| Most of the metro tracks in China use the fastener system to provide track flexibility.However,with the gradual expansion of cities,people’s rhythm of life continues to grow.The increases the requirements for the speed of metro trains,passenger load,and travel interval,and results in frequent track structural damage problems.Thus,many track fasteners began to have broken anchor bolts,which seriously affected the normal operation of the metro and posed a huge threat to traffic safety.Therefore,this paper studies the fracture problem of anchor bolts of metro e-clip fasteners.The main research contents are as follows:(1)Field investigation and test.This paper investigates and tests the typical fracture section of the anchor bolts.According to statistics,it is found that the anchor bolt fracture problem mainly occurs on the inner side of the inner rail fastener in the curved section,with much concentration on the points of the spiral to curve.The bolt fracture surfaces have obvious fatigue crack source,crack propagation,and final rupture regions,which can basically be regarded as fatigue failure.Subsequently,a torque wrench is used to test the installation torque of the anchor bolts in the curve section,and it is found that there are many loose or over-tightened bolts on site.In order to obtain the relationship between the installation torque and the pre-tightening force of T30 bolts,needle strain gauges are used to measure the strain of the bolts during the installation process.Finally,the dynamic response of the track during the vehicle operation is tested.It is found that there is rail corrugation with a characteristic wavelength of about 50 mm in this section.(2)Establishment of the fastener analysis model.Based on field investigation and vehicle-track coupling dynamics,this paper uses multi-body dynamics software UM to establish a vehicle-track coupling dynamics model for curved sections,and uses fieldmeasured rail corrugation as the irregularity in the model.In addition,based on the material elastoplastic constitutive and nonlinear contact theory,the finite element software ABAQUS is used to establish a refined model of the e-clip fastener according to the fastener designs.This model can more accurately reflect the stress state of each fastener component.(3)Vehicle-track dynamic response analysis in the curved section.After field investigation,some problems are identified in this section,such as uneven fastener stiffness,off-balance superelevation and rail corrugation.In order to explore the relationship between track dynamic response characteristics and anchor bolt fracture in curved sections,this chapter derives the corresponding relationship between bolt torque and fastener assembly stiffness and simulates and analyzes vehicle and track dynamic responses under different conditions.It is found that the inner rail wheel-rail lateral force has a load peak of about 20 k N at the points of the spiral to curve,and it maintains a relatively high level in the round curve section;appropriately increasing the driving speed and timely grinding the steel rail can effectively reduce the lateral load vibration of the inner rail.(4)Fatigue life calculation and crack growth simulation of anchor bolts.Through the analysis of the fastener refined model,it can be seen that there is a significant stress concentration in the nut when the anchor bolt is in service;the fatigue analysis software FE-SAFE found that the fatigue life of the anchor bolt is affected by its installation torque and the lateral load of the wheel and rail.When installing anchor bolts in this section,the installation torque should be controlled at least 150 k N·mm;the bolt cracks initiate at high-stress positions,and expand in the direction of maximum shear stress at the initial stage of expansion,and the medium-term expansion direction is perpendicular to the principal stress direction.Later,due to stress and strain exceeding the material limit,the bolt fractures under static load.(5)Improvement measures are proposed.To avoid the continuous loosening of bolts,it is necessary to increase inspection frequency,formulate a reasonable retightening cycle,and ensure the quality of spring washers and anchor bolts;strengthen the loosening-proof ability of bolts,such as increasing the installation torque to 250 k N·mm in dangerous sections,using double spring washers,and so on;improve the wheel-rail interaction,such as grinding the rail in time and increasing the vehicle speed appropriately;replace grade6.8 bolts and so on.There are 128 figures,33 tables and 88 references. |
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