Predicting stress corrosion crack growth rates when linear elastic fracture mechanics conditions are not operative

Abstract

The growth rate of a stress corrosion crack in situations where linear elastic fracture mechanics (LEFM) conditions are not operative is predicted on the basis that the crack tip opening angle (CTOA) is related to the growth rate dc/dt, the functional relation between the CTOA and dc/dt being obtained by coupling theoretical results for crack growth under small-scale yielding conditions in an inert environment, with the experimentally determined power law relation between the crack tip stress intensity K and dc/dt for environmentally-assisted crack growth under LEFM conditions. Then, by assuming that the same CTOA-dc/dt relation applies to non-LEFM conditions, and by determining the CTOA under these conditions, it is in principle possible to predict the stress corrosion crack growth rate under non-LEFM conditions. A specific model: the plane strain deformation of a solid with two symmetrically situated deep cracks, and with tension of the small remaining ligament, is analyzed in detail, and the effects of the extent of plastic deformation and loading pattern (i.e., displacement or load control), on the predicted stress corrosion crack growth rate, are examined in detail. The results are compared with those obtained via application of the K versus dc/dt relation, its conversion to a J versus dc/dt correlation and then the determination of J, and also with those obtained on the assumption that a K approach is derectly applicable. The extent to which these latter approaches give conservative or non-conservative growth rate predictions when compared with the present paper's predictions, is discussed in relation to the extent of plastic deformation and loading pattern.