A Study Of Fatigue Assessment Of Welded Joint And Casing Based On Field Intensity Approach

In this paper,a fatigue life evaluation method for the combustor with complex welds is conducted. An important method for fatigue assessment of welded joint—"local approach"is reviewed and discussed. The principles,analysis,procedures and factors involved in those local approaches are discussed. The deficiencies of them are pointed out and analyzed. On the basis of the work above, the researches are conducted, which concerns mainly with local approaches of fatigue assessment of welded joint, the fatigue assessment of welded joints based on stress field intensity method and fatigue assessment of model casing.In consideration of the fact that high stress concentration is often found at welded joints, a new local parameter—"stress field intensity"(SFI) is introduced to assess fatigue behavior of welded joints in the paper. The factors which have great effects on field radius and important parameters for the calculation of stress field intensity are studied. Different weigh functions are used to analyze the relationship between SFI and field radius for butt welded joint,which is combined with the test results of model flat specimens, and actual field radius is determined. The problems in application of SFI to the evaluation of fatigue life of complex welded structures are studied. Different weigh functions are used for the zone with high stress gradient and that with high strain gradient,and reasonable calculation approaches of SFI are presented. The procedure of fatigue assessment of welded joints based on stress field intensity approach is presented. A program is developed to calculate the stress field intensity with APDL provided by commercial CAE software ANSYS.Finally, an elastic-plastic finite element analysis of model casing is conducted. The assessment value of fatigue life of model casing based on field intensity approach is obtained. A comparison among the results obtained by stress field intensity approach, local stress-strain approach and experiments is made respectively,in which SFI method is proved to be a method with higher precision.