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Plastic-elastic Model for Water-based Lubrication Considering Surface Force

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Chinese Journal of Mechanical Engineering 2022年第5期35卷 208-218页

作者： Shuowen Zhang Mingbo Zhao Chenhui Zhang State key laboratory of tribology Tsinghua UniversityBeijing 100084China

Water-based lubrication is an effective method to achieve superlubricity,which implies a friction coefficient in the order of 10−3 or *** numerical,analytical,and experimental studies confirm that the surface force effect is crucial for realizing water-based *** enhance the contribution of the surface force,soft and plastic materials can be utilized as friction pair materials because of their effect in increasing the contact area.A new numerical model of water-based lubrication that considers the surface force between plastic and elastic materials is developed in this study to investigate the effect of plastic flow in water-based *** the complexity of residual stress accumulation in lubrication problems,a simplified plastic model is proposed,which merely calculates the result of the dry contact solution and avoids repeated calculations of the plastic *** results of the two models show good *** deformation reduces the local contact pressure and enhances the function of the surface force,thus resulting in a lower friction coefficient.

关键词： Numerical model Water-based lubrication Mixed lubrication Plastic model Superlubricity

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

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Friction 2020年第4期8卷 643-665页

作者： Jianbin LUO Xiang ZHOU State key laboratory of tribology Tsinghua UniversityBeijing 100084China

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.

关键词： superlubricitive engineering superlubricity liquid superlubricity solid superlubricity two-dimensional(2D)material lubrication

Simulation of Dual-Electrode Capacitively Coupled Plasma Discharges

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Plasma Science and Technology 2016年第12期18卷 1175-1180页

作者：路益嘉季林红程嘉 State key laboratory of tribology Department of Mechanical EngineeringTsinghua University

Dual-electrode capacitively coupled plasma discharges are investigated here to lower the non-uniformity of plasma density. The dual-electrode structure proposed by Jung splits the electrode region and increases the flexibility of fine tuning non-uniformity. Different RF voltages,frequencies, phase-shifts and electrode areas are simulated and the influences are discussed. RF voltage and electrode area have a non-monotonic effect on non-uniformity, while frequency has a monotonic effect. Phase-shift has a cyclical influence on non-uniformity. A special combination of 224 V voltage and 11% area ratio with 10 MHz lowers the non-uniformity of the original set（200 V voltage and 0% area ratio with 10 MHz） by 46.5%. The position of the plasma density peak at the probe line has been tracked and properly tuning the phase-shift can obtain the same trace as tuning frequency or voltage.

关键词： dual-electrode non-uniformity capacitively coupled plasma fluid model

Drag reduction methods at solid‒liquid interfaces

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Friction 2022年第4期10卷 491-515页

作者： Min LIU Liran MA State key laboratory of tribology Tsinghua UniversityBeijing 100084China

Friction drag is a nonnegligible matter when relative motion happens between solid and liquid phase,which brings many inconveniences in ship navigation,fluid transportation,microfluid devices,*** various methods have been developed focusing on friction drag *** this article,a review of several widely studied drag reduction methods is given,specially,their advantages and limitations in practical applications are ***,a comparison of different methods is made and the development prospect of drag reduction is concluded.

关键词： drag reduction microstructures superhydrophobic surfaces supercavitation polymer additives

Friction Characteristics of Impregnated and Non-Impregnated Graphite against Cemented Carbide under Water Lubrication

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Journal of Materials Science & Technology 2017年第10期33卷 1203-1209页

作者： Gaolong Zhang Ying Liu Fei Guo Xiangfeng Liu Yuming Wang The State key laboratory of tribology Tsinghua University Beijing 100084 China

The friction behavior of resin-impregnated and non-impregnated graphite sliding against a cemented carbide in dry, oil, and water environments using a ring–ring configuration was investigated. Friction coefficients were recorded at various speeds. The results showed that the impregnated graphite exhibited much better friction properties under water or oil lubrication than non-impregnated graphite, and the impregnated graphite could remain in the stable friction regime under high pressure × velocity（pv）.Based on scanning electron microscopy and Raman spectroscopy analyses, the different characteristics between impregnated and non-impregnated graphite were able to be attributed to the structure of the graphite and wettability of the lubricants.

关键词： Friction Resin-impregnated graphite Non-impregnated graphite Cemented carbide Water lubrication

Unlocking the secrets behind liquid superlubricity:A state-ofthe-art review on phenomena and mechanisms

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Friction 2022年第8期10卷 1137-1165页

作者： Tianyi HAN Shuowen ZHANG Chenhui ZHANG State key laboratory of tribology Tsinghua UniversityBeijing 100084China

