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Piya, A. K., Yang, L., Omar, A. A., Emami, N. & Morina, A. (2024). Synergistic lubrication mechanism of nanodiamonds with organic friction modifier. Carbon, 218, Article ID 118742.
Open this publication in new window or tab >>Synergistic lubrication mechanism of nanodiamonds with organic friction modifier
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2024 (English)In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 218, article id 118742Article in journal (Refereed) Published
Abstract [en]

Nanoparticles and organic friction modifiers (OFMs) as lubricant additives have shown great potential in friction and wear reduction by forming tribofilms which prevent direct contact at the sliding interface. Potential mechanisms for the formation of these tribofilms remain poorly understood, limiting the ability to optimise the performance of the entire tribosystem. Incorporation of nanoparticles and OFM together in a lubricant could provide a unique solution to enhance frictional and wear properties. In this study, Nanodiamonds (NDs) and Glycerol Monooleate (GMO) have been added to a PAO base oil containing low concentration of Zinc dialkyl dithio-phosphate (ZDDP) to produce a novel lubricant combination that significantly reduces coefficient of friction (COF) and wear. Experimental studies showed that NDs reacted with additives present in the lubricant combination to expedite tribofilm formation. Friction reduction performance can be attributed to the encapsulation of carboxylated NDs due to tribochemical interaction with GMO, their mechanical interlocking in the tribofilm and polishing effect of NDs. The visible presence of NDs in tribofilms and the formation of a thicker tribofilm layer with NDs have been corroborated for the first time in this study. Synergy achieved among NDs, GMO, and low concentration ZDDP to formulate a novel environmentally friendly lubricant with advanced tribological performance has been shown, providing a great potential to develop sustainable tribological solutions for a wide variety of engineering applications.

Place, publisher, year, edition, pages
Elsevier Ltd, 2024
Keywords
Friction, Nanodiamond, Organic friction modifier, Tribofilm, Wear
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-103514 (URN)10.1016/j.carbon.2023.118742 (DOI)2-s2.0-85180401423 (Scopus ID)
Funder
EU, Horizon 2020, Marie Skłodowska-Curie (860246)
Note

Validerad;2024;Nivå 2;2024-02-13 (joosat);

Full text license: CC BY

Available from: 2024-01-08 Created: 2024-01-08 Last updated: 2024-02-13Bibliographically approved
Dhakal, N., Espejo, C., Morina, A. & Emami, N. (2024). Tribological performance of 3D printed neat and carbon fiber reinforced PEEK composites. Tribology International, 193, Article ID 109356.
Open this publication in new window or tab >>Tribological performance of 3D printed neat and carbon fiber reinforced PEEK composites
2024 (English)In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 193, article id 109356Article in journal (Refereed) Published
Abstract [en]

This work investigates the tribological behavior of neat and carbon fiber-reinforced polyether-ether-ketone (PEEK) materials processed using the fused filament fabrication (FFF) technique. The reciprocating sliding behavior of printed polymers against stainless steel (SS) under dry and water-lubricated conditions was studied. The running-in behavior and evolution of friction were dependent on the material combination and sliding conditions. PEEK reinforced with 10 wt% carbon fibers was optimal considering tribological performance. Neat PEEK exhibited a combination of abrasive and adhesive wear mechanisms, while composites primarily showed fiber-matrix debonding and delamination during sliding. The outcome of this work has significance in improving the processing design of PEEK-based materials in extrusion-based 3D printing for tribological applications.

Keywords
3D printing, Tribology, Polymer composites, PEEK, Friction and wear, Dry sliding, Water lubrication
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-104347 (URN)10.1016/j.triboint.2024.109356 (DOI)2-s2.0-85183995970 (Scopus ID)
Funder
EU, Horizon 2020, 860246
Note

Validerad;2024;Nivå 2;2024-02-21 (signyg)

Full text license: CC BY

Available from: 2024-02-21 Created: 2024-02-21 Last updated: 2024-02-21Bibliographically approved
Khan, S. A., Emami, N. & Ramalho, A. (2023). Custom-tailored cross-cylinder tribotest to emulate wear mechanism in drilling of CFRP-Ti stacks. Tribology International, 186, Article ID 108589.
Open this publication in new window or tab >>Custom-tailored cross-cylinder tribotest to emulate wear mechanism in drilling of CFRP-Ti stacks
2023 (English)In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 186, article id 108589Article in journal (Refereed) Published
Abstract [en]

