Residual monotonic stress-strain property of Q690 high-strength steel: Experimental investigation and constitutive model

Residual monotonic stress-strain properties of Q690 high-strength steel (HSS) with pre-fatigue damage were investigated, which provided the basis for studying the residual resistance performance of HSS structures after an earthquake. Three monotonic tensile test specimens, nine low-cycle fatigue test specimens and twenty-seven prefatigue test specimens were included in this study. For the fatigue strain amplitude, the 0.75%, 1.0% and 1.5% were considered. From the low-cycle fatigue experimental results, the relationship between the fatigue life and fatigue strain amplitude of Q690 HSS was clarified through a predictive equation. The number of loading cycles was controlled to perform the pre-fatigue damage test, where the fatigue damage ratios were controlled to be 0.3, 0.6 and 0.8. Cracks were observed on the surfaces of the test specimens with pre-fatigue damage. A tensile coupon test was then conducted to clarify the residual mechanical properties of Q690 HSS with pre-fatigue damage. The effects of the fatigue damage ratios and fatigue strain amplitudes on the residual monotonic mechanical properties of Q690 HSS were determined. The stress-strain curve of the specimen with pre-fatigue damage was similar to that of the virgin specimen. The strength properties of Q690 HSS were reduced by prefatigue damage. The effects of the fatigue damage ratios on the key mechanical properties of Q690 HSS were quantified using predictive equations. A predictive method for the residual monotonic stress-strain properties of Q690 HSS with different pre-fatigue damages was proposed, which included predictive equations for key mechanical parameters and a nonlinear constitutive model. The proposed predictive method for the residual mechanical properties of Q690 HSS with pre-fatigue damage can be used in theoretical and numerical analyses as a material model.