iMechanica - Dislocation
https://imechanica.org/taxonomy/term/605
enLooking for Postdocs in Atomistic Simulations of Crystal Defects
https://imechanica.org/node/26062
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/73">job</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/871">postdoc</a></div><div class="field-item odd"><a href="/taxonomy/term/93">molecular dynamics</a></div><div class="field-item even"><a href="/taxonomy/term/1301">crystals</a></div><div class="field-item odd"><a href="/taxonomy/term/3280">defects</a></div><div class="field-item even"><a href="/taxonomy/term/605">Dislocation</a></div><div class="field-item odd"><a href="/taxonomy/term/420">cracks</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>Please see <a href="https://recruitingapp-5424.de.umantis.com/Vacancies/369/Description/2">the MPIE website for the job description & online application </a></p>
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</div></div></div>Mon, 20 Jun 2022 12:50:32 +0000Erik Bitzek26062 at https://imechanica.orghttps://imechanica.org/node/26062#commentshttps://imechanica.org/crss/node/26062Research Scientist Positions on Computational Mechanics/Solid Mechanics at Institute of High Performance Computing, A*STAR Research Entities, Singapore
https://imechanica.org/node/25532
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/73">job</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/162">computational mechanics</a></div><div class="field-item odd"><a href="/taxonomy/term/179">solid mechanics</a></div><div class="field-item even"><a href="/taxonomy/term/605">Dislocation</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>We seek candidates with good research experience in computational mechanics, solid mechanics, and plasticity theory. The candidate is to use computational modeling to study the dislocation-mediated microstructure evolution and material behavior in various manufacturing processes.</p>
<p>The desired candidate will have:</p>
<p>· Ph.D. in Mechanical Engineering / Solid Mechanics / Material Science</p>
<p>· Solid background in the mechanics of materials, nonlinear continuum materials, dislocation theory of plasticity of metals</p>
<p>· Good background in fracture mechanics of material, damage modeling at different length scales</p>
<p>· Expertise in Finite Element analysis of nonlinear solids, and fracture behavior</p>
<p>· Familiarity with multiscale modeling and multi-physics modeling for additive manufacturing processes</p>
<p>· Strong coding skills for scientific computing in Python/ Matlab/ Fortran/ C/C++</p>
<p>· Proficient in using commercial finite element tools such as ABAQUS</p>
<p>· Strong skills to develop user sub-routines and user-defined elements in a commercial FEM platform</p>
<p>· Good publication track record</p>
<p>· Good presentation and communication skills</p>
<p>Contact: Dr Zhang Zhiqian, <a href="mailto:zhangz@ihpc.a-star.edu.sg">zhangz@ihpc.a-star.edu.sg</a> (Valid until 1st Feb 2022; Please note only shorlisted candidates will be informed for interview.)</p>
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</div></div></div>Wed, 27 Oct 2021 09:43:30 +0000Su Zhoucheng25532 at https://imechanica.orghttps://imechanica.org/node/25532#commentshttps://imechanica.org/crss/node/25532Three Ph.D. Positions in Computational Atomistic Modeling
https://imechanica.org/node/23989
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/73">job</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/1188">atomistic simulation</a></div><div class="field-item odd"><a href="/taxonomy/term/6176">computational materials science</a></div><div class="field-item even"><a href="/taxonomy/term/32">fracture mechanics</a></div><div class="field-item odd"><a href="/taxonomy/term/9188">nano mechanics</a></div><div class="field-item even"><a href="/taxonomy/term/605">Dislocation</a></div><div class="field-item odd"><a href="/taxonomy/term/87">crack</a></div><div class="field-item even"><a href="/taxonomy/term/91">interface</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p class="MsoNormal"><span lang="EN-US" xml:lang="EN-US">The Department of Materials Science and Engineering of the Friedrich-Alexander-Universität (FAU) Erlangen-Nürnberg is inviting applications for three doctoral research positions to begin immediately. The successful applicants will work together with Prof. Erik Bitzek on studying the atomistic origins of materials failure in the context of (1) semi-brittle fracture in the ERC-funded Project micro<em>K</em>Ic: Microscopic Origins of Fracture Toughness; (2) nanomechanics and small-scale plasticity within the research training group GRK 1896 “In Situ Microscopy with Electrons, X-rays and Scanning Probes”; (3) properties of defects in complex intermetallic phases within the Collaborative Research Center SFB 1394 “Structural and Chemical Atomic Complexity: From Defect Phase Diagrams to Material Properties”.</span></p>
<p class="MsoNormal"><span lang="EN-US" xml:lang="EN-US">Applicants should have </span><span>a master’s degree with good to excellent marks in Physics, Material Science, </span><span lang="EN-US" xml:lang="EN-US">Mechanical Engineering, </span><span>Chemistry, or a related field</span><span lang="EN-US" xml:lang="EN-US">. E</span><span>xperience in performing numerical simulations, preferably using Molecular Dynamics</span><span lang="EN-US" xml:lang="EN-US">, and in scientific programming </span><span>are advantageous.</span><span> </span><span>In addition, a solid background in mechanical behavior of materials</span><span lang="EN-US" xml:lang="EN-US">, </span><span>physical metallurgy</span><span lang="EN-US" xml:lang="EN-US"> and t</span><span>hermodynamics </span><span lang="EN-US" xml:lang="EN-US">is</span><span> highly desirable. Excellent oral and written communication skills and the ability to work well in a dynamic and collaborative research environment are essential.</span></p>
<p class="MsoNormal"><span>The position is full-time, and payment follows the German TV-L 13 scale. The starting date is as soon as possible. The </span><span lang="EN-US" xml:lang="EN-US">FAU </span><span>Erlangen-Nürnberg intends to increase the number of women in research and teaching positions and, therefore, strongly encourages female researchers to apply. Disabled applicants will be preferentially considered in case of equivalent qualification.</span></p>
<p class="MsoNormal"><span>Please send your application (including a cover letter describing your research interests, curriculum vitae, transcript of records as well as contact information of two references) to </span><a href="mailto:comp-mat-sci-jobs@ww.uni-erlangen.de"><span>comp-mat-sci-jobs@ww.uni-erlangen.de</span></a><span>.</span></p>
