(Mühendislik) Strain hardening, or work hardening, is an increase in the strength of a material due to plastic deformation. In metallic solids permanent change of shape is usually carried out on a microscopic scale by defects called dislocations which are created by stress and rearrange the material by moving through it. At normal temperatures these defects do not anneal out of the material but build up as the material is worked, interfering with one another's motion and thus increasing strength and decreasing ductility