Fatigue behaviour of welded joints of Q690D high strength steel

High strength steel (HSS) has a broad application prospect in the field of bridge engineering, better meets the lightweighting of bridges. However, there is still a considerable lack of research on the fatigue properties of HSS. In order to study the fatigue properties of welded joints (WJ) of Q690D HSS, high cycle fatigue tests on unequal thickness butt welds (UTBW) and cross fillet welds (CFW) of Q690D HSS were carried out in this paper. The corresponding S-N curves were fitted. The fatigue properties are also evaluated in comparison with the existing research results. The research results show that the UTBW and CFW of Q690D HSS have good fatigue performance. The fatigue strength of UTBW is 1.96 times higher than the recommended value of GB50017. The design curve of BS7608 can better predict the fatigue life of UTBW when the number of cycles is more than 50,000 times. The fitted curve of CFW is lower than the design curve of GB50017 in the high stress area, and the fatigue strength of 95 % guarantee rate is similar to the recommended value of GB50017. The fatigue displacement curves can be roughly divided into a flat growth phase and a fast growth phase, the flat growth phase accounts for more than 90 % of the fatigue life. The fatigue strength of WJ did not show a clear pattern of change with the improvement of steel strength grade, and the distribution of fatigue parameters m and C of different strength grades of steel is more discrete.