Vibration Fatigue Strength Analysis And Optimization Of Straddle Monorail Vehicle Bogie Frame With Weld Structure

With the rapid development of urban traffic,the urban rail transit system is often used to solve the serious traffic congestion problem.Straddle monorail transportation system is an effective solution.Compared with subway and tram,straddle monorail has the advantages of strong climbing ability,low turning radius,low running noise,low cost,short construction period and small space occupation.It can be used not only as a supplement to the large urban rail transit system,but also as the main means of transportation in small and medium-sized cities.Bogie is an important part of straddle monorail vehicle,and it is the basis of bearing and transferring force.In order to ensure the safety and reliability of straddle monorail vehicles,the structure of bogie frame must be analyzed.Therefore,the static strength analysis,dynamic characteristic analysis,vibration fatigue analysis and structure optimization of the straddle monorail vehicle bogie frame considering the influence of weld seam are carried out in this paper.The main research work of this paper is as follows:(1)The finite element model of bogie frame with weld structure is established by using finite element software Hypermesh.According to EN13749-2011,TBT1335/1996 and UIC615-4 standard,the static load of each working condition is determined.The loads of bend and crosswind are determined by dynamic simulation software ADAMS.(2)The static strength of the bogie frame including weld is calculated under seven typical working conditions.The results show that the maximum stress of the frame is less than the yield limit of the material under each typical working condition.Therefore,its static strength meets the design requirements.However,except for the hoisting condition,values of the maximum stress of the frame under the other six working conditions are in the weld position at the gear box,where the maximum stress value of supernormal linear braking condition reache 296.5 MPa,which will affect the fatigue strength of the bogie frame to a certain extent.(3)The dynamic characteristics of bogie frame are analyzed.Firstly,the free mode and constraint mode of the framework are analyzed,and the low-order natural frequency of the constraint mode is similar to that of the excitation frequency.At the same time,the frequency response of bogie frame is analyzed based on modal method,and the frequency response of bogie frame is obtained by modal mode mode and stress superposition.(4)The weld structure in bogie frame is defined by fatigue analysis software FEMFAT.Meanwhile,based on the frequency response of the frame and the load time history determined by ADAMS,the random vibration fatigue life of the bogie frame with weld structure is analyzed based on Dirlik method.The results show that the weakest fatigue strength position of bogie frame is the weld at the installation of the frame gearbox under full load straight line condition and 20% ratio of bend condition.The fatigue life of the weld is 52.46 years and 35.11 years under two conditions respectively,and its fatigue life meets the design requirements.(5)The structure optimization design of the weld structure of the bogie frame is carried out.The vibration fatigue analysis of bogie frame with the weld structure after the optimization is implemented.The results show that,in the case of meeting stiffness and strength,the fatigue life of the gear box weld increased by 69.6% and 50.0% under full load straight line condition and 20% ratio of bend condition,respectively,compared with the original one-sided fillet weld of the frame.It can effectively improve the overall fatigue strength of bogie frame and provide reference for practical engineering application.