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15 "burgers" - dislocations and overlayers

"burgers" presents a model for dislocation motion in crystalline solids. It displays the two planes of atoms on either side of a slip plane. Single dislocations (of either sign) or two or more dislocations can be introduced oriented at any angle with respect to the Burgers vector. The screw and edge dislocations are limiting cases. A shear stress can be applied and the critical shear stress for failure of the perfect crystal, for dislocation motion, and for kink motion along a dislocation can be empirically determined. An impurity of variable pinning strength may be introduced and its pinning strength measured. A Frank-Read source is also illustrated.

"burgers" was programmed by Russ Thompson.

"burgers" represents dislocations in an unconventional manner, showing only the plane of atoms on the two sides of the dislocation glide plane. Think of the red atoms as below the glide plane, the blue atoms as above the glide plane. The figures show an edge dislocation on the left, a screw dislocation in the middle, and a full dislocation loop on the right.

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This 80K animation starts with an array of 4 dislocations, 2 edges at the right and left, and 2 screws at the top and bottom. The program runs for the first 7 frames with no applied stress. The array anneals to a loop and shrinks with time because of the line tension. Before the 8th frame, a stress is applied in the sense which drives the blue plane to the left. This exerts an "effective pressure" on the inside of the loop which overwhelms the effect of the line tension and the loop expands until it leaves the field of view. At what stress will the loop be in (unstable) equilibrium?


An edge dislocation is pinned by the yellow impurity atom. The figure shows the equilibrium configuration with an applied stress driving the dislocation to the left.


The four frames below show four stages in the generation of a dislocation loop by a Frank-Read source. With this size array the loop leaves the limited field of view before the next is generated. With a larger array the completed loop may be seen, but the simulation is slow!
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Table of contents for Chapter 15 of "Simulations for Solid State Physics"
  1. Introduction
  2. About the "burgers" model
  3. Perfect crystal
  4. Single dislocation
    1. Dislocation geometry
    2. Dislocation width and energy
  5. Critical shear stress with dislocations
  6. Impurity pinning
  7. Dislocation interactions
  8. Frank-Read source
  9. Summary
  10. Appendix: "burgers" -- the program
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