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Publications (10 of 46) Show all publications
Shao, J., Willatzen, M., Shi, Y. & Wang, Z. L. (2019). 3D mathematical model of contact-separation and single-electrode mode triboelectric nanogenerators. Nano Energy, 60, 630-640
Open this publication in new window or tab >>3D mathematical model of contact-separation and single-electrode mode triboelectric nanogenerators
2019 (English)In: Nano Energy, ISSN 2211-2855, E-ISSN 2211-3282, Vol. 60, p. 630-640Article in journal (Refereed) Published
Abstract [en]

Based on a set of finite-sized charged planes (FSCP), a simple time-dependent three-dimensional spatial model for the electric potential and electric field in an inhomogeneous medium composed of dielectric materials and metal contacts is proposed and used to assert triboelectric nanogenerator operation. Solving the problem of FSCP makes the three-dimensional spatial model relevant for practical TENG applications and allow for accurate and reliable results. Connecting the metal contacts to an electric resistance, Kirchhoff's law is used to derive a first-order time-dependent differential equation for the mobile charges on the metal contacts and the displacement current. Specially, the displacement current (Maxwell's displacement current) in a TENG equals to the conduction current in the external circuit is obtained. We then consider two important types of triboelectric nanogenerators: the contact-separation (CS) mode and the single-electrode (SEC) mode. A forced movement of the dielectric materials and/or the metal contacts leads to currents flowing in the system and a time-varying electrical potential, and therefore the generation of electrical power. Then, new and more accurate capacitance equations for CS and SEC modes of TENGs are extracted. Several examples of energy harvesting scenarios are finally analyzed.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
triboelectric nanogenerator, 3D mathematical model, Displacement current, Contact-mode, Single-electrode mode
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-73336 (URN)10.1016/j.nanoen.2019.03.072 (DOI)
Note

Validerad;2019;Nivå 2;2019-04-12 (johcin)

Available from: 2019-03-28 Created: 2019-03-28 Last updated: 2019-04-12Bibliographically approved
Björling, M. & Shi, Y. (2019). DLC and Glycerol: Superlubricity in Rolling/Sliding Elastohydrodynamic Lubrication. Tribology letters, 67(1), Article ID 23.
Open this publication in new window or tab >>DLC and Glycerol: Superlubricity in Rolling/Sliding Elastohydrodynamic Lubrication
2019 (English)In: Tribology letters, ISSN 1023-8883, E-ISSN 1573-2711, Vol. 67, no 1, article id 23Article in journal (Refereed) Published
Abstract [en]

Low friction is one of the most important parameters for the development of machine components and machines with high efficiency. Many of the common machine components of today such as gears, rolling element bearings and cam-followers are defined by their non-conformal contacts leading to high-contact pressures, typically 1–4 GPa. The lubrication of such contacts is usually called elastohydrodynamic lubrication (EHL). Diamond-like carbon (DLC) coatings and glycerol have individually been shown to produce low friction in boundary, mixed and full film lubrication. A few studies have been conducted using both glycerol and DLC-coated surfaces to achieve even lower friction in pure sliding boundary-lubricated contacts. However, the literature is lacking studies of how the combination of glycerol and DLC performs in non-conformal rolling/sliding contacts where many common machine components operate. Such a study is presented in this article where a ball-on-disc test rig is used to investigate the performance of the combination of DLC and glycerol at pressures up to 1.95 GPa at various entrainment speeds and slide-to-roll ratios. The investigation shows that the DLC-glycerol combination provides very low friction values, in some cases, below the superlubricity threshold of 0.01, possibly shown for the first time at such high pressure in a non-conformal rolling/sliding contact. The low friction mechanism in full film lubrication is a combination of the low pressure-viscosity and high temperature-viscosity sensitivity of glycerol in combination with thermal insulation of the DLC coating and is presented as thermally assisted liquid superlubricity.

