Discussion: “Modeling of Film Thickness and Traction in a Variable Ratio Traction Drive Rig,” (Sharif, K. J., Evans, H. P., Snidle, R. W., and Newall, J. P., 2004, ASME J. of Tribology, 126(1), pp. 92–104)

Abstract

Ordinary shear-thinning affects EHL film thickness by reducing the central thickness from the theoretical Newtonian value 1 and ordinary shear-thinning affects traction in point contacts by shifting the logarithmic traction gradient to higher rates 2 in a manner indistinguishable from a reduction in pressure dependence of low shear viscosity at high pressure 2. The models selected by the authors for shear-thinning are not recognizable as ordinary shear-thinning. The authors’ Eq. (10) was Eyring’s sinh law model for thixotropy 3. Thixotropy should not be an issue here since the traction fluid is not known to contain wax and in any event the waxy structures studied by Eyring were quite weak with approximately τo=0.01 MPa3. Eyring made very clear his opinion that the sinh law, Eq. (10), is not an accurate description of shear-thinning 4. The authors’ Eq. (11) is not constitutive as it results from inhomogeneous shear 5.