Enhancement of hydrodynamic friction by periodic variation of contact stiffness

A common way to increase friction during lubricated sliding is to increase energy dissipation in the slider or the substrate, for example, by bulk viscoelasticity. It has recently been shown that lubricated friction can also be enhanced by surface architecture, specifically by periodic variation of near-surface stiffness. We study this phenomenon by considering a rigid cylinder undergoing lubricated sliding on a substrate with a periodic variation in mechanical stiffness. We model the process using the Reynolds theory for transient elasto-hydrodynamic lubrication (t-EHL). We developed a numerical scheme to solve this t-EHL problem and used it to study how surface variation in stiffness affects the motion of the cylinder, the distribution of hydrodynamic pressure, the liquid film thickness, and the friction force. Our results indicate that increasing the variation of the near-surface stiffness can significantly increase the friction force. The numerical method developed in this work can be applied to other transient EHL problems with slight modification. Our results provide insight into the mechanism of friction enhancement and can guide design of surfaces to control friction during lubricated sliding.