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Advances in Computational Materials Tribology

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A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Mechanics of Materials".

Deadline for manuscript submissions: closed (10 August 2023) | Viewed by 27947

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Special Issue Editor

Dr. Stefan J. Eder

E-Mail Website1 Website2
Guest Editor

1. AC2T research GmbH (Austrian Center of Competence for Tribology), Wiener Neustadt, Austria
2. Institute for Engineering Design and Product Development, TU Wien, Vienna, Austria
Interests: atomistic modeling of tribological contacts; microstructure evolution; polycrystalline materials and alloys; near-surface deformation mechanisms; tribochemistry; reactive molecular modeling; tribofilm formation; nanoscopic analysis of surface finishing processes

Special Issue Information

Dear Colleagues,

Materials science as well as tribology, the scientific field interested in friction, lubrication, and wear, are both of an inherently multiscale nature spanning several length and time scales from the electronic to the component level. With ever-increasing computational resources, the field of computational materials tribology is becoming more and more important as previously purely academic simulation studies can now be developed into useful surface engineering tools. Here, the perspective of a materials scientist on a sliding interface may provide completely new insights into the near-surface microstructural evolution of a material. Recent advances in reactive interaction potentials for molecular dynamics simulation even allow for the study of mechanochemical contributions to the development of interfacial films. The systems that can nowadays be treated using a palette of computational methods will usually feature much higher degrees of realism and sheer complexity than can be achieved with purely theoretical approaches, while at the same time being able to provide more precision and detail than most experiments. Although many of the mechanisms acting in tribological contacts are generally understood, computational materials tribology can be seen as a tool for finding out which mechanisms matter under which conditions and how they interact.

In this Special Issue, we call for computational studies focusing on nano- and microscale aspects of tribological contact evolution. These include, but are not limited to, plastic deformation near tribologically loaded surfaces, microstructural aspects of surface finishing or abrasive wear, or the formation of protective films by interaction between lubricant additives and sliding surfaces.

We are confident that some of the findings presented in this Special Issue will lead to better control of friction and wear in future moving mechanical systems and, thus, have a significant positive impact towards improving efficiency, durability, and environmental compatibility in a time where resource and energy efficiency are discussed not only in the scientific community but also on the evening news. Therefore, we believe that this topic is appealing to the readership of Materials.

Attention tribologists and materials scientists...Prof. Dr. Carsten Gachot and I cordially invite you to ViViMaT, the Vienna Virtual Materials Tribology Workshop, which will take place free of charge on our YouTube channel (link below) starting Nov. 16th, with a live stream Q&A event on Dec. 3rd, 1600 CET.

Please kindly find the link to our YouTube channel where the workshop will take place:

https://www.youtube.com/channel/UC5Zju5imk57HY_TTO-hajAA

Dr. Stefan J. Eder
Guest Editor

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Keywords

microstructural evolution in tribological interfaces
sliding contacts
abrasive contacts
surface finishing
tribofilm formation
atomistic modeling
mesoscopic modeling (mesh-based/meshless)
phase field simulation
reactive molecular dynamics simulation
mechanochemistry

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Published Papers (11 papers)

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Research

22 pages, 14261 KiB

Open AccessArticle

An Analytical Model for the Normal Contact Stiffness of Mechanical Joint Surfaces Based on Parabolic Cylindrical Asperities

