Search Results (199)

In the ElastoHydrodynamic Lubrication (EHL) meshing contact model for rough interfaces with convex–concave textured micro-asperities, the geometric morphology of the meshing interface exhibits pronounced multiscale characteristics: the macroscale manifests as the correlation between Interface-Enriched Lubrication (IEL) performance and meshing Anti-Scuffing Load-Bearing Capacity (ASLBC), while the microscale corresponds to the textured morphology of rough interfaces. In numerical simulations of EHL meshing contact, such cross-scale disparities necessitate solving large-scale systems of analytical solution equations. Assuming periodicity or quasi-periodicity at the microscale, various established methods enable decoupling the macroscopic and microscopic scales, such formalized approaches constitute homogenization theory. However, classical asymptotic assumptions may introduce considerable approximation errors. This study proposes a micro-texture-informed homogenized contact model based on multiscale characterization that incorporates the coupled effects of gear interface meshing forces and thermo-elastic deformations, effectively extending the applicability of classical asymptotic homogenization methods. Full article

A precise understanding of the electrical properties of bearings is of great interest in many areas of application, especially in the context of electrification. The understanding of electrical properties allows for damage detection and sensory utilization of bearings. Previous research into the capacitive properties of rolling bearings has been limited to ball bearings. Cylindrical roller bearings, which are predominantly used in applications with large radial loads, have not been investigated so far. This paper develops a method to calculate the capacitance of cylindrical roller bearings. The calculation of the raceway–surface contact capacitance is adapted from ball bearings. In addition, a calculation method for the electrical capacitance in the flange contact is derived. Both calculation methods account for the geometric and operating conditions of the bearing and do not include any correction factors. To validate the calculation model, the capacitance of NU-208 and NJ-208 cylindrical roller bearings is measured and compared with the model results. Full article

With the changing demands of society, gears, as fundamental components of mechanical devices, are evolving towards higher reliability and longer service life. To address the issue of thermal scuffing at the gear meshing interface, we propose the introduction of micro/nano-textures to improve the thermal elastohydrodynamic lubrication characteristics of the meshing surfaces, thereby enhancing the lubrication performance and anti-scuffing load capacity of the gear surfaces. First, finite element models with different microstructural features were established. Then, numerical calculations were conducted using computational fluid dynamics (CFD) software to analyze the impact of various micro-texture configurations on the lubrication performance of the tooth surface. Finally, an orthogonal experiment was performed to optimize the groove length, groove width, and areal density of the micro-textures in order to obtain the best processing parameters. The results show that, compared with the triangular, rectangular and trapezoidal micro-textures, the wedge-shaped micro-texture produces the largest pressure difference at the meshing-in and meshing-out points of the texture grooves, which causes the dynamic pressure effect to be more obvious. Compared with the triangular, rectangular and trapezoidal micro-textures, the wedge-shaped micro-texture has the largest bearing capacity and the smallest friction coefficient, so it has better bearing capacity and anti-friction and wear performance. The process parameters were optimized through orthogonal experiments, and the optimal combination of process parameters was obtained as the areal density of 50%, the depth of micro-pits of 12 µm, and the width of micro-pits of 200 µm. Under these optimal parameters, the pressure difference at the meshing-in and meshing-out points of the wedge micro-texture increased significantly by 255.6% compared to the initial model, and the oil film friction coefficient decreased by 17.857% relative to the initial model. These results demonstrate that the micro-texture with optimal parameters significantly enhances the lubrication and anti-friction/wear performance of the tooth surface. Full article

A multibody simulation model for deep-groove ball bearings is presented. The model considers friction in both the raceway and cage contacts, resulting from radial and axial loads. The model is validated against experimental measurements for a 6319 bearing under oil-bath lubrication over a speed range of 500–3000 min⁻¹ and two load ratios ($C/P=10$ and 6.5). Predicted friction torques show good agreement with measurements, with deviations between 5.5% and 22% at moderate speeds. In addition, electrical contact capacitances are calculated for a 6208 bearing and compared with an analytical approach, showing deviations in the range of 10–14%. Beyond friction prediction, the fully dynamic approach enables time-resolved analysis of roller kinematics and the identification of instability limits under axial excitation. The developed tool therefore enables reliable bearing loss prediction, supports efficiency-oriented drivetrain design, and provides a basis for electro-tribological and stability investigations. Full article