Place, publisher, year, edition, pages
Springer, 2019
Keywords
Traction, EHL, Coatings, friction reducing, Superlubricity, Friction, Thermal effects in EHL, DLC, Glycerol
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-72541 (URN)10.1007/s11249-019-1135-1 (DOI)000455190400002 ()2-s2.0-85059784212 (Scopus ID)
Note

Validerad;2019;Nivå 2;2019-01-25 (inah)

Available from: 2019-01-14 Created: 2019-01-14 Last updated: 2019-01-25Bibliographically approved
Zhang, Y., Zhu, W., Li, J., Zhu, Y., Wang, A., Lu, X., . . . Shi, Y. (2019). Effects of ionic hydration and hydrogen bonding on flow resistance of ionic aqueous solutions confined in molybdenum disulfide nanoslits: Insights from molecular dynamics simulations. Fluid Phase Equilibria, 489, 23-29
Open this publication in new window or tab >>Effects of ionic hydration and hydrogen bonding on flow resistance of ionic aqueous solutions confined in molybdenum disulfide nanoslits: Insights from molecular dynamics simulations
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2019 (English)In: Fluid Phase Equilibria, ISSN 0378-3812, E-ISSN 1879-0224, Vol. 489, p. 23-29Article in journal (Refereed) Published
Abstract [en]

Single-layer molybdenum disulfide (MoS2) is a novel two-dimensional material that has attracted considerable attention because of its excellent properties. In this work, molecular dynamics simulations were performed to investigate the effect of different kinds of alkali metal ions (Li+, Na+, and K+) on the flow resistance of ionic aqueous solutions confined in MoS2 nanoslits under shearing. Three slit widths (i.e. 1.2, 1.6, and 2.0 nm) were investigated. Simulation results showed that the friction coefficient followed the order of K+ < Na+ < Li+. The friction coefficient decreased with the increasing of slit width. Unique confined spatial distributions of different types of ionic aqueous solutions led to different confined ionic hydrations for different cations. These differences lead to different orientations of surrounding water molecules and then form different hydrogen bond (HB) networks. The friction coefficient was greatly dependent on the number of HBs per water; i.e., the larger the number of HBs formed, the lower was the flow resistance.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
MoS2, Ionic aqueous solutions, Molecular simulations, Flow resistance, Nanoconfinement
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-72909 (URN)10.1016/j.fluid.2019.02.012 (DOI)2-s2.0-85061545923 (Scopus ID)
Note

Validerad;2019;Nivå 2;2019-02-26 (svasva)

Available from: 2019-02-15 Created: 2019-02-15 Last updated: 2019-02-26Bibliographically approved
Yu, Q., Zhang, C., Dong, R., Shi, Y., Wang, Y., Bai, Y., . . . Zhou, F. (2019). Novel N, P-containing oil-soluble ionic liquids with excellent tribological and anti-corrosion performance. Tribology International, 132, 118-129
Open this publication in new window or tab >>Novel N, P-containing oil-soluble ionic liquids with excellent tribological and anti-corrosion performance
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2019 (English)In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 132, p. 118-129Article in journal (Refereed) Published
Abstract [en]

Two oil-soluble ionic liquids N, N-trimethyl-N-hexadecyl ammonium bis(2-ethylhexyl) phosphate (NP-16))and 1,2-bis-NN-dimethyl-N-cetylammonium bis (2-ethylhexyl) phosphate (NP-16-2-16) have been synthesized and investigated as a potential friction reduction and anti-wear lubricant additive with anti-corrosion properties. The results indicate that the addition of 1.0 wt % NP-16 into PAO10 can significantly reduce friction coefficient and improve its anti-wear performance under RT and 100 °C. The performance is obviously better than that of traditional additives ZDDP and tricresyl phosphate. PAO10 + 1.0 wt % NP-16 even outperformed the PAO10 with about 40% lower friction and 2 orders of magnitude less wear. The analysis results of SEM, EDS and XPS show that an FePO4 or nitrogen-containing tribofilm is formed on the friction interface when NP-16 and NP-16-2-16 are selected as additives, which play a key role in reducing friction and wear.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Oil-soluble ionic liquids, Lubricity, Anti-wear performance, Lubricating mechanism
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-72457 (URN)10.1016/j.triboint.2018.12.002 (DOI)000456758700012 ()2-s2.0-85058810711 (Scopus ID)
Note

Validerad;2019;Nivå 2;2019-01-04 (svasva)

Available from: 2019-01-04 Created: 2019-01-04 Last updated: 2019-02-11Bibliographically approved
Wu, J., Mu, L., Feng, X., Lu, X., Larsson, R. & Shi, Y. (2019). Poly(alkylimidazolium bis(trifluoromethylsulfonyl) imide)-Based Polymerized Ionic Liquids: A Potential  High-Performance Lubricating Grease. Advanced Materials Interfaces, 6(5), Article ID 1801796.
Open this publication in new window or tab >>Poly(alkylimidazolium bis(trifluoromethylsulfonyl) imide)-Based Polymerized Ionic Liquids: A Potential  High-Performance Lubricating Grease
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2019 (English)In: Advanced Materials Interfaces, ISSN 2196-7350, Vol. 6, no 5, article id 1801796Article in journal (Refereed) Published
Abstract [en]

