This paper concerns the assessment of weld defects influencing crack growth and fracture behavior of joints. Welded T -joints made of steel plates, with or without fatigue cracks along the weld toes, were tested in reversed loading to reproduce fractures starting from the weld toes. The effects of fatigue cracks were studied by comparing test and FE analysis results and by looking into the state of stress and strain at the region near the weld toes.
The Kobe Earthquake revealed that tensile failures frequently started with ductile cracks growing from weld toes. These cracks changed to a fast unstable failure as they grew, when adverse effects were combined. The stable crack growth from the weld toes and its change to fast failure are the subject of study in a series of tests of welded T-joints recently performed by the authors (Kurobane et a1. 1997). A welded T-joint configuration was selected because it had the simplest possible form and yet reproduced brittle fracture as observed during the earthquake. Namely, each specimen had a main plate, with a rib plate groove welded at the center of the main plate. Details of specimens are shown later. When a compressive static load was applied to the rib plate, the weld toes sustained large plastic strain. A nonlinear finite element analysis was found to accurately reproduce load versus deflection relationships until crack depth reached about 0.5 to 2.5 mm. The initiation of first ductile cracks was found to be predicted by a simple function of stress triaxiality, von Mises" equivalent stress and maximum uniform strain of material (Wang et aI., 1996). Ductile cracks therefore gave no appreciable effect on loaddeflection curves until they reached about 0.5 to 2.5 mm in depth, as far as they grew stably.
