Influence of Surface Texture on Micro EHL in Boundary Regime Sliding

2012 ◽  
Author(s):  
Robert Erck ◽  
Oyelayo O. Ajayi ◽  
Cinta Lorenzo-Martin ◽  
George R. Fenske
Keyword(s):  
Thin Film ◽  
Coefficient Of Friction ◽  
Elastohydrodynamic Lubrication ◽  
Asperity Contact ◽  
Disc Surface ◽  
Lubrication Regime ◽  
Uncoated Steel ◽  
Constant Friction ◽  
The Coefficient Of Friction ◽  
Hydrogenated Amorphous

A hard steel ball was slid against textured coated and uncoated steel disks that had strongly directionally ground surfaces. The friction coefficient during ball-on-disk rotating low-speed lubricated sliding was continuously measured. The coefficient of friction rose from ≈ 0.12, which is typical for boundary lubrication regime, to as high as 0.45 whenever the ball was sliding parallel to the grinding ridges on the disc surface. The persistence of this “spike” in the friction was observed to be correlated with the hardness of the disc surface and the nature of the coating. We propose that the frictional spike is due to loss of micro-elastohydrodynamic lubrication, combined with side leakage, leading to intimate asperity-asperity contact. As a result, the coefficient of friction is close to that which is obtained there is no or minimal lubrication. This conclusion is supported by enhanced and persistent frictional spikes in tests conducted with discs coated with a very hard nitride thin film, and constant friction for a disk coated with hydrogenated amorphous carbon, which has low coefficient of friction when there is no/minimal lubrication.

Numerical Modeling of Mixed Lubrication and Flash Temperature in EHL Elliptical Contacts

2007 ◽  
Vol 130 (1) ◽  
Author(s):  
Neelesh Deolalikar ◽  
Farshid Sadeghi ◽  
Sean Marble
Keyword(s):  
Surface Deformation ◽  
Elastohydrodynamic Lubrication ◽  
Mixed Lubrication ◽  
Asperity Contact ◽  
Lubrication Regime ◽  
Predicting Performance ◽  
Pure Rolling ◽  
Rolling Element ◽  
Contact Pressures ◽  
Film Lubrication

Highly loaded ball and rolling element bearings are often required to operate in the mixed elastohydrodynamic lubrication regime in which surface asperity contact occurs simultaneously during the lubrication process. Predicting performance (i.e., pressure, temperature) of components operating in this regime is important as the high asperity contact pressures can significantly reduce the fatigue life of the interacting components. In this study, a deterministic mixed lubrication model was developed to determine the pressure and temperature of mixed lubricated circular and elliptic contacts for measured and simulated surfaces operating under pure rolling and rolling/sliding condition. In this model, we simultaneously solve for lubricant and asperity contact pressures. The model allows investigation of the condition and transition from boundary to full-film lubrication. The variation of contact area and load ratios is examined for various velocities and slide-to-roll ratios. The mixed lubricated model is also used to predict the transient flash temperatures occurring in contacts due to asperity contact interactions and friction. In order to significantly reduce the computational efforts associated with surface deformation and temperature calculation, the fast Fourier transform algorithm is implemented.

Study of the micro/nano-texture design to improve the friction properties of DLC thin films

2021 ◽  
pp. 2140027
Author(s):  
Young Woo Kwon ◽  
Mun Ki Bae ◽  
Ri-Ichi Murakami ◽  
Tae Hwan Jang ◽  
Tae Gyu Kim
Keyword(s):  
Thin Film ◽  
Coefficient Of Friction ◽  
Surface Friction ◽  
Low Friction ◽  
Frictional Wear ◽  
The Coefficient Of Friction ◽  
Surface Contact Area ◽  
Photolithography Process ◽  
Texture Design ◽  
Pattern Width

In this study, a DLC pattern was fabricated through a photolithography process that constitutes a part of the semiconductor process, to investigate the frictional wear characteristics. The photolithography was used to produce negative patterns with a pattern width of 10 [Formula: see text]m or 20 [Formula: see text]m and a pattern depth of 500 nm on the DLC surface. The change in the coefficient of friction of the surface was investigated through a ball-on-disk tribology test on the fabricated micro/nano-sized DLC pattern. The DLC pattern fabricated by the photolithography process showed a superior coefficient of friction to that of the general DLC sample. These results show that the decrease in the surface friction coefficient of the patterned DLC thin film is due to the reduction in the surface contact area owing to the modification of the micro/nano-texture of the surface as well as the low friction characteristics of the DLC.

