Critical Evaluation of Atomistic Simulations of 3D Dislocation Configurations

1995 ◽  
Vol 408 ◽  
Author(s):  
Vijay B. Shenoy ◽  
Rob Phillips
Keyword(s):  
Atomistic Simulation ◽  
Critical Evaluation ◽  
Line Tension ◽  
Peierls Stress ◽  
Atomistic Simulations ◽  
Lattice Resistance ◽  
New Challenges ◽  
Fixed Boundaries ◽  
Important Objective ◽  
Approximate Scheme

AbstractThough atomistic simulation of 3D dislocation configurations is an important objective for the analysis of problems ranging from point defect condensation to the operation of Frank-Read sources such calculations pose new challenges. In particular, use of finite sized simulation cells produce additional stresses due to the presence of fixed boundaries in the far field which can contaminate the interpretation of these simulations. This paper discusses an approximate scheme for accounting for such boundary stresses, and is illustrated via consideration of the lattice resistance encountered by straight dislocations and simulations of 3D bow out of pinned dislocation segments. These results allow for a reevaluation of the concepts of the Peierls stress and the line tension from the atomistic perspective.

Critical Evaluation of Atomistic Simulations of 3D Dislocation Configurations

1995 ◽  
Vol 409 ◽  
Author(s):  
Vijay B. Shenoy ◽  
Rob Phillips
Keyword(s):  
Atomistic Simulation ◽  
Critical Evaluation ◽  
Line Tension ◽  
Peierls Stress ◽  
Atomistic Simulations ◽  
Lattice Resistance ◽  
New Challenges ◽  
Fixed Boundaries ◽  
Important Objective ◽  
Approximate Scheme

AbstractThough atomistic simulation of 3D dislocation configurations is an important objective for the analysis of problems ranging from point defect condensation to the operation of Frank-Read sources such calculations pose new challenges. In particular, use of finite sized simulation cells produce additional stresses due to the presence of fixed boundaries in the far field which can contaminate the interpretation of these simulations. This paper discusses an approximate scheme for accounting for such boundary stresses, and is illustrated via consideration of the lattice resistance encountered by straight dislocations and simulations of 3D bow out of pinned dislocation segments. These results allow for a reevaluation of the concepts of the Peierls stress and the line tension from the atomistic perspective.

scholarly journals The Orowan Stress Measurement of Twinning Dislocations in Magnesium

Metals ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 1020
Author(s):  
Xiao-Zhi Tang ◽  
Ya-Fang Guo
Keyword(s):  
Precipitation Hardening ◽  
Stress Measurement ◽  
Line Tension ◽  
Metallic Alloys ◽  
Atomistic Simulations ◽  
Stick Slip ◽  
Lack Of Information ◽  
Classic Theory ◽  
Orowan Stress ◽  
Bypass Mechanism

The interaction between a lattice dislocation and non-shearable precipitates has been well explained by the Orowan bypass mechanism. The calculated additional shear stress facilitates the evaluation of precipitation hardening in metallic alloys. The lack of information about how a twinning dislocation behaves in the same scenario hinders our understanding of the strengthening against twin-mediated plasticity in magnesium alloys. In the current study, the bowing and bypassing of a twining dislocation impeded by impenetrable obstacles are captured by atomistic simulations. The Orowan stress measurement is realized by revealing the stick-slip dynamics of a twinning dislocation. The measured Orowan stress significantly deviate from what classic theory predicts. This deviation implies that the line tension approximation may generally overestimate the Orowan stress for twinning dislocations.

Science or Snake Oil? Teaching Critical Evaluation of “Research” Reports on the Internet

2002 ◽  
Vol 29 (4) ◽  
pp. 321-324 ◽  
Author(s):  
Patricia A. Connor-Greene ◽  
Dan J. Greene
Keyword(s):  
Quality Control ◽  
Critical Thinking ◽  
Small Group ◽  
Group Discussion ◽  
Critical Evaluation ◽  
Problem Based Learning ◽  
Small Group Discussion ◽  
Easy Access ◽  
The Internet ◽  
New Challenges

The proliferation of information on the Internet introduces new challenges for educators. Although the Internet can provide quick and easy access to a wealth of information, it has virtually no quality control. Consequently, the Internet has rendered faculty more essential than ever as teachers of the analytic and evaluative skills students need to become educated consumers of information. In this article we describe an exercise using small-group discussion and individual problem-based learning to teach critical thinking about the Internet. Data from the exercise and from student evaluations support both its need and students' perceptions of its effectiveness.

