On the mechanism of multi-valued friction in unsteady sliding line contacts operating in the regime of mixed-film lubrication

Systematic analyses are presented to reveal the mechanism of multi-valued friction behavior in lubricated sliding contacts with time-varying velocities. The analyses are based on the theoretical results generated by a mixed-film friction model developed in this paper for line contacts. The model, which integrates theories of transient elastohydrodynamics and asperity contact mechanics, is validated by comparing its results with published experimental data. The results and the subsequent analyses disclose that strong multi-valued friction behavior can only be generated in the mixedfilm lubrication regime with simultaneous presence of significant asperity contacts and hydrodynamic squeeze. Principal factors which influence the magnitude of dynamic friction are investigated in the paper. Being instructive to the design oftribocontacts in precise-motion control systems, the analyses suggest means to minimize the undesirable multi-valued friction behavior through proper selection of system parameters.