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dislocations

Regarding LAMMPS

Is there anyone using LAMMPS for nano-mechanics? or for dislocation analysis?

I would like to discuss few things.

Lucia Nicola's picture

PhD position at Delft University of Technology, NL

We welcome applications for a 4 year PhD positon in the field of computational mechanics and materials science. Further details in the attachment.

Massimiliano Gei's picture

4th International Symposium on Defect and Material Mechanics (ISDMM09), TRENTO, July 6th-9th, 2009

The Solid Mechanics group of the University of Trento (Italy) announces ISDMM09, the fourth international meeting devoted to Mechanics of Material Forces, following the workshops held at Kaiserslautern (2003), Symi (2005) and Aussois (2007), and will be held in the alpine city of Trento, Italy, from July 6th to 9th, 2009.

Abstract submission: January 31, 2009

More info: http://portale.unitn.it/events/isdmm09

Postdoctoral position in Computational Solid Mechanics - School Of Mechanical Engineering Purdue University

A postdoctoral position is available starting Fall 2008 in the area of computational solid mechanics. A successful candidate is expected to have a strong background in multiscale modeling and programming experience. While experience in plasticity using finite element methods or dislocation dynamics is a plus , all outstanding candidates will be considered.

Applicants must provide a detailed resume and  at least three references to: Prof. Marisol Koslowski, marisol@purdue.edu.

Postdoctoral position in Multiscale Modeling

The Computational Solid Mechanics group under the direction of Prof. Marisol Koslowski in the School of Mechanical Engineering at Purdue has an opening for a postdoctoral position in the area of multiscale modeling as part of the project “Plasticity in ultrafine grained materials” funded by DOE. A successful candidate is expected to have a strong background in computational solid mechanics and programming experience. While experience in plasticity using dislocation dynamics or phase field methods is a plus, all outstanding candidates will be considered.

Julia R. Greer's picture

Effective Use of Focused Ion Beam (FIB) in Investigating Fundamental Mechanical Properties of Metals at the Sub-Micron Scale

I would like to share some of our more recent findings on nano-pillar compression, namely the role of the surface treatment in plastic deformation at the nano-scale. Recent advances in the 2-beam focused ion beams technology (FIB) have enabled researchers to not only perform high-precision nanolithography and micro-machining, but also to apply these novel fabrication techniques to investigating a broad range of materials' properties at the sub-micron and nano-scales. In our work, the FIB is utilized in manufacturing of sub-micron cylinders, or nano-pillars, as well as of TEM cross-sections to directly investigate plasticity of metals at these small length scales. Single crystal nano-pillars, ranging in diameter between 300 nm and 870 nm, were fabricated in the FIB from epitaxial gold films on MgO substrates and subsequently compressed using a Nanoindenter fitted with a custom-fabricated diamond flat punch. We show convincingly that flow stresses strongly depend on the sample size, as some of our smaller specimens were found to plastically deform in uniaxial compression at stresses as high as 600 MPa, a value ~25 times higher than for bulk gold. We believe that these high strengths are hardened by dislocation starvation. In this mechanism, once the sample is small enough, the mobile dislocations have a higher probability of annihilating at a nearby free surface than of multiplying and being pinned by other dislocations. Contrary to this, if the dislocations are trapped inside the specimen by a coating, the strengthening mechanism is expected to be different. Here we present for the first time the comparison of plastic deformation of passivated and unpassivated single crystal specimens at the sub-micron scale. The role of free surfaces is investigated by comparing stress results of both as-FIB'd, annealed, and alumina-passivated pillars. Preliminary results show that ALD-coated pillars exhibit much higher flow stresses at equivalent sizes and strains compared with the uncoated samples. We also found that while FIB damage during pillar fabrication might account for a small portion of the strength increase, it is not the major contributor.

Robert Gracie's picture

A new finite element method for dislocations based on interior discontinuities

Comments and feedback of the following paper would be appreciated.

Abstract:

A new technique for the modelling of multiple dislocations based on introducing interior discontinuities is presented. In contrast to existing methods, the superposition of infinite domain solutions is avoided; interior discontinuities are specified on the dislocation slip surfaces and the resulting boundary value problem is solved by a finite element method. The accuracy of the proposed method is verified and its efficiency for multi-dislocation problems is illustrated. Bounded core energies are incorporated into the method through regularization of the discontinuities at their edges. Though the method is applied to edge dislocations here, its extension to other types of dislocations is straightforward.

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