Experimental study on multiaxial ratchetting-fatigue interaction of SUS301L stainless steel tubular welded joint

The multiaxial low-cycle fatigue tests of SUS301L stainless steel tubular welded joints are conducted to investigate their multiaxial ratchetting and ratchetting-fatigue interaction. The strain distribution in the welded joint and its whole-life evolution are acquired by using the digital image correlation (DIC) method. The experimental results demonstrate that the heterogeneous multiaxial ratchetting is observed in the different regions of welded joint if the multiaxial fatigue loadings are asymmetrical (with a non-zero axial mean stress) and depends remarkably on different loading paths and loading levels. Analogous to the uniaxial one, the highest ratchetting strain occurs in the fusion zone (FZ) of welded joint and the increase of ratchetting strain rate in the later stage of multiaxial fatigue tests is attributed to the fatigue damage; meanwhile, the multiaxial ratchetting strain produced under the asymmetrical fatigue loading condition apparently shortens the fatigue life of welded joint, compared with that under the symmetrical loading condition (with a zero axial mean stress). The fatigue life of welded joint is also dependent on the applied loading levels and loading paths. This study provides a solid data support to establish a life-prediction model to assess the multiaxial fatigue life of welded joint with considering ratchetting.