Oscillatory and steady shear viscosity: The Cox–Merz rule, superposition, and application to EHL friction

Development of an Ultrasonic Sensing Technique to Measure Lubricant Viscosity in Engine Journal Bearing In-Situ

“…A similar comparison was conducted numerically by Sharma and McKinley (2013). Bair (2014) first applied the Cox-Merz rule at high rotational frequencies (10 7 Hz) using an impedance spectrometer microbalance, and discovered that for the polymer based oils tested this rule is no longer valid. The matching layer ultrasound viscometer results in section 6.3 show the same behaviour.…”

“…Here, the same approach is implemented for the oscillatory case, replacing by μ , as done by Bair et al (2014). Application of equation (7. The agreement with the ultrasonic data and that predicated by the modified Carreau model is reasonable for both oils.…”

“…Equations (4.23) and (4.24) are valid for low ultrasonic rotational frequencies, but Bair (2014) showed experimentally, using a quartz resonator microbalance, that at high rotational frequency (MHz) the Cox Merz rule (and consequently the Laun"s rule) holds only for purely Newtonian liquids. For more complex structures (such as the one of lubricant oils) the viscoelastic parameters measured with the ultrasonic viscometer deviate from the measurement made with conventional steady shear viscometers.…”

Reply to the Comment by Scott Bair, Philippe Vergne, Punit Kumar, Gerhard Poll, Ivan Krupka, Martin Hartl, Wassim Habchi, Roland Larson on “History, Origins and Prediction of Elastohydrodynamic Friction” by Spikes and Jie in Tribology Letters

“…[15]. Since publication of our paper Bair et al have reviewed the applicability of the Cox-Merz rule for simple molecular liquids [16]. They found poor agreement between oscillatory and high stress viscometry even at the limited combination of (shear stress x strain rate) conditions attainable using such viscometry.…”

Frictional Response of Lubricant in EHL Contact under Transient Bi-directional Shear Loading

“…This rule is mainly applied to the data from vibrational viscometers (often employing cut quartz crystal or shear impedance spectrometer) to characterize the rheological parameters and complex responses of lubricants (low-shear viscosity, shear thinning, timedependence, linear or non-linear viscoelastic behaviour, etc.). However, it turned out that this rule is applicable only in a very limited range of operating conditions with respect to EHL [32]. did not recur during the reciprocation of motion, their origin is attributed to the dynamic response of the measuring system (not to the response of lubricant) to excited vibrations.…”