Study On The Service Performance Of The Track Connecting Bolt Of The Medium-Low Speed Maglev Traffic Track

With the progress and development of society and the continuous development of maglev transportation technology,the medium-low speed maglev transportation system has gradually become a new type of urban rail transit.In the medium-low speed maglev structure,the track structure is directly affected by electromagnetic force,and the track connecting bolt connecting the track and the sleeper has become the key of the maglev track structure.Aiming at the problem of the service performance of the connecting bolts of the medium-low speed maglev track,according to the actual situation of the mediumlow speed maglev track structure and the specific size of each component in the structure,this paper uses finite element software to establish the finite element model of the medium-low speed maglev track structure,and studies the service performance of the connecting bolts of the track in the medium-low speed maglev structure,with a view to the construction of the medium-low speed maglev line and provide theoretical reference and reasonable suggestions for the design and maintenance of maglev transportation.This paper mainly studies the following aspects:(1)Establish the finite element model of bolt connection structure and the finite element model of maglev track structure and verificationThe finite element model of bolted connection structure and the finite element model of medium-low speed maglev track structure are established by using the finite element software.The former includes threaded bolts and upper and lower clamps;the latter includes track model,bolt entity model,sleeper model and track bearing block model.Each model is simplified and replaced properly according to the actual size of the site and the comprehensive consideration of the actual operation conditions,and the S1 line of Beijing maglev is tested on site,and the reliability of the structure model of the mediumlow speed maglev track established in this paper is verified according to the field test data.(2)Study on mechanical properties of bolts in bolted structureThe finite element analysis software is used to simulate the pre tightening process of high-strength bolt connection structure with screw thread and various situations under different alternating loads.According to different bolt standards,the strength of highstrength bolt in this structure is checked and found that the bolt meets the standards.The bolt connection structure under pre tightening state is analyzed and found that the maximum stress points are all out at the first circle contacting the bottom of the thread,the bolt load is mainly borne by the first three circles of thread;the stress at the top of the thread with the same number of turns is smaller than that at the bottom of the thread,and the Mises stress of the thread decreases with the increase of the number of turns;at the same time,the pre tightening process of the bolt structure with different pre tightening forces is analyzed,with the decrease of the pre tightening force,The Mises stress of each part of the thread also decreases gradually;the analysis and calculation are carried out for various situations when the bolt structure bears the alternating load with different amplitude and frequency.With the increase of the alternating load amplitude,the cumulative plastic strain of the thread bottom increases,and the relative sliding amplitude of each circle of the thread surface node increases,the bolt is more likely to be damaged;with the increase of the alternating load frequency,the thread is more likely to be damaged with the increase of cumulative plastic strain at the tooth bottom,the relative slip amplitude of the joint on the thread surface increases,and the bolt is more likely to be damaged.(3)Study on the static performance of the medium-low speed maglev track connecting boltBased on the finite element model of medium-low speed maglev track array structure,the static performance of bolts with different vehicle weight and different bolt grades is analyzed under normal installation conditions,and the stress of bolts at different positions is compared and analyzed.It is found that the stress of bolts inside the track array is greater than that of bolts outside the track,and the bolts inside the track array are more likely to be damaged.As for the analysis of bolts of different grades,it can be known that the use of high The grade bolt is conducive to improving the reliability of the mediumlow speed maglev structure;for the analysis under different vehicle loads,it can be known that the maximum Mises stress of the bolt under full load is greater than that under no load,but there is not much difference,which shows that the vehicle weight has little influence on the bolt under the static load of the train.(4)Study on the dynamic performance of the connecting bolt of the medium-low speed maglev trackBased on the finite element model of the medium-low speed maglev track structure,the dynamic load of each bolt,i.e.bolt axial force,is analyzed under the action of the actual dynamic load of the train.The analysis is mainly aimed at different train operation speed,different pre tightening force and different bolt looseness.When the train operation speed is different and the train speed is 60km/h,the bolt axial force is the largest and the bolt is most likely to be damaged;when the bolt preload is different,the larger the preload is,the smaller the dynamic load of the bolt will be.According to the analysis of different bolt loosening conditions,it is found that the normal installation of the train,the inside bolt at the direction of train arrival loosening,and the sleeper anchor bolt loosening three conditions have little impact on other bolts except the inside bolt at the direction of train arrival.For this bolt,when the bolt loosening,the axial force of the bolt increases obviously,and the sleeper anchor bolt loosening has little effect on this bolt,so the inside bolt at the direction of train arrival loosening will seriously threaten the safety of the train operation,and the inside bolt at the direction of train arrival loosening has little effect on the connecting bolt of the track.(5)Analysis of the fatigue performance of the connecting bolt of the medium-low speed maglev trackThe fatigue performance analysis of the medium-low speed maglev track structure was carried out,and it was found that the bolt at the direction of train arrival had the greatest impact on the fatigue life of the medium-low speed maglev track structure.When the bolt at the direction of train arrival was loosened,the medium-low speed maglev track structure had the smallest fatigue life is significantly reduced.For different speeds of the bolt at the direction of train arrival loosening,the fatigue life decreases the most at high speeds.At the same time,when high-grade bolts are used,In the case of the bolts at the direction of train arrival are loose.the fatigue life of the bolt can be significantly extended.