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  • 101.
    Moreno, Silvia Suñer
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Tipper, Joanne
    Institute of Medical and Biological Engineering, University of Leeds.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Investigation of wear and wear particles from a novel nanocomposite UHMWPE material for total joint replacements2012Conference paper (Refereed)
  • 102.
    Namachivayam, Karthik
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Trindade, Bruno
    epartment of Mechanical Engineering, CEMMPRE, University of Coimbra, Coimbra 3030-788, Portugal.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Mechanochemical preparation of core-shell structured hydrophobic UHMWPE-onion-like carbon composites2022In: Journal of Molecular Structure, ISSN 0022-2860, E-ISSN 1872-8014, Vol. 1255, article id 132403Article in journal (Refereed)
    Abstract [en]

    Hydrophobic composites are prepared from Ultra High Molecular Weight Polyethylene (UHMWPE) and onion-like carbon (OLC), employing a solvent-free mechanochemical process consisting of milling at 250 rpm for 60 min. The encapsulation of OLC on the surface of UHMWPE microspheres increased with the increasing composition of OLC from 0.5 to 5 wt.%, thereby mimicking the core-shell structure. The consolidated composite with 5 wt.% of OLC exhibited a higher water contact angle (WCA) of about 111.18°, compared to pure UHMWPE (94.80°).

  • 103.
    Nikonovich, Maksim
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements. CEMMPRE, Department of Mechanical Engineering, University of Coimbra, Portugal.
    Costa, Joana F.S.
    CEMMPRE, Department of Chemical Engineering, University of Coimbra, Coimbra, Portugal.
    Fonseca, Ana C.
    CEMMPRE, Department of Chemical Engineering, University of Coimbra, Coimbra, Portugal.
    Ramalho, Amilcar
    CEMMPRE, Department of Mechanical Engineering, University of Coimbra, Portugal.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Structural, thermal, and mechanical characterisation of PEEK-based composites in cryogenic temperature2023In: Polymer testing, ISSN 0142-9418, E-ISSN 1873-2348, Vol. 125, article id 108139Article in journal (Refereed)
    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.

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  • 104.
    Nikonovich, Maksim
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements. CEMMPRE, Department of Mechanical Engineering, University of Coimbra, Portugal.
    Ramalho, Amilcar
    CEMMPRE, Department of Mechanical Engineering, University of Coimbra, Portugal.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Effect of cryogenic aging and test-environment on the tribological and mechanical properties of PEEK composites2024In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 194, article id 109554Article in journal (Refereed)
    Abstract [en]

    This study investigated mechanical and tribological properties of polyetheretherketone (PEEK) and PEEK composites, before and after aging in liquid nitrogen for 5 months. Tribological tests conducted at 25 °C and at − 100 °C in air and in high vacuum (10−5 Pa) environment revealed the effect of matrix modification, fillers, environment, temperature, and cryogenic aging on their performances. Cryogenic aging of the polymers resulted in cryogenic embrittlement and decrease of the fracture toughness by around 10% and increase of wear rate by at least 20%. Very low coefficient of friction (0.02) was achieved in cryogenic vacuum environment for carbon fiber, graphite, and PTFE reinforced PEEK. The results indicate the significant impact of aging, temperature and environment on PEEK and its composites.

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  • 105.
    Nunes, Stephanie
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements. Materials Engineering Department, Federal University of Rio Grande do Sul, Porto Alegre, Brazil; Institute of Mechanics and Mechanical Engineering, Riga Technical University, Riga, Latvia.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Fernberg, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Saseendran, Sibin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Department of Polymer Materials and Composites, Research Institutes of Sweden, Piteå, Sweden.
    Esposito, A.
    Normandie Univ, UNIROUEN, INSA Rouen, CNRS, Groupe de Physique des Matériaux, 76000 Rouen, France.
    Amico, S.C.
    Materials Engineering Department, Federal University of Rio Grande do Sul, Porto Alegre, Brazil.
    Varna, Janis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Physical aging effect on viscoelastic behavior of polymers2022In: Composites Part C: Open Access, ISSN 2666-6820, Vol. 7, article id 100223Article in journal (Refereed)
    Abstract [en]

    The effect of physical aging on the viscoelastic (VE) behavior of epoxy resin is investigated experimentally performing strain-controlled tests at various temperatures on specimens aged at different temperatures (TA) for different times (tA). The aging effect is analyzed using as a framework Schapery's type of thermo-aging-rheologically simple (T-A-R simple) VE model that contains aging-state and test-temperature dependent shift factor. Experiments show that in first approximation, the shift factor can be presented as the product of aging related shift factor aA and temperature related factor aT. It is found that for short aging times the change rate of the aging shift factor with tA does not depend on TA, whereas for long tA at high TA the rate increases. Shift factors alone are not able to explain differences in relaxation curves for almost “fully” aged specimens aged at different high TA, It is shown that a T-A-R complex VE model with two additional aging-dependent functions can describe the observed discrepancies.

