In the designing process of an outer sole of a shoe, the grip properties on various surfaces must be considered, for example on wet marble, wet manholes and oily floors in kitchens and factories. It is known that adhesion between rubber and a floor has an influence on static and dynamic friction coefficients. Thus, it is expected that surface and interfacial free energies of rubber, floors, and lubricants contribute to static and dynamic friction coefficients under lubricated conditions. Spreading coefficient derived from interfacial free energies of the rubber, the floor and the lubricant indicates spreading ability of lubricant between the rubber and the floor. Work of adhesion derived from surface and interfacial free energies of the rubber and the floor indicates peel-off work of this system. In this paper, the relation among static and dynamic friction coefficients, spreading coefficients and work of adhesion were investigated. The results explained that both the static and dynamic friction coefficients had negative correlations to the spreading coefficients. On the other hand, the positive correlations between both friction coefficients and work of adhesion were obtained.
As a first step to develop a method of in situ analysis of tribological behavior under oil lubrication, surfaces after the tribo-test with the remaining lubricating oil were analyzed with Raman spectroscopy. A ball-on-disk type tribo-test using a S45C disk and a SUJ2 ball was performed, and then its friction track of the disk surface was analyzed by Raman spectroscopy. Polysulfide and mineral oil were used as the lubricating oil without dilution. In addition to each lubricant peak, iron disulfide (FeS2) tribofilm peaks were detected on the friction track in the case of polysulfide, whereas the magnetite (Fe3O4) peak was detected on the friction track in the case of mineral oil. FeS2 intensity increased overtime in the case of the test at 200°C. In this way, tribofilm and oxide were detected as the remaining lubricating oil by Raman spectroscopy, which therefore suggests that Raman spectroscopy is an effective analysis method to investigate the formation process of tribofilm and oxide under oil lubrication.