Research On Fatigue Damage Characteristics Of Integral Droppers Under Double-Pantograph

With the development of high-speed and heavy-load railway trains,the use of double-pantograph to collect power has become a trend.However,this also makes the dynamic forces and vibration amplitudes that the droppers have to withstand more complex,resulting in frequent occurrence of wire and strand breakage,which seriously affects the safe operation of railways.Therefore,studying the mechanism and process of fatigue fracture of droppers under double pantograph conditions is of great research value for optimizing the service performance of droppers and extending their fatigue life.The main research contents and conclusions of the thesis are as follows:(1)A finite element model of the contact wire and pantograph was established,and the dynamic characteristics of the droppers under double and single pantograph conditions were analyzed through pantograph-wire coupling simulation.The results showed that under the action of double pantograph,the compression amplitude and dynamic force supported by the droppers were greater and lasted longer,making the droppers more prone to fatigue failure and fracture due to bending.(2)Numerical analysis was carried out on the droppers and clamping tube section.The analysis results showed that the area with the highest local stress was the droppers at the clamping tube,followed by the side wires of the integral droppers.The greater the stress on the copper wire,the greater the frictional force,making it more prone to fatigue cracks,which can weaken its resistance to bending fatigue.With the increase of fatigue cycles,the areas with high stress would break first.(3)Fatigue tests were conducted on droppers specimens using the self-built fatigue testing platform in the research group,and the bending fatigue life(S-N)curve was obtained.The study showed that the amplitude had the greatest influence on the fatigue life of the droppers,and the fatigue life of the droppers sharply decreased with the increase of amplitude.Scanning electron microscopy(SEM)and transmission electron microscopy(TEM)were used to observe the material at the micro level,and it was found that tiny holes,extrusion ridges,and intrusion grooves gradually appeared on the material surface as the fatigue cycles increased.After a certain number of cycles,these holes and intrusion grooves would generate micro cracks,which continued to extend towards the loading end,eventually leading to the formation of the main crack.With the increase of fatigue cycles,the main crack would continue to expand,ultimately causing the droppers to fracture.The main reason for this was bending fatigue.(4)The droppers specimens on the fatigue testing platform were subjected to electrification treatment,and the morphology and composition of their fracture surfaces were analyzed.The analysis results showed that the bending alternating load caused fatigue cracks to sprout on the surface of the droppers copper wire,and the current overload acted as a "catalyst",accelerating the oxidation and corrosion of the droppers surface,further expanding the cracks and weakening the droppers resistance to bending fatigue.The bending alternating load and current-induced plasticity cooperated with each other,jointly deteriorating the droppers fatigue life,and ultimately causing the droppers to fracture.