Corrosion- and Creep- Induced Instability-Modeling of Fatigue-Cracking in Various Alloys

Crack propagation, the terminal phase in many mechanical-strength failures, is often deleteriously accelerated by environmental corrosion effects. Data to characterize such effects is costly to obtain, particularly if the thresholds of fatigue and corrosion sensitivities are to be defined. Accurate predictive models are needed to extend the available data base and thus its utility in corrosion engineering. The model attempt ascribes the crack growth to the necessity to maintain a state of tensile stability at the crack tip. Discretely sized crack-tip micro-ligamants are assumed to control they are strained by the loading of the crack when the loading ceases their stability is upset by creep stress relaxation and by surface corrosion it is resoted to equilibrium by an increment of extra straining which requires crack growth. Stress corrosion and fatigue crack propagation data on some 13 alloys has been culled from the literature and uniaxial and cyclic flow properties measured for each.