Fatigue design of welded joints from the wrought magnesium alloy AZ31 (ISO-MgAlZn1) by the local stress concept with the fictitious notch radius of r(f)=1.0 mm and 0.05 mm

Abstract

The investigations were carried out with three different types of MIG- and TIG-welded magnesium joints of the alloy AZ31. The evaluation of the results showed that the local stress concept using the fictitious notch radius of r(f) = 1.0 mm can be applied to magnesium welded joints from plates with thicknesses >= 5 mm independently of the weld geometries (fully or partially penetrated butt welds, transversal stiffeners). Design curves are proposed for different stress ratios, i.e. R = -1 as well as 0 and 0.5, which allow the consideration of residual stresses as well as load induced mean stresses. The results permit also the suggestion of Delta sigma = 28 MPa as FAT-value for the IIW-Fatigue Design Recommendations. Further, the FAT-value Delta sigma = 73 MPa for the fictitious radius of r(f) = 0.05 mm to be applied to welded thin magnesium joints is derived, too. These FAT-values are compared with already known data for steel and aluminium joints. A linear relationship between the FAT-values and the Young's modulus is determined.