Finite element analysis of fatigue crack growth with interspersed mode I and mixed mode overloads

The fatigue crack growth in components or structures is influenced by the service loading. In contrast to a uniform fatigue crack growth during a constant amplitude loading, an overload for instance, which is interspersed into this constant amplitude loading, leads to a retardation effect. Within the scope of this paper fatigue crack growth under variable amplitude loading in a real structure is modelled using an elastic-plastic finite element analysis. It can be shown that due to an overload depending on the overload ratio Rol and the mode I/mode II ratio plastic deformations occur, which on the one hand reduce the near-tip closure and cause a far-field closure. On the other hand, the plastic deformations change the stress distribution along the crack flanks as well as along the ligament. A comparison of the numerically determined fatigue crack growth rates with the experimental data shows a good agreement.