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Prajapati, D. K., Hansen, J. & Björling, M. (2024). An assessment of the effect of surface topography on coefficient of friction for lubricated non-conformal contacts. Frontiers in Mechanical Engineering, 10, Article ID 1360023.
Open this publication in new window or tab >>An assessment of the effect of surface topography on coefficient of friction for lubricated non-conformal contacts
2024 (English)In: Frontiers in Mechanical Engineering, E-ISSN 2297-3079, Vol. 10, article id 1360023Article in journal (Refereed) Published
Abstract [en]

Determining an accurate state of lubrication is of utmost importance for the precise functionality of machine elements and to achieve elongated life and durability. In this work, a homogenized mixed-lubrication model is developed to study the effect of surface topographies on the coefficient of friction. Various measured real surface topographies are integrated in the model using the roughness homogenization method. The shear-thinning behavior of the lubricant is incorporated by employing the Eyring constitutive relation. Several Stribeck curves are generated to analyze the effect of roughness lays and root mean square (RMS) roughness on the coefficient of friction. The homogenized mixed lubrication model is validated against experimental rolling/sliding ball-on-disc results, and a good agreement between simulated and experimental coefficient of friction is found.

Place, publisher, year, edition, pages
Frontiers Media SA, 2024
Keywords
coefficient of friction, mixed-lubrication, non-conformal contacts, roughness homogenization, shear thinning, surface roughness lay, two-scale modeling
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Identifiers
urn:nbn:se:ltu:diva-104358 (URN)10.3389/fmech.2024.1360023 (DOI)2-s2.0-85184727548 (Scopus ID)
Note

Funder: Kempe Foundation (SMK-2043);

Full text license: CC BY

Available from: 2024-02-22 Created: 2024-02-22 Last updated: 2024-02-22
Higashitani, Y., Kawabata, S., Björling, M. & Almqvist, A. (2023). A traction coefficient formula for EHL line contacts operating in the linear isothermal region. Tribology International, 180, Article ID 108216.
Open this publication in new window or tab >>A traction coefficient formula for EHL line contacts operating in the linear isothermal region
2023 (English)In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 180, article id 108216Article in journal (Refereed) Published
Abstract [en]

Many mechanical products including rolling/sliding parts are used with various lubricants and operating conditions. Increasing the efficiency and reliability of products requires an essential understanding of the traction characteristics of the rolling/sliding parts. Many researchers have investigated the traction characteristics of rolling/sliding EHL contacts considering shear-thinning, thermal effects, and roller compliance. There are, however, only a few papers concerning the modeling of traction characteristics in the linear isothermal region at low slide-to-roll ratios. We propose a prediction formula for the dimensionless traction coefficient for EHL line contacts in the linear isothermal region. The formula was obtained by numerical simulations using a fully-coupled finite-element EHL line contact solver, and it is applicable for the piezoviscous rigid/elastic, and the isoviscous rigid/elastic regimes.

Place, publisher, year, edition, pages
Elsevier Ltd, 2023
Keywords
EHL, FEM, Friction, Lubrication, Machine Element, Modelling, Rolling/sliding, Traction
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-95492 (URN)10.1016/j.triboint.2023.108216 (DOI)2-s2.0-85146236992 (Scopus ID)
Funder
Luleå University of Technology
Note

Validerad;2023;Nivå 2;2023-02-03 (sofila);

Funder: DENSO CORPORATION

Available from: 2023-02-03 Created: 2023-02-03 Last updated: 2024-02-07Bibliographically approved
Johansson, P., Marklund, P., Björling, M. & Shi, Y. (2023). Effect of Oxygen and Moisture on the Friction and Wear of Carbon Fiber-Reinforced Polymers. Lubricants, 11(9), Article ID 412.
Open this publication in new window or tab >>Effect of Oxygen and Moisture on the Friction and Wear of Carbon Fiber-Reinforced Polymers
2023 (English)In: Lubricants, ISSN 2075-4442, Vol. 11, no 9, article id 412Article in journal (Refereed) Published
Abstract [en]