by Yuzhu Bai, Qi An, Shuangfu Suo, Weikun Wang and Xiaohong Jia

Materials 2023, 16(5), 1883; https://doi.org/10.3390/ma16051883 - 24 Feb 2023

Cited by 3 | Viewed by 1991

Abstract

The analytical results of normal contact stiffness for mechanical joint surfaces are quite different from the experimental data. So, this paper proposes an analytical model based on parabolic cylindrical asperity that considers the micro-topography of machined surfaces and how they were made. First, the topography of a machined surface was considered. Then, the parabolic cylindrical asperity and Gaussian distribution were used to create a hypothetical surface that better matches the real topography. Second, based on the hypothetical surface, the relationship between indentation depth and contact force in the elastic, elastoplastic, and plastic deformation intervals of the asperity was recalculated, and the theoretical analytical model of normal contact stiffness was obtained. Finally, an experimental test platform was then constructed, and the numerical simulation results were compared with the experimental results. At the same time, the numerical simulation results of the proposed model, the J. A. Greenwood and J. B. P. Williamson (GW) model, the W. R. Chang, I. Etsion, and D. B. Bogy (CEB) model, and the L. Kogut and I. Etsion (KE) model were compared with the experimental results. The results show that when roughness is Sa 1.6 μm, the maximum relative errors are 2.56%, 157.9%, 134%, and 90.3%, respectively. When roughness is Sa 3.2 μm, the maximum relative errors are 2.92%, 152.4%, 108.4%, and 75.1%, respectively. When roughness is Sa 4.5 μm, the maximum relative errors are 2.89%, 158.07%, 68.4%, and 46.13%, respectively. When roughness is Sa 5.8 μm, the maximum relative errors are 2.89%, 201.57%, 110.26%, and 73.18%, respectively. The comparison results demonstrate that the suggested model is accurate. This new method for examining the contact characteristics of mechanical joint surfaces uses the proposed model in conjunction with a micro-topography examination of an actual machined surface. Full article

(This article belongs to the Special Issue Advances in Computational Materials Tribology)

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19 pages, 6937 KiB

Open AccessArticle

Experimental and Numerical Study of the Mixed Lubrication Considering Boundary Film Strength

by Shengwei Zhang, Zhijun Yan, Ze Liu, Yuanyuan Jiang, Haocheng Sun and Shibo Wu

Materials 2023, 16(3), 1035; https://doi.org/10.3390/ma16031035 - 24 Jan 2023

Cited by 7 | Viewed by 1642

Abstract

For the influence of boundary film on the lubrication state of sliding friction pairs, a boundary film strength model was proposed that can comprehensively reflect the influences of film thickness, pressure, shear stress and temperature. The model parameters were obtained through fitting the test results. Then, a mixed lubrication model considering boundary film strength was established by coupling the boundary film strength model with the hydrodynamic lubrication model and the asperity contact model. The calculation program was developed using the Fortran language, which can effectively capture the tribological characteristics and action ratios of the fluid, boundary film and dry friction components. Simultaneously, the mixed lubrication model was applied to the journal bearing. A parametric analysis was performed to investigate the influences of different working conditions on lubrication performance. Under current operating conditions, the results show that: when the speed is above 200 r/min or the viscosity is higher than 0.09 Pa·s, the boundary film breakdown rate is almost 0 and the friction coefficient is lower than 0.02; when the roughness is reduced from 1.8 μm to 0.8 μm, the ultimate load of the journal bearing rises from 27 MPa to 36 MPa, an increase of about 33%; when the load exceeds 36 MPa or the temperature is higher than 100 °C, more than 25% of the boundary film breaks and the dry friction component accounts for more than 60% of the total friction, which leads to a sudden increase in the friction coefficient. Hence, the study of mixed lubrication considering boundary film strength provides theoretical guidance for accurately reflecting the actual lubrication state and improving the mechanical energy efficiency of friction pairs. Full article

(This article belongs to the Special Issue Advances in Computational Materials Tribology)

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14 pages, 3624 KiB

Open AccessArticle

Experimental and Numerical Investigation of Static and Dynamic Characteristics of Bio-Oils and SAE40 in Fluid Film Journal Bearing

by Muhammad Imran Sadiq, Wan Aizon W. Ghopa, Mohd Zaki Nuawi, Mohammad Rasidi Rasani and Mohd Anas Mohd Sabri

