Crack Initiation Model for Stress Corrosion Cracking in alpha -Brass

摘要

A crack-tip opening displacement model which takes into account the development of corrosion pits and the initiation of microcracks as a function of applied stress and electropotential has been formulated for alpha -brass in non-tarnishing ammoniacal solution. In this model, designed for K less than or equal to Ksub ISCC/, it is assumed that corrosion pits form and grow during the early stages of stress corrosion cracking. Once a critical corrosion pit depth is achieved, the strain energy release rate is large enough to initiate a microcrack. The predictions of this model in terms of the time to microcrack initiation (incubation time) are found to be in good agreement with all the experimental results obtained so far. Metallographic observations and scanning electron microscopy provided additional information on the transition from pitting to microcrack initiation. It was found that the critical pit dimensions for microcrack initiation are 5 to 10 mu m deep (depending on stress). The calculated K/sub ISCC/ is consistent with that for macrocrack propagation. (ERA citation 09:031196)