Molecular Dynamics Simulation Study of Mechanical Effects of Lubrication on a Nanoscale Contact Process

Using molecular dynamics simulation, we study the effect of a lubricant on indentation and scratching of a Fe surface. By comparing a dry reference case with two lubricated contacts-differing in the adsorption strength of the lubricant-the effects of the lubricant can be identified. We find that after an initial phase, in which the lubricant is squeezed out of the contact zone, the contact between the indenter and the substrate is essentially dry. The number of lubricant molecules confined in the tip-substrate gap increases with the lubricant adsorption energy. Trapped lubricant broadens the tip area active in the scratching process-mainly on the flanks of the groove-compared to a dry reference case. This leads to a slight increase in chip height and volume, and also contributes to the scratching forces.