T11e l~iezoviscous eflect is accurately characterized for a numher of rel)rr.setrtative Irthricating oil base stocks and a siniple, well-(l~fitrerl Iryrlrocurhori. Proceduws for the generation of accurute presstr,r-~~i.scosity coefficients are outlined. Tlie reciprocal cr.sytirptotic iso~~iscous pressure niay he measured to u~irhin per11rt11.s 1%. Tlre piezovi.scous effect niay he important to automotive jirel ecotroniy. Tlie depart~cre from exporzential behavior at very l o~l ~~~S S I I I Z ' hecon~es nrore prvrloutzced at high temperature.
A High Pressure Flow Visualization Cell has been designed and constructed to perform a fundamental investigation of the deformation behavior of liquid lubricants under lubricated concentrated contact conditions. A pressure of 0.3 GPa and a shear stress between parallel plates of about 25 MPa has been demonstrated. Time averaged velocity profiles show no continuous slip either in the bulk or at walls. Localized slip at shear bands inclined to the walls was demonstrated to occur during nonlinear shear response. The number of shear bands increases with shear rate (and shear stress) from as few as one at the onset of non-Newtonian flow until the shear region is essentially filled with bands with a spatial periodicity of 7 μm. Bands are typically inclined 19 deg off the solid surfaces in a direction which reduces the compressive normal stress due to shear on the plane of the band.
The nature of real shear-thinning in elastohydrodynamic contacts is well-known from both experimental measurement and nonequilibrium molecular dynamics to follow a power-law. Shear-thinning will affect the film thickness when the Newtonian limit is low enough to occur in the inlet zone (less than about 1 MPa shear stress). Then kinetic theory tells us that film thinning should occur for molecular weight greater than 2000 kg/kmol. We present a review of generalized Newtonian models, flow curves for real lubricants and comparison of calculated and measured film thickness. The calculations utilize measurable liquid behavior, in contrast to most previous work.
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