Toughening of nanocrystalline materials through shear-coupled migration of grain boundaries

 A theoretical model has been proposed to illustrate the effect of shear-coupled migration of grain boundaries on crack growth in deformed nanocrystalline materials. The shear-coupled migration process is initiated by the stress concentration near the tip of a mode I crack. The results obtained show that the coupled shear plays a key role in enhancing the fracture toughness of nanocrystalline materials, and the shear-coupled migration process can serve as an effective toughening mechanism in nanocrystalline materials.