  • 106.
    Palmeira Belotti, Luca
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Vadivel, Hari Shankar
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Tribological performance of hygrothermally aged UHMWPE hybrid composites2019In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 138, p. 150-156Article in journal (Refereed)
    Abstract [en]

    In this work, the effect of hygrothermal aging on friction and wear of water lubricated, Ultra High Molecular Weight Polyethylene (UHMWPE) hybrid composites were evaluated. Graphene Oxide (GO), Nano Diamonds (ND) and Short Carbon Fibers (SCF) were used as reinforcements as they previously exhibited promising improvements in the tribological behavior of UHMWPE in water-lubricated sliding contacts. Hygrothermal aging and pin-on-disc tribological experiments were performed to evaluate the response of the UHMWPE composites. It was observed that the friction and wear of the composites were not significantly affected by the aging conditions, which was attributed to the structural integrity of the newly developed UHMWPE based hybrid composites.

  • 107.
    Piya, Afrina Khan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements. School of Mechanical Engineering, University of Leeds, LS2 9JT, Leeds, UK.
    Yang, L.
    School of Mechanical Engineering, University of Leeds, LS2 9JT, Leeds, UK.
    Omar, A. Al Sheikh
    School of Mechanical Engineering, University of Leeds, LS2 9JT, Leeds, UK.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Morina, A.
    School of Mechanical Engineering, University of Leeds, LS2 9JT, Leeds, UK.
    Synergistic lubrication mechanism of nanodiamonds with organic friction modifier2024In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 218, article id 118742Article in journal (Refereed)
    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.

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  • 108.
    Pupure, Liva
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Al-Maqdasi, Zainab
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Gong, Guan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Effect of Nano-reinforcement on the Time-dependent Properties of Graphene Modified High Density PolyethyleneManuscript (preprint) (Other academic)
  • 109.
    Ramanenka, Dmitrij
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Enqvist, Evelina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Mechanical and thermal characterisation of novel UHMWPE-nano composite: A copmarrative study against virgin UHMWPE2013Conference paper (Refereed)
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  • 110.
    Rodiouchkina, Maria
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Berglund, Kim
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Dry sliding wear and friction behavior of self-lubricating polymer composite bearing materials under extreme operating conditions2017Conference paper (Refereed)
  • 111.
    Safari, Alaleh
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Cervantes, Michel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Bio-lubricant Behavior under Reciprocating Motion in Mini-Channel2016Conference paper (Refereed)
    Abstract [en]

    Synovial fluid (SF) is articular joint lubrication. It contains a linear biopolymer called Hyaluronic acid(HA), which causes the viscoelastic behavior. Several studies on viscoelasticity of synovial fluid orHA solutions with different concentration and molecular weight have been carried out withrheometers. However, there are very few studies on the effect of viscoelasticity on HA solutionsmovement and velocity distribution inside the joint gap. Therefore, in this study, HA solutions withdifferent concentrations were studied under a sinusoidal reciprocating movement inside a rectangularmini-channel. This study focuses on deriving velocity distribution along channel width with MicroParticle Image Velocimetry (micro-PIV). Very high viscosity of the HA solutions suggests a quasisteadybehavior for this solution under investigated sinusoidal movement. However, the resultsindicated that the steady state laws are not applicable for estimating the HA behavior because ofspecial polymeric behavior of the HA chains inside the solutions.

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  • 112.
    Safari, Alaleh
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Cervantes, Michel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Viscoelastic behaviour effect of hyaluronic acid on reciprocating flow inside mini-channel2016In: Lubrication Science, ISSN 0954-0075, E-ISSN 1557-6833, Vol. 28, no 8, p. 521-544Article in journal (Refereed)
    Abstract [en]

    One of the most successful surgeries during the 21st century is total joint replacement (TJR) with material combination of polymer-on-metal (PoM). Despite its success, wear particle generation at the interface of the polymer and metal causes eventually implant loosening. Investigating and understanding the wear particles distribution should help in designing implants with better performances. First step towards characterising wear particle distribution is deriving the lubricant behaviour and velocity distribution inside implant gap. Different hyaluronic acid (HA) solutions were subjected to a sinusoidal movement in straight rectangular channels. The velocity profiles along the channel width were measured with Micro Particle Image Velocimetry. HA solution behaviour was found to be dependent on the concentration. Results showed significant differences between the water (Newtonian) and HA behaviour in unsteady flow. The unsteady behaviour of the lubricant depended strongly on its non-Newtonian viscoelastic behaviour which was due to the time dependent nature of HA solution.

