A theoretical analysis of dislocation emission from an elliptical blunt crack tip in nanocrystalline solid

•There is an optimal position of nanotwin to make the dislocations most susceptible to emit from crack tips.•There is a critical inclination of nanotwin oriental making dislocations hardest to launch.•The increase of crack length and grain size will make the dislocation emission of crack tip difficult.•The dislocation pileup makes the dislocation emission from crack tips difficult. A theoretical model describing edge dislocation emission from an elliptical blunt crack tip in nanocrystalline solid is established to consider the effect of the nanotwin and dislocation pileup at twin boundary. The nanotwin is represented by a wedge disclination quadrupole and some dislocations are deposited on one of twin boundaries. The complex variable function method is used to calculate the force acting on the first dislocation emitted from the tip of blunt crack, and expressions of critical stress intensity factors corresponding to dislocation emission are obtained. Then the influence of the dislocation emission angle, the position and orientation of the twin, the strength of nanotwin, the shape and the surface effects of the elliptical blunt crack on the critical stress intensity factor for dislocation emission is analyze in detail. The results shows that the effect of nanotwin on dislocations emitting from crack tip depends on its position and azimuth. There is an optimal position that dislocations are most easily emitted from the crack tip. The dislocation pileup at the twin boundary will increase the critical stress intensity factors for dislocation emission, making the dislocation emission from crack tip difficult, thus reducing the toughness of the material contributed by dislocation emission. In addition, the surface stress has a significant effect on the critical stress intensity factor.