This ongoing research seeks to improve stress corrosion cracking (SCC) life prediction methodology by developing a fundamentally-based crack tip strain rate equation for use in SCC crack growth rate algorithms. The time-based mathematical derivative of a continuum mechanics equation for crack tip strain ahead of a nonstationary crack in a work hardening material is used to formulate a crack tip strain rate expression. The resulting expression allows determination of the effect of material properties and loading parameters, such as yield strength and stress intensity factor, on crack tip strain rate. Additionally, the effect of enhanced SCC observed in cold worked materials is addressed using crack tip
strain rate arguments. Limitations of the application of continuum mechanics equations to SCC phenomena are discussed. An experimental method is under development that will allow high-
resolution measurement of crack mouth opening displacement rate for a fracture mechanics specimen with a growing crack. Measurements will allow comparison of material, cold work, crack growth rate, and creep effects on crack mouth opening displacement rate, which is related to the crack tip strain rate, after subtracting out the geometric contributions from changes in crack length (measured using direct current potential drop). The challenge of quantifying strain rate local to a growing crack tip continues.