Three-dimensional effects on fatigue crack closure in the small-scale yielding regime - a finite element study

Plasticity induced closure often strongly influences the behaviour of fatigue cracks at engineering scales in metallic materials. Current predictive models generally adopt the effective stress-intensity factor (DeltaK(eff) = K-max-K-op) in a Paris law type relationship to quantify crack growth rates. This work describes a 3D finite element study of mode I fatigue crack growth in the small-scale yielding (SSY) regime under a constant amplitude cyclic loading with zero T -stress and a ratio K-min/K-max = 0. The material behaviour follows a purely kinematic hardening constitutive model with constant hardening modulus. Dimensional analysis suggests, and the computational results confirm, that the normalized remote opening load value, K-op/K-max, at each location along the crack front remains unchanged when the peak load (K-max), thickness (B) and material flow stress (sigma (0)) all vary to maintain a fixed value of . Through parametric computations at various K levels, the results illustrate the effects of normalized peak loads on the through-thickness opening-closing behaviour and the effects of sigma(0)/E, where E denotes material elastic modulus. The examination of deformation fields along the fatigue crack front provides additional insight into the 3D closure process.