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

Abstract

Investigations were carried out with three different types of MIG- and TIG-welded joints of the magnesium alloy AZ31(ISO-MgAl3Zn1): fully or partially penetrated butt welds, transversal stiffeners. 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 t >= 5 mm independently of the weld geometries. 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 also permit the suggestion of Delta sigma = 28 MPa for r(f) = 1.0 mm as FAT-value in the IIW-Fatigue Design Recommendations. Further, the FAT-value Delta sigma = 73 MPa is also derived for the fictitious radius of r(f) = 0.05 mm to be applied to welded thin magnesium joints (t < 5 mm). These FAT-values are compared with data already known for steel and aluminium joints. A linear relationship between the FAT-values and the Young's modulus is determined. (C) 2008 Elsevier Ltd. All rights reserved.