Q690高强钢疲劳损伤后力学性能试验研究

服役结构材料疲劳损伤后的残余力学性能对结构可靠性的评估有着至关重要的作用。为此，对Q690高强钢经不同疲劳损伤后的残余力学性能进行了试验研究。根据Q690高强钢在不同疲劳荷载作用下的疲劳寿命，设定了3级疲劳荷载和9组损伤振动次数，并将Q690高强钢试件在各疲劳荷载下进行不同次数的预损伤疲劳振动。然后，对这些具有不同疲劳损伤的试件进行静力拉伸试验，观察试件的断裂模式并获得应力-应变曲线，对比分析具有不同疲劳损伤试件的屈服强度、抗拉强度和伸长率等力学性参数的变化规律。结果表明：Q690高强钢经疲劳损伤后的断口位置和截面形貌均发生明显变化；疲劳损伤后Q690高强钢在静力拉伸作用下的应力-应变关系曲线均无屈服平台，拉伸过程中出现位移不变、拉力突然减小的卸载现象，造成应力-应变关系曲线出现振荡；Q690高强钢的弹性模量受疲劳损伤影响相对较小，但是屈服强度、抗拉强度、伸长率、屈服应变和极限应变却随疲劳损伤增加而减小。根据试验结果，建立了Q690高强钢力学性能参数与疲劳损伤之间的拟合公式，利用该公式可对具有不同疲劳损伤的Q690高强钢结构的力学性能进行有效评估。

Experimental study on mechanical properties of Q690 high strength steel after fatigue damage

The residual mechanical performance of in-service structure after fatigue damage is regarded as a crucial indicator for structural reliability assessment. The residual strength of Q690 high strength steel subjected to different levels of fatigue damage was investigated. According to the fatigue life of Q690 high strength steel, three fatigue loads and nine life fractions were first determined. Fatigue damage was induced by subjecting the specimens to these nine different life fractions under three fatigue loads.And then subsequent tensile tests were conducted on these damaged specimens to obtain their stress-strain curves and associated mechanical properties (yield strength, ultimate strength, Young’s modulus and ultimate elongation). Significant differences are observed in the position and the morphological features of Q690 high strength steel after different fatigue damages. In addition, there is no yield plateau in the stress-strain curves of Q690 high strength steel under static tension after fatigue damages. Meanwhile, the stress-strain curves exhibit many wrinkles which are attributed to the phenomenon of strain invariance and stress reduction. Furthermore, significant reductions in the yield strength, ultimate strength and ultimate elongation are observed due to the effect of fatigue damage. In contrast, the influence of fatigue damage on Young’s modulus is negligible. Based on the test data, a new set of predictive equations are proposed to determine the mechanical properties of Q690 steel with different fatigue damages, which can effectively evaluate the mechanical properties of Q690 high strength steel after fatigue damage.