Carbon fiber-reinforced polytetrafluoroethylene (CF/PTFE) composites are frequently used in tribological dry gas applications, such as in dynamic seals in reciprocating hydrogen gas compressors and Stirling engines, due to their superior friction and wear. Due to the increasing concerns regarding fluoropolymers as possible pollutants of harmful per- and poly-fluoroalkyl substances (PFAS) emissions, replacements for PTFE should be investigated. The literature indicates that CF-reinforced polyetheretherketone (CF/PEEK) may have similar favorable tribological properties to CF/PTFE. However, the tribological behavior of CF/PEEK in dry gas is poorly understood, and no direct comparison has been made between the two materials. The aim of this study was to compare the effect of oxygen and moisture on the friction and wear of CF/PTFE and CF/PEEK. Tribological tests were carried out with a tri-pin-on-disc tribometer in a nitrogen environment with individually controlled contents of oxygen and moisture. The results showed that the effect of oxygen and moisture are distinctly different for CF/PTFE and CF/PEEK. While CF/PTFE performs best in oxygen-deficient environments, CF/PEEK performs best in moisture-enriched environments. Complementary tests with a PTFE composite filled with both CF and PEEK suggested that the environmental sensitivity can be significantly reduced by combining the two polymers.

Place, publisher, year, edition, pages
MDPI, 2023
Keywords
polymer composite, dry gas, environment, ultralow wear
National Category
Applied Mechanics
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-101549 (URN)10.3390/lubricants11090412 (DOI)
Note

Validerad;2023;Nivå 2;2023-10-03 (joosat);

Available from: 2023-10-03 Created: 2023-10-03 Last updated: 2023-10-12Bibliographically approved
Chen, J., Parsi, P. K., Marklund, P., Björling, M. & Shi, Y. (2023). Graphene-enhanced, wear-resistant and thermal-conductive, anti-/de-icing Gelcoat composite coating. Advanced Composites and Hybrid Materials
Open this publication in new window or tab >>Graphene-enhanced, wear-resistant and thermal-conductive, anti-/de-icing Gelcoat composite coating
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2023 (English)In: Advanced Composites and Hybrid Materials, ISSN 2522-0128Article in journal (Refereed) Accepted
National Category
Materials Engineering
Identifiers
urn:nbn:se:ltu:diva-103447 (URN)10.1007/s42114-023-00820-3 (DOI)2-s2.0-85181582111 (Scopus ID)
Available from: 2024-01-02 Created: 2024-01-02 Last updated: 2024-01-16
Johansson, P., Elo, R., Fadaei Naeini, V., Marklund, P., Björling, M. & Shi, Y. (2023). Insights of the Ultralow Wear and Low Friction of Carbon Fiber Reinforced PTFE in Inert Trace Moisture Environment. Tribology letters, 71(3), Article ID 100.
Open this publication in new window or tab >>Insights of the Ultralow Wear and Low Friction of Carbon Fiber Reinforced PTFE in Inert Trace Moisture Environment
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2023 (English)In: Tribology letters, ISSN 1023-8883, E-ISSN 1573-2711, Vol. 71, no 3, article id 100Article in journal (Refereed) Published
Abstract [en]

Ultralow wear rates and low friction have been observed for carbon fiber reinforced PTFE (CF/PTFE) when sliding against steel or cast iron in dry gas environments. Although the strong environmental sensitivity of this tribosystem is well known, the origin of the outstanding tribological performance in dry gas remains unanswered. Some researchers attribute the low friction and wear to the formation of carbon-rich surfaces in the absence of oxygen and moisture in the environment. However, low friction between carbon surfaces is generally dependent on moisture. In this paper, extensive analyzes are conducted on the tribofilms formed on the CF/PTFE surface and the steel counterface after sliding in a high-purity nitrogen environment. TEM analysis of a cross-section of the tribofilm on the steel surface reveals that the sliding surface consists mainly of iron (II) fluoride and not carbon, even though a significant amount of carbon was observed near the surface. XPS and TEM analysis further revealed that the tribofilm formed on the worn composite surface consisted of nanoparticle agglomerates, anchored to the PTFE matrix and to each other by carbon with turbostratic structure. Turbostratic carbon also formed an ultrathin and surface-oriented superficial layer on top of the agglomerates. Governing mechanisms of the low friction and wear of the CF/PTFE—steel tribosystem were investigated by complementary tribotests with pure graphite samples and MD simulations of the identified surfaces. These indicated that the low friction between the carbon and iron fluoride in the tribofilms is due to poor adhesion between the distinctly different surfaces.