<p class="MsoNormal"><strong><span lang="EN-US" xml:lang="EN-US">About FAU: </span></strong><span lang="EN-US" xml:lang="EN-US">The FAU is Germany 10th largest university and has been ranked Germany’s most innovative university in the 2019 Reuters Innovation Ranking. </span><span>It is located in the metropolitan area of Nuremberg (3.5 Mio inhabitants), in the northern part of Bavaria.</span><span lang="EN-US" xml:lang="EN-US"> The FAU is </span><span>home to Germany’s largest and oldest Materials Science and Engineering Departmen</span><span lang="EN-US" xml:lang="EN-US">t, which is consistently ranked amongst the top 2 according to the German Science Foundation (DFG). </span></p>
</div></div></div>Wed, 12 Feb 2020 17:55:30 +0000Erik Bitzek23989 at https://imechanica.orghttps://imechanica.org/node/23989#commentshttps://imechanica.org/crss/node/23989Comparative modeling of the disregistry and Peierls stress for dissociated edge and screw dislocations in Al
https://imechanica.org/node/23963
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/76">research</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/605">Dislocation</a></div><div class="field-item odd"><a href="/taxonomy/term/2375">phase-field modeling</a></div><div class="field-item even"><a href="/taxonomy/term/1910">multiscale modeling</a></div><div class="field-item odd"><a href="/taxonomy/term/12752">Peierls-Nabarrow model</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p><a href="https://doi.org/10.1016/j.ijplas.2020.102689">https://doi.org/10.1016/j.ijplas.2020.102689</a></p>
<p>Abstract</p>
<p>Many elementary deformation processes in metals involve the motion of dislocations. The planes of glide and specific processes dislocations prefer depend heavily on their atomic core structures. Atomistic simulations are desirable for dislocation modeling but their application to even sub-micron scale problems is in general computationally costly. Accordingly, continuum-based approaches, such as the phase-field microelasticity, phase-field dislocation dynamics (PFDD), generalized Peierls-Nabarro (GPN) models, and the concurrent atomistic–continuum (CAC) method, have attracted increasing attention in the field of dislocation modeling because they well represent both short-range cores interactions and long-range stress fields of dislocations. To better understand their similarities and differences, it is useful to compare these methods in the context of benchmark simulations and predictions. In this paper, we apply the CAC method and different PFDD variants – one of them is equivalent to a GPN model – to simulate an extended (i.e., dissociated) dislocation in Al with initially pure edge or pure screw character in terms of the disregistry. CAC and discrete forms of PFDD are also employed to calculate the Peierls stress. By conducting comprehensive convergence studies, we quantify the dependence of these measures on time/grid resolution and simulation cell size. Several important but often overlooked differences between PFDD/GPN variants are clarified. Our work sheds light on the advantages and limitations of each method, as well as the path towards enabling them to effectively model complex dislocation processes at larger length scales.</p>
</div></div></div>Mon, 03 Feb 2020 07:28:32 +0000Shuozhi Xu23963 at https://imechanica.orghttps://imechanica.org/node/23963#commentshttps://imechanica.org/crss/node/23963Modeling dislocations with arbitrary character angle in face-centered cubic transition metals using the phase-field dislocation dynamics method with full anisotropic elasticity
https://imechanica.org/node/23674
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/76">research</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/6692">phase field</a></div><div class="field-item odd"><a href="/taxonomy/term/605">Dislocation</a></div><div class="field-item even"><a href="/taxonomy/term/2682">elastic anisotropy</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p><a href="https://doi.org/10.1016/j.mechmat.2019.103200">https://doi.org/10.1016/j.mechmat.2019.103200</a></p>
<p>Abstract</p>
<p>In this study, we present a phase-field dislocation dynamics (PFDD) method that includes full anisotropic elasticity. We apply it to calculate the equilibrium core structures of dislocations with arbitrary character angle in eight face-centered cubic transition metals. The calculations investigate the effects of the gradient energy density in the total energy density and the choice of the averaging scheme to determine the isotropic equivalent elastic moduli (i.e., Voigt, Reuss, and Hill). We show that the addition of the gradient energy term increases the intrinsic stacking fault (ISF) widths for the edge and screw dislocations in most of the metals studied here, but decreases the ISF widths for the edge dislocations in four metals: Ir, Ni, Pd, and Rh. The analysis indicates that among the three isotropic averaging schemes, the Voigt isotropic equivalent modulus best predicts the ISF widths of the edge dislocations and the Reuss scheme for the ISF widths of the screw dislocations, compared to the full elastic anisotropy. Finally, a critical character angle (~60o) is revealed, at which the PFDD simulations with full elastic anisotropy and those with the isotropic Hill average predict the same ISF width. Our work advances the basic understanding of the elastic anisotropic effects on the equilibrium dislocation core structures and can help guide the choice of isotropic averaged moduli.</p>
</div></div></div>Sat, 12 Oct 2019 01:05:23 +0000Shuozhi Xu23674 at https://imechanica.orghttps://imechanica.org/node/23674#commentshttps://imechanica.org/crss/node/23674Postdoc Opening in Computational Materials Science at Rutgers University
https://imechanica.org/node/23669
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/73">job</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/169">Plasticity</a></div><div class="field-item odd"><a href="/taxonomy/term/545">damage</a></div><div class="field-item even"><a href="/taxonomy/term/605">Dislocation</a></div><div class="field-item odd"><a href="/taxonomy/term/10046">patterning</a></div><div class="field-item even"><a href="/taxonomy/term/26">cracking</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>The microMechanics of Deformation Research Group (<a href="https://mmod.rutgers.edu/">mMOD</a>) in the Department of Materials Science and Engineering at Rutgers University is seeking a Post-Doctoral Associate to participate in a pair of collaborative projects with a Department of Energy National Laboratory. The projects are focused on using discrete dislocation dynamics (DDD) simulations to understand dislocation patterning in deformed metals, and molecular dynamics (MD) simulations to understanding crack initiation in hydrogen-affected steels. Simulations will be paired with electron microscopy and mechanical testing conducted at the national lab. Interested candidates should apply at <a href="https://jobs.rutgers.edu/postings/102214">jobs.rutgers.edu/postings/102214</a>. Contact Prof. Ryan Sills (<a href="mailto:ryan.sills@rutgers.edu">ryan.sills@rutgers.edu</a>) with questions.</p>
