A damage model for fatigue crack propagation from moderate to high ΔK levels

Different approaches have been developed to address the difficult issue of crack propagation simulation under monotonic loading. However, numerical models that can also account for crack growth under cyclic loading are much less numerous. The aim of the paper is to develop a numerical model to predict the behaviour of cracked panels under monotonic as well as under cyclic loading. In particular, the model has to simulate fatigue crack propagation at high ?K levels for a wide variety of metallic alloys including aluminium alloys, titanium alloys and steels. An advanced fatigue model, developed in the framework of Continuum damage mechanics (CDM), is discussed in this paper. The CDM approach, initially proposed by Lemaitre, considers the effects associated to a given damage configuration through the definition of a thermodynamic state variable. This proper thermodynamic framework provides numerical robustness. This study examines the possibility to use such models to simulate fatigue crack propagation. The analysis of fracture modes and of ?K curves at different load ratios suggests that two damage mechanisms are involved in fatigue crack propagation. To improve the damage description of the Lemaitre model, two distinct damage variables are introduced. The evolution of the first one, called static damage, follows the classical Lemaitre formulation. The second one, cyclic damage is related to cyclic cumulated plastic strain.