Study On Load And Fatigue Failure Behaviour Of Dropper In High-speed Catenary

High-speed railways have become an important part for the development of rail transit due to the advantages such as fast speed,high efficiency,energy saving,environmental protection,safety and comfort.The catenary is the only source of traction power for high-speed EMUs.It is both a transmission line and a mechanical slideway for the pantograph of an EMU.It consists of contact suspension and support and positioning structures.In contact suspension,the dropper connects the contact wire with the messenger wire or the elastic wire.It plays the role of stabilizing the geometric parameters of the suspension in the space and determining the position of the contact wire above the track.It is a key component of the high-speed railway catenary.The number of droppers is huge.According to the mileage of China's high-speed railway as of 2019,it can be estimated more than 8 million droppers are in service currently.Once one of them fails,it may cause a pantograph to collide with it and cause a pantograph-catenary accident.In some cases,the equipment is damaged.And in other cases,the train may stop,which affects the normal operation of the high-speed railway.The current research on the onsite load and characteristics of the dropper is not enough to fully support the study of the fatigue life.The testing methods for the fatigue performance of the droppers need to be improved.In addition,there is also a lack of research on the fatigue life models of the droppers.Therefore,it is urgent to carry out the research on the failure behavior of the dropper integrated with the pantograph-catenary system,component load characteristics,fatigue test methods,failure analysis,and fatigue life model.The thesis studies the transient slack and lateral vibration of droppers.Through pantograph-catenary dynamic simulation,the law of dropper slack is statistically measured.The non-contact measurement method is used to measure and characterize the lateral vibration behavior of droppers.Based on the theory of string vibration,the lateral vibration mechanism of the dropper is revealed.Studies have shown that during the dynamic action of pantographcatenary,transient slack of the droppers is common.The degree of dropper slack is related to the position of the catenary,train speed,and pantograph characteristics.In order to establish a model that can simulate the actual vibration behavior of a dropper with a small amount of calculation,a multi-rigid body dynamics model is established in this paper.The model is able to simulate the transient slack and lateral vibration of a dropper,and its effectiveness is verified by experiments.This computer simulation method makes the overall vibration of the dropper realized.On one hand,compared with the dropper model which is simplified as a single unit,this method can reflect more details of the dropper vibration.On the other hand,compared with the full solid modeling method of the stranded wire structure,the calculation amount of this method is small and the calculation speed is fast.Based on this,the influence of the dropper vibration boundary conditions and its properties of dropper itself is studied by combining simulation and experiments,including the tensioning speed of the dropper,the compression amplitude,and the load holding time,dropper length,upper spring stiffness,messenger wire simulation mass,etc.Regarding the fatigue test method of droppers,this article does not limit to the standard,and proposes a dropper fatigue test method that the lower part of the dropper is driven by a linear motor,and uses springs and other buffers to simulate the buffering of the upper end.Compared with the test methods and devices stipulated in the existing standards,the test method of driving the lower end of the dropper is closer to the actual working condition.The lateral vibration process of the dropper can be controlled,and the longitudinal tensioning speed of the dropper can be also controlled.The frequency no longer affects the fatigue load of the droppers.The long-term stability of the fatigue load is higher.And the test device has a longer life.In terms of the fatigue failure mechanism and life model of the dropper,and based on the overall fatigue test of the dropper,this paper analyzes the failure process of the main string of droppers from a microscopic perspective,and proposes the deformation of the strand to cause the wear between the strands,thereby accelerating the main string breaking.The fatigue failure mechanism of the dropper,meanwhile,a fatigue life model of the dropper based on the principle of damage accumulation under variable amplitude load is established.This model breaks the single evaluation of the number of tests in the traditional dropper fatigue test results.The load of the dropper fatigue test process is decomposed.The damage accumulation under different load levels is examined separately.A more specific damage characterization method is proposed in the field of dropper fatigue test.The study of the fatigue load and fatigue model of the dropper can provide important theoretical and technical support for the life prediction and health management of the highspeed catenary dropper.It can expect that transforming the maintenance method of catenary dropper from the current daily maintenance and regular maintenance to an accurate state maintenance.Thereby the risk of pantograph-catenary accidents caused by fatigue failure of the droppers can be greatly reducing.The work load of catenary maintenance can be greatly reducing.It has important guiding significance for improving the operational reliability and maintenance efficiency of the high-speed catenary.