Thesis (M.S.)--State University of New York at Binghamton, Thomas J. Watson School of Engineering and Applied Sciences, Systems Science and Industrial Engineering Department, 2006. / Includes bibliographical references.

<p>The present thesis thoroughly treats a special friction reduction phenomenon that may appear in boundary lubricated tribological contacts, of the type encountered in numerous mechanical components made of steel. The phenomenon involves the formation of a special type of tribofilm that offers very low coefficients of friction. Typically the friction level becomes halved when the film is formed, compared to when it is not formed. Since boundary lubricated mechanical components are so common in all sorts of machinery, the technical and economical potential of this phenomenon is gigantic.</p><p>The tribofilm is produced on the steel surface, resulting in friction coefficient reduction from typically 0.08–0.1 to 0.04–0.06. The tribofilm is formed from the metal in the carbon coating and sulfur in the oil additive. The main film studied was WS₂, which is a well-known low-friction material. It includes easy shearing atomic planes, in the same fashion as the solid lubricants MoS₂ and graphite. Virtually no carbon is present in the tribofilm, despite carbon being the main constituent of both the coating and the additive. No films form on the Me-DLC coated part.</p><p>It was also found that WSi₂-particles could result in the formation of WS₂-containing tribofilms. It was concluded that they, just as the W-DLC film, were sufficiently weak to mill down to very small particles, and chemically reactive in the prevailing tribological conditions. However, WC particles were too stable, both mechanically and chemically, to result in any film formation.</p><p>The chemical driving forces for formation of the tribofilms were analyzed using EkviCalc, a commercial software for thermodynamical calculations based on minimization of Gibbs free energy for a system as a function of temperature and pressure. The simulations indeed confirmed that both WS₂ and MoS₂ should be expected to be stable compounds, coexisting with FeS, in the studied environment. As a spin-off result, the thermodynamical calculations indicated that coatings of the Cr-C type should impose very little tribochemical wear of the uncoated steel surface, and even reduce the forma-tion of FeS (the “traditional” tribofilm) on the steel surface in S-containing environments. </p><p>As a final spin-off, the thermodynamical calculations indicate that the Ti-C coating should be very resistant to tribochemical wear in the S-containing environment. </p>

No description available.

The present thesis thoroughly treats a special friction reduction phenomenon that may appear in boundary lubricated tribological contacts, of the type encountered in numerous mechanical components made of steel. The phenomenon involves the formation of a special type of tribofilm that offers very low coefficients of friction. Typically the friction level becomes halved when the film is formed, compared to when it is not formed. Since boundary lubricated mechanical components are so common in all sorts of machinery, the technical and economical potential of this phenomenon is gigantic. The tribofilm is produced on the steel surface, resulting in friction coefficient reduction from typically 0.08–0.1 to 0.04–0.06. The tribofilm is formed from the metal in the carbon coating and sulfur in the oil additive. The main film studied was WS2, which is a well-known low-friction material. It includes easy shearing atomic planes, in the same fashion as the solid lubricants MoS2 and graphite. Virtually no carbon is present in the tribofilm, despite carbon being the main constituent of both the coating and the additive. No films form on the Me-DLC coated part. It was also found that WSi2-particles could result in the formation of WS2-containing tribofilms. It was concluded that they, just as the W-DLC film, were sufficiently weak to mill down to very small particles, and chemically reactive in the prevailing tribological conditions. However, WC particles were too stable, both mechanically and chemically, to result in any film formation. The chemical driving forces for formation of the tribofilms were analyzed using EkviCalc, a commercial software for thermodynamical calculations based on minimization of Gibbs free energy for a system as a function of temperature and pressure. The simulations indeed confirmed that both WS2 and MoS2 should be expected to be stable compounds, coexisting with FeS, in the studied environment. As a spin-off result, the thermodynamical calculations indicated that coatings of the Cr-C type should impose very little tribochemical wear of the uncoated steel surface, and even reduce the forma-tion of FeS (the “traditional” tribofilm) on the steel surface in S-containing environments. As a final spin-off, the thermodynamical calculations indicate that the Ti-C coating should be very resistant to tribochemical wear in the S-containing environment.

No description available.

<p>Human joints are able to withstand millions of loading cycles with loads regularly more than 3 times an individual's body weight in large part due to the unique bearing properties of articular cartilage, a strong, slippery tissue that covers the ends of long bones. PRG4 is a boundary lubricating glycoprotein present on the cartilage surface and in the synovial fluid surrounding it. While evidence that PRG4 lubricates and preserves normal joint function is strong, little is known of its effect on cartilage surface properties, the mechanism by which it lubricates, or its postulated role of preventing wear on joints. The effect of PRG4 on cartilage friction, wear, structure, morphology, and the mechanisms by which it mediates these factors are studied here. Methods to study these parameters at the microscale using atomic force microscopy are also developed. </p><p>Cartilage of mice with the Prg4 gene (which expresses PRG4) deleted is shown to be different in a number of ways from wild type cartilage. The uppermost layer is thicker and less uniform and the surface is rougher and softer. There is also a loss of proteoglycans, structural components of cartilage, from the underlying superficial tissue, and apparent tissue damage in some cases. Wear in the presence of PRG4 in shown to be significantly lower than in its absence, a finding which may have direct implications for prevention and treatment of osteoarthritis. It appears that PRG4 needs to be present in solution, not merely on the cartilage surface to have this effect, indicating that adsorption properties are important for wear prevention.</p> / Dissertation

