Measurements of real non-Newtonian response for liquid lubricants under moderate pressures

A thorough characterization of all viscous flow properties relevant to stea dy simple shear was carried out for five liquid lubricants of current inter est to tribology. Shear stresses were generated to values significant to co ncentrated contact lubrication. Two types of non-Newtonian response were ob served: shear-thinning as a power-law fluid and near rate-independence. Fun ctions and parameters were obtained for the temperature and pressure depend ence of the viscosity and of the time constant for the Carreau-Yasuda equat ion. Results are consistent with free volume and kinetic theory, but direct ly contradict many assumptions currently utilized for numerical simulation and for extracting rheological properties from contact measurements.