A study was made of the effect of film stiffness and thickness upon the stress field of a film-covered mode-III crack, and dislocation emission from the interface between the film and the substrate was analyzed. The results showed that the image force and the interaction force between 2 dislocations that formed a dipole with a core size of 2b were functions of the film stiffness, but depended weakly upon the film thickness when the latter was greater than 20b. Emission of the dislocation dipole from the interface became more difficult when the film was harder than the substrate, and the thickness was great. Dislocation emission from the crack tip occurred before dislocation dipole emission from the interface. When the film was softer than the substrate, both the critical applied stress intensity factor for dislocation emission from the crack tip, and the critical applied stress intensity for dislocation dipole emission from the interface, were larger than that for dislocation emission from a crack tip without any film.

T.Y.Zhang, C.F.Qian: Mechanics of Materials, 1996, 24[2], 159-73