Deformation and pressure in an elastohydrodynamic contact

The influence of the heat transfer field on anomalous film formation under elastohydrodynamic lubrication (EHL) conditions was studied. Liquid lubricant film shapes between a transparent disc and steel ball friction pair were investigated by white light optical interferometry. The fatty alcohol 1-dodecanol was used as the representative lubricant to develop anomalous film shapes. A sapphire disc and glass disc, which have different thermal conductivities, were used as the transparent bounding surface. Experiments were performed wherein the applied load, sliding conditions and ambient temperature were varied. The temperature of the lubricant film was estimated by a simple model with the measured traction coefficient. The estimated temperature and maximum Hertzian pressure were compared with the phase diagram of 1-dodecanol obtained using a diamond anvil cell to investigate the phase state of the lubricant film. It was found that the anomalous film shape was stably formed in the solid-state regime of the phase diagram whereas the film exhibited unique characteristics such as the collapse behaviour in high sliding conditions and liquid-like behaviour of the traction with a remaining thickened film part in the liquid state regime.

Temperature, pressure and film thickness measurements for an offset half bearing

Investigation of the discharge-voltage method of measuring the thickness of oil films formed in a disc machine under conditions of elastohydrodynamic lubrication

An improved mesh stiffness model of helical gear pair considering axial mesh force and friction force influenced by surface roughness under EHL condition

A methodology is proposed to study the interplay between tooth wear and contact fatigue under elastohydrodynamic lubrication condition. The modeling methodology includes the influence of contact fatigue on wear and the influence of wear on contact fatigue. First, the changes in film pressure and film thickness of oil at each meshing point caused by contact fatigue are introduced according to the surface wear model, and the change of wear model is analyzed to study the effect of contact fatigue on wear. Then, according to the elastohydrodynamic lubrication theory, the change in film pressure affected by tooth surface wear is analyzed to study the effect of wear on contact fatigue. Finally, the influence of lubrication conditions on the interplay between tooth surface wear and contact fatigue is analyzed. In addition, an experimental fatigue study is performed and introduced into the model predictions to improve the accuracy of the proposed methodology.

The effects of nanotexturing on oil film thickness and shape under pointcontact elasto-hydrodynamic lubrication (EHL) conditions were experimentally investigated. A disk-onball friction tester with an optical interferometer was used to measure oil film thickness and to observe the oil film shape. Periodic groove structures with a spiral, perpendicular, or parallel shape and with various groove depths and distances were formed by irradiation of a femtosecond laser onto the surface of steel balls. These nanotextured balls were tested under a load of 20 N and at rotational speeds from 1.0 to 3.0 m/s. Most of the balls with nanotexturing had a thicker oil film than those without texturing. The groove depth and angle were the key parameters determining the thickness of the oil film as they controlled the amount of side leakage of oil from the contact point. Optimization of these parameters resulted in an oil film that was almost twice as thick as that on the ball without texturing.

Temperatures of meshing gears under conditions of elastohydrodynamic lubrication

In this paper a full numerical solution for the thermoelastohydrodynamic problem in elliptical contacts is presented, and the method of computation is also described. The film pressure, thickness, and film shape, the three dimensional temperature distribution within both the film and the bounding solids, as well as the coefficients of the sliding and rolling frictions have all been determined for different rolling velocities and slide-roll ratios. The results obtained indicate the film temperature increases as the rolling velocity or slide-roll ratio increases. The effects of thermal action on the pressure distribution, the film shape and thickness, and the friction factors are also given. The problem studied in this paper is steady-state, the lubricant is assumed to be Newtonian.

Measurements of oil film thickness according to the capacitive method as carried out on a disc machine with discs having a surface roughness of 10 μin c.l.a. showed marked deviations from the theoretical values predicted by Dowson and Higginson (1)†, especially in the region of small film thickness, i.e. smaller than 0–6 μm (23·6 [μin). In this paper the authors show that surface roughness is the cause of this discrepancy.

In the previous paper, the authors investigated the fluctuation of oil film pressure and the vibration of cylinders caused by a periodic change in the width of the contact surface. The calculated results were obtained by solving a Reynolds equation and an equation of the cylinder motion simultaneously, on the condition that the load on the cylinder is so low that the elastic deformation is negligible. In this paper, the effect of the contact-surface-width variation on the elastohydrodynamic line contact has been studied by solving the above-mentioned equations with a formula of elastic deformation and with a formula of the pressure dependence of viscosity. One of these calculated results indicates that, under the condition of elastohydrodynamic lubrication, the oil film shape is changed with time similar to wave motions.

