Fatigue Simulation Analysis Of Notched Specimen Based On Master S-N Curve

Railway vehicles often use some discrete components with rounded corners, keyways and bosses and other geometric shapes, such as couplers and gear boxes, these geometric discontinuities of these sites is called "notch". As the notch sites often produce stress concentration, stress concentration will produce crack, reduce fatigue life of components, so the fatigue life of notched specimen will have a significant impact of fatigue life of the entire structure, even to the safe and stable operation of the railway.Professor Dong Pingsha proposed a master curve method. It is the newest method to calculate the fatigue life of welded structures. The method cdnsists of two key technologies:the mesh-insensitive structural stress method and a master△SS-N curve with equivalent structure stress range for the parameter. Notch parts and welded structures have many similarities, such as the location of dangerous point is easy to determine, it often located in the notch. If this method could be applied to the non-welded structures, it will bring huge economic benefits. Based on the master S-N curve method and aluminum notched specimens as the research object, the contents of this paper can be summarized as follows:Firstly, detailed analysis the master△SS-N curve method, discovered the mesh-insensitive structural stress method is not only suitable for welded structures, but also for other non-notched specimen welded structures.Secondly, research the relationship between the equivalent structural stress of welded structures with various parameters, discovered self-balancing notch stress field is divided into bilinear area by the reference thickness is determined by testing of welded joints, and short crack stress intensity factor amplification factor is also obtained by testing of welded joints. If this method is used to assess the fatigue strength of notched specimen, the value will be re-determined.Thirdly, high-value residual stress was found in the welded structures. The fatigue life was not too much influenced by the effect of mean stress, but for the non-welded notched specimen, it was significant. Considering the influence of the mean stress, correct the corrected Paris crack propagation formula, defined a new equivalent structural stress△Sg Finally, using the finite element method and the formulas of equivalent structural stress to get the equivalent structural stress of dangerous point of aluminum alloy plate-notched specimens. The master ASg-N curve under different confidence is obtained by binary linear regression analysis.