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A B S T R A C T In this study, the fatigue strength of inclined butt welds subjected to a proportional multiaxial stress state generated by uniaxial loading is studied in nominal and local stress concepts. The local methodologies studied included principal stress hypothesis, von Mises stress hypothesis and modified Wöhler curve method. Nominal methodologies included modified Gough-Pollard interaction equation, the design equation in Eurocode3 and the interaction equation in DNV standard. Results are evaluated along with data published in relevant literature. It is observed that both local and nominal stress assessment methods are able to estimate multiaxial fatigue strength. No obvious difference in fatigue strength is observed in the nominal stress concept, but the notch stress concept is able to capture a decrease in fatigue strength in shear-dominated joints. It is concluded that modified Wöhler curve method is a suitable tool for the evaluation of fatigue strength in joints dominated by both normal and shear stresses.Keywords fatigue strength; multiaxial stress ratio; multiaxial stress state; welded joints; weld inclination.N O M E N C L A T U R E FAT 95% = Fatigue strength corresponding to 2 × 10 6 cycles at failure with a survival probability of 95% and a confidence level of 75% FAT 50% = Fatigue strength corresponding to 2 × 10 6 cycles at failure with a survival probability of 50% and a confidence level of 75% E s = Elongation specified E = Young's modulus NA = Not applicable N f = Number of cycles to failure R = Stress ratio R y = Ratio of minimum yield to ultimate tensile strength of the material CV = Comparison value dependent on type of loading and material T = Triaxiality F = Applied load A = Weld throat area a = Weld throat size l = Weld length L = Length of flat plates t = Thickness of plates w = Specimen width w = Damage state variable f wd = Weld metal ultimate tensile strength k = Slope of SN curve k o = Slope of design SN curve Correspondence: M. Khurshid.

After post weld treatment with high frequency mechanical impact (HFMI) treatment of welds, a significant increase of fatigue life (up to a factor of 10) can be achieved. During the last years numerous experimental tests of welded joints with simple geometry under constant amplitude loading have been performed to quantify the positive effect of high frequency mechanical impact treatment. Due to the lack of methods for the prediction of the high frequency mechanical impact benefits, a widespread use of this process is not the case yet. Furthermore, it is still not clear if the results of these fatigue tests can be transferred to complex geometries and complex loading conditions such as in industrial applications. Therefore, an approach to assess the fatigue life of complex welded structures under variable amplitude loading was developed. For this purpose, high frequency mechanical impact treatment and fatigue load of simple welded specimen made of S690QL steel were simulated with finite element analysis (FEA) firstly. Then, the needed damage parameters for the fatigue life correlation were evaluated from the finite element postprocessing. The calculated life time to crack initiation was in good agreement with the experimental fatigue test results. In the next step, this procedure was implemented on a welded arm of an evacuator of type EW180B of the company Volvo Construction Equipment made of S700MC. The variable amplitude load measured under real service condition was transferred to single constant amplitude load cycles using a rainflow-counting algorithm. By simulation and damage mechanics evaluation of each load cycle the total damage sum could be calculated and compared with the experimental results from Volvo Construction Equipment.Keywords: Fatigue / welding / residual stresses / high frequency mechanical impact (HFMI) / finite element analysis (FEA) Nach einer Schweißnahtnachbehandlung mittels Hochfrequenzhämmern (engl. high frequency mechanical impact treatment (HFMI)) kann eine signifikante Lebensdauerverlängerung des Bauteils (bis zu einem 10-fachen) festgestellt werden. Während der letzten Jahre wurde dieser positive Effekt vielfach experimentell mit einfachen Proben-

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