In this paper, considering the influence of high-temperature and high-pressure environments on the operating characteristics of rotary combined seals, a mathematical model of rotary composite seals is established based on the thermo-elastohydrodynamic lubrication theory. Furthermore, based on a static analysis of the composite seal and by using the deformation influence coefficient matrix method under the small deformation theory, the elastic deformation distribution of the composite seal under the action of oil film pressure is determined. Combined with the hydrodynamic lubrication equation, the energy equation for the temperature field, and the viscosity-temperature equation, the thermo-elastohydrodynamic lubrication model of the rotary composite seal is solved using the finite difference method, and the oil film thickness distribution and oil film pressure distribution during the operation of the composite seal are calculated. The results show that the sealing medium pressure has a significant effect on the sealing performance. In the axial direction, the oil film pressure first increases and then decreases, while remaining within a stable fluctuation range. Full article

Helical gear transmissions in wind turbine gearboxes operate under high torque, variable speed, and complex rolling–sliding contact conditions, where friction-induced wear evolves in a spatially non-uniform manner. However, most existing dynamic models assume uniform or mild wear and therefore fail to capture the nonlinear coupling between localised tooth surface degradation, gear mesh dynamics, and vibration response. In this work, a nonlinear dynamic model of a helical gear pair is formulated by incorporating time-varying mesh stiffness, elasto-hydrodynamic lubrication (EHL)-based friction forces, and wear-dependent contact geometry. The governing equations of motion are derived to explicitly account for the influence of inhomogeneous tooth wear on the contact load distribution and frictional excitation during meshing. Wear evolution is represented as a spatially varying modification of tooth surface topology, enabling the progressive coupling between wear depth, mesh stiffness perturbations, and dynamic transmission error. The model is employed to analyse the effects of non-uniform wear on system stability, vibration spectra, and dynamic response under wind turbine operating conditions. Numerical results reveal that uneven wear introduces nonlinear modulation of gear mesh forces and generates characteristic sidebands and amplitude variations in the vibration signal that are absent in conventional mild-wear formulations. These wear-induced dynamic features provide mathematically traceable indicators for the onset and progression of uneven tooth degradation. The proposed framework establishes a physics-based link between wear evolution and measurable vibration responses, providing a rigorous foundation for advanced vibration-based diagnostics and model-driven condition monitoring of wind turbine gearboxes. Full article

Reducing friction in the piston ring–cylinder liner contact is a key area for improving the efficiency of internal combustion engines. While tribological studies commonly focus on the top dead centre region using linear tribometers, the mid-stroke regime—with its higher sliding velocities—remains experimentally inaccessible to most conventional test methods. This study presents a rotating ring-on-liner tribometer that enables investigations at constant relative speed by transitioning the motion from oscillating to rotating. A cylindrical substitution geometry for the piston ring specimen is derived through a coupled elastohydrodynamic and asperity contact simulation approach to reproduce realistic load-sharing behaviour. Experimental results from starved lubrication tests demonstrate stable contact conditions with a low coefficient of variation in wear, confirming good reproducibility. Stepwise performed Stribeck tests at 40 °C and 100 °C reveal characteristic friction–velocity behaviour, including the transition from mixed to hydrodynamic lubrication. Although the test rig’s maximum sliding speed and steady-state thermal conditions differ from fired engine environments, the methodology closes an important gap between low-speed linear tribometers and complex floating-liner systems. The presented approach provides a flexible and robust platform for controlled parametric studies of ring-on-liner contacts under application-relevant lubrication regimes. Full article

This study was conducted to investigate and identify correlations among sensory and comprehensive consumer test results with rheological, textural, and tribological properties of milk chocolate in response to varying levels of particle size and emulsifier. To simulate realistic oral conditions, artificial saliva was incorporated into instrumental analyses. Rheological analysis revealed that increasing particle size and emulsifier concentration significantly reduced plastic viscosity, while emulsifier concentration alone increased yield stress due to structural reorganization within the fat phase. Tribological measurements demonstrated that larger particles increased friction in boundary and mixed lubrication regimes, whereas emulsifiers reduced friction in these regimes by enhancing fluid film formation. Under elastohydrodynamic conditions and with artificial saliva, friction was more influenced by the interaction between particle size and emulsifier level. Textural analysis showed that both parameters significantly influenced hardness, with saliva further softening the samples, especially those with higher emulsifier levels. Sensory evaluations indicated that emulsifiers enhanced flavor release and mouthfeel attributes, while smaller particles contributed to smoother texture and more balanced flavor perception. Consumer acceptance tests confirmed that samples with smaller particles and higher emulsifier levels received the highest scores in overall liking, taste, and texture. Instrumental parameters strongly correlated with key sensory attributes, with yield stress showing the highest positive associations with creaminess, smoothness, fat/milk flavor, and liking, while higher viscosity and friction were negatively linked to flavor release and mouthfeel. Instrumental hardness negatively correlated with cacao intensity and astringency, while saliva-induced softening was positively associated with sweetness and liking, highlighting the role of dynamic oral softening. Full article

