•A complete multi-DOF dynamic model for defective cases is established.•The effects of outer raceway defect on bearing dynamic behaviors are revealed.•The traction in ball-raceway contact changes ...rapidly around defect exit event.•The defect greatly affects load characteristics and angular misalignments.•Reciprocating collisions between ball and pocket will result from surface defect.
Angular contact ball bearing plays a significant role in guaranteeing the service performance of the mechanical equipment. However, the occurrence of localized defect dramatically affects the tribo-dynamic performance of the bearing, which can further result in serious accidents. Considering the influence of cage and oil lubrication, this paper proposes a complete multi-degree-of-freedom (DOF) dynamic model for defective angular contact ball bearing by analyzing the full multi-body interactions. The defect is modeled in the geometrical constraint relationships to replace the excitation functions proposed in previous studies. Based on the analysis of high-speed conditions, the effects of outer raceway defects with different sizes and position angles on the dynamic behaviors of the bearing are revealed. It is found that the defect significantly influences the load characteristics and the angular misalignments, and the traction in the ball-raceway contact shows an abrupt change around the defect exit event. The results also show that the reciprocating collisions between the ball and the cage pocket occur in the defective case which are affected by the defect scale and the bearing speed.
Friction and wear are considered as one of the major issues for engineering applications where surface interactions exist. Textured surface with modified surface functionalities as well as ...lubrication condition will greatly affect the tribological performance. In this work, laser-based surface treatment methods were developed to modify the physicochemical properties of the textured surfaces. The surface microstructure, contact angle, chemical composition and tribological performance under different lubrication conditions of the fabricate surfaces were evaluated and analyzed. The experimental results indicate that the surfaces fabricated by laser texturing combined with chemical immersion or long-time storage in air obtain distinct superhydrophobicity, and the superhydrophobic surfaces render significantly reduced friction coefficient in both starved-water or starved-oil environments. It is believed that the surface texture, wettability and chemistry have combined effects on the tribological performance, which can facilitate the formation of a relative thicker lubricant film on the friction zone, and thus the effective contact area between the friction ball and the surface is reduced. This work is expected to provide effective methods to design and fabricate textured surfaces with different surface properties aiming to enhance the tribological performance, thus benefiting various industrial sectors that have strong demand for anti-friction surface.
Display omitted
•Facile laser-based treatment methods were developed to alter surface properties.•Laser-induced superhydrophobic surface exhibits reduced friction coefficient.•Superhydrophobic surface renders lower friction coefficient with water lubrication.•The underlying mechanism for friction coefficient reduction is investigated.•This work can provide useful guidance for fabrication of anti-friction surface.
Many fretting-prone contacts are surrounded by oils, although they are not intended to lubricate them. To study the fretting behavior of contacts whose edge is exposed to engine oil, self-mated ...34CrNiMo6 +QT steel was employed with a large annular flat-on-flat contact. A displacement-controlled loading was tested in a range, encompassing stick and gross sliding. No stick-to-slip transition with displacement amplitude was observed up to a tangential-to-normal traction ratio of 1.6, compared to that of 0.5 in dry contact. Beyond that, a typical peak-to-stabilized friction curve was reached in oil with a steady-state value of roughly 0.4, lower than that of dry contact. Adhesive wear existed as the dominant wear mechanism, and the severity of adhesion increased with higher loading.
•High traction ratio in slip-stick, even more than friction peak in gross sliding.•While high-level of traction ration, mild surface damage was seen in slip-stick.•Reduced and earlier friction peaks with displacement amplitude in gross sliding.•Higher tangential loading led to more martensite grain refining and strain hardening.•Formation of carbonaceous phases like graphite on fretted surfaces in gross sliding.
