This paper presents new results on the effects of surface roughness in a point EHL contact. For several lubricants, abnormal lubricant aggregations were observed in the area of artificial roughness feature under rolling–sliding conditions. In these cases, compared to known roughness effects, the aggregated lubricant causes enhanced deformation of roughness feature producing a higher average separation of surfaces and presumably higher local pressure variations. The lubricant aggregation led to the maximum film thickness increase of 70–240 nm above the smooth surface
profile.
It was discussed that a local increase of film thickness should be connected with a local decrease of average lubricant speed to maintain flow continuity. Lower average lubricant speed can be achieved by non-linear continues through-film speed profile or by the presence of slip zone (shear localization) somewhere across the film. Then, the character of roughness feature could contribute to lubricant aggregation by its shape. Lubricant aggregation was observed predominantly for lubricants giving a high traction force and with a high pressure-viscosity coefficient. Therefore, at least for some fluids, the possibility of lubricant phase transition cannot be fully excluded. Some results support thermal effects considerations while the others do not. Finally, more data with other features are necessary to explore this lubricant aggregation in depth. Nevertheless, this phenomenon could provide an extra protecting function against wear of surfaces in concentrated contacts.