Notch size effects in the fatigue limit of steel

The fatigue behaviour of grooved test specimens has been investigated in this paper. It is shown that there are two kinds of size effects connected to notches: statistical size effect and geometric size effect. The statistical size effect is calculated based on the distribution of the maximum depth of initiated cracks in specimens with varying stress area. The geometric size effect depends on the stress gradient and can be estimated with the help of the linear elastic fracture mechanics. It is concluded that the notch size effect in blunt notches can be explained with those two factors. When the notch gets sharper, after certain limit the magnitude of the plastic portion of the strain starts to play an important role in the fatigue crack initiation, and the fatigue limit is lower than that predicted by statistical and geometric size effects. Another estimation method shall be used to that kind of notches.