Molecular Dynamics Simulation on Boundary Lubrication: The Effect of Cycloalkane Carbon Content

Molecular dynamics(MD) simulation is adopt to investigate the boundary lubrication behaviors of cycloalkane lubricants on nanoscale. The effects of lubricant molecular carbon content and loads on boundary lubrication are studied. The boundary lubrication model with single asperity for friction analysis is set up. The distributions of density are illustrated in the direction of the film thickness when the pressure changes from 25 to 500 MPa. The converse shear velocity is enforced on each wall. The friction, the normal pressure and the stress of the system are calculated. The results show that all the four cycloalkane lubricants are stratified. With the increase of carbon content in lubricant molecule, the trough value in the middle of density distribution curve get higher, the number of the atoms between layers get larger, and the stratification become less obvious. The bearing capacity of the lubricating film increases with the carbon content of the lubricant molecules. The cyclohexane and cyclododecane lubricating films are successively broken at 50 MPa, the cyclotetracosane lubricating film is broken at 100 MPa, while the bearing capacity of the cyclotetradecane exceeds 500 MPa. The friction coefficient of cyclohexane oil film under boundary lubrication is simulated, which is in accordance with the experimental measurement.