TITLE:
Fatigue Limit Prediction and Estimation for the Crack Size Rendered Harmless by Peening for Welded Joint Containing a Surface Crack
AUTHORS:
Ryutaro Fueki, Koji Takahashi, Keiji Houjou
KEYWORDS:
Welded Joint, Peening, Fatigue Limit, Compressive Residual Stress, Fracture Mechanics
JOURNAL NAME:
Materials Sciences and Applications,
Vol.6 No.6,
June
5,
2015
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.