A fully plastic microcracking model for transgranular stress-corrosion cracking in planar-slip materials

Abstract

It has been confirmed that transgranular stress-corrosion cracking (T-SCC) can be discontinuous under slow strain-rate testing, at least for materials which deform by planar slip(i.e., those which have low stacking-fault energy). Interpretation of the load and current transients shows that the crack velocity is on the order of 100 μm/s, depending on the environment — too slow to be explained by a running brittle crack and too fast to be explained by Faradaic dissolution. Support of such an interpretation is given by the agreement between predictions of crack area by mechanical analysis of the load transients (taking into account the elastic displacement of the load train and of the specimen because of both the changing load and the crack advance) and the predictions from analysis of the current transients, as well as the agreement of such predictions with the resulting crack-advance distance determined from fractography. Such agreement follows if the assumption is made that cracking is fully plastic, that is, if deformation accompanies cracking such that the nominal stress on the uncracked cross section is maintained at the flow stress. The significance of this finding with respect to a corrosion-assisted microcleavage model is discussed.