Investigating the Behavior of Various Lubrication Regimes under Dynamic Conditions Using Nonequilibrium Molecular Dynamics

Abstract

It is crucial to comprehend how the oil film varies under dynamic operating conditions and the accompanying friction properties to better grasp the friction mechanism and control friction behavior. To model the friction characteristics under boundary lubrication (BL) and elastohydrodynamic lubrication (EHL), nonequilibrium molecular dynamics simulations with various numbers of hexadecane molecules as lubricating oil were conducted in this research under the conditions of dynamic speed and dynamic load. All the dynamic operating conditions have the form of sine waves, with various frequencies and amplitudes. According to the findings, the friction force is strongly connected with interfaces where relative sliding takes place, whose number, velocity difference, and the degree of solidification have significant influences. The variation of amplitude under dynamic load can cause a regular change in the density of the lubricating layer, while the variation of frequency can cause a change in molecular layer's range of motion. Both effects are crucial for friction. The structure of the lubricating layer with lower friction varies with various frequencies for dynamic velocity. Both high and small amplitudes of velocity offer advantages to form a stable film structure at low frequencies in the BL and EHL regions, while the amplitude in the BL area has minimal association with friction at high frequencies. At high frequencies in the EHL region, the friction rises as the amplitude of velocity grows and the lubricating layer becomes more unstable.

Understanding Water Diffusion Behaviors in Epoxy Resin through Molecular Simulations and Experiments

“…Molecular dynamics has been proven to be a powerful method to reveal micromechanism from atomic-scale perspectives. − Although molecular dynamics is widely employed in current research to analyze the effect of water on the properties of epoxy resin, − the majority of efforts are mainly focused on the impact of different water concentrations on material properties in the equilibrium state of the system by manually adding water molecules, without an understanding of the diffusion process of water. It is noted that nonequilibrium molecular dynamics enables detailed analysis of properties of a nonequilibrium system caused by external disturbances, thermodynamic gradients, and other factors, which is particularly effective for probing the mechanisms of dynamic behaviors such as transport and diffusion .…”