Molecular Interactions at Asperity Contacts Under Boundary Lubrication

Boundary lubrication plays a crucial role in determining the service performance and operational lifespan of mechanical components. However, continuum mechanics models and experimental studies are unable to elucidate the dynamic evolution of intermolecular interactions at the interface under boundary lubrication from a microscopic perspective, including phenomena such as asperity contact and lubricant film rupture. In this study, a molecular dynamics simulation approach was employed to construct a boundary lubrication friction model incorporating lubricant molecules, aiming to investigate the influence of applied load and asperity height on the dynamic evolution of atomic interactions at the interface from the perspective of energy variation, under conditions both with and without asperity contact. The results indicate that van der Waals interactions dominate the frictional response, and severe asperity contact leads to a sharp increase in van der Waals energy, which in turn results in a decrease in normal force, thereby increasing the friction coefficient. When the upper and lower surfaces remain separated by the lubricant, an increase in van der Waals energy leads to higher friction force, consequently elevating the friction coefficient. In the absence of contact, the friction coefficient decreases with increasing load; however, once asperity contact occurs, higher loads accelerate lubricant film failure and intensify direct interfacial contact, leading to more pronounced stick–slip oscillations and increased wear. This study provides atomic-scale insights for the design and performance optimization of boundary lubrication interfaces.