</div></div></div>Thu, 10 Oct 2019 12:35:06 +0000rbsills23669 at https://imechanica.orghttps://imechanica.org/node/23669#commentshttps://imechanica.org/crss/node/23669Ab initio-informed phase-field modeling of dislocation core structures in equal-molar CoNiRu multi-principal element alloys
https://imechanica.org/node/23513
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/76">research</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/11633">high entropy alloys</a></div><div class="field-item odd"><a href="/taxonomy/term/605">Dislocation</a></div><div class="field-item even"><a href="/taxonomy/term/7824">Ab initio calculations</a></div><div class="field-item odd"><a href="/taxonomy/term/10625">phase field methods</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p><a href="https://doi.org/10.1088/1361-651X/ab3b62">https://doi.org/10.1088/1361-651X/ab3b62</a></p>
<p>Abstract</p>
<p>In this work, selecting the equal-molar CoNiRu multi-principal element alloy (MPEA) as a model material, we study dislocation core structures starting from first principles. We begin by sifting through all possible configurations to find those corresponding to elastic stability and energetically favored face-centered cubic (fcc) phases and, then, for these configurations, employ a phase field-based model to predict the extent of dislocations lying within them. The main findings are that for the fcc phase, (i) large variations in atomic configuration for the same chemical composition can cause significant changes in the generalized stacking fault energy surface and (ii) the dispersion in defect fault energies are chiefly responsible for substantial variations in the intrinsic stacking fault (ISF) widths of screw and edge dislocations. For instance, positive the ISF energy can vary by 10 times, with the lower values correlated with entirely Ni and Ru atoms and higher values with only Co and Ru atoms across the slip plane. Variations in lattice parameter and stiffness tensor accompany local differences in atomic configuration are also taken into account but shown to play a lesser role. We find that the dislocation can experience profound variations (3–7-fold changes) in its associated ISF width along its line, with the screw dislocation experiencing a greater variation than the edge dislocation (6.02–43.22 Å for the screw dislocation, and 19.6–62.62 Å for the edge dislocation). We envision that the ab initio-informed phase-field modeling method developed here can be readily adapted to MPEAs with other chemical compositions.</p>
</div></div></div>Thu, 15 Aug 2019 22:59:32 +0000Shuozhi Xu23513 at https://imechanica.orghttps://imechanica.org/node/23513#commentshttps://imechanica.org/crss/node/23513A comparison of different continuum approaches in modeling mixed-type dislocations in Al
https://imechanica.org/node/23393
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/76">research</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/2375">phase-field modeling</a></div><div class="field-item odd"><a href="/taxonomy/term/605">Dislocation</a></div><div class="field-item even"><a href="/taxonomy/term/10954">concurrent atomistic-continuum</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p><a href="https://doi.org/10.1088/1361-651X/ab2d16">https://doi.org/10.1088/1361-651X/ab2d16</a></p>
<p>Abstract</p>
<p>Mixed-type dislocations are prevalent in metals and play an important role in their plastic deformation. Key characteristics of mixed-type dislocations cannot simply be extrapolated from those of dislocations with pure edge or pure screw characters. However, mixed-type dislocations traditionally received disproportionately less attention in the modeling and simulation community. In this work, we explore core structures of mixed-type dislocations in Al using three continuum approaches, namely, the phase-field dislocation dynamics (PFDD) method, the atomistic phase-field microelasticity (APFM) method, and the concurrent atomistic-continuum (CAC) method. Results are benchmarked against molecular statics. We advance the PFDD and APFM methods in several aspects such that they can better describe the dislocation core structure. In particular, in these two approaches, the gradient energy coefficients for mixed-type dislocations are determined based on those for pure-type ones using a trigonometric interpolation scheme, which is shown to provide better prediction than a linear interpolation scheme. The dependence of the in-slip-plane spatial numerical resolution in PFDD and CAC is also quantified.</p>
</div></div></div>Wed, 26 Jun 2019 23:42:26 +0000Shuozhi Xu23393 at https://imechanica.orghttps://imechanica.org/node/23393#commentshttps://imechanica.org/crss/node/23393Phase-field-based calculations of the disregistry fields of static extended dislocations in FCC metals
https://imechanica.org/node/23124
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/76">research</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/605">Dislocation</a></div><div class="field-item odd"><a href="/taxonomy/term/2375">phase-field modeling</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p><a href="http://dx.doi.org/10.1080/14786435.2019.1582850">http://dx.doi.org/10.1080/14786435.2019.1582850</a></p>
<p>Abstract</p>
<p>In the continuum context, the displacements of atoms induced by a dislocation can be approximated by a continuum disregistry field. In this work, two phase-field (PF)-based approaches and their variants are employed to calculate the disregistry fields of static, extended dislocations of pure edge and pure screw character in two face-centred cubic metals: Au and Al, which have distinct stable stacking fault energy and elastic anisotropy. A new truncated Fourier series form is developed to approximate the generalised stacking fault energy (GSFE) surface, which shows significant improvement over the previously employed Fourier series form. By measuring the intrinsic stacking fault (ISF) width and partial dislocation core size in different ways, the PF-based disregistry fields are quantitatively compared against those predicted by molecular statics. In particular, two new measures for the ISF widths are proposed and shown to overcome drawbacks of the more commonly used standards in the literature. Our calculations also show that continuum formulation of the elastic energy and the GSFE for a homogeneous surface can successfully characterise the core structure. Last, our comparisons highlight the significance of including the gradient energy in the free energy formulation when an accurate description of the dislocation core structure is desired.</p>
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</div></div></div>Thu, 28 Feb 2019 01:01:35 +0000Shuozhi Xu23124 at https://imechanica.orghttps://imechanica.org/node/23124#commentshttps://imechanica.org/crss/node/23124Generalized continua concepts in coarse-graining atomistic simulations
