The Molecular Dynamics Simulation Of N-Heptane's Microscopic Properties As The Friction Lubrication

Friction phenomenon exists in every aspect of daily life and industrial production.For issues related to research, to form a new discipline-tribology (tribology).Caused a lot of useless friction energy loss, also can cause contact surface between the wear and tear, damage to equipment, reduce the service life of equipment, for energy and the environment have caused great harm. According to data shows, because of the friction loss of primary energy sources in about a third of the total primary energy sources in the world-2/3.Therefore, reduces friction can protect equipment, increase the service life of mechanical equipment, save energy and protect the environment. Along with the advance of modern science and technology, the scale of the lubricating oil film, has reached the micro-scale microscopic scales of lubricating oil film is no longer satisfy the continuity of fluid theory, reflects the properties of similar to solid, and also is a kind of solid sex, the continuity of traditional theory for micro tribology are no longer applicable, so for micro-scale mechanism of lubrication friction phenomenon revealed, the emphasis is put on a lot of scientific research workers for microscale a lot of research on lubrication friction phenomenon, in the aspect of experiment and numerical simulation are made a lot of research results, continue to reveal the microscopic mechanism.In experiments, numerical calculation and molecular dynamics in these three methods, molecular dynamics method in revealing the lubricating mechanism of microcosmic lubricating film has obvious advantages.Molecular dynamics simulation, from the perspective of molecules and atoms, adopt the principle of statistical mechanics, from the statistical calculation of lubrication friction phenomenon in nature.This article adopts the method of molecular dynamics, the system research of the limit between the two layers of iron atoms of n-heptane and microstructure characteristic of fluid rheological properties, specific content is as follows:(1) this paper introduces the basic situation and tribology, raises the research background and significance of the micro tribology, based on the research progress of molecular dynamics method was introduced.(2) a brief introduction to basic principle of molecular dynamics simulation of n-heptane molecular force field and potential function, as well as the physical parameters of n-heptane statistical method.(3) the molecular force field and the refined n-heptane is the choice of potential function.Through the use of relatively simple alkanes (paraffin is one of the main components of the lubricating oil, and at the same time the development of molecular force field is based on paraffin), using the methods of molecular dynamics, the application of different atomic force field and atomic force field system of n-heptane are simulated under different temperature of viscosity, density and thermal conductivity, so as to choose the lowest cost, calculation results, the most accurate atomic force field and potential function.Through a series of simulation found that OPLS-CHARMM joint atomic force field calculation results of viscosity, thermal conductivity and density of in good agreement with the experimental value, is a kind of economical and accurate atomic force field.Microscopic features(4) thin film lubrication research.Use the OPLS-CHARMM joint atomic force field was carried out on the thin film lubrication simulation calculation, the calculation results show that the bigger the temperature, the greater the density, the stronger the compressibility, system highly reduced, has adsorption film produced in near the wall, and with the increase of temperature and thickening.Height, the lower the pressure, the greater the system, the more easily cambium-like structure, but inside the fluid remains part of the fluid characteristics, this shows that the thin film lubrication is a transition state, and is a kind of can exist independently of the transition state.(5) the microscopic characteristics of boundary lubrication research.Use the OPLS-CHARMM joint atomic force field simulated calculation of boundary lubrication.Calculation results show that when the oil film can be divided into five layers, hierarchical structure is very clear, when both temperature and load effect on the formation of the layered structure is not large, the friction force increases as the temperature rise, when the pressure increases.Friction increases, but the near surface molecular adsorption and its type of solid lubricant molecules remained stable. When the lubricating film thickness further reduce, three molecular layer, the influence of pressure of lubrication film is very significant, when the pressure of 250 mpa, lubricating film layer structure is not obvious, continue to increase the load, when the load of 500 mp, lubricating film layer structure is very obvious can be divided into three layers, the system is highly reduced, increase the friction, lubrication film is easy to fracture.(6) convex peak contact microscopic characteristics research.The research results show that when the pressure of 250 mpa, lubricating film in the 335 k fracture, increase pressure to 500 mp, the lubricating film rupture happened in 315 k.At the same time in this paper, the effect of shear rate on the lubrication film rupture was investigated, the results showed that the shear rate, the greater the carrying capacity of the lubricating film. The upper metal material to Cu, explore the friction material on the convex peak of the contact, the results show that:the iron atom layer on layer of copper atoms causing the cutting action, small deformation friction, friction is reduced.