Boundary interactions of rough non-Gaussian surfaces

Abstract

Surface topography is important as it influences contact load-carrying capacity and operational efficiency through generated friction, as well as wear. As a result, a plethora of machining processes and surface finishing techniques have been developed. These processes yield topographies, which are often non-Gaussian, with roughness parameters that alter hierarchically according to their interaction heights. They are also subject to change through processes of rapid initial running-in wear as well as any subsequent gradual wear and embedding. The stochastic nature of the topography makes for complexity of contact mechanics of rough surfaces, which was first addressed by the pioneering work of Greenwood and Williamson, which among other issues is commemorated by this contribution. It is shown that their seminal contribution, based on idealised Gaussian topography and mean representation of asperity geometry should be extended for practical applications where surfaces are often non-Gaussian, requiring the inclusion of surface-specific data which also evolve through process of wear. The paper highlights a process dealing with practical engineering surfaces from laboratory-based testing using a sliding tribometer to accelerated fired engine testing for high performance applications of cross-hatched honed cylinder liners. Such an approach has not hitherto been reported in literature.

Thermohydrodynamics of lubricant flow with carbon nanoparticles in tribological contacts

“…In the case of the former, it would be necessary to accurately determine the Eyring and limiting shear stresses of the base oil and that with the inclusion of nanoparticles under the conditions experienced in the pin-on-disc contact, rather than a nominal value measured through standard viscometry, generally of low to medium shear at relatively low pressures. In the case of the latter a non-Gaussian, surface specific boundary friction model in line with the recently reported in [25] would represent prediction of boundary friction more faithfully. Inter-particle forces and those between the particles and atoms of the solid contacting surfaces would play a role in their in situ distribution in transit through the contact.…”

“…This term was originally developed for fairly smooth surfaces with a Gaussian distribution of asperity heights. Various rather laborious models exist which extend the application of the Greenwood and Tripp model for non-Gaussian surfaces such as those by Leighton et al [24,25] for elastic interaction of asperities, Kogut and Etsion [26] for elasto-plastic adhesive dry contact and Chong et al [27] for wet asperities subjected to elastic deformation and adhesion. Table 2 shows that roughness of the surfaces in the current study does not completely conform to a Gaussian distribution and hence ideally a more accurate model needs to be developed.…”

Nano and microscale contact characteristics of tribofilms derived from fully formulated engine oil

“…A reciprocating sliding-strip tribometer, shown in Figure 2, is used to reproduce specific piston compression ring-liner contact conditions at top dead centre reversal in transition from compression to power stroke [37][38][39]. Generated friction is measured using a floating plate, mounted upon ultra-low friction bearings.…”

Multiscale Friction in Lubricant-Surface Systems for High-Performance Transmissions Under Mild Wear

“…Equations (12) and (13) are based on the assumption of a Gaussian distribution of asperity peak heights. This is not true however for all engineering surfaces and non-Gaussian surfaces surface-specific distributions can be obtained through interferometry [39]. The topographical measurements in Table 1 show a kurtosis, Sku ∼ 3 and a skewness of Ssk ∼ 0 , indicating Gaussian asperity height distribution and justifying the use of method expounded in [38].…”