| With the great advance of urbanization in our country since 21st century,the urban rail vehicles with the characteristics of energy saving,fast speed and large carrying capacity has attracted more and more attention by many municipal government At the same time,the quality and safety standard of rail vehicle products are also higher.Aluminum alloy has the advantages of low density,good weldability and excellent corrosion resistance,making it a common metal material used in EMU and urban rail train.However,as welding materials,there exists two problems of welding residual deformation and welding fatigue in the process of structural design and manufacturing.In the view of welding quality,the control of welding deformation directly determines the welding quality,while welding quality is the key factor that affects the welding fatigue strength.In an aluminum alloy car body,side wall is the most important part as a connection between the underframe and the ceiling,and the unbalanced heat input during the welding process will result in residual stress along the welding joint,and then lead to welding deformation.The subsequent process of car body assembly will be seriously affected by excessive deformation.Therefore,the prediction and control of welding deformation should be considered in the early designing stage,what's more,welding joints are the most vulnerable structures in the body,so the fatigue strength should be reasonably predicted to ensure the reliability of the body design.The main contents of the thesis are as follows:First of all,taking the 6005-T6 aluminum alloy as the research object,numerical simulation of temperature field,stress and strain field has been studied based on ABAQUS for thin plate,and the feasibility of the software has been tested by simulating the welding filler process using birth and death element.The influence of process parameters such as welding speed and welding current on welding deformation has been studied as well.Secondly,the welding deformation on the aluminum alloy car body sidewall of mass transit train has been simulated based on thermoelastic-plastic finite element method.The sidewall structure is accurately modeled by 8-node hexahedral elements and the moving double ellipsoid heat source is applied to simulate the MIG automatic welding process.Three welding sequences have been designed based on the engineering practice,the influence of welding sequence on the welding deformation of the aluminum alloy sidewall is discussed under different welding sequences by comparing the simulation results.The results showed that welding deformation can be affected under different welding sequences and the sequence from the outside to the inside can control the welding deformation of the sidewall better.Then,the welding deformation of side wall after welding has been calculated by using inherent strain method,and the result was compared with the results of thermal-elastic-plastic method.The output shows that there existed discrepancy but in the range of allowable accuracy between the two kinds of method to predict welding deformation.The validity of inherent strain method which can predict welding deformation in an efficient way,and also can ensure the correctness of the results has been tested.Finally,two sections of side wall have been accurately modeled using solid elements,and fatigue life has been predicted by master S-N curve method.The fatigue life of the weld butt joint in the model has been computed under various fatigue loads referring to actual tests,the fatigue limit is 25.4MPa.Through the above analysis of aluminum alloy welding joint,engineering guidance for aluminum alloy side walls welding process parameters has been provided,and the data of butt joint of aluminum alloy has been supported for anti-fatigue design. |
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