Tribological behavior and thermoelastic instability demonstrated in ball-bearing -like specimens operating in dry contacts and with grease lubrication

Ball-bearing-like specimens are prepared with different groove factors (GF) to simulate a ball screw operating in dry contact and grease lubrication. The fluctuations of frictional coefficient μ are identified as instabilities in the running-in process and in the tribo contacts through the model developed for the threshold value μ_threshold. The thermoelastic instability in the running-in is dominated by the surface roughness (R_a) and the GF, and is thus governed by the slip ratio (SR). The inception of running-in instability is the earliest when SR is the highest. With a fixed GF, an increase in R_a results in a SR rise. Wear coefficient increases by raising SR. The time for instability inception of base material is shortened by increasing SR.