| Large and complex machinery plays an important role in modern engineering,and the operating conditions are very harsh,and the load is also very complex.Fatigue damage has become one of the main failure modes of mechanical structures.Fatigue damage involves many fields,such as: bridges,rail vehicles,airplanes and aerospace fields.The damage caused by fatigue problems has the characteristics of concealment and suddenness,which often causes huge losses to the society.Considering the importance of fatigue life prediction and the problems faced by fatigue life prediction nowadays,it is necessary to establish a complete and accurate fatigue life prediction model.For complex engineering problems,damage accumulation prediction is an important part of predicting fatigue life,but linear damage accumulation prediction methods are difficult to give effective predictions.Therefore,nonlinear cumulative damage theory and related models have attracted much attention.This paper conducts in-depth analysis and improvement research on the Manson-Halford model in the nonlinear cumulative damage model.On this basis,a fatigue life prediction method considering the uncertainty of the S-N curve is developed and applied to the fatigue life prediction of the bogie frame structure.Based on the Manson-Halford model,the characteristics of considering the effect of load loading sequence but not the interaction effect between loads are discussed in depth.The power constant is discussed first,and it is found that the power constant has a greater influence on the fatigue life prediction.Then a new improved model is proposed based on the characteristics of the existing improved model.A unified expression is given for a series of such improved models.In the improved model,the higher power terms of the pre and post stress ratio reflect the influence of the interaction between the loads.Combined with the natural law,the suggestion that the power exponent k should be the natural constant e is given,and an example is given to verify it.The results show that,compared with the existing models,the improved Manson-Halford model proposed in this paper has higher fatigue life prediction accuracy.In order to obtain a fatigue life prediction result consistent with the actual situation,the uncertainty of the S-N curve needs to be considered.Based on the generalized chaotic polynomial method,combined with the improved Manson-Halford model proposed in this paper to predict the probabilistic fatigue life.It is verified by the experimental data of typical aluminum alloy corner joints of EMU train.The results show that the fatigue life prediction method based on the generalized polynomial chaos method is similar to the Monte Carlo method.This provides another effective algorithm for the uncertainty calculation problem,which improves the fatigue prediction method based on the S-N curve and cumulative damage theory.Finally,this article takes the fast three-axle truck bogie frame with a speed of 160km/h as the research object,combined with the actual operating conditions,and conducts a finite element analysis based on the UIC515-4 standard.Based on the analysis results,multiple welds with relatively concentrated stress in the static strength analysis were selected to evaluate the welds using the Manson-Halford improved model,and the results were compared with the results of Miner’s low.The results show that the fatigue damage results calculated by the Miner model are too conservative compared to the improved Manson-Halford model proposed in this paper.By using the chaotic polynomial method,the probabilistic fatigue life prediction of the bogie frame is carried out considering the probabilistic uncertainty of S-N curve at the place where the weld stress is large.In this paper,the Manson-Halford model is developed and improved,and a probabilistic fatigue life prediction method considering the uncertainty of S-N curve is proposed,which provides theoretical support for fatigue life evaluation and engineering management of welded structures. |
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