While drilling of CFRP-Ti stacks, tool experiences complex tribomechanical interaction due to dissimilar workpiece constituents. For emulating tool wear behavior, the typical tribotest configuration such as reciprocating and pin-on-disc test are not representative for imitating contact scenario underwent during the drilling operation. Cross-cylinder tribotest is an effective test configuration to emulate contact in different manufacturing processes by providing fresh contact surface during sliding. In this work, for the first-time, tool wear of WC-Co cylinders was analyzed in cross-cylinder configuration against multi-material stack arrangement. Moreover, cross-cylinder testing against multi-material [CFRP-Ti]n workpiece showed cyclic variation in coefficient of friction against different workpiece constituents and wear mechanism is a combination of adhesive and abrasive wear on WC-Co tool, comparable to actual drilling operation.

Place, publisher, year, edition, pages
Elsevier, 2023
Keywords
Cross-cylinder tribotest, CFRP-Ti stacks, Difficult-to-machine materials, Wear
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-97629 (URN)10.1016/j.triboint.2023.108589 (DOI)2-s2.0-85159118215 (Scopus ID)
Funder
EU, Horizon 2020, 860246
Note

Validerad;2023;Nivå 2;2023-05-29 (joosat);

Funder: FCT – Fundaçao para a Ciencia e a Tecnologia, (UIDB/00285/2020, LA/P/0112/2020)

Available from: 2023-05-29 Created: 2023-05-29 Last updated: 2023-05-29Bibliographically approved
Gangwani, P., Kalin, M. & Emami, N. (2023). Does a Compatibilizer Enhance the Properties of Carbon Fiber-Reinforced Composites?. Polymers, 15(23), Article ID 4608.
Open this publication in new window or tab >>Does a Compatibilizer Enhance the Properties of Carbon Fiber-Reinforced Composites?
2023 (English)In: Polymers, E-ISSN 2073-4360, Vol. 15, no 23, article id 4608Article in journal (Refereed) Published
Abstract [en]

We have evaluated the effectiveness of compatibilizers in blends and composites produced using a solvent manufacturing process. The compatibilizers were two different types of polyethylene (linear low-density and high-density) grafted with maleic anhydride (MAH) and a highly functionalized, epoxy-based compatibilizer with the tradename Joncryl. The selected material combinations were an ultra-high-molecular-weight polyethylene (UHMWPE) with MAH-based materials as compatibilizers and a polyphenylene sulfide plus polytetrafluoroethylene (PPS-PTFE) polymer blend with an epoxy-based compatibilizer. The findings revealed that while the compatibilizers consistently enhanced the properties, such as the impact strength and hardness of PPS-based compositions, their utility is constrained to less complex compositions, such as fibrous-reinforced PPS or PPS-PTFE polymer blends. For fibrous-reinforced PPS-PTFE composites, the improvement in performance does not justify the presence of compatibilizers. In contrast, for UHMWPE compositions, compatibilizers demonstrated negligible or even detrimental effects, particularly in reinforced UHMWPE. Overall, the epoxy-based compatibilizer Joncryl stands out as the only effective option for enhancing mechanical performance. Thermal and chemical characterization indicated that the compatibilizers function as chain extenders and enhance the fiber–matrix interface in PPS-based compositions, while they remain inactive in UHMWPE-based compositions. Ultimately, the incompatibility of the compatibilizers with certain aspects of the manufacturing method and the inconsistent integration with the polymer are the main reasons for their ineffectiveness in UHMWPE compositions.

Keywords
compatibilizer, carbon fiber, polymer composites, UHMWPE, PTFE, PPS
National Category
Polymer Technologies Composite Science and Engineering
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-103507 (URN)10.3390/polym15234608 (DOI)001116168000001 ()38232010 (PubMedID)2-s2.0-85179133014 (Scopus ID)
Note

Validerad;2024;Nivå 2;2024-02-13 (signyg);

Funder: Marie Skłodowska-Curie (860246); ARRS (P2-0231);

Full text license: CC BY

Available from: 2024-01-08 Created: 2024-01-08 Last updated: 2024-02-13Bibliographically approved
Somberg, J., Gonçalves, G. & Emami, N. (2023). Graphene oxide versus graphite and chemically expanded graphite as solid lubricant in ultrahigh molecular weight polyethylene composites. Tribology International, 187, Article ID 108643.
Open this publication in new window or tab >>Graphene oxide versus graphite and chemically expanded graphite as solid lubricant in ultrahigh molecular weight polyethylene composites
2023 (English)In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 187, article id 108643Article in journal (Refereed) Published
Abstract [en]

