| With the large-scale construction and operation of China’s rail transit,the safety report on the fracture of rail fastening clips is constantly seen.Fastener system is the most important connection in the railway track structure.On the one hand,the failure of fastening clips will affect the stability of the rail.On the other hand,it will bring great hidden danger to the traffic safety due to the breaking and splashing of fastening clips caused by the abnormal load.Obviously,the traditional fatigue design method of the fastening clips of railway fastener can only meet the fatigue fracture problem in the normal life period,which can not well reflect the abnormal high-frequency fracture problem caused by the rail corrugation.In order to explore the fatigue failure evaluation criteria of rail fastener system under special load conditions,firstly,the load modes of rail fastener system(i.e.displacement and acceleration)under normal fatigue load or abnormal high-frequency impact load of train are analyzed based on the statistical data characteristics of rail corrugation measured on site and vehicle-track coupled dynamics.Then,a three-dimensional finite element model of fastener system reflecting material/geometric nonlinearity and contact nonlinearity between components is established to explore and analyze the static/dynamic loading mode of fastening clip in service and the influencing factors of abnormal fracture.Finally,the fatigue crack initiation mechanism of fastening clip under long-term train load is analyzed based on the multiaxial fatigue theory of critical plane and linear fatigue damage accumulation theory,and the fatigue crack initiation life of this type of clip under abnormal load conditions is predicted.The main conclusions are as follows:Through the comparative analysis of the load modes of the rail fastener system under the normal fatigue load and abnormal high frequency impact load of the train,it is found that rail corrugation can significantly increase the vertical and horizontal vibration acceleration of the rail and the random dynamic load of the wheel rail.The increase rate of wheel-rail response enhances significantly with the increase of the train operating speed,and the lateral vibration acceleration of rail in the curved section is more sensitive than in the straight section.From the perspective of frequency domain,the main frequency of excitation frequency of wheel rail system is mainly affected by the wave length of rail corrugation and the operation speed of train.According to the field operation of this paper,the main frequency induced by rail corrugation is about 833 Hz.According to the characteristics of fatigue brittle failure and the finite element analysis,it is found that the fracture of fastening clip is mainly subjected to the composite loading mode of maximum tensile shear stress,so the maximum principal stress criterion can better evaluate the loading mechanism of fatigue crack of fastening clip.As for type DT-III fastening clip,the toe load of fastening clip is mainly related to the installation range,while the insertion depth of middle limb and the rigidity of rail pad have little influence on buckle pressure.However,when the installation range and the insertion depth of the middle limb are too large,stress concentration will occur on the inner surface of the small arc of the back arch of the fastening clip,resulting in early damage and cracks.The main factor that affects the natural frequency of the fastening clip in service is the installation range,followed by the rigidity of the rail pad,and the insertion depth of the middle limb of the fastening clip has little effect on the natural frequency.In fact,the natural frequency is affected by the dynamic displacement of the rail when the subway train passes.According to the site operation situation,the dynamic natural frequency of the fastening clip is about738～882 Hz,where the resonance phenomenon is prone to occur under the dynamic load induced by the rail corrugation.Although the rail corrugation has little effect on the dynamic natural frequency of the fastening clip,the inertial force effect of the abnormal vibration acceleration induced by it may lead to the problem of abnormal fracture and splash of the fastening clip.The fatigue crack initiation life of fastening clip is greatly affected by the toe load and vibration acceleration.Specifically,the inertial force effect caused by the vibration acceleration under the resonance condition of the fastening clip is one of the main reasons for initiating the initial fatigue crack initiation and subsequent abnormal fracture problem. |
PDF Full Text Request