamics for Single Crystal Pillar at Submicron Scale
A Book

by Yinan Cui

  • Publisher : Springer
  • Release : 2016-10-26
  • Pages : 131
  • ISBN : 9811030324
  • Language : En, Es, Fr & De
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This thesis transports you to a wonderful and fascinating small-scale world and tells you the origin of several new phenomena. The investigative tool is the improved discrete dislocation-based multi-scale approaches, bridging the continuum modeling and atomistic simulation. Mechanism-based theoretical models are put forward to conveniently predict the mechanical responses and defect evolution. The findings presented in this thesis yield valuable new guidelines for microdevice design, reliability analysis and defect tuning.

Thermally Activated Mechanisms in Crystal Plasticity

Thermally Activated Mechanisms in Crystal Plasticity
A Book

by D. Caillard,J.L. Martin

  • Publisher : Elsevier
  • Release : 2003-09-08
  • Pages : 452
  • ISBN : 9780080542782
  • Language : En, Es, Fr & De
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KEY FEATURES: A unified, fundamental and quantitative resource. The result of 5 years of investigation from researchers around the world New data from a range of new techniques, including synchrotron radiation X-ray topography provide safer and surer methods of identifying deformation mechanisms Informing the future direction of research in intermediate and high temperature processes by providing original treatment of dislocation climb DESCRIPTION: Thermally Activated Mechanisms in Crystal Plasticity is a unified, quantitative and fundamental resource for material scientists investigating the strength of metallic materials of various structures at extreme temperatures. Crystal plasticity is usually controlled by a limited number of elementary dislocation mechanisms, even in complex structures. Those which determine dislocation mobility and how it changes under the influence of stress and temperature are of key importance for understanding and predicting the strength of materials. The authors describe in a consistent way a variety of thermally activated microscopic mechanisms of dislocation mobility in a range of crystals. The principles of the mechanisms and equations of dislocation motion are revisited and new ones are proposed. These describe mostly friction forces on dislocations such as the lattice resistance to glide or those due to sessile cores, as well as dislocation cross-slip and climb. They are critically assessed by comparison with the best available experimental results of microstructural characterization, in situ straining experiments under an electron or a synchrotron beam, as well as accurate transient mechanical tests such as stress relaxation experiments. Some recent attempts at atomistic modeling of dislocation cores under stress and temperature are also considered since they offer a complementary description of core transformations and associated energy barriers. In addition to offering guidance and assistance for further experimentation, the book indicates new ways to extend the body of data in particular areas such as lattice resistance to glide.

Modeling and Simulation of Microstructure Evolution and Deformation in an Irradiated Environment

Modeling and Simulation of Microstructure Evolution and Deformation in an Irradiated Environment
A Book

by Stephanie Anne Pitts

  • Publisher : Unknown Publisher
  • Release : 2019
  • Pages : 286
  • ISBN : 9876543210XXX
  • Language : En, Es, Fr & De
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The ability to predict the behavior of structural components in a nuclear power plant is critical to the nuclear industry. Structural metals in the primary loop of nuclear power plants must endure challenges such as irradiation and mechanical and thermal loading, and these structural metal components must continue to function in potential transient and accident conditions throughout the operational lifetime of the power plant. This extreme operational environment changes the metal microstructure by creating additional defects. The physical interactions of dislocations with these defects govern how the metal will respond to future conditions. Therefore predicting the mechanical response of these metals requires a set of physically based and reliable models of dislocation and defect interactions. These microstructure elements include glide mobile and immobile dislocations, geometrically necessary dislocations, twinning dislocations, irradiation defects, and thermal aging defects. We present here a continuum dislocation dynamics crystal plasticity framework to capture the interaction mechanisms of these dislocations and defects, verified with a combination of benchmark problems and comparisons with experimental data for two different types of structural metals: Îł iron and nickel-based alloys. In our simulations of Îł iron we highlight the advantages of applying a Monte Carlo stochastic model of cross slip dislocation motion and show the importance of capturing the 3D nature of glide dislocation and self-interstitial atom loop radiation defect interactions. We demonstrate coupling of glide dislocations with geometrically necessary dislocations to capture the influence of lattice bending, including the sensitivity of the geometrically necessary dislocations to changes in the grain boundary angle. We further examine the interaction of glide dislocations with the twin dislocations and thermally aged defects which have been observed in a nickel-based alloy with additional models. Finally we assess the reliability of this crystal plasticity framework by comparing two dislocation glide velocity models across the range of normal operation temperatures. In successfully applying our crystal plasticity framework to multiple metals, we provide further evidence of the reliability of our approach. The results of this mechanism-based continuum dislocation dynamics crystal plasticity framework can be used to inform engineering scale models throughout the nuclear industry.

