Lubricants

14 pages, 4638 KiB

Open AccessArticle

Superlubricity in EHL Contacts with Water-Containing Gear Fluids

by Mustafa Yilmaz, Michael Mirza, Thomas Lohner and Karsten Stahl

Lubricants 2019, 7(5), 46; https://doi.org/10.3390/lubricants7050046 - 27 May 2019

Cited by 29 | Viewed by 6170

Fluid friction in elastohydrodynamically lubricated (EHL) contacts depends strongly on the lubricant considered. Synthetic oils can have significantly lower fluid friction than mineral oils. Water-containing fluids have the potential to significantly reduce fluid friction further. The aim of this study is to investigate [...] Read more.

Fluid friction in elastohydrodynamically lubricated (EHL) contacts depends strongly on the lubricant considered. Synthetic oils can have significantly lower fluid friction than mineral oils. Water-containing fluids have the potential to significantly reduce fluid friction further. The aim of this study is to investigate the film formation and frictional behavior of highly-loaded EHL contacts with water-containing fluids. Comparisons are made with mineral and polyalphaolefin oils. Measurements at an optical EHL tribometer show good lubricant film formation of the considered water-containing gear fluids. Measurements at a twin-disk test rig show coefficients of friction smaller than 0.01, which is referred to as superlubricity, for all considered operating conditions. Full article

(This article belongs to the Special Issue Gear Tribology)

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18 pages, 12597 KiB

Open AccessArticle

Effect of Plastic Deformation and Damage Development during Friction of fcc Metals in the Conditions of Boundary Lubrication

by Alexey Moshkovich, Vladislav Perfilyev and Lev Rapoport

Lubricants 2019, 7(5), 45; https://doi.org/10.3390/lubricants7050045 - 23 May 2019

Cited by 12 | Viewed by 4188

Abstract

The main goal of the presented work was the analysis of the interaction between deformed microstructures and friction and the wear properties of four face centered cubic (fcc) metals. Pure fcc metals such as Ag, Cu, Ni, and Al with different values of [...] Read more.

The main goal of the presented work was the analysis of the interaction between deformed microstructures and friction and the wear properties of four face centered cubic (fcc) metals. Pure fcc metals such as Ag, Cu, Ni, and Al with different values of stacking fault energy (SFE) were chosen for pin-on-disk tests in lubricated conditions. Friction properties of the four fcc metals are presented herein as their Stribeck curves. The transition from elasto-hydrodynamic lubrication (EHL) to boundary lubrication (BL) regions depends mainly on the values of SFE, hardness, and contact temperature. The acoustic emission (AE) parameters were analyzed in the transition from the EHL to the BL region. The models of friction in different lubricant conditions related to the AE waveforms were proposed. The nanocrystalline top surface layers characterized the deformed structure during friction of Ag in the BL region. The lamellar cross-sectional microstructure was formed in the subsurface layers of Ag, Cu, and Ni in the friction direction. Steady state friction and wear in the BL conditions were explained by a balance between the hardening and the dynamic recovery, which was strongly dependent on the SFE and the temperature. The interaction between the deformed structure, the friction, and the wear properties of the studied metals rubbed in the BL region is discussed herein. Full article

(This article belongs to the Special Issue Friction Mechanisms)

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12 pages, 4934 KiB

Open AccessArticle

Scratching Cu|Au Nanolaminates

by Adrien Gola and Lars Pastewka

Lubricants 2019, 7(5), 44; https://doi.org/10.3390/lubricants7050044 - 21 May 2019

Cited by 3 | Viewed by 4003

Abstract

We used molecular dynamics simulations to study the scratching of Cu|Au nanolaminates of 5 nm layer thickness with a nanoscale indenter of 15 nm radius at normal forces between

0.5 μ

N and

2 μ

N. Our simulations show that Au layers wear [...] Read more.

We used molecular dynamics simulations to study the scratching of Cu|Au nanolaminates of 5 nm layer thickness with a nanoscale indenter of 15 nm radius at normal forces between

0.5 μ

N and

2 μ

N. Our simulations show that Au layers wear quickly while Cu layers are more resistant to wear. Plowing was accompanied by the roughening of the Cu|Au heterointerface that lead to the folding of the nanolaminate structure at the edge of the wear track. Our explorative simulations hint at the complex deformation processes occurring in nanolaminates under tribological load. Full article

(This article belongs to the Special Issue Friction Mechanisms)

