IMPROVEMENT OF FATIGUE LIMIT BY SHOT PEENING FOR HIGH-STRENGTH STEEL CONTAINING A CRACK-LIKE SURFACE DEFECT: INFLUENCE OF STRESS RATIO

ABSTRACT It is well known that shot peening (SP) prevents the initiation and propagation of fatigue cracks and improves the fatigue limit of metals. It was recently reported that a surface crack can be rendered harmless by SP. Actual pressure vessels are generally operated under a positive stress ratio ( ). However, the effects of SP on the improvement of fatigue limits under remain unclear. If these effects were clarified, the structural integrity of pressure vessels could be advanced. Thus, in this study, we investigated the influence of SP on fatigue limits and on the crack size that could be rendered harmless by SP under . High-strength steel specimens containing a semi-circular slit were subjected to SP. Bending fatigue tests were carried out under R = 0.4. The fatigue limits of the SP specimens increased 50~100% compared with Non-SP specimens. Slits under 0.2 mm in depth were successfully rendered harmless by SP. The increasing ratios of the fatigue limit under R = 0.4 were lower than those under R = 0. However, the size of semi-circular slit that can be rendered harmless by SP remained the same. The size of the slit that can be rendered harmless can be predicted by calculating stress intensity factors