  • 113.
    Safari, Alaleh
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Cervantes, Michel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Bio-lubricant flow behaviour in mini-channels2016In: Lubrication Science, ISSN 0954-0075, E-ISSN 1557-6833, Vol. 28, no 4, p. 221-242Article in journal (Refereed)
    Abstract [en]

    One of the most common causes of failures in total joint replacements is the generation of wear particles within the joint. This contributes to bone lost and aseptic loosening of the implant, eventually requiring its replacement. Many studies have been carried out to improve the wear characteristics of bearing surfaces in total joint replacement. From the lubrication point of view, the friction behaviour of surfaces and rheology of the joint lubricant (synovial fluid) have been extensively studied. However, little attention has been paid to the interaction between the lubricant and the bearing surfaces. The aim of this study is to develop a methodology for studying the behaviour of bio-based lubricant in mini-channels. For this purpose, micro-particle image velocimetry was used in order to characterise the lubricant behaviour. Channels made of relevant materials such as ultra-high molecular weight polyethylene, cobalt–chromium–molybdenum alloy and titanium–aluminium–vanadium alloy with 1 and 1.5 mm width, 45 mm length and 2 mm depth were experimentally investigated. Results suggested that the used polymeric solution interaction with solid surfaces is very sensitive to the polymer concentration in the lubricant. Moreover, it was observed that there exist differences between water (Newtonian reference fluid) and the polymeric solution behaviour even at very simple movements; although usually, the properties of this lubricant at high shear rates are estimated by water properties.

  • 114.
    Safari, Alaleh
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Cervantes, Michel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Reciprocation Flow Behavior of Bio-Lubricant in Mini-Channels2015Conference paper (Refereed)
  • 115.
    Safari, Alaleh
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Cervantes, Michel Jose
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics. Water Power Laboratory , Norwegian University of Science and Technology .
    Viscoelasticity and shear-thinning effects on bio-polymer solution and suspended particle behaviours under oscillatory curve Couette flow conditions2018In: Biosurface and Biotribology, ISSN 2405-4518, Vol. 4, no 1, p. 1-17Article in journal (Refereed)
    Abstract [en]

    Formation of wear particles within total hip replacement is one of the main causes of its failure. In addition to improving the lubrication and wear resistance of materials used as bearing surfaces, understanding of wear particle distribution patterns within lubricants inside an implant gap could be used to improve design parameters and implants’ lifespan. In this study, the behaviours of biolubricants (with compositions similar to human joint synovial fluid) and suspended particles were investigated by micro-particle image velocimetry in curved mini channels under oscillatory Couette flow conditions. The studied biolubricants had shear-thinning viscoelastic characteristics. The authors found that increasing shear-thinning, elasticity or motion frequency levels did not affect the trend behaviours of biolubricant flows due to the low strain values of the experimental conditions applied. However, suspended particles formed strings along flow directions and exhibited cross-stream migration to channel walls. Motion frequency, fluid shear thinning and elasticity characteristics and channel dimensions strongly affected particle behaviours.

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  • 116.
    Safari, Alaleh
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Espanol, Montserrat
    Biomaterials, Biomechanics and Tissue Engineering Group, Department of Materials Science and Metallurgy, Technical University of Catalonia.
    Ginebra, Maria-Pau
    Biomaterials, Biomechanics and Tissue Engineering Group, Dept. of Materials Science and Metallurgy, Technical University of Catalonia.
    Cervantes, Michel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics. Water Power Laboratory, Norwegian University of Science and Technology.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Effect of dynamic loading versus static loading on the frictional behavior of a UHMWPE pin in artificial biolubricants2017In: Biosurface and Biotribology, ISSN 2405-4518, Vol. 3, no 1, p. 35-44Article in journal (Refereed)
    Abstract [en]

    To obtain reliable results from in vitro measurements on the tribological behavior of joint implant materials, the parameters of the measurements must simulate in vivo conditions. Although the nature of the load in human joints is dynamic, most of the studies using simple pin-on-disk tribometers were performed with a constant load. The current study focused on investigating the effect of dynamic loading in comparison with static loading in the tribological behavior of ultra-high-molecular-weight polyethylene (