Fatigue limit of nodular cast iron containing casting defects

In the present study, the high cycle fatigue behaviour of a nodular cast iron has been investigated. The influence of casting defects has been analysed by considering two different types of defects : surface and internal microshrinkages. It has been shown that the fatigue limit is strongly dependent on defect size and position. Long fatigue crack propagation thresholds, experimentally determined in air and in high vacuum, were used to evaluate the fatigue limit associated with surface or internal defects considered as pre-existent cracks. This approach appears to be not relevant even for large defects. This tends to support that casting defects cannot be identified as cracks and that the initiation period cannot be neglected.