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The purpose of this paper is to investigate the effect of peening on the fatigue limit of steels for welded structure with a crack in the weld toe zone.

An artificial semi-circular slit was created in the weld toe, and peening was conducted. Then, bending fatigue tests were carried out.

First, owing to the shot peening, the maximum slit depths that can be rendered harmless were 1.0 and 1.2 mm in SUS316 and SM490, respectively. Second, during the fatigue test, the fracture of a peened specimen originated outside the slit, which indicated that peening eliminated the effect of the slit on the fatigue limit. Third, the fatigue limit of a slit specimen was improved by the enhanced residual stress distribution and the decreased stress concentration due to plastic deformation at the weld toe.

There are very few studies about which a fatigue crack is rendered harmless by residual compressive stress, as a result the structures could be continued to use. Moreover, the study defining the concept about rendering crack harmless and systematic investigation was not able to be found.