https://imechanica.org/node/22472
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/76">research</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/1910">multiscale modeling</a></div><div class="field-item odd"><a href="/taxonomy/term/2885">Generalized Continuum</a></div><div class="field-item even"><a href="/taxonomy/term/605">Dislocation</a></div><div class="field-item odd"><a href="/taxonomy/term/3514">phonon</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p><a href="https://link.springer.com/chapter/10.1007/978-3-319-77504-3_12">https://link.springer.com/chapter/10.1007/978-3-319-77504-3_12</a></p>
<p>Abstract</p>
<p>Generalized continuum mechanics (GCM) has attracted increased attention in the context of multiscale materials modeling, an example of which is a bottom-up GCM model, called the atomistic field theory (AFT). Unlike most other GCM models, AFT views a crystalline material as a continuous collection of lattice points; embedded within each point is a unit cell with a group of discrete atoms. As such, AFT concurrently bridges the discrete and continuous descriptions of materials, two fundamentally different viewpoints. In this chapter, we first review the basics of AFT and illustrate how it is realized through coarse-graining atomistic simulations via a concurrent atomistic-continuum (CAC) method. Important aspects of CAC, including its advantages relative to other multiscale methods, code development, and numerical implementations, are discussed. Then, we present recent applications of CAC to a number of metal plasticity problems, including static dislocation properties, fast moving dislocations and phonons, as well as dislocation/grain boundary interactions. We show that, adequately replicating essential aspects of dislocation fields at a fraction of the computational cost of full atomistics, CAC is established as an effective tool for coarse-grained modeling of various nano/micro-scale thermal and mechanical problems in a wide range of monatomic and polyatomic crystalline materials.</p>
</div></div></div>Tue, 26 Jun 2018 20:30:11 +0000Shuozhi Xu22472 at https://imechanica.orghttps://imechanica.org/node/22472#commentshttps://imechanica.org/crss/node/22472Modeling dislocations and heat conduction in crystalline materials: atomistic/continuum coupling approaches
https://imechanica.org/node/22466
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/76">research</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/1910">multiscale modeling</a></div><div class="field-item odd"><a href="/taxonomy/term/605">Dislocation</a></div><div class="field-item even"><a href="/taxonomy/term/7535">heat conduction</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p><a href="http://dx.doi.org/10.1080/09506608.2018.1486358">http://dx.doi.org/10.1080/09506608.2018.1486358</a></p>
<p>Abstract</p>
<p>Dislocations and heat conduction are essential components that influence properties and performance of crystalline materials, yet the modelling of which remains challenging partly due to their multiscale nature that necessitates simultaneously resolving the short-range dislocation core, the long-range dislocation elastic field, and the transport of heat carriers such as phonons with a wide range of characteristic length scale. In this context, multiscale materials modelling based on atomistic/continuum coupling has attracted increased attention within the materials science community. In this paper, we review key characteristics of five representative atomistic/continuum coupling approaches, including the atomistic-to-continuum method, the bridging domain method, the concurrent atomistic-continuum method, the coupled atomistic/discrete-dislocation method, and the quasicontinuum method, as well as their applications to dislocations, heat conduction, and dislocation/phonon interactions in crystalline materials. Through problem-centric comparisons, we shed light on the advantages and limitations of each method, as well as the path towards enabling them to effectively model various material problems in engineering from nano- to mesoscale.</p>
</div></div></div>Tue, 26 Jun 2018 05:26:26 +0000Shuozhi Xu22466 at https://imechanica.orghttps://imechanica.org/node/22466#commentshttps://imechanica.org/crss/node/22466Inertia of Dislocation Motion and Negative Mechanical Response in Crystals
https://imechanica.org/node/22025
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/76">research</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/605">Dislocation</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p><span>Dear Colleagues,</span></p>
<p class="MsoNormal"><span lang="EN-US" xml:lang="EN-US">Please see attached a recent article published in <em>Scientific Reports</em> on the fundamental nature of dislocation motion in crystals. Leave your comments or whatever you think of it.</span></p>
<p class="MsoNormal"><span lang="EN-US" xml:lang="EN-US">Link: <a href="https://www.nature.com/articles/s41598-017-18254-5">https://www.nature.com/articles/s41598-017-18254-5</a></span></p>
<p class="MsoNormal"> </p>
<p class="MsoNormal"><span lang="EN-US" xml:lang="EN-US">Best,</span></p>
<p class="MsoNormal"><span lang="EN-US" xml:lang="EN-US">Yizhe</span></p>
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<tr class="odd"><td><span class="file"><img class="file-icon" alt="PDF icon" title="application/pdf" src="/modules/file/icons/application-pdf.png" /> <a href="https://imechanica.org/files/s41598-017-18254-5.pdf" type="application/pdf; length=4525031">s41598-017-18254-5.pdf</a></span></td><td>4.32 MB</td> </tr>
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</div></div></div>Fri, 12 Jan 2018 02:43:44 +0000Yizhe_Tang22025 at https://imechanica.orghttps://imechanica.org/node/22025#commentshttps://imechanica.org/crss/node/22025Validation of the concurrent atomistic-continuum method on screw dislocation/stacking fault interactions
https://imechanica.org/node/21388
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/76">research</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/1910">multiscale modeling</a></div><div class="field-item odd"><a href="/taxonomy/term/605">Dislocation</a></div><div class="field-item even"><a href="/taxonomy/term/11692">stacking fault</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p><a href="http://dx.doi.org/10.3390/cryst7050120">http://dx.doi.org/10.3390/cryst7050120</a></p>
<p>Abstract</p>
