Research Of Fatigue Strength Effects And Their Influence Laws For The Typical Welding Parts

Engineering incidents on fatigue failure of welded structure continue to emerge alonewith mass of welded production in recent years. Premature failure of welded structure hashappened with inappropriate choice of joints type since designs of most critical welding partsof locomotive under-frame base on static strength, while it is less taken reference toanti-fatigue. On the other hand, technical considerations are not comprehensive enoughin the assessment due to the engineers have a little knowledge of joints’ anti-fatigue propertiesand welded fatigue design. Therefore, it must to be solved that proposing the fatigue designsuitable for the locomotive under-frame based on the specifications summary of weldedstructure fatigue design.(1) Fatigue designs of welded structure in the IIW and BS have been summarized, andthe sprit of welded design in Load and Resistance Factor Design Specification has beenshown without shelter. It is absorbed to lay the foundation of welding standardsfor locomotive industry by a comparative analysis of the similarities and differences amongthe standards.(2) The four typical joints have been summarized by re-classification to the differentclassify-ways of joints among the standards. Then stress concentration impacting onthe fatigue strength discussed.(3) The problem that Gaussian heat source loading on the complex plane has been solvedby loading with the Gaussian function in the past based on the welding simulation of the25#steel butt joint in the6mm thick. Self-balancing residual stress is consistent with theactual basically after welding, which paves the cornerstones for the welding simulation of thethick docking.(4) Welding simulations of butt joints, T-joints and lap joints of plate in the specificationhave been taken by programming the16Mn steel welding simulation. From the angle ofthe welding residual stress, it is considered the impact on the fatigue strength combined withthin sheet simulation results.(5)The analysis of load overlay mechanism with the elastic-plastic model when the jointsexisting initial residual stress are under cyclic loading based on sheet and plate weldingresidual stress simulation. The results show that the secondary yield occurred at dangerousstructure and its average stress large significantly, and it is necessary to consider theinfluence of residual stress in the assessment of welded structures.It can provide a theoretical reference to designers so that the design of welded joints ismore reasonable. In addition, a more effective assessment on fatigue of welded structures can be given by analysis and summarizing the residual stress distribution of the different type ofjoints welded. It has a great meaning of theory and engineering.