This paper presents a general theoretical approach to evaluate the leakage flow, stiffness and damping of annular seals in turbulent flow regime including fluid inertia using turbulent lubrication theory. Fluid inertia effect has been incorporated by perturbing the pressure and fluid velocities following the procedure cited in the literature for laminar flow. Turbulent lubrication theory based on eddy viscosity model has been followed to develop turbulent Reynolds equation. Perturbation theory for small amplitude vibration of the journal center has been followed to determine stiffness and damping of the seal. Theoretical analysis presented is general and seal geometry effect can be incorporated through film shape description.

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This paper is in continuation of its part I. It presents the rotordynamic behavior of a circular seal and multilobe seal for various L/D ratio, taper ratio and eccentricity ratio in the turbulent flow regime considering the effect of fluid inertia. The paper has been focused particularly on the leakage flow, stiffness and damping coefficients of a plain and a taper annular seals. Rotordynamic coefficients have been evaluated for various seal configurations for water as the working fluid.

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Effect of di-tert-dodecyl disulfide as an additive on decomposition of MAC oil on the nascent surface of bearing steel 52100 was investigated. After the removal of surface contamination layer, active sites were generated, on which tribochemical decomposition of MAC oil occurred. The additive prolonged the induction period of the decomposition. Hydrogen and gaseous hydrocarbons desorbed as tribochemical reaction products. Desorption rate of hydrogen and gaseous hydrocarbons increased proportionally with sliding velocity and linearly with the cube root of load. XPS analysis revealed tribochemical reaction between additive and nascent surface occurred, which induced formation of iron sulfide and decrease of activity of nascent surface. As a result, decomposition of MAC oil decreased correspondingly.

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In order to develop guidelines for developing lubricants of high performance for aluminum die casting, we conducted tribological evaluation tests on the thermal and lubricating characteristics of inorganic powders and waxes. Specifically, we measured the thermal conductivity of various inorganic powders and then selected powders superior in heat insulation. Next, we investigated the thermal behavior of the waxes contained in powder lubricants by thermogravimetry. In addition, by using a friction tester, we evaluated the lubrication performance of the composite lubricants at high temperatures of 250ºC and 350ºC. With all of these results, we proposed composite lubricants for aluminum die casting.

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PVA (poly (vinyl alcohol)) hydrogel is one of the anticipated materials for artificial cartilage. In previous research, authors found that the structure of protein boundary film on rubbing surface is a key essence for wear reduction of PVA hydrogel. The aim of this study is to understand the mechanisms of wear reduction of PVA hydrogel through in situ observation on forming protein boundary film on the rubbing surface. Reciprocating apparatus was constructed on the stage in inverted fluorescent microscope. A sliding pair of a spherical reciprocating upper specimen of PVA hydrogel and a flat stationary lower specimen of cover glass was tested. Lubricants were single and binary protein solutions, in which fluorescent-labeled bovine serum albumin and human serum γ-globulin were used as additives. When single protein was added to lubricants, albumin formed a loosely adsorbed film on rubbing surface, whereas γ-globulin adsorbed firmly and formed a smooth and uniform boundary film. When both of albumin and γ-globulin were added into lubricants, the stability of protein boundary film varied with the concentration and ratio of two kinds of proteins in lubricants. These results indicate that there is suitable content and ratio of proteins added into lubricants to form a stable boundary film.

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