ON THE BEHAVIOR OF AN OIL LUBRICATED FRETTING CONTACT

Although many engineering situations involving fretting damage are lub ricated, comparatively little has been reported on this aspect of fret ting wear. The viscosity of the lubricating oil and its boundary layer performance are expected to influence fretting behaviour, in addition to the normal fretting parameters, such as stroke and contact force. This paper examines the effect of lubrication regime, oil viscosity an d stroke on the behaviour of a ball-against-flat specimen arrangement. Ball and flat specimens were both manufactured from a bearing steel ( SUJ2). Polybutane oils, without additives, covering a range of viscosi ties from 1 to 10 000 cSt, and fretting strokes up to 35 mu m were inv estigated. The lubricating oil was added to the fretting interface aft er 0, 3 and 2000 fretting cycles had been completed. Lubrication regim e, oil viscosity and stroke were all found to affect fretting behaviou r in terms of both coefficient of friction (or traction coefficient) a nd wear. For strokes less than 9 mu m, i.e. for conditions approaching almost complete 'stick', coefficient of friction values under oil lub rication were well in excess of double those observed without it. Thes e high values suggest that the oil was unable to penetrate into the fr etting contact region, but did maintain a shield around it, so that me tal-on-metal contact was maintained under oxygen deprived conditions. The lowest values of steady state coefficient of friction (approximate to 0.2) were observed when oil lubrication was applied after 2000 cyc les had been completed, indicating that surface roughening and the pre sence of oxide films and oxidised debris assisted penetration of the l ubricant into the fretting contact zone. (C) 1997 Elsevier Science S.A .