Effects of groove factor and surface roughness of raceway in ball-bearing-like specimens on tribological behavior and the onsets of two instabilities of dry contacts

Abstract Ball-bearing-like specimens are prepared with three groove factors ( GF ≡ r / D ; r : radius of groove; D : diameter of ball). Analyses of operating conditions are conducted for the thrust loads applied to the dry-contact specimens running with the maximum contact stress close to 2.0 GPa. The combined effect of surface roughness ((Ra) inner ) of the inner raceway and groove factor becomes the controlling factor for the slip ratio ( SR ) arising at the tribocontact of ball and inner raceway, and the average friction coefficient ( μ ¯ ) of specimen. Both the inception time (T BR ) of the instability in the running-in process and the inception time (T BS ) of the instability arising in specimen's base material are governed by the average value ( S R ¯ ) of SR . The wavinesses of raceway are the controlling factor for the significant rise of frictional torque in the running-in regime and the T BR value. The fluctuations of frictional torque arising at the time behind T BR are confirmed to be the instability arising in the base material. The theoretical prediction for T BS is determined when μ ¯ reaches the threshold value, ( μ ¯ ) threshold . For the specimens with the same GF, increasing (Ra) inner can elevate S R ¯ and μ ¯ . In the specimens with a relatively smaller (Ra) inner , GF is the dominant factor for S R ¯ ; however, (Ra) inner becomes the dominant factor for S R ¯ if the inner raceway is prepared with a relatively larger (Ra) inner . Increasing GF can result in a μ ¯ reduction, irrespective of the (Ra) inner value. Both T BS and T BR are reduced by the increasing S R ¯ . The wear losses of ball and the two raceways, however, increase as increasing S R ¯ .