Graphene oxide (GO), chemically expanded graphite (CEG) and graphite were evaluated as solid lubricant for ultrahigh molecular weight polyethylene composites. Under dry conditions, the addition of all solid lubricants increased the coefficient of friction by up to 38%. For the composites corrugated stick–slip features were observed which correlate with a decrease in matrix degree of crystallinity. GO had the lowest effect on the crystallisation, resulting in the lowest relative increase in friction coefficient of only 13%. Under water lubrication, GO, CEG and graphite were equally effective in reducing friction and wear. The highest friction for the neat matrix was found to be due to a transfer film, which was suppressed by the addition of the solid lubricants.

Place, publisher, year, edition, pages
Elsevier, 2023
Keywords
Chemically expanded graphite, Graphene oxide, Polymer composite, Solid lubricants
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear) Textile, Rubber and Polymeric Materials
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-98894 (URN)10.1016/j.triboint.2023.108643 (DOI)2-s2.0-85161662377 (Scopus ID)
Funder
Vinnova, 2017–03609
Note

Validerad;2023;Nivå 2;2023-06-26 (hanlid)

Available from: 2023-06-26 Created: 2023-06-26 Last updated: 2023-09-05Bibliographically approved
Dhakal, N., Wang, X., Espejo, C., Morina, A. & Emami, N. (2023). Impact of processing defects on microstructure, surface quality, and tribological performance in 3D printed polymers. Journal of Materials Research and Technology, 23, 1252-1272
Open this publication in new window or tab >>Impact of processing defects on microstructure, surface quality, and tribological performance in 3D printed polymers
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2023 (English)In: Journal of Materials Research and Technology, ISSN 2238-7854, Vol. 23, p. 1252-1272Article in journal (Refereed) Published
Abstract [en]

Additive manufacturing (AM), also known as three-dimensional (3D) printing, of polymer-based materials is growing as a time-efficient, economical, and environmentally sustainable technique for prototype development in load-bearing applications. This work investigates the defects arising from the processing in material extrusion-based AM of polymers and their impact on the part performance. The influence of raster angle orientation and printing speed on tribological characteristics, microstructure, and surface finish of acrylonitrile butadiene styrene (ABS) fabricated in a heated build chamber was studied. Comprehensive analysis with fractography and tomography revealed the formation, distribution, and locations of internal voids, while surface defects were studied with the topography analysis of as-printed surfaces. Surface roughness and tribological results show that printing speed can be optimally increased with a minimal impact on interlayer bonding and part performance. Increased printing speed allowed up to 58% effective reduction in printing time obtaining comparable mechanical properties at varying process parameters. 3D printed ABS exhibited dry sliding friction coefficients in the range of 0.18–0.23, whilst the maximum specific wear rate was 6.2 × 10−5 mm3/Nm. Higher surface roughness and increased printing speed exhibited delayed running-in during dry sliding, while insignificant influence was observed for steady-state friction and wear behaviors. The findings indicate that improved surface finish and reduced internal defects can be achieved with a controlled build environment allowing for higher printing speed. The observations in this study are evidence that 3D printing can be adapted for the sustainable manufacturing of polymeric components for tribological applications.

Place, publisher, year, edition, pages
Elsevier, 2023
Keywords
3D printing, Tribology, Friction, Polymers, Porosity, Surface roughness
National Category
Manufacturing, Surface and Joining Technology Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-95552 (URN)10.1016/j.jmrt.2023.01.086 (DOI)2-s2.0-85149695807 (Scopus ID)
Funder
EU, Horizon 2020, 860246
Note

Validerad;2023;Nivå 2;2023-03-21 (joosat);

Licens fulltext: CC BY License

Available from: 2023-02-08 Created: 2023-02-08 Last updated: 2023-04-21Bibliographically approved
Kneissl, L. M., Gonçalves, G., Joffe, R., Kalin, M. & Emami, N. (2023). Mechanical properties and tribological performance of polyoxymethylene/short cellulose fiber composites. Polymer testing, 128, Article ID 108234.
Open this publication in new window or tab >>Mechanical properties and tribological performance of polyoxymethylene/short cellulose fiber composites
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2023 (English)In: Polymer testing, ISSN 0142-9418, E-ISSN 1873-2348, Vol. 128, article id 108234Article in journal (Refereed) Published
Abstract [en]

