The behaviour of heavily loaded line contacts with transverse roughness

1999 ◽  
Vol 213 (4) ◽  
pp. 309-320 ◽  
Author(s):  
C. J. Hooke
Keyword(s):  
Surface Roughness ◽  
Full Range ◽  
Numerical Results ◽  
Operating Conditions ◽  
Entrainment Velocity ◽  
Original Surface ◽  
Line Contacts ◽  
Transverse Roughness ◽  
Inlet Length

In heavily loaded, piezoviscous contacts the surface roughness tends to be flattened inside the conjunction by any relative sliding of the surfaces. However, before it is flattened, the roughness affects the inlet to the contact, producing clearance variations there. These variations are then convected through the contact, at the entrainment velocity, producing a clearance distribution that differs from the original surface. The present paper explores this behaviour and establishes how the amplitude of the convected clearance varies with wavelength and operating conditions. It is shown that the primary influence is the ratio of the wavelength to the inlet length of the conjunction. Where this ratio is large, the roughness is smoothed and there is little variation in clearance under the conjunction. Where the ratio is small, significant variations in clearance may occur but the precise amplitude and phasing depend on the ratio of slide to roll velocities and on the value of a piezoviscous parameter, c. The numerical results agree closely with existing solutions but extend these to cover the full range of operating conditions.

Surface roughness modification in elastohydrodynamic line contacts operating in the elastic piezoviscous regime

1998 ◽  
Vol 212 (2) ◽  
pp. 145-162 ◽  
Author(s):  
C. J. Hooke
Keyword(s):  
Surface Roughness ◽  
Spatial Distribution ◽  
Analytical Solution ◽  
Film Thickness ◽  
Numerical Solutions ◽  
Entrainment Velocity ◽  
Original Surface ◽  
Ehd Lubrication ◽  
Line Contacts

In heavily loaded elastohydrodynamic (EHD) lubrication contacts operating in the piezoviscous regime, the original surface roughness is largely flattened as it enters the conjunction and is replaced by an inlet generated clearance variation. This clearance variation is convected through the contact at the entrainment velocity. It has a spatial distribution that differs (except for rolling without slip) from the original surface and a different amplitude. This amplitude may be smaller or greater than that of the original profile. An analytical solution of this behaviour is presented for contacts operating well inside the elastic piezoviscous regime for the situation where the roughness is relatively small compared with the film thickness. This solution allows the main features of surface roughness modification to be understood and produces results that compare well with the few numerical solutions available.

Adiabatic Approximate Solution for Static and Dynamic Characteristics of Turbulent Partial Journal Bearings With Surface Roughness

1994 ◽  
Vol 116 (4) ◽  
pp. 672-680 ◽  
Author(s):  
H. Hashimoto ◽  
M. Mongkolwongrojn
Keyword(s):  
Surface Roughness ◽  
Approximate Solution ◽  
Dynamic Characteristics ◽  
High Speed ◽  
Journal Bearings ◽  
Numerical Results ◽  
Operating Conditions ◽  
Finite Width ◽  
Homogeneous Surface ◽  
Static And Dynamic Characteristics

Hydrodynamic bearings are generally used for a long term, so the bearing surfaces may be roughened for many reasons such as wear, impulsive damage, foreign particles, cavitation erosion, rust, and so on. Under the turbulent operating conditions of high speed bearings, the surface roughness may result in considerable increase in both film pressure and temperature. This paper describes an adiabatic approximate solution for the static and dynamic characteristics of 180 deg partial journal bearings with homogeneous surface roughness. Applying the modified lubrication equation and energy equation, considering the combined effects of turbulence and surface roughness, to the finite width 180 deg partial journal bearings, the static and dynamic characteristics such as pressure and temperature distributions, Sommerfeld number, attitude angle, spring and damping coefficients and whirl onset velocity are obtained numerically. In the numerical analysis of the temperature distribution, adiabatic boundary conditions are assumed and then the heat transfer effect to the journal and bearing-bush surfaces is omitted. The numerical results are indicated in graphic form for various relative roughness under the mean Reynolds number of Re = 5000 and 10,000. Moreover, some numerical results of static characteristics are compared with the experimental results.

