Fatigue crack growth modelling considering a damage regularization approach

A non-local Gurson–Tvergaard–Needleman (GTN) model coupled with cyclic plasticity and a node release scheme is proposed to simulate fatigue crack growth (FCG). Crack propagation is driven by the accumulation of cyclic plastic strain, while microvoid evolution modifies the local plastic response through progressive material degradation. To prevent the numerical instabilities associated with strain localization and softening, an integral non-local regularization approach was applied to the GTN damage model. The proposed framework provides FCG rate predictions in good agreement with experimental results in the upper part of the Paris regime and substantially reduces mesh sensitivity for medium and high ΔK levels. Near threshold conditions, very fine meshes are still required to resolve the steep stress and strain gradients ahead of the crack tip. The results further show that the appropriate non-local characteristic length is closely related to the reverse plastic zone size, providing a physically based interpretation of the regularization length and supporting the hypothesis that the reverse plastic zone defines the fatigue process zone.