Title: Effects of defect size in root region on fatigue strength of fillet welded joints—root failure of non‐load‐carrying cruciform fillet welded joints due to toe treatment (2<sup>nd</sup>report)
Abstract: Summary This paper describes an investigation of the effects of the defect size in the root region on the fatigue strength of non‐load‐carrying cruciform fillet welded joints by FEM analysis, fatigue tests, and hardness tests. The results may be summarised as follows. Through TIG dressing of the toe region of fillet welded joints, joints have a fatigue limit of 1.4‐2.5 times that of as‐welded joints even where they have defects (of around 0.2‐4 mrn) in the direction perpendicular to the load direction in the root region and even where root failure occurs. The fatigue strength is also found to decrease with an increasing defect size in the root region. The reason why the fatigue strength determined by failure from the root region with a high stress concentration factor is generally higher than that determined by toe failure from the toe region with a low stress concentration factor is that there is a difference in the fatigue crack growth rate. For fully penetrated fillet welded joints, the stress concentration factor of the root region is as low as less than 1.0, whereas that of the toe region is as high as around 1.5 even where ideal TIG dressing is performed, so that toe failure occurs even in fillets with TIG‐dressed toes. The fatigue strength improvement found is at best around 1.6‐2 times that of as‐welded fillets. The FEM analysis results suggest that, if the defect size in the root region is kept below around 0.2 mm, the maximum stress concentration factor of the root region will be lower than that of the toe region treated by ideal TIG dressing. The limiting value of the defect size in the root region producing root failure is considered to be around 0.2 mm. If the defect size in the root region is kept to a value of less than 0.2 mm, root failure does not occur, and the AW fatigue strength can be improved around 1.6‐2‐fold by TIG dressing of the toe region. In the zone where the stress concentration factor of the root region is higher than that of the toe region (RK> 1), it is found that, in the low‐stress range, the fatigue strength of the toe region is higher than that of the root region and that root failure readily occurs. In the high‐stress range, both toe failure and root failure occur. The stress concentration factor of the root region is influenced by the ratio of the amount of load inflow through the rib into the fillet and is maximised at an intermediate root defect size. The fatigue strength of the root region is only slightly dependent on the stress concentration factor ratio RK. The FEM analysis results suggest that, unless toes are TIG‐ dressed, toe failure will occur, even where joints have defects in the root region.
Publication Year: 1994
Publication Date: 1994-01-01
Language: en
Type: article
Indexed In: ['crossref']
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Cited By Count: 2
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