Polymers prepared from ionic liquids are widely called polymerized ionic liquids (PILs). Compared to monocationic and dicationic ILs, PILs have higher molecular weights, charge, and greater intermolecular interactions, which make PILs have a higher possibility to generate better lubricity. PILs of poly‐alkylimidazolium bis(trifluoromethylsulfonyl)imide (PImC6NTf2) is studied herein. Dicationic ILs of 1,1′‐(pentane‐1,5‐diyl)‐bis(3‐butylimidazolium) bis(trifluoromethylsulfonyl)imide (BIm5‐(NTf2)2) is used as additive to decrease the crystallization temperature of PImC6NTf2. Lubricity of PImC6NTf2 and PImC6NTf2+BIm5‐(NTf2)2, as well as BIm5‐(NTf2)2 for comparison is evaluated under severe conditions, i.e., 3.0 to 3.5 GPa and 200 °C. The rheological study suggests that PImC6NTf2 can be classified into grease. Tribological test results show that PImC6NTf2 has much better antiwear property than BIm5‐(NTf2)2, especially at 3.5 GPa. Adding 4% BIm5‐(NTf2)2 to PImC6NTf2 is able to reduce friction under high pressure. At 200 °C, PImC6NTf2 exhibits excellent lubricity. The mixture of 96%PImC6NTf2+4%BIm5‐(NTf2)2 shows even better antiwear property than neat PImC6NTf2 and exhibits the highest friction reducing property among the ILs at 200 °C. It is speculated that the robust strength of PILs and strong adhesion between PILs and solids are key factors in achieving the excellent antiwear property.

Place, publisher, year, edition, pages
John Wiley & Sons, 2019
Keywords
grease, high pressure and high temperature, lubricity, polymerized ionic liquids
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-72623 (URN)10.1002/admi.201801796 (DOI)000460657100002 ()
Note

Validerad;2019;Nivå 2;2019-03-11 (johcin)

Available from: 2019-01-18 Created: 2019-01-18 Last updated: 2019-04-12Bibliographically approved
Mu, L., Ma, X., Guo, X., Chen, M., Ji, T., Hua, J., . . . Shi, Y. (2019). Structural strategies to design bio-ionic liquid: Tuning molecular interaction with lignin for enhanced lubrication. Journal of Molecular Liquids, 280, 49-57
Open this publication in new window or tab >>Structural strategies to design bio-ionic liquid: Tuning molecular interaction with lignin for enhanced lubrication
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2019 (English)In: Journal of Molecular Liquids, ISSN 0167-7322, E-ISSN 1873-3166, Vol. 280, p. 49-57Article in journal (Refereed) Published
Abstract [en]

Lignin strengthened ionic liquids (ILs) have shown high potential to be used as high performance green lubricants. Strengthened lignin-ILs molecular interaction is an effective approach to improve their lubrication properties. The molecular interactions of ILs’ cation and anion containing different functional groups with lignin and efficiency on the lubricating properties have rarely been studied yet. In this work, a series of novel green lubricants with dissolved lignin in [Choline][Amino Acid] ([CH][AA]), [Tetramethylammonium][Glycine] ([N 1111 ][Gly]) and [Tetrabutylammonium][Glycine] ([N 4444 ][Gly]) ILs have been synthesized and their tribological properties were systematically investigated. The longer alkyl chain in cation without reciprocal H-bond interaction between ILs’ cation and anion has the positive effect on the anti-wear properties. In addition, the less steric effect and more negative natural charges of amino acid anion synergistically contribute to the stronger H-bond interaction between lignin and choline base ILs, which enhances lubrication film strength and thus resulting in the better tribological property of ILs/lignin green lubricants. Specifically, the wear volume loss of the steel disc lubricated by [N 4444 ][Gly] with the addition of 15% lignin is only 12% of the one lubricated by pure [N 4444 ][Gly]. This work presents a method to tune molecular interaction between lignin and ILs via the structural design of ILs’ cation and anion, which are revealed as the key factor that bridges the individual components and improves overall lubricating properties. 

