Abstract
Small fatigue cracks may propagate at higher rates than expected values based on long crack data and linear-elastic fracture mechanics, and even at lower stress intensity factor ranges than the thresholds of long cracks. Since it was reported that crack size effects were more remarkable in corrosion fatigue (CF) than mechanical fatigue, the small-crack growth mechanism has been one of the most attractive subject for CF researchers. Small CF cracks are classified into some categories according to their size scales and growth stages as well as mechanical fatigue cracks, and further into chemically small cracks of which the range is wider than the others. A number of mechanism models of small-CF-crack growth have been proposed and are classified into several groups in this paper as follows; hydrogen embrittlement models, anodic dissolution models, film rupture/slip dissolution models, chemisorption/softening models, crack closure restraint models, and distribution/coalescence models. The researches on small CF cracks, which are still in progress, are expected to contribute to the clarification of fracture mechanism of metallic materials, the development of sophisticated methods of life prediction, and so on.
