Effect Of Crimping Method Of Clamp Tube On Fretting Fatigue Of Integral Dropper

Fretting fatigue exists widely in automobile,railway,aerospace,electrical and other fields.Fretting fatigue will accelerate the initiation and propagation of cracks in the damage zone of mechanical parts,which will eventually reduce the service life of mechanical parts and cause them to fail in advance.The dropper is one of the key parts in the catenary system of high-speed railway.It is of important reference value and guiding significance for the protection of the dropper against the fretting damage to carry out the current fretting fatigue test on it and reveal its damage mechanism.In this thesis,the integral dropper is taken as the research object.Firstly,the static simulation of the dropper is carried out by ABAQUS,and the reasons for the damage of the dropper are compared and analyzed from three aspects: preload,inter strand wear of dropper,and pressing of clamp tube.Then,the w+b fretting fatigue test machine with independently designed fretting fatigue device was used to test the bending fretting fatigue of the integral dropper with different pressing methods of.clamp tube The microcharacterization of the clamp tube and the dropper were analyzed by means of stereomicroscope(SM),scanning electron microscope(SEM),energy spectrometer(EDS),white light interferometer(WIL)and X-ray photoelectron spectroscopy(XPS).The main conclusions are as follows:(1)Through the ABAQUS finite element simulation,it can be co ncluded that the preload of the dropper will cause surface stress of the copper wire.With the preload increases,the surface stress becomes greater.There is also a high value of contact stress between adjacent copper wires.The relative displacement will cause elliptical wear spots on the surface of the copper wire,and the plastic deformation will be slight;the pressing of the clamp tube will cause obvious stress concentration,and the copper wire will have obvious plastic deformation.(2)According to the relevant regulations of railways,the tensile test was carried out on the dropper of the clamp tube with different compression distance.What meets the criteria were reverse compression distance with 4.8 mm,5.0 mm and forward compression with 5.0 mm.The experimental results show that the fretting fatigue life ranges from high to low: 4.8 mm reverse compression>5.0 mm forward compression >5.0 mm reverse compression.(4)After the dropper has undergone bending fretting fatigue test,it has broken at the position of the clamp tube,and the fracture profile of the strands is complicated.The main features are crack source,secondary crack,and dimple.(5)The damage between the strands is severe,and the damage characteristics are different in different areas.When the damage position is close to the clamp tube,the relative displacement between the strands is small,the stress between the strands is large,and the grinding pit depth is deeper.On the loading position of bending fatigue load,the relative displacement between the lines is the largest,the stress between the lines is at a medium level,so the length of the grinding pit is long;when the distance to the loading position of the bending fatigue load is far,the displacements and stresses between lines are small,and the wear between the them in this area is slight.(6)The fretting fatigue life of the dropper is different at different current strengths.As the strength of the current increases,the life of the dropper decreases.When the current intensity is 200 A,raindrop-like wear debris were found on the surface of the damaged area of the clamp tube.This is a typical current-carrying wear characteristic,which is mainly caused by the arc discharge phenomenon.The increase of the current intensity exacerbated the oxidative wear of the copper wires.A large number of debris were observed on the surface of the damaged area at the current intensity of 100 A and200 A,and the surface oxidation degree increased with the increase of the current intensity.The increase of the strong current will also increase the temperature of the copper wire surface and promote the production of CuO...