Contact modeling and stiffness of a rough surface under mixed lubrication condition

A method of using a quadratic function of rotary asperities to be equivalent to asperity is established based on a measurement experiment on rough surface topography. A micro-contact model of a rough surface that includes elastic, elastic-plastic, and pure plastic deformation states is re-derived using the theory of contact mechanics and the method of probability statistics. A rough surface contact stiffness model under mixed lubrication is proposed in accordance with the rough surface contact stiffness, which consists of solid surface and lubrication medium contact stiffness. The influence of the lubrication medium, solid material, and asperity size parameters on contact stiffness is analyzed. Results show that elastic modulus, acoustic impedance, and the size parameters of the asperities of the solid part are the main factors that affect the contact stiffness of the solid part. The acoustic impedance of the lubricating medium mainly affects the contact stiffness of the lubrication part. The contact stiffness of the rough surface under mixed lubrication is a superposition of the solid and lubrication parts, and it is greater than that without the lubrication medium. The model established in this study fully considers the deformation state in practical engineering, which includes asperities and the lubrication state of rough surfaces. It provides a reference for the performance prediction of mechanical surfaces.