<p>Dislocation/stacking fault interactions play an important role in the plastic deformation of metallic nanocrystals and polycrystals. These interactions have been explored in atomistic models, which are limited in scale length by high computational cost. In contrast, multiscale material modeling approaches have the potential to simulate the same systems at a fraction of the computational cost. In this paper, we validate the concurrent atomistic-continuum (CAC) method on the interactions between a lattice screw dislocation and a stacking fault (SF) in three face-centered cubic metallic materials—Ni, Al, and Ag. Two types of SFs are considered: intrinsic SF (ISF) and extrinsic SF (ESF). For the three materials at different strain levels, two screw dislocation/ISF interaction modes (annihilation of the ISF and transmission of the dislocation across the ISF) and three screw dislocation/ESF interaction modes (transformation of the ESF into a three-layer twin, transformation of the ESF into an ISF, and transmission of the dislocation across the ESF) are identified. Our results show that CAC is capable of accurately predicting the dislocation/SF interaction modes with greatly reduced DOFs compared to fully-resolved atomistic simulations.</p>
</div></div></div>Fri, 07 Jul 2017 14:43:27 +0000Shuozhi Xu21388 at https://imechanica.orghttps://imechanica.org/node/21388#commentshttps://imechanica.org/crss/node/21388Comparing EAM potentials to model slip transfer of sequential mixed character dislocations across two symmetric tilt grain boundaries in Ni
https://imechanica.org/node/21387
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/76">research</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/1910">multiscale modeling</a></div><div class="field-item odd"><a href="/taxonomy/term/605">Dislocation</a></div><div class="field-item even"><a href="/taxonomy/term/1632">grain boundary</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p><a href="http://dx.doi.org/10.1007/s11837-017-2302-1">http://dx.doi.org/10.1007/s11837-017-2302-1</a></p>
<p>Abstract</p>
<p>Slip transfer via sequential pile-up dislocations across grain boundaries (GBs) plays an important role in plastic deformation in polycrystalline face-centered cubic (FCC) metals. In this work, large scale concurrent atomistic-continuum (CAC) method simulations are performed to address the slip transfer of mixed character dislocations across GBs in FCC Ni. Two symmetric tilt GBs, a Σ3{111} coherent twin boundary (CTB) and a Σ11{113} symmetric tilt GB (STGB), are investigated using five different fits to the embedded-atom method (EAM) interatomic potential to assess the variability of predicted dislocation-interface reaction. It is shown that for the Σ3 CTB, two of these potentials predict dislocation transmission while the other three predict dislocation absorption. In contrast, all five fits to the EAM potential predict that dislocations are absorbed by the Σ11 STGB. Simulation results are examined in terms of several slip transfer criteria in the literature, highlighting the complexity of dislocation/GB interactions and the significance of multiscale modeling of the slip transfer process.</p>
</div></div></div>Fri, 07 Jul 2017 14:41:36 +0000Shuozhi Xu21387 at https://imechanica.orghttps://imechanica.org/node/21387#commentshttps://imechanica.org/crss/node/21387Is it safe to assume that the change in a dislocations' burger's vector size is negligible during loading?
https://imechanica.org/node/20713
<div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p><span>As a result of loading, there is grain distortion, which results in lattice distortion. when lattice distortion happens, then lattice parameter changes. The change in lattice parameter, (a), results in a dislocation's burger's vector size change, since it has the lattice parameter size in its formula. Consequently, one can conclude that the size of burger's vector of a dislocation changes as a result of loading! . Still, is it practically safe to assume that the the change in its size is negligible compared to its initial size before loading?</span></p>
</div></div></div><div class="field field-name-taxonomy-forums field-type-taxonomy-term-reference field-label-above"><div class="field-label">Forums: </div><div class="field-items"><div class="field-item even"><a href="/forum/390">Materials Forum</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-above"><div class="field-label">Free Tags: </div><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/605">Dislocation</a></div></div></div>Wed, 21 Dec 2016 16:27:07 +0000arash.p.j20713 at https://imechanica.orghttps://imechanica.org/node/20713#commentshttps://imechanica.org/crss/node/20713Is there a way to measure the magnitude of a dislocation burger's vector via high precision optical microscopes?
https://imechanica.org/node/20712
<div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>I need to calculate the size or magnitude of the burger's vector of a dislocation in crystalline materials, metals. Obviously and typically, it can be measured via XRD or the electron microscopy methods, TEM and SEM. The question is:</p>
<p id="yui_3_14_1_1_1482337187787_2054">could it also be measured via high precision optical microscopes, as precise as 1nm ?</p>
</div></div></div><div class="field field-name-taxonomy-forums field-type-taxonomy-term-reference field-label-above"><div class="field-label">Forums: </div><div class="field-items"><div class="field-item even"><a href="/forum/390">Materials Forum</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-above"><div class="field-label">Free Tags: </div><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/605">Dislocation</a></div><div class="field-item odd"><a href="/taxonomy/term/11465">Burger's vector</a></div><div class="field-item even"><a href="/taxonomy/term/11466">Optical Microscopy</a></div><div class="field-item odd"><a href="/taxonomy/term/2777">SEM</a></div><div class="field-item even"><a href="/taxonomy/term/957">TEM</a></div></div></div>Wed, 21 Dec 2016 16:23:18 +0000arash.p.j20712 at https://imechanica.orghttps://imechanica.org/node/20712#commentshttps://imechanica.org/crss/node/20712A revisit to atomistic rationale for slip in shape memory alloys
https://imechanica.org/node/20621
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/76">research</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/303">Shape memory alloy</a></div><div class="field-item odd"><a href="/taxonomy/term/1188">atomistic simulation</a></div><div class="field-item even"><a href="/taxonomy/term/605">Dislocation</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p><img class="imgLazyJSB figure large nrmImg" src="http://ars.els-cdn.com/content/image/1-s2.0-S0079642516300743-gr4.jpg" alt="Microstructure in real-life SMA components is polycrystalline in nature, where ..." width="533" height="499" border="0" data-thumbeid="1-s2.0-S0079642516300743-gr4.sml" data-fulleid="1-s2.0-S0079642516300743-gr4.jpg" data-imgeids="1-s2.0-S0079642516300743-gr4.jpg" data-thumbheight="164" data-thumbwidth="175" data-fullheight="499" data-fullwidth="533" data-loaded="true" /></p>
