Corrosion fatigue crack growth mechanisms in welded joints of marine steel structures

海洋钢结构焊接接头的腐蚀疲劳裂纹扩展机理

This paper presents a model of fatigue crack growth in a welded joint and a two-dimensional model of anodic dissolution based on Donahue model and anodic dissolution mechanism,respectively.In addition,a model for predicting the corrosion fatigue crack growth rate in welded joints of steel marine structures is established and crack growth mechanisms are analyzed.The results show that during early stages of crack growth,corrosion fatigue crack growth rate in welded joints is mainly controlled by corrosion action,whereas cyclic loading becomes more influential during the later stage of crack propagation.Loading frequency and effective stress ratio can affect rupture period of protective film at the corrosion fatigue crack tip and the length of corrosion crack increment,respectively,which changes the influence of corrosion action on crack growth rate.However,the impact of stress amplitude on crack growth rate is only significant when crack propagation is caused by cyclic loading.Welding residual stress not only improves the effective stress ratio of cyclic loading,but also promotes crack closure and increases corrosion fatigue crack growth rate in welded joints.Compared to corrosion action,welding residual stress has a more significant influence on crack growth caused by cyclic loading.

本文分别基于Donahue模型和阳极溶解机理,提出了焊接接头疲劳裂纹扩展模型和阳极溶解二维模型。此外,建立了预测海洋钢结构焊接接头腐蚀疲劳裂纹扩展速率的模型,并分析了裂纹扩展机理。结果表明,在裂纹扩展的早期阶段,焊接接头的腐蚀疲劳裂纹扩展速率主要受腐蚀作用控制,而在裂纹扩展的后期,受到循环载荷的影响更大。加载频率和有效应力比会分别影响保护膜在腐蚀疲劳裂纹尖端的破裂时间和腐蚀裂纹扩展长度,从而改变腐蚀作用对裂纹扩展速率的影响。但是,应力振幅对裂纹扩展速率的影响仅在周期性载荷引起裂纹扩展时才显着。焊接残余应力不仅提高了循环载荷的有效应力比,而且还促进了裂纹的闭合并提高了焊接接头的腐蚀疲劳裂纹扩展率。与腐蚀作用相比,焊接残余应力对循环载荷引起的裂纹扩展的影响更大。