Lubrication Science最新文献

It is very crucial to solve the Reynolds equation quickly and accurately using the numerical methods in the research field of fluid lubrication. For the static Reynolds equation of self-acting gas journal bearings, the typical solution algorithm of the finite difference method is put forward and a new solution algorithm of the finite difference method is proposed. Secondly, the Reynolds equation is solved numerically with the same parameters and the pressure distribution of gas bearings is obtained. Finally, the numerical solution from the new solution algorithm can be obtained with less number of iterations and the less computing time under the different computational grids and bearing numbers. Therefore, the new solution algorithm of the finite difference method is superior to the typical solution algorithm of the finite difference method.

In this research, an angular contact ball bearing with two-half inner rings is used as a carrier. Considering the two-phase flow characteristics of oil and air in the bearing, the flow characteristics of lubricating oil inside the bearing with under-race lubrication are studied. Based on the volume of fluid (VOF) method and the standard k–ε turbulent flow model, the characteristics of oil and air two-phase flow inside the ball bearing are analysed. The bearing internal pressure field distribution, streamline distribution, and other flow properties for the different radial working clearances, pocket clearances and guide clearances are determined. The distribution of the lubricating oil in key areas is observed. The oil phase volume fraction of the key lubrication areas, such as the cage pocket surface and the inner and outer ring surfaces is used to evaluate the influence of different structural parameters on the bearing lubrication performance. The lubrication influences of the inner and outer guides of the cage are evaluated, and the internal flow characteristics of the bearing are analysed with different guide clearances. The results show that with the radial working clearance range from 0.100 to 0.145 mm, the pressure in the working contact area of the bearing decreases 26%. The pocket clearance ranges from 0.48 to 0.28 mm, and the pressure in the working contact area of the bearing significant increases from 0.642 to 1.165 MPa. From this perspective, the larger the radial working clearance and pocket clearance are, the more favourable it is for bearing lubrication. For bearings with under-ring lubrication, when the bearing adopts outer guidance, the distribution of lubricating oil in the key areas of the bearing is worse than that for internal guidance. However, the pressure in the working contact area of the bearing slightly increases from 0.642 to 0.759 MPa with the inner guide clearance increasing from 0.4 to 0.8 mm.

This study presents the impact of full and partial surface waviness on the dynamic and stability performance of the journal bearing. The Reynolds equation is modified to account for the impact of surface waviness, and the lubricant domain is discretized using the Finite element method to obtain dynamic characteristics such as stiffness and damping coefficients and stability parameters, that is, threshold speed. Different wave numbers in the axial, circumferential and mixed directions are considered at variable wave amplitudes in different regions at an average eccentricity ratio of 0.6 to obtain the optimum values. The obtained results reveal that by application of waviness in the full region and partial waviness in the pressure-reducing region on the bearing surface provides the enhanced value of stability parameter, fluid film stiffness and dynamic coefficients as compared to the simple journal bearing under the same working conditions.

This manuscript proposes an enhanced technique for the friction stir welding (FSW) of ceramic particle-reinforced aluminium-related metal matrix composites. The proposed technique is the joint implementation of both the Aquila Optimizer and Pelican Optimization Algorithm. This proposed method aims is to enhance the welding efficiency, quality, and overall performance of the weld joints. The test is conducted in an all-purpose machine at cutting speeds that permit temperatures that are comparable to the FSW of stainless-steel, aluminium alloys and copper. Reaction–diffusion studies are conducted to better understand the diffusion-control process under tool wear, and the tool wear rate is determined by the length of the cutting tool's nose tip. Rotational speed at 10 mm/min is examined. SiC exhibits the highest performance of aluminium and stainless steel. As the fraction of SiC increases to 18%, the axial force and rotational speed of FSW also increase.

Liquid sodium hybrid bearing is mechanical pump shaft bottom key support components, that play a balanced radial force of the impeller by fluid effect, in order to improve the bearing performance, based on the calculation model, simulation analysis, structure improvement and other aspects of analysis, this paper based on the theory of fluid mechanics of bearing finite element model for numerical calculation and analysis of flow field. Under different eccentricities and vibration velocities, the influence of structure improvement on bearing capacity is analysed. The results show that the bearing capacity of the liquid sodium hybrid bearing is mainly the hydrostatic bearing capacity, and the hydrodynamic pressure only plays an auxiliary role. After the improvement of the load-bearing structure, the load-bearing capacity is increased by 4%–7.3%. And the leakage is reduced by 27%–38% when the depth of the annular groove is 0.6 mm.

