Emission of an edge dislocation from a thin-film-covered crack

The emission of an edge dislocation from a thin-film-covered crack is studied in order to investigate the effects of a passive film on stress-corrosion cracking. The results show that the crack stress field in the film due to the applied loads is enhanced by a harder film or abated by a softer film. For an edge dislocation in the film, both the slip component of the image force and the shielding effect are stronger when the film is harder. Under pure mode II or III loadings a harder thin film makes the dislocation emission easier and a softer film makes the dislocation emission more difficult if the film thickness is smaller than a critical value. The opposite is also true if the film thickness is larger than the critical value. Under pure mode I loadings, however, a harder thin film makes the dislocation emission more difficult and a softer film makes the dislocation emission easier for the two film thicknesses used in this study.