Correlation of high frequency QCM sphere-plate stiffness measurements with macroscopic frictional contacts in thin film and bulk stainless steel materials

We compare friction coefficient values mu for stainless steel contacts, obtained directly using a ball on disk tribometer and/or a basic da Vinci method, with values inferred from two microscale analysis methods reported in the literature that treat the response of a Quartz Crystal Microbalance (QCM) to rubbing contacts with one or more ball bearings. The microscale analysis methods both employ a Cattaneo-Mindlin slip scenario to relate contact stiffness to QCM response. Analysis Method 1 involves sweeps of the QCM amplitude of vibration while ball bearings are held in continuous contact with the oscillating electrode. It obtains mu from the slope of the associated frequency or bandwidth shift trace. We find that this method yields values for mu that compare favorably with macroscale values when the bandwidth dependence on vibrational amplitude is utilized. Method 2 obtains mu by analyzing the shifts in frequency and bandwidth that occur when ball bearings are brought in and out of contact with a QCM's oscillating electrode at a fixed vibrational amplitude. We find that this method yields values for mu that compare favorably with macroscale values when the measurements are performed with a contact comprised of 3 close-packed ball bearings situated symmetrically about the center of the QCM electrode. Overall, the results validate the combination of assumptions employed in the analysis methods, and support the methods as a viable means for linkage of macro and nanoscale tribological measurements. (C) 2020 Elsevier B.V. All rights reserved.