dislocations

Darren C. Pagan a, Romain Quey b, Matthew P. Kasemer c

a Materials Science and Engineering, The Pennsylvania State University, University Park PA 16802, US

b Mines Saint-Etienne, Univ. Lyon, CNRS, UMR 5307 LGF, F–42023 Saint-Etienne, France

c Mechanical Engineering, The University of Alabama, Tuscaloosa AL 35487, US

1. Introduction

I have a post-doc position for up to 18 months at Imperial College London, funded by Rolls Royce, working on dislocation mechanics modelling for problems occuring in materials for nuclear energy applications, full advert and application from the link below. Closing date 27th October 2022, starting as soon as possible, at least within the next 6 months. https://www.imperial.ac.uk/jobs/description/ENG02285/research-assistant-associate-mechanics-mod

http://dx.doi.org/10.1063/5.0080849

Abstract

I have a post-doc position for 24 months at Imperial College London, funded by Rolls Royce, working on dislocation mechanics modelling for problems in nuclear materials, full advert and application from the link below. Closing date 14th November 2021, starting as soon as possible, at least within the next 6 months.

https://www.imperial.ac.uk/jobs/description/ENG01880/research-associate-...

The Max-Planck-Institut für Eisenforschung (Düsseldorf, Germany) offers a position in the department Structure and Nano-/Micromechanics of Materials (Prof. G. Dehm): PhD student or postdoc position in “Atomistic Computer Simulation of Grain Boundary Structure and Mechanics”

Understanding how grain boundaries influence plasticity will lead to significant advances in material design. In the context of the department’s research, the overarching aim of this PhD project is to connect grain boundary structures in fcc metals to physical properties.

The microelectronics revolution is one of the most influential drivers of current industrial developments. To probe the mechanical properties of ever shrinking materials and components, nanoindentation has come to be an omnipresent and indispensable method. In a recent combined experimental and computational approach, an international team of scientists was for the first time able to resolve the dynamic atomistic processes taking place at the elastic-plastic transition during nanoindentation.

Dear fellow mechanicians,

I wanted to share our recent paper in Large scale ab-initio simulations of dislocations. A link with free access is provided. 

https://authors.elsevier.com/a/1aRRW508Hm3Z7

https://www.sciencedirect.com/science/article/pii/S0021999120300231?dgci...

https://arxiv.org/pdf/1907.02604.pdf

 A demonstration through an example is given of how the Volterra dislocation formulation in linear elasticity can be viewed as a (formal) limit of a problem in plasticity theory. Interestingly, from this point of view the Volterra dislocation formulation with discontinuous displacement, and non-square-integrable energy appears as a large-length scale limit of a smoother microscopic problem. This is in contrast to other formulations using SBV functions as well as the theory of Structured deformations where the microscopic problem is viewed as discontinuous and the smoother plasticity formulation appears as a homogenized large length-scale limit.

(To appear in Journal of Elasticity).

Title of the project: Ab initio modelling of interactions between dislocations and solutes in body-centered cubic metals

Research area: Solid State Physics, Materials Science

Summary of the project:

Amit Acharya

(in Journal of Elasticity)

The kinematic theory of Weingarten-Volterra line defects is revisited, both at small and finite deformations. Existing results are clarified and corrected as needed, and new results are obtained. The primary focus is to understand the relationship between the disclination strength and Burgers vector of deformations containing a Weingarten-Volterra defect corresponding to different cut-surfaces.

Given a distribution of defects on a structured surface, such as those represented by 2-dimensional crystalline materials, liquid crystalline surfaces, and thin sandwiched shells, what is the resulting stress field and the deformed shape? Motivated by this concern, we first classify, and quantify, the translational, rotational, and metrical defects allowable over a broad class of structured surfaces. With an appropriate notion of strain, the defect densities are then shown to appear as sources of strain incompatibility.

Chiqun Zhang            Amit Acharya

The utility of the notion of generalized disclinations in materials science is discussed within the physical context of modeling interfacial and bulk line defects like defected grain and phase boundaries, dislocations and disclinations. The Burgers vector of a disclination dipole in linear elasticity is derived, clearly demonstrating the equivalence of its stress field to that of an edge dislocation. We also prove that the inverse deformation/displacement jump of a defect line is independent of the cut-surface when its g.disclination strength vanishes. An explicit formula for the displacement jump of a single localized composite defect line in terms of given g.disclination and dislocation strengths is deduced based on the Weingarten theorem for g.disclination theory at finite deformation. The Burgers vector of a g.disclination dipole at finite deformation is also derived.

Short course at Centre International de Sciences Mechanique (CISM), Udine.

May 22-26, 2017

Lecturers:  S Forest, I Groma, D McDowell, S Mesarovic, J-N Roux, H Zbib

The flyer is attached.  Register at:   http://www.cism.it/courses/C1703/ 

Summary 

Akanksha Garg, Craig Maloney

(accepted mannuscript in Journal of Mechanics and Physics of Solids)

Amit Acharya                       Michael Widom

To appear in Journal of the Mechanics and Physics of Solids

Motivated by results of the topological theory of glasses accounting for geometric frustration,
we develop the simplest possible continuum mechanical model of defect dynamics in metallic
glasses that accounts for topological, energetic, and kinetic ideas. A geometrical description
of ingredients of the structure of metallic glasses using the concept of local order based on
Frank-Kasper phases and the notion of disclinations as topological defects in these structures is
proposed. This novel kinematics is incorporated in a continuum mechanical framework capable
of describing the interactions of disclinations and also of dislocations (interpreted as pairs of
opposite disclinations). The model is aimed towards the development of a microscopic understanding
of the plasticity of such materials. We discuss the expected predictive capabilities of
the model vis-a-vis some observed physical behaviors of metallic glasses.

Prof. Wei Cai at the Mechanical Engineering Department of Stanford University is seeking a postdoctoral researcher to lead a project on the modeling of grain structure evolution in the surface layer under friction.  The major task of this project is the development of a phase field model for grain/sub-grain structure evolution under friction.  It is likely that molecular dynamics and dislocation dynamics simulations would be required as well to obtain a good physical understanding of the process.

 R. Brenner   A. J. Beaudoin    P. Suquet    A. Acharya

(to appear in Philosophical Magazine)

Position Description: Two postdoctoral associate positions, one in computations and one in experiments, are available at Rice University. The first position is in the area of atomistic and molecular modeling of nanoscale defects, dislocations and mechanics of complex, low symmetry compounds. The computational techniques will be integrated to approaches from statistical mechanics and physical chemistry to provide quantitative predictions of properties of complex materials across different time- and length-scales. 

European Commission' s JRC (Joint Research Centre) is organizing the 3rd workshop on physics based material models and experimental observations (http://iwpmeo.org/) in collaboration with University of Oxford, Max-Planck-Institut für Eisenforschung and Middle East Technical University. The workshop will be held in Izmir/Turkey on 2-4 June 2014.

Amit Acharya         Claude Fressengeas

Springer Proceedings in Mathematics and Statistics on Differential Geometry and Continuum Mechanics, Vol. 137, pages 123-165. Ed: G. Q Chen, M. Grinfeld, R.J. Knops (Proceedings of  Workshop held at the Intl. Centre for Mathematical Sciences in Edinburgh, 2013.)