Place, publisher, year, edition, pages
Springer, 2023
Keywords
Self-lubricating composite, Tribochemistry, Friction mechanisms, TEM, XPS
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements; Applied Physics
Identifiers
urn:nbn:se:ltu:diva-99263 (URN)10.1007/s11249-023-01770-z (DOI)2-s2.0-85167413955 (Scopus ID)
Note

Validerad;2023;Nivå 2;2023-08-07 (joosat);

Licens fulltext: CC BY License

Available from: 2023-08-07 Created: 2023-08-07 Last updated: 2023-10-12Bibliographically approved
Chen, J., Marklund, P., Björling, M. & Shi, Y. (2023). In-situ polymerized siloxane urea enhanced graphene-based super-fast, durable, all-weather elec-photo-thermal anti-/de-icing coating. Journal of Science: Advanced Materials and Devices, 8(3), Article ID 100604.
Open this publication in new window or tab >>In-situ polymerized siloxane urea enhanced graphene-based super-fast, durable, all-weather elec-photo-thermal anti-/de-icing coating
2023 (English)In: Journal of Science: Advanced Materials and Devices, ISSN 2468-2284, Vol. 8, no 3, article id 100604Article in journal (Refereed) Published
Abstract [en]

Previous investigations on anti-/de-icing techniques have primarily focused on mild laboratory conditions, which have limited practical applicability due to their short service life. Consequently, there is an urgent demand for the development of durable anti-/de-icing technologies capable of withstanding complex environmental conditions. In this research endeavour, we have successfully formulated a hydrophobic coating based on graphene. To circumvent the challenges associated with environmentally unfriendly organic solvents, we utilized a graphene water slurry as the foundational material and subsequently incorporated a poly (vinyl alcohol)-water solution. The resulting solution was subjected to in situ polymerization of a siloxane urea crosslinked polymer, yielding the desired coating solution. Following a solution spraying and drying process, the ultimate product obtained was the hydrophobic conductive graphene (HCG) siloxane Coating. The HCG siloxane Coating exhibits a conductivity of 66 S/m, enabling it to melt ice droplets within a mere 10 s, whereas conventional coatings require 20–500 s for the same task. A comprehensive field test conducted during an entire winter period on a high mountain situated within the Arctic Circle in Finland demonstrated the excellent anti-icing properties of the developed coating when subjected to approximately 310 W/m2 power. Furthermore, the coating exhibited satisfactory de-icing performance under approximately 570 W/m2 power, successfully removing ice accumulations within approximately 10 min. Throughout the field test, temperatures frequently plummeted to −20 °C, accompanied by wind speeds reaching up to 12 m/s. Material characterization revealed that the micro-nano structure of the coating surface, which engenders favourable hydrophobic behaviour, was primarily attributed to the phase separation resulting from hydrophilic and hydrophobic interactions. Moreover, the semi-interpenetrating structure formed by the polyvinyl alcohol molecular chains and in-situ polymerized siloxane urea ensured the coating's strength.

Place, publisher, year, edition, pages
Elsevier, 2023
Keywords
Anti-/de-icing, Coating, Conductive, Graphene
National Category
Materials Chemistry
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-99303 (URN)10.1016/j.jsamd.2023.100604 (DOI)2-s2.0-85165422965 (Scopus ID)
Funder
Swedish Research Council Formas, 2019-00904Swedish Research Council, 2019-04941Swedish Energy Agency, 2018-003910Interreg Nord
Note

Validerad;2023;Nivå 2;2023-08-09 (hanlid)

Available from: 2023-08-09 Created: 2023-08-09 Last updated: 2023-09-05Bibliographically approved
Johansson, P., Marklund, P., Björling, M. & Shi, Y. (2023). Mechanisms behind the environmental sensitivity of carbon fiber reinforced polytetrafluoroethylene (PTFE). Friction
Open this publication in new window or tab >>Mechanisms behind the environmental sensitivity of carbon fiber reinforced polytetrafluoroethylene (PTFE)
2023 (English)In: Friction, ISSN 2223-7690, E-ISSN 2223-7704Article in journal (Refereed) Epub ahead of print
Abstract [en]

