The crack nucleation in hierarchically nanotwinned metals

The nanocrystalline (NC) metals with hierarchical twin lamellae exhibit excellent mechanical properties. However, recent efforts are mainly focused on the effects of primary twin boundaries (TB) and grain boundaries (GB) on crack nucleation. Few investigations have been performed on secondary twin boundary (STB) effect on crack nucleation in hierarchically nanotwinned metal. A relevant model is established to describe the crack nucleation criteria quantitatively. Actually, the crack advance mainly depends on the energy of crack nucleation and the energy of pile-up dislocations. Furthermore, predictions about the site of crack nucleation are made for different hierarchically nanotwinned metals. This work will help us better understand the deformation mechanism and the failure behavior in NC materials with hierarchically nanostructures.