Continuum Model Analysis of QCMNanotribological Data to ObtainFriction Coefficients for 304SSContacts Lubricated by Water andTiO2 Nanoparticle Suspensions

摘要

We report a study of the response of a Quartz Crystal Microbalance (QCM) torubbing contacts in air, water and aqueous suspensions of 40 nm TiO2 nanoparticles.Measurements were performed with a contact comprised of 3 close-packed 304SS ballbearings situated symmetrically about the center of a 304SS QCM electrode with 2 nmrms roughness. Two continuum methods were employed to infer macroscale frictioncoefficients μ employing QCM nanotribological data recorded in the Cattaneo-Mindlin(CM) slip regime at vibrational amplitudes that varied between 1 and 17 nm. The “slope”Method 1 involved sweeps of the QCM amplitude of vibration as ball bearings were heldin continuous contact with the oscillating electrode. The “contact” Method 2 obtainedμ by analyzing the shifts in frequency and bandwidth that occur at a fixed uo to solvefor μ. when ball bearings were brought in and out of contact with the QCM’s electrode.The results for dry and water lubricated contacts compared favorably with macroscalefriction coefficients reported in the literature. The model failed to adequately describecontacts lubricated with the NP suspension, but its continuum nature did not appear tobe the dominant factor underlying failure. The failure was more likely attributable to eithera lack of a CM slip regime when NP were present at the interface and/or the fact thatthe amplitude of vibration was close in size to the individual NP contacting regions, inviolation of a key underlying assumption of the model.