Study On The Assessment Methods Of Fatigue Failure In Stainless Steel Welded Joints

S-N curves of welded joints made by SAF2205 two-phase stainless steel and 1Cr18Ni9Ti austenite stainless steel are studied based on the results of fatigue tests. The influence of the different material for welded joint and the joint geometry on S-N curve is discussed by comparison with the test result of welded joints of the two materials. It indicates that the constant m and the fatigue resistance value which is at 2×106 cycles are different from the value recommended by IIW obviously. The fatigue assessment result of stainless steel welded joints that is given by IIW S-N curve is conservative. In addition, the different joint geometries lead to the difference of local stress concentration of welded joints, so nominal stress S-N curve is affected evidently.In order to investigate the influence of the welding residual stress for the fatigue performance of the welded joints, the welding residual stress is calculated by the software ANSYS. Firstly, the temperature field of welded joints is simulated. Basing on the result, the welding residual stress is calculated, at the same time, the distribution characteristics of residual stress, which for the welded joints especially for the fatigue fracture zone, are studied. It indicates that the welding residual stress of the D joints in here is high, and the result depends on the minimum FE size.In the theories, Dang Van criterion and volumetric approach (VA) are mainly discussed. Dang Van criterion is advanced by the French welding institute, which is used to evaluate the local fatigue limit of fillet weld. Considering the welding residual stress, the fatigue assessment of D joints is researched by the J.J.Janosch formula, and the influencing factor and the applicability are discussed. It indicates that there is a difference between the characteristic fatigue resistance that is the assessment result and the valuation that is advanced by Dang Van criterion. After researching, it discovers that the calculating results are affected by the minimum FE size and the welding defect.Volumetric approach (VA) is one of the methods proposed in recent years that used for the fatigue assessment and fatigue life prediction. The volumetric approach is applied to the fatigue assessment of welded joints in stainless steel with four types of geometrical modes in here, and its feasibility and the effect of the finite element calculation on this method were discussed. It was shown that, for welded joints, VA local average stress (σave|Ω is an universal fatigue restraining parameter, the fatigue intension expressed by (σave|Ω is independent of the joint geometries, and dependent of the minimum FE size and the materials. The result can offer the important gist for predigesting the fatigue assessment of welded joints. At the same time, VA is modified with the Dang Van criterion, and it is applied to the fatigue assessment of welded joints in duplex stainless steel SAF2205 with two types of geometrical modes in here. The rationality and availability are proving by the calculating result.