Surface roughness modification in EHL line contacts-the effect of roughness wavelength, orientation and operating conditions

1999 ◽  
pp. 193-202 ◽  
Author(s):  
C.J. Hooke
Keyword(s):  
Surface Roughness ◽  
Operating Conditions ◽  
Line Contacts

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.

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.

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.

scholarly journals The Effect of Surface Roughness on Diffusion and Chemical Reaction Controlled Limiting Currents on a Rotating Cylinder Electrode in Deaerated Solutions with and Without CO2

CORROSION ◽  
10.5006/2552 ◽  
2018 ◽  
Vol 74 (9) ◽  
pp. 971-983 ◽  
Author(s):  
M. Al-Khateeb ◽  
R. Barker ◽  
A. Neville ◽  
H.M. Thompson
Keyword(s):  
Mass Transfer ◽  
Surface Roughness ◽  
Sherwood Number ◽  
Schmidt Number ◽  
Rotating Cylinder ◽  
Operating Conditions ◽  
Limiting Current ◽  
Surface Roughening ◽  
Rotating Cylinder Electrode ◽  
Effect Of Surface

The influence of surface roughness on mass transfer on a rotating cylinder electrode apparatus is investigated experimentally for a roughness pattern consisting of grooves parallel to the direction of fluid flow. Mass transfer from four different samples, with roughness values of 0.5 μm, 6 μm, 20 μm, and 34 μm, is measured using the limiting current technique for a range of rotational speeds in NaCl solutions saturated with N2 at pH = 3 and 4. Comparison with available correlations for the Sherwood number in literature (which are independent of surface roughness and are either for specific or arbitrary roughness patterns) shows that H+ mass transfer only correlates well for particular levels of roughness and that their accuracy can be increased if a correlation is utilized which is a function of surface roughening. A new correlation for Sherwood number as a function of the Reynolds number, Schmidt number, and surface roughness is proposed which agrees well with the mass transfer observed from all of the rough surface cases considered for this particular roughness pattern. Complementary experiments in CO2 environments were used to assess the combined limiting current associated with H+ and H2CO3 reduction (with the latter occurring via the buffering effect and being associated with the slow CO2 hydration step). Although the increase in sample roughness clearly leads to an increase in the rate of H+ mass transfer, in the CO2 environments considered, surface roughness is found to have no significant influence on the limiting current contribution from H2CO3, which can therefore be determined from Vetter’s equation across this range of operating conditions.

Relating Surface Roughness to Subsurface Stress

2005 ◽  
Author(s):  
A. Martini ◽  
S. B. Liu ◽  
B. Escoffier ◽  
Q. Wang
Keyword(s):  
Surface Roughness ◽  
Stress Field ◽  
Point Contact ◽  
Surface Characteristics ◽  
Operating Conditions ◽  
Surface Design ◽  
Dry Contact ◽  
Subsurface Stress ◽  
The Relationship ◽  
Machined Surfaces

Understanding and anticipating the effects of surface roughness on subsurface stress in the design phase can help ensure that performance and life requirements are satisfied. The specific approach taken in this work to address the goal of improved surface design is to relate surface characteristics of real, machined surfaces to subsurface stress fields for dry contact. This was done by digitizing machined surfaces, simulating point contact numerically, calculating the corresponding subsurface stress field, and then relating stress results back to the surface. The relationship between surface characteristics and subsurface stress is evaluated using several different approaches including analyses of trends identified through stress field visualization and extraction of statistical data. One such approach revealed a sharp transition between cases in which surface characteristics dominated the stress field and those in which bulk, or global contact effects dominated the stress. This transition point was found to be a function of the contact operating conditions, material properties, and most interestingly, the roughness of the surface.

Traction in EHL Line Contacts Using Free-Volume Pressure-Viscosity Relationship With Thermal and Shear-Thinning Effects

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
Punit Kumar ◽  
M. M. Khonsari
Keyword(s):  
Free Volume ◽  
Elastohydrodynamic Lubrication ◽  
Approximate Equation ◽  
Shear Thinning ◽  
Operating Conditions ◽  
Limiting Shear Stress ◽  
Line Contacts ◽  
Traction Coefficient ◽  
Simulation Results ◽  
Volume Equation

This paper investigates the traction behavior in heavily loaded thermo-elastohydrodynamic lubrication (EHL) line contacts using the Doolittle free-volume equation, which closely represents the experimental viscosity-pressure-temperature relationship and has recently gained attention in the field of EHL, along with Tait’s equation of state for compressibility. The well-established Carreau viscosity model has been used to describe the simple shear-thinning encountered in EHL. The simulation results have been used to develop an approximate equation for traction coefficient as a function of operating conditions and material properties. This equation successfully captures the decreasing trend with increasing slide to roll ratio caused by the thermal effect. The traction-slip characteristics are expected to be influenced by the limiting shear stress and pressure dependence of lubricant thermal conductivity, which need to be incorporated in the future.

