This master’s thesis describes the influence of conformity on friction in rolling bearings. The coefficient of friction is measured on an experimental machine - Mini Traction Machine 2 – using ball-on-disc method. The results are plotted in graphs which showing the dependence of the coefficient of friction at spin-to-roll ratio for specific conformity, normal load and speed in the contact area. The influence of load, speed or different lubricant viscosity is verified for a given value of conformity. Experimentally obtained data are compared with the mathematical model developed in MatLab, within this thesis.

The excellent lubrication present within mammalian synovial joints attracted scientific interest, and some close-to-realistic models were applied to study the mechanism in vitro. In this project, the synergistic lubrication of synovial fluid was investigated by using 1,2-Dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC), hyaluronic acid (HA), and phosphate-buffered saline (PBS buffer) to mimic the synovial fluid. Lubrication by the model synovial fluid was studied using borosilicate glass specimens in Mini-Traction Machine (MTM). The experiments proved that the DPPC vesicle solution and mixed DPPC/HA solution had excellent lubrication ability, stemming both from adsorption of a lubricious layer at the surface of glass specimens and from presence of material reservoir available for repair of wear defects in the lubricious layer. Comparing the macroscale results obtained in this project by MTM with the results in previous studies on microscale by using AFM, we concluded that the microscale study of synergistic lubrication could predict macroscale results, even though some differences were detected due to limited possibilities for exact replication of experimental conditions at the two scales.

The possible use of graphene and its derivatives dissolved in water as a green lubricant is an interesting avenue of research from tribological perspective. In this study, a highly concentrated stock solution of aqueous Graphene employing Polyethylene Glycol(PEG) as surfactant was diluted using proportionate volumes of De-Ionized (D.I.) water to generate target concentrations of Graphene in solution ranging from 15 μg/ml to 350 μg/ml . These samples were then tested for both sliding and rolling contacts. The sliding contact tests included the use of both 4-ball Tribometer test rig and triborheometer. The rolling contact tests were performed on Mini Traction Machine. The tested graphene-PEG-water admixtures held significant friction and wear advantage over D.I. Water and surfactant solutions under the same testing conditions. / Den möjliga användningen av grafen och dess derivat upplöst i vatten som ett grönt smörjmedel är en intressant forskningsaveny ur ett tribologiskt perspektiv. I denna studie späddes en högkoncentrerad grafenlösning med av-joniserat (D.I.) vatten för att alstra mållösningskoncentrationer av greven mellan 15 μg/ml och 350 μg/ml. Den testade grafenlösningen hade polyetylenglykol som ytaktivt ämne Proven testades sedan för både glidande och rullande kontakter. De glidande kontakttesten innefattade användandet av både en 4-kuletribometer och en triborometer. De rullande kontakttesterna utfördes med en Mini-traktionsmaskin. De testade proverna uppvisade signifikanta friktions- och förslitningsfördel jämfört med D.I. vatten och ytaktiva lösningar under samma testförhållanden