Characterization of Friction Regime with Relaxation Tribometer: First Results on Lubricated Contacts by Simple Fluids and Emulsions

Abstract

A novel method for friction measurements has recently been developed: the so-called “relaxation tribometer”. It is based on a lubricated contact submitted to a constant normal load, with one solid being supported by a 1-D mechanical oscillator, able to return to its equilibrium position through damped oscillations. The complete analysis of the time response of amplitude during elastic recovery is compared to a simple mechanical model. This allows us to identify and quantify precisely two different contributions of friction: the linear velocity-dependent contribution (typically “viscous-type” damping, by the parameter zeta), and the solid-like contribution (typically “solid” friction coefficient at zero speed, mu). The electric contact resistance (ECR) signal, which confirms the lubrication regime, is obtained by using an electric resistance detection device. In this study, tribological properties of pure glycerol (GL) and 1,3-buthylene glycol (13BG) are characterized and compared. The ECR signal of GL gives evidence for a fully fluid contact, which is characteristic for a full film lubrication regime. Interestingly, this lubrication regime is maintained when increasing the normal load from 50 to 500 mN. For 13BG, evidence is given for a boundary lubrication regime. Emulsions with GL and 13BG are also investigated. In addition, lubrication regimes of the emulsions are found to be close to those of the raw materials (GL and 13BG). The capabilities of this new technique are expected to bring new insights into friction measurement and characterization of contacts lubricated by complex fluids.

Keywords

• viscous damping
• tribology
• friction coefficient
• vibration energy decay measurement
• cosmetic ingredient