A Critical Evaluation of New Challenges Pertaining to the Activities of Translation and Interpretation in Sub-Saharan Africa

2021 ◽  
pp. 25-38
Author(s):  
Milburga ATCERO
Keyword(s):  
Critical Evaluation ◽  
Sub Saharan Africa ◽  
Afrique Subsaharienne ◽  
New Challenges ◽  
Sub Saharan

Cette contribution vise à évaluer de façon critique les nouveaux défis liés à la traduction et à l’interprétation (TI) dans une Afrique subsaharienne caractérisée par sa grande diversité linguistique. L’auteur espère identifier et suggérer des méthodologies pouvant être appliquées pour rapprocher cette région du reste du monde. Il identifie, en outre, la nécessité pour l’Afrique subsaharienne de mettre en œuvre des politiques et pratiques qui favorisent le multilinguisme. Elles sont principalement basées sur la pluralité des langues, avec un espace adéquat pour les langues internationales, étant donnée le rôle crucial des parcours scolaires sur ce continent. Dans l’environnement de travail dynamique d’aujourd’hui, différentes institutions reconnaissent le rôle important joué par la TI dans la recherche et le renforcement de l’efficacité des individus comme des organisations. L’auteur s’appuie sur un cadre logique illustrant l’importance de la traduction dans les sphères socioculturelles et linguistiques, pour la production de connaissances sur l’Afrique. Il soutient que la traduction devrait être considérée comme une occasion d’explorer la diversité des possibles dans la littérature africaine. Il conclut en décrivant les méthodes envisageables et les nouvelles orientations.

Length Scale Effects in Materials Deformation of Nano and Microscale Au Structures

2009 ◽  
Author(s):  
Jie Lian ◽  
Junlan Wang
Keyword(s):  
Mechanical Properties ◽  
Elastic Modulus ◽  
Size Effect ◽  
Sample Size ◽  
Atomistic Simulation ◽  
Scale Effects ◽  
Elastic Recovery ◽  
Boundary Effect ◽  
Dislocation Nucleation ◽  
Atomistic Simulations

In this study, intrinsic size effect — strong size dependence of mechanical properties — in materials deformation was investigated by performing atomistic simulation of compression on Au (114) pyramids. Sample boundary effect — inaccurate measurement of mechanical properties when sample size is comparable to the indent size — in nanoindentation was also investigated by performing experiments and atomistic simulations of nanoindentation into nano- and micro-scale Au pillars and bulk Au (001) surfaces. For intrinsic size effect, dislocation nucleation and motions that contribute to size effect were analyzed for studying the materials deformation mechanisms. For sample boundary effect, in both experiments and atomistic simulation, the elastic modulus decreases with increasing indent size over sample size ratio. Significantly different dislocation motions contribute to the lower value of the elastic modulus measured in the pillar indentation. The presence of the free surface would allow the dislocations to annihilate, causing a higher elastic recovery during the unloading of pillar indentation.

Synergistic effect of supercritical CO2 and organic solvent on exfoliation of graphene: experiment and atomistic simulation studies

2019 ◽  
Vol 21 (39) ◽  
pp. 22149-22157 ◽  
Author(s):  
Lixi Liu ◽  
Yan Chen ◽  
Fei Dang ◽  
Yilun Liu ◽  
Xiaogeng Tian ◽  
...  
Keyword(s):  
Synergistic Effect ◽  
Organic Solvent ◽  
Supercritical Co2 ◽  
Atomistic Simulation ◽  
Atomistic Simulations ◽  
Simulation Studies

The synergistic effect of scCO2 and organic solvent on exfoliation of graphene was studied by experiments and atomistic simulations.

Atomistic Simulation of ½ Screw Dislocations in BCC Tungsten

2008 ◽  
Vol 59 ◽  
pp. 247-252 ◽  
Author(s):  
Jan Fikar ◽  
Robin Schäublin ◽  
Carolina Björkas
Keyword(s):  
Screw Dislocation ◽  
Atomistic Simulation ◽  
Bond Order ◽  
Analytical Approach ◽  
Atomistic Simulations ◽  
Screw Dislocations ◽  
Atom Model ◽  
Embedded Atom ◽  
Bond Order Potential

Atomistic simulations are used to describe the ½<111> screw dislocation in tungsten. Two different embedded atom model (EAM) potentials and one bond-order potential (BOP) are compared. A new analytical approach for constructing asymmetrical screw dislocations is presented.

