MEASURED TRANSITIONS BETWEEN STICKING AND SLIPPING AT LUBRICATED LINECONTACTS

Sets of unsteady friction experiments are presented. The data allow an interpretation to be made of the principal physical phenomena that oc cur during the transitions that take place during impending slip or st ick in interrupted sliding. The rest geometry is that of a lubricated line contact, to which different patterns of velocity oscillation are applied. During acceleration from a rest or near-rest condition, a tan gential contact stiffness and a microslip regime are observed before m acroscopic sliding takes place. We also note a region of ''microstick, '' somewhat analogous to microslip, which makes it difficult to unambi guously identify a particular point where sticking actually begins. Hi gh frequency vibrations were also monitored, and while interesting, do not appreciably affect the main friciton behavior. The friction behav ior is considerably more complicated than for dry contacts. Implicatio ns to the modeling of unsteady lubricated friction are discussed.