Study On Fatigue And Fracture Mechanism Of Non-Shoulder Fastening Spring Clip In Unballasted Track Of High-Speed Railway

As an important part of track structure,fastener system can maintain track geometry and provide elasticity and insulation.It is very important for fastener system to ensure the stability and safety of track structure.In recent years,with the increase of train speed,axle load of train and railway traffic volume,the fatigue and fracture problem of spring clips is becoming more and more serious,which restricts transportation efficiency and threatens driving safety.In this paper,based on static analysis,fatigue theory,fracture theory,sweep frequency analysis,I study the damage mechanism of spring clips,reveal the fracture cause,simulate the fracture process,predict the fatigue life of spring clips before and during the fracture process,and some optimization suggestions are put forward.The main work and conclusions are as follows:?1?Rail and WJ-7 fastener system 3D solid finite element model is established according to real size.Contact relations are ealed with nonlinear contact theory.60Si2MnA,the meterial of spring clips use the bi-linear material model.The mesh type of spring clips is C3D10I,which can improve the accuracy of stress results.The evaluation methodology of spring clip use the fourth strength theory?Mises criterion?as the evaluation index of clip strength and the third strength theory?Tresca criterion?as an auxiliary evaluation indicator of clip strength.The modal test using the reciprocation of acoustic and vibration is used to verify the correctness of the model.?2?To reveal the fracture mechanism of the spring clip from stress and strain views,static mechanical properties of the spring clip are researched systematically in various installation states,in various vertical displacement of rail and in various lateral displacement of rail.The spring clip in service is under combined stress of tension and compression,bending,twist,cut.In various installation states,in various vertical displacement of rail and in various lateral displacement of rail,the maximum Mises stress,the maximum shear stress and the maximum plastic strain of the spring clip all appear on the connection of the inner and the outer arc of the rear end of the spring clip.The maximum principal stress of spring clips appear on the outer arc of the rear end of the spring clip.The arc of the rear end of the spring clip is the area where the spring clip is likely to break.?3?The fatigue performance is analyzed when the spring clip is on the condition of different installed loads of 20kN,26.21kN,30kN,40kN and same history of vertical displacement of rail obtained by testing.The fatigue life prediction methods include the Basquin rule in the stress-life method?Goodman mean stress correction?,the Brown Miller criterion in the strain-life method?Morrow mean stress correction?,Miner linear fatigue damage accumulative theory,Rain flow counting method.the larger the installed load is,the lower the fatigue life of the spring clip has.The fatigue life is 10e10.1972 times,10e10.0903 times,10e10.0175 times,10e9.7717 times,10e9.5548 times using the Basquin rule?Goodman mean stress correction?,Miner linear fatigue damage accumulative theory,Rain flow counting method while the spring clip is in the elastic state.And the fatigue life is 10e13.4707 times,10e12.608 times,10e10.5285 times,10e10.0369 times,10e9.8812 times using the Brown Miller criterion?Morrow mean stress correction?,Miner linear fatigue damage accumulative theory,Rain flow counting method while the spring clip has plastic deformation.The contaction between the arc of the rear end of the spring clip and the iron pad,the outer arc of the rear end of the spring clip have low fatigue life.?4?The fracture process of spring clips and the fatigue life in the process of fracture are studied when a spring clip is in the state of same installed load?26.21kN?and various amplitudes of cyclic vertical displacement of rail?0?1?0mm,0?1.5?0mm,0?2?0mm?,various installed loads?20kN,26.21 kN,30 kN,40 kN?and same amplitude of cyclic vertical displacement of rail?0?1.5?0mm?based on the stress intensity factor theory,maximum circumferential stress theory,fatigue crack propagation theory?using the Paris formula?for crack fatigue propagation in the theory of fracture mechanics.The life of the fracture process of a spring clip will reduce with the increase of the installed load or the variation amplitude of cyclic loading.The fatigue life of the previous case is 194510 times,132420 times,88524 times respectively and the fatigue life of the latter case is 164422 times,132420 times,94282 times,52165 times respectively.The speed of fatigue expansion increases with the increase of the crack depth.?5?Based on the sweep frequency theory,optimized proposals from the point of view of installed load,density and modulus of elasticity are put forward combined with the excitation frequency in the range of 514Hz?578Hz caused by rail corrugation when the high speed train passes through the unballasted track.The spring clip is prone to generate resonance when the installed load is under load or severe overload.It's good for the spring clip in the state of slight overload.It's recommended that the installed load is in the range of 27-38kN.When the installed load is 26.21kN,It's recommended that the density is smaller than 6800kg · m^-3 or bigger than 12200kg · m^-3.And when the installed load is 26.21 kN,It's recommended that the modulus of elasticity is in the range of 156000?202000MPa or bigger than 225000MPa.