In this study, Reometer AR2000 is used to investigate the effect of shear rate on viscosity of emulsion. And a model for the effective viscosity of emulsion is established. Moreover, another model for the hydrodynamic lubrication with binary mixtures of non-Newton fluids is developed. The coupled modified Reynolds are solved by combining the advanced multilevel method with the Newton-Raphson method. The effect of shear rate on lubrication characteristics of hydrodynamic lubrication of emulsion is investigated in cold rolling process. Research results show that the viscosity of emulsion is decreased with increasing the shear rate. Hence,the oil film thickness, oil preasure and oil concentration under hydrodynamic lubrication are increased with decreasing the slide-to roll ratio. Emulsion will be Newton fluid under high shear rate. In the cold rolling process, the emulsion shows the high shear rate, and the elastic deformation of roller and strip are considersd. Hence the end point of plastic zone of strip is moved to oulet zone due to the lubricated zone is increased, so that the film thickness is higher than that for rigid body. When roller radius is increased, the effective elastic modulus and the thickness reduction of strip are decreased, then the lubrication characteristics in cold rolling process are influenced by elastic deformation. When the rolling speed is increased , the inlet film thickness is increased, and the roll torque is slightly increased, but the rolling force and peak preasure are almost not influenced.

Abstract This study proposes a model to predict the effect of lubricant starvation on EHL behavior of line contact, including the boundaries among the starved, fully flooded, and over-flooded lubrications. A pre-inlet region is analyzed to overcome the discontinuous phenomenon of film thickness at the position of the meniscus presented in the previous model under the starvation. The relationship between the film thickness of the supply region and the position of the meniscus is established. The prediction formulas for the minimum film thickness required to achieve the fully flooded condition is expressed in terms of the load and the speed. This formula can be used to predict the fully flooded/starved boundary under certain of flow rate in the supply end. In the analysis of the pre-inlet region, the surface speed, the pressure and the mass flow rate are assumed to be continuous with the supply region and the pressure region, so that its film thickness can be calculated by the mass flow rate equation. However, when the backflow occurs in the boundary between the pre-inlet and pressure region, only part of the film thickness flows into the pressure region, and the rest film only performs recirculation. When no backflow is observed at this boundary, the film thickness in the pre-inlet region easily rises and continuously connects to the pressure region. If the film thickness in the supply end is increased, the surface speed gradually decreases at the inlet end of the pre-inlet region. When the film thickness in the supply end increases to twice as high as the minimum film thickness that required to achieve the fully flooded condition, the surface speed at the inlet end of the pre-inlet region becomes stationary. Hence, when the film thickness in the supply end continues to increase to more than twice, the backflow occurs at the supply region, and this behavior is called the over-flooded lubrication.

Three flexure pivot pad bearings (FPBs) with different preloads are evaluated for use in high performance applications by comparing them to a hybrid hydrostatic bearing (HHB). One application of these bearings is in turbopumps for liquid rocket engines. To evaluate bearing performance, the lift-off speed of the shaft from the bearing surface is experimentally determined. Experimental data of lift-off are collected using a circuit running through the shaft and the designed bearing. Other methods for measuring liftoff speeds were attempted but did not yield consistent results. Water is used as a lubricant to simulate a low viscosity medium. In comparison to load-capacity-based predictions for FPBs, the experimental results showed lower lift-off speeds, higher load capacities, higher eccentricity ratios, and lower attitude angles. The bearings’ predicted load capacity determined lift-off speed predictions, but the experimental results show no clear trend relating lift-off speed to load capacity. This was for a range of running speeds, with the design speed defined as the final speed in a particular test case. At 0.689 bar supply pressure and for a design speed of 3000 rpm, the HHB showed greater load capacities and lower eccentricities than the FPBs, but the FPBs had lower lift-off speeds and attitude angles. In fact, the FPBs in the load-between-pad orientation outperformed the HHB in the load-on-pocket orientation with lower lift-off speeds for the shaft weight-only case. An increased supply pressure lowered the lift-off speeds in the HHB tests. If the load in the bearing application remains relatively small, a FPB could be substituted for an HHB.

In this study, a electrical pitting tester and SEM are employed to investigate the effects of supply voltage, supply current, and oil film thickness on the electrical behavior, the action forces, and the formation mechanism of electric pitting for the lubricated surface of steel pair at sliding speed of 1£gm/sec using an additive of MoS2 in paraffin base oil under DC electric field. According to the experimental results and the observations of the surface pitting, two electrical pitting regimes are found under the influences of shaft voltage, oil film thickness, and particle concentration of additive, namely, pitting and no- pitting regimes in static condition. The area of pitting regime increases with increasing additive concentration and supply current. Furthermore, The ratio of pitting area to the interface power increases rapidly with increasing additive concentration and oil film thickness. This results from the molten plateau that directly connects two specimens, and the interface power is mainly consumed at the heating of the plateau and the interfacial materials. However, the weld strength of the plateau isn¡¦t influenced with additive concentration. It is known from the observations of the surface pitting in dynamic pitting occurs that the pitting width increases with increasing oil film thickness and additive concentration. Finally, the formation processes of electric pitting on the lubricated surface for both static and sliding conditions are deduced from the results of the normal force, the friction force, the interface impedance and the observations of the surface pitting.