Effects of residual stress, weld toe notch and weld defects on fatigue of welded steel structures.

摘要

In studying the fatigue behavior of fillet welded railroad tank car shell structures, the effects of welding residual stress, weld toe notch and weld defects on the fatigue of fillet welded A515 steel specimens were evaluated.; Both hole-drilling and sectioning measurement techniques were used to obtain residual stress information. Pad-on-plate weld specimens were designed to simulate the tank car structure for welding residual stress measurement. Simple bead-on-plate and fillet weld specimens, which have similar welding residual stresses near the weld end toe to the pad-on-plate specimens, were designed to be as compact as possible for fatigue testing.; As-welded and stress-relieved simple weld specimens were tested under pulsed tension and alternating cyclic load conditions to determine stress-life and fatigue crack propagation properties. Weld toe stress concentration effects were determined by strain gage measurement. Fracture surface features and crack initiation sites were studied by visual analysis, scanning electron microscopy and optical microscopy.; Welding residual stresses were found to be biaxial tension-compression near the weld end toe and biaxial tension-tension near the weld center toe. Longitudinal tensile residual stress was significantly relieved when the applied longitudinal tensile cyclic load was greater than 14 Ksi. Test results did not show a consistent effect of tensile residual stress on the fatigue strength under pulsed tension loads. However, tensile residual stress had a significant influence on the fatigue strength under alternating cyclic loads.; The weld end toe was associated with a stress concentration factor of approximately 3 and was the most critical factor in initiating fatigue cracks. Weld defects, such as slag inclusions, lack of fusion, and porosity were found to significantly affect the fatigue strength of a welded joint when the load magnitude or mean stress was low. An equivalent crack concept, based on linear elastic fracture mechanics theory, was introduced to quantify the weld toe stress concentration effect. This concept was shown to be effective for fatigue design and fatigue life prediction of welded structures.