Fatigue strength evaluation of under-matched welded joints made of 800-MPa class steel based on the local strain approach

Abstract

It is clear that usages of high-strength steels for steel bridges are effective to reduce weight of the bridges, and therefore, it may lead to the cost reduction of the bridges. However, adoptions of high-strength steels might result in under-matched joints, and significance of under-matched welded joints made of over 700-MPa class steels on fatigue strength and estimation of a local strain approach on the joints are not clear yet. This paper presents fatigue test results of under-matching welded joints made of 800-MPa class steels containing incomplete penetration under higher stress range region. Test results indicate that the fatigue strength in higher stress range region is less than that made of mild-strength steels, and showed that the cause of reduction of fatigue strength is that under-matched welded joints caused strain concentration and ductile crack propagation at around weld roots. This paper also presents applicability of a simple estimation method of the effective notch strain from nominal strain proposed by a previous study, and the estimation method can evaluate the effect of under-matching welded joints under higher stress range region.