BEHAVIOR OF EHL FILMS IN RECIPROCATING MOTION

The behavior of elastohydrodynamic lubrication (EHL) films formed betw een a steel ball and an oscillating glass disk is examined by means of the optical interferometry technique, and the results obtained are co mpared with those of tests conducted under unidirectional conditions. The surface traction is also measured. The film profile in the contact area breathes cyclically because the wedging and squeezing actions ar e not in phase. In reciprocation under pure sliding, the thick oil fil m entrapped between both surfaces at the stroke end moves towards the exist side at about half the velocity of the glass disk. Under conditi ons of a short stroke and a high frequency, air bubbles produced in th e downstream result in oil starvation in the next stroke, so that the EHL film collapses. In the full EHL regime, the central oil film thick ness and the surface traction at the stroke center are almost the same as those under unidirectional conditions. It is also found that the o il behaves like a non-Newtonian fluid, and as a result the behavior of EHL films varies with oil and type of motion.