Non-steady state lubrication of counterformal contacts

A theoretical study has been undertaken of the phenomenon
of non-steady state lubrication of concentrated point and line contacts. This has been based upon a study of the effect of squeeze-film action in both hydrodynamically and elastohydrodynamically lubricated contacts.

The work described in this thesis is in two main sections.
The first is concerned with squeeze-film lubrication of lightly loaded point contacts where the surfaces are taken to be rigid. A complete analytical solution is developed considering both piezoviscous and isoviscous fluids. Formulae representing the relationships between the controlling parameters of hydrodynamic lubrication of point contacts with a pure squeeze action became available.

In the second section general numerical solutions to the
non-steady state hydrodynamic and elastohydrodynamic lubrication problems for line contacts are developed. The finite difference approximation method has been used to solve simultaneously the Reynolds, elasticity and load equations at successive time steps. To avoid convergence difficulties and reduce computing effort a tri-diagonal matrix algorithm has been incorporated. A wide range
of line contact lubrication problems is considered. These include the hydrodynamic and elastohydrodynamic lubrication of cylinders with either pure squeeze-film action or under combined 'entraining' and 'squeeze-film' action. Graphical representations of pressure distributions and film shapes are presented in time sequence as the gap between the two cylinders changes. The variations of the dimensionless minimum film thickness, velocity of approach and peak
pressure under various loading conditions are also included. The formation and development of the elastic indentation under constant load with squeeze-film action and with the combined effect of squeeze and entraining action has been ascertained.

It has been established that the squeeze-film action plays
an effective role in the enhancement of the smallest value of the minimum film thickness occurring under oscillating loading conditions. This effect is more pronounced in elastohydrodynamic than in hydrodynamic lubrication.

This general analysis of time dependent lubrication
problems for both hydrodynamic and elastohydrodynamic conditions permits specific studies to be undertaken of realistic machine components operating under non-steady state conditions.