PPT Slide
This high stress either can initiate yielding ond the other side of the barrier, or in other instances, it can nucleate a crack at the barrier.
Dislocations piled up against a barrier produce a back stress acting to oppose the motion of additional dislocations along the slip plane in the slip direction.
The dislocations in the pile-up will be tightly packed together near the head of the array and more widely spaced toward the source (Fig. 5-27).