A numerical method to investigate the mixed lubrication performances of journal-thrust coupled bearings

2019 ◽  
Vol 71 (9) ◽  
pp. 1099-1107
Author(s):  
Guo Xiang Guo Xiang ◽  
Yanfeng Han ◽  
Renxiang Chen ◽  
Jiaxu Wang Jiaxu Wang ◽  
Ni Xiaokang
Keyword(s):  
Thrust Bearing ◽  
Load Capacity ◽  
Elastohydrodynamic Lubrication ◽  
Hydrodynamic Pressure ◽  
Mixed Lubrication ◽  
Hydrodynamic Effect ◽  
Asperity Contact ◽  
Content Type ◽  
Lubrication Regime ◽  
Coupled Effect

Purpose This paper aims to present a numerical model to investigate the mixed lubrication performances of journal-thrust coupled bearings (or coupled bearings). Design/methodology/approach The coupled hydrodynamic effect (or coupled effect) between the journal and the thrust bearing is considered by ensuring the continuity of the hydrodynamic pressure and the flow field at the common boundary. The mixed lubrication performances of the coupled bearing are comparatively studied for the cases of considering and not considering coupled effect. Findings The simulated results show that the hydrodynamic pressure distributions for both the journal and thrust bearing are modified due to the coupled effect. The decreased load capacity of the journal bearing and the increased load capacity of the thrust bearing can be observed when the coupled effect is considered. And the coupled effect can facilitate in reducing the asperity contact load for both the journal and thrust bearing. Additionally, the interaction between the mixed lubrication behaviors, especially for the friction coefficient, of the journal and the thrust bearing is significant in the elastohydrodynamic lubrication regime, while it becomes weak in the mixed lubrication regime. Originality/value The developed model can reveal the mutual effects of the mixed lubrication behavior between the journal and the thrust bearing.

Some Tribological Properties of an Ionic Liquid

2005 ◽  
Author(s):  
Takashi Nogi
Keyword(s):  
Ionic Liquid ◽  
Coefficient Of Friction ◽  
Tribological Properties ◽  
Friction And Wear ◽  
Wear Performance ◽  
Lubrication Regime ◽  
Pin On Disc ◽  
The Coefficient Of Friction

Some tribological properties of an ionic liquid were investigated by using a pin-on-disc friction and wear tester. Due to running-in, the coefficient of friction of the ionic liquid decreased with time to a very low value of 0.02 which suggests that the lubrication regime was hydrodynamic at the end of the tests. Anti-wear performance of the ionic liquid was substantially comparable to a paraffin-based oil.

Friction and wear studies of silicon in sliding contact with thin-film magnetic rigid disks

1993 ◽  
Vol 8 (7) ◽  
pp. 1611-1628 ◽  
Author(s):  
Bharat Bhushan ◽  
Sreekanth Venkatesan
Keyword(s):  
Thin Film ◽  
Single Crystal ◽  
Coefficient Of Friction ◽  
Amorphous Carbon ◽  
Friction And Wear ◽  
Single Crystal Silicon ◽  
Crystal Silicon ◽  
Carbon Transfer ◽  
Zn Ferrite ◽  
The Coefficient Of Friction

Silicon is an attractive material for the construction of read/write head sliders in magnetic recording applications from the viewpoints of ease of miniaturization and low fabrication cost. In the present investigation we have studied the friction and wear behavior of single-crystal, polycrystalline, ion-implanted, thermally oxidized (wet and dry), and plasma-enhanced chemical vapor deposition (PECVD) oxide-coated silicon pins while sliding against lubricated and unlubricated thin-film disks. For comparison, tests have also been conducted with Al2O3–TiC and Mn–Zn ferrite pins which are currently used as slider materials. With single-crystal silicon the rise in the coefficient of friction with sliding cycles is faster compared to Al2O3–TiC and Mn–Zn ferrite pins. In each case, the rise in friction is associated with the burnishing of the disk surface and transfer of amorphous carbon and lubricant (in the case of lubricated disks) from the disk to the pin. Thermally oxidized (under dry oxygen conditions) single-crystal silicon and PECVD oxide-coated single-crystal silicon exhibit excellent tribological characteristics while sliding against lubricated disks, and we believe this is attributable to the chemical passivity of the oxide coating. In dry nitrogen, the coefficient of friction for single-crystal silicon sliding against lubricated disks behaves differently than in air, decreasing from an initial value of 0.2 to less than 0.05 within 5000 cycles of sliding. We believe that silicon/thin-film disk interface friction and wear is governed by the uniformity and tenacity of the amorphous carbon transfer film and oxygen-enhanced fracture of silicon.

