Friction-speed characteristics of elastohydrodynamically lubricated contacts with anomalous film shapes

An optical elastohydrodynamically lubricated (EHL) test rig was modified, so that the measurement of friction and mapping of the lubricated contact could be executed simultaneously. Pure sliding tests using viscous polybutene oils were carried out with very slow entrainment speeds to achieve isothermal conditions. The experimentally obtained friction-speed curves are characterized by anomalous wave shapes with two inflection points, a peak and a valley. This deviates from the traditional Stribeck curve, which is characterized by a monotonic increasing trend from EHL regime to hydrodynamic lubrication regime. Comparing the abnormal friction-speed curve with the corresponding film shapes, the two inflection points closely relate to the appearance of a dimple at the inlet of the contact and the loss of elastic deformation of the contact surfaces, respectively. Previous numerical studies hypothesized that the anomalous EHL film shape is due to boundary slippage. The present finding of a reduction in friction with the anomalous EHL film shapes gives further support to this hypothesis. © 2011 Authors.