Multiaxial fatigue behavior of boxing welded joints of a JIS SM400B steel (12 mm thick plate) was examined using a biaxial fatigue test system. For a specimen, two stiffeners were attached to a main plate by a CO2 semi-automatic boxing welding. Residual stress measurement and finite element (FE) analyses were also done. Fatigue tests were performed under both uniaxial and biaxial (mainly out-of-phase) cyclic loads, and both results were compared and examined.
It was found that fatigue cracks in the biaxial test specimens were initiated at the boxing weld toes and propagated almost in the direction of lateral loads. And the relation between stress range near a weld toe, Δσ5, and crack initiation life, Nc, was almost common in the biaxial and the uniaxial tests, proving that the increase of Δσ5 due to the lateral loads is fully effective to the increase of cyclic fatigue damage because of the high tensile welding residual stress near the boxing weld toe. On the other hand, failure life, Nf, was slightly longer in the biaxial tests than in the uniaxial ones.
Finally a simple life estimation for the biaxial tests was made using the results of the FE analyses and the uniaxial tests, giving a little conservative results due to overestimation of stress range Δσ5 and the difference in crack propagation life between the uniaxial and the biaxial tests.