Deep-sea gear transmission systems encounter critical lubrication challenges arising from the synergistic coupling of extreme hydrostatic pressure and cryogenic temperatures. These environmental stressors induce exponential viscosity escalation in lubricants, precipitating severe fluidity degradation, elevated startup resistance, and lubrication starvation. Concurrently, seawater intrusion triggers lubricant emulsification, additive deactivation, and electrochemical corrosion at meshing interfaces, collectively escalating the risk of catastrophic lubrication failure and compromising long-term operational reliability. This study systematically elucidates the lubrication degradation mechanisms inherent to deep-sea environments and proposes targeted mitigation strategies. Through comprehensive characterization of deep-sea environmental parameters and their impact on lubricant rheological behavior, we critically evaluate the applicability and inherent limitations of conventional Thermal Elasto-Hydrodynamic Lubrication (TEHL) theory under extreme conditions. Our analysis reveals that established TEHL frameworks necessitate substantial modification to accurately capture pressure-viscosity-temperature coupling phenomena and seawater contamination kinetics. Meshing interface texturing, as an effective anti-friction and wear-mitigation strategy, is investigated to delineate its mechanistic pathways for enhancing lubricant film formation and tribological performance under starved lubrication regimes. Key findings demonstrate that optimized micro-texture architectures can effectively compensate for viscosity-induced fluidity deficits and attenuate the deleterious effects of seawater ingress. Critical knowledge gaps are identified, and future research trajectories are charted: (i) multiphysics coupling models integrating thermo-hydrodynamic, chemo-physical, and mechanical degradation processes; (ii) synergistic texture-coating design paradigms; (iii) high-pressure low-temperature experimental validation protocols; and (iv) engineering implementation frameworks for deep-sea gear transmission systems. This review establishes theoretical foundations and provides technical guidelines for robust lubrication design and long-term operational stability of deep-sea transmission equipment. Full article

This study tests TiO₂ and SiO₂ nanolubricants in PAG oil using a Mini Traction Machine and an Ultra Shear Viscometer. The loads were 20 N and 40 N. The entrainment speeds ranged from 2.5 to 500 mm/s. The slide-to-roll ratio (SRR) ranged from 25 to 150%. The nanoparticle concentrations were 0.01, 0.03, and 0.05%. The ball size was 19.05 mm, and the disc was 46 mm. All tests were run at 40 °C. Only the 0.05% concentration lowered traction compared with PAG at a fixed SRR. TiO₂ at 0.05% showed the largest drop, up to 4.89% at 20 N and 2.99% at 40 N. However, lower concentrations increased traction. All the nanolubricants reduced wear. TiO₂ at 0.03% gave the lowest wear, with a reduction of about 35 µm at 40 N. Nanolubricant samples stayed between 40.2 and 40.5 °C, while PAG reached about 41.0 °C. TiO₂ produced slightly lower temperatures than SiO₂. Ultra-shear tests from 40 to 100 °C showed shear thinning. In most conditions, TiO₂ at 0.05% kept the highest viscosity at 40 and 60 °C, up to 12% above PAG. SiO₂ showed smaller changes. TiO₂ delivered better friction, wear, temperature, and viscosity performance. Overall, both nanolubricants at 0.03% are suitable when wear reduction and thermal stability are prioritised over traction reduction, such as in refrigeration applications, while the 0.05% suits high-load or high-shear use. Full article

