Experimental investigation and numerical simulation on fatigue crack behavior of bridge steel WNQ570 base metal and butt weld

The experimental study on the fatigue crack growth rate and the threshold of high strength bridge steel WNQ570 base metal and butt weld has been performed. Two data processing methods are conducted to derive fatigue crack growth parameters of 95% survival probability. It turns out that the fatigue crack growth rate based on each specimen data is larger than that based on group method of data processing in terms of normal stress intensity range (10-70 MPa m0.5). The fatigue crack growth rates increase and the fatigue crack growth thresholds decrease with increasing stress ratios. For WNQ570 of the batch utilized in this research, the fatigue crack growth rate of base metal is lower than butt weld. The fatigue crack performance of WNQ570 base metal is also better than other common bridge steels including HPS485W, 14MnNbq, Q345qD and the universal steel performance provided by BS7910 and IIW-1823-07. Based on the measured FCGR parameters, numerical simulation by Franc3D and ABAQUS can precisely predict the fatigue life of compact tension specimens, which demonstrates that simulation method is appropriate to be applied to fatigue assessment practice of whole steel bridges based on linear elastic fracture mechanics (LEFM).