STATIC FRICTION OF CONTACTING REAL SURFACES IN THE PRESENCE OF SUBBOUNDARY LUBRICATION

A model for calculating the static friction coefficient of contacting real (rough) surfaces in the presence of very thin liquid films (sub-b oundary: lubrication) is det eloped. The liquid has a very high affini ty for the surfaces and its thickness is of the order of the surface r oughness average. An extension of the Greenwood and Williamson (GW) as perity model and an improved Derjaguin, Muller and Toporov (DMT) adhes ion model are utilized for calculating die contact and adhesion forces , respectively. The effects oft the liquid film thickness and the surf ace topography on the static friction coefficient are investigated. A critical film thickness is found above which the friction coefficient increases sharply. The critical thickness depends on the surface rough ness and the external normal load. This phenomenon is more profound fo r very smooth surfaces and small normal loads, in agreement with publi shed experimental work on magnetic hard disk interfaces.