scholarly journals A New Film Parameter for Rough Surface EHL Contacts with Anisotropic and Isotropic Structures

2021 ◽  
Vol 69 (2) ◽  
Author(s):  
Jonny Hansen ◽  
Marcus Björling ◽  
Roland Larsson
Keyword(s):  
Surface Roughness ◽  
Hydrodynamic Lubrication ◽  
Major Advance ◽  
Microscopic Scale ◽  
Film Parameter ◽  
Anisotropic Structures ◽  
Surface Irregularities ◽  
Optimal Efficiency ◽  
The 1960S ◽  
Ball On Disc

AbstractNumerous tribological contacts worldwide rely on adequate lubrication quality for proper functionality. Despite this, there is no existing approach to accurately predict the state of lubrication. The default model since introduced in the 1960s—the $$\Lambda$$ Λ -ratio, defined as the oil film thickness over the surface roughness height—is unpredictable and may yield erroneous results. Here, we put forward a framework for a new updated film parameter, $${\Lambda }^{*}$$ Λ ∗ , which accounts for the elasto-hydrodynamic lubrication (EHL) effects induced by surface irregularities on the microscopic scale (micro-EHL). This new film parameter was validated in ball-on-disc tribological tests with engineering surfaces comprising isotropic and anisotropic structures. As expected, the new model was found to accurately predict the experimentally measured true mixed and full-film EHL regimes. The ability to accurately predict the mode of lubrication represents a major advance in designing tribological interfaces for optimal efficiency and durability.

scholarly journals Lubricant film formation in rough surface non-conformal conjunctions subjected to GPa pressures and high slide-to-roll ratios

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Jonny Hansen ◽  
Marcus Björling ◽  
Roland Larsson
Keyword(s):  
Surface Roughness ◽  
Film Formation ◽  
Operating Conditions ◽  
Thin Film Lubrication ◽  
Initial State ◽  
Oil Film ◽  
Post Test ◽  
Surface Irregularities ◽  
Film Lubrication ◽  
Ball On Disc

AbstractA ball-on-disc machine was employed in a highly idealised setting to study the interplay between oil film formation and surface irregularities in single-sided rough elasto-hydrodynamic lubricated (EHL) conjunctions. The tests were operated under GPa pressures and high slide-to-roll ratios in a situation where the separating gap was smaller than the combined surface roughness height. Under the initial state of solid contact interference and with the operating conditions held fixed, surfaces were found to gradually conform such that a fully separating oil film of nanometre thickness eventually developed—a thin film lubrication state known as micro-EHL. Additionally, with a previously developed approach for 3D surface re-location analysis, we were able to very precisely specify the pertained nature of surface transformations, even at the asperity scale, by comparing the post-test surfaces to those in the virgin state. The surface roughness Sq was reduced by up to 17% after running-in, while the speed required for full film EHL was reduced by a remarkable 90%. Hence, full film EHL is possible even in cases where the Λ-ratio falsely suggests boundary lubrication. This discrepancy was attributed to the way surfaces are deformed inside the contact, i.e., through the establishment of micro-EHL.

On the effects of two-dimensional Reynolds roughness in hydrodynamic lubrication

1978 ◽  
Vol 364 (1716) ◽  
pp. 89-106 ◽  
Keyword(s):  
Surface Roughness ◽  
Numerical Computation ◽  
Autocorrelation Function ◽  
Reynolds Equation ◽  
Hydrodynamic Lubrication ◽  
The Other ◽  
Roughness Height ◽  
Two Dimensional ◽  
Roughness Effects ◽  
Dimensional Surface

The hydrodynamic lubrication of rough surfaces is analysed with the Reynolds equation, whose application requires the roughness spacing to be large, and the roughness height to be small, compared with the thick­ness of the fluid film. The general two-dimensional surface roughness is considered, and results applicable to any roughness structure are obtained. It is revealed analytically that two types of term contribute to roughness effects: one depends on the shape of the autocorrelation function and the other does not. The former contribution was neglected by previous workers. The numerical computation of an example shows that these two contributions are comparable in magnitude.

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.

