Traction structural stress analysis of fatigue behaviors of girth butt weld within welded cast steel joints

Due to its good mechanical properties, aesthetic and structural advantages, welded cast steel joints are widely utilized in engineering applications. The fatigue failure mode of girth butt weld between the cast steel node and the connecting steel tubular member was not well characterized. In this paper, fatigue tests of typical types of welded cast steel joints with different welding details were conducted. Fatigue failure mode and nominal S-N curves obtained from these tests were compared with that of an additional type of welded joint obtained from the literature. Then the equivalent structural stress parameter was selected to analyze the fatigue performance of the welded cast steel joint. The following conclusions can be drawn: (1) The traction structural stress concentration factor is higher at the weld root than at the weld toe for all five types of welding details, so the crack initiates at the weld root, which is consistent with test results; (2) Different lab-testing setups have an effect on the fatigue life of welded cast steel joints, and the traction structural stress can capture this test condition effect efficiently; (3) All fatigue data of 5 different test conditions fall within the 99% confidence interval of the master S-N curve. Furthermore, the scatter band of fatigue data processed by the traction structural stress method, is smaller than that processed through the nominal stress method. This suggests that the traction structural stress method is more suitable for the fatigue design for welded cast steel joints.