Fatigue Strength of Spheroidal Graphite Cast Iron in Cylindrical Notched Bar

In this paper, rotating bending fatigue tests were carried out to investigate the fatigue strength of plain and notched specimens of spheroidal graphite cast iron. The fatigue limit of the plain specimen depends on the propagating limit of micro cracks which are nucleated from the graphite or the nodule. The maximum length of the micro non-propagating cracks is nearly equal to 200 µm. Therefore, the fatigue strength σ_{w 1} of the notched specimen is insensitive to the notch root radius. The fatigue strength σ_{w 2} increases as the notch root radius decreases, because the micro non-propagating crack is filled with graphite and oxide. Moreover, it is found that the fatigue strength of an arbitrary notched specimen can be estimated on the basis of the linear notch mechanics.