Small Fatigue Cracks: A Statement of the Problem and Potential Solutions

The current status of the problem of small cracks in fatigue is presented. Several classes of small cracks are distinguished, and their individual characteristics described. Specifically, for cracks small compared with microstructural size scales, for cracks small compared with the extent of local plasticity or for cracks which are either chemically or physically small (e.g. about 1 mm or less), comments are made on the origins of differences in behavior between large and small cracks, on the question of the "driving force" for small crack advance and on the possible existence of intrinsic thresholds for crack growth. Finally, some thoughts are offered on the use of smallcrack methodology in life prediction analyses and in alloy design.