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 tractor (ΔK 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 (σ 0 ) all vary to maintain a fixed value of K = K max/σ0 √B. 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 σ 0 /E, where E denotes material elastic modulus. The examination of defamation fields along the fatigue crack front provides additional insight into the 3D closure process.