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13 pages, 16699 KiB

Open AccessArticle

Possibilities of Dry and Lubricated Friction Modification Enabled by Different Ultrashort Laser-Based Surface Structuring Methods

by Stefan Rung, Kevin Bokan, Frederick Kleinwort, Simon Schwarz, Peter Simon, Jan-Hendrik Klein-Wiele, Cemal Esen and Ralf Hellmann

Lubricants 2019, 7(5), 43; https://doi.org/10.3390/lubricants7050043 - 17 May 2019

Cited by 21 | Viewed by 4415

Abstract

In this contribution we report on the possibilities of dry and lubricated friction modification introduced by different laser surface texturing methods. We compare the potential of Laser-Induced Periodic Surface Structures and Laser Beam Interference Ablation on 100Cr6 steel in a linear reciprocating ball-on-disc [...] Read more.

In this contribution we report on the possibilities of dry and lubricated friction modification introduced by different laser surface texturing methods. We compare the potential of Laser-Induced Periodic Surface Structures and Laser Beam Interference Ablation on 100Cr6 steel in a linear reciprocating ball-on-disc configuration using 100Cr6 steel and tungsten carbide balls with load forces between 50 mN and 1000 mN. For dry friction, we find a possibility to reduce the coefficient of friction and we observe a pronounced direction dependency for surfaces fabricated by Laser Beam Interference Ablation. Furthermore, Laser-Induced Periodic Surface Structures result in a load-dependent friction reduction for lubricated linear reciprocating movements. This work helps to identify the modification behaviour of laser generated micro structures with feature sizes of approximately 1 µm and reveals new possibilities for surface engineering. Full article

(This article belongs to the Special Issue Laser-Induced Periodic Surface Nano- and Microstructures for Tribological Applications)

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14 pages, 3808 KiB

Open AccessArticle

Micro-Pitting and Wear Assessment of PAO vs Mineral-Based Engine Oil Operating under Mixed Lubrication Conditions: Effects of Lambda, Roughness Lay and Sliding Direction

by Aleks Vrček, Tobias Hultqvist, Yannick Baubet, Marcus Björling, Pär Marklund and Roland Larsson

Lubricants 2019, 7(5), 42; https://doi.org/10.3390/lubricants7050042 - 16 May 2019

Cited by 13 | Viewed by 5575

Abstract

Under certain operating conditions, rolling contacts have been shown to experience some challenges when lubricated with engine oils containing zinc dialkyldithophosphate (ZDDP) anti-wear additive. In order to better understand the main damage mechanisms during various operating conditions, further studies are needed. This article [...] Read more.

Under certain operating conditions, rolling contacts have been shown to experience some challenges when lubricated with engine oils containing zinc dialkyldithophosphate (ZDDP) anti-wear additive. In order to better understand the main damage mechanisms during various operating conditions, further studies are needed. This article studies micro-pitting and wear damages of bearing steel surfaces under mixed lubrication conditions in a ball-on-disc setup, lubricated with different engine oils. Based on the results, micro-pitting and wear damage is shown to be highly case-dependent. In general, PAO-based engine oil tends to eliminate micro-pitting damage compared to mineral-based engine oil at less severe lubricating conditions. Moreover, a critical lambda was found for both oils, where the highest micro-pitting damage was observed. Full article

(This article belongs to the Special Issue Elastohydrodynamic (EHD) Lubrication)

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11 pages, 6489 KiB

Open AccessArticle

On the Simulation of the Micro-Contact of Rough Surfaces Using the Example of Wet Friction Clutch Materials

by Katharina Voelkel, Markus Rothemund, Sebastian Albarracin Garibello, Vincent Kramer, Hermann Pflaum and Karsten Stahl

Lubricants 2019, 7(5), 41; https://doi.org/10.3390/lubricants7050041 - 14 May 2019

Cited by 8 | Viewed by 5075

Abstract

Friction behavior in a sliding contact is strongly influenced by the surface topography of the bodies in contact. This also applies to friction clutches. Even small differences in surface topography may cause significant differences in friction behavior. Thus, it is important to be [...] Read more.