Materials 2022, 15(10), 3595; https://doi.org/10.3390/ma15103595 - 18 May 2022

Cited by 6 | Viewed by 1610

Abstract

Mineral-based oils are the market leaders when it comes to their consumption in different types of rotating machines. Recently, a lot of attention has been given to the bio-oils and lubricants due to their better thermophysical, tribological, and environmental characteristics for use in journal bearing and other rotating machines. The superior physical properties of bio-oils have instigated this research in order to evaluate their dynamic characteristics that can cause the harmful dynamic instabilities in rotating machinery. The dynamic characteristics of the fluid film are influenced by temperature, eccentricity ratio, and rotational speed. In this work, the effect of temperature is experimentally measured on the dynamic viscosity of bio-oils and mineral-based oil. The dynamic viscosity measured is then computationally used to estimate the hydrodynamic pressure response of three bio-oils (rapeseed, palm olein, and soybean) and SAE40, a mineral-based oil, to check their performance in the rotor bearing system. It is found that at 40 °C, the hydrodynamic pressure for SAE40 is observed to be 2.53, 2.72, and 3.32 times greater than those of rapeseed, palm olein, and soybean oil, respectively, whereas, at 125 °C, the hydrodynamic pressure for SAE40 is observed to be 8% and 4.3% less than those of rapeseed and palm olein, respectively, but 14% greater than that of soybean oil. Hence, the increasing temperature has less effect on the viscosity and hydrodynamic pressure of bio-oils compared to SAE40. Therefore, for high-temperature applications, the bio-oils can be used with further processing. The superior response of bio-oils is also an indication for better dynamic characteristics. Full article

(This article belongs to the Special Issue Advances in Computational Materials Tribology)

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17 pages, 2294 KiB

Open AccessEditor’s ChoiceArticle

Relating Dry Friction to Interdigitation of Surface Passivation Species: A Molecular Dynamics Study on Amorphous Carbon

by Kerstin Falk, Thomas Reichenbach, Konstantinos Gkagkas, Michael Moseler and Gianpietro Moras

Materials 2022, 15(9), 3247; https://doi.org/10.3390/ma15093247 - 30 Apr 2022

Cited by 9 | Viewed by 2436

Abstract

Friction in boundary lubrication is strongly influenced by the atomic structure of the sliding surfaces. In this work, friction between dry amorphous carbon (a-C) surfaces with chemisorbed fragments of lubricant molecules is investigated employing molecular dynamic simulations. The influence of length, grafting density and polarity of the fragments on the shear stress is studied for linear alkanes and alcohols. We find that the shear stress of chain-passivated a-C surfaces is independent of the a-C density. Among all considered chain-passivated systems, those with a high density of chains of equal length exhibit the lowest shear stress. However, shear stress in chain-passivated a-C is consistently higher than in a-C surfaces with atomic passivation. Finally, surface passivation species with OH head groups generally lead to higher friction than their non-polar analogs. Beyond these qualitative trends, the shear stress behavior for all atomic- and chain-passivated, non-polar systems can be explained semi-quantitatively by steric interactions between the two surfaces that cause resistance to the sliding motion. For polar passivation species electrostatic interactions play an additional role. A corresponding descriptor that properly captures the interlocking of the two surfaces along the sliding direction is developed based on the maximum overlap between atoms of the two contacting surfaces. Full article

(This article belongs to the Special Issue Advances in Computational Materials Tribology)

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14 pages, 3425 KiB

Open AccessEditor’s ChoiceArticle

Numerical Analysis of the Relationship between Friction Coefficient and Repose Angle of Blast Furnace Raw Materials by Discrete Element Method

by Shiyu Wei, Han Wei, Henrik Saxen and Yaowei Yu

Materials 2022, 15(3), 903; https://doi.org/10.3390/ma15030903 - 25 Jan 2022

Cited by 15 | Viewed by 3509

Abstract

In recent years, the discrete element method (DEM) has been widely used to study the factors affecting the repose angle and calibrate particle parameters for simulations. In this paper, DEM is used to study the effects of the coefficient of rolling and static friction of pellet, sinter and coke particles on the repose angle. By comparison of the results of simulations and physical experiments, the coefficients of rolling and static friction suitable for simulation work are determined. The results demonstrate that repose angle increases with the coefficient of rolling and static friction, but the rate of increase gradually decays, when the coefficient of rolling friction exceeds 0.4 or the coefficient of static friction exceeds 0.35. The coefficient of static friction has a greater impact on the repose angle than the coefficient of rolling friction. The rougher of the base surface, the larger the repose angle of the formed particle piled. It can be concluded that appropriate coefficient of rolling and static friction for simulations can be obtained by the outlined procedure. Full article

(This article belongs to the Special Issue Advances in Computational Materials Tribology)

