Research On Fatigue Strength Of Welded Components For High Speed Freight Car Bogie

In order to fit the fast development of Chinese railway transportation, it is imperative that the high-speed freight trains, of which the running speed is 120-160 km/h or more high, should be operated as soon as possible. The development of high-speed freight car is one of the most important reseach items and the bogie is its core technique. It is indicated that welded frame bogie is the certain running gear technique mode for Chinese high-speed freight car. The fatigue strength of welded frame and bolster, which is the key loaded componets of bogie, directly influences the running security and reliability of the car in its life span.Currently, the systemic and deep research on fatigue strength of dynamically loaded welded steel structures are lacking in Chinese rolling stock applications. But it's indicated from the numerous running practices that the fatigue failure problems of car welded components have been very serious, so it is imperative that deep research on its mechanism should be done and practical fatigue analysis methods should be used to solve the problems occurred. Thus in this paper, combining with the national science and technology pillar program and aiming at the study of welded components for 160km/h high-speed freight car bogie which has been developed newly, the following three aspects were investigated systemically:1. Research on the project fatigue analysis technique for dynamically loaded welded steel structures;2. Research on the fatigue design loads and assessment criteria for welded components of high-speed freight car bogie;3. Research on the fatigue strength analysis and assessment for welded frame and bolster of high-speed freight car bogie.Firstly, based on systemically reviewing, summarizing and analyzing the former and latest international research results, three fatigue analysis approaches which is propitious to project applications for welded structures, including nominal stress method, surface extrapolation hot spot stress method and Battelle hot spot stress method, and four key fatigue effect factors including welding residual stresses, low stress range cycles, multiaxial stresses and post weld improvement techniques were studied roundly and profoundly. For practical project applications, the sound application manner of different fatigue analysis approaches and the rational modification criteria of various fatigue effect factors were discussed and summarized.Secondly, by comparing different methods, it's included that for bogie welded components, two types of fatigue design loads defining methods based on strength testing codes are most practical in current project applications. Farthermore the limitations of both methods and their applicability while using in different line conditions were discussed. By detailedly analyzing the actual loading characteristic of different structural positions on welded frame and bolster for high-speed freight car bogie, and systemically investigating the fatigue damage effecting pattern and extent of relevant loads defining factors, the two above loads defining methods were improved and colligate reasonably. Then the fatigue design loads and strength assessment criteria for welded components of high-speed freight car bogie were determined.Finally, based on the three project fatigue analysis methods for welded structures, the rational modification criteria of various fatigue effect factors, the fatigue design loads and strength assessment rules summarized or determined in this paper, the fatigue strength analysis of welded frame and bolster for 160km/h high-speed freight car bogie were carried out. And according to the assessment results, the improved scheme for structural optimization design and welding technology were presented. By comparing the theoretical calculating results with the prototype fatigue testing results and combining with the current running practices of bogie welded loaded components, the reliability and advantage of the methods presented in this paper were validated.