Defects vs. Small Notches Competition in Fatigue Failure Initiation of Cast Steel

In the field of cast metals, fatigue strength assessment necessarily deals with the strength reduction caused by randomly distributed small-sized defects. When components are taken into account, stress raisers due to component geometry are possible crack initiation sites as well as defects. For the investigation of the overall performance, an appropriate model considering notch sensitivity of parent material and defect behavior shall be used. Unfortunately, several mechanical models of material sensitivity to notches and defects require the knowledge of the un-defected material strength, which is not obtainable in this case. In this contribution, experimental fatigue tests have been carried out on plane and notched specimens, considering small size notches as well. An appropriate analysis of the generated results allowed the evaluation of the material behavior and its notch sensitivity according to critical distances theories. The obtained results have been confirmed also direct inspection of broken samples.