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Influence of grain boundary sliding and grain size on dislocation emission from a crack tip

This article establishes a theoretical model to study the effect of grain boundary sliding deformation on the dislocation emission from the crack tip in nanocrystalline solids. Within our description, stress concentration near the crack initiates grain boundary sliding which results in the formation the dipole of disclinations at triple junctions of grain boundaries. The grain size-dependent criterion for the dislocation emission from a semi-infinite crack tip is derived. The influence of the grain size and the features of dipole of disclinations on the critical stress intensity factors for dislocation emission is evaluated. It is shown that grain boundary sliding deformation enhances the critical stress intensity factor for dislocation emission. The critical stress intensity factor will increase with the decrement of the grain size, which indicates that the emission of the dislocation becomes more difficult for smaller size of grain due to the effect of grain boundary sliding deformation.