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<tr class="odd"><td><span class="file"><img class="file-icon" alt="PDF icon" title="application/pdf" src="/modules/file/icons/application-pdf.png" /> <a href="https://imechanica.org/files/A%20revisit%20to%20atomistic%20rationale%20for%20slip%20in%20shape%20memory%20alloys.pdf" type="application/pdf; length=12279051">A revisit to atomistic rationale for slip in shape memory alloys.pdf</a></span></td><td>11.71 MB</td> </tr>
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</div></div></div>Fri, 25 Nov 2016 20:02:49 +0000Piyas Chowdhury20621 at https://imechanica.orghttps://imechanica.org/node/20621#commentshttps://imechanica.org/crss/node/20621Competing mechanisms between dislocation and phase transformation in plastic deformation of single crystalline yttria-stabilized tetragonal zirconia nanopillars
https://imechanica.org/node/20249
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/76">research</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/1082">phase transformation</a></div><div class="field-item odd"><a href="/taxonomy/term/605">Dislocation</a></div><div class="field-item even"><a href="/taxonomy/term/11294">Nanopillar</a></div><div class="field-item odd"><a href="/taxonomy/term/9919">Zirconia</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>Molecular dynamics (MD) is employed to investigate the plastic deformation mechanisms of single crystalline yttria-stabilized tetragonal zirconia (YSTZ) nanopillars under uniaxial compression. Simulation results show that the nanoscale plastic deformation of YSTZ is strongly dependent on the crystallographic orientation of zirconia nanopillars. For the first time, the experimental explored tetragonal to monoclinic phase transformation is reproduced by MD simulations in some particular loading directions. Three distinct mechanisms of dislocation, phase transformation, and a combination of dislocation and phase transformation are identified when applying compressive loading along different directions. The strength of zirconia nanopillars exhibits a sensitive behavior depending on the failure mechanisms, such that the dislocation-mediated deformation leads to the lowest strength, while the phase transformation-dominated deformation results in the highest strength.</p>
<p>Acta Materialia 120 (2016) 337-347</p>
<p><span><a href="http://authors.elsevier.com/a/1Tef94r9SU3pVv">http://authors.elsevier.com/a/1Tef94r9SU3pVv</a></span></p>
<p> </p>
</div></div></div>Thu, 01 Sep 2016 19:41:22 +0000mohsenzaeem20249 at https://imechanica.orghttps://imechanica.org/node/20249#commentshttps://imechanica.org/crss/node/20249A critical thickness condition for graphene and other 2D materials
https://imechanica.org/node/19952
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/76">research</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/10730">2D materials</a></div><div class="field-item odd"><a href="/taxonomy/term/605">Dislocation</a></div><div class="field-item even"><a href="/taxonomy/term/11177">critical thickness</a></div><div class="field-item odd"><a href="/taxonomy/term/671">graphene</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>B. C. McGuigan, P. Pochet, and H. T. Johnson, Critical thickness for interface misfit dislocation formation in two-dimensional materials, Phys. Rev. B 93, 214103, 2016.</p>
<p>URL: <a href="http://link.aps.org/doi/10.1103/PhysRevB.93.214103">http://link.aps.org/doi/10.1103/PhysRevB.93.214103</a></p>
<p>In this work, we report a critical thickness analysis for dislocation formation in 2D lateral heterostructures. The analysis applies to graphene, h-BN, and other 2D materials. We compare a fully atomistic approach to a continuum critical thickness theory, for the limiting cases of thin "films" on much thicker "substrates", and for cases in which the "film" and "substrate" are of comparable thickness -- also known as the compliant substrate case. By comparing atomistic and continuum formulations, we compute the effective dislocation core cutoff radii for graphene and h-BN, as well as the dislocation core energies. The work provides a comprehensive critical thickness analysis for 2D materials, and paves the way for defect-free growth of strained 2D lateral heterstructures.</p>
<p><img src="http://htj.mechanical.illinois.edu/images/graphene_HJ_toc.png" alt="graphene/h-BN interface misfit dislocation" width="780" height="245" /></p>
</div></div></div>Mon, 06 Jun 2016 20:14:18 +0000Harley T. Johnson19952 at https://imechanica.orghttps://imechanica.org/node/19952#commentshttps://imechanica.org/crss/node/19952Sequential slip transfer of mixed-character dislocations across Σ3 coherent twin boundary in FCC metals: a concurrent atomistic-continuum study
https://imechanica.org/node/19410
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/76">research</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/10953">slip transfer</a></div><div class="field-item odd"><a href="/taxonomy/term/605">Dislocation</a></div><div class="field-item even"><a href="/taxonomy/term/7153">fcc</a></div><div class="field-item odd"><a href="/taxonomy/term/10954">concurrent atomistic-continuum</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p><a href="http://dx.doi.org/10.1038/npjcompumats.2015.16">http://dx.doi.org/10.1038/npjcompumats.2015.16</a></p>
<p>Abstract</p>
<p>Sequential slip transfer across grain boundaries (GB) has an important role in size-dependent propagation of plastic deformation in polycrystalline metals. For example, the Hall–Petch effect, which states that a smaller average grain size results in a higher yield stress, can be rationalised in terms of dislocation pile-ups against GBs. In spite of extensive studies in modelling individual phases and grains using atomistic simulations, well-accepted criteria of slip transfer across GBs are still lacking, as well as models of predicting irreversible GB structure evolution. Slip transfer is inherently multiscale since both the atomic structure of the boundary and the long-range fields of the dislocation pile-up come into play. In this work, concurrent atomistic-continuum simulations are performed to study sequential slip transfer of a series of curved dislocations from a given pile-up on Σ3 coherent twin boundary (CTB) in Cu and Al, with dominant leading screw character at the site of interaction. A Frank-Read source is employed to nucleate dislocations continuously. It is found that subject to a shear stress of 1.2 GPa, screw dislocations transfer into the twinned grain in Cu, but glide on the twin boundary plane in Al. Moreover, four dislocation/CTB interaction modes are identified in Al, which are affected by (1) applied shear stress, (2) dislocation line length, and (3) dislocation line curvature. Our results elucidate the discrepancies between atomistic simulations and experimental observations of dislocation-GB reactions and highlight the importance of directly modeling sequential dislocation slip transfer reactions using fully 3D models.</p>