Oils and grease have beneficial effects on moving parts such as connecting rod, gears, shafts, and engine to reduce wear and friction. The properties of lubricants such as tribological and ...rheological properties are an important role in oils and grease characterization. Nano additives on lubricant oils play an important role in anti-wear; reduce the coefficient of friction and enhance the rheological properties. The Tribological and rheological behavior of base oil 15W50 which have different concentrations of multi-wall Carbon Nanotubes (MWCNTs) (0.5, 1, 1.5, and 2 wt%), and constant amount of graphene nanosheets (GNSs) (0.5 wt%) were investigated. This research is the first one in studying the effect of hybrid nano additives of (MWCNTs) and (GNs) on the tribological and rheological properties of lubricant oils. Tribological characterization was carried out on four ball testing model under different loads (200, 400, 600, and 800 N). The kinematic viscosity, flash point, pour point, and thermal conductivity of nanofluid added 15W50 lubricant are estimated and compared with base oil. The results showed that nano additives improve the wear scar and coefficient of friction by 78% and 48%, respectively. The flash point, thermal conductivity, kinematic viscosity, and pour point, were improved by 15%, 77%, 76.8%, and 20%, respectively compared with the base oil. The hybrid addition of CNTs/GNs nanoparticles enhanced the properties of 15W50 engine oil.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, GIS, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Bubble evolution and shear thinning effect are main factors affecting lubrication behavior of bubbly oil. In this study, a thermohydrodynamic lubrication model for the bubbly oil considering the ...bubble evolution and the shear thinning effect was established based on the multiphase mixtures theory. The influence of bubble evolution and shear thinning effect on the static behavior of bubbly oil lubricated bearing was analyzed, and an experimental study was conducted to verify the model. The result shows that the bubble radius is mainly dependent on the liquid pressure; the bearing static behavior is affected by the bubble evolution through the interface effect; the shear thinning effect of the pure oil can be enhanced with regarding the bubble evolution effect.
•A thermohydrodynamic lubrication model for the bubbly oil was established based on the multiphase mixtures theory.•Bubble evolution and shear thinning effect on the lubrication performance of bubbly oil is discovered.•The bubble evolution process can be calculated with using the thermohydrodynamic lubrication model established.•An in-depth physical research on the bubbly oil lubrication is conducted through a case study with using journal bearing.
•Magnesium silicate hydroxide (MSH) nanotubes with serpentine structure were prepared.•Friction and wear of Mg alloy/steel pairs in oil with MSH nanotubes were studied.•Chemical states and mechanical ...behaviors of the tribofilm on Mg alloy were studied.•Wear mechanisms of surface-modified MSH as oil additive to Mg alloy were revealed.
Efficient lubrication of magnesium alloys is a highly challenging topic in the field of tribology. In this study, magnesium silicate hydroxide (MSH) nanotubes with serpentine structures were synthesized. The tribological behavior of AZ91D magnesium alloy rubbed against GCr15 steel was studied under lubricating oil with surface-modified MSH nanotubes as additives. The effects of the concentration, applied load, and reciprocating frequency on the friction and wear of the AZ91D alloy were studied using an SRV-4 sliding wear tester. Results show a decrease of 18.7–68.5% in friction coefficient, and a reduction of 19.4–54.3% in wear volume of magnesium alloy can be achieved by applying the synthetic serpentine additive under different conditions. A suspension containing 0.3 wt.% MSH was most efficient in reducing wear and friction. High frequency and medium load were more conducive to improving the tribological properties of magnesium alloys. A series of beneficial physical and chemical processes occurring at the AZ91D alloy/steel interface can be used to explain friction and wear reduction based on the characterization of the morphology, chemical composition, chemical state, microstructure, and nanomechanical properties of the worn surface. The synthetic MSH, with serpentine structure and nanotube morphology, possesses excellent adsorbability, high chemical activity, and good self-lubrication and catalytic activity. Therefore, physical polishing, tribochemical reactions, and physical-chemical depositions can occur easily on the sliding contacts. A dense tribolayer with a complex composition and composite structure was formed on the worn surface. Its high hardness, good toughness and plasticity, and prominent lubricity resulted in the improvement of friction and wear, making the synthetic MSH a promising efficient oil additive for magnesium alloys under boundary and mixed lubrication.
