Dislocation climb in two-dimensional discrete dislocation dynamics

Davoudi, Kamyar M.; Nicola, Lucia; Vlassak, Joost J.

doi:10.1063/1.4718432

Cited by 60 publications

(31 citation statements)

References 45 publications

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“…In the sought framework, the continuum theories of elasticity and stress-affected diffusion are used as a basis, and both glide and climb motion of dislocations are accounted for. Climb-enabled dislocation plasticity has known increasing interest in the past few years (Mordehai et al, 2008;Keralavarma et al, 2012;Davoudi et al, 2012;Ayas et al, 2014;Po and Ghoniem, 2014;Geslin et al, 2014); also see Raabe (1998); Gao et al (2010); Arsenlis et al (2012) and Geers et al (2014). This paper contains the theoretical foundations of the creep simulations reported by Keralavarma (2011) and Keralavarma et al (2012) and reports additional simulations.…”

Section: Introductionmentioning

confidence: 93%

“…Mordehai et al (2008) developed an analytical climb kinetic model that takes explicit account of the osmotic force contribution using equilibrium solutions for the climb rate of dislocations in a prescribed uniform vacancy field. Their kinetic law was used in 3D DD simulations of diffusion-controlled dislocation loop coarsening (Bakó et al, 2011) and irradiation hardening in BCC iron as well as in 2D DD simulations of thin films (Davoudi et al, 2012) and creep (Keralavarma et al, 2012). Gao et al (2010) included the effect of pipe diffusion in a 3D DD simulation, but neglecting bulk diffusion.…”

Section: Introductionmentioning

confidence: 99%

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High-temperature discrete dislocation plasticity

Keralavarma

Benzerga

2015

Journal of the Mechanics and Physics of Solids

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A framework for solving problems of dislocation-mediated plasticity coupled with point-defect diffusion is presented. The dislocations are modeled as line singularities embedded in a linear elastic medium while the point defects are represented by a concentration field as in continuum diffusion theory. Plastic flow arises due to the collective motion of a large number of dislocations. Both conservative (glide) and nonconservative (diffusion-mediated climb) motions are accounted for. Time scale separation is contingent upon the existence of quasi-equilibrium dislocation configurations. A variational principle is used to derive the coupled governing equations for point-defect diffusion and dislocation climb. Superposition is used to obtain the mechanical fields in terms of the infinite-medium discrete dislocation fields and an image field that enforces the boundary conditions while the point-defect concentration is obtained by solving the stress-dependent diffusion equations on the same finite-element grid. Core-level boundary conditions for the concentration field are avoided by invoking an approximate, yet robust kinetic law. Aspects of the formulation are general but its implementation in a simple plane strain model enables the modeling of high-temperature phenomena such as creep, recovery and relaxation in crystalline materials. With emphasis laid on lattice vacancies, the creep response of planar single crystals in simple tension emerges as a natural outcome in the simulations. A large number of boundary-value problem solutions are obtained which depict transitions from diffusional to power-law creep, in keeping with long-standing phenomenological theories of creep. In addition, some unique experimental aspects of creep in small scale specimens are also reproduced in the simulations.

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Section: Introductionmentioning

confidence: 93%

Section: Introductionmentioning

confidence: 99%

High-temperature discrete dislocation plasticity

Keralavarma

Benzerga

2015

Journal of the Mechanics and Physics of Solids

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“…Dislocation climbs out the glide plane only if the climb distance is larger than the minimum distance between adjacent slip planes and the distance is equal to the magnitude of the Burgers vector. In particular, the time increment of dislocation climb is 100 times larger than that for glide [21][22] . In addition, they mutually block their movement if dislocations on inclined glide planes approach closely.…”

Section: Introductionmentioning

confidence: 99%

Evolution of surface grain structure and mechanical properties in orthogonal cutting of titanium alloy

