Analysis Of Fracture Reason Of DT-Ⅲ Type Fastener Clip

Each part in fastener system plays an irreplaceable and important role.Because of the high manufacturing accuracy of fastener parts,the requirements for installation and use environment are also stricter.On the track of high-speed train operation,the damage and failure of fastener parts will reduce the overall function of fastener,and the safety of running will also be affected.From January 2017 to July 26th,there were 221 breakage of bullet strips on line 11 of Shenzhen urban rail transit,with a ratio of 0.62 per thousand damage and a discontinuous fracture.Among them,200 ballistic strips were damaged in rail corrugated zone,accounting for 90.4%of the total damage;21 ballistic strips were damaged in non-rail corrugated zone,accounting for 9.6%of the total damage.The elastic bar is the main component to realize the function of the fastener system.Its failure often occurs during its use,resulting in intensified wheel rail forces,accelerated damage to all parts of the vehicle and track,and even endangers traffic safety.In order to achieve the purpose of safe and stable operation of the train,it is necessary to study the fracture problem of the elastic strip at the scene.The rail corrugation or wheel polygon generated by a certain driving section has a relatively constant wavelength,and the relative speed of the train and the train running together determines that the violent interaction between the wheels and tracks is concentrated in a certain frequency range.At the same time,due to the relatively large axle load and high speed,the vibration load generated by the wheel rail interaction will have extremely high energy in the frequency range,and will be transmitted to the clip on the rail bottom by rail.At this time,if the frequency of vibration load is close to the natural frequency of the elastic bar assembly,it will cause the resonance of the stripe,resulting in the fracture of the elastic strip.This paper takes DT-Ⅲ fastener spring of Shenzhen Metro Line 11 as the research object,establishes numerical simulation calculation model by NX software,simulates the actual working state of Ⅲ spring in fastener system with finite element method on the basis of non-linear contact theory,theoretically analyses the modal characteristics of spring in free state and installation state,and analyses the manufacturing error of spring.At last,the vibration characteristics of the elastic rod under the actual working condition are tested and analyzed.The analysis and test results confirm each other,and put forward some related suggestions and preventive measures.The main conclusions are as follows:(1)When the elastic bar is assembled,the hammering method is applied to the excitation.If the indoor test is carried out,the laser sensor and the sound pressure sensor are the preferred vibration pickup equipment.If the field test is carried out,the acceleration sensor should be selected.(2)In the free state,the Ⅲ type bar has four modes in the 0～2000Hz range.In the assembly state,the Ⅲ type stripe has a two order mode in the 0-2000Hz range.(3)In the range of manufacturing tolerances,the modal frequencies of the same order of the Ⅲ type elastic bars decrease with the increase of the front arch large arc arch height H1,the rear arch small arc arch height H2 and the length L,and increase with the increase of diameter.(4)In the assembled state,the modal frequencies of the same order of the Ⅲspring are negatively correlated with the length of the insertion of the iron cushion plate into the middle limb.(5)The sensitive frequency range of the Ⅲ type stripe under normal assembly state is 706.70～798.08Hz.(6)According to the test section,the main frequency of the wave mill is 30mm-50mm,and the sensiti-ve frequency of the stripe is 706Hz minimum.In order to avoid resonance,the speed of the train is not greater than 75km/h.(7)When the wheel rail force excitation frequency is close to or consistent with the natural frequency of the elastic strip,it will cause the resonance effect of the elastic bar,and the vibration energy of the bar will increase sharply,resulting in the fracture of the elastic strip.