Experimental research on fatigue performance of high-strength structural steel series

The mechanical properties and fatigue performance of four typical high-strength structural steels (HSSs) with grades of 460, 550, 690, and 960 MPa were experimentally investigated. The influence of the HSS plate thickness t (e.g., 10 mm and 20 mm) was also considered. The results show that as the HSS steel grade increases, the scale of the yield plateau in the tensile test gradually decreases and becomes insignificant. The developments of the strain and stress are also limited, leading to a significant increase in yield ratio, i.e., from 0.68 in Q460 to 0.95 in Q960. In a high-cycle fatigue test, the fatigue strength of the HSS increases significantly along with an increase in steel grade and is remarkably higher than that recommended by current standards. In the natural S−N fitting results, the fatigue strength of the HSS increases in the steel grade order of Q460, Q550, Q690, and Q960, with the values of fatigue strength being 177 < 227 < 233 < 251 MPa, respectively. The ratio of the fatigue strength to yield strength gradually decreases from 0.43 in Q460–10 to 0.26 in Q960–10 as the steel grade increases, signifying the lag effect of the growth in fatigue strength compared with the static strength. The slope m of the HSS S−N curves in the natural fitting is closer to 3.0 when the steel grade is relatively lower (Q550 MPa and below) and is closer to 4.0 or even 5.0 at higher steel grades (690 MPa and above). Based on the experimental analysis, S−N design curves are recommended for the each HSS material analyzed in the study, to reflect their actual fatigue performance.