The tribo-performance behaviors of lubricated textured point contacts have been explored herein at relatively high contact loads (up to 3 GPa) under reciprocating motion (0.2 and 0.4 m/s) employing low (ν@40 ℃ = 100 cSt) and high (ν@40 ℃ = 422 cSt) viscous oils. In this experimental study, two contacts (flat conventional surface vs. polished ball and textured flat surface vs. polished ball surface) have been created for the investigations of friction, wear, and contact potential (ability for film formation). It is found that in the presence of texture at the concentrated contacts, the coefficient of friction and wear have reduced considerably with high viscous oil irrespective of operating parameters. However, low viscous oil has yielded an increase in the wear under identical operating parameters. The contact potential (an indirect indication of film formation during the running-in period) in the presence of texture develops rapidly as compared to the conventional surface with both oils. It has demonstrated a reduction in the running-in period in the presence of textures at the contacts. The optical microscope images of worn surfaces of balls and tracks have also been presented for the quantification of wear and understanding of the associated mechanisms.

Tribo-behaviours of grease-lubricated textured point contacts were experimentally explored at heavy loads (characterized in term of Hertzian pressure, P H  = 1.5–3.0 GPa) and relatively low sliding speeds (0.2 and 0.4 m s−1) under the linear reciprocating motion employing lithium-based low and high consistency greases. Two contacts (grounded plate versus lapped ball & grounded textured plate versus lapped ball) were employed for the comparative investigations of friction coefficient, specific wear rate, and contact potential. Effects of grease consistency on the greases’ rheological behaviours have also been found at two temperatures 25 °C and 80 °C using controlled stress rheometer. Overall, textured concentrated contacts yielded a low coefficient of friction (reduction up to 24.6%), reduced specific wear rate of the ball (decrease up to 89.5%) and better development of contact potential in comparison to conventional contacts. The transmission electron microscopy (TEM) of used greases collected from textured contacts revealed less degradation in soap fibres. Moreover, the x-ray photoelectron spectroscopy (XPS) revealed the formation of ferric oxide (Fe2O3) and ferrous-ferric oxide (Fe3O4) protective chemical films on the worn surfaces of balls of the conventional and textured contacts.

The understanding of the relationship between molecular structure and viscosity–temperature behaviour of a lubricant system is a subject of considerable importance. The quantitative distribution and types of different classes of hydrocarbons such as aromatics, paraffins (normal and iso) and naphthenes determine the physico‐chemical behaviour of a lubricant system. The study of molecular structure and molecular alignment of hydrocarbons constituting a lubricant helps in the development of lubricating oil with desired physico‐chemical properties. The present study highlights the application of nuclear magnetic resonance spectroscopic technique for deriving detailed hydrocarbon structural features present in API groups II and III base oils produced through catalytic hydrocracking/isodewaxing processes. The viscosity–temperature and viscosity–pressure properties, such as viscosity index, pour point, elastohydrodynamic film thickness and cold cranking simulator viscosity, were determined. The structural features of these base oils such as various methyl branched structures of isoparaffins and branching index, which are characteristics of high performance molecules, were correlated with the above‐mentioned properties to explain their physico‐chemical properties, particularly low temperature properties. The molecular dynamics parameters such as diffusion coefficient and T1 relaxation times estimated from the nuclear magnetic resonance spectral studies have provided sufficient evidence for the dependence of these properties on these high performance molecules present in various types of methyl structures of isoparaffins of groups II and III base oils compared with conventional group I base oils. Results are explained on the basis of molecular structural differences of hydrocarbons present in these base oils and diffusion measurement studies. On the basis of the studies, molecular engineering concept for the designing of a high performance base oil molecule is proposed. Copyright © 2012 John Wiley & Sons, Ltd.

Five commercial olefin copolymer (OCP) viscosity index (VI, improvers have been characterised at the molecular level. The copolymer compositions have been determined using ' H a n d 13C-N M R spectroscopy. The microstructural parameters, such as cornonomer sequence distribution, number average sequence lengths and run number, have been determined by 13C-NMR spectroscopy. N M R spectral editing techniques, e.g. Distortionless Enhancement via Polarisation D-ansfer (DEPT) have been used for peak assignments. This analytical approach aims at correlating the microstructural parameters with the physical properties and performance of these VI improvers, to be communicated later.A viscosity index improver is an oil soluble polymer that significantly alters the oil viscosity, increasing its effect with temperature. This type of polymer, in addition, makes the thickened oil non-Newtonian. The degree of non-Newtonian behaviour imparted to an oil is another important characteristic of the polymer in relation to its effectiveness as a VI The effective viscosity of a lubricant in critical engine areas influencing key performance characteristics is a function not only of shear rate, but also of the response of the particular polymer VI improver's chemistry and constitution, to the shear rate and t e m p e r a t~r e .~~?~ An important class of VI improvers is that of olefin copolymers, primarily derived from ethylene and propylene comonomers. The chemical and associated physical characteristics which make these copolymers most suitable for use as VI

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