Friction behavior in a sliding contact is strongly influenced by the surface topography of the bodies in contact. This also applies to friction clutches. Even small differences in surface topography may cause significant differences in friction behavior. Thus, it is important to be able to characterize the micro-contact of the rough sliding surfaces, which are, in the case of a clutch, steel plate and friction material. One important measure for the characterization of the micro-contact is the real area of contact. Another important aspect is the contact pattern. The article introduces a method to implement a FEM (Finite Element Method) model from real surface measurements. Real surface topography of the friction pairing is considered. The simulation method is applied to different friction pairings and operating conditions. Computational results with rough and smooth steel plates, new and run-in friction linings, and different nominal surface pressure verify the model. In addition, the results on real area of contact between a steel and a friction plate are compared with published values. Full article

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17 pages, 3369 KiB

Open AccessArticle

Performance Evaluation of MQL Parameters Using Al₂O₃ and MoS₂ Nanofluids in Hard Turning 90CrSi Steel

by Tran Minh Duc, Tran The Long and Tran Quyet Chien

Lubricants 2019, 7(5), 40; https://doi.org/10.3390/lubricants7050040 - 8 May 2019

Cited by 71 | Viewed by 5352

Abstract

Hard machining has gained much attention to be an alternative solution for many traditional finish grinding operations due to high productivity, ease to adapt to complex part contours, the elimination of cutting fluids, good surface quality, and the reduction of machine tool investment. [...] Read more.

Hard machining has gained much attention to be an alternative solution for many traditional finish grinding operations due to high productivity, ease to adapt to complex part contours, the elimination of cutting fluids, good surface quality, and the reduction of machine tool investment. However, the enormous amount of heat generated from the cutting zone always requires the high-grade inserts and limits the cutting conditions. The MQL technique with nanofluids assisted for hard machining helps to improve the cutting performance while ensuring environmentally friendly characteristics. This paper focuses on the development of MQL technique by adding Al₂O₃ and MoS₂ nanoparticles to the base fluids (soybean oil and water-based emulsion) for the hard turning of 90CrSi steel (60÷62 HRC). The analysis of variance (ANOVA) is used to evaluate the performance of MQL parameters in terms of cutting forces and surface roughness. The study reveals that a better performance of coated carbide inserts is observed by using MQL with Al₂O₃ and MoS₂ nanofluids. In addition, the fluid type, nanoparticles and nanoparticle concentration have a strong effect on cutting performance. The interaction influence among the investigated variables is also studied in order to provide the technical guides for further studies using Al₂O₃ and MoS₂ nanofluids. Full article

(This article belongs to the Special Issue Recent Research in Nanolubricants)

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35 pages, 14491 KiB

Open AccessArticle

Investigations of the Friction Losses of Different Engine Concepts. Part 1: A Combined Approach for Applying Subassembly-Resolved Friction Loss Analysis on a Modern Passenger-Car Diesel Engine

by Christoph Knauder, Hannes Allmaier, David E. Sander and Theodor Sams

Lubricants 2019, 7(5), 39; https://doi.org/10.3390/lubricants7050039 - 26 Apr 2019

Cited by 34 | Viewed by 9237

Abstract

This work presents the application of a combined approach to investigate the friction losses in a modern four-cylinder passenger-car diesel engine. The approach connects the results from engine friction measurements using the indication method and the results from journal-bearing simulations. The utilization of [...] Read more.

This work presents the application of a combined approach to investigate the friction losses in a modern four-cylinder passenger-car diesel engine. The approach connects the results from engine friction measurements using the indication method and the results from journal-bearing simulations. The utilization of the method enables a subassembly-resolved friction loss analysis that yields the losses of the piston group, crankshaft journal bearings, and valve train (including the timing drive and crankshaft seals). The engine and engine subassembly friction losses are investigated over the full speed and load range, covering more than 120 engine operation points at different engine media supply temperatures ranging from 70 to 110

^{\circ}

C. The subsequently decreasing lubricant viscosity due to higher engine media supply temperatures allow for the identification of friction reduction potentials as well as possible risks due to an onset of mixed lubrication. Furthermore, additional strip-tests have been conducted to determine the friction losses of the crankshaft radial lip seals, the timing drive, and the crankshaft journal bearings, thus enabling a verification of the calculated journal-bearing friction losses with measurement results. For the investigated diesel engine, a friction reduction potential of up to 21% could be determined when increasing the engine media supply temperature from 70 to 110

^{\circ}

C, at engine speeds higher than n = 1500 rpm and part load operating conditions. At low engine speeds and high load operations, the friction loss reduction potential is considerably decreased and below 8%, indicating mixed lubrication regimes at the piston group and valve train. Full article

(This article belongs to the Special Issue Automotive Tribology)

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Lubricants, Volume 7, Issue 5 (May 2019) – 8 articles

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