A Numerical Model for Wet-adhesive Line Contact

Typical rough surface contact models are meant for dry conditions. They often assume hemispherical shaped asperities when predicting load carrying capacity between the opposing surfaces (e.g. isotropic surfaces). However, modern engineering surfaces are often modified to reduce friction. Surface modifications (e.g. plateau honing in engine cylinder liners) produce anisotropic surfaces, dominated by directional features, resembling ridges. They act as micro-reservoirs, trapping fluids to enhance the lubrication process, leading to lower friction. However, the ridges resemble cylinder-on-a-flat contact, when for example a ring of parabolic face-width profile passes over a cross-hatch honed liner surface. These render the typical rough surface contact models inappropriate when applied to understand the contact behavior of such surfaces. Therefore, as a first approximation to understand anisotropic rough surfaces dominated by directional features, the current study proposes a wet-adhesion line contact model. The model includes the influence of boundary lubrication and asperity adhesion upon the contact load carrying capacity and its deformation. The model considers contribution to boundary lubrication at the assumed smooth summits of asperities due to solvation in diminishing gaps. Solvation has an oscillatory characteristic of fluid molecules. This phenomenon not only generates load carrying capacity, but also prevents direct surface-to-surface interaction. It is also shown that as a result of boundary adsorbed film formation, fluid with long chain molecules and boundary active ends (e.g. 16-mer or hexadecane) has a more significant effect in reducing the chance of adhesion in diminishing gaps, when compared with fluids of simple spherical molecules.