| With the rapid development of urban rail transit,the demand for railway vehicles is also increasing in society.Stainless steel railway carbody is gradually becoming the main carbody in subway vehicles with its advantages of high corrosion resistance,high cost performance and light quality.For the purpose of achieving a lightweight carbody,the structural design of the carbody may result in a situation where the structural stiffness is reduced the strength requirements are satisfied.As a result,the planeness of the side wall skin becomes poor,which seriously affects the aesthetics of the carbody.The author find that the deformation of the side walls are slight after the welding process.However,significant unevenness in the sidewall skin will appear after the assembling process.The reasons are pretty complicated.The poor structural rigidity and weak anti-deformation ability of the side wall of the carbody are the important reasons for the unevenness of the side wall.Therefore,this paper takes B-type stainless steel carbody as the research object.It also investigates the reasons affecting the insufficient stiffness of the side wall structure by combining the numerical simulation method.The side wall skin deformation problem is discussed and solutions are suggested combined the method of numerical simulation to study the reasons affecting the lack of structural stiffness for the side wall,and discussed the side wall skin deformation problem and proposesd solutions.The main research contents and conclusions of this paper are as follows:（1）3D modeling of carbody and finite element analysis of side wall stiffness.The finite element model of the carbody is established and analyzed based on the specific structure of the carbody and the material parameters of the components.According to the analysis results,it can be seen that the strength of the carbody is satisfied to the standard,while the transverse deformation of the side wall is too large to cause the insufficient bending stiffness.The maximum transverse deformation of the side wall skin is obviously larger than that of the framework,which can indicate that the local structure of the framework is not enough to restrain the side wall skin,leading to its excessive free deformation.Therefore,the structural stiffness of the side wall can be improved from three aspects: enhancing the skeleton structure,improving the side wall framework stiffness,and optimizing the structural stiffness of the side wall skin.（2）Enhancing the framework structure.Add structural reinforcement to the framework corresponding to the area of the side wall skin with large deformation to increase the restraint of the side wall skin.From the finite element analysis results it can be seen that the deformation of the side wall and the framework with reinforcement is almost same as the original structure,and the maximum deformation of the side wall skin corresponding to the reinforced area is reduced by 4.8%.（3）Improving the stiffness of side wall framework.The column in the framework is formed by the stretch bending instead of the press bending.This is the use of stainless steel materials in large plastic deformation will exhibit significant work hardening characteristics to improve the strength and stiffness of the material.Using the finite element analysis method and stiffness analysis theory,it is concluded that the bending stiffness and torsional stiffness of the stretch bending-formed column are improved by 11.5% and 3.9%,respectively compared with the press bending-formed column.The finite element analysis of the side walls with high stiffness columns shows that the maximum deformation of the side wall is reduced by 3.4% and the maximum lateral deformation of the side wall skin is reduced by 8.3% compared with the original structure.It indicates that the stiffness of the side wall is enhanced by using the columns formed by stretch-bending process.（4）Creating tensile hardening side wall skin.Using the work hardening effect of austenitic stainless steel SUS301L-DLT,the side wall skin is stretched to improve the strength and stiffness of the side wall skin before the carbody was assembled.The maximum pre-stretching amount of the side wall skin to meet the assembly requirements can be determined to be 1.36% by finite element analysis.The uniaxial tensile and three-point bending tests prove that the tensile strength and bending strength are improved after pre-stretching by 1.36%.The optimization scheme is calibrated using finite element analysis,and it is found that the original framework deformation barely changed significantly with the use of tensile hardened wall panels,but the lateral deformation of the side wall skin is reduced by 5.3%.（5）Comparative analysis of side wall skin deformation before and after optimization.According to the structural characteristics,five measurement locations are selected on the side wall skin for the finite element analysis results and side wall planeness measurement inspection before and after side wall optimization.The comparison of finite element results show that the planeness of the side wall skin after stiffness optimization at five locations A,B,C,D and E improved by 8.4%,8.2%,12.7%,11.4% and 12.9%,respectively,compared with the original structural planeness;and the comparison of test inspection results show that the planeness of the new side wall skin at five locations A,B,C,D and E are improved by6.3%,12.7%,14.0%,18.8% and 11.5%,respectively.Comprehensive simulation and test results can be obtained,the side wall structural stiffness optimization scheme used in this project is reasonable,the finite element simulation of the carbody side wall structural stiffness is more accurate,and the research results have certain reference significance for production. |
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