Study on safety of circular tubular t-joints containing fatigue crack based on failure assessment diagram (FAD)

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.