Nanostructures as an inert additive to the lubricant act as a tiny friction reduction element by providing asperity filling, polishing, and film formation mechanism at the nanoscale dimension under the boundary layer regime. Here, we explore the synthesis and tribology application of iron-carbon-based nanoparticles encapsulated multiwall carbon nanotubes (Fe-C-CNTs). Three Fe-C nanoparticles phase that is, Fe₃C-CNTs, Fe₃C-Fe-CNTs, and Fe-CNTs are synthesised. In particular, the emphasis here is on the effect of nanoparticle phase variation on the tribology property. The tribology property of the prepared nanomaterials is studied by dispersing it in commercially used Servo gearbox oil. The coefficient of friction and wear is found reduced in all dispersions compared to the base gearbox oil confirming the manifestation of nanoscale mechanisms at the tribo-interface. It is revealed that the phase variation shows more impact on the alteration of friction coefficient compared to the dispersion concentration variation analysed using ANOVA two-way technique. Further, the diameter and composition analysis of the wear scar is used to comprehend the underlying mechanism of the encapsulated particle phase variation. The findings suggest that the Fe-CNTs dispersions are efficient in reducing friction to a larger extent but also promote the interface oxidation leading to enhanced wear and roughness whereas, Fe₃C-CNTs and Fe₃C-Fe-CNTs are chemically stable providing smooth sliding and less wear.

Minimising the friction force of the archwire-bracket sliding contact is crucial for achieving a high-quality orthodontic treatment. Micro-dimples and micro-grooves textures were successfully produced on the two slot surfaces of the stainless steel orthodontic brackets with the laser surface texturing technology. The effect of surface texture on reducing the friction and wear behaviour of the stainless steel archwire-bracket sliding contact combinations in artificial saliva environment was investigated. Friction coefficients of less than 0.15 and mild wear were obtained by using the three rows micro-grooves textured bracket with a width of 60 μm and a spacing of 150 μm. The friction and wear performance was further enhanced with the addition of orthodontic wax materials. It was strongly argued that the synergetic effects of the fabricated micro-grooves texture and the added orthodontic wax materials leading to the outstanding friction and wear behaviour of the archwire-bracket sliding contacts.

The tribological performance of two polymeric friction modifiers, one based on an ester-based compound and another based on an ethoxylated fatty ester and an organic friction modifier, oleamide, was studied at 50, 90 and 140°C using a Mini Traction Machine equipped with optical interferometry and electrical contact resistance. The ability to form surface film is found to vary among the friction modifiers and with temperature and rubbing duration. Despite a thinner film being formed, polymeric friction modifier (PFMs) exhibited lower friction and wear than oleamide at all the studied temperatures. Further, the PFMs reduced boundary friction more effectively at higher temperature. In accordance with lower boundary friction, a smoother surface topography characterized by low wear was exhibited by PFM lubricated surfaces at higher temperatures. Scanning electron microscopy-energy dispersive x-ray analysis and time-of-flight secondary ion mass spectrometry provided insights on the tribofilm formation. The improvement in the tribological performance of PFMs is attributed to temperature-induced conformation transition of adsorbed polymer chains on the surface. The results are corroborated by data obtained from dynamic light scattering and gel permeation chromatography.

Regular lard (RL) was chemically modified into isopropyl-branched lard (BL). The isopropyl group was introduced into the triglyceride structure via a reaction of carbon–carbon double with isopropyl bromide in presence of ethylaluminum sesquichloride. The reaction was confirmed with gas chromatography–mass spectroscopy, nuclear magnetic resonance, infrared spectroscopy. The physical, tribological and chemical properties of the RL, BL and their blendings in polyalphaolefin (PAO) and high-oleic sunflower oil (HOSuO) were investigated. The BL exhibited better solubility both in HOSuO and PAO than RL. Compared to RL, BL exhibited higher density, viscosity, improved oxidative stability and cold flow properties both as a neat material and blendings in HOSuO or PAO. However, BL displayed lower viscosity index (197 vs. 162) compared to RL. Both RL and BL displayed similar lubricity as HOSuO and showed potential such as a good lubricity additive in PAO even in small amounts (~10 wt%). This study reveals introducing alkyl branching into lard can lead to improved physico-chemical properties and lubrication performance.

Wheel-rail adhesion is important to the traction and braking of railway vehicles. This paper develops a three-dimensional numerical model considering surface roughness and temperature to investigate water-contaminated adhesion characteristics. A simplified elastohydrodynamic lubrication model considering the thermal effect is developed to obtain the normal load carried by liquid film and asperities. Meanwhile, a third body layer (3BL) model, which considers the effects of pressure and temperature on 3BL, is used to calculate the tangential stress and friction coefficient of asperity contact. To verify the numerical model, firstly, the results are compared with the existing experimental results at low and high speeds. In addition, the effects of surface roughness and temperature on adhesion coefficient are investigated. Furthermore, the elastoplastic behaviour of the tangential stress and the adhesion characteristics for large creepages are studied. The obtained adhesion-creepage curve can represent the decreasing trend after reaching saturation because of temperature.