Single Crystal Plasticity by Modeling Dislocation Density Rate Behavior

Single Crystal Plasticity by Modeling Dislocation Density Rate Behavior
A Book

by Anonim

  • Publisher : Unknown Publisher
  • Release : 2010
  • Pages : 329
  • ISBN : 9876543210XXX
  • Language : En, Es, Fr & De
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The goal of this work is to formulate a constitutive model for the deformation of metals over a wide range of strain rates. Damage and failure of materials frequently occurs at a variety of deformation rates within the same sample. The present state of the art in single crystal constitutive models relies on thermally-activated models which are believed to become less reliable for problems exceeding strain rates of 104 s−1. This talk presents work in which we extend the applicability of the single crystal model to the strain rate region where dislocation drag is believed to dominate. The elastic model includes effects from volumetric change and pressure sensitive moduli. The plastic model transitions from the low-rate thermally-activated regime to the high-rate drag dominated regime. The direct use of dislocation density as a state parameter gives a measurable physical mechanism to strain hardening. Dislocation densities are separated according to type and given a systematic set of interactions rates adaptable by type. The form of the constitutive model is motivated by previously published dislocation dynamics work which articulated important behaviors unique to high-rate response in fcc systems. The proposed material model incorporates thermal coupling. The hardening model tracks the varying dislocation population with respect to each slip plane and computes the slip resistance based on those values. Comparisons can be made between the responses of single crystals and polycrystals at a variety of strain rates. The material model is fit to copper.

Crystal Plasticity

Crystal Plasticity
A Book

by Wojciech Polkowski

  • Publisher : MDPI
  • Release : 2021-04-27
  • Pages : 438
  • ISBN : 3036508384
  • Language : En, Es, Fr & De
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The book presents a collection of 25 original papers (including one review paper) on state-of-the art achievements in the theory and practice of crystals plasticity. The articles cover a wide scope of research on materials behavior subjected to external loadings, starting from atomic-scale simulations, and a new methodological aspect, to experiments on a structure and mechanical response upon a large-scale processing. Thus, a presented contribution of researchers from 18 different countries can be virtually divided into three groups, namely (i) “modelling and simulation”; (ii) “methodological aspects”; and (iii) “experiments on process/structure/properties relationship”. Furthermore, a large variety of materials are investigated including more conventional (steels, copper, titanium, nickel, aluminum, and magnesium alloys) and advanced ones (composites or high entropy alloys). The book should be interested for senior students, researchers and engineers working within discipline of materials science and solid state physics of crystalline materials.

Dislocation-Density-Function Dynamics Simulation for Crystal Plasticity

Dislocation-Density-Function Dynamics Simulation for Crystal Plasticity
A Full-Dynamics, All-Dislocation Approach

by Hing-Shun Leung

  • Publisher : Unknown Publisher
  • Release : 2017-01-26
  • Pages : 329
  • ISBN : 9781361035603
  • Language : En, Es, Fr & De
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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

Texture Informed Crystal Plasticity Finite Element Modeling of Polycrystalline Material Deformation