Natural fibers are promising bio-based materials to use as reinforcements in polymer composites as often more affordable and accessible alternatives to fossil-based fibers, especially because of their superior sustainability. Polyoxymethylene (POM) is a widely used engineering thermoplastic, which has a melting temperature suitable for processing with natural fibers. In this study, such composites consisting of POM and regenerated cellulose fibers have been developed and studied in terms of their mechanical, thermal, tribological and structural properties. Tensile and flexural moduli increased with incorporation of 30 wt% fibers up to 89% and 79% respectively, crystallinity increased as well by a maximum of approx. 11% at 30% fiber content. Furthermore, the specific wear rate was improved for the composite with 10 wt% fibers, showing a decrease of roughly 80%. This study investigates the processing parameters and tribo-mechanical performance of POM-based natural fiber composites as an important route towards future sustainable polymer composites in load bearing applications.

Place, publisher, year, edition, pages
Elsevier Ltd, 2023
Keywords
Cellulose fibers, Characterization, Polyoxymethylene, Processing, Tribology
National Category
Composite Science and Engineering
Research subject
Machine Elements; Polymeric Composite Materials
Identifiers
urn:nbn:se:ltu:diva-101977 (URN)10.1016/j.polymertesting.2023.108234 (DOI)2-s2.0-85174143660 (Scopus ID)
Funder
EU, Horizon 2020, 860246
Note

Validerad;2023;Nivå 2;2023-11-08 (marisr);

License fulltext: CC BY-NC-ND

Available from: 2023-10-31 Created: 2023-10-31 Last updated: 2023-11-08Bibliographically approved
Nikonovich, M., Costa, J. F. .., Fonseca, A. C., Ramalho, A. & Emami, N. (2023). Structural, thermal, and mechanical characterisation of PEEK-based composites in cryogenic temperature. Polymer testing, 125, Article ID 108139.
Open this publication in new window or tab >>Structural, thermal, and mechanical characterisation of PEEK-based composites in cryogenic temperature
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2023 (English)In: Polymer testing, ISSN 0142-9418, E-ISSN 1873-2348, Vol. 125, article id 108139Article in journal (Refereed) Published
Abstract [en]

Thermal, thermo-mechanical and mechanical properties of four different commercially available polyetheretherketones (PEEK) based materials were investigated. PEEK matrix was either modified and/or reinforced with carbon fibres, graphite and/or PTFE. Impact strength was measured at three different temperatures: 25 °C, −100 °C, and −195 °C. At 25 °C, thermal stability and mechanical properties, including the elastic modulus, compression, and impact strength, were enhanced with the addition of carbon fibres. Matrix modification had a minor impact on thermal stability, while the mechanical properties decreased, except for impact strength. At −100 °C, the mechanical properties of the neat polymers were improved, including increased impact strength by 20% compared to values at 25 °C. Addition of fillers hindered the rise of impact strength due to complex mechanisms caused by different coefficients of thermal expansion of reinforcements and matrix. At −195 °C, the significant increase of impact strength was revealed for unmodified PEEK reaching 30 times higher values than at 25 °C, while matrix modification suppressed the rise of impact strength. The scratch test indicated the superior behaviour of unfilled PEEK during the tested load range (up to 15 N), while the effect of the fillers was observed at much lower load threshold of 7 N.

Place, publisher, year, edition, pages
Elsevier, 2023
Keywords
Cryogenic temperature, Fractography, Impact behaviour, Polymer-matrix composites (PMCs), Thermal properties
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear) Polymer Technologies
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-99484 (URN)10.1016/j.polymertesting.2023.108139 (DOI)2-s2.0-85164561685 (Scopus ID)
Funder
EU, Horizon 2020, 860246
Note

Validerad;2023;Nivå 2;2023-08-11 (hanlid)

Available from: 2023-08-11 Created: 2023-08-11 Last updated: 2023-08-11Bibliographically approved
Khan, S. A., Oliveira, J., Ferreira, F., Emami, N. & Ramalho, A. (2023). Surface Roughness Influence on Tribological Behavior of HiPIMS DLC Coatings. Tribology Transactions, 66(3), 565-575
Open this publication in new window or tab >>Surface Roughness Influence on Tribological Behavior of HiPIMS DLC Coatings
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2023 (English)In: Tribology Transactions, ISSN 1040-2004, E-ISSN 1547-397X, Vol. 66, no 3, p. 565-575Article in journal (Refereed) Published
Abstract [en]

