Fatigue Life Analysis And Optimization Design Of Welded Structure Of Railway Vehicles

As an important connecting structure of railway freight car body,welded structure has more and more fatigue damage,which causes vehicle safety accidents and also brings huge economic losses.Therefore,it is of practical significance and application value to predict the fatigue life of welded structure and optimize the structure.This paper takes a railway freight car body as the research object,and mainly carries out the following research:Firstly,the finite element model of the freight car body is established,and four working conditions are established with reference to AAR Maintenance Standard Manual: Specification for Design and Manufacture of Freight Cars,and the static strength is checked and modal analysis is carried out.The calculation results show that the static strength of the freight car structure meets the standard under the three working conditions of static load,traction and compression,while the von Mises stress at the welding seam of the shifting seat exceeds the material yield limit under the working condition of blocking the car.In addition,the first-order bending frequency of the car body is 21.11 Hz,and the dynamic performance of the car body is good.Secondly,the pseudo-structural stress method is used to analyze the fatigue of the dangerous position(the welding seam of the shifting seat)of the freight car,and the fatigue parameters are obtained.The analysis results show that the fatigue life of the shifting seat under this working condition can not meet the use requirements,and the structure of the shifting seat needs to be improved.In order to meet the technological requirements,the improvement method adopts the way of adding ribs to the weak parts of the shifting seat.After improvement,the stress in this area is obviously reduced.Thirdly,with three ribs as the design domain,the minimum volume as the goal,and the maximum von Mises stress value in the shifting seat area as the constraint,the topology optimization of the shifting seat ribs is carried out by using Opti Struct software,and the optimized structure is reconstructed.Through further size optimization,the quality of the ribs is reduced by 54.96% compared with the original structure,and the fatigue life of the welding seam of the shifting seat of the car body is also obviously increased.Finally,according to the stress distribution of the optimized car body under other three working conditions,six welds in key parts of the car body are determined,and their fatigue lives are evaluated and compared by nominal stress method and structural stress method respectively.The calculation results show that all six welds have reached the design life.By comparison,it can be seen that the fatigue life assessment based on structural stress method is conservative compared with nominal stress method.