Friction coefficients measured at lubricated planar contacts during start-up.

Measurements of instantaneous coefficients of friction and associated motions during startup at a planar contact are presented for four different lubrication conditions. The various patterns of transient behaviour are discussed. Difficulties in interpreting static friction coefficients during rapidly tangential loads are described in relation to the motion data. It is shown that a molybdenum disulphide grease yields a friction characteristic that is quite different from either dry or boundary lubricated conditions in the presence of liquid lubricants. Transition distances from a static or maximum initial friction to kinetic conditions were examined and found to be considerably longer than had been previously found for concentrated contacts. Some suggestions regarding future studies of unsteady friction behaviour are made.