Research On Fracture Mechanism Of The Integrated Droppers Body Used In High Speed Railway

The hanging string is a key component of the high-speed railway contact network connecting the bearing cable and the contact line.It plays the dual role of force bearer and current carrier.During the process of installation,the length of the hanging string at different positions should be adjusted to keep the contact line and the train at a constant distance,ensuring the normal flow of the train and reducing the impact of the pantograph on the contact net.The total mileage of high-speed railway in our country continues to increase;the environment of constructing railway is complex and changeable;the speed of railway operation continues to increase.Therefore,there are higher requirements on the overall performance of the hanging string.In recent years,with the increase of the service years,the breakage of the hanging strings used in the high-speed railway occurred from time to time,which brings a lot of troubles to the operation of the high-speed railway.Therefore,exploring the internal and external causes of the breakage of the hanging string with the purpose of ensuring the normal and safe operation of high-speed railway is of great significance.In this paper,the crimping type overall hanging string is taken as the research object.Through the research on the fracture of the line body including observation,composition analysis,finite element simulation as well as friction and wear test,pulse current action mechanism analysis,etc.,the cause of breakage of the hanging string is systematically studied.By conducting the observation and composition analysis on the failed chord fracture morphology,it is found that the fracture of the hanging string is the result of a combination of factors:stress concentration,friction and wear,low cycle fatigue,electro-plastic effect,tensile force,environmental corrosion,and material defects.These influencing factors interact with each other,and eventually leads to the fracture of the overall hanging string body.The finite element analysis software ANSYS Workbench was used to simulate the stress distribution between the hanging strings.The analysis results show that there is a relatively obvious stress concentration phenomenon between the hanging string strands and between the filaments.In order to analyze the contact state between the chords,an orthogonal contact model was introduced.By changing the contact load and the depth of contact,the distribution of stress between filaments under different contact conditions was analyzed.On the friction and wear tester,the effects of different contact loads and sliding speeds on the friction coefficient and wear depth of copper-magnesium alloy suspension materials were investigated by means of orthogonal contact friction.The study found that the friction coefficient of copper-magnesium alloy suspension wire materials is not constant.It changes with the contact load and sliding speed of the contact surface.When the contact load rises and the sliding speed increases,the friction coefficient of the hanging string material will decrease and the wear depth will also change.Under the condition of electrifying,the tensile test of the hanging string body is carried out.It is found that the magnitude of the pulse current changes the deformation resistance of the material and changes its mechanical tensile properties and plastic deformation ability.The pulse current of the same parameters was applied to the same hanging string material for pretreatment.It was found that the stress-strain curve of the hanging string material changed regularly under different pretreatment time.As the pretreatment time increased,the tensile strength of the material decreased.The plastic deformation is enhanced and the recrystallization behavior occurs inside the material.According to the technical requirements of China Railway Industry Standard TB/T20174-2010 electrified contact network parts test method,the overall scheme of the fatigue test for hanging string is formulated.It uses eccentric wheel form in order to meet the vibration state of the hanging string at different amplitudes as far as possible.