High loaded oscillating bearings are used on several industrial fields such as robotics, wind power, aeronautics and aerospace. These bearings are subjected to extremely high local contact pressures ...and relatively low oscillatory speed. In this work, endurance tests on commercial single row spherical roller bearings enable to propose a degradation scenario for the bearing lifecycle. Topographical analyses carried out at each phase of the bearing life allowed to understand the degradation evolution at the interface between the inner-ring raceway and rolling elements. The analysis of the experimental results, with the support of numerical stress analysis, led to the understanding of the involved accommodation mechanisms. Then, a comparison with the wear processes in deep-groove ball bearings is provided.
•Roller bearings under high load oscillation are investigated and compared to ball bearings.•The overall surface and damage evolution of roller bearings are analyzed.•The competition between surface and subsurface accommodation mechanisms are highlighted.•The role of the grease on the surface protection is analyzed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SBCE, SBJE, UILJ, UPUK
Changes in color and texture of green bean pods (Phaseolus vulgaris L. cv. Estefania) as a function of temperature and time of cooking were studied for various techniques where the vacuum is applied ...in different ways: cook-vide and sous-vide. A central composite rotatable design was used to establish the best conditions to provide maximum greenness (a* very negative) and minimum firmness for both cooking methods using a range of firmness measured with puncture test. A significant regression model was found to describe the color changes (−a*, greenness) and texture (puncture test and Kramer cell test) with regard to the factors time (in the range of 13.8–56.21 min) and temperature (in the range of 77.9–92.1 °C). The optimum value for cooking temperature was 92 °C for both treatments. The best cooking times were 28 and 14 min for 1 and 7 days of storage by sous-vide treatment, respectively. The optimal cooking times were 22 and 19 min for 1 and 7 days of storage by cook-vide treatment, respectively. Sensory tests were conducted with 84 consumers. Results show that sous-vide treatment is better preferred than cook-vide and traditional cooking.
► We studied the effect of vacuum cooking on green beans pods (texture and colour). ► We optimized vacuum treatments in function of time and temperature conditions. ► We modeled greenness and texture in both vacuum treatments. ► We compared by means a sensory test the vacuum treatments and traditional cooking. ► Consumers preferred sous-vide treatment due to texture and flavor.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPUK
► Tribological properties of nc-TiAlN/a-Si
3N
4 thin films. ► Deposition parameters influence the Si content and residual stress. ► Increasing Si content enhances mechanical properties and wear ...resistance. ► Higher Si
3N
4 amorphous phase increases toughness and adhesion of the coating. ► Si content and deposition parameters are critical factors to control the endurance of the coating.
In this work, the endurance of TiAlSiN nanocomposite thin films subjected to tribological solicitation is studied. These coating were deposited on M2 steel substrate by magnetron sputtering. Dry sliding experiments were conducted at ambient temperature against WC–Co ball. Coefficients of friction, wear rates and endurances were correlated with the composition, microstructure, mechanical properties, residual stress and adhesion of the coatings. The hardness and elastic modulus were found dependent not only on the composition but also on the residual stress induced by the deposition process. Friction coefficient was found to be independent on Si content while the wear rate is strongly reduced for higher Si contents. The formation of a nanocomposite microstructure, the amount of amorphous Si-based phase and both, wear resistance and adhesion are shown as the critical factors to determine the endurance of the coating.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPUK
Several industrial applications require bearings to work under slow oscillating motions and very high contact pressures (aircraft actuators, wind turbine, robotic arms, etc.). Hence, a boundary ...lubrication regime predominates. However, grease provides the lubrication essential to assure bearing integrity. In this study, the mechanisms involved in protecting the contact surfaces are investigated. High loaded oscillating movements have been applied on a commercial greased deep groove ball bearing. The morphology of its contact was observed using Scanning Electron Microscopy (SEM), revealing superficial transformations. Further, with an extreme surface X-Ray Photoelectron Spectroscopy (XPS) analysis, three cross-sections made by a nanomachining process (FIB) were investigated using Transmission Electron Microscopy (TEM). The analyses revealed a modified layer at the contacts generated by grease interactions.
•Slow oscillations and high contact pressure result to a starve lubrication regime.•Greases can provide additives suitable for extremes conditions close to contacts.•Thermophysical reactions of additives create solid protective layers in contacts.•Multi-technique approach of a stratified modified layer.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SBCE, SBJE, UILJ, UPUK
MoS2 is a well-known lubricant for vacuum application. However, the role of contamination in achieving low friction and long wear life in industrial applications remains unclear as the literature ...presents some contradictions. A former study performed in ultrahigh vacuum showed that in a sliding macro contact, the origin of low friction was primarily due to the formation of a 3rd body layer, its trapping and its ability to flow plastically inside the contact. The study showed a homogenisation of the chemical elemental composition of the material and the internal coating contaminants throughout the contact and the 3rd body. To study that homogenisation and to verify if a chemical rearrangement occurred at a molecular level under friction, Time-of-Flight Secondary Ion Mass Spectroscopy analyses are performed. Firstly, they show that the MoS2 coating made by Physical Vapour Deposition is not a “MoS2” but is a complex MoxSyOz structure. Secondly, they show that a chemical rearrangement of the material with the internal contaminants effectively occurs in ultrahigh vacuum and leads to the formation of a unique MoSxOy phase. Such a phase shows the beneficial role of reasonable contamination on the tribological behaviour.
