Low-Cycle Fatigue of SUS 304 Stainless Steel under TwoStep Loading (Effect of Prefatigue Damage on Microcrack Growth Rate)

Two-step loading LCF tests were conducted on a cyclic hardening SUS 304 stainless steel to examine the effect of prefatigue damage on the subsequent crack growth rate after switching the strain level. The effect of prefatigue damage yielded overshooting and undershooting of stress amplitude in comparison with single strain cycling and subsequently caused acceleration and retardation of the microcrack growth rate. Those trends were reversed depending on the combination of the level of the first and the second strain amplitude. Martensitic transformation measured by the X-ray diffraction method revealed that increasing strain amplitude promotes the transformation and results in acceleration of microcrack growth.