Distinguish between sessile dislocation and glissile dislocation?

Answer 1

A sessiledislocation has a Burger's Vector that does not lie in the primary slip plane of the crystal, so it is immobile offering an obstacle to the movement of other dislocations.

A glissile dislocation has Burger's Vector that does not lie in the primary slip plane of the crystal and thus is able to move in that plane.

Dislocation that can move by pure slip are called Glissle.Dislocation which cannot glide, but have to move by some form of mass transport are called sessile.

In crystals, the dislocation core spreads to certain crystallographic planes containing the dislocation line. If the core spreads into one of such planes, the core is planer and is glissile.If the core spreads into several non-parallel planes of the zone of dislocation line, it is non-planar and sessile. In the former case dislocation moves easily in the plane of the core spreading, while in the later case, it moves only with difficulty. Shockley partial is a partial dislocation, the Burger vector of which lies in the plane of the fault. Then, Shockley partials are glissile. A Frank partial is a partial dislocation, the Burgers vector of which is not parallel to the fault. Then, Frank partials are sessile.