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The safety assessment of welded structures still remains an importantindustrial problem. In this study, a simple diffusion bonded bi-material junction hasbeen made in order to analyse the Mismatch effect. It consists of an assembly of ferriticand austenitic steels which are representative of nuclear pressure vessel. Tests wereperformed on various specimens including: smooth and notched tensile bars, Charpyspecimens and single-edge notch bend specimens. Homogeneous and bimaterialstructures were tested. Smooth and notch tensile bars tests were used to adjust theparameters of local approach based on the Gurson model according to the “localapproach of fracture” procedure. On deeply notched specimens, the effect of thedistance between the notch root and the interface on fracture initiation and crackpropagation direction was studied. Tests were modeled using elasto–plastic finiteelement simulations. The correct test/computation agreement shows that the adjustedparameters on the homogeneous specimens can be transferred to heterogeneousstructures. In particular, simulation well reproduces the experimental crack pathbifurcation.