Nucleating, blunting or propagating of a nanocrack in dislocation free zones of thin crystals

<正> Nucleating, blunting or propagating of nanocracks in dislocation free zones (DFZs) of ductile and brittle metals have been studied through in situ tensile tests in TEM and analyzed using micro-fracture mechanics. The results show that in either ductile or brittle metals, many dislocations could be emitted from a loaded crack tip and a dislocation free zone formed after equilibrium. The stress in the DFZ might be up to the cohesive strength and then a nanocrack initiated in the DFZ or sometimes at the blunt crack tip. In ductile metals, a nanocrack would quickly blunt into a void or a notch during constant displacement. In brittle metals, a nanocrack would propagate into a cleavage crack rather than blunt.