On the finite element analysis of fatigue crack closure-2. Numerical results

The opening and closing behavior of fatigue cracks is studied with an elastic-plastic finite element model which has been described and evaluated in Part I. Special attention is given to the effects of maximum stress, strain hardening and yield stress. Normalized crack opening stresses decrease with increasing maximum stress and this dependency is stronger for lower stress ratios and lower hardening moduli. Results are interpreted in terms of an interaction between residual deformations and crack opening displacements. The ratio of yield stress to elastic modulus has little effect on crack opening behavior. Data for forward and reversed plastic zone sizes and shapes are presented, demonstrating some dependence on closure. The effects of different constitutive models are investigated, including the influence of mean stress relaxation. Crack closing levels are shown to be lower than crack opening levels, especially at lower stress ratios and higher maximum stresses. Biaxial stresses may also influence the closure behavior of mode I cracks, especially at higher maximum stresses. Opening levels are generally higher for equibiaxial loading and lower for pure shear loading.