A dedicated experimental rig is presented for a half-journal bearing operating under highly loaded, well-controlled hydrodynamic lubrication conditions relevant to turbomachinery. The apparatus combines pressure measurements in the film, distributed temperature measurements in the shaft and bush, and ultrasonic film-thickness measurements that map the circumferential film-thickness profile across the lubrication region. Experiments are reported for normal loads of 5–20 kN and shaft speeds of 1000–4000 rpm with controlled oil supply conditions. The measured pressure and temperature trends are consistent with established hydrodynamic lubrication behaviour. The film thickness measurements confirm full-film operation across the tested operating envelope, while indicating increased uncertainty in regions affected by cavitation. A correlation for the temperature rise due to viscous heating is proposed as a compact representation of the data. The rig design and accompanying measurements provide a benchmark-quality data set intended for validation and development of thermal elasto-hydrodynamic lubrication (TEHL)/computational fluid dynamics (CFD) models under high load and speed conditions. Full article

Addressing the challenge of optimizing the fatigue life of cylindrical roller bearings under high-speed and heavy-duty conditions, a collaborative multi-parameter optimization design method is proposed. First, a novel five-parameter profiling equation is introduced to overcome the limitations of traditional profiling methods based on the elastohydrodynamic lubrication property of the roller–raceway contact pair. Second, a nonlinear constrained optimization model that comprehensively considers key bearing structural parameters and the new profiling characteristics is constructed. In this model, the fatigue life is taken as the direct optimization objective, and geometric constraints, strength conditions, and lubrication performance are contained. Finally, using a NU2218E cylindrical roller bearing as the study case, the synchronous optimization achieved about a 196% enhancement in fatigue life over that of optimizing structural or profiling parameters alone. The proposed multi-parameter collaborative optimization framework and the innovative profiling approach provide new technical approaches and theoretical foundations for the design of high-performance rolling bearings. Full article

This paper investigates the impact of lubrication and thermal effects on the performance of single-metal seals in roller cone bits, and it establishes the geometric, material, and operating parameter models for the single-metal seal. Based on the theory of statistics, the Greenwood–Williamson (G–W) model is employed to predict the contact stress of micro-protrusions on the sealing pair surface. This study establishes a Thermal Elastohydrodynamic Lubrication (TEHL) coupling model for single-metal seals, which utilizes the deformation matrix method to characterize the microscopic deformation of the sealing interface. The central difference method is applied to solve the oil film thickness and temperature distribution in the axial and film thickness directions of the sealing surface. The results indicate that the sealing zone is predominantly under rough peak contact pressure, operating in a mixed-lubrication state. Oil film thickness negatively correlates with static contact pressure, and seal pressure and pre-compression displacement significantly influence lubrication performance. Experiments validate the numerical simulation results, with a mean relative error of less than 15%, confirming the model’s effectiveness. This study offers a theoretical basis for optimizing single-metal seal design, enhancing the reliability and lifespan of roller cone bits in harsh conditions. Full article

The thermal elastohydrodynamic lubrication problem of non-orthogonal surface gear pairs under point contact conditions was studied. Firstly, a mathematical model is established through a comprehensive contact and lubrication analysis. On this basis, the Reynolds equation, energy equation, film thickness equation, viscosity-pressure–viscosity-temperature relationship, and density equation are coupled and solved, and the finite difference method is adopted for numerical solution. The distribution characteristics of oil film pressure, oil film thickness, and temperature rise at different meshing points were systematically analyzed. The results show that during the meshing cycle, the maximum pressure of the oil film at the meshing point first increases and then decreases, while the minimum oil film thickness is the opposite. Near the point S3, the meshing state is close to pure rolling, with the lowest friction coefficient and temperature rise. Furthermore, the heat absorbed by the lubricating oil film through forced convection accounts for only approximately 1% of the total frictional heat, indicating that at the moment of gear meshing contact and in the microscopic region, frictional heat is mainly dissipated through heat conduction. Full article

The cage shape plays a critical role in controlling lubricant distribution and replenishment and enhancing lubrication performance within rolling bearings. This study investigates the effect of four tailored cage shapes on lubricant migration and frictional characteristics at both Ball-Cage (B-C) and Ball-Disc (B-D) contacts. Utilizing a bearing cage friction and lubrication test rig (BCFL), adapted from an optical elastohydrodynamic lubrication (EHL) apparatus, the variation in grease films and friction forces was examined under varying entrainment speeds, grease properties, and grease quantities. Cage-induced lubricant redistribution on the ball surface, replenishment at the B-D contact, and the formation mechanism of thicker film thickness were recognized. The influence of cage design for four distinct shapes on mechanisms enhancing grease lubrication efficiency and friction reduction was examined. The findings provide critical insights for designing next-generation self-aligning cage structures with improved lubrication performance and reduced friction force. Full article