3 Edge dislocation

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This edge dislocation was made by displacing the atoms to the right of the dislocation line one lattice constant to the left, thereby giving locally an extra row of atoms (an extra plane of atoms thinking of the half-crystal extending up towards us out of the plane of the screen). When you first click run the atoms in the vicinity of the dislocation relax to their new equilibrium positions.

How much shear stress is required to move the dislocation? How does it compare with the stress required to shear the perfect crystal? Note that the crystal overall is being sheared as the dislocation moves, at least until it leaves the crystal.

Add your own dislocation by pressing the RIGHT mouse button and dragging horizontally somewhere in the array. You will have displaced part of the blue crystal by one lattice constant in the x-direction with respect to the rest of the blue crystal. (See Special features for more detail.)

alpha is the compressive force constant between atoms in the same row. With the program running grab its slider handle and watch the width of the dislocation as alpha is varied from 2 to 20.(You can drag the slider beyond the end of its range!) Can you explain this variation qualitatively? How does the shear force required to drive the dislocation through the crystal depend upon the width of the dislocation? Why?