Vibration Fatigue Theory And Experimental Research Of Clips For Damping Fasteners In Small Radius Curves Of Subway

After several years of operation in the Chinese subway vibration reduction section,rail short-wave corrugation will develop in the small radius curve section.This will cause high-frequency vibration of the wheel and rail,resulting in fatigue failure of the fastener clips.In severe cases,the clips will splash and hit the car’s body,jeopardizing the safety of driving.Therefore,there is an urgent need to study the fracture mechanism of the fastener clips,to provide theoretical guidance for the design of the track structure and the effective control of maintenance.In this paper,based on the refined finite element model of the revised damping fastener system,combined with the rigid-flexible coupling dynamic model of the curved section,the vibration fatigue damage of the clip in the curved section is analyzed.Then,the high and low-frequency composite fatigue test of the clip is designed.And a new mean stress correction model that can take the clip line shape first-order is proposed.Finally,based on this model,the vibration fatigue characteristics of the clips in the curved section under different working conditions are obtained.The main conclusions of the paper are as follows:(1)The maximum equivalent stress of the clips in the normal installation state is 1410 MPa.It appeared on the inner side of the small arc in the inner arch of the clip,which was consistent with the site of the fracture.The first-order mode shape of the clip is the vertical and lateral combined vibration of the large arc of the front arch and the toe end.The first-order natural frequency is around 806 Hz.(2)The influence of rail short-wave corrugation on the vibration energy of the fastener clip is mainly concentrated in the bandwidth of 700～875Hz.The vertical force of the wheel and rail reduces the stress of the inner and outer rail clips and reduces the elastic range.The lateral force and overturning angle increase the working edge stress of the outer rail clip and decrease the non-working edge stress,so that the inner rail clip working edge stress first increases and then decreases,and the non-working edge stress first decreases and then increases.The calculation shows that the vibration fatigue damage of the clip in the curved segment is larger than that of the straight and the alleviation curve segment.(3)When the external excitation frequency is close to the natural frequency of the clip,the clip appears dynamic amplification.There is a certain error between the traditional mean stress correction model and the high and low-frequency composite fatigue test results of the clips.The reasons for the existence of errors can be roughly divided into the following aspects: material processing technology,stress conditions,test frequency,and line size.Considering the test results comprehensively,a mean stress correction model considering the clip line shape is proposed.(4)With the increase in vehicle speed,the passing frequency of rail corrugation increases.This aggravates the stress concentration at the small arc of the inner arch of the clip,which further increases the cyclic stress of high frequency and low amplitude.As the speed increases,the linear damage of the inner rail of the curve decreases,and the outer rail increases.However,the influence of the change of the curve radius on the vibration fatigue life of the clip is lower than that of the speed change.