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

Abstract

The smoothing of fillet toe results in improvement of fatigue strength, but at the same time it seems to develop a liability to root failure occurrence.The purpose of this study is to investigate the relation between root failure and stress concentration in toe smoothed non-load carrying type cruciform fillet welded joint and the effects of lack of joint penetration on fatigue strength of the fillet joint.Lack of joint penetration in the welds was deliberately introduced by a special method of putting a half cut core wire on the weld joint. After weldig, toes were TIC dressed. In fatigue tests, the maximum stress of fatigue cycle was fixed to yield, stress of the material (Max. stress=Yield stress (const.)=559MPa, Min. stress=variable).Main results obtained are summarized as follows:1) The root failure seems to be apt to occur if the elastic stress concentration factor at the TIG dressed toe is less than about 1.6 in the present tests.2) The difference in heights of lack of joint penetration, 0.92 mm and 1.64 mm, shows no significant effects on fatigue strength.3) The root failure occurs in general at a lower stress range than the stress range where a toe failure follows a root crack.4) The most important condition for preventing a root failure is to allow no lack of joint penetration (rib side) i.e. slit perpendicular to the loading direction.