Study On The Local Criterion Of Fatigue Performance In Aluminum Alloy Welded Joints

There is growing interest in the structural use of aluminum alloys, for suchapplications as automotive and railway vehicles, high-speed ships and aerospacevehicles. Welding is the primary joining method and welded joints can exhibit poorfatigue properties, so fatigue is a major design criterion. In this paper the fatigueresistance and S-N curves of welded joints made by aluminum alloy 3A21 and 5083are investigated based on the results of fatigue tests. The parameters of curves and thefatigue resistance of butt and gusset welded joints are calculated. The influence of thejoint geometry for welded joint and the toe of weld on fatigue resistance is discussedand the test results of aluminum alloys welded joints are compared with the results ofsteel welded joint. It indicates that the different loading and joint geometries lead tothe difference of local stress concentration of welded joints and the toe of weldinfluence the degree of local stress concentration evidently affecting the fatigueresistance of welded joints.In order to investigate the influence of the welding residual stress for the fatigueperformance of the welded joints, the welding residual stress is calculated by thesoftware ANSYS. Firstly, the temperature field of welded joints is simulated. Basingon the result, the welding residual stress is calculated, at the same time, thedistribution characteristics of residual stress, which for the welded joints especiallyfor the fatigue fracture zone, are studied. It indicates that the welding residual stressof the B and D joints in here is high, and the result depends on the minimum FE size.In the theories, Dang Van criterion is mainly discussed.The local approach is a new approach of fatigue estimates for welded joints. Thevalidity of the local approaches for aluminum alloy welded joint is investigated byusing the results of fatigue tests of 3A21 gusset-welded joints. Based on thethree-dimensional finite element analysis of welded joints, the maximum principalstress and residual stress are calculated and the influence of the element size on localapproaches is discussed. It is shown that the local approaches based the steel weldedjoints does not apply to aluminum alloy welded joint, so after amending thematerial constants,α=0.5,β=51MPa, the results of assessment are accorded with theresults of experiment. The element size has the influence upon the local parameterβexp. , when the minimum size of three-dimensional element is less than 0.65mm thenumerical results has smaller influence on the fatigue estimates.