Use of the Inverse Approach to Investigate the Stresses in Rough Elastohydrodynamic Contacts

2001 ◽  
Vol 124 (1) ◽  
pp. 109-113 ◽  
Author(s):  
K. Y. Li ◽  
C. J. Hooke
Keyword(s):  
Point Contact ◽  
Surface Profile ◽  
Companion Paper ◽  
Operating Conditions ◽  
Point Contacts ◽  
Roughness Effects ◽  
Inverse Approach ◽  
Transverse Roughness ◽  
Ellipticity Ratio ◽  
Good Agreement

The inverse approach, described in detail in a companion paper, is applied to two contacts. The first is a line contact with transverse roughness; the second a point contact with an ellipticity ratio of four containing an isolated transverse surface feature. In each case the surface profile was monitored as the operating conditions became more severe. These profiles were used to define the surface in a multi-level EHL solver and the pressures and subsurface stresses calculated. After allowing for the build up of residual stress, the maximum subsurface stress was compared with the yield strength of the rough surface. Good agreement was obtained indicating, first, that EHL theory is accurate for the rolling case examined and, second, that the Hooke-Venner hypothesis of equivalence between roughness effects in line and point contacts is valid.

An Experimental Evaluation of the Hamrock and Dowson Minimum Film Thickness Equation for Fully Flooded EHD Point Contacts

1981 ◽  
Vol 103 (2) ◽  
pp. 284-294 ◽  
Author(s):  
K. A. Koye ◽  
W. O. Winer
Keyword(s):  
Experimental Data ◽  
Statistical Analysis ◽  
Film Thickness ◽  
Experimental Evaluation ◽  
Point Contact ◽  
Major Axis ◽  
Point Contacts ◽  
Lubricant Film Thickness ◽  
Minimum Film Thickness ◽  
Ellipticity Ratio

Fifty-seven measurements of the minimum lubricant film thickness separating the elastohydrodynamically lubricated point contact of a steel crowned roller and a flat sapphire disk were made by an optical interferometry technique. The data collected were used to evaluate the Hamrock and Dowson minimum EHD film thickness model over a practical range of contact ellipticity ratio where the major axis of the contact ellipse is aligned both parallel and perpendicular to the direction of motion. A statistical analysis of the measured film thickness data showed that the experimental data averaged 30 percent greater film thickness than the Hamrock and Dowson model predicts.

Flow Continuity of Isothermal Elastohydrodynamic Point-Contact Lubrication under Different Numerical Iteration Configurations

2021 ◽  
pp. 1-26
Author(s):  
Liangwei Qiu ◽  
Shuangbiao Liu ◽  
Zhijian Wang ◽  
Xiaoyang Chen
Keyword(s):  
Error Control ◽  
Multigrid Method ◽  
Point Contact ◽  
Elastohydrodynamic Lubrication ◽  
Operating Conditions ◽  
Point Contacts ◽  
Numerical Iteration ◽  
Mesh Method ◽  
Iteration Methods ◽  
Relaxation Factors

Abstract Elastohydrodynamic Lubrication (EHL) in point contacts can be numerically solved with various iteration methods, but so far the flow continuity of such solutions has not been explicitly verified. A series of closed regions with the same inlet side boundary is defined and two treatments to total all flows related to the other boundaries of the closed regions are defined to enable flow continuity verifications. The multigrid method and the traditional single mesh method with different relaxation configurations are utilized to solve different cases to evaluate computation efficiencies. For the multigrid method, the combination of a pointwise solver together with hybrid relaxation factors is identified to perform better than other combinations. The single mesh method has inferior degrees of flow continuity than the multigrid method and needs much smaller error control values of pressure to achieve a decent level of flow continuity. Because flow continuity has a physical meaning, its verifications should be routinely included in any self-validation process for any EHL results. Effects of control errors of pressure, mesh sizes, differential schemes and operating conditions on flow continuities are studied. Then, trends of film thickness with respect to speed are briefly discussed with meshes up to 4097 by 4097.

