| Currently,in our country's big and medium-sized metallurgy companies,in order to expediently rise,move and unload the works,we adopt a lot of cranes. Among them includes a lot of port cranes. In recent years, along with the highly developed economy of our country, the production of steel rises increasingly, the load works of cranes have enlarged greatly. At the same time, there appear all kinds of metal problems. Among these problems the most common and also the most serious is the trouble in crane metal structures which mostly are troubles of fatigue crack. Hence, researching the reasons that crack happened and the tendency of the crack's expanding is the problem that most engineers and technicians are fully concerned with. The crane's metal structure intensity calculation and fatigue analysis is fully complex, among existing different analysis means, the means based on the FEM is regarded as the comparatively consummate one.This paper takes one transporter grab ship unloader in MISCO as the research object. Takes a research on the whole structure of the FEM by MSC.Patran, and fatigue longevity of its important component, main beam. Researches of the fatigue crack growth of its support leg. Processes the structures'diagnose valuation and then give repair suggestion.First, this paper discusses the importance of preceding the research on the grab ship unloader's metal structures and especially the research on the fatigue longevity. It also puts the main content of the problem and elaborates its significance in theory and practice. Then this paper introduces the theory: the fracture mechanics and software such as Patran,Nastran and fatigue research software: MSC.Fatigue.Second, this paper gives the finite modeling and calculation to the grab ship unloader's structure by MSC.Patran and MSC.Nastran. In the processes of making modeling, we take more attention to the multi-point constraint. By the calculation, we make such conclusion that the quiet intensity and rigidity meet the demands; calculating stress of the back cantilever root of beam approaches the allowing stress. There is big deflection which causes big camber at the middle of beam .This has influenced the car's normal movement. Apparently, it's a design bug. After study, we put forward some schemes of the modification. Then we use the FEA software to analyze the structure again, result proves that the modification schemes presented in this paper can effectively cut down the stress and deflection of the cantilever root. Prevent the incidence of structure's rupture accident. This scheme of modification is successful.On the bases of introducing the technology on fatigue FEA, in view of the present conditions in the centre of the project as to the unloader metal structure's fatigue research, this paper makes use of the software MSC.Fatigue to proceed the fatigue analysis on this main beam structure under certain loads, by the analysis,we can get the cloudy pictures of the fatigue life distribution, and can clearly see every parts fatigue life. Therefore this analysis can supply theory basis for grab ship unloader's design and improvement and fatigue research. Build a sub-model of the grab ship unloader's leg where a crack at the weld appears, analyse the structure's fatigue life and find the reasons for the occurrence of cracks and for the further analysis of crack growth .The calculation result is basically consistent with actual situation. This paper has important engineering practical value.At the end of this paper, some conclusions on this subject's practical and academic signficance are presented, this paper also submits the research directions in the future, point out that utilizing the fatigue analysis's FEM and the fracture mechanics synthetically to the crane's metal structure fatigue analysis is complete and integrated ,this should become one of the fatigue research orientation for the future cranes.
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