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

The current status o f the problem of small cracks in fatigue is presented. Several classes o f small cracks are distinguished, and their individual characteristics described. Specifically, for cracks small compared with microstructural size scales, for cracks small compared with the ex tent o f 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 o f differences in behavior between large and small cracks, on the question o f the "driving force" for small crack advance and on the possible existence o f intrinsic thresholds for crack growth. Finally, some thoughts are offered on the use o f smallcrack methodology in life prediction analyses and in alloy design.