Experimental study on residual monotonic mechanical properties of high-performance Q690 steel with pre-fatigue damage

In this paper, we conduct an experimental study of the fatigue performance and monotonic tensile properties with pre-fatigue damage of seismic and corrosion resistant Q690 structural steel (abbreviation high-performance Q690 steel). Based on fatigue cumulative damage theory, S-N curves and fatigue cumulative damage curves of high performance Q690 steel were obtained. According to the static mechanical properties with different degree of fatigue damage, the related curves between fatigue damage degree and residual mechanical properties were proposed. Finally, based on the Rambeger-Osgood constitutive relationship, a constitutive model for high performance Q690 steel considering fatigue damage is proposed. The results indicated that the high performance Q690 steel showed good fatigue performance. Its limit fatigue strength is 630 MPa (0.86fy) approximately, which is higher than fatigue limit values specified in steel design standards. In addition, the fatigue crack propagation stage and transient fracture stage accounted for a relatively small proportion of fatigue life. The static mechanical properties with pre-fatigue damage of high performance Q690 steel is similar to the AISI 1045 steel. As the fatigue damage degree increases, the elasticity modulus of high performance Q690 steel decreases and yield strength increases. Whereas, pre-fatigue damage has little effect on ultimate strength and elongation. Finally, a new constitutive model considering fatigue damage was proposed, which was found better simulating tensile curves with different fatigue damage.