Fatigue Strength Analysis Of CRH₂ EMU Carbody Based On FEM

The carbody of EMU is the main bearing structure, which bears various complex dynamic loads, and carbody fatigue strength is the key factor to ensure operation safety and reliability. Research shows that when the speed of EMU up to 200km/h or more, fatigue load carbody bearing is not just the traditional mechanical alternating load, and the impact of aerodynamic load on carbody fatigue strength is becoming more and more non-ignorable. On the basis of building the finite element model of the head-vehicle carbody of CRH₂, this thesis is to analyze the carbody fatigue strength under the action of traditional mechanical alternating load and aerodynamic load.Firstly, set up the calculation model of the head-vehicle carbody. After fully research the structure characteristics of carbody, use the equivalent section method to simplify the hollow carbody structure to the entity structure on the basis of equal strength principle, and use SolidWorks 3D design software to establish the three-dimensional geometric model of carbody by reasonably simplifying the details. Then open the model design platform of Workbench software and import the geometric model, and get the finite element model of carbody through meshing.Secondly, by consulting the related literature of aerodynamic load of high-speed train, the aerodynamic load carbody bearing is divided into three kind working conditions, they are high-speed passing each other, passing through tunnels and passing each other in tunnels, and the fatigue strength of carbody structure is analyzed by combining these three working condition aerodynamic loads with mechanical alternating load. Using the transient analysis function of Workbench software, through finite element calculation, get the time history of all nodes stress of carbody under the combined action of above-mentioned aerodynamic loads and mechanical fatigue loads. Multi-axial stress is converted into uniaxial stress by the method of maximum principal stress, and then estimate carbody fatigue strength through plotting the points of maximum principal stress of all time points within Goodman fatigue limit diagram, which is the modified Goodman fatigue limit diagram of carbody main material A7N01 S and complete the drawing in advance.In addition, according to the requirements of carbody strength checking standard, fatigue strength should be estimated from two aspects, they are fatigue limit diagram and fatigue life. On the basis of transient analysis, using the stress fatigue plugin of Workbench, calculate the fatigue life, safety coefficient and fatigue damage of carbody. In the process of this calculation, Goodman theory is chosen to amend the influence of mean stress, and the S-N curves of carbody materials is inputted manually.Finally, in order to completely evaluate carbody fatigue strength under the action of dynamic load, based on the discourse of modal analysis theory and the meaning of carbody modal analysis, this thesis analyze the free state modal of carbody. Using the modal analysis function of Workbench, complete the modal analysis of the head-vehicle carbody under free state, and extract the inherent frequency values of the preceding 30 order modal, and extract the vibration chart of vertical bending and torsional deformation of low-order modal of carbody. At last, according to the related standards, make evaluation to the modal of carbody.