Crack tip mechanisms: a numerical analysis

Fatigue crack propagation is usually studied using da/dN-∆K curves obtained experimentally. However, the use of ∆K does not provide any information into the mechanics which occur at the crack tip and are effectively responsible for fatigue crack growth. The objective here is to study crack tip phenomena using the CTOD. The aspects studied are the crack closure level, the elastic regime of ∆K and the crack tip plastic deformation, which was related with fatigue crack propagation. The elastic load range, ∆Kel, was found to increase linearly with material’s yield stress. Well defined relations were found between the elastic and the plastic deformations, which greatly depend on material. The fatigue crack growth rate, obtained experimentally, was plotted versus plastic CTOD range, δp, for the different materials. Finally, the CTOD versus load curves were used to predict fatigue threshold and to study material hardening after crack propagation.