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Amino acid, Hydrogen bond, Ionic liquids, Lignin, Lubrication, Structure
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-72933 (URN)10.1016/j.molliq.2019.02.022 (DOI)2-s2.0-85061426516 (Scopus ID)
Note

Validerad;2019;Nivå 2;2019-02-18 (svasva)

Available from: 2019-02-18 Created: 2019-02-18 Last updated: 2019-02-18Bibliographically approved
Mu, L., Wu, J., Matsakas, L., Chen, M., Rova, U., Christakopoulos, P., . . . Shi, Y. (2019). Two important factors of selecting lignin as efficient lubricating additives in poly (ethylene glycol): Hydrogen bond and molecular weight. International Journal of Biological Macromolecules, 129, 564-570
Open this publication in new window or tab >>Two important factors of selecting lignin as efficient lubricating additives in poly (ethylene glycol): Hydrogen bond and molecular weight
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2019 (English)In: International Journal of Biological Macromolecules, ISSN 0141-8130, E-ISSN 1879-0003, Vol. 129, p. 564-570Article in journal (Refereed) Published
Abstract [en]

Lignin, one of the most abundant natural polymers, has been successfully used as an effective lubricant additive with high value. The chemical structure of lignin is very diverse and strongly affected by both the source of lignin (i.e. plant species) and the lignin extraction process. In this work, a series of lignin from different biomass sources (hard or soft wood) and extraction process (organosolv with or without acid catalyst) has been successfully incorporated into poly(ethylene glycol) (PEG) and fortified lubricating properties were achieved. The effects of different lignin on the rheological, thermal and tribological properties of the lignin/EG lubricants were systematically investigated by different characterization techniques. Lignin in PEG significantly improves the lubricating property, where a wear reduction of 93.8% was observed. The thermal and lubrication properties of the PEG lubricants filled with different kinds of lignin are tightly related to the synergistic state of hydrogen bonding and molecular weight distribution. Lignin with broader molecular weight distribution and higher hydroxyl content shows better adhesion on metal surfaces and strengthened lubricating film, which could be used as the efficient lubricating additives. This work provides a criterion for selecting appropriate lignin as the efficient lubricant additive and accelerates the application of lignin.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Lignin, Lubrication, Poly (ethylene glycol), Hydrogen bonding, Molecular weight
National Category
Bioprocess Technology Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements; Biochemical Process Engineering
Identifiers
urn:nbn:se:ltu:diva-72899 (URN)10.1016/j.ijbiomac.2019.01.175 (DOI)2-s2.0-85061540788 (Scopus ID)
Note

Validerad;2019;Nivå 2;2019-02-20 (svasva)

Available from: 2019-02-14 Created: 2019-02-14 Last updated: 2019-02-26Bibliographically approved
Wu, J., Huang, X., Berglund, K., Lu, X., Feng, X., Larsson, R. & Shi, Y. (2018). CuO nanosheets produced in graphene oxide solution: An excellent anti-wear additive for self-lubricating polymer composites. Composites Science And Technology, 162, 86-92
Open this publication in new window or tab >>CuO nanosheets produced in graphene oxide solution: An excellent anti-wear additive for self-lubricating polymer composites
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2018 (English)In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 162, p. 86-92Article in journal (Refereed) Published
Abstract [en]

In the present work, graphene oxide is used as template to produce CuO nanosheets, which solves aggregation and dispersion problems of CuO nanosheets resulting in improved lubricating performance. SEM and AFM studies show that CuO nanosheets are present in fusiform flake shape with a thickness, width and length of around 13, 400 and 1000 nm, respectively. CuO nanosheets were added to the carbon fibers reinforced Polytetrafluoroethylene (CF/PTFE) to study their lubricating performance. It is interesting, from fractured surfaces of composites, to find that CuO nanosheets enhance the interface properties between carbon fibers and PTFE. The wear resistance property of CF/PTFE is remarkably improved after filling CuO nanosheets. For example, the wear rate is reduced by 51% after filling 1.5 wt % CuO nanosheets. The wear resistance improvement effect of CuO nanosheets is much better than that of commercial CuO nanogranules and CuO nanorods. Worn surfaces and counter-surfaces studying indicates that CuO nanosheets can not only prevent the rubbed-off of PTFE or the detachment of CF, but also improve the properties of transfer films, which greatly reduce the adhesive wear and abrasive wear.