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11 pages, 7038 KiB

Open AccessArticle

Numerical and Experimental Research on the Brushing Aluminium Alloy Mechanism Using an Abrasive Filament Brush

by Xiuhua Yuan, Chong Wang, Qun Sun and Ling Zhao

Materials 2021, 14(21), 6647; https://doi.org/10.3390/ma14216647 - 4 Nov 2021

Cited by 2 | Viewed by 1846

Abstract

Abrasive filament brushes have been widely used in surface processes for a wide range of applications, including blending, edge-radiusing, and polishing. However, the associated brush mechanics of material removal is still not clear. In order to analyze the brush grinding of aluminium alloy, this paper constructed a kinematic model of a single filament, simulated the scratch process of a single abrasive grain, and investigated the brush force and material removal based on the finite element approach. The simulated result shows that the brush grinding can be changed from elastic–plastic deformation to chip formation when increasing the brush speed to 1000 r/min. The normal and tangential forces increase linearly and quadratically with the increase in the rotation speed (500–5000 r/min), respectively, and increase linearly with the increase in the penetration depth (0.1–1 mm), which is consistent with the experiment results. In addition, the amount of material removal initially increases with the increase in penetration depth, and then decreases. This paper provides a new approach to understanding the process of material removal and is helpful for the selection of reasonable brush parameters in the intelligent grinding control application. Full article

(This article belongs to the Special Issue Advances in Computational Materials Tribology)

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14 pages, 4370 KiB

Open AccessArticle

On the Origin of Plastic Deformation and Surface Evolution in Nano-Fretting: A Discrete Dislocation Plasticity Analysis

by Yilun Xu, Daniel S. Balint and Daniele Dini

Materials 2021, 14(21), 6511; https://doi.org/10.3390/ma14216511 - 29 Oct 2021

Cited by 5 | Viewed by 1952

Abstract

Discrete dislocation plasticity (DDP) calculations were carried out to investigate a single-crystal response when subjected to nano-fretting loading conditions in its interaction with a rigid sinusoidal asperity. The effects of the contact size and preceding indentation on the surface stress and profile evolution due to nano-fretting were extensively investigated, with the aim to unravel the deformation mechanisms governing the response of materials subjected to nano-motion. The mechanistic drivers for the material’s permanent deformations and surface modifications were shown to be the dislocations’ collective motion and piling up underneath the contact. The analysis of surface and subsurface stresses and the profile evolution during sliding provides useful insight into damage and failure mechanisms of crystalline materials subject to nano-fretting; this can lead to improved strategies for the optimisation of material properties for better surface resistance under micro- and nano-scale contacts. Full article

(This article belongs to the Special Issue Advances in Computational Materials Tribology)

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10 pages, 5771 KiB

Open AccessArticle

The Force Cone Method Applied to Explain Hidden Whirls in Tribology

by Claus Mattheck, Christian Greiner, Klaus Bethge, Iwiza Tesari and Karlheinz Weber

Materials 2021, 14(14), 3894; https://doi.org/10.3390/ma14143894 - 13 Jul 2021

Cited by 1 | Viewed by 2553

Abstract

In tribologically loaded materials, folding instabilities and vortices lead to the formation of complex internal structures. This is true for geological as well as nanoscopic contacts. Classically, these structures have been described by Kelvin–Helmholtz instabilities or shear localization. We here introduce an alternative explanation based on an intuitive approach referred to as the force cone method. It is considered how whirls are situated near forces acting on a free surface of an elastic or elastoplastic solid. The force cone results are supplemented by finite element simulations. Depending on the direction of the acting force, one or two whirls are predicted by the simplified force cone method. In 3D, there is always a ring shaped whirl present. These modelling findings were tested in simple model experiments. The results qualitatively match the predictions and whirl formation was found. The force cone method and the experiments may seem trivial, but they are an ideal tool to intuitively understand the presence of whirls within a solid under a tribological load. The position of these whirls was found at the predicted places and the force cone method allows a direct approach to understand the complex processes in the otherwise buried interfaces of tribologically loaded materials. Full article

(This article belongs to the Special Issue Advances in Computational Materials Tribology)

