The effects of the constitutive behaviour of alloys on their resistance to fatigue crack growth under variable amplitude loading

A common feature of most real cyclic load spec h-a is the presence of overloads, and of sporadic or repeated compressive loading, which strongly affect the fatigue life of the structure [1,2]. These effects are generally attributed to the plasticity-induced crack closure phenomenon [3]. As this phenomenon involves cyclic plasticity at the crack tip it should be strongly affected by the cyclic plastic behaviour of the material, namely its cyclic hardening or softening and its Bauschinger effect [4]. Finite element analyses [5] of plasticity-induced crack closure have therefore been conducted in order to understand the interactions between material hardening and crack closure. The computations have been performed by using the Chaboche [6] plastic constitutive behaviour, and the code Abaqus. The cyclic plastic behaviour of the material is found to affect strongly the crack behaviour after an overload or an underload. The experimental data obtained on a 0.4 % Carbon mild steel confirm the numerical results.