Fatigue assessment of welded joints in AlMg4.5Mn aluminium alloy by local approaches

The industrially used fatigue strength assessment concepts basing on nominal and/or structural stresses cannot consider and describe in detail the local stress-strain state in the root of a weld. To some extent they take account of the local geometry of a welded joint by assigning a detail category, but they do not relate to the local values responsible for crack initiation and propagation. Therefore, the application of appropriate local approaches promise a more precise description of the fatigue behaviour of welded joints. For welded joints of steel different local approach variants were applied with more or less success and further investigations are still focusing on this subject. Thus, few knowledge is available for the application of local approaches on welded joints of aluminium especially for a wide range of stress concentration factors. Therefore in the present paper, the existing local approaches are verified respect by the example of the AlMg4.5Mn W28 aluminium alloy (EN-AW 5083, AA 5083). The fatigue behaviour of aluminium welded joints with a wide stress-concentration range (Kt = 1.4 to 15.2) was investigated. The cyclic material properties of parent (base) material and weld metal (deposite) in unnotched (Kt = 1.0) and notched states (Kt = 2.5 to 12.9) were generated in order to derive strain-and load-controlled S-N curves and micro-support material constants. To differ the phase of crack initiation and propagation, the first technical crack depth a = 0.5 and 1.0 mm was detected and crack propagation rate was measured.