Simple Flexible Boundary Conditions for the Atomistic Simulation of Dislocation Core Structure and Motion

1992 ◽  
Vol 291 ◽  
Author(s):  
Roberto Pasianot ◽  
Eduardo J. Savino ◽  
Zhao-Yang Xie ◽  
Diana Farkas
Keyword(s):  
Atomistic Simulation ◽  
Dislocation Line ◽  
Dislocation Core ◽  
Dislocation Motion ◽  
Peierls Stress ◽  
Rigid Boundary ◽  
The Past ◽  
Structure And Motion ◽  
Linear Effects ◽  
Dislocation Core Structure

ABSTRACTFlexible boundary codes for the atomistic simulation of dislocations and other defects have been developed in the past mainly by Sinclair [1], Gehlen et al.[2], and Sinclair et al.[3]. These codes permitted the use of smaller atomic arrays than rigid boundary codes, gave descriptions of core non-linear effects and allowed fair assessments of the Peierls stress for dislocation motion. Green functions (continuum or discrete) or surface traction forces were used to relax the boundary atoms.A much simpler approach is followed here. Core and mobility effects at the boundary are accounted for by a dipole tensor centered at the dislocation line, whose components constitute six more parameters of the minimization process. Results are presented for [100] dislocations in NiAl. It is shown that, within the limitations of the technique, reliable values of the Peierls stress are obtained.

Domain Reduction Method for Periodic Nanostructure Modeling: Gold Nanorods, Carbon Nanotubes and Graphene Applications

2010 ◽  
Author(s):  
Eduard G. Karpov ◽  
Dong Qian
Keyword(s):  
Atomistic Simulation ◽  
Reduction Method ◽  
Atomistic Simulations ◽  
Fine Scale ◽  
Coarse Scale ◽  
Benchmark Data ◽  
Domain Reduction ◽  
Interfacial Boundary ◽  
Nanocrystalline Structures ◽  
Domain Reduction Method

A domain-reduction approach for the simulation of one- and two-dimensional nanocrystalline structures is demonstrated. In this approach, the domain of interest is partitioned into coarse and fine scale regions and the coupling between the two is implemented through a multiscale interfacial boundary condition. The atomistic simulation is used in the fine scale region, while the discrete Fourier transform is applied to the coarse scale region to yield a compact Green’s function formulation that represents the effects of the coarse scale domain upon the fine/coarse scale interface. This approach facilitates the simulations for the fine scale, without the requirement to simulate the entire coarse scale domain. Robustness of the proposed domain-reduction method is demonstrated via comparison and verification of the results with benchmark data from fully atomistic simulations. Demonstrated applications include deformation of crystalline Au (111) nanorods, CNT bending and buckling, and graphene nanoindentation.

Atomistic Simulations for Multiscale Modeling in bcc Metals

1999 ◽  
Vol 121 (2) ◽  
pp. 120-125 ◽  
Author(s):  
John A. Moriarty ◽  
Wei Xu ◽  
Per So¨derlind ◽  
James Belak ◽  
Lin H. Yang ◽  
...  
Keyword(s):  
Multiscale Modeling ◽  
Strength Properties ◽  
Peierls Stress ◽  
Boundary Structure ◽  
Atomistic Simulations ◽  
Interatomic Potentials ◽  
Ideal Strength ◽  
Bcc Metals ◽  
Kink Pair ◽  
Grain Boundary Structure

Quantum-based atomistic simulations are being used to study fundamental deformation and defect properties relevant to the multiscale modeling of plasticity in bcc metals at both ambient and extreme conditions. Ab initio electronic-structure calculations on the elastic and ideal-strength properties of Ta and Mo help constrain and validate many-body interatomic potentials used to study grain boundaries and dislocations. The predicted Σ5 (310) [100] grain boundary structure for Mo has recently been confirmed in HREM measurements. The core structure, γ surfaces, Peierls stress, and kink-pair formation energies associated with the motion of a/2〈111〉 screw dislocations in Ta and Mo have also been calculated. Dislocation mobility and dislocation junction formation and breaking are currently under investigation.

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