Abstract
In this study, the effects of portable pneumatic needle-peening (PPP) on the bending fatigue limit of a low-carbon steel SM490A welded joint containing a semi-circular slit on the weld toe were investigated. PPP was applied to the specimens with a semi-circular slit with depths of a = 0.4, 0.8, 1.2, and 1.6 mm. Then, three-point bending fatigue tests were carried out under R = 0.05. The fatigue limits of low-carbon steel welded specimens containing a semi-circular slit were increased for peened specimens compared with non-peened specimens. Peened specimens having a semicircular slit with a depth of a = 1.2 mm had high fatigue limits, almost equal to those of the non-slit peened specimens. It was concluded that a semi-circular slit with a depth of less than a = 1.2 mm can be rendered harmless by peening. Then, the fatigue improvement by peening was predicted. The fatigue limits before and after peening could be estimated accurately by using a modified Goodman diagram considering the effects of residual stress, stress concentration, and Vickers hardness. Moreover, the maximum depth of a semi-circular slit that can be rendered harmless by PPP was estimated based on fracture mechanics assuming that the semi-circular slit was equivalent to a semi-circular crack. The prediction results were almost consistent with the experimental results.
Highlights
Welded joints are often used in large steel structures such as bridges, ships, and pressure vessels
The welded joints reduce the fatigue limit of structures as a result of stress concentration caused by a discontinuous portion of the weld bead and tensile residual stress in the weld toe resulting from the effect of the heat accompanying the weld process
Fatigue cracks often initiate at the welded joint, leading to structural fracture
Summary
Welded joints are often used in large steel structures such as bridges, ships, and pressure vessels. Fatigue cracks often initiate at the welded joint, leading to structural fracture. Non-destructive inspection has a detection limit, i.e., small cracks below the limit cannot be detected. These undetected cracks are left until the regular inspection, so these cracks result in a high cost for treatment in the future and decrease the reliability of the welded structures. If these fatigue cracks could be rendered harmless, the structural integrity could be significantly improved and maintenance cost reduced
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