Scuffing Performance

The tribology TRL methodology addresses superficial tribology attributes of wear, scuffing and fatigue in a logical sequence of TRL 3 tests. Wear and scuffing are initially addressed with subsequent tests for wear and fatigue. Wear is intimately connected with both scuffing and surface initiated fatigue. A high speed scuffing load capacity test method is frequently used as a primary test to screen and qualify aviation oils and bearing/gear materials. AISI 9310 carburized gear steel is frequently used to evaluate aviation oils for scuffing performance. A MIL-PRF-23699 (or SAE AS57680) standard (STD) oil is frequently used as a baseline oil to rank other aviation oils for scuffing. While a scuffing test, conducted with high sliding velocities and a baseline gear steel AISI 9310, is more in line with gears than bearings, it does have relevance to bearing skidding conditions. Load capacity scuffing tests have been found to be a good TRL 3 screening test for aviation bearings and gears.

The operating conditions for this test method were derived from a Ryder high speed gear scuffing test developed during the early days of synthetic jet engine oils. To accomplish this, the sliding velocity (Us) on the active tooth profile, where scuffing initiates, was selected as a controlling parameter. The entraining velocity (Ue) was adjusted to create an appropriate level of lambda (h/σ), where the application of a continuing increase in load (i.e. stress) causes a thermally driven scuffing event. The resulting entraining velocity, Ue is 5.7 m/s and the sliding velocity, Us is 8.8 m/s