ABSTRACT
Heterostructured materials have been reported as a new class of materials with superior mechanical properties, which has been attributed to the development of back stress. Back stress is developed in soft zones to offset the applied stress, making them appear stronger, while forward stress makes hard zones appear weaker. Several dislocation models on the formation of back stress have been proposed. The back stress is produced by geometrically necessary dislocations, which is in turn believed needed to accommodate strain gradient in the gradient plasticity theory. Back stress has been considered playing a critical role in the strengthening of metal matrix composites. It is also often associated with the Buaschinger effect. However, neither back stress nor Bauschigner effect has been accepted as a major player in strengthening metallic materials by the general materials community. Recently, it has been observed that local shear bands occurred across, and hetero-boundary-affected region was formed near the HS zone boundary.
