Effects of Specimen Diameters on the Distribution of Corrosion Fatigue Cracks

The distribution of corrosion fatigue cracks observed on the un-notched round specimen surface differs with specimen diameter, especially in the low stress amplitude region. At a constant fatigue life ratio, many long cracks are initiated on the larger specimen, 12 mm (diameter), in comparison with the smaller specimen, 6 mm (diameter). On the other hand, in the high stress amplitude region of corrosion fatigue and fatigue in laboratory air, the distribution of cracks during the fatigue process does not depend on specimen diameters. In the low stress amplitude region of corrosion fatigue, crack growth rate does not show the usual behavior of the dependence of crack length, but shows only the dependence of stress amplitude. This unusual crack growth behavior explains why the distribution of corrosion fatigue cracks in the low stress amplitude region changes with specimen diameters.