Lubrication analysis and wear mechanism of heavily loaded herringbone gears with profile modifications in full film and mixed lubrication point contacts

A Computer Thermal Model of Mixed Lubrication in Point Contacts

Journal of Tribology ◽

10.1115/1.1631012 ◽

2004 ◽

Vol 126 (1) ◽

pp. 162-170 ◽

Cited By ~ 45

Author(s):

Wen-Zhong Wang ◽

Yu-Chuan Liu ◽

Hui Wang ◽

Yuan-Zhong Hu

Keyword(s):

Surface Temperature ◽

Thermal Model ◽

Reynolds Equation ◽

Equation System ◽

Mixed Lubrication ◽

Successful Implementation ◽

Asperity Contact ◽

Point Contacts ◽

Wide Range ◽

Lubrication Conditions

This paper presents a transient thermal model for mixed lubrication problems in point contacts. The model deterministically calculates pressure and surface temperature by simultaneously solving a system of equations that govern the lubrication, contact and thermal behaviors of a point contact interface. The pressure distribution on the entire computation domain is obtained through solving a unified Reynolds equation system without identifying hydrodynamic or asperity contact regions. The point heat source integration method is applied to determine the temperature distributions on contact surfaces. The interactions between pressure and temperature are considered through incorporating viscosity-temperature and density-temperature relations in the Reynolds equation, then solving the equation system iteratively. With the successful implementation of an FFT-based algorithm (DC-FFT) for calculation of surface deformation and temperature rise, the numerical analysis of lubricated contact problems, which used to involve a great deal of computation, can be performed in acceptable time. The model enables us to simulate various lubrication conditions, from full film elastohydrodynamic lubrication (EHL) to boundary lubrication, for a better understanding of the effect of surface roughness. Numerical examples are analyzed and the results show that the present model can be used to predict pressure and surface temperature over a wide range of lubrication conditions, and that the solution methods are computationally efficient and robust.

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Deterministic solutions and thermal analysis for mixed lubrication in point contacts

Tribology International ◽

10.1016/j.triboint.2005.11.002 ◽

2007 ◽

Vol 40 (4) ◽

pp. 687-693 ◽

Cited By ~ 13

Author(s):

Wen-zhong Wang ◽

Yuan-zhong Hu ◽

Yu-chuan Liu ◽

Hui Wang

Keyword(s):

Thermal Analysis ◽

Mixed Lubrication ◽

Point Contacts

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Frictional behaviour of engineering surfaces in overall lubrication regimes of point contacts

Proceedings of the Institution of Mechanical Engineers Part J Journal of Engineering Tribology ◽

10.1177/1350650111414333 ◽

2011 ◽

Vol 225 (11) ◽

pp. 1071-1080 ◽

Cited By ~ 3

Author(s):

S Wang ◽

Y-Z Hu ◽

Q-C Tan

Keyword(s):

Friction Coefficient ◽

Contact Area ◽

Area Ratio ◽

Mixed Lubrication ◽

Point Contacts ◽

Friction Behaviour ◽

True Contact Area ◽

Contact Area Ratio ◽

True Contact ◽

Frictional Behaviour

The aim of the present paper is to study experimentally and numerically the frictional behaviour of engineering surfaces within all lubrication regions of point contacts. For this reason, a numerical solution proposed elsewhere by the current authors, which can predict friction under the different lubrication modes of elastohydrodynamic, mixed, and boundary lubrications, is introduced. Based on a deterministic model of mixed lubrication, the solution was combined with the variation of the lubricating films’ physical state during the transition of lubrication modes. Results show that roughness amplitude has a great effect on the transition of friction regimes. In addition, it is also observed that variation of the friction coefficient has nearly the same trend as the true contact area ratio in the mixed lubrication state. Meanwhile, it is concluded that transverse roughness has better film-forming capacity than longitudinal roughness and thus leads to a lower magnitude of friction coefficient if the operating conditions are the same. Analysis of the mechanism of friction behaviour suggests that the true contact area ratio determines the friction behaviour of engineering surfaces in mixed lubrication. In smooth contacts, the comparison of experiment tests and simulation results suggests that friction variation results from gradual change of the liquid lubricant to solid-like matter with diminishing film thickness.

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A computer model of mixed lubrication in point contacts

Tribology International ◽

10.1016/s0301-679x(00)00139-0 ◽

2001 ◽

Vol 34 (1) ◽

pp. 65-73 ◽

Cited By ~ 23

Author(s):

Yuan-zhong Hu ◽

Hui Wang ◽

Wen-zhong Wang ◽

Dong Zhu

Keyword(s):

Computer Model ◽

Mixed Lubrication ◽

Point Contacts

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Simulations and Measurements of Sliding Friction Between Rough Surfaces in Point Contacts: From EHL to Boundary Lubrication

Journal of Tribology ◽

10.1115/1.2736432 ◽

2007 ◽

Vol 129 (3) ◽

pp. 495-501 ◽

Cited By ~ 33

Author(s):

Wen-zhong Wang ◽

Shun Wang ◽

Fanghui Shi ◽

Yu-cong Wang ◽

Hai-bo Chen ◽

...

Keyword(s):

Shear Stress ◽

Boundary Lubrication ◽

Fluid Shear Stress ◽

Sliding Friction ◽

Rough Surfaces ◽

Numerical Approach ◽

Mixed Lubrication ◽

Engineering Practice ◽

Asperity Contact ◽

Point Contacts

This paper presents a numerical approach to simulate sliding friction between engineering surfaces with 3D roughness in point contacts. The numerical approach is developed on the basis of the deterministic solutions of mixed lubrication, which is able to predict the locations where the asperity contacts occur, and the pressure distribution over both lubrication and contact areas. If the friction coefficients over the contacting asperities have been determined, total friction force between the surfaces can be calculated by summing up the two components, i.e., the boundary friction contributed by contacting asperities and the shear stress in hydrodynamic regions. The frictions from asperity contact were determined in terms of a limiting shear stress or shear strength of boundary films while the fluid shear stress in the lubrication areas was calculated using different rheology models for the lubricant, in order to find which one would be more reliable in predicting fluid tractions. The simulations covered the entire lubrication, regime, including full-film Elastohydrodynamic Lubrication (EHL), mixed lubrication, and boundary lubrication. The results, when being plotted as a function of sliding velocity, give a Stribeck-type friction curve. This provides an opportunity to study friction change during the transition of lubrication conditions and to compare friction performance on different rough surfaces, which is of great value in engineering practice. Experiments were conducted on a commercial test device—universal material tester (UMT) to measure friction at a fixed load but different sliding velocities in reciprocal or rotary motions. The results also give rise to the Stribeck friction curves for different rough surfaces, which are to be compared with the results from simulations. The samples were prepared with typical machined surfaces in different roughness heights and textures, and in point contacts with steel ball. Results show that there is a general agreement between the experiments and simulations. It is found that surface features, such as roughness amplitude and patterns, may have a significant effect on the critical speed of transition from hydrodynamic to mixed lubrication. In the regime of mixed lubrication, rougher samples would give rise to a higher friction if the operation conditions are the same.

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