Carbon fiber reinforced polytetrafluoroethylene (CF/PTFE) composites are known for their exceptional tribological performance when sliding against steel or cast iron in inert gas environments. Compared to experiments in humid air, about an order of magnitude lower wear rate and several times lower coefficient of friction have been reported for tests conducted in dry nitrogen and hydrogen. Moreover, trace moisture has been shown to affect the friction and wear significantly of this tribosystem, although a possible effect of oxygen cannot be ruled out due to uncertainties regarding the oxygen concentrations. While several studies have pointed out the environmental sensitivity of CF/PTFE, the understanding of the underlying mechanisms are very limited. The objective of this research is to investigate the individual and combined effect of oxygen and moisture on the tribological behavior of CF/PTFE sliding against steel. Additionally, this study aims to elucidate the underlying mechanisms that govern the environmental sensitivity of the system. Climate-controlled three-pin-on-disc experiments were conducted in nitrogen atmospheres at various concentrations of oxygen and moisture. The tribological results clearly demonstrate that both moisture and oxygen contribute to increased friction and wear. However, the adverse effect was much more pronounced for oxygen than moisture. A qualitative method was developed to estimate the tribofilm coverage on the CF/PTFE surface. Results showed strong correlation between high coverage of strongly adhered tribofilm and low wear rate. Moreover, a loosely adhered tribofilm was observed on top of the CF/PTFE surface in presence of moisture. FTIR analysis indicated that the loosely adhered tribofilm found in the moisture-enriched environment contained a significant amount of adsorbed water, which may explain the lower coefficient of friction in presence of moisture compared to oxygen. The adsorbed water in the loosely adhered tribofilm could be an indication of moisture-driven lubrication by the non-graphitic carbon in the tribofilm.

Place, publisher, year, edition, pages
Springer Nature, 2023
Keywords
polymer composite, tribofilm, tribochemistry, atmosphere
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-101605 (URN)10.1007/s40544-023-0824-9 (DOI)
Note

Full text license: CC BY

Available from: 2023-10-09 Created: 2023-10-09 Last updated: 2023-12-06
Mehamud, I., Björling, M., Marklund, P. & Shi, Y. (2023). Small Size and Low-Cost TENG-Based Self-Powered Vibration Measuring and Alerting System. Advanced Electronic Materials, 9(6), Article ID 2300111.
Open this publication in new window or tab >>Small Size and Low-Cost TENG-Based Self-Powered Vibration Measuring and Alerting System
2023 (English)In: Advanced Electronic Materials, E-ISSN 2199-160X, Vol. 9, no 6, article id 2300111Article in journal (Refereed) Published
Abstract [en]

Vibration measurement systems containing sensors, signal conditioning, and data acquisition devices, are important for monitoring motors, gearboxes, turbines, etc. Microelectromechanical and piezoelectric sensors are predominantly used for vibration measurements. However, they are not cost-effective, flexible in design, and incapable of self-powering. Recently, triboelectric nano-generator (TENG)-based vibration sensors have been considered as a possible alternative to resolve this problem, and tremendous progress has been achieved. Previous work on TENG-based sensors is limited to optimizing the sensor design, while the signal conditioning and data acquisition of TENG signal still need investigation for actual applications. This work develops a TENG-based vibration measurement device and self-powered alerting system that is integrated with the signal condition and data acquisition systems. The experimental results show that the proposed measurement system successfully measures signals within the range of 0–1800 Hz frequency. Meanwhile, the TENG generates a high output, up to 80 V and 0.55 µA from small size TENG area (3.6 cm2). The signal is adequate to harvest energy for self-powering to drive alerting components (harvest 320 mJ in 36 h, which drives alarming for duration of 1.5 s). The proposed device is cost-effective (30 $), small (105 cm3), and consumes less power (0.18 W) in comparison to commercial devices.

Place, publisher, year, edition, pages
John Wiley and Sons Inc, 2023
Keywords
energy harvesting, self-powered, triboelectric nanogenerators, vibrations
National Category
Mechanical Engineering Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-97065 (URN)10.1002/aelm.202300111 (DOI)000972778900001 ()2-s2.0-85153042088 (Scopus ID)
Funder
Swedish Research Council Formas, 2019‐00904, 2022‐01047Swedish Research Council, 2019–04941
Note

Validerad;2023;Nivå 2;2023-07-05 (hanlid)

