Elastohydrodynamic Lubrication

In the previous chapter we discussed the formation of a hydrodynamic film of lubricant to support a normal load without examining the effects of the size of this load or, more usefully, the value of the load per unit area. We now look more closely at ‘highly loaded’ contacts, where loads act over relatively small contact areas. Such contacts are to be found in the so-called ‘line contacts’ of gear teeth and roller bearings and the ‘point contact’ of ball-bearings. As the contact areas in the latter cases are typically only about one-thousandth of those occurring in such situations as journal bearings, the mean pressures will be about one thousand time greater. We may appreciate that such high pressures will affect the behaviour so that the hydrodynamic solutions which were used to study journal and pad bearings will have to be modified. Indeed we shall find that these high pressures can lead both to changes in the viscosity of the lubricant and elastic deformation of the bodies in contact, with consequent changes in the geometry of the bodies bounding the lubricant film.