Effects of Defect Size at Root Region on Fatigue Strength of Fillet Welded Joint. Root Failure Resulting from Toe Treatment of Non-Load-Carrying Cruciform Fillet Welded Joints(Report 2).

to be apt to decrease with an increasing root defect size.(2) The reason that fatigue strength in root failure at root where stress concentration factor is higher than that at toe is generally higher than fatigue strength in toe failure at toe where stress concentration factor is lower than that at root seems to lie in the difference of crack growth rate between the two regions.(3) As the stress concentration factor at the root of a complete penetrated fillet welded joint below 1.0 and even when the stress concentration factor at toe region was decreased by applying TIG treatment to toe region, it was about 1.5 at the best, it was likely that a fatigue failure of the joint occurred at toe region and the limit of improvement on the fatigue strength was about 1.6-2 times as large as that of a joint as welded.(4) From the results of FEM analyses, it is considered that if the root defect size can be limited to a value lower than 0.2 mm, the fatigue strength of the fillet joint can be improved to.1.6-2 times that of a joint as welded without occurrence of a root failure by applying TIG treatment to toe region.