Effect of cooperative grain boundary sliding and migration on emission of dislocations from a crack tip in nanocrystalline materials

Interaction of the cooperative grain boundary sliding and migration with a crack in deformed nanocrystalline materials is investigated using the complex variable method. Effects of the two disclination dipoles produced by the cooperative deformation on the emission of lattice dislocations from the crack tip are theoretically described. The complex form expressions of the stress field and the force field are derived. The critical stress intensity factors for the first dislocation emission are calculated. Influences of disclination strength, grain size, locations of the two disclination dipoles as well as crack length on the critical stress intensity factors are discussed in detail. Results show that, the cooperative deformation has great influence on dislocation emission from the crack tip. In general, the cooperative deformation can promote the lattice dislocation emission from the crack tip, thus improve the toughness of the nanocrystalline materials.

► Effect of cooperative GB sliding and migration on dislocation emission is studied.
► The critical SIF for dislocation emission from crack tip in NC material is divided.
► The cooperative deformation can promote the dislocation emission from crack tip.
► There is a critical grain size making the dislocation emit without any loadings.
► The shorter crack can be easily blunted, and the longer crack tends to grow.