Analysis of the Contribution of Adhesion and Ploughing to Shoe-Floor Lubricated Friction in the Boundary Lubrication Regime

2011 ◽  
Author(s):  
Caitlin Moore ◽  
Kurt Beschorner ◽  
Pradeep L. Menezes ◽  
Michael R. Lovell
Keyword(s):  
Coefficient Of Friction ◽  
Boundary Lubrication ◽  
Ambient Conditions ◽  
Lubrication Regimes ◽  
Lubrication Regime ◽  
Material Hardness ◽  
Lubrication Layer ◽  
The Coefficient Of Friction ◽  
Dry Conditions ◽  
Pin On Disk

Slip and fall accidents cost billions of dollars each year. Shoe-floor-lubricant friction has been shown to follow the Stribeck effect, operating primarily in the boundary and mixed-lubrication regimes. Two of the most important factors believed to significantly contribute to shoe-floor-lubricant friction in the boundary lubrication regime are adhesion and ploughing. Experiments were conducted using a pin-on-disk tribometer to quantify adhesion and ploughing contributions to shoe-floor friction in dry and lubricated conditions. The coefficient of friction between three shoe materials and two floor materials of different hardness and roughness were considered. Experiments were conducted under six lubricants for a sliding speed of 0.01 m/sec at ambient conditions. It was found that the contribution of adhesion and ploughing to shoe-floor-lubricant friction was significantly affected by material hardness, roughness, and lubricant properties. Material hardness and roughness are known to affect adhesion, with increased hardness or increased roughness typically resulting in decreased adhesion. The smoothest shoe material, while also being the hardest, resulted in the greatest adhesional contribution to friction. The roughest material, while also being the softest, resulted in the lowest adhesional contributions under dry conditions. Canola oil consistently resulted in the lowest percent of full adhesion and water consistently resulted in the highest percent of full adhesion, presumably due to the thickness, of the boundary lubrication layer. Ploughing contribution was dependent upon the hardness of the shoe and floor materials. A positive correlation was found between the shoe and floor hardness ratio and ploughing coefficient of friction.

scholarly journals The Effect of Surface Texture on Lubricated Fretting

Materials ◽  
2020 ◽  
Vol 13 (21) ◽  
pp. 4886
Author(s):  
Agnieszka Lenart ◽  
Pawel Pawlus ◽  
Andrzej Dzierwa ◽  
Slawomir Wos ◽  
Rafal Reizer
Keyword(s):  
Coefficient Of Friction ◽  
Surface Texture ◽  
Friction And Wear ◽  
Normal Load ◽  
Disc Surface ◽  
The Coefficient Of Friction ◽  
42Crmo4 Steel ◽  
Ball Diameter ◽  
Steel Balls ◽  
Effect Of Surface

Experiments were conducted using an Optimol SRV5 tester in lubricated friction conditions. Steel balls from 100Cr6 material of 60 HRC hardness were placed in contact with 42CrMo4 steel discs of 47 HRC hardness and diversified surface textures. Tests were carried out at a 25–40% relative humidity. The ball diameter was 10 mm, the amplitude of oscillations was set to 0.1 mm, and the frequency was set to 80 Hz. Tests were performed at smaller (45 N) and higher (100 N) normal loads and at smaller (30 °C) and higher (90 °C) temperatures. During each test, the normal load and temperature were kept constant. We found that the disc surface texture had significant effects on the friction and wear under lubricated conditions. When a lower normal load was applied, the coefficient of friction and wear volumes were smaller for bigger disc surface heights. However, for a larger normal load a higher roughness corresponded to a larger coefficient of friction.

