| In this paper, based on facts that crack surfaces are characteristic of fractal and aimed at the fatigue behaviors electronic beam (EB) welded joint of GH4169, the damage mechanics theory and fractal theory are combined to the analysis of the high cycle fatigue damage and the evaluation of lifetime of GH4169 alloy welded joints.Stress versus fatigue life curve for GH4169 welded joints is obtained through fatigue tests of GH4169 weld joints. Moreover, the strains of welded joint measured by the strain gauge are researched.Qualitative analysis is applied to macro and micro damage of GH4169 welded joint and fracture surface morphologies of GH4169 welded joints in different load levels with scanning electron microscope is analyzed. It is found that all fatigue sources are at the surface of GH4169 welded joints.Based on the fractal theory, the fracture surfaces of GH4169 welded joints are analyzed quantitatively. The fractal dimensions of the crack surfaces are obtained by box-counting method, which is based on the secondary electron images, and the relationships between fractal dimensions and loadings as well as fatigue life are established.Moreover, the high cycle fatigue fractal damage evolution of GH4169 welded joint is established according to the definition of fractal damage. Based on the result of fatigue tests and fractal dimensions of the fracture surfaces, a unified equation for high cycle fatigue fractal damage evolution depended on stresses is established.Finally, fatigue life prediction of EBW GH4169 casing is presented with the help of Monte-Carlo method, the life prediction for EBW GH4169 casing is obtained, in which the reliability index is 99.87 and confidence is 95%.
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