Available from: 2023-05-10 Created: 2023-05-10 Last updated: 2023-09-05Bibliographically approved
Fadaei Naeini, V., Björling, M., Larsson, A. & Larsson, R. (2023). Unraveling the pressure-viscosity behavior and shear thinning in glycerol using atomic scale molecular dynamics simulations. Journal of Molecular Liquids, 390(part A), Article ID 122990.
Open this publication in new window or tab >>Unraveling the pressure-viscosity behavior and shear thinning in glycerol using atomic scale molecular dynamics simulations
2023 (English)In: Journal of Molecular Liquids, ISSN 0167-7322, E-ISSN 1873-3166, Vol. 390, no part A, article id 122990Article in journal (Refereed) Published
Abstract [en]

In order to increase the usage and explore new applications of glycerol as a replacement for fossil-based lubricants its properties needs to be known at the fundamental level. In this study, the viscosity of pure glycerol at high pressures and strain rates has been investigated using of molecular dynamics (MD) simulations, utilizing both the Green-Kubo (GK) formalism and the SLLOD algorithm. Although the viscosity acquired by the GK method is in agreement with the corresponding experimental values at low pressure, a significant distinction was identified between the viscosity obtained by the GK method and the experimental values at higher pressures (P > 0.5 GPa). This results in a clear difference between the viscosity-pressure coefficient attained by the GK method and the corresponding experimental value. The SLLOD method using a non-equilibrium MD (NEMD) platform was exploited to take into account the simultaneous effects of strain rate and pressure on viscosity. As a result, the pressure-viscosity coefficient acquired by the SLLOD algorithm approaches the experimental value. By combining the experimental outputs for viscosity at low strain rates ( < 104 s−1) with the SLLOD outputs at higher rates ( > 105 s−1), the evolutions of glycerol viscosity with pressure and strain rate were ultimately achieved. Implementing this computational platform depicts the shear thinning process in pure glycerol in a wide range of pressures and strain rates.

Place, publisher, year, edition, pages
Elsevier, 2023
Keywords
Glycerol, Pressure-viscosity coefficient, Green-Kubo Formalism, SLLOD algorithm, Shear thinning, Molecular dynamics simulation
National Category
Condensed Matter Physics
Research subject
Machine Elements; Applied Physics
Identifiers
urn:nbn:se:ltu:diva-102857 (URN)10.1016/j.molliq.2023.122990 (DOI)2-s2.0-85171625047 (Scopus ID)
Funder
The Kempe Foundations, JCK-1903.2Knut and Alice Wallenberg FoundationSwedish Research Council, 2021-05621
Note

Validerad;2023;Nivå 2;2023-11-23 (joosat);

CC BY 4.0 License

Available from: 2023-11-23 Created: 2023-11-23 Last updated: 2023-11-23Bibliographically approved
Hansen, J., Björling, M. & Larsson, R. (2022). A new film parameter with micro elasto-hydrodynamics. In: 7th World Tribology Congress (WTC 2022): . Paper presented at 7th World Tribology Congress (WTC 2022), Lyon, France, July 10-15, 2022. , Article ID MON-T1-S2-R4.
Open this publication in new window or tab >>A new film parameter with micro elasto-hydrodynamics
2022 (English)In: 7th World Tribology Congress (WTC 2022), 2022, article id MON-T1-S2-R4Conference paper, Oral presentation with published abstract (Other academic)
Abstract [en]

A new semi-analytical model for estimating the lubrication quality in rough surface elasto-hydrodynamiclubricated (EHL) contacts is presented. The model was derived upon the basis of an idealized micro-EHLcontact, and was subsequently extended to account for real engineering surfaces comprising isotropic andanisotropic roughness lay. Model validation was made against ball-on-disc experiments in which the true mixedand EHL regimes where identified by means of the electrical-contact-resistance signal (ECR). While, theconventional approach, the Λ-ratio, was found to grossly mispredict the transition to the EHL and mixedlubrication(ML) regime boundary, the new film parameter was found to be surprisingly accurate.

Keywords
Λ-ratio, micro-EHL, mixed lubrication, running-in
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-92911 (URN)
Conference
7th World Tribology Congress (WTC 2022), Lyon, France, July 10-15, 2022
Funder
Swedish Foundation for Strategic ResearchSwedish Research Council
Note

Funder: Norrbottens forskningsråd; Scania CV AB

Available from: 2022-09-09 Created: 2022-09-09 Last updated: 2023-09-05Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0002-4271-0380

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