Free surface effect and dislocation pile-up relaxation
As a result of image forces, dislocation are attracted by free surfaces. This feature is at the origin of size effects in samples of sub-micronic dimension. Illustration is made with the case of one spiral dislocation source in a polycrystal thin foil. During plastic deformation dislocation pile-ups are formed against the grain boundaries. At large stress dislocations accumulated in the pile-up can cross-slip, hence relaxing the pattern formed at the grain boundaries.
Free surface effect and dislocation pile-up relaxation