Effects of Surface Roughness on Sliding Friction in Lubricated-Point Contacts: Experimental and Numerical Studies

2007 ◽  
Vol 129 (4) ◽  
pp. 809-817 ◽  
Author(s):  
Shun Wang ◽  
Yuan-zhong Hu ◽  
Wen-zhong Wang ◽  
Hui Wang
Keyword(s):  
Surface Roughness ◽  
Sliding Friction ◽  
Operating Conditions ◽  
Point Contacts ◽  
Machining Processes ◽  
Friction Behavior ◽  
Type Curves ◽  
Lubrication Regimes ◽  
Wide Range ◽  
Transverse Roughness

The objective of the present work is to investigate experimentally and numerically the influences of surface roughness, produced by typical machining processes, on friction performances in lubricated-point contacts. Prior to the full experimental investigation, a series of tests had been conducted to examine the experimental errors, resulting from repeated tests on the same specimen but at different tracks, with different amounts of lubricant supply, or after the sample reinstallation. Then, the effects of amplitude and texture of surface roughness on friction behavior are investigated in rotational and reciprocal-mode tests, respectively. The measured friction, averaged over the repeated tests and plotted as a function of sliding speed, shows Stribeck-type curves, which manifest the transition from full-film, mixed, to boundary lubrication. Results show that the roughness amplitude imposes a strong influence on the magnificence of friction and the route of lubrication transition. It is also observed that transverse roughness would give rise to a smaller friction coefficient than the longitudinal one under the same operating conditions. Moreover, the deterministic numerical solution of mixed lubrication has been extended to evaluate friction between rough surfaces over a wide range of lubrication regimes. The numerical simulation results are compared and agree very well with experiments.

Numerical investigation of sliding friction behaviour and mechanism of engineering surfaces

2019 ◽  
Vol 71 (2) ◽  
pp. 205-211 ◽  
Author(s):  
Xiaogang Zhang ◽  
Yali Zhang
Keyword(s):  
Surface Roughness ◽  
Friction Coefficient ◽  
Sliding Friction ◽  
Normal Load ◽  
Numerical Results ◽  
Operating Conditions ◽  
Friction Mechanism ◽  
Content Type ◽  
Optimal Surface ◽  
Friction Behaviour

Purpose This study aims to investigate the sliding friction behaviour and mechanism of engineering surfaces. Design/methodology/approach A new numerical approach is proposed. This approach derives the macroscale friction coefficient from microscale asperity interactions. By applying this approach, the sliding friction behaviour under different operating conditions were investigated in terms of molecular and mechanical components. Findings Numerical results demonstrate an independent relationship between normal load and friction coefficient, which is governed by the saturated plastic ratio. Numerical results also demonstrate that under very small load, an increase in load increases the friction coefficient. In addition, numerical results confirm the existence of optimal surface roughness where the friction coefficient is the lowest. For the surface profiles used in the current calculation, an optimal surface roughness value is obtained as Rq = 0.125 μm. Originality/value This new approach characterizes the deterministic relationship between macroscale friction coefficient and microscale asperity molecular/mechanical interactions. Numerical results facilitate the understanding of sliding friction mechanism.

The Minimum Film Thickness in Lubricated Line Contacts during a Reversal of Entrainment—Piezoviscous Behaviour

1992 ◽  
Vol 206 (6) ◽  
pp. 417-424 ◽  
Author(s):  
C J Hooke
Keyword(s):  
Film Thickness ◽  
Elastohydrodynamic Lubrication ◽  
Lubrication Theory ◽  
Rate Of Change ◽  
Operating Conditions ◽  
Entrainment Velocity ◽  
Residual Film ◽  
Minimum Film Thickness ◽  
Line Contacts ◽  
Important Exception

In many line contacts the operating conditions, such as load, entrainment velocity and contact radii, vary with time. Generally, the results from standard elastohydrodynamic lubrication theory, derived for constant conditions, can be used to obtain a quasi-steady prediction of film thickness that is sufficiently accurate for design purposes. An important exception to this is where the entrainment direction changes because, under those conditions, the quasi-steady approach predicts that there will be no clearance between the surfaces while in practice a residual film will persist. A previous paper showed that the minimum film thickness during entrainment reversal depends primarily on the rate of change of entrainment velocity. Limit expressions for the minimum clearance in the four regimes of lubrication were obtained. The present paper is part of a programme to develop a minimum film thickness chart for entrainment reversal and deals with the transition between the rigid-piezoviscous and the elastic-piezoviscous regimes.