</div></div></div>Sun, 31 Jan 2016 14:39:01 +0000Shuozhi Xu19410 at https://imechanica.orghttps://imechanica.org/node/19410#commentshttps://imechanica.org/crss/node/19410In Situ Atomic-Scale Observation of Twinning Dominated Deformation in Nanoscale Body-Centred Cubic Tungsten
https://imechanica.org/node/18034
<div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/8074">deformation twinning</a></div><div class="field-item odd"><a href="/taxonomy/term/605">Dislocation</a></div><div class="field-item even"><a href="/taxonomy/term/10364">Body-centred cubic</a></div><div class="field-item odd"><a href="/taxonomy/term/10365">nanocrystal</a></div><div class="field-item even"><a href="/taxonomy/term/6864">pseudoelasticity</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p><span lang="EN-GB" xml:lang="EN-GB"><span>In situ atomic-scale observation of twinning-dominated deformation in nanoscale body-centred cubic tungsten</span></span></p>
<p><span lang="EN-GB" xml:lang="EN-GB"><span>By </span></span><span><span>Jiangwei Wang, Zhi Zeng, Christopher R. Weinberger, Ze Zhang, Ting Zhu & Scott X. Mao</span></span></p>
<p><span><span>Nature Materials (2015) doi:10.1038/nmat4228</span></span></p>
<p><span lang="EN-GB" xml:lang="EN-GB"><a href="http://www.nature.com/nmat/journal/vaop/ncurrent/full/nmat4228.html">http://www.nature.com/nmat/journal/vaop/ncurrent/full/nmat4228.html</a></span></p>
<p> </p>
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<tr class="even"><td><span class="file"><img class="file-icon" alt="PDF icon" title="application/pdf" src="/modules/file/icons/application-pdf.png" /> <a href="https://imechanica.org/files/nmat4228_Twin%20in%20BCC%20W.pdf" type="application/pdf; length=2024808" title="nmat4228_Twin in BCC W.pdf">Main text</a></span></td><td>1.93 MB</td> </tr>
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</div></div></div>Mon, 09 Mar 2015 22:44:56 +0000Jiangwei Wang18034 at https://imechanica.orghttps://imechanica.org/node/18034#commentshttps://imechanica.org/crss/node/18034Surface dislocation nucleation
https://imechanica.org/node/2617
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/76">research</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/605">Dislocation</a></div><div class="field-item odd"><a href="/taxonomy/term/1744">nanowire</a></div><div class="field-item even"><a href="/taxonomy/term/1745">activation volume</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>
</p>
<p>
<img class="image img_assist_properties" src="/files/images/image005_2.img_assist_properties.png" alt="Surface dislocation nucleation" title="Surface dislocation nucleation" width="157" height="200" align="baseline" /></p>
<p>
<span>Ting Zhu, Ju Li, Amit <span class="spelle"><span>Samanta</span></span>, Austin Leach and Ken Gall, “Temperature and strain-rate dependence of surface dislocation nucleation”, <em>Physical Review Letters</em>, 100, 025502 (2008).</span>
</p>
<p><span><span>Dislocation nucleation is essential to the plastic deformation of small-volume crystalline solids. The free surface may act as an effective source of dislocations to initiate and sustain plastic flow, in conjunction with bulk sources. Here, we develop an atomistic modeling framework to address the probabilistic nature of surface dislocation nucleation. We show the activation volume associated with surface dislocation nucleation is characteristically in the range of 1-10b^3, where b is the Burgers vector. Such small activation volume leads to sensitive temperature and strain-rate dependence of the nucleation stress, providing an upper bound to the size-strength relation in nanopillar compression experiments.</span></span></p>
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</div></div></div>Thu, 24 Jan 2008 16:24:57 +0000Ting Zhu2617 at https://imechanica.orghttps://imechanica.org/node/2617#commentshttps://imechanica.org/crss/node/2617Dislocation Dynamics in Multiwalled Carbon Nanotubes
https://imechanica.org/node/2610
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/76">research</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/139">Carbon nanotube</a></div><div class="field-item odd"><a href="/taxonomy/term/605">Dislocation</a></div><div class="field-item even"><a href="/taxonomy/term/1736">high-resolution electron microscopy (HRTEM)</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>
PRL 100, 035503 (2008) Jianyu Huang, Feng Ding, Boris I. Yakobson
</p>
<p>
Dislocation dynamics dictate the mechanical behavior of materials. Dislocations in periodic crystalline<br />
materials have been well documented. On the contrary, dislocations in cylindrical carbon nanotubes, particularly in multiwalled carbon nanotubes (MWCNTs), remain almost unexplored. Here we report that a room temperature 1/2 [0001] sessile dislocation in a MWCNT becomes highly mobile, as characterized by its glide, climb, and the glide-climb interactions, at temperatures of about 2000 C. The dislocation glide leads to the cross-linking of different shells; dislocation climb creates nanocracks; and the interaction of two 1/2 [0001] dislocations creates kinks.We found that dislocation loops act as channels for mass transport. These dislocation dynamics are drastically different from that in conventional periodic crystalline materials due to the cylindrical, highly anisotropic structures of MWCNTs.
</p>
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</div></div></div>Thu, 24 Jan 2008 01:51:10 +0000Jianyu Huang2610 at https://imechanica.orghttps://imechanica.org/node/2610#commentshttps://imechanica.org/crss/node/2610The dislocations and grain bounday.
https://imechanica.org/node/2451
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/76">research</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/605">Dislocation</a></div><div class="field-item odd"><a href="/taxonomy/term/1632">grain boundary</a></div><div class="field-item even"><a href="/taxonomy/term/1633">Hall-Petch</a></div><div class="field-item odd"><a href="/taxonomy/term/1634">pile up</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>
When dislocation meet the grain boundary. The grain boundary present obstacles to dislocation motion. A usual point is that the dislocation will pile up against the grain boundary(But from the expriments , it seldomly see this phenomenon.). Macroscopic yielding occours when the adjacent grain can deform plastically Which maybe effected by the emission of dislocation from the grain boundary, or in another way , the pileup dislocation can produce a stress concentration which can active the dislocation source in the adjacent grain. As we knowe ,in polycrystalline, the material will express a Hall-Petch relationship between the yielding stress and the grain dimension. There are many models to explain the H-P relationship,such as pile-up dislocations, average fress distance....