Experimental and numerical investigation on single dent with marginal bump in EHL point contacts

2017 ◽  
Vol 69 (5) ◽  
pp. 798-807
Author(s):  
Xue-feng Wang ◽  
R.F. Hu ◽  
Weiyan Shang ◽  
Fuzhou Zhao
Keyword(s):  
Applied Load ◽  
Surface Defects ◽  
Contact Region ◽  
Point Contact ◽  
Operating Conditions ◽  
Experimental Investigations ◽  
Point Contacts ◽  
Content Type ◽  
Entrainment Velocity ◽  
Static Conditions

Purpose The dent is one of typical surface defects on the surfaces of the machine elements and it is not in fact inerratic. This work aims to investigate the effect of a single dent with a marginal bump on the film shape in elastohydrodynamic lubrication (EHL) point contacts. Design/methodology/approach The experimental investigations of a single dent with marginal bump were carried out using multi-beam interferometry in EHL point contacts. In the meantime, its numerical simulation was also finished using multi-level method and multilevel multi-integration method. The effects of the entrainment velocity and the applied load as well as the slide-roll ratio on the film were chiefly discussed. Meanwhile, the comparison of films between smooth and dented surfaces was conducted under simple sliding conditions. Findings Under pure sliding conditions, the minimum film thickness presents itself near the marginal bump at lower entrainment velocity. The inlet dimple before the marginal bump is subjected to the operating conditions. Under pure rolling conditions, the shape of the dent is almost unchanged when it is passing through the contact region at lower entrainment velocity. The dent depth hardly depends on the applied load under static conditions. However, larger load enhances the inlet dimple and the elastic deformation of the dent with the marginal bump under pure sliding conditions. Originality/value This work is helpful to understanding the effect of the marginal bump before the single dent on point contact EHL films.

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.

scholarly journals Resistive properties of Janson’s point contacts in the conditions of polarization inversion

2021 ◽  
pp. 81-88
Author(s):  
Alexander Pospelov ◽  
Gennadii Kamarchuk ◽  
Mykola Sakhnenko ◽  
Andrii Savitskii ◽  
Valeriya Proskurina ◽  
...  
Keyword(s):  
Electric Field ◽  
Exposure Time ◽  
Sensitive Element ◽  
Point Contact ◽  
Electrode System ◽  
Operating Conditions ◽  
Design Parameters ◽  
Point Contacts ◽  
Linear Distribution ◽  
Conduction Channel

The sensitive element of a new quantum sensor generation is the Janson dendritic point contact. Analytes that are in the space surrounding the sensitive element are able to interact with the freshly formed surface of the conduction channel of the Janson quantum point contact, as well as with the surface of the dendrite during its growth. This interaction provides the influence of the substances under study on the configuration of the output characteristic of the sensor, represented by the system conductivity histogram. The conductivity histogram is built on the basis of the chrono-resistogram of the self-oscillating point-contact cyclic switchover effect, which is directly recorded under self-oscillation conditions. In the structure of the sensor element, Janson's dendritic point contact is immersed in an electrolyte and in an electric field forms a chrono-resistogram, which depends on the environment composition. The paper considers one of the aspects of such chrono-resistograms formation. The features of a gapless electrochemical system in the process of realizing the point-contact cyclic switchover effect are analyzed. Modeling the sensitive element in the form of a gapless electrode system allowed explaining the mechanism and dynamics of the transition “Janson point contact – dendrite and counter electrode in the electrolyte”. The most important parameter of the gapless electrode system is the coordinate of the polarization inversion boundary. It is shown that the idea of the coordinate of the polarization inversion boundary plays a fundamental role in modeling the resistive properties of a point-contact system and its lifetime. The synthesized mathematical models describe well the experimentally obtained dependences of the resistance on the exposure time of the nanostructure in an electric field. It was found that the dependence of the contact resistance on the exposure time, obtained under the assumption of a linear distribution of the anodic polarization along the main axis of the conduction channel, is described by a differential equation in which the growth rate of resistance is directly proportional to the cube of this resistance. The materials obtained make it possible to purposefully optimize the design parameters and operating conditions of sensor devices based on Janson point contacts for the analysis of complex gaseous and liquid mixtures.

scholarly journals Transient analysis of isothermal elastohydrodynamic circular point contacts

2001 ◽  
Vol 215 (10) ◽  
pp. 1159-1172 ◽  
Author(s):  
D Jalali Vahid ◽  
H Rahnejat ◽  
Z M Jin ◽  
D Downson
Keyword(s):  
Transient Analysis ◽  
Solution Method ◽  
Numerical Solutions ◽  
Flat Glass ◽  
Point Contact ◽  
Elastohydrodynamic Lubrication ◽  
Point Contacts ◽  
Good Qualitative Agreement ◽  
Circular Point ◽  
Good Agreement

In this paper a solution method is presented for the transient isothermal elastohydrodynamic lubrication of point contact conjunctions, based upon the Newton-Raphson scheme and low iteration relaxation. The numerical results are compared with the numerical and experimental observations of others for the circular point contact of a ball against a flat glass disc under oscillating conditions. Good agreement has been found with other numerical solutions. The comparison with the experimental results shows good qualitative agreement.

