Static friction experiments and verification of an improved elastic-plastic model including roughness effects

An experimental study was conducted to measure the static friction coefficient under constant normal load and different interface conditions. These include surface roughness dwell time, displacement rate, as well as the presence of traces of lubricant and wear debris at the interface. The static friction apparatus includes accurate measurement of friction, normal and lateral forces at the interface (using a high dynamic bandwidth piezoelectric force transducer), as well as precise motion control and measurement of the sliding mass. The experimental results show that dry surfaces are more dependent on the displacement rate prior to sliding inception compared to boundary lubricated surfaces in terms of static friction coefficient. Also, the presence of wear debris, boundary lubrication, and rougher surfaces decrease the static friction coefficient significantly compared to dry smooth surfaces. The experimental measurements under dry unlubricated conditions were subsequently compared to art improved elastic-plastic static friction model, and it was found that the model captures the experimental measurements of dry surfaces well in terms of the surface roughness.