Texture Informed Crystal Plasticity Finite Element Modeling of Polycrystalline Material Deformation
A Book

by Zhe Leng

  • Publisher : Unknown Publisher
  • Release : 2014
  • Pages : 329
  • ISBN : 9876543210XXX
  • Language : En, Es, Fr & De
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The interaction between the dislocation and the grain boundaries is also incorporated in the model. For the near grain boundary regions, particular consideration and finite element formula is applied to account for the additional activation energy term as well as the geometric compatibility of the grain boundary during dislocation penetration events, both of the energy term and the geometric barrier depend on the grain boundary character. The formulations applied here provide a reasonable methodology to understand how the interactions between dislocation and grain boundary affect the overall mechanical behavior and the microstructure, and quantitative comparisons of predicted geometrically necessary dislocation distributions with the those determined experimentally indicates a reasonable agreement, further analysis also indicates that stress concentration, as well as the dislocation patterning, depends highly on the grain boundary characters.

Gradient Plasticity Model and Its Implementation Into MARMOT.

Gradient Plasticity Model and Its Implementation Into MARMOT.
A Book

by Anonim

  • Publisher : Unknown Publisher
  • Release : 2013
  • Pages : 329
  • ISBN : 9876543210XXX
  • Language : En, Es, Fr & De
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The influence of strain gradient on deformation behavior of nuclear structural materials, such as boby centered cubic (bcc) iron alloys has been investigated. We have developed and implemented a dislocation based strain gradient crystal plasticity material model. A mesoscale crystal plasticity model for inelastic deformation of metallic material, bcc steel, has been developed and implemented numerically. Continuum Dislocation Dynamics (CDD) with a novel constitutive law based on dislocation density evolution mechanisms was developed to investigate the deformation behaviors of single crystals, as well as polycrystalline materials by coupling CDD and crystal plasticity (CP). The dislocation density evolution law in this model is mechanism-based, with parameters measured from experiments or simulated with lower-length scale models, not an empirical law with parameters back-fitted from the flow curves.

Understanding the Deformation Mechanisms in Ni-based Superalloys with Using Crystal Plasticity Finite Element Method

Understanding the Deformation Mechanisms in Ni-based Superalloys with Using Crystal Plasticity Finite Element Method
A Book

by Tianju Chen

  • Publisher : Unknown Publisher
  • Release : 2020
  • Pages : 89
  • ISBN : 9876543210XXX
  • Language : En, Es, Fr & De
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"Ni-based superalloy is considered as a good candidate due to its excellent resistance to elevated temperature deformation for long term period application. Understanding the deformation and failure mechanisms of Ni-Based superalloys is very helpful for providing design guidelines for processing Ni-based superalloys. Experimental characterization indicates that the deformation mechanisms of Ni based superalloy is strongly microstructure dependent. Besides, damage transform from the void nucleation to the macro cracks by voids growth leading to the failure of the Ni-based superalloys are also showing strong microstructure sensitivity. Therefore, this work focuses on the prediction and comprehension of the deformation and void growth behavior in Ni based superalloy at different working conditions via crystal plasticity finite element modeling and simulation. Physically based crystal plasticity frameworks were developed for newly Ni-based superalloy Haynes 282. It was found that dislocation shearing through the precipitates were acting as the main contributor to the strength of Haynes 282 at room temperature and 815°C. Our analysis of the creeping behavior of Haynes 282 exhibited that resistance of general climb replaced by the resistance induced by the deposited climb dislocation density. In addition, in the study of void growth behavior, our simulation results demonstrated that as the main loading axis perpendicular to the grain boundary (GB), voids grow more slowly on tilt GBs in bicrystals than those in single and bicrystals with twist GBs. And tilt GBs would promote the void grow into irregular shape"--Abstract, page iv.

Strengthening Mechanisms in Crystal Plasticity

Strengthening Mechanisms in Crystal Plasticity
A Book

by Ali Argon

  • Publisher : Oxford University Press on Demand
  • Release : 2008
  • Pages : 404
  • ISBN : 0198516002
  • Language : En, Es, Fr & De
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Technologically important metals and alloys have been strengthened throughout history by a variety of empirical means. The scientific bases of the central mechanisms of such forms of strengthening, developed over the past several decades are presented here in a comprehensive form through mechanistic models and associated experimental results.

