Comment on Neupert, T.; Bartel, D. Evaluation of Various Shear-Thinning Models for Squalane Using Traction Measurements, TEHD and NEMD Simulations. Lubricants 2023, 11 , 178.

The shear thinning observed in viscometers, which has been so successful in establishing the effects of shear-dependent viscosity on film thickness, should be used for evaluation of shear-thinning models because we have confidence in their accuracy. The field of EHL (elastohydrodynamic lubrication) may be the only one in science in which a model for shear-dependent viscosity would be evaluated by means other than viscometer measurements. One of the oils used by Johnson and Tevaarwerk [[4]] to generate traction curves was Shell Turbo 33, a mineral oil with a low inflection pressure at the experimental temperatures, so that the slower-than-exponential piezoviscous response did not appear [[5]]. For nearly a century, viscometer measurements at EHL pressures [[2]] have indicated that the pressure response, which is slower than exponential, is restricted to the lowest pressures and becomes faster than exponential or at least exponential above an inflection pressure. [Extracted from the article]