Proceedings of the Institution of Mechanical Engineers,Part C: Journal of Mechanical Engineering Science

The methods of measuring the rheological properties of EHD lubricants are reviewed, but for pressures in excess of 1.0 GPa there is currently no simple alternative to the disc machine. A technique has been developed which enables disc machine traction tests to be carried out at constant mean film temperature. Isothermal tests provide further evidence for the existence of a limiting shear stress τ_c at which the fluid shears in the manner of a plastic solid. At stresses below this limit the experimental data are found to be in very good accord with the non-linear Maxwell rheological model based on the Eyring theory of fluid flow proposed by Johnson and Tevaarwerk and by Hirst and Moore. The model incorporates three fluid properties: shear modulus G, viscosity τ and Eyring stress τ₀. Disc machine measurements of τ, τ₀ and the limiting shear stress τ_c for three fluids—a mineral oil HVI 650, a synthetic polyphenyl ether 5P4E and a traction fluid Santotrac 50—are presented for a range of pressures (0.6–2.5 GPa) and temperatures (40–120°C).

The rheological behaviour of the lubricant in an elastohydrodynamic contact depends upon the properties of the fluid and the imposed conditions of load, speed and temperature. For a lubricant of known rheological properties, it is shown how a ‘map’ can be constructed in which different areas of the map correspond to different regimes of behaviour. The coordinates chosen for the map are non-dimensional pressure and a parameter which is closely related to the film thickness. Given the load, speed and temperature, the operating conditions can be located as a point in the map.

Maps have been constructed for three fluids: a mineral oil, polyphenyl ether 5P4E and a traction fluid. In general the maps display four regimes: (a) Newtonian, (b) Eyring, (c) viscoelastic and (d) elastic-plastic. Appropriate constitutive equations are proposed for each regime from which the traction forces can be predicted.

The maximum traction coefficients calculated in this way are well supported by experiment.

A novel rheometer is described, in which extensional viscosity and elastic shear compliance are determined simultaneously from pressure measurements taken on steady state polymer melt flows through an open-ended die with successive, similarly shaped, converging and diverging zones. Equations incorporating practically realistic simplifying approximations are developed for the calculation of extensional viscosity and shear compliance from the measured pressure data. The construction of a prototype rheometer is described, and results from its operation are presented. Agreement between these results and published melt elasticity data for a low-density polyethylene material gives evidence to confirm the basic rheometric principle and flow analysis. The implications of pressure measurement errors are discussed. Assembly of the new composite-geometry rheometer in series with a conventional capillary viscometer would give in-line shear viscosity characterization simultaneously and facilitate on-line processing of pressure data from the converging and diverging flows by microcomputer to provide complete characterizations for practical use in polymer process machinery design. The work represents a significant advance on the basic empirical power law modelling process used for many years by practising engineers to represent shear viscosity phenomena as a basis for design. No other methodology is currently available to suit the engineer.

A heavy load analytic theory is developed which describes the way in which surface asperities cause variations in hydrodynamic pressure in an elastohydrodynamic conjunction. The theory is restricted to rigid sinusoidal asperities with a circumferential lay. It is shown that the magnitude of the pressure ripple increases with increasing asperity amplitude-film thickness ratio and decreases with decreasing wavelength, increasing load and increasing radius of curvature of the bodies. Pressure ripple magnitudes can vary from ∼10⁶ Pa to infinite pressure spikes and it is suggested that elastic deformation of the asperities is to be expected at the higher values. Consideration is given to the way in which the theory may be applied to real surfaces.

When machining materials such as stainless steel and titanium the removed chip is characterized by a serrated (saw-tooth) outer surface and large cyclic variations in macrostrain within the chip. The present paper presents a model for the process producing such chips. The model is shown to represent accurately experimental results derived from cine films and photomicrographs of the chip formation process obtained when maching stainless steel.

This paper develops a simplified numerical technique for the analysis of heat generation and cage slip in high-speed axially loaded ball bearings. The model compares well with experimental results and has shown the characteristic slip behaviour associated with ball bearings. It has been possible to use the model to investigate the nature and causes of slip in lightly loaded ball bearings and it has been shown that the mechanism is primarily dependent upon the spin power, which falls rapidly as slip sets in. The characteristics of slip in ball bearings are shown to be quite different to those in roller bearings.

A rigid-body analysis is presented of the forces which occur in a chain bearing during articulation.

Coulomb frictional effects due to unlubricated contact are included, as these provide the energy source for deleterious wear processes and affect the force distribution. The analysis differentiates between the two types of chain bearing—open end leading or open end trailing—and the results show that the force characteristics in each are significantly different.

Experimental verification of the chain link tension is good.

In a previous paper (1), the contact forces in a chain bearing during articulation were established. The present note describes the application of these results to the theoretical evaluation of efficiency for a conventional chain transmission using cranked link (or offset) type chain.