Molecular Degradation of Lubricants in Sliding Elastohydrodynamic Contacts

Abstract

The extent of lubricant degradation in a sliding elastohydrodynamic contact has been investigated. The lubricant was subjected to peak Hertz pressures of approximately 109 N/m2 and average shear rates of 106 to 107 s−1 . Hydrocarbon lubricants, bulk polymers and polymer containing hydrocarbon solutions were examined. Small samples (10−8 m3 ) of test lubricant were extracted from the entrance and exit regions of the EHD contact. These samples were then analyzed to determine alterations in the molecular weight distribution. In addition, a microcapillary viscometer was developed to determine viscosity changes. Degradation resulting in up to a 70 percent viscosity loss was found in fluids which had molecular weights of over 1000. High degrees of correlation were found between molecular weight loss, viscosity loss and the energy dissipated in the contact.