Grain sizes effect on crack blunting considering nano-grain rotation and dislocation-GB interactions

The grain sizes effect on crack blunting in nanocrystalline (NC) materials is extracted theoretically in this paper. Within our description, a part of dislocations emitted from crack tip can penetrate through grain boundaries (GB) and nano-grain rotation (NGR) is considered simultaneously. The calculated effective stress intensity factors indicate that crack growth is suppressed, which is highly sensitive to the grain sizes. Our results provide a reasonable explanation for the experimental phenomena that micro-cracks tend to form and grow in nanocrystalline matrix in bimodal Al. In addition, GB misorientation effect on the crack blunting is investigated in detail. It is found that the decrease of GB misorientation is helpful to the crack blunting for more emissive dislocations. Meanwhile, NGR could induce strong crack blunting for small grain size. However, NGR exhibits a weak effect on crack blunting for large grain size.