Effect of nanotwin near a branched crack tip on crack blunting in deformed nanocrystalline materials

A theoretical model is established that mainly addresses the influence of nanotwin near the tip of branched crack on crack blunting in deformed nanocrystalline materials. Using the complex variable method of Muskhelishvili and conformal mapping technique, the solutions of complex potentials are derived in closed forms. The critical stress intensity factors for the emission of first lattice edge dislocation from the branched crack tip are obtained. The effects of typical parameters such as the relative length between the main crack and the branched crack, the angle between their planes as well as the relative thickness of the nanotwin band on the dislocation emission from the branched crack tip are evaluated in detail. The results indicate that the shorter branched crack is more easily induced to blunting through dislocation emission from its tip, while the longer main crack tends to propagate. The main crack shows a shielding effect to the tip of branched crack for the dislocation emission. Furthermore, the larger the relative thickness of the nanotwin band is, the easier is the dislocation emitted from the branched crack tip.