Study on the normal contact stiffness of the fractal rough surface in mixed lubrication

Abstract

In this paper, an elastic interface model is developed to theoretically analyze the contact stiffness of a mixed lubrication surface where the solid and the lubricant contacts have to-be-determined contributions to the whole contact stiffness. The interfacial contact stiffness is composed of the solid contact stiffness and the lubricant contact stiffness, in which the two components are associated with each other via the equivalent thickness of lubricant. Based on the combination of two widely acknowledged ultrasonic measurement models and the Taylor approximating equation, the derivation of the lubricant contact stiffness is mostly affected by the material properties and the equivalent thickness of lubricant, and the equivalent thickness is determined by the solid contact properties under the mixed lubrication condition. Results of the mathematical analysis show that the contact stiffness of the mixed lubrication surface is larger than that of the dry rough surface due to the presence of lubricant. The interfacial contact stiffness of the mixed lubrication is obviously affected by the surface topography and the lubricant property. The proportions of contact stiffness contributed from the solid part and the lubricant part are varying with the contact area and the surface topography. Model predictions are compared with experiment results to verify the accuracy of proposed model. The analysis of the interfacial contact stiffness involved in mixed lubrication provides a theoretical basis for the performance prediction of machine tools, and might be useful to elucidate the contact properties by ultrasonic pulse probing in real engineering applications.

A review of recent advances in tribology

“…The interplay between body temperature and lubricant rheology has been found to affect film thickness and traction in a complicated way [584]. Transient EHL solutions reveal more details of time-dependent pressure and film thickness under varying speeds or loads [588−591], and contact stiffness and damping have been defined to characterize dynamic responses of lubricating films [592,593]. Many researchers have tried to integrate multifactorial considerations into one sophisticated numerical model so that the effects resulting from several factors can be analyzed simultaneously [584−588].…”

Prediction of the normal contact stiffness between elastic rough surfaces in lubricated contact via an equivalent thin layer

“…For the lubricated rough surfaces, the normal interfacial stiffness consists of the micro-asperity contact and the lubricant part, acting in parallel (Dwyer-Joyce et al, 2011; Gonzalez-Valadez et al, 2005; Sun et al, 2018; Wang et al, 2018). The normal stiffness of the lubricated interface can be written aswhere k s is the solid component of the normal contact stiffness per unit and k l is the lubricant component of the contact stiffness.…”

Theoretical and Experimental Study on Normal Contact Stiffness of Plane Joint Surfaces With Surface Texturing

“…On the other hand, Majumbar and Bhushan [6] proposed a theoretical model (M-B model) from the perspective of fractal geometry, which considered the contact characteristics of joint surfaces, and it also solved the problem of scale dependence in statistical models. Based on the above work, the research on the contact characteristics of joint surfaces has been further improved, such as considering multifractal domain [7], elastic-plastic deformation characteristics [8], surface processing methods [9], surface finish [10], lubrication [11] and so on. Also, the research on normal contact stiffness of joint surfaces is gradually developed.…”