基于失效评定图(FAD)研究含疲劳裂纹T型圆钢管节点的安全性

STUDY ON SAFETY OF CIRCULAR TUBULAR T-JOINTS CONTAINING FATIGUE CRACK BASED ON FAILURE ASSESSMENT DIAGRAM (FAD)

失效评定曲线(FAD)常用来评价焊接结构在出现裂纹后的安全性,为了验证这种曲线在评价焊接管结构在节点部位出现疲劳裂纹后安全性的适用性,采用实验测试和有限元分析的方法研究了3个含疲劳裂纹的T型管节点试件在静力作用下的极限承载能力及破坏过程。3个T型管节点试件首先进行疲劳实验在焊趾处产生表面裂纹,然后通过在支管端部施加轴向拉力作用检测节点的破坏过程。基于自行开发的含表面裂纹T型管节点的有限元网格自动产生程序以及ABAQUS分析软件,研究了在管节点破坏过程中表面裂纹最深点的应力强度因子大小,并通过实验的荷载-位移曲线确定了T节点试件的塑性极限承载力。在这些结果的基础上,验证了FAD在评价含疲劳裂纹的焊接管节点安全性方面的适用性。研究结果标明:FAD在评价含疲劳裂纹管节点的安全性方面是安全可靠的,但偏于保守。

A failure assessment diagram （FAD） is usually used to evaluate the safety of welded structures containing cracks. To study the applicability of FAD in assessing the safety of welded tubular structures after fatigue crack initiates in the joint connection, the ultimate strength and the failure process of 3 tubular joints containing fatigue cracks subjected to static loads are analyzed through experimental tests and finite element analyses. Firstly, the 3 specimens are tested under fatigue loading till surface crack initiates along the weld toe. Thereafter, an axial tensile load is applied at a brace end to observe the failure process of the tubular joints. The stress intensity factor （SIF） at the deepest point of the surface crack is calculated by using the automatic finite element mesh generator and the finite element software ABAQUS. The plastic collapse load is also determined from the experimental load-displacement curve. Based on the above results, the applicability of FAD in assessing the safety of welded tubular joints containing fatigue cracks is discussed. The results show that it is safe and reliable to apply FAD to assess the safety of cracked tubular joints, but the estimation is relatively conservative.