Computer Simulations of Crystal Plasticity at Different Length Scales

Computer Simulations of Crystal Plasticity at Different Length Scales
A Book

by Bingqing Cheng,程冰清

  • Publisher : Unknown Publisher
  • Release : 2017-01-27
  • Pages : 329
  • ISBN : 9781361348031
  • Language : En, Es, Fr & De
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This dissertation, "Computer Simulations of Crystal Plasticity at Different Length Scales" by Bingqing, Cheng, 程冰清, 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: Crystal plasticity has been an active research field for several decades. The crystal plasticity of the bulk materials has its key relevance in the industrial process. Besides, the plasticity of nano-sized materials becomes a topic attracting a lot of interest recently. In the Part I of the thesis, molecular dynamics (MD) simulations were used to study the plasticity of small nanoparticles. Firstly, the coalescence process of Cu nanoparticles was explored. It was found that a peculiar type of five-fold twins in the sintered products were formed via an unseen before dislocation-free process involving a series of shear waves and rigid-body rotations. Secondly, a similar study on the heating of a single nanoparticle was conducted. The same dislocation-free shear wave mechanism was spotted again. In this mechanism, a cluster of atoms rearranges in a highly coordinated way between different geometrical configurations (e.g. fcc, decahedral, icosahedral) without involving dislocations. Thirdly, simulations on the sintering of many nanoparticles were performed, and the governing processes during the consolidation were discussed. The findings in this part of the thesis can provide some guidance for controlling the motifs of nanoparticles. In Part II of the thesis, the emphasis was switched to the crystal plasticity at larger spatial and temporal scales. A dislocation density-based model was developed in our research group. This model employs a dynamics formulation in which the force on each group of dislocation density is calculated with the Taylor and mutual elastic interactions taken into account. The motion of the dislocation densities is then predicted using a conservative law, with annihilation and generation considered. The new dislocation density-based model was used in this work to simulate the plastic deformation of single crystals under ultrasonic irradiation. Softening during vibrations as well as enhanced cell formation was predicted. This is the first simulation effort to successfully predict the cell formation phenomenon under vibratory loadings. DOI: 10.5353/th_b5317059 Subjects: Crystals - Plastic properties - Computer simulation

Statistical Analysis and Constitutive Modeling of Crystal Plasticity Using Dislocation Dynamics Simulation Database

Statistical Analysis and Constitutive Modeling of Crystal Plasticity Using Dislocation Dynamics Simulation Database
A Book

by Shamseddin Akhondzadeh

  • Publisher : Unknown Publisher
  • Release : 2021
  • Pages : 329
  • ISBN : 9876543210XXX
  • Language : En, Es, Fr & De
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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.

Dynamical Dislocation Models of Crystal Plasticity

Dynamical Dislocation Models of Crystal Plasticity
A Book

by Peter Paul Gillis,BROWN UNIV PROVIDENCE R I.,Brown University. Division of Engineering,United States. Office of Naval Research

  • Publisher : Unknown Publisher
  • Release : 1964
  • Pages : 110
  • ISBN : 9876543210XXX
  • Language : En, Es, Fr & De
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For glide occurring in a single system, a general relation is established between the rate of plastic strain, and the configuration and velocity distribution of dislocations in a monocrystal. This relation is applied to various idealized configurations, and the concept of dislocation density is defined for the case of parallel, straight dislocation lines. An elementary model of mechanical behavior is developed, assuming that the average velocity of dislocations is represented by a quasiviscous relation, and that the time rate of increase of dislocations is proportional to the number of dislocations and their average velocity. This model is investigated under three loading conditions, both by analytic and digital computer techniques. An improved model is derived by additionally assuming a dislocation stalemating rate proportional to the square of the number of dislocations and their average velocity. Finally, models are proposed which exhibit strain-hardening. The hardening mechanisms considered are: effect of strain on dislocation mobility; the reduction of average velocity caused by spatial fluctuations in the stress field; and stalemating interactions between fixed and mobile dislocations. Stress-strain curves are calculated based upon these models, and for one model the constant load strain-time problem is solved in closed form. (Author).

