Synchronous observation with friction measurement prior to and during occurrence of scuffing

In the current work, scuffing phenomenon was investigated by a direct observation of a contact area. A ball-on-disc test rig was used, which produced a point contact area between a rotating sapphire disc and a stationary steel ball. Sequence of the friction and photograph in the contact area was synchronously obtained prior to and during occurrences of scuffing. Experiments were conducted in a dry condition and a lubricated condition with hexadecane. In the lubricated condition, wear debris accumulated in the inlet zone entered suddenly into the contact area to sharply increase the friction coefficient. On the other hand, macro plastic flow occurred in the whole contact area in the dry condition during a rapid increase in friction coefficient.