Some aspects of the non-Newtonian behaviour of fluids in elastohydrodynamic lubrication.

In considering the experimental evidence for non-Newtonian behaviour, which has often been interpreted in terms of viscoelasticity, deviations from established theories, which assume a Newtonian fluid with viscosity dependent upon temperature and pressure, are sought. It is, therefore, vital to isolate inherent non-Newtonian behaviour from deviations arising from other unrelated processes. Non-Newtonian behaviour which has been detected is of two main types: inlet region effects (which may also arise from incomplete filling) and Hertzian zone effects (which may be attributed, at least in part, to the consequences of viscous heating). The thesis therefore presents a new theoretical analysis of the temperature distribution in the Hertzian zone and an analytical treatment of the effect of inlet starvation upon film thickness in order to aid the recognition of inherent non- Newtonian behaviour in the analysis of experiments. Experiments with markedly non-Newtonian lubricants (a series of silicones of differing chemical structure) are reported and an attempt is made to relate their hydrodynamic performance and degree of non-Newtonian behaviour to their molecular geometry. A four disc machine, employing a low elastic modulus (perspex) central specimen has been developed to examine non-Newtonian behaviour under conditions which reproduce the kinematics of low conformity contacts but which eliminate the influences of pressure and temperature whose unavoidable presence poses the major problem in the interpretation of experiments with conjunctions between metallic specimens. Excellent agreement is found between the experimental results and published non-Newtonian behaviour obtain from oscillatory shear measurements.