•Original MoS2 coating is a complex MoxSyOz structure.•Tribologically induced chemical rearrangement was identified inside the contact.•Chemical rearrangement leads to the formation of a lubricious MoSxOy phase.•Coating internal contamination takes part in MoSxOy formation and so is beneficial.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPUK
Friction in highly loaded lubricated contacts (where the pressure is greater than 1 GPa) may present a plateau at intermediate slide-to-roll ratio, known in the literature as the limiting shear ...stress (LSS) plateau. Its physical origins and its dependence to the operating conditions are still unclear, that is why predicting friction in such contacts still remains an issue. Apart from the nature of the lubricant, the two main parameters influencing the friction plateau value are pressure and temperature. The literature provides several empirical expressions of the LSS which either consider the pressure influence only, or both pressure and temperature but almost always with coupled terms. Therefore, the published LSS values derived from friction measurements can be considered as the macroscopic consequence of the influence of pressure and temperature but also of shear heating that occurs in sliding highly loaded contacts. In this paper, the contribution of each parameter was studied separately, i.e. through experiments accrued out under nominal isothermal conditions, but conducted at different temperatures and pressures on two lubricants: a synthetic ester (benzyl benzoate) and a turbine mineral oil. A new LSS model was derived, based only on the mechanical (i.e. shear) contribution to the LSS. Surprisingly, a simple linear dependence of the LSS with both pressure and temperature was found, revealing that the influence of each of the two parameters is decoupled from the other. As far as we know, this is the first time that such an uncoupled LSS model in pressure and temperature is reported. This work offers a better quantification of the response of lubricants submitted to very high pressure and high shear: it should help to improve friction prediction in highly loaded lubricated contacts.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Organophosphorus compounds are common additives included in liquid lubricants for many applications, in particular automotive applications. Typically, organic phosphites function as ...friction-modifiers whereas phosphates as anti-wear additives. While the antiwear action of phosphates is now well understood, the mechanism by which phosphites reduce friction is still not clear. Here we study the tribochemistry of both phosphites and phosphates using gas phase lubrication (GPL) and elucidate the microscopic mechanisms that lead to the better frictional properties of phosphites. In particular, by in situ spectroscopic analysis we show that the friction reduction is connected to the presence of iron phosphide, which is formed by tribochemical reactions involving phosphites. The functionality of elemental phosphorus in reducing the friction of iron-based interfaces is elucidated by first principle calculations. In particular, we show that the work of separation and shear strength of iron dramatically decrease by increasing the phosphorus concentration at the interface. These results suggest that the functionality of phosphites as friction modifiers may be related to the amount of elemental phosphorus that they can release at the tribological interface.
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IJS, KILJ, NUK, UL, UM, UPUK
The effects of temperature, pressure and shear stress on the viscosity of simplified automotive lubricants—polymer-thickened base oil solutions—were investigated. Various polymers—with different ...molecular weights and conformations (comb, linear and star)—were used at low concentration (1.2 % w/w) in a hydrocracked mineral base oil: a poly(alkylmethacrylate), an olefin copolymer and a poly(isoprene-styrene hydrogenated). Their rheological behavior was studied and modeled with a Vogel-Tamman and Fulcher equation, a modified Williams-Landel-Ferry-Yasutomi relationship and a Carreau-Yasuda-like formula. Then, the Einstein’s law was used to rapidly and simply determine the hydrodynamic radii of polymers as a function of temperature and pressure. Calculations from Flory equations, intrinsic viscosities and direct measurements confirmed the relevance of this methodology. Finally, molecular considerations allowed a good understanding of the rheological response of polymer solutions.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
In this study, tribochemical reactions of borate ester additives on steel surfaces were simulated experimentally by gas phase lubrication. Trimethylborate (TMB) was employed as a model molecule of ...the borate chemical function. TMB was introduced under gas phase up to 5 hPa in a new tribometer dedicated to gas phase lubrication. Friction tests were conducted at room temperature. In order to identify the nature of the generated tribofilm, X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) analyses were carried out inside and outside the track of the tested samples. The results showed a reduction of the friction coefficient down to 0.2 by increasing the TMB gas pressure. This reduction in friction was induced by the formation of a tribofilm of iron oxide partially digested by a borate glass network. The reduction in friction was attributed to the formation of the borate glass. The digestion of abrasive iron oxides by the borate glass was purported to be responsible for the reduction in the wear. The tribochemical reaction of TMB on steel surfaces is discussed in relation to the hard and soft acid base (HSAB) principle.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Tribofilms, formed by tribochemical reactions between steel surface and trimethylphosphite in gas phase, have been characterized by various structural and analytical techniques including transmission ...electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and energy dispersive spectroscopy (EDS). Focus ion beam technique has been used to prepare cross-sections of the tribofilm for further TEM and EDS analyses. Cross-sectional views of tribofilms obtained by gas phase lubrication show that tribofilm has an inhomogeneous thickness ranging from 10 to 50nm and is amorphous. Complementary XPS and EDS analyses confirm the formation of various iron phosphides as the major component of the tribofilms, with a preferential nucleation of Fe3P stoichiometry at the interface between steel and tribofilm.
► Tribofilm was formed with phosphite lubricant additives. ► Cross-section of the tribofilm was investigated. ► Amorphous iron phosphide tribofilm is formed. ► Stoichiometry of iron phosphide changed at the interface with steel substrate.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPUK
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