Simulation of Plasto-Elastohydrodynamic Lubrication in Line Contacts of Infinite and Finite Length

2015 ◽  
Vol 137 (4) ◽  
Author(s):  
Tao He ◽  
Jiaxu Wang ◽  
Zhanjiang Wang ◽  
Dong Zhu
Keyword(s):  
Surface Roughness ◽  
Finite Length ◽  
3D Model ◽  
Three Dimensional ◽  
Elastohydrodynamic Lubrication ◽  
Axial Direction ◽  
Contact Length ◽  
Line Contact ◽  
Line Contacts ◽  
3D Surface Topography

Line contact is common in many machine components, such as various gears, roller and needle bearings, and cams and followers. Traditionally, line contact is modeled as a two-dimensional (2D) problem when the surfaces are assumed to be smooth or treated stochastically. In reality, however, surface roughness is usually three-dimensional (3D) in nature, so that a 3D model is needed when analyzing contact and lubrication deterministically. Moreover, contact length is often finite, and realistic geometry may possibly include a crowning in the axial direction and round corners or chamfers at two ends. In the present study, plasto-elastohydrodynamic lubrication (PEHL) simulations for line contacts of both infinite and finite length have been conducted, taking into account the effects of surface roughness and possible plastic deformation, with a 3D model that is needed when taking into account the realistic contact geometry and the 3D surface topography. With this newly developed PEHL model, numerical cases are analyzed in order to reveal the PEHL characteristics in different types of line contact.

Numerical and Experimental Investigation of Interface Bonding Via Substrate Remelting of an Impinging Molten Metal Droplet

1996 ◽  
Vol 118 (1) ◽  
pp. 164-172 ◽  
Author(s):  
C. H. Amon ◽  
K. S. Schmaltz ◽  
R. Merz ◽  
F. B. Prinz
Keyword(s):  
Heat Transfer ◽  
Numerical Model ◽  
Molten Metal ◽  
Thermal Stresses ◽  
Initial Conditions ◽  
Metal Droplet ◽  
Solid Substrate ◽  
Numerical Results ◽  
Operating Conditions ◽  
Analytical Approaches

A molten metal droplet landing and bonding to a solid substrate is investigated with combined analytical, numerical, and experimental techniques. This research supports a novel, thermal spray shape deposition process, referred to as microcasting, capable of rapidly manufacturing near netshape, steel objects. Metallurgical bonding between the impacting droplet and the previous deposition layer improves the strength and material property continuity between the layers, producing high-quality metal objects. A thorough understanding of the interface heat transfer process is needed to optimize the microcast object properties by minimizing the impacting droplet temperature necessary for superficial substrate remelting, while controlling substrate and deposit material cooling rates, remelt depths, and residual thermal stresses. A mixed Lagrangian–Eulerian numerical model is developed to calculate substrate remelting and temperature histories for investigating the required deposition temperatures and the effect of operating conditions on remelting. Experimental and analytical approaches are used to determine initial conditions for the numerical simulations, to verify the numerical accuracy, and to identify the resultant microstructures. Numerical results indicate that droplet to substrate conduction is the dominant heat transfer mode during remelting and solidification. Furthermore, a highly time-dependent heat transfer coefficient at the droplet/substrate interface necessitates a combined numerical model of the droplet and substrate for accurate predictions of the substrate remelting. The remelting depth and cooling rate numerical results are also verified by optical metallography, and compare well with both the analytical solution for the initial deposition period and the temperature measurements during droplet solidification.

A Starved Mixed Elastohydrodynamic Lubrication Model for the Prediction of Lubrication Performance, Friction and Flash Temperature With Arbitrary Entrainment Angle

2017 ◽  
Vol 140 (3) ◽  
Author(s):  
Wei Pu ◽  
Dong Zhu ◽  
Jiaxu Wang
Keyword(s):  
Surface Roughness ◽  
Film Thickness ◽  
Elastohydrodynamic Lubrication ◽  
Industrial Applications ◽  
Operating Conditions ◽  
Flash Temperature ◽  
Machined Surface ◽  
Lubrication Performance ◽  
Wide Range ◽  
Starved Lubrication

In this study, a modified mixed lubrication model is developed with consideration of machined surface roughness, arbitrary entraining velocity angle, starvation, and cavitation. Model validation is executed by means of comparison between the obtained numerical results and the available starved elastohydrodynamic lubrication (EHL) data found from some previous studies. A comprehensive analysis for the effect of inlet oil supply condition on starvation and cavitation, mixed EHL characteristics, friction and flash temperature in elliptical contacts is conducted in a wide range of operating conditions. In addition, the influence of roughness orientation on film thickness and friction is discussed under different starved lubrication conditions. Obtained results reveal that inlet starvation leads to an obvious reduction of average film thickness and an increase in interasperity cavitation area due to surface roughness, which results in significant increment of asperity contacts, friction, and flash temperature. Besides, the effect of entrainment angle on film thickness will be weakened if the two surfaces operate under starved lubrication condition. Furthermore, the results show that the transverse roughness may yield thicker EHL films and lower friction than the isotropic and longitudinal if starvation is taken into account. Therefore, the starved mixed EHL model can be considered as a useful engineering tool for industrial applications.

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