海洋环境下耐候钢十字非传力焊接接头腐蚀疲劳性能试验研究

Experimental Study of Corrosion Fatigue Performance of Non-Load-Carrying Cruciform Fillet Welds in Marine Environment

腐蚀疲劳严重危害在役钢桥服役安全。为研究海洋环境下耐候钢桁梁桥焊接节点的腐蚀疲劳性能,对23个Q420qFNH耐候钢十字非传力角焊缝焊接接头进行实验室干/湿交替中性盐雾加速腐蚀及腐蚀后疲劳试验,采用失重法得到试件的失重率和腐蚀速率,对接头腐蚀形貌及疲劳断裂失效的宏观断口形态进行分析,拟合得到经历不同腐蚀时长后试件的名义应力和热点应力S~N曲线。结果表明:耐候钢十字非传力角焊缝焊接接头疲劳裂纹均萌生于焊趾处并沿板厚扩展失效,疲劳寿命由焊缝控制,接头焊趾附近腐蚀坑的形成与生长加剧了焊接接头的疲劳裂纹萌生;焊接接头的疲劳性能劣化程度随腐蚀损伤效应的增加而增加,但疲劳强度折减量与腐蚀时间并未呈线性关系,锈层逐渐具有保护性;未腐蚀前名义应力和热点应力疲劳强度等级分别建议采用《公路钢结构桥梁设计规范》中的FAT80和Eurocode 3规范的FAT110进行评估,腐蚀后的疲劳强度折减量建议参照美国耐候钢桥指南规定C类细节选取。

Corrosion fatigue poses severe threats to safety of in-service steel bridges.To study the corrosion fatigue performance of welded joints in the weathering steel truss girder bridge exposed to marine environment,23 specimens made of Q420qFNH weathering steel that entail non-load-carrying cruciform fillet welds were prepared to conduct in-house fatigue tests before and after using dry/wet alternating neutral salt spray to accelerate corrosion.The mass loss rate and corrosion rate were obtained in the weight loss test,the corrosion morphology of welded joints as well as the microscopic fracture cross-section of the failed welded joints was analyzed and the S-N curves of nominal stresses and hot-spot stresses of the specimens with different corrosion exposure durations were fitted.The results demonstrate that the fatigue cracks all initiated at the welding toes of the cruciform fillet welds and propagated along the thickness of the plates till failure.The fatigue life of the girder is controlled by welded joints,and the occurrence and propagation of fatigue pits near welded joints exacerbate the fatigue cracking of the welded joints.As the fatigue damage effect escalates,the fatigue performance degradation of welded joints gets intensified,but the fatigue strength reduction amount does not reveal linear relationship with the corrosion duration,and the rusty layer gradually exerts a shielding effect.Before corrosion,the nominal stress fatigue strength grade can be rated using FAT80 given by the Specifications for Design of Highway Steel Bridge,and the hot-spot stress fatigue using FAT110 suggested in Eurocode 3.The fatigue strength reduction amount after corrosion can be predicted referencing the Guidelines for the Use of Weathering Steel in Bridges.