Bai

Tong

et al. 2016

J. Mater. Res.

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Abstract:In this study, a mesoscale dislocation simulation method was developed to study the orthogonal cutting of Titanium alloy. The evolution of the surface grain structure and its effects on the mechanical properties was studied using two-dimensional climb assisted dislocation dynamic technology. The motions of edge dislocations in an elastic matrix such as dislocation nucleation, lock, interaction with obstacles and grain boundaries, and annihilation were tracked. The results showed that the machined surface has a graded microstructure composed of ultrafine grains. A grain refinement process was observed in micro-cutting of titanium alloy. The process can be described as follows: (i) the development of dislocation lines in original grains, (ii) the formation of dense dislocation bands, (iii) the transformation of dislocation bands into subgrain boundaries, and (iv) the continuous dynamic recrystallization in subgrain boundaries. The fine-grains formed in this process bring appreciable scale effect and a mass of dislocations pile up in the grain boundary and persistent slip band (PSB). In particular, the flow stress and hardening rate was reduced by dislocation climb. However, this effect is significantly weakened when grain size was less than 1.65 µm. In addition, a Hall-Petch type relation is predicted depending on the amount of slips, the dislocation density, the grain arrangement and the range of grain sizes to which a Hall-Petch expression is fit. The numerical results obtained were compared with experimental data gathered from literature and a satisfied agreement was found.

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“…Nevertheless, climb is an important recovery mechanism at larger strains (see, e.g., [4,10]). Temperature dependence of the vacancy migration energy and that of the preexponential coefficient of diffusivity in aluminum are very small [48].…”

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confidence: 99%

“…In recent years, deformation at elevated temperatures and incorporating dislocation climb into DDD codes have come to receive much attention [2][3][4][5][6][7][8][9][10][11][12][13][14]. Increasing temperate affects several parameters of simulations including elastic constants, drag coefficients in both 2d and 3d DDD, and critical nucleation stress, tnuc, and nucleation time of Frank-Read sources, tnuc, in 2d DDD.…”

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confidence: 99%

Temperature dependence of the yield strength of aluminum thin films: Multiscale modeling approach

Davoudi

2017

Scripta Materialia

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Modeling deformation at elevated temperatures using discrete dislocation dynamics (DDD) is a recent area of high interest. However, the literature dedicated to this subject fails to address the variations of DDD parameters with temperature. This study aims to investigate the effect of temperature on the yield strength of aluminum thin films in two-dimensional DDD simulations. To this end, the temperature dependence of DDD parameters has been studied using molecular dynamics, three-dimensional DDD simulations, and the existing experimental results. Based on these calculations, we observed 18% decrease in the yield strength when temperature was increased from 100 K to 600 K. Discrete dislocation dynamics (DDD) is a powerful tool that has been successfully applied to simulate plastic deformation in crystalline materials specially at the micron and submicron scales in various modeling problems. In this method, the material is modeled as a continuous medium containing dislocations as the main plastic carriers, where evolution of dislocations is tracked. In the formulation of the DDD approach, it is assumed that the motion of a dislocation of unit length is governed by:where v is the dislocation velocity, m * is the effective mass, B is the drag coefficient, and F(t) is the driving force arising from externally applied stresses, image stresses, self-stress, interactions with other defects, and the lattice friction (Peierls stress). In this method, long range interactions between dislocations are calculated through theory of elasticity; short range interactions are determined based on local rules.DDD is implemented either in two-or three-dimensional frameworks. Three-dimensional DDD (3d DDD) includes dislocations in realistic geometries and many dislocation phenomena such as junction formation and cross-slip. 2d simulations include only infinitely long edge dislocations.In 2d approach, Frank-Read (FR) sources are represented by points; when the resolved shear stress exceeds a prescribed nucleation stress during a period of time, called nucleation time, the *

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Dislocation climb in two-dimensional discrete dislocation dynamics

Cited by 60 publications

References 45 publications

High-temperature discrete dislocation plasticity

High-temperature discrete dislocation plasticity

Evolution of surface grain structure and mechanical properties in orthogonal cutting of titanium alloy

Temperature dependence of the yield strength of aluminum thin films: Multiscale modeling approach

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