Dislocation Pile-Ups
Dislocations frequently pile u on slip planes at barriers such as grain boundaries, second phases, or sessile dislocations.
The leading dislocation in the pile-up is acted on not only by the applied shear stress but also by the interaction force with the other dislocations in the pile-up.
This leads to high concentration of stress in the pile-up, the stress on the dislocation at the head of a pile-up can approach the theoretical shear stress of the crystal.