Surface contact fatigue is the main failure mode in many mechanical components, such as gears, bearings, and cam-followers. A fatigue life prediction model is proposed for finite line contact under starved thermal elastohydrodynamic lubrication (TEHL) condition in this paper. Then, the effects of inlet oil-supply thickness, slide-to-roll ratio (SRR), and operating conditions on the lubrication performance and fatigue life are investigated. The results show that the lubrication characteristics and fatigue life of finite line contact are obviously different from those of fully flooded situation by introducing the starved lubrication condition. For example, the severe starved conditions lead to a significant increase in friction coefficient and decreased fatigue life. The variation of SRR has an important influence on the fatigue life. With the increase of SRR, the fatigue life decreases firstly and then increases. The stress concentration occurs near the surface when speed is low. In addition, under the low-speed situation, rotation speed variation has little effect on the fatigue life.

PurposeThe purpose of this paper is to investigate the performance of an ultra-thin film lubricated conjunction through the elastohydrodynamic lubrication of point contacts for various ridge shapes and sizes located within the contact zone including flat-top, triangle and cosine wave profiles, considering the influence of surface forces of solvation and Van der Waals’ in addition to the hydrodynamic effect to predict an optimum geometric characteristics for surface texture for lubricated conjunctions.Design/methodology/approachSurface features are simulated in a variety of sizes and shapes including flat-top, triangle and cosine wave profiles. While estimating the elastic deformation of the contacting surfaces, surface forces of solvation and Van der Waals’ are taken into account. The Reynolds equation is solved using the Newton–Raphson method to get the pressure profile and film thickness including the elastic deformation, and surface feature.FindingsThe geometrical characteristics of the ridge, its placement in relation to the contact zone and its height all have a significant impact on the performance of ultra-thin film lubricated conjunction. When the triangular-shaped ridge is present in contact, it forecasts even sharper peaks in film thickness and pressure. More friction, wear and eventually contact fatigue are brought on by this more acute pressure and film thickness peaks. The flat-top ridge shape shows a better performance for lubricated conjunction where, the minimum film thickness value is comparable to that obtained for the case of a smooth contact surface. This behavior is attributed to the effect of intermolecular force of solvation. An increase in the size of the ridge results in a step increase in the film thickness for different ridge shapes, particularly for the flat-topped ridge pattern.Originality/valueEvaluation of the performance of elastohydrodynamic lubricated ultra-thin film conjunction related to film thickness and pressure profile for various ridge surface features of different amplitudes, shapes and sizes located through the contact zone considering the influence of surface forces of solvation and Van der Waals’ in addition to the hydrodynamic effect.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-03-2023-0062/

This paper presents the results of a transient analysis of elastohydrodynamic lubrication (EHL) of two parallel cylinders in line contact with a non-Newtonian lubricant under oscillatory motion. Effects of the transverse harmonic surface roughness are also investigated in the numerical simulation. The time-dependent Reynolds equation uses a power law model for viscosity. The simultaneous system of modified Reynolds equation and elasticity equation with initial conditions was solved using the multigrid, multilevel method with full approximation technique. The film thickness and the pressure profiles were determined for smooth and rough surfaces in the oscillatory EHL conjunctions, and the film thickness predictions were verified experimentally. For an increase in the applied load on the cylinders or a decrease in the lubricant viscosity, there is a reduction in the minimum film thickness, as expected. The predicted film thickness for smooth surfaces is slightly higher than the film thickness obtained experimentally, owing primarily to cavitation that occurred in the experiments. The lubricant film under oscillatory motion becomes very thin near the ends of the contact when the velocity goes to zero as the motion direction changes, but a squeeze film effect keeps the fluid film thickness from decreasing to zero. This is especially true for surfaces of low elastic modulus. Harmonic surface roughness and the viscosity and power law index of the non-Newtonian lubricant all have significant effects on the film thickness and pressure profile between the cylinders under oscillatory motion.

A microstructured surface was created on a steel surface by whirling electrical discharge texturing (WEDT) since it was considered that the microstructures could act as lubricant reservoirs to assist the formation of a lubricating film, resulting in reduced friction. In this study, friction tests under engine oil were carried out over a range of loads and sliding speeds. In addition, the surface characteristics of the microstructured surface were also investigated to optimize the friction characteristics of the textured surface through pin-on-disc friction tests. It was found that under the mixed lubrication condition near the boundary condition, textured surfaces with texture-area ratio of approximately 6% and a mean crater diameter of 35 μm were considered as the optimal conditions for reducing the friction coefficient. However, a texture-area ratio of approximately 4% and a mean crater diameter of 35 μm were considered as the optimal conditions for reducing the friction coefficient under the mixed lubrication condition near the elastohydrodynamic lubrication condition. It was considered that when the normal load decreased, the lubrication region changed from the mixed lubrication condition to the hydrodynamic lubrication condition, which meant that the actual contact surface area decreased. The decrease in the actual contact surface area with decreasing texture-area ratio led to a reduction in the friction coefficient. Finally, it was clarified that the friction coefficient was reduced under the optimized conditions of the microstructured surface through a pin-on-disc friction test.

Non-newtonian thermal analysis of an EHD contact lubricated with MIL-L-23699 oil