Experimental investigation on fatigue crack growth performance of Q690D steel butt weld

Fatigue damage of welded joints is gradually becoming one of the key problems affecting the service safety of steel bridges under repeated vehicle loads. The fatigue crack growth rate (FCGR) tests of compact tensile (CT) specimens of two plate thicknesses under three stress ratios were carried out with Q690D high strength steel (HSS) butt weld (BW) in this paper. The FCGR and fatigue crack growth threshold (FCGT) under different stress ratios were obtained. Expressions for the FCGR and FCGT that can synthesize the effects of stress ratio were established. A new method to determine the crack closure parameters of Q690D HSS BW was also given. On the basis of McEvily model, the calculation formula of FCG for Q690D HSS BW was derived. The results show that the Q690D HSS BW of this batch have good FCG performance. And the greater the plate thickness, the better the FCG performance of the specimens taken perpendicular to the rolling direction. The FCGR recommended by BS7910 specification is 1.71-2.92 times that of the Q690 HSS BW in this study. The FCGR increases with the increase of stress ratio. When the stress ratio increases from 0.1 to 0.2, the FCGR increases by 49.48 %, whereas FCGR increases by 129.65 % when the stress ratio increases from 0.2 to 0.5. The stress ratio has a greater influence on the FCGR parameters for plates of smaller thickness. And the FCGT decreases linearly with the increase of stress ratio.