Austempered ductile iron-to-steel dissimilar arc-welded joints: fatigue strength assessment according to local approaches

The design of mechanical components increasingly requires the adoption of different materials in the same structure with the aim of improving its performance. One of the available solutions is to adopt dissimilar arc-welded joints, which typically must withstand high fatigue loadings during in-service life. In a recent paper, the fatigue strength of EN-JS-1050 austempered ductile iron-to-S355J2 steel dissimilar arc-welded joints was experimentally investigated by testing some typical welded details in the as-welded conditions, under either axial or four-point bending loadings. In the present work, previous experimental campaign has been extended by fatigue testing other ADI-to-steel joint details. The fracture surfaces of all tested joints have been analysed to identify the fatigue crack initiation locations. Then, experimental fatigue results have been re-analysed to determine the fatigue strength category of each welded detail, which have been compared with those provided by International Standards for corresponding homogeneous steel joints. Afterwards, the local approach based on the Peak Stress Method (PSM) combined with the averaged Strain Energy Density (SED) fatigue criterion, has been used for the first time for fatigue strength assessment of ADI-to-steel dissimilar arc-welded joints. First, the structural volume size R0 has been calibrated for joints exhibiting fatigue crack initiation and propagation at the ADI side; then, a PSM-based fatigue design curve has been determined by fitting the available experimental results.