Based on the wear analysis of a propeller hub bearing, wear tests are designed under different marine environments to illustrate wear failure mechanisms. The results reveal that the wear failure ...characteristics of the propeller hub bearing are primarily abrasive wear, accompanied by adhesion and oxidation wears, and plastic deformation. These results agree well with the wear morphologies of the torsional fretting wear tests under starvation lubrication. The wear tests confirm that the wear failure of the propeller hub bearing is owing to the coexistence of multiple wear mechanisms, which is attributed primarily to the superimposed wear behaviors induced by loading, continuous fretting wear, and starvation lubrication in the local contact areas. Hence, the negative effects of interfacial micro-protrusion adhesion and fracture during oil lubrication are difficult to eliminate. Moreover, The uneven radial loads of the contact surfaces of the propeller hub bearing also exhibit a significant influence on the thickness and formation of the oil film at the friction interface.
Display omitted
•Wear failure mechanisms of bearing coated with NAB alloys had been studied.•The designed wear tests were conducted by a self-assemble tribological platform.•Wear failure morphologies of bearing and wear tests results had been discussed.•Physical model at the different wear stages was established.
A friendly solid-liquid lubrication system, which is the key to solve the environmental harm caused by phosphorus and sulfur additives in lubricants, has attracted the attention. In this paper, the ...TiN-Cu/PAO solid-liquid composite system was constructed in situ by tribochemical reaction based on the performance of nitride film and base oil. The results show that when rubbing in PAO, the carbon-based films deriving from PAO will form at the contacting interface. From the perspectives of surface energy, friction products and simulation calculation, the mechanisms of friction and wear reduction of the solid-liquid composite system was systematically investigated. Meanwhile, the degradation process of PAO molecules during friction was revealed from the molecular level, including adsorption, dehydrogenation, C-C bond breaking and reconstruction.
The vehicle fleet in some regions of the world continues to age, so it is difficult to reduce the consumption of fuels, meet environmental objectives and mitigate the cost it represents. Studies ...exist regarding low mileage vehicles, yet it is important to know the effect generated by high mileage vehicles, which represents a higher percentage in the word. This work was based on the oil degradation. A maximum value of decrease in viscosity of 31% was found, from which the lubrication efficiency of the oil decreases. This also leads to a significant increase in gCO2/km and fuel consumption. In a deeper analysis of the Nissan Tsuru, we found an annual excess of 69.25 Lt of fuel consumption that produces 129.024 Kg additional of CO2 (12.18gCO2/km) with a cost of $1,414.08 Mexican pesos. Due to the average vehicle age in Mexico (15.3 years), these results can be taken as an average for the 45 million plus cars that are currently in circulation. Also, 5.806 million tons of CO2 are generated that represent 3.6% of all current emissions. This leads to a consumption of 3.11 billion liters of fuel at a cost of $63.63 billion Mexican pesos. This methodology can be generalized for different brands of cars and oils in countries with a vehicle fleet similar, in search of improving the monitoring and proper use of automotive oil. In addition, this provides information on the negative effects, so that the countries can establish procedures and strategies for compliance with low pollution policies.
•Procedure to predict fuel economy, CO2 emissions and additional cost for the end user.•The brands analyzed here, belong to a group with average age of 15.3 years.•A minimum of viscosity was found, with a decrease of 27–31%.•Annually in excess, the Tsuru car consumes 69 Lt of fuel and produces 129 Kg of CO2.•With an additional expense of $1,414.08 Mexican pesos (56.92 euros).
The Potassium Titanate-Ti3C2Tx nanocomposite was successfully synthesized by a simple one-step chemical process using Ti3C2Tx and potassium hydroxide at room temperature. Compare to Ti3C2Tx ...nanosheets, the Potassium Titanate-Ti3C2Tx exhibits superior tribological properties.
Display omitted
A potassium titanate-Ti3C2Tx nanocomposite was synthesized using a facile, low-temperature and environmentally friendly process. The morphology and microstructure of the as-prepared samples were analyzed by means of XRD, SEM, TEM, and XPS. The tribological property of the nanocomposite as additive in base oil was evaluated. The results reveal that the in-situ formed potassium titanate nanowires with average diameter of 30nm and the uniform distribution on the surface of Ti3C2Tx nanosheets. Compare to Ti3C2Tx nanosheets, the average friction coefficient and wear scar width of the oil containing potassium titanate-Ti3C2Tx nanocomposites are decreased by 4.9% and 22% under the same conditions. The excellent tribological performance is attributed to the synergic effects of the two components in the nanocomposite structure.
