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MeVArc Summary: Dislocations

Marc Fivel – 3D Discrete Dislocation Dynamics Simulations TEM video showing a Frank Read Source in action Persistent Slip Band formation – Model/Simulation/Experimental Evidence Aarne Pohjonen – Dislocation mechanisms on a near surface void Steve Fitzgerald – Dislocations

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MeVArc Summary: Dislocations

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  1. Marc Fivel – 3D Discrete Dislocation Dynamics Simulations TEM video showing a Frank Read Source in action Persistent Slip Band formation – Model/Simulation/Experimental Evidence AarnePohjonen – Dislocation mechanisms on a near surface void Steve Fitzgerald – Dislocations Model for protrusion formation under E field supported by simulations Details of the experimental evidence for the required voids May explain conditioning and BD resistance ranking by crystal structure MeVArc Summary: Dislocations { Nick Shipman - Wednesday, 03 August 2011

  2. 1. TEM video showing a Frank-Read source in action Taken using Transverse-Electron-Microscopy TRDIS simulation of Frank Read source “A Frank-Read Source is a mechanism explaining the generation of multiple dislocations in specific well spaced slip planes in crystals when they are deformed.” Wikipedia

  3. 2. Persistent Slip Band Formation • The diagrams on the right show a way in which slip bands can be formed by a dislocation moving sideways across and interacting with other dislocations. A schematic view of persistent slip bands and a composite TEM image in which the channels are clearly visible.

  4. 2. Persistent Slip Band Formation One frame from the new nodal 3D discrete dislocation simulation code Numodis which was used to simulate low strain fatigue in AISI 316L Steel. ~10um An SEM image courtesy of Markus Aicheler showing the damage due to pulse surface heating on copper.

  5. 3. Model for protrusion formation under externally applied E field The concept is as follows:- Protrusions can be created by prismatic loops which are drawn to the surface due to an externally applied E filed. But how are the prismatic loops formed? By the interaction of dislocations with near surface voids. Definitions Prismatic loop – platelet of extra atoms Void

  6. 3. Model for protrusion formation under externally applied E field

  7. 4. Details of experimental evidence of required voids 5. Things this theory can help explain • Possible reason for conditioning: voids are “used up” • Possible reason for rank by crystal structure: dislocations travel at different speeds in different structures • Steel has highest breakdown resistance: full of C which significantly impedes dislocation motion

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