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21 pages, 4828 KiB

Open AccessArticle

Influence of the 6061 Aluminium Alloy Thermo-Viscoplastic Behaviour on the Load-Area Relation of a Contact

by André Rudnytskyj, Stefan Krenn, Georg Vorlaufer and Carsten Gachot

Materials 2021, 14(6), 1352; https://doi.org/10.3390/ma14061352 - 11 Mar 2021

Cited by 4 | Viewed by 3631

Abstract

The contact between solids in metal-forming operations often involves temperature-dependent viscoplasticity of the workpiece. In order to estimate the real contact area in such contexts, both the topography and the deformation behaviour should be taken into account. In this work, a deterministic approach is used to represent asperities in appropriately shaped quadratic surfaces. Such geometries are implemented in indentation finite element simulations, in which the indented material has thermo-viscoplastic properties. By creating a database of simulation data, investigations in terms of contact load and area for the specifically shaped asperities allow for an analysis on the influence of the material properties on the load–area relation of the contact. The temperature and viscoplasticity greatly define how much load is supported by a substrate due to an indenting asperity, but the description of the deformation behaviour at small values of strain and strain rate is also relevant. The pile-up and sink-in regions are very dependent on the thermo-viscoplastic conditions and material model, which consequently affect the real contact area calculation. The interplay between carried load and contact area of a full surface analysis indicates the role that different sized asperities play in the contact under different thermomechanical conditions. Full article

(This article belongs to the Special Issue Advances in Computational Materials Tribology)

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11 pages, 6130 KiB

Open AccessArticle

The Unusual Tribological Properties of Graphene/Antimonene Heterojunctions: A First-Principles Investigation

by Xian Jiang, Zhibin Lu and Renhui Zhang

Materials 2021, 14(5), 1201; https://doi.org/10.3390/ma14051201 - 4 Mar 2021

Cited by 8 | Viewed by 1852

Abstract

The extremely low friction between incommensurate two-dimensional (2D) materials has drawn more attention in the recent years. Structural superlubricity is a fascinating tribological phenomenon that is achieved in 2D heterojunctions despite the aligned or misaligned contacts that occur due to the disappearance of the lateral interactions between two incommensurate contacting surfaces. In this study, using the first-principles method, we report the computational realization of structural superlubricity for graphene/antimonene heterojunctions at the nanoscale. The calculated results clearly demonstrate that structural superlubricity between graphene and antimonene monolayers could be achieved under the misaligned contacts. The structural superlubricity is mainly attributed to lower work of separation, which maintains superlow friction coefficients. Full article

(This article belongs to the Special Issue Advances in Computational Materials Tribology)

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16 pages, 4630 KiB

Open AccessArticle

Effect of Temperature on the Deformation Behavior of Copper Nickel Alloys under Sliding

by Stefan J. Eder, Philipp G. Grützmacher, Manel Rodríguez Ripoll, Daniele Dini and Carsten Gachot

Materials 2021, 14(1), 60; https://doi.org/10.3390/ma14010060 - 25 Dec 2020

Cited by 21 | Viewed by 3285

Abstract

The microstructural evolution in the near-surface regions of a dry sliding interface has considerable influence on its tribological behavior and is driven mainly by mechanical energy and heat. In this work, we use large-scale molecular dynamics simulations to study the effect of temperature on the deformation response of FCC CuNi alloys of several compositions under various normal pressures. The microstructural evolution below the surface, marked by mechanisms spanning grain refinement, grain coarsening, twinning, and shear layer formation, is discussed in depth. The observed results are complemented by a rigorous analysis of the dislocation activity near the sliding interface. Moreover, we define key quantities corresponding to deformation mechanisms and analyze the time-independent differences between 300 K and 600 K for all simulated compositions and normal pressures. Raising the Ni content or reducing the temperature increases the energy barrier to activate dislocation activity or promote plasticity overall, thus increasing the threshold stress required for the transition to the next deformation regime. Repeated distillation of our quantitative analysis and successive elimination of spatial and time dimensions from the data allows us to produce a 3D map of the dominating deformation mechanism regimes for CuNi alloys as a function of composition, normal pressure, and homologous temperature. Full article

(This article belongs to the Special Issue Advances in Computational Materials Tribology)

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