Understanding the Deformation Mechanisms in Nanostructured Metals by a Novel Discrete Crystal Plasticity Finite Element Model

Understanding the Deformation Mechanisms in Nanostructured Metals by a Novel Discrete Crystal Plasticity Finite Element Model
A Book

by Rui Yuan

  • Publisher : Unknown Publisher
  • Release : 2017
  • Pages : 146
  • ISBN : 9876543210XXX
  • Language : En, Es, Fr & De
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"Implementation of nanostructured metals and alloys for use in engineering applications requires a detailed knowledge of the underlying deformation mechanisms in these materials. It is well known that plastic deformation in metals and alloys is mainly mediated by dislocation activities. Nonetheless, TEM observations and atomistic simulations indicate that dislocation-mediated plasticity in nanostructured metals and alloys is significantly different from that in their coarse-grained counterparts. Therefore, this dissertation focuses on the exploration of the deformation mechanisms in nanostructured metals via crystal plasticity finite element modeling and simulation. A statistical grain boundary dislocation source model accounting for dislocation nucleation and slip events was developed and incorporated into a 3D discrete crystal plasticity finite element model to study the mechanical behaviors of nanostructured metals including nanocrystalline, nanotwinned and heterogeneous lamellar structured metals. It was found that a Hall-Petch scaling of strength emerged from grain size limitation on dislocation source length, and that the Hall-Petch slope depended sensitively on texture and was proportional to the Taylor factor. Furthermore, it was shown that experimentally observed scaling between yield strength and twin thickness in columnar-grained nanotwinned Cu arose from statistical variability in dislocation source length, and that reducing twin thickness could increase plastic anisotropy as a result of the increase in mean stress to emit dislocations. In addition, it was revealed that a heterogeneous lamellar structure consisting of a nanocrystalline layer sandwiched between two coarse-grained lamellae could effectively homogenize plastic strain in the nanocrystalline layer, leading to suppressed strain heterogeneity and enhanced ductility"--Abstract, page iv.

Mesoscale Models

Mesoscale Models
From Micro-Physics to Macro-Interpretation

by Sinisa Mesarovic,Samuel Forest,Hussein Zbib

  • Publisher : Springer
  • Release : 2018-11-19
  • Pages : 344
  • ISBN : 3319941860
  • Language : En, Es, Fr & De
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The book helps to answer the following questions: How far have the understanding and mesoscale modeling advanced in recent decades, what are the key open questions that require further research and what are the mathematical and physical requirements for a mesoscale model intended to provide either insight or a predictive engineering tool? It is addressed to young researchers including doctoral students, postdocs and early career faculty,

Crystal Dislocations: Their Impact on Physical Properties of Crystals

Crystal Dislocations: Their Impact on Physical Properties of Crystals
A Book

by Peter Lagerlof

  • Publisher : MDPI
  • Release : 2019-01-09
  • Pages : 316
  • ISBN : 303897465X
  • Language : En, Es, Fr & De
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This book is a printed edition of the Special Issue "Crystal Dislocations: Their Impact on Physical Properties of Crystals" that was published in Crystals

Magnesium Technology 2017

Magnesium Technology 2017
A Book

by Kiran N. Solanki,Dmytro Orlov,Alok Singh,Neale R. Neelameggham

  • Publisher : Springer
  • Release : 2017-02-14
  • Pages : 689
  • ISBN : 3319523929
  • Language : En, Es, Fr & De
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The Magnesium Technology Symposium, the event on which this collection is based, is one of the largest yearly gatherings of magnesium specialists in the world. Papers represent all aspects of the field, ranging from primary production to applications to recycling. Moreover, papers explore everything from basic research findings to industrialization. Magnesium Technology 2017 covers a broad spectrum of current topics, including alloys and their properties; cast products and processing; wrought products and processing; forming, joining, and machining; corrosion and surface finishing; ecology; and structural applications. In addition, there is coverage of new and emerging applications.