Historic timeline of obstetric anaesthesia

2016 ◽  
Author(s):  
Alistair G. McKenzie
Keyword(s):  
Rapid Sequence Induction ◽  
Late Pregnancy ◽  
Spinal Block ◽  
Major Advance ◽  
Acid Aspiration ◽  
Obstetric Anaesthesia ◽  
Neuraxial Anaesthesia ◽  
Caudal Analgesia ◽  
The 1960S ◽  
Acid Aspiration Syndrome

Foremost in the history of obstetric anaesthesia was the introduction of inhalational analgesia by James Simpson in 1847, first with ether and then chloroform. Nitrous oxide was first used in obstetrics in 1880. Neuraxial anaesthesia in obstetrics began with spinal block by Oskar Kreis in 1900, and within 25 years included pudendal, caudal, and paracervical blocks. From 1902 there was a vogue for ‘twilight sleep’, which remained in use until the 1950s. Spinal anaesthesia only became popular with the advent of procaine in 1905; favour declined in the United Kingdom from 1948 and did not return until 40 years later. In 1930, Aburel described the pain pathways of labour. Continuous caudal analgesia for labour was popularized from 1942; it was superseded by the lumbar epidural approach in the 1960s. The arrival of lidocaine in 1950 was a major advance. Another important event in the 1960s was the elucidation of the supine hypotensive syndrome of late pregnancy. In the 1940s, intravenous barbiturates became popular. Mendelson published on the acid aspiration syndrome in 1946. It took 40 years to establish a reliable system of prevention, including fasting, antacids, and rapid sequence induction. This developed piecemeal, aided by recommendations from the British Confidential Enquiries into Maternal Deaths reports beginning in 1957. Neuraxial anaesthesia advanced: 24-hour epidural services (1960s), bupivacaine (1970s), epidural opioids (1980s), use of low-concentration bupivacaine with fentanyl mixtures, patient-controlled epidural and combined spinal–epidural analgesia (1990s), and pencil-point spinal needles (1990s). From the 1980s obstetric anaesthetists have assumed key roles in management of labour, preeclampsia/eclampsia, major haemorrhage, and perioperative care.

Hydrodynamic Performance Produced by Nanotexturing in Submicrometer Clearance With Surface Roughness

2014 ◽  
Vol 137 (1) ◽  
Author(s):  
Tomoko Hirayama ◽  
Heinosuke Shiotani ◽  
Kazuki Yamada ◽  
Naoki Yamashita ◽  
Takashi Matsuoka ◽  
...  
Keyword(s):  
Surface Roughness ◽  
Hydrodynamic Lubrication ◽  
Surface Texturing ◽  
Wave Model ◽  
Physical Models ◽  
Hydrodynamic Performance ◽  
Stribeck Curve ◽  
Spiral Groove ◽  
Transition Speed ◽  
Lubrication Regime

Surface texturing is a promising way to expand the hydrodynamic lubrication regime and thereby modify the tribological properties of sliding surfaces. Spiral-groove textures in particular have attracted much attention over the past several decades because they produce a thicker lubrication film in the gap. However, no research has been reported on the effect of periodic texturing with a several 100 nm depth on hydrodynamic performance in submicrometer clearance with surface roughness. The purpose of the study reported here was to investigate the effect of such nanotexturing on hydrodynamic performance. This was done by conducting ring-on-disk friction tests, focusing on the existence of surface roughness in the narrow clearance. The samples were rings with various degrees of surface roughness and disks with spiral-groove textures produced by femtosecond laser processing. The friction coefficients experimentally obtained were plotted as a Stribeck curve and compared with a theoretical one calculated using a Reynolds equation formulated from two physical models, the Patir–Cheng average flow model and a sinusoidal wave model. The results showed that surface roughness did not affect the friction coefficient in the hydrodynamic lubrication regime. However, the hydrodynamic lubrication regime gradually shrank with an increase in surface roughness, and mild transitions to the mixed lubrication regime were observed at higher rotational speeds. The minimum clearances reached at the transition speed were almost the same, about 200–300 nm, for all experiments regardless of surface roughness.

scholarly journals Hydrodynamic lubrication of rough surfaces

1982 ◽  
Vol 383 (1785) ◽  
pp. 439-446 ◽  
Keyword(s):  
Surface Roughness ◽  
Film Thickness ◽  
Reynolds Equation ◽  
Hydrodynamic Lubrication ◽  
Rough Surfaces ◽  
Homogenization Method ◽  
Squeeze Film ◽  
Spatial Average

Using the two-space homogenization method we derive an averaged Reynolds equation that is correct to O (< H 6 > — < H 3 > 2 ), where H is the total film thickness and the angle brackets denote a spatial average. Applications of this mean Reynolds equation to a squeeze-film bearing with a sinusoidal or an isotropic surface roughness are discussed.