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Another argument such as dislocation can transmite the grain boundary. So how can we consider the slip resistance associated with slip penetration events across grain boundaries?<br />
Also some scholars has claim that the grain boundary can absorb dilocations and aslo emite dislocations.
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So the which mechanism is true in grain boundary, whether dislocation can pile up across boundary, when will a dislocation can penetrate to the adjacent grain, when can grain boundary absorb a dislocation , which and when cause the grain bounday to emite a dislocation.
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I appreciate your points and discussion. Will you please express your points or attach the paper about this topic?
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</div></div></div>Wed, 12 Dec 2007 14:34:18 +0000Xu Zhang2451 at https://imechanica.orghttps://imechanica.org/node/2451#commentshttps://imechanica.org/crss/node/2451Dislocations 2008 International Conference
https://imechanica.org/node/1909
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/74">conference</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/169">Plasticity</a></div><div class="field-item odd"><a href="/taxonomy/term/605">Dislocation</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>
We are pleased to announce <strong><em><a href="http://micro.stanford.edu/Dislocations2008">Dislocations 2008</a></em></strong>, an international conference on the fundamentals of plastic deformation and other physical phenomena where the dislocations play pivotal roles.<span> </span>The conference will take place on October 13-17, 2008 at the Gold Coast Hotel, Hong Kong, China.<span> </span>More information about the <em>Dislocations 2008</em> conference can be found at the following web site:
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<span> </span><a href="http://micro.stanford.edu/Dislocations2008">http://micro.stanford.edu/Dislocations2008</a>
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<strong><span>The purpose</span></strong><strong><span> </span></strong><span>of the <em>Dislocations</em> conferences is to bring together a diverse community interested in the fundamentals of dislocation behavior and plastic deformation. Relevant research topics include new experimental techniques, theory and computer simulations of dislocations in all types of materials.<span> </span></span>
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The Dislocations 2008 conference is the third one in the series, following <em>Dislocations 2000</em> (NIST, Washington, DC, USA) and <em>Dislocations 2004</em> (French Riveria, France).<span> </span>The conference style will be similar to that of a Gordon conference.<span> </span>There will be no parallel sessions while considerable time will be dedicated to focused discussions.<span> </span>The number of attendees will be limited to 200.
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Please feel free to circulate this newsletter to interested colleagues.<span> </span>The <em>Dislocations 2008</em> web site will soon be able to accept abstract submissions.
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Alfonso Ngan and Wei Cai
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Dislocations 2008 Organizing Committee
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<img src="http://micro.stanford.edu/Dislocations2008/images/logo.gif" alt="Dislocations 2008 Logo" title="Dislocations 2008" width="195" height="146" /></p>
</div></div></div>Wed, 12 Sep 2007 02:31:16 +0000Cai Wei1909 at https://imechanica.orghttps://imechanica.org/node/1909#commentshttps://imechanica.org/crss/node/1909Question: Is the local energy dictating dislocation emission constant for single crystal?
https://imechanica.org/node/1868
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/77">opinion</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/605">Dislocation</a></div><div class="field-item odd"><a href="/taxonomy/term/1040">Crystal plasticity</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>
Hi everyone, in my size dependence study, I find the local energy dictating dislocation emission is almost constant for varied sized samples, in given directions of single crystal. I don't know this is an interesing finding, or just a common sense. Will you give me some suggestion, Thank you!
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Kejie
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<tr class="odd"><td><span class="file"><img class="file-icon" alt="PDF icon" title="application/pdf" src="/modules/file/icons/application-pdf.png" /> <a href="https://imechanica.org/files/attachment%20for%20Ajit%20R.%20Jadhav.pdf" type="application/pdf; length=27418" title="attachment for Ajit R. Jadhav.pdf">attachment for Ajit R. Jadhav.pdf</a></span></td><td>26.78 KB</td> </tr>
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</div></div></div>Sat, 01 Sep 2007 10:38:40 +0000Kejie Zhao1868 at https://imechanica.orghttps://imechanica.org/node/1868#commentshttps://imechanica.org/crss/node/1868Integral Formulations for 2D Elasticity: 1. Anisotropic Materials
https://imechanica.org/node/819
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/76">research</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/605">Dislocation</a></div><div class="field-item odd"><a href="/taxonomy/term/606">integral equation</a></div><div class="field-item even"><a href="/taxonomy/term/607">boundary element method</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>Might also be useful for simulating dislocation motion in a finite body.
</p><p>Several sets of boundary integral equations for two dimensional elasticity are derived from Cauchy integral theorem.These equations reveal the relations between displacements and resultant forces, between displacements and tractions, and between the tangential derivatives of displacements and tractions on solid boundary.Special attention is given to the formulation that is based on tractions and the tangential derivatives of displacements on boundary, because its integral kernels have the weakest singularities.The formulation is further extended to include singular points, such as dislocations and line forces, in a finite body, so that the singular stress field can be directly obtained from solving the integral equations on the external boundary without involving the linear superposition technique often used in the literature. Body forces and thermal effect are subsequently included. The general framework of setting up a boundary value problem is discussed and continuity conditions at a non-singular corner are derived.<span> </span>The general procedure in obtaining the elastic field around a circular hole is described, and the stress fields with first and second order singularities are obtained. Some other analytical solutions are also derived by using the formulation.<span> </span></p>
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<tr class="odd"><td><span class="file"><img class="file-icon" alt="PDF icon" title="application/pdf" src="/modules/file/icons/application-pdf.png" /> <a href="https://imechanica.org/files/New_integrals.pdf" type="application/pdf; length=291657" title="New_integrals.pdf">New_integrals.pdf</a></span></td><td>284.82 KB</td> </tr>
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</div></div></div>Thu, 08 Feb 2007 21:29:39 +0000Honghui Yu819 at https://imechanica.orghttps://imechanica.org/node/819#commentshttps://imechanica.org/crss/node/819Error | iMechanica