Fatigue Behavior of Long and Short Cracks in Wrought and Powder Aluminum Alloys.

The fatigue behavior of short cracks, which are small compared to the scale of the microstructure, small compared to the scale of local plasticity or simply physically small i.e., approximately 1 mm, must be considered as one of the major factors limiting the application of defect-tolerant fatigue design for airframe and engine components. Accordingly, this program is aimed at identifying factors which govern the growth of such short cracks in a series of commercial aluminum alloys, with specific reference to behavior at near-threshold levels. In this report, the fundamental basis for the study is described in terms of i a detailed review of the factors which lead to differences in long and short crack behavior, and ii a theoretical analysis of the influence of crack deflection and closure mechanisms on long and short crack behavior. It is concluded that many anomalies in the behavior of short fatigue cracks can be traced primarily to closure and deflection mechanisms, and accordingly an experimental program is prepresented with the objective of isolating these effects. Author