Movement pattern of an ellipsoidal nanoparticle confined between solid surfaces: Theoretical model and molecular dynamic
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ISSN 2223-7690 CN 10-1237/TH
RESEARCH ARTICLE
Movement pattern of an ellipsoidal nanoparticle confined between solid surfaces: Theoretical model and molecular dynamics simulation Junqin SHI1,2, Xiangzheng ZHU1, Kun SUN1, Liang FANG1,3,* 1
State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an 710049, China
2
State Key Laboratory of Solidification Processing, Center of Advanced Lubrication and Seal Materials, Northwestern Polytechnical University, Xi’an 710072, China
3
School of Mechanical and Electrical Engineering, Xiamen University Tan Kah Kee College, Zhangzhou 363105, China
Received: 13 March 2020 / Revised: 26 April 2020 / Accepted: 07 May 2020
© The author(s) 2020. Abstract: The movement pattern of ellipsoidal nanoparticles confined between copper surfaces was examined using a theoretical model and molecular dynamics simulation. Initially, we developed a theoretical model of movement patterns for hard ellipsoidal nanoparticles. Subsequently, the simulation indicated that there are critical values for increasing the axial ratio, driving velocity of the contact surface, and lowering normal loads (i.e., 0.83, 15 m/s, and 100 nN under the respective conditions), which in turn change the movement pattern of nanoparticles from sliding to rolling. Based on the comparison between the ratio of arm of force (e/h) and coefficient of friction (μ), the theoretical model was in good agreement with the simulations and accurately predicted the movement pattern of ellipsoidal nanoparticles. The sliding of the ellipsoidal nanoparticles led to severe surface damage. However, rolling separated the contact surfaces and thereby reduced friction and wear. Keywords: movement pattern; friction and wear reduction; ellipsoidal nanoparticle additive; molecular dynamics simulation
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Introduction
Lubrication is an important method to reduce friction and wear, and it improves the durability and reliability of materials and reduces energy consumption [1, 2]. Among the different lubrication regimes, the boundary lubrication exhibits high friction and wear behavior [3]. Currently, the addition of friction modifier additives (i.e., organic friction modifiers and nanoparticles) to tribology and lubrication systems is considered as a useful method for friction and wear reduction [2–5]. Given their thermal stability at high temperatures, nanoparticles can be popular solid lubricating additives and can * Corresponding author: Liang FANG, E-mail: [email protected]
play important roles in emission reduction and improving fuel economy [5]. Different types of nanoparticles, such as metal, metal oxide, metal carbonate, fullerenes, silica, and carbon compound, have been developed as solid lubricants and lubricant modifiers for friction modification and wear resistance [3, 6–14]. The tribological properties of metal nanoparticle additives (like Fe, Cu, Ni, and Co) in base lubricants indicate that they play a significant role in decreasing friction and wear by forming a tribo-layer [6–9]. Metal oxide nanop
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