Numerical Simulations in Lubrication

A special issue of Lubricants (ISSN 2075-4442).

Deadline for manuscript submissions: closed (15 July 2022) | Viewed by 8358

Special Issue Editor


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Guest Editor
School of Mechanical, Materials Mechatronic and Biomedical Engineering, Faculty of Engineering and Information Sciences (EIS), University of Wollongong, Northfield Avenue, Wollongong, NSW 2522, Australia
Interests: molecular dynamics simulation; thin film simulation; reactive molecular dynamics; carbon based tribofilm; aqueous copolymer lubricants; tribochemistry; quantum calculation; ab initio MD simulation

Special Issue Information

Dear Colleagues,

Nowadays, there is a pressing need to reduce the thickness of lubricating films to a scale of a few to tens of nanometres to reduce the friction loss while still bringing in significant cost benefits in transportation or metal-forming industries. This calls for insights into their atomic mechanisms, where the in situ phenomena cannot be observed by experimental instruments. The development of numerical methods ranging from the atomic to mesoscale has opened a new approach for researchers to be able to gain a comprehensive understanding about the behaviour of confined systems at different levels. Under severe conditions of loading pressure and sliding conditions, mechanical properties of tribo-surfaces, the chemical reactions of adsorbed lubricant molecules, and rheological properties of dynamic fluid films are different from bulk materials. However, the theoretical investigation at the molecular level is still yet to be attempted due to substantial efforts in numerical methodology development, as well as applying it for all lubricants and their specific applications.

This Special Issue reports on state-of-the-art research progress, covering not only the fundamentals of thin film lubrication, but also its applications to industrial practices. The attention is placed on applying numerical methods, such as the following:

  • MD simulations of thin film lubrication;
  • tribochemistry in lubrication;
  • DFT calculations of reaction at tribosurface-lubricant interfaces;
  • ab initio MD simulations of confined shear systems;
  • mesoscale simulations of lubrication.

Dr. Thi Dinh Ta
Guest Editor

Manuscript Submission Information

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Keywords

  • molecular dynamics simulation
  • tribochemistry
  • thin film lubrication
  • ab initio molecular dynamics simulation
  • mesoscale molecular dynamics simulations

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Published Papers (3 papers)

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Research

19 pages, 6749 KiB  
Article
Analysis of a Low-Loss Gear Geometry Using a Thermal Elastohydrodynamic Simulation including Mixed Lubrication
by Felix Farrenkopf, Andreas Schwarz, Thomas Lohner and Karsten Stahl
Lubricants 2022, 10(9), 200; https://doi.org/10.3390/lubricants10090200 - 24 Aug 2022
Cited by 9 | Viewed by 2454
Abstract
Low-loss gears are an interesting design approach for increasing the efficiency and thermal load limits of gearboxes. The loss-optimized gear geometry concentrates sliding around the pitch point, which results in low load-dependent gear power losses. In this study, a method for modeling transient [...] Read more.
Low-loss gears are an interesting design approach for increasing the efficiency and thermal load limits of gearboxes. The loss-optimized gear geometry concentrates sliding around the pitch point, which results in low load-dependent gear power losses. In this study, a method for modeling transient EHL (elastohydrodynamically lubricated) contacts in gear mesh considering mixed lubrication and thermal effects is introduced and applied to analyze the tribological behavior of a low-loss gear geometry. Special focus is placed on local frictional losses to analyze the role of the thermal effects of the gear mesh. Although a thermal reduction in fluid friction is observed, the overall effect on total frictional losses of the low-loss gear geometry is evaluated to be very small. The edge geometry strongly influences the lubricant film thickness and frictional power losses. Full article
(This article belongs to the Special Issue Numerical Simulations in Lubrication)
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15 pages, 4491 KiB  
Article
Assessment of Stability and Thermophysical Properties of Jojoba Nanofluid as a Metal-Cutting Fluid: Experimental and Modelling Investigation
by Gaurav Gaurav, Govind Sharan Dangayach, Makkhan Lal Meena and Abhay Sharma
Lubricants 2022, 10(6), 126; https://doi.org/10.3390/lubricants10060126 - 16 Jun 2022
Cited by 4 | Viewed by 2496
Abstract
Nanofluids based on vegetable oil have emerged as ecological alternatives to conventional cutting fluids. Jojoba-seed oil has recently been identified as adequate for use in metal cutting. Aiming to assess the stability and thermophysical properties of jojoba nanofluids, this article reports an experiment- [...] Read more.
Nanofluids based on vegetable oil have emerged as ecological alternatives to conventional cutting fluids. Jojoba-seed oil has recently been identified as adequate for use in metal cutting. Aiming to assess the stability and thermophysical properties of jojoba nanofluids, this article reports an experiment- and modelling-based investigation. The stability, viscosity and thermal conductivity of jojoba MoS2 nanofluid were studied across a broad range of temperatures and concentrations of nanoparticles. The functional relationship of the viscosity and thermal conductivity to the temperature and concentration was determined by regression analysis. In addition to confirming known phenomena, vis-à-vis the effect of the concentration and temperature on the viscosity and thermal conductivity, this study shows that the increase in the thermal conductivity in line with the concentration stagnates after an initial sharp rise due to an increase in the attractive forces between the particles. The viscosity displays a second-order interactive relationship with the temperature and concentration of the nanoparticles, whereas thermal conductivity follows a complex third-order interaction model. In addition to being economical, jojoba nanofluid matches or surpasses the nanofluid prepared using commercially available mineral-oil-based cutting fluid (LRT 30)—which is specially designed for the minimum-quantity lubrication method of metal cutting. Conclusively, this investigation paves the way for the shop-floor application of jojoba nanofluid in metal-cutting operations. Full article
(This article belongs to the Special Issue Numerical Simulations in Lubrication)
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18 pages, 2215 KiB  
Article
Edge Pressures Obtained Using FEM and Half-Space: A Study of Truncated Contact Ellipses
by Michael Juettner, Marcel Bartz, Stephan Tremmel, Martin Correns and Sandro Wartzack
Lubricants 2022, 10(6), 107; https://doi.org/10.3390/lubricants10060107 - 1 Jun 2022
Cited by 5 | Viewed by 2533
Abstract
In rolling or gear contacts, truncation of the contact ellipse can occur, for example, when an undercut extends into the contact area. For an elastic calculation approach, the edge constitutes a mathematical singularity, which is revealed by a theoretically infinitely high pressure peak. [...] Read more.
In rolling or gear contacts, truncation of the contact ellipse can occur, for example, when an undercut extends into the contact area. For an elastic calculation approach, the edge constitutes a mathematical singularity, which is revealed by a theoretically infinitely high pressure peak. However, when elastic–plastic material behavior is taken into account, the pressure peak is limited by local hardening and yielding of the material, leading to plastic deformations. As a result, those calculations are rather challenging and the results partly unexpected due to the discontinuity contained in the geometry. Nevertheless, to the authors’ knowledge, hardly any published studies exist on elastic–plastic simulations of truncated contact ellipses. Therefore, a numerical study concerning the contact of a rigid ball with an elastic–plastic plane is presented. Due to an undercut in the plane, a quarter of the theoretical Hertzian contact ellipse is cut off. The aim of the study is to investigate the influence of the undercut angle on the pressure distribution and the elastic and plastic deformation at the edge. The use of FEM shows that the undercut angle has a significant effect on the characteristics of the contact. The results obtained using FEM are then used as a reference for comparison with a semi-analytical method (SAM). It is shown that the SAM, based on the half-space, provides comparable results only for very small undercut angles. Full article
(This article belongs to the Special Issue Numerical Simulations in Lubrication)
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