Fatigue damage model for annealed type 304 stainless steel under complex strain histories

The model divides the fatigue damage process into three stages: a) Slip, b) Initiation and c) Propagation. These stages are related to the generation of persistent slip bands, initiation of permanent damage and propagation of damage to fracture. However, the stages are not determined by quantitative microscopic analyses but by an engineering approach which estimates the 'apparent' life for each stage by the effect of prior straining on the subsequent fatigue behavior. The conclusions of the program were: 1. Low-cycle fatigue damage is not generated in a linear manner. 2. At least three stages of damage are involved. 3. The sequence of strain levels is important. Decreasing strain levels are more damaging than increasing strain levels. 4. The relative rate of crack initiation decreases with decreasing constant total strain level. (orig./HP)