THE EFFECTS OF OVERLOADS ON SUSTAINED-LOAD CRACK-GROWTH IN A NICKEL-BASE SUPERALLOY .1. ANALYSIS

Analytical procedures are presented for predicting the retardation effects of cyclic overloads on the sustained load crack growth rate in Inconel 718 at 649-degrees-C. The Wheeler model is used in a crack growth computer program, CRACKS, by representing sustained load by equivalent fatigue cycles per 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.