Dr. U. P. Singh

Dr. U. P. Singh

Associate Professor
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2.     Summary of Some Research Contributions

2.1     Lubrication Works

    With the increasing industrial and scientific application of bearings, the use of non–Newtonian lubricants has taken on added significance. It has been also shown that the addition of small amounts of long-chained polymer additives (viscosity index improvers) to a Newtonian fluid produces a desirable non–Newtonian lubricant. The additives raise the viscosity index of lubricants and increase their stability by minimizing the sensitivity to the change in shearing stress with strain rate and thermal variation. These lubricants behave like pseudoplastic, dilatant, and viscoelastic fluids depending on the nature and quantity of the additives. However, most of the lubricants added with commercial additives behave like pseudoplastic or dilatant lubricants, which have a considerable influence on the various performance properties of machine elements.

    To study the effects of the lubricant additives on the performance and stability of the various types of hydrostatic, hydrodynamic, and squeeze film bearings, many non-Newtonian fluid models such as power law, couple stress, micropolar, Herschel–Bulkley, Bingham, Powel–Eyring, Ree-Eyring, Cross and Ellis models have been adopted in theoretical investigations. However, to the best of the author’s knowledge, many of these models either work for a limited range of strain rates or lack experimental verification. For illustration, the deviations from experimental data have been verified for Bingham and Ree-Eyring models and a narrow range of experimental agreement of viscosity data have been shown for the power law model , whereas experimental data is scarcely available for couple stress and micropolar models. Therefore, in order to predict the performance characteristics of the bearings and thereby the machine elements accurately, a more realistic lubricant model is required for the theoretical investigation. A brief survey of different fluid models and their limitations, the development of lubrication science, and a perspective observation of the bearings have been presented in chapter one.

    In many of my investigations, the Rabinowitsch fluid model has been adopted for the theoretical investigation of the performance properties of thin film lubricated bearings. The importance of this model lies in the fact that it fits the viscosity data over a wide range of shear rates and experimental verification on film lubricated bearing is available for a standard lubricant (spindle oil) and a common commercial additive (polyisobutylene).

    The objective of most of the works is the analytical study of the influence of non-Newtonian lubricants on various performance characteristics of hydrostatic thrust, hydrodynamic slider, and squeeze film (cylinder-plate and sphere-plate) bearings. To account for the dominant effects of rotational inertia in hydrostatic thrust bearings, the energy integral approach has been adopted to derive the expression for pressure gradient. The mathematical complicacy of the Rabinowitsch fluid model compels us to apply the perturbation technique to solve the modified Reynolds equation for hydrodynamic and squeeze film bearings. In case of hydrostatic thrust bearings, Newtonian and pseudoplastic lubricants have been considered because the experimental as well as theoretical data was available for operating and physical parameters (supply pressure, bearing radius, supply hole radius, viscosity, and coefficient of pseudo-plasticity). However, for the slider and squeeze film bearings, dilatant lubricants have been also considered for the availability of theoretical data only for operating as well as physical parameters.

    In some papers, combined effects of non-Newtonian pseudoplastic lubricant and centrifugal inertia on various performance properties of a stepped circular plate, annular plate, and curved plates hydrostatic thrust bearings have been investigated.

    In some works, the theoretical analysis has been made to investigate the effect of non–Newtonian pseudoplastic and dilatant lubricants on the static and dynamic characteristics of pivoted curved slider bearings.

    Some other investigations analyze the squeezing characteristics “between a long cylinder and a flat plate” and “between a sphere and a flat plate” respectively for non-Newtonian pseudoplastic and dilatant lubricants.

2.2    Summary of Approximation Theory Related Works

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