Effects of Friction Modifiers on Wheel and Rail Wear and Damage under Water Pollution Conditions

With the increase of passenger flow of subway vehicles, the running speed increases, the departure interval becomes shorter, and the wheel-rail wear and damage are aggravated, which affects the running performance and safety of rail transit. Friction modifiers (FM) for wheel-rail system friction control can effectively reduce wear and damage. However, the wheel-rail system is open and influenced by rain and other natural environmental factors. Aiming at the problem of water pollution at the interface of subway wheel-rail caused by rainfall and other factors, the GPM-60 friction and wear testing machine was utilized to carry out experimental research on the effects of different friction modifiers on wheel-rail wear and rolling contact fatigue damage under watery working conditions. In order to simulate the effects of three kinds of FM on wheel-rail wear and damage behavior under wear conditions, the wheel-rail specimens were pre-run together for 5 000 cycles in dry condition so that the surface of the specimens showed slight fatigue damage. Then, the wheel-rail specimens were continued for 40 000 cycles under each working condition. Wheel and rail samples were taken from CL60 wheel steel and U75V hot rolled rail, respectively. The experiment used three different water volumes: anhydrous, 0.6 mL/min, and 1.5 mL/min. It aimed to study the variations in wheel track adhesion coefficient, wear rate, plastic deformation, and wheel track damage. Three types of friction modifiers were tested: water-based FM, metal-based FM, and solid FM. The impact of water volume at the wheel-track interface on the performance of these friction modifiers was investigated. The results showed that the adhesion coefficient was about 0.49 in dry conditions. After applying three kinds of FM, the adhesion coefficient could be regulated in the range of 0.3~0.4. After adding water based on a friction regulator, the adhesion coefficient of the wheel-rail interface under the medium of water-based FM and metal-based FM did not vary much, fluctuating around 0.34 and 0.3, respectively. The coefficient of adhesion under solid FM media decreased significantly, down to 0.28, and showed an increasing trend with the increase in the number of cycles. The addition of water increased the wear rate of wheel, rail and total wear rate under the three FM media. With the addition of water, the surface damage of the wheel specimens under the three FM media increased significantly, the surface damage of the rail specimens increased slightly, and the thickness of the plastic deformation layer changed to different degrees. After adding water, the crack length and depth of wheel specimens under water-based FM and solid FM media increased, and the crack length and depth of wheel specimens under metal-based FM decreased. The rolling contact fatigue damage of the wheel specimens was aggravated by water intervention, and the "oil wedge effect" was the main reason for the severe rolling contact fatigue damage of the wheel specimens under water contamination conditions. The study's conclusions provided some theoretical support for the friction control of subway wheels and rails in rainy weather.