Lubrication in soft rough contacts: A novel homogenized approach. Part I - Theory

Abstract

We study the lubricated steady sliding contact between rough surfaces of (elastically) soft solids. A novel mean field theory of mixed lubrication is presented, which takes into account the coupled effect of asperity-asperity and asperity-fluid interactions. We calculate the fluid flow factors, and discuss the nature of the transition from the boundary lubrication regime, where the normal load is supported by the asperity-asperity interactions (sometimes mediated by boundary films), to the hydrodynamic regime, where a thin fluid film prevents direct contact between the mating surfaces.

Loading-unloading hysteresis loop of randomly rough adhesive contacts

“…Contact mechanics between rough surfaces plays a crucial role in a large number of engineering applications, ranging from seals [1,2], boundary and mixed lubrication [3,4], adhesive systems and friction [5][6][7]. Recently, an increasing interest in these topics has been motivated by the increasing efforts made to face up new technological challenges, such as the manufacturing of novel bio-inspired adhesives [8][9][10], the optimization of seals [11,12], the extreme downsizing of mechanical and electrical devices.…”

Experimental Evidence of Micro-EHL Lubrication in Rough Soft Contacts

“…A possible reason for such a behavior has been recently proposed in Refs. [18] and [19], where the authors showed that, at least in terms of asperities flattening, the strength of the fluid-asperity interactions is maximum for the transverse roughness, i.e. when the roughness grooves are aligned perpendicularly to the sliding direction (see also [20]- [24]).…”

“…However, to the best of authors' knowledge, the role played by the roughness anisotropy on the solid contact and lubricant dynamics at the interface of soft contacts has not been investigated yet. In this paper we focus on the experimental investigation of the effects of roughness anisotropy on the soft mixed lubrication and make use of recent theoretical and numerical developments [18]- [24] to, at least qualitatively, explain the behavior observed in our experimental investigations. Our setup consists of a metal ball in a steady-sliding contact with a fixed (anisotropically) rough PDMS substrate, see Fig.…”

“…[16], [17] and in Refs. [18], [19], where a novel mean field theoretical model has been presented to describe mixed lubrication conditions. However, to the best of authors' knowledge, the role played by the roughness anisotropy on the solid contact and lubricant dynamics at the interface of soft contacts has not been investigated yet.…”

Interfacial separation between elastic solids with randomly rough surfaces: Comparison between theory and numerical techniques

“…In this paper, we will show how the theory can be extended to also predict the distribution of interfacial separations P (u). This quantity is of crucial importance for problems like leak-rate of seals Lorenz & Persson, 2010a,b) or mixed lubrication (Persson, 2010;Scaraggi et al, 2011;Lorenz & Persson, 2010c). The analytical results will be compared to numerical solutions obtained using (a) a half-space method based on the Boussinesq equation (BEM), (b) a Green's function molecular dynamics technique and (c) smart-block molecular dynamics.…”