Nodule influence on fatigue crack growth thresholds in nodular cast iron

The influence of microstructure i.e. nodules (voids) on the fatigue thresho ld value in nodular cast iron is numerically investigated. It is qualitativ ely shown that the fatigue threshold value is unaffected by the individual nodules and that the threshold value is proportional to the bulk Young's mo dulus. Furthermore it is shown that nodules (voids) do not influence the cr ack tip conditions (stress-intensity factor and crack tip opening displacem ent) if the voids do not lie very close to the tip for physically long crac ks. It is concluded that linear elastic fracture mechanics is valid for the se types of materials and no influence of the nodules need be taken into co unt for fatigue calculations when dealing with long cracks.