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

摘要

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 ((mu) over bar) 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 ((SR) over bar) 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 (mu) over bar reaches the threshold value, ((mu) over bar)(threshold). For the specimens with the same GF, increasing (Ra)(inner) can elevate (SR) over bar and (mu) over bar. In the specimens with a relatively smaller (Ra)(inner), GF is the dominant factor for (SR) over bar; however, (Ra) inner becomes the dominant factor for (SR) over bar if the inner raceway is prepared with a relatively larger (Ra)(inner). Increasing GF can result in a (mu) over bar reduction, irrespective of the (Ra)(inner) value. Both TBS and TBR are reduced by the increasing SR. The wear losses of ball and the two raceways, however, increase as increasing (SR) over bar.