Nanoscale elastoplastic adhesion of wet asperities

Abstract

Accurate prediction of friction is crucial for design and efficient operation of many devices, comprising various contacts. In practice, contacting surfaces are rough and often wet. There are several mechanisms, which contribute to friction, including viscous shear of a coherent fluid film, as well as that of a thin adsorbed layer of boundary active molecular species. Additionally, adhesion and elastoplastic deformation of asperities on counterface surfaces may occur. Traditional friction models are based on statistical representation of surface topography as well as description of boundary shear films based on the theoretical lubricant film Eyring shear stress. The study reports a more realistic friction model than the traditional ones, which do not take into account the wet nature of the asperities. The fluid-surface interaction is a main contribution of the article, not hitherto reported in literature. It is shown that ignoring the effect of surface wetness can lead to the over-estimation of boundary friction and under-estimation of contact load-carrying capacity.

Thermohydrodynamics of lubricant flow with carbon nanoparticles in tribological contacts

“…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.…”

Elastoplastic contact of rough surfaces: a line contact model for boundary regime of lubrication

“…They also considered an elastic-fully plastic model to describe plastic deformation of asperities in contact. However, in this study, the terms dP a and dA a are predicted based on the approach proposed by Chong et al [28] using the elastoplasticity model of Jackson and Green [23]. The model considers the elastoplasticity transition of contact deformation instead of assuming an elastic then fully plastic asperity deformation.…”

“…According to Chong et al [28], when the normalised deflection dd/d c is less than the deflection transition from elastic to elastoplastic, d t , Hertzian theory applies for both terms of dP a and dA a (Fig. 4).…”

“…These models could also be adapted for asperity level contacts if necessary. Adapting the fractal approaches proposed by Yan and Komvopoulos [26] and later extended by Morrow and Lovell [27] for rough surface adhesion, Chong et al [28] applied the elastoplasticity deformation asperity model proposed by Jackson and Green [23] to predict friction in fractal-represented surfaces. They considered nano-scale wet asperity interactions using a molecular level simulation via statistical mechanics for idealised fluid molecules [29,30].…”

Surface specific asperity model for prediction of friction in boundary and mixed regimes of lubrication

“…The Greenwood and Tripp model [10] was extended by Pullen and Williamson [15] to account for the plastic deformation of asperities and further improved by Cheng et al [16] for an elasto-plastic model. A recent extension of the model for combined elasto-plastic and adhesion of asperities for fairly smooth surfaces, using fractal geometry was reported by Chong et al [17]. Nevertheless, the original Greenwood and Tripp model [10] has been widely used in many applications [18][19][20][21].…”