Weld residual stress and fatigue strength of flanged edge welded joints in ferritic stainless steel

Flanged edge welded joints are often used to join the same edge planes of two thin plates in a ferritic steel structure. They have crack-like incomplete root penetration, where stress concentration is very high. When the structures are subjected to repeated stress which exceeds a certain fatigue limit, fatigue cracks will initiate and propagate from the flanged edge welded joints. However, the fatigue behavior of the welded joint has not been investigated. In this research, in order to investigate the weld residual stress near the weld root tip of the flanged edge welded joints, both the measurement using sectioning method and the thermo-elastoplastic analysis were carried out. In addition, fatigue tests and fatigue crack propagation analyses were also performed on the welded joint to clarify the fatigue strength quantitatively. The experimental and analytical results of the residual stress showed that there was high compressive residual stress near the weld root tips. The fatigue test results indicated that all fatigue cracks in eight test specimens initiated at the weld roots. Their fatigue strengths at 2 × 10⁶ cycles for the weld throat section was approximately 1.9 MPa and the fatigue limit was about 1.2 MPa. The results of fatigue life analysis showed that when the main plate thickness varied from 1.0 mm to 4.0mm, the fatigue strength increased in proportion to approximately 0.7 times of the main plate thickness.