The Lubrication Regime at Pin-Pulley Interface in Chain CVTs

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
G. Carbone ◽  
M. Scaraggi ◽  
L. Soria
Keyword(s):  
Pressure Distribution ◽  
High Pressures ◽  
Elastohydrodynamic Lubrication ◽  
Asperity Contact ◽  
Normal Stress Distribution ◽  
Lubrication Regime ◽  
Starting Point ◽  
High Fatigue ◽  
Variable Transmission ◽  
Pressure Peak

This paper deals with the strongly nonstationary squeeze of an oil film at the interface between the chain pin and pulley in chain belt continuously variable transmission. We concentrate on the squeeze motion as it occurs as soon as the pin enters the pulley groove. The duration time to complete the squeeze process compared with the running time the pin takes to cover the entire arc of contact is fundamental to understand whether direct asperity-asperity contact occurs between the two approaching surfaces to clarify what actually is the lubrication regime (elastohydrodynamic lubrication (EHL), mixed, or boundary) and to verify if the Hertzian pressure distribution at the interface can properly describe the actual normal stress distribution. The Hertzian pressure solution is usually taken as a starting point to design the geometry of the pin surface; therefore, it is of utmost importance for the designers to know whether their hypothesis is correct or not. Taking into account that the traveling time, the pin spends in contact with the pulley groove, is of about 0.01 s, we show that rms surface roughness less than 0.1 μm, corresponding to values adopted in such systems, guarantees a fully lubricated EHL regime at the interface. Therefore, direct asperity-asperity contact between the two approaching surfaces is avoided. We also show that the Hertzian solution does not properly represent the actual pressure distribution at the pin-pulley interface. Indeed, after few microseconds a noncentral annular pressure peak is formed, which moves toward the center of the pin with rapidly decreasing speed. The pressure peak can grow up to values of several gigapascals. Such very high pressures may cause local overloads and high fatigue stresses that must be taken into account to correctly estimate the durability of the system.

Pristine and Alkylated MoS2 Nanosheets for Enhancement of Tribological Performance of Paraffin Grease Under Boundary Lubrication Regime

2019 ◽  
Vol 141 (7) ◽  
Author(s):  
Sooraj S. Rawat ◽  
A. P. Harsha ◽  
Deepak P. Agarwal ◽  
Sangita Kumari ◽  
Om P. Khatri
Keyword(s):  
Coefficient Of Friction ◽  
Tribological Performance ◽  
Wear Volume ◽  
Mos2 Nanosheets ◽  
Lubricating Grease ◽  
Metal Soap ◽  
Paraffin Oil ◽  
Lubrication Regime ◽  
The Coefficient Of Friction ◽  
Worn Surface

In the present study, lubricating grease was developed with paraffin oil and 12-lithium hydroxy stearate metal soap as a thickening agent. MoS2 nanosheets were synthesized by hydrothermal method and functionalized with 1-octadecanethiol (i.e., MoS2-ODT). The MoS2 and MoS2-ODT nanosheets were dispersed in the grease with different concentrations to evaluate its tribological performance. Tribological results unveiled that the addition of MoS2 nanosheets in grease appreciably reduced the coefficient of friction and mean wear volume of tribo-interfaces as compared with pure grease. Energy dispersive spectroscopy (EDS) spectrum revealed the deposition of MoS2 on the worn surface and confirmed a thin tribo-film which protects steel tribo-pair against wear.

scholarly journals Relation between the cooling time and friction results in braking tests

2012 ◽  
Vol 3 (2) ◽  
pp. 156-164
Author(s):  
P.D. Neis ◽  
G.L.P.G. Zanetti ◽  
E. Schmidt ◽  
Y. Perez Delgado ◽  
P. De Baets ◽  
...  
Keyword(s):  
Coefficient Of Friction ◽  
Disk Surface ◽  
Laboratory Scale ◽  
Cooling Time ◽  
Current Paper ◽  
Considerable Reduction ◽  
Oxidation Degree ◽  
Disc Surface ◽  
The Coefficient Of Friction

The current paper intends to evaluate the influence of the cooling time on friction results duringbraking performed on a laboratory-scale tribometer. At the same time, a possible correlation between theoxidation process and emissivity on the disk surface during cooling time is investigated. Sample and diskused in the tests are from a commercial available brake car. Procedure includes changes in the coolingtimes, where 4 different conditions are experienced: 18s, 90s, 600s and 24h. Friction curves revealdifferences between the results obtained with 18s, 90s and 600s. Likewise, when a cooling time of 24h isused, the first stop shows a considerable reduction in the coefficient of friction. It was not possible to find outthe reason for this effect since relationship between friction and oxidation degree, verified by means ofemissivity on the disc surface, could not be encountered.

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