Constraint corrected cycle-by-cycle analysis of crack growth retardation under variable amplitude fatigue loading

Abstract

Various models exist to predict load interaction effects on fatigue crack growth in variable amplitude loading conditions. Stress overloads have the potential to strongly retard or even arrest a propagating fatigue crack. Whereas global analysis methods (making use of equivalent quantities) allow to describe stochastic loading scenarios, describing the effects of deterministic overloads requires cycle-by-cycle analysis techniques. Within this category, plastic zone models have proven to be effective and pragmatic in terms of calibration. Current models, however, do not account for the effect of crack tip constraint on the plastic zone size, whose estimation is a requirement. This paper develops a novel (“extended”) crack growth formulation based on the traditional plastic zone based Wheeler’s model, taking into account the effect of out-of-plane constraint (plane stress versus plane strain). Calibration of the model requires characterization of shut-off overload ratios for different stress intensity factor levels. The “extended Wheeler” model gives better agreement with experimental tests results than the original and modified Wheeler model.