Influence of Surface Roughness Effects on the Lubrication Performance of External Gear Machines

2017 ◽  
Author(s):  
Divya Thiagarajan ◽  
Andrea Bratto ◽  
Andrea Vacca
Keyword(s):  
Surface Roughness ◽  
Surface Profile ◽  
Operating Conditions ◽  
Gap Model ◽  
Roughness Effects ◽  
Lateral Plate ◽  
Surface Finishes ◽  
Lubrication Performance ◽  
Wide Range ◽  
The Impact

In pressure compensated external gear machines (EGMs), lateral lubricating interfaces exist between floating lateral bushings and gears. These interfaces are primarily responsible for supporting the high pressure bearing loads in these gaps and promoting good operating efficiencies of these units. A fully coupled fluid-structure-thermal interaction lateral gap model has been developed previously in the authors’ research team which considers this highly coupled physical phenomena to predict the lubrication performance of the interface under full film as well as mixed film conditions. In the current work, capabilities of the lateral gap model are utilized in studying the impact of the variations in surface finishes on the performance of a commercially available EGM chosen for this study. Lateral plate designs of varying surface roughness are chosen for the same EGM unit, to analyze their influence on the lubricating performance of the unit. Detailed surface profile measurements were carried out on these lateral plates under study to determine precise inputs to the lateral gap model. Resulting numerical simulations from the gap model over different operating conditions are used to examine the significant performance features associated with the lateral interface which are affected by such surface variations. Furthermore, the paper compares the simulated leakages obtained directly from the lateral gap model for each of the lateral plate designs, with corresponding experimental data over a wide range of operating conditions.

Analysis of isothermal elastohydrodynamic point contacts lubricated by Newtonian fluids using multigrid methods

1997 ◽  
Vol 211 (7) ◽  
pp. 493-508 ◽  
Author(s):  
P Ehret ◽  
D Dowson ◽  
C M Taylor ◽  
D Wang
Keyword(s):  
Smooth Surface ◽  
Multigrid Method ◽  
Integration Method ◽  
Large Range ◽  
Three Dimensional ◽  
Point Contact ◽  
Elastohydrodynamic Lubrication ◽  
Point Contacts ◽  
Dimensional Surface ◽  
Good Agreement

A multigrid multi-integration method has been used to solve the elastohydrodynamic lubrication (EHL) point contact problem over a large range of loads. Solutions obtained with the multigrid method are compared with those computed with an effective influence Newton method. Good agreement has been obtained, which validates the results obtained by both of these independent methods. Smooth surface problems have been used to test the multigrid method, but an example that takes into account a wavy surface has demonstrated the robustness and the large potential of the multigrid method to analyse EHL problems with three-dimensional surface roughness.

The Effects of Surface Texture on EHL Point Contacts

1996 ◽  
Vol 118 (1) ◽  
pp. 59-66 ◽  
Author(s):  
Xiaolan Ai ◽  
Herbert S. Cheng
Keyword(s):  
Surface Texture ◽  
Pressure Fluctuations ◽  
Three Dimensional ◽  
Point Contact ◽  
Maximum Pressure ◽  
Point Contacts ◽  
Random Roughness ◽  
Minimum Film Thickness ◽  
Transverse Roughness ◽  
Effect Of Surface

The effect of surface texture on EHL point contact is studied numerically by using the multigrid method. Numerical simulations have been performed for waviness and random roughness with three different orientations, transverse, oblique and longitudinal. Results reveal a strong domination of unidirectional Couette flow in the EHL conjunction. The geometrical variations at inlet of the contact are transported downstream throughout the EHL conjunction. As a consequence, the oblique surface roughness striations are largely distorted, forming nearly longitudinal wavy passages. Results show that the oblique roughness induces local three dimensional EHL pressure fluctuations. The maximum pressure is higher than that of the transverse roughness. For sinusoidal waviness, oblique orientation gives the smallest minimum film thickness as compared with those of longitudinal and transverse waviness.

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.

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