Interfaces and grain-boundaries in crystals usually act as strong barriers to dislocation glide. The dislocation lines accumulated against such barriers are at the origin of a long range internal stress field that contribute to strain hardening during plastic deformation. This feature is illustrated bellow with two examples: 1-accumulation of dislocations line in a capped layer and 2-accumulation of Orowan dislocation loops around hard particles in a soft matrix.
Examples of kimatic strain hardening process