Experimental analysis of a high pressure lubricated contact under dynamic normal excitation force

Abstract

Lubrication processes in high pressure contacts are of great importance in many applications (valves, gears, bearings, cams…). The analysis performed for better understanding of film forming capability of lubricant is usually made considering only static conditions. Unfortunately, contacts are often undergoing dynamic excitations that may be periodic or random dynamic normal forces. From a tribological point of view it is important to account for the effects of the dynamic loading on lubricating film genesis. On the other side, from a dynamic point of view, it is necessary to evaluate the effects of lubricant flow under controlled slide/roll conditions on the dynamic response of the contact and particularly it's damping properties. That is why we have developed a new set-up based on an optical EHL rig fitted with a rig which has been adapted to superimpose an external normal load excitation on the static one. With this new machine, we are able to simultaneously measure the evolution of the oil film thickness and the dynamic response of the contact under harmonic loading. In this paper, the capabilities of the apparatus are presented. From a dynamical point of view, modal properties are firstly explored both experimentally and theoretically. The model used is based on the finite element method for which the linearised stiffness of the contact is introduced. From a tribological point of view, the required optical acquisition is adapted to the dynamic properties of the contact response. Some preliminary results are given which illustrate the originality of the test rig.