The effects of overloads on sustained-load crack growth in a nickel-base superalloy. I, Analysis

Analytical procedures for predicting the retardation effects of cyclic overloads on the sustained load crack growth rate in Inconel 718 at 649 deg C. The Wheeler model is used in a crack growth computer program, CRACKS, by representing sustained load by equivalent fatigue cycles/unit time and an equivalent stress ratio, R. A new model, the exponential overload (EXPOL) model, is developed based on the concept of a crack growing at a retarded rate through an overload plastic zone. The analytical procedures use a minimum of empirical constants and are capable of accurately representing the time-dependent sustained load crack growth behavior with single or multiple cyclic overloads.