Fatigue strength of welded joints made of high‐strength steels

Abstract

AbstractBy rearranging existing fatigue test results, fatigue performance of typical welded joints, (longitudinal, cruciform and out‐of‐plane gusset welded joint) are discussed with respect to the dependence on steel strength and on joint size. The relationship between fatigue strength and steel strength was not clear for longitudinal welded joints of small specimens and large‐scale girder specimens. For cruciform welded joints and out‐of‐plane gusset welded joints, fatigue strength of small joint specimens is independent of the steel strength, but that of girder specimens decreases with increase in steel strength. In addition, fatigue strengths of these two types of welded joints decrease with increase in joint size, especially for girder specimens.In order to discuss these relationships in detail, fatigue tests with out‐of‐plane gusset welded joint specimens and large‐scale girder specimens, including web gusset joints made of JIS SM570 and 900 MPa class steel were carried out. From the fatigue tests, similar tendencies were found to those obtained from existing test results. Although fatigue tests of joint specimens showed no difference in fatigue strength, crack initiation life and crack propagation rate between the steel strengths, fatigue strength of girder specimens made of 900 MPa class steels is much lower than for JIS SM570. In addition, fatigue strength of the girder specimens is considerably lower than that of the joint specimens. This difference results mainly from an increase in stress concentration due to joint geometry, and combination of nominal stress and shear stress in the girder specimens. It was found that the influence of the combination can be approximately evaluated from the nominal principal stress.