The application of diamond-like carbon (DLC) coatings in dry machining of difficult-to-machine materials has been gaining popularity due to high inertness, low coefficient of friction (COF), and high hardness of these coatings. Although the effect of surface roughness on the tribological properties of DLC coatings is of paramount importance, usually it is overlooked and coatings performance analysis was accomplished generally on highly polished substrates. The generation of polished surfaces is a time-consuming, labor-intensive process and, in most cases, not feasible for the industry due to its high cost. This article focuses on determining the effect of substrate (cemented carbide, WC-Co) surface roughness on the load-bearing capacity and tribological properties of DLC coatings deposited by High Power Impulse Magnetron Sputtering (HiPIMS) in Ne–Ar gas plasma. The DLC films were deposited onto WC-Co substrates with three different surface roughness profiles and their tribological performance were evaluated using a reciprocating tribotest. The high surface roughness resulted in increased wear rate due to high levels of asperities and increased potential for premature delamination of the coatings, while also causing severe damage to the counterbody due to inhibition of transfer film formation.

Place, publisher, year, edition, pages
Taylor & Francis, 2023
Keywords
Coefficient of friction, DLC coating, HiPIMS, surface roughness, WC-Co substrate, wear
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear) Manufacturing, Surface and Joining Technology
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-97262 (URN)10.1080/10402004.2023.2197472 (DOI)000982395600001 ()2-s2.0-85158865287 (Scopus ID)
Funder
EU, Horizon 2020, 860246
Note

Validerad;2023;Nivå 2;2023-05-22 (hanlid);

Funder: FCT–Fundação para a Ciência e a Tecnologia (UIDB/00285/2020, LA/P/0112/2020)

Available from: 2023-05-22 Created: 2023-05-22 Last updated: 2023-05-23Bibliographically approved
Al-Maqdasi, Z., Pupure, L., Emami, N. & Joffe, R. (2023). Time-dependent properties of high-density polyethylene with wood/graphene nanoplatelets reinforcement. Polymer Composites, 44(1), 465-479
Open this publication in new window or tab >>Time-dependent properties of high-density polyethylene with wood/graphene nanoplatelets reinforcement
2023 (English)In: Polymer Composites, ISSN 0272-8397, E-ISSN 1548-0569, Vol. 44, no 1, p. 465-479Article in journal (Refereed) Published
Abstract [en]

The effect of graphene nanoplatelets (GNPs) on the long-term performance of wood fiber/high-density polyethylene (HDPE) composite is investigated by using short-term creep tests with an efficient, faster data analysis approach. Previously, it was shown that the addition of GNPs at 15 wt% into HDPE reduces the viscoplastic (VP) strain developed during 2 h creep by ~50%. The current study shows that 25 and 40 wt% wood content in HDPE reduce the VP strains developed during 2 h creep time by >75% with no noticeable effect of the increased wood content. However, further addition of GNPs results in more than 90% total reduction in the VP strains. The current study shows that the development of the VP strains in the hybrid composites follows Zapas model. Viscoelastic (VE) response of these composites is nonlinear and thus is described by Schapery's model. Parameters for VP and VE models are obtained from the creep experiments and were validated in a separate loading-unloading test sequence. Results show a very good agreement between experiments and predictions for the studied materials as long as the micro-damage is not present.

Place, publisher, year, edition, pages
John Wiley & Sons, 2023
Keywords
creep, graphene nanoplatelets, multiscale composites, time-dependent properties, viscoelasticity, viscoplasticity, wood fibers
National Category
Composite Science and Engineering
Research subject
Polymeric Composite Materials; Machine Elements
Identifiers
urn:nbn:se:ltu:diva-90137 (URN)10.1002/pc.27110 (DOI)000877029700001 ()2-s2.0-85141407844 (Scopus ID)
Funder
European Regional Development Fund (ERDF), 1.1.1.2/VIAA/4/20/646EU, Horizon 2020, 777810 Nano2Day
Note

Validerad;2023;Nivå 2;2023-04-19 (hanlid);

Available from: 2022-04-08 Created: 2022-04-08 Last updated: 2023-04-19Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0001-8676-8819

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