Superlubricity,the state of ultralow friction between two sliding surfaces,has become a frontier subject in ***,a state-of-the-art review of the phenomena and mechanisms of liquid superlubricity are presented based on our ten-year research,to unlock the secrets behind liquid superlubricity,a major approach to achieve *** overview of the discovery of liquid superlubricity materials is presented from five different categories,including water and acid-based solutions,hydrated materials,ionic liquids(ILs),two-dimensional(2D)materials as lubricant additives,and oil-based lubricants,to show the hydrodynamic and hydration contributions to liquid *** review also discusses four methods to further expand superlubricity by solving the challenge of lubricants that have a high load-carrying capacity with a low shear resistance,including enhancing the hydration contribution by strengthening the hydration strength of lubricants,designing friction surfaces with higher negative surface charge densities,simultaneously combining hydration and hydrodynamic contribution,and using 2D materials(e.g.,graphene and black phosphorus)to separate the contact of ***,uniform mechanisms of liquid superlubricity have been summarized for different liquid lubricants at the boundary,mixed,and hydrodynamic lubrication *** the best of our knowledge,almost all the immense progresses of the exciting topic,superlubricity,since the first theoretical prediction in the early 1990s,focus on uniform superlubricity *** review aims to guide the research direction of liquid superlubricity in the future and to further expand liquid superlubricity,whether in a theoretical research or engineering applications,ultimately enabling a sustainable state of ultra-low friction and ultra-low wear as well as transformative improvements in the efficiency of mechanical systems and human bodies.

关键词： liquid superlubricity hydrodynamic lubrication hydration lubrication surface potential surface forces

Control of Magnetic Particle Size in Ferrofluid and Its Effect on Rheological Properties

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Chinese Journal of Mechanical Engineering 2022年第3期35卷 227-235页

作者： Siyu Chen Decai Li State key laboratory of tribology Tsinghua UniversityBeijing 100084China

Rheological properties are the theoretical basis and the key to common problems in ferrofluid applications,therefore they are expected to be adjustable to satisfy different technical requirements through altering the microstructure of ferrofluid during the process of *** this paper,Four ferrofluid samples with different magnetic particle size were prepared by controlling the concentration of precursor solution during co-precipitation process and the rheological properties of these samples were *** samples exhibited field-controlled rheological *** magnetic field would enhance the formation of microstructures,resulting in an increase of *** with the increase of shear rate,microstructures tended to be destroyed,causing viscosity to *** were two opposing mechanisms of the influence of precursor solution *** one hand,the reduction of the precursor solution concentration would produce primary magnetic particles of smaller *** on the other hand,the surfactant became insufficient to completely coat the magnetic particles because of an increased specific surface area,causing the magnetic particles to aggregate and form secondary clustering structures which strongly enhanced the magnetoviscous effect and weakened the viscoelastic effect.

关键词： Ferrofluid Rheology Magnetoviscous effect Viscoelastic effect

Dynamic friction energy dissipation and enhanced contrast in high frequency bimodal atomic force microscopy

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Friction 2022年第5期10卷 748-761页

作者： Xinfeng TAN Dan GUO Jianbin LUO State key laboratory of tribology Tsinghua UniversityBeijing 100084China

Dynamic friction occurs not only between two contact objects sliding against each other,but also between two relative sliding surfaces several nanometres *** emerging micro-and nano-mechanical systems that promise new applications in sensors or information technology may suffer or benefit from noncontact *** we demonstrate the distance-dependent friction energy dissipation between the tip and the heterogeneous polymers by the bimodal atomic force microscopy(AFM)method driving the second order flexural and the first order torsional vibration *** pull-in problem caused by the attractive force is avoided,and the friction dissipation can be imaged near the *** friction dissipation coefficient concept is proposed and three different contact states are determined from phase and energy dissipation *** contrast is enhanced in the intermediate setpoint *** work offers an effective method for directly detecting the friction dissipation and high resolution images,which overcomes the disadvantages of existing methods such as contact mode AFM or other contact friction and wear measuring instruments.

关键词： dynamic friction energy dissipation contact states image contrast bimodal atomic force microscopy(AFM)

Extremely low friction on gold surface with surfactant molecules induced by surface potential

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Friction 2023年第4期11卷 513-523页

作者： Tianyang GAO Jinjin LI Weiqi WANG Jianbin LUO State key laboratory of tribology Tsinghua UniversityBeijing 100084China

An extremely low friction state was observed on the gold surface induced by applying a specific negative potential in cationic surfactant *** friction force showed a remarkable reduction from 8.3 to 3.5×10−2 nN(reduced by 99.6%)with increasing the period of negative applied potential,and the final friction coefficient could reduce down to 3×10−*** extremely low friction state was robust,and it also exhibited an excellent load bearing capacity,which cannot be damaged by a high ***,the extremely low friction state achieved under negative applied potential could keep stable even after the removal of potential,but failed in a short time,once a specific positive potential was *** was demonstrated that there was a stable electro-adsorption of surfactant molecules on the gold surface induced by applying a negative potential,leading to the formation of a bilayer structure on the gold *** hydration layers of the bilayer on the gold surface and micelles on the silica probe provided a shear plane with an extremely low shear strength,leading to the extremely low friction state on the gold *** study provides a method to achieve extremely low friction state by applied potential.

关键词： extremely low friction applied potential surfactant load bearing capacity