Heat Transfer at Aluminum-Water Interfaces: Effect of Surface Roughness

2012 ◽  
Author(s):  
H. Sam Huang ◽  
Jennifer L. Wohlwend ◽  
Vikas Varshney ◽  
Ajit K. Roy
Keyword(s):  
Heat Transfer ◽  
Finite Element Method ◽  
Surface Roughness ◽  
Finite Element ◽  
Thermal Conductance ◽  
Md Simulations ◽  
Macroscopic Scale ◽  
Microscopic Scale ◽  
Scale Surface ◽  
Element Method

In this paper, we studied the effect of microscopic surface roughness on heat transfer between aluminum and water by molecular dynamic (MD) simulations and macroscopic surface roughness on heat transfer between aluminum and water by finite element (FE) method. It was observed that as the microscopic scale surface roughness increased, the thermal boundary conductance increased. The thermal conductance increases 20% when the ratio of the amplitude of the surface roughness to the width of the system was changed from 0 to 1. At the macroscopic scale, different degrees of surface roughness were studied by finite element method. The heat transfer was observed to enhance as the surface roughness increases. The surface roughness was found to enhance the heat transfer both at the microscopic scale and at the macroscopic scale. Based upon the calculations at the microscopic scale by MD simulations and at the macroscopic scale by Finite Element method, a procedure was proposed to obtain the thermal conductance of surface roughness at the length scale of macroscopic and able to include the macroscopic scale surface roughness.

Lubrication of a Porous Bearing With Surface Corrugations

1982 ◽  
Vol 104 (1) ◽  
pp. 127-134 ◽  
Author(s):  
J. Prakash ◽  
K. Tiwari
Keyword(s):  
Surface Roughness ◽  
Hydrodynamic Lubrication ◽  
Rough Surfaces ◽  
Stochastic Theory ◽  
Circular Plates ◽  
Operating Characteristics ◽  
Roughness Effects ◽  
Porous Bearing

The paper considers the surface roughness effects in hydrodynamic porous bearings. On the basis of stochastic theory of hydrodynamic lubrication of rough surfaces developed by Christensen, different forms of Reynolds type equations, as applicable to a general porous bearings are derived for various types of surface roughness pattern. To illustrate the functional effects of surface roughness on the operating characteristics of a porous bearing, the case of nonrotating circular plates in normal approach is analyzed. It is shown that surface roughness may considerably influence the operating characteristics of porous bearings. The direction of the influence, however, depends upon the type of roughness assumed.

scholarly journals The Non-Unicity of the Film Thickness in the Hydrodynamic Lubrication: Novel Approach Generating Equivalent Micro-Grooves and Roughness

2021 ◽  
Vol 26 (3) ◽  
pp. 44-61
Author(s):  
M. El Gadari ◽  
M. Hajjam
Keyword(s):  
Film Thickness ◽  
Reynolds Equation ◽  
Pressure Field ◽  
Hydrodynamic Lubrication ◽  
Hydrodynamic Pressure ◽  
New Approach ◽  
Initial Film ◽  
Surface Finishes ◽  
Novel Approach ◽  
The 1960S

Abstract Since the 1960s, all studies have assumed that a film thickness “h” provides a unique pressure field “p” by resolving the Reynolds equation. However, it is relevant to investigate the film thickness unicity under a given hydrodynamic pressure within the inverse theory. This paper presents a new approach to deduce from an initial film thickness a widespread number of thicknesses providing the same hydrodynamic pressure under a specific condition of gradient pressure. For this purpose, three steps were presented: 1) computing the hydrodynamic pressure from an initial film thickness by resolving the Reynolds equation with Gümbel’s cavitation model, 2) using a new algorithm to generate a second film thickness, 3) comparing and validating the hydrodynamic pressure produced by both thicknesses with the modified Reynolds equation. Throughout three surface finishes: the macro-shaped, micro-textured, and rough surfaces, it has been demonstrated that under a specific hydrodynamic pressure gradient, several film thicknesses could generate the same pressure field with a slight difference by considering cavitation. Besides, this paper confirms also that with different ratios of the averaged film thickness to the root mean square (RMS) similar hydrodynamic pressure could be generated, thereby the deficiency of this ratio to define the lubrication regime as commonly known from Patir and Cheng theory.

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