Friction in lubricated soft-on-hard, hard-on-soft and soft-on-soft sliding contacts

Friction in lubricated soft contacts is examined using a ball-on-disc tribometer with the focus on the effect of configuration. In the soft-on-hard and hard-on-soft configurations, one of the contact-pair members is soft while the other one is hard. In the soft-on-soft configuration, both members are soft. For a soft disc, time-dependent viscoelastic deformations contribute to friction. Upon correction for the hysteretic losses, estimated using a theoretical model, the friction coefficient in the full-film regime does not depend on configuration. This holds also for high loads, when the deformations are finite. The combined effect of configuration and surface roughness on the transition from the full-film to the mixed lubrication regime is also examined.