すみ肉溶接継手の疲労強度に及ぼすルート部欠陥寸法の影響

止端処理に起因する荷重非伝達十字すみ肉溶接継手のルート破壊(第2報)

抄録

In order to investigate the effects of defect size at root region on fatigue strength of non-load-carrying cruciform fillet welded joints, finite element analysis, fatigue test and hardness test were carried out. Main results obtained are summarized as follows:
(1) It was confirmed that a fillet welded joint had fatigue limit 1.4-2.5 times as large as that of a joint as welded by TIG treatment at fillet weld toe region even if it had defect perpendicular to the load direction (about 0.2-4 mm) at root region and suffered a root failure. And the fatigue strength seemed 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.