A FULLY PLASTIC MICROCRACKING MODEL FOR TRANSGRANULAR STRESS-CORROSION CRACKING IN PLANAR-SLIP MATERIALS

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 sta cking-fault energy). Interpretation of the load and current transients shows that the crack velocity is on the order of 100 mum/s, depending on the environment-too slow to be explained by a running brittle crac k and too fast to be explained by Faradaic dissolution. Support of suc h an interpretation is given by the agreement between predictions of c rack area by mechanical analysis of the load transients (taking into a ccount the elastic displacement of the load train and of the specimen because of both the changing load and the crack advance) and the predi ctions from analysis of the current transients, as well as the agreeme nt of such predictions with the resulting crack-advance distance deter mined from fractography. Such agreement follows if the assumption is m ade that cracking is fully plastic, that is, if deformation accompanie s cracking such that the nominal stress on the uncracked cross section is maintained at the flow stress. The significance of this finding wi th respect to a corrosion-assisted micro-cleavage model is discussed.