GATE MT 2020 Q26. In the edge dislocation configuration given in the figure, dislocations X and Y are fixed and separated by a distance 2h on the same slip plane. Dislocation Z is free to glide on a parallel slip plane. The two slip planes are separated by a distance h. Which one of the following statements is TRUE regarding the stability of dislocation Z at positions 1, 2 and 3? Assume all dislocations have identical Burgers vector.

Correct answer is option B.

•  When two dislocations of same kind on parallel slip plane( when they are one over other, like position 2) stable equilibrium exists.
• Any dislocation near stress field of dislocation should not be present.
• Position 1 – dislocation at position 1 is repelled by dislocation on bottom plane at position X and Y. It can neither go left nor right. Thus, it is unstable.
• Position 2 – tensile field of dislocation at position 2 is cancelled by compressive field of dislocation at position Y. But it is being repelled by dislocation at position X.
• Position 3 – dislocation at position 3 is repelled by both dislocation at X and Y.