A dislocation–density grain boundary interaction scheme, a grain boundary misorientation-dependent dislocation–density relationship and a grain boundary sliding model were used to account for the behaviour of nanocrystalline aggregates with grain sizes ranging from 25 to 200nm. The schemes were coupled to a dislocation-density multiple-slip crystalline plasticity formulation and specialized finite-element algorithms were used to predict the response of nanocrystalline aggregates. The schemes were based upon slip-system compatibility, local resolved shear stresses and immobile and mobile dislocation–density evolution. A conservation law for dislocation-densities was used to balance dislocation–density absorption, transmission and emission from the grain boundary. The relationship between yield stress and grain size was consistent with the Hall-Petch relationship. The results also indicated that grain-boundary sliding and grain-size effects affected crack behaviour via local dislocation-density and slip evolution at critical grain boundaries. Moreover, the predictions indicated that grain-boundary sliding increased with decreasing grain size, and resulted in lower normal stresses in critical locations. Thus, grain-boundary sliding could off-set the strength increases associated with decreases in grain size.

Grain Size, Grain Boundary Sliding and Grain Boundary Interaction Effects on Nanocrystalline Behavior. J.Shi, M.A.Zikry: Materials Science and Engineering A, 2009, 520[1-2], 121-33