Stainless steel, as Chromium-Nickel (Cr-Ni) alloys, has recently gained increased interest for construction owing to the combination of excellent corrosion resistance and mechanical strength. In particular, duplex grades, with a balanced austenite ferrite microstructure, show greater proof strength and ductility than that of standard austenitic stainless steel groups which were often used in bridges in corrosive environments over the last decades (Baddoo and Kosmac 2010). The interest for stainless steel for bridges also increased due to the good fatigue resistance of duplex welded components (Zilli et al. 2008). The EN 1.4162 and 1.4062 duplex grades are characterized by a lower Nickel and Molybdenum content which makes them price-stable, but more prone to pitting corrosion at the same time. In mildly corrosive environments, they can be a good alternative to protected carbon steel (w.r.t. maintenance) or austenitic grades (w.r.t. initial price). Additionally, it has been proven recently that those grades have corrosion resistance which is comparable to the austenitic stainless steels EN 1.4307 and EN 1.4404 grades (Iversen 2006). This research project seeks to bring enlightenment to fatigue behaviour of EN 1.4162 welded details via two main tasks: (1) Through experimental investigations: the tests will comprise the determination of the cyclic stress-strain hysteretic curves of the base material and the welded zone as well as the development of Wöhler curves for selected welded details. Constant amplitude cyclic tension tests will be performed. The tested details will then be submitted to post-weld treatments and the improvement of the fatigue resistance will be assessed. This is the only way to assess the fatigue resistance of duplex welded structural details. The Wöhler curves, both with and without post-weld treatments, will be compared with the current carbon steel design rules and further recommendations will be made for the inclusion of the beneficial effect of post-weld treatment; (2) Through numerical studies based on the former experimental investigations: finite element models, initially developed to reproduce the experiments, will then be used to generate a series of parametric studies further nourishing the previous experimental investigation. The hot spot stress, already measured experimentally, will also be assessed numerically. This contribution is focussed on one objective which is to calculate the possible weight reduction in an existing carbon steel girder bridge, when lean duplex welded components are used. The benefit from the greater mechanical properties of the latter are considered according to the latest published design rules for stainless steel (EN 1993-1-4 2006, DMSSS 4th edition 2017). The fatigue design is made using the hot spot stress method (Hobbacher 2016) combined with finite element (FE) models to assess the local stress distribution, considering selected relevant details along the girder.
