Static friction between rough surfaces: Exploring the role of surface structure and molecular interactions

Static friction at fractal interfaces

https://doi.org/10.1016/j.triboint.2015.09.016

In this work, the role of surface fractality, roughness and atomic/molecular friction are explored with relation to static friction between pairs of rough surfaces. This work represents one of the few studies investigating friction between pairs of rough surfaces, rather than rough on flat conditions. The interplay of surface fractality and atomic friction are revealed here with implications for the design of surface treatment procedures.

On left, interaction between rough surfaces, on right evolution of surface fractality 

Abstract

Tribological phenomena are governed by combined effects of material properties, topology and surface-chemistry. We study the interplay of multiscale surface structures with molecular-scale interactions towards interpreting static frictional interactions at fractal interfaces. By spline-assisted-discretization we analyse asperity interactions in pairs of contacting fractal surface-profiles. For elastically deforming asperities, force analysis reveals greater friction at surfaces exhibiting higher fractality, with increasing molecular-scale friction amplifying this trend. Increasing adhesive strength yields higher overall friction at surfaces of lower fractality owing to greater true-contact-area. In systems where adhesive-type interactions play an important role, such as those where cold-welded junctions form, friction is minimised at an intermediate value of surface profile fractality found to be around 1.3–1.5. Results have implications for systems exhibiting evolving surface structures.