Effects of dislocation pile-up and nanocracks on the main crack propagation in crystalline metals under uniaxial tensile load

摘要

The interaction between the main crack propagation and micro-defects (i.e. dislocations, grain boundaries and nanocracks) under uniaxial tensile load is investigated theoretically. The mode of crack propagation is analyzed by considering the competition mechanism between the main crack propagation and crack initiation due to dislocation pile-up at a grain boundary. The results show the crack initiation at a grain boundary is easier than the main crack growth when the main crack is relatively small. For a relatively large main crack, the conclusion is reverse. The fracture toughness can be improved due to the dislocation emission from the main crack tip. Nanocrack initiation at grain boundaries and their triple junctions is often encountered, so the effect of a nanocrack on the main crack propagation is studied. The results show the nanocrack has a shielding effect on the main crack propagation when it is located in front of the main crack tip, while it has an enhancement effect on the main crack propagation when it is located behind the main crack tip. This work provides some new information of fracture mechanics, and these results are helpful for analyzing and explaining micro-mechanisms of fracture in crystalline metals.