Strong Crack Blunting by Hierarchical Nanotwins in Ultrafine/Nano-grained Metals

A theoretical model is proposed to illustrate the effect of detwinning of the secondary twin lamellae on the emission of lattice dislocations from a semi-infinite crack tip in a hierarchically nanotwinned metal. The results obtained show that the potential of the crack tip to emit dislocations can be optimized and greatly enhanced by tuning the secondary twin spacing, which leads to strong crack blunting. Moreover, the hierarchical structure is able to produce significant toughening at very thin secondary twin lamellae, as observed in molecular dynamics simulations. As a result, the proposed model suggests a novel toughening mechanism in ultrafine/nano-grained metals.