Fluid Rheological Effects in Sliding Elastohydrodynamic Point Contacts With Transient Loading: 1—Film Thickness

Abstract

This paper describes an experimental investigation of the elastohydrodynamic problem. The investigation was limited to a study of nominal point contacts in pure sliding motion. The profile of the lubricant film separating the bearing surfaces was determined during a transient of the normal load. During this transient the Hertzian contact stresses were increased from zero to a maximum of 150,000 lbf/in2 in approximately 45 milli-secs. The sliding velocities used in this study were varied from 13.7 to 92.1 ips. The resulting mean shear rate, however, was typically 107 reciprocal seconds. Both pure and polymer-blended naphthenic and paraffinic oils, in addition to several synthetic fluids, were studied. On the basis of the film thickness profiles obtained for the polymer-blended oils, it was concluded that the ambient value of viscosity often used in theoretical considerations does not characterize the behavior of the system. It was also found that the rapid application of the normal load had a negligible effect on the film thickness profile. During this investigation the contact traction was also measured. The results of those measurements are reported in the companion paper, “Fluid Rheological Effects in Sliding Elastohydrodynamic Point Contacts With Transient Loading: II—Traction.”