ALL-ATOM MOLECULAR DYNAMICS SIMULATION OF SUBMICRON THICKNESS EHL OIL FILM

ABSTRACT All-atom molecular dynamics simulations of an elastohydrodynamic lubricating oil film have been performed to study the effect of the oil film thickness (large spatial scale; thickness: 430 nm, MD time: 25 ns) and the effect of pressure (long time scale; thickness: 10 nm, MD time: 50 ns, external pressure: 0.1 to 8.0 GPa). Fluid layers of n-hexane are confined between two solid Fe plates by a constant normal force. Traction simulations are performed by applying a relative sliding motion to the Fe plates. In a long spatial scale simulation, the mean traction coefficient was 0.03, which is comparable to the experimental value of 0.02. In a long time scale simulation, a transition of the traction behavior is observed around 0.5 GPa to 1.0 GPa which corresponds to a change from the viscoelastic region to the plastic-elastic region which have been experimentally observed. This phase transition is related to a suppressed fluctuation of the molecular motion. INTRODUCTION Machine elements in which large loads are transmitted such as a traction drive continuously variable transmission (CVT) work in the elastohydrodynamic lubrication (EHL) regime. The molecular dynamic behavior of the oil film under EHL is not well understood, since long trajectories of a ensembles of large number of fluid molecules are required to analyze the drastic phase transition induced by high pressur