|英文题名||Multi-scale simulation method of three-dimensional thin-film lubrication system and its application|
|关键词||准连续方法 薄膜润滑系统 多尺度模拟 石墨烯涂层|
Film lubrication refers to the use of a thin film of fluid to separate the surfaces of two solid substrates to avoid wear due to dry friction caused by direct contact with the substrate surface. In precision machinery work, the lubrication film between the friction pairs is often in the lubrication state of a dozen to several tens of nanometers in thickness. The macroscopic friction behavior will be traced back to the molecular contact process, and the traditional friction analysis is no longer applicable. Therefore, it is of great significance to study the theory of thin film lubrication in basic theoretical research and engineering applications in the fields of micro-nano technology and nano-tribology.
Due to the computational speed and storage limitations of computers, using the fully-atomistic simulation to treat systems that involve macroscopic to microscopic tribological processes is difficult to achieve. It is necessary to couple the traditional continuum methods with the fully-atomistic methods to create a multi-scale coupling methods. In this thesis, we developed a multi-scale simulation method , which is named as free-energy-corrected hybrid atomistic coarse-graining method of three-dimensional thin-film lubrication system. Monte Carlo simulation is used to investigate the reversible slip process of three-dimensional thin-film lubrication system with face-centered cubic LJ crystal structures. Firstly, the fully-atomistic simulation was used to verify that the elastic deformation of the solid substrate has a significant effect on the shear stress of the film lubrication system by changing the thickness of the solid substrate. Second, a multi-scale model containing an elastic solid substrate is established by coupling the fully-atomistic description of the near region of the solid substrate with the finite element description of the far region. In the process of finite element coarse graining in the far area of the solid substrate, local and non-local finite element units were respectively used. Studies have shown that both the shear stress profiles and the average separation profiles calculated by the two coarse-grained treatment methods can reproduce the results calculated by the fully-atomistic simulation, and can greatly improve the computational efficiency. Finally, based on the effective simulation of mono-layer fluid atom film lubrication, a three-dimensional thin film lubrication system with multi-layer fluid atoms was further studied by using this multi-scale simulation method. Through the analysis of the calculation results, it is found that the maximum shear stress decreases with the increasing of the number of fluid atomic layers, and increases with the increasing of positive pressure of the system.
In order to saving resources and protecting the environment, using water as a green and clean lubricant to replace the traditional oil lubricants is a problem which is worth to explore and research. However, the low viscosity of water and its tendency to chemically interact with metals have limited it to be an effective lubricant. Both the domestic and foreign research shows that due to the excellent properties of graphene, coating the metal with graphene can effectively prevent the metal from reacting with water, so that water can be used as a clean lubricant. This paper further applies the hybrid atomistic and coarse-grained multi-scale simulation method developed in this thesis to the single-crystal copper thin-film lubrication system with water as a lubricant and graphene as the coatings, and researched the tribological and lubricant characteristics of this system. Results shown that the graphene coating can effectively reduce the interaction between water molecules and the copper substrate, so that the friction of the system is greatly reduced.
Key words: Quasicontinum method, Thin-film lubrication system, Multi-scale simulation, Graphene coating
|赵园格. 三维薄膜润滑系统的多尺度模拟方法及其应用[D]. 北京. 中国科学院大学,2018.|