Interaction of a thin-film-covered mode III crack with screw dislocations: Emission of a screw dislocation dipole from the interface

The effects of film stiffness and thickness on the stress field of a film-covered mode III crack and the dislocation dipole emission from the interface between the film and the substrate have been studied. The results show that the image force and interaction force between the two dislocations that form a dipole with a core size of 2 b are functions of the film stiffness, but weakly depend on the film thickness when the thickness is larger than 20 b. The emission of the dislocation dipole from the interface becomes more difficult if the film is harder than the substrate and its thickness is large and vice versa. Dislocation emission from the crack tip occurs prior to dislocation dipole emission from the interface. When the film is softer than the substrate, both the critical applied stress intensity factor for dislocation emission from the crack tip and the critical applied stress intensity factor for dislocation dipole emission from the interface are larger than that for dislocation emission from a crack tip without any film.