Effect of Periodic Large Strain Cycles on the Fatigue Behavior of Steels

Data are reported for smooth specimens of SAE 4340, RQC-100, and Man-Ten steels subjected to constant stress amplitude cycling below the conventional fatigue limit. The presence of occasional large strain cycles, or overstrains, in the history resulted in finite lives. Possible causes of this effect are discussed, and it is shown that the deformation response of these steels is altered by overstrain. Inelastic strain-life data for the periodic overstrain and initial overstrain tests fall on the same line in a log-log plot that represents the nonoverstrain tests at shorter lives. The use of inelastic strain as a fatigue damage parameter is discussed.