Place, publisher, year, edition, pages
Elsevier, 2018
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-68387 (URN)10.1016/j.compscitech.2018.04.020 (DOI)000438180500010 ()2-s2.0-85046114065 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-05-09 (andbra)

Available from: 2018-04-17 Created: 2018-04-17 Last updated: 2018-08-09Bibliographically approved
Li, Y., Xi, Y. & Shi, Y. (2018). Estimation of rolling friction coefficients in a tribosystem using optical measurements (ed.). Industrial Lubrication and Tribology, 70(4), 680-686
Open this publication in new window or tab >>Estimation of rolling friction coefficients in a tribosystem using optical measurements
2018 (English)In: Industrial Lubrication and Tribology, ISSN 0036-8792, E-ISSN 1758-5775, Vol. 70, no 4, p. 680-686Article in journal (Refereed) Published
Abstract [en]

Purpose

This paper presents a method to measure the rolling friction coefficient in an easy and fast way. The aim is to measure the rolling friction coefficient between a small steel ball and a cylindrical aluminum surface.

Design/methodology/approach

An analytical model of the tribosystem of a freely rolling ball and a cylindrical surface is established. The rolling friction coefficient is evaluated from images recorded by a high-speed camera. The coefficient between a 1.58 mm diameter steel ball and a cylindrical aluminum surface is measured. A background subtraction algorithm is used to determine the position of the small steel ball.

Findings

The angular positions of the ball are predicted using the analytical model, and good agreement is found between the experimental and theoretical results.

Originality/value

An optical method for evaluating the rolling friction coefficient is presented, and the value of this coefficient between a small steel ball and a cylindrical aluminum surface is evaluated.

Place, publisher, year, edition, pages
Emerald Group Publishing Limited, 2018
National Category
Applied Mechanics Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Experimental Mechanics; Machine Elements
Identifiers
urn:nbn:se:ltu:diva-5804 (URN)10.1108/ILT-04-2016-0087 (DOI)000434250800012 ()2-s2.0-85048166333 (Scopus ID)3fccd069-0a30-4736-8462-4ac31ed3db8e (Local ID)3fccd069-0a30-4736-8462-4ac31ed3db8e (Archive number)3fccd069-0a30-4736-8462-4ac31ed3db8e (OAI)
Note

Validerad;2018;Nivå 2;2018-06-05 (svasva)

Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-06-21Bibliographically approved
Mu, L., Wu, J., Matsakas, L., Chen, M., Vahidi, A., Grahn, M., . . . Shi, Y. (2018). Lignin from Hardwood and Softwood Biomass as a Lubricating Additive to Ethylene Glycol. Molecules, 23(3), Article ID 537.
Open this publication in new window or tab >>Lignin from Hardwood and Softwood Biomass as a Lubricating Additive to Ethylene Glycol
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2018 (English)In: Molecules, ISSN 1420-3049, E-ISSN 1420-3049, Vol. 23, no 3, article id 537Article in journal (Refereed) Published
Abstract [en]

Ethylene glycol (EG)-based lubricant was prepared with dissolved organosolv lignin from birch wood (BL) and softwood (SL) biomass. The effects of different lignin types on the rheological, thermal, and tribological properties of the lignin/EG lubricants were comprehensively investigated by various characterization techniques. Dissolving organosolv lignin in EG results in outstanding lubricating properties. Specifically, the wear volume of the disc by EG-44BL is only 8.9% of that lubricated by pure EG. The enhanced anti-wear property of the EG/lignin system could be attributed to the formation of a robust lubrication film and the strong adhesion of the lubricant on the contacting metal surface due to the presence of a dense hydrogen bonding (H-bonding) network. The lubricating performance of EG-BL outperforms EG-SL, which could be attributed to the denser H-bonding sites in BL and its broader molecular weight distribution. The disc wear loss of EG-44BL is only 45.7% of that lubricated by EG-44SL. Overall, H-bonding is the major contributor to the different tribological properties of BL and SL in EG-based lubricants.

Place, publisher, year, edition, pages
MDPI, 2018
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear) Bioprocess Technology Chemical Process Engineering
Research subject
Machine Elements; Biochemical Process Engineering; Chemical Technology
Identifiers
urn:nbn:se:ltu:diva-67800 (URN)10.3390/molecules23030537 (DOI)000428514100028 ()29495559 (PubMedID)2-s2.0-85043353975 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-03-01 (andbra)

Available from: 2018-03-01 Created: 2018-03-01 Last updated: 2019-04-02Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0001-6085-7880

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