Effect of undercut defects on high-cycle fatigue behavior of welded joints

Abstract

Welding is a rapid and flexible connection method that enables the construction of a broad range of steel bridges. However, weld defects are inevitably introduced in the welded joints of steel bridges. These defects significantly reduce the fatigue resistance of the joints. Undercut defects are among the most common types of weld defects. The effects of undercut defects on the high-cycle fatigue behavior of welded joints in steel bridges were determined using a combination of experimental and numerical approaches. Four groups of a total of 48 butt and cruciform welded joint specimens were fabricated and tested under different stress conditions. The results indicate that the fatigue cracks in the BW1 and CW1 specimens (without undercuts) were initiated at the weld toes and propagated into the plate thickness. The fatigue cracks in the BW2 and CW2 specimens (with undercuts) were initiated at the roots of the undercut defects and propagated into the plate thickness. Therefore, a transition of the fatigue crack source occurred in the BW2 and CW2 specimens. The failure surface of each specimen is elliptical. The fatigue resistances (97.7 % possibility of survival) of the butt and cruciform welded joints without undercuts at 2 million cycles are 100.8 and 73.2 MPa, respectively. The fatigue resistances of butt and cruciform welded joints with undercuts of 0.5 mm depth and radius are reduced by 43.6 % and 13.5 %, respectively. Furthermore, the numerical results showed that the fatigue strength of butt and cruciform welded joints decreased significantly with the increase in undercut depth and plate thickness, but increased significantly with the increase in undercut radius.