Superlubricity has been developing very rapidly in recent years as a new and important area in tribology. Many new phenomena and materials, as well as some new mechanisms in both liquid and solid superlubricity have been obtained. In liquid superlubricity, tens of new kinds of liquids with superlubricity have been found (e.g., water-based liquids, oil-based lubricants, and liquids combined with additives of two-dimensional (2D) materials that exhibit very good superlubricity properties under high pressure). In the field of solid superlubricity, more materials with superlubricity have been observed, including graphene-to-graphene surfaces, highly oriented pyrolytic graphite to graphene surfaces, and heterostructure surfaces where a friction coefficient as low as 0.00004 has been obtained. However, superlubricity is still under laboratory research. What is the future of superlubricity? What is the barrier restricting superlubricity from industrial applications? How do we transfer superlubricity from scientific research to industrial application? These questions and application fields of superlubricity in near future have been analyzed, and the concept of “superlubricitive engineering” has been proposed in the present work.

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Superlubricitive engineering—Future industry nearly getting rid of wear and frictional energy consumption

Polygonisation is a common nonuniform wear phenomenon occurring in railway vehicle wheels and has a severe impact on the vehicle–track system, ride comfort, and lineside residents. This paper first summarizes periodic defects of the wheels, including wheel polygonisation and wheel corrugation, occurring in railways worldwide. Thereafter, the effects of wheel polygonisation on the wheel–rail interaction, noise and vibration, and fatigue failure of the vehicle and track components are reviewed. Based on the different causes, the formation mechanisms of periodic wheel defects are classified into three categories: (1) initial defects of wheels, (2) natural vibration of the vehicle–track system, and (3) thermoelastic instability. In addition, the simulation methods of wheel polygonisation evolution and countermeasures to mitigate wheel polygonisation are presented. Emphasis is given to the characteristics, effects, causes, and solutions of wheel polygonisation in metro vehicles, locomotives, and high-speed trains in China. Finally, the guidance is provided on further understanding the formation mechanisms, monitoring technology, and maintenance criterion of wheel polygonisation.

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Polygonisation of railway wheels: a critical review

Prediction of wheel and rail wear under different contact conditions using artificial neural networks

This paper presents an investigation into the mechanism of polygonal wear of metro train wheels through experiments conducted at field sites. The experiments comprise dynamic behaviour test of vehi...

An investigation into the mechanism of the out-of-round wheels of metro train and its mitigation measures

Friction and wear maps of copper metal matrix composites with different iron volume content

The purpose of this research was to study the braking behaviors of Cu-based composite pad under real operating conditions of high-speed train. A series of pad-on-disk braking tests was performed with the initial braking speed (IBS) from 80 to 380 km/h. Results showed that the coefficient of friction (COF) of the brake pad demonstrated a three-stage feature with the increase in IBS. It decreased from 0.395 to 0.358 with the increase in IBS from 80 to 200 km/h, then increased to 0.398 when IBS reached 320 km/h; and fell again to 0.379 at 380 km/h. Similarly, the pad also displayed three wear regimes as IBS increased, i.e., (1) mild wear (80–160 km/h), (2) moderate wear (200–250 km/h), and (3) severe wear (300–380 km/h). Surface morphologies and phase analyses indicate that the evolution of the COF mainly depends upon the state of friction film. The formation or completion of friction film regularly contributes to a lower COF and wear rate, while the destruction of friction film results in a higher COF and wear rate. Besides, the “lubricants” induced by high braking temperature are also responsible for the change in the COF. As IBS increased, the key wear mechanisms changed from abrasion, plowing, and oxidation to delamination at 250 km/h.

The Braking Behaviors of Cu-Based Metallic Brake Pad for High-Speed Train Under Different Initial Braking Speed

Experiments were conducted at field sites to investigate the mechanism of the polygonal wear of electric locomotive wheels. The polygonal wear rule of electric locomotive wheels was obtained. Moreover, two on-track tests have been carried out to investigate the vibration characteristics of the electric locomotive's key components. The measurement results of wheels out-of-round show that most electric locomotive wheels exhibit polygonal wear. The main centre wavelength in the 1/3 octave bands is 200 mm and/or 160 mm. The test results of vibration characteristics indicate that the dominating frequency of the vertical acceleration measured on the axle box is approximately equal to the passing frequency of a polygonal wheel, and does not vary with the locomotive speed during the acceleration course. The wheelset modal analysis using the finite element method (FEM) indicates that the first bending resonant frequency of the wheelset is quite close to the main vibration frequency of the axle box. The FEM...

Experimental investigation into the mechanism of the polygonal wear of electric locomotive wheels

This paper presents a detailed investigation of out-of-round electric locomotive wheels through extensive measurement conducted at field sites. More than 2000 wheels, of seven types of locomotives ...

Zefeng Wen

Papers

Polygonisation of railway wheels: a critical review

The Braking Behaviors of Cu-Based Metallic Brake Pad for High-Speed Train Under Different Initial Braking Speed

An investigation into the mechanism of the out-of-round wheels of metro train and its mitigation measures

Experimental investigation into the mechanism of the polygonal wear of electric locomotive wheels

Measurement and assessment of out-of-round electric locomotive wheels