Hydrodynamic Lubrication and Wear in Wavy Contacting Face Seals

1978 ◽  
Vol 100 (1) ◽  
pp. 81-90 ◽  
Author(s):  
A. O. Lebeck ◽  
J. L. Teale ◽  
R. E. Pierce
Keyword(s):  
Surface Roughness ◽  
Hydrodynamic Lubrication ◽  
Surface Profile ◽  
Operating Conditions ◽  
Face Seal ◽  
Hydrodynamic Load ◽  
Surface Waviness ◽  
Wear Rates ◽  
Elastic Deflection ◽  
Face Seals

A model of face seal lubrication is proposed and developed. Hydrodynamic lubrication for rough surfaces, surface waviness, asperity load support, elastic deflection, and wear are considered in the model. Predictions of the ratio of hydrodynamic load support to asperity load support are made for a face seal sealing a low viscosity liquid where some contact does occur and surface roughness is important. The hydrodynamic lubrication is caused by circumferential surface waviness on the seal faces. Waviness is caused by initial out of flatness or any of the various distortions that occur on seal ring faces in operation. The equilibrium solution to the problem yields one dimensional hydrodynamic and asperity pressure distributions, mean film thickness, elastic deflection, and friction for a given load on the seal faces. The solution is found numerically. It is shown that the fraction of hydrodynamic load support depends on many parameters including the waviness amplitude, number of waves around the seal, face width, ring stiffness, and most importantly, surface roughness. For the particular seal examined the fraction of load support would be small for the amount of waviness expected in this seal. However, if the surface roughness were lower, almost complete lift-off is possible. The results of the analysis show why the initial friction and wear rates in mechanical face seals may vary widely; the fraction of hydrodynamic load support depends on the roughness and waviness which are not necessarily controlled. Finally, it is shown how such initial waviness effects disappear as the surface profile is altered by wear. This may take a long or short time, depending on the initial amount of hydrodynamic load support, but unless complete liftoff is achieved under all operating conditions, the effects of initial waviness will vanish in time for steady state conditions. Practical implications are drawn for selecting some seal parameters to enhance initial hydrodynamic load support without causing significant leakage.

Fundamental Differences Between Newtonian and Non-Newtonian Micro-EHL Results

1995 ◽  
Vol 117 (1) ◽  
pp. 29-35 ◽  
Author(s):  
L. Chang ◽  
W. Zhao
Keyword(s):  
Surface Roughness ◽  
Numerical Methods ◽  
Practical Interest ◽  
Operating Conditions ◽  
Convergence Criteria ◽  
Governing Equations ◽  
Rheological Models ◽  
Dimensionless Parameters ◽  
Machine Elements ◽  
Thinning Effect

Numerical analyses of micro-EHL problems have shown remarkably different results with Newtonian and non-Newtonian rheological models. However, no consensus has been reached whether a Newtonian model can be used in micro-EHL analysis. It is difficult to prove the point numerically as researchers use different numerical methods, grid sizes, time steps, and convergence criteria. This paper analytically studies the fundamental differences between Newtonian and non-Newtonian micro-EHL results. Algebraic governing equations are derived in terms of dimensionless parameters of the problem. Results are obtained for a range of key dimensionless parameters of practical interest. These results suggest that Newtonian and non-Newtonian micro-EHL results would be qualitatively different and the differences would be most pronounced with surface roughness of short wavelengths. Since surface roughness of machine elements contains substantial short-wavelength contents, a Newtonian rheological model is likely to generate misleading micro-EHL results under all operating conditions under which the shear-thinning effect of the lubricant is significant.

Effects of Flap Wheel Grinding Parameters on Surface Roughness for Stainless Steel

2014 ◽  
Vol 548-549 ◽  
pp. 506-509 ◽  
Author(s):  
Jirayu Somgumnerd ◽  
Viboon Tangwarodomnukun ◽  
Suksan Prombanpong
Keyword(s):  
Surface Roughness ◽  
Stainless Steel ◽  
Surface Finish ◽  
Operating Conditions ◽  
Success Factor ◽  
Polishing Process ◽  
Fine Surface ◽  
Key Success Factor ◽  
Selection Of

The polishing process plays an important role in the stainless steel cookware since an appearance is one of the prime quality criterions of the product. Typically, there are three sequential steps in the polishing process using abrasive flap wheel, sisal and cloth respectively. The abrasive flap wheel is the first step in the process which aims to rapidly create fine surface finish on the product. Thus, the selection of appropriate flap wheel as well as operating conditions in order to achieve surface finish within the required cycle time i.e. 12 seconds are the key success factor. Therefore, the experimental design is conducted and analyzed. It is found that there are four factors which influence the surface roughness: grits size of flap wheel, polishing time, velocity, and force. It can also be concluded from the analysis that the roughness is directly proportional to grit size and force but it is inversely proportional to velocity. In addition, the optimal condition for the case study can also be obtained.

Roughness in elastohydrodynamic contacts

2010 ◽  
Vol 224 (12) ◽  
pp. 2599-2609 ◽  
Author(s):  
C J Hooke ◽  
K Y Li
Keyword(s):  
Surface Roughness ◽  
Surface Topography ◽  
Operating Conditions ◽  
Surface Slip ◽  
Fluid Rheology ◽  
Contact Pressures

Surface roughness can reduce the life of any elastohydrodynamically lubricated (EHL) component. However, the process is complex with details of the operating conditions, relative surface slip, fluid rheology, as well as surface topography influencing the behaviour. Because of this, it is unlikely than any generally applicable rules will be found which can be used to relate surface roughness to life. Instead, an approach that enabled rapid predictions of the contact pressures and clearances stresses in EHL contacts was developed by the authors and is extended here to include the calculation of the subsurface stresses.

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