Experimental Investigations On The Wheel/Rail Adhesion At High Speeds And Adhesion Enhancement

High-speed railway in China has gradually extended to the isolated areas with few people,large slopes,luxuriant vegetation,high humidity,complicatedly geographical environments and other factors etc.,all resulting in an urgent problem for solving wheel/rail adhesion.Traction/braking and normal operational safely of high-speed trains required the better wheel/rail adhesion.The method of angular velocity is mostly reported for many scholars to carry out a lot of experimental studies on wheel/rail adhesion and adhesion enhancement,but linear velocity of adhesion enhancement test is still under the meidum low speed between 0.8 and 120 km/h,due to the limitation of test devices.In this thesis,the wheel/rail high-speed rolling contact fatigue two-disc testing machine newly built in the National Laboratory of Modern Rail Transit(NLT),is used to systematically test both the wheel/rail adhesion characteristics at high speed and the measures of adhesion enhancement under low adhesion conditions.The maximum linear velocity is up to 200 km/h during the tests,which will offer foundational data for ensuring the adhesion control of high-speed trains and their safe,reliable and low-cost operations.The main purposes for thesis are to perform the low adhesion testing caused by the third-body materials such as water,oil and leaf contamination between wheel and rail,and the effect of sand used for adhesion enhancement.The necessity of high-speed wheel/rail adhesion research and the measures of adhesion enhancement are firstly introduced in the first chapter detailly,based on which the background and meaning of wheel/rail adhesion testing and the current research status at home and abroad.In the second chapter,the method,main parameters and experimental rules of high-speed rolling contact fatigue two-disc testing machine are described detailly.Chapter 3 shows that the effect of the third-body materials such as water,oil and leaf contamination between the wheel and rail on adhesion coefficient,some parameters such as different speed,creepage,axle load and temperature all are also considered.The results show that the adhesion coefficient always rises firstly to the maximum value of 3%(the saturated creepage),and then begans reducing slightly to an constant value when the creepage increases.The third-body materials such as water,oil and leaf contamination can significantly reduce wheel/rail adhesion coefficient leading to low adhesion problems.For example,At the axle load of 14 t and speed of 200 km/h,water,oil and leaf contamination can result in the decrease of wheel/rail adhesion coefficient to 0.064,0.049,0.055,respectively.The influence of axle load on the adhesion coefficient is relatively small in oil conditions,for example,when the axle load increases from 12 t to 16 t,the rising amplitude of the adhesion coefficient is only 0.01.Water temperature has the large impact on the adhesion coefficient,as the water temperature drops from 35? to 0.5?,the adhesion coefficient decreases from 0.071 to 0.045,i.e.,the adhesion coefficient decreases as the water temperature decreases.When the testing speed is variation from 50 to 200 km/h under the third-body materials,the adhesion coefficient decreases as the speed increases and among at the presence of the third-body materials,the adhesion coefficient of the water is the largest,the next leaf contamination,and the least the oil.The chapter 4 carried out the test of the adhesion enhancement effect of sand under the third-body materilas such as water,oil and leaf contamination.The results show that under the water conditions,the adhesion coefficient increases with the increase of particle size of the sand and the amount of sand spraying,the optimal particle size is 0.85~1 mm and the amount of the optimal sand spraying is about 40 g/min.Sand can significantly rise the adhesion coefficient under the third-body materials between wheel and rail.For example,based on the best parameters sanding when the axle load of 14 t and the speed of 200 km/h,the adhesion coefficient with the water,oil and leaf contamination can increase to 0.25,0.18,and 0.22,respectively.When the testing speed is between 50 km/h and 200 km/h,the variational trends of the adhesion coefficient with the testing speed is not related to the sand.It should also be noted that the sand can cause a lot of pitting damage on wheel/rail surface,and significantly aggravate the roughness results in adhesion enhancement.Based on the testing results mentioned above,the parameters of the numerical model of three-dimensional high-speed wheel/rail adhesion is derived in the fifth chapter,appling to the testing machine.It can predict the extreme cases(two disc testing machine may not be operate due to the dangers)under the third-body materials such as water,oil and leaf contamination,which can provide a safe and reliable method for the study of wheel/rail adhesion characteristics.Finally,the conclusions and prospects are given.