| In view of the many advantages of plate-type grid structure, application in our country, regardless of the scale or quantity, ranks front of the world. Suspending crane is set up in plate-type grid structure. Alternating load produced by suspending crane brings fatigue problem to the plate-type grid structure. Plate-type grid structure fatigue mainly includes the fatigue of bar, welded hollow sphere and hanging point connection. And the fatigue of the hanging point connection is the key part of plate-type grid structure fatigue damage. Crossed plate-welded hollow spherical connection as one of the main hanging point form, its theoretical and experimental study is less, and relevant fatigue design method is not established in the current national rules and regulations. As a result,it seriously restricts the extensive use of suspending crane in industrial buildings.In this thesis, based on the National Scientific and Natural funds (50678109,51178286), the fatigue performance of crossed plate-welded hollow spherical node in plate-type grid structure was analysed in theory and experiment. The related work and conclusion are as follows: (1) By means of the software ANSYS,25different crossed plate-welded hollow spherical nodes (sourced for Q235B) were analysed with20nodes of SOLID95entity model. And the influence of welded hollow ball diameter-D, welded hollow ball thickness-ts、cross-shaped board width-B, crossed plate thickness-tp and weld leg size-hf are discussed detailedly. Calculation formular of the stress concentration factor of crossed plate-welded hollow spherical node is established and the value ranges in3.176～5.365. Research result reveals the relationship between stress concentration and fatigue damage source, explains that why the crossed plate-welded hollow spherical node fatigue strength is extremely low, and sets up a theoretical foundation for fatigue design method on the basis of hot stress amplitude.(2) Designing the loading device that matchs the fatigue specimens, using Amsler fatigue testing machine (Switzerland),we successfully completed the constant amplitude fatigue test of25crossed plate-welded hollow spherical node s, and the fatigue test data were obtained(six data were abnormal). By Collecting the pre-existing domestic nine constant amplitude fatigue test data, the thesis got the S-N curve with regression statistical analysis of a total of28fatigue test data.(3) Based on the S-N curve, with hot spot stress and hot spot stress amplitude as design parameters, two kinds of constant amplitude fatigue design method of crossed plate-welded hollow spherical node in plate-type grid structure are established. If N=2×106, it gets [△σ]2×106=19.66MPa and [△σh] 2×106=62.44MPa.The establishment of constant amplitude fatigue design method provides beneficial supplement for relevant national codes or specifications, and expands the categorys of node fatigue design method.(4) In order to reveal the variable amplitude fatigue performance of crossed plate-welded hollow spherical node,14node fatigue specimens were tested for variable amplitude by typical load pattern, and14effective fatigue test data were obtained. Through dealing with the test data, using the laws of Miner linear cumulative damage theory and Corten-Dolan nonlinear cumulative damage theory, the life estimation of variable amplitude fatigue specimens were respectively gotten.The result shows that the adopting of Corten-Dolan theory to cross plate-welded hollow spherical node for fatigue life estimation is reasonable.(5) By means of magnifier and electron microscopy, metallographic analysis of the4typical constant amplitude and4variable amplitude fracture section were done.It reveals the fatigue failure mechanism of crossed plate-welded hollow spherical node under constant amplitude and variable amplitude and fracture characteristics,and the randomness of constant fatigue fracture is often far less than the variable amplitude fatigue fracture; Combined with the theoretical and metallographic analysis,it gets the result that the end of crossed plate is the main fatigue damage origin.(6)The calculation for the fatigue life of crossed plate-welded hollow spherical connection by using fracture mechanics is feasible. Theoretical estimate and experimental result are basically identical, it has a certain error between them.The error is in30%or so. The initial crack length of node has a large influence on the crack development life, and the fracture toughness has a small influence on fatigue life. |
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