Fatigue crack growth behavior of fine-grained steel S460N under proportional and non-proportional loading

In the present investigations a series of fatigue crack growth experiments has been conducted using thin-walled, hollow cylinders with a notch. The cylinders are made of fine-grained steel S460N. Cyclic tension–compression, torsion and proportional as well as non-proportional combinations of both loadings have been applied. For these experiments the crack-initiation locations and the crack growth lives as well as the crack growth curves and the crack paths have been identified. Depending on the loading type initiation of two to four cracks at different positions of the notch has been observed. The location of crack-initiation correlates well with the location of the maximum notch root stress amplitude calculated assuming elastic material behavior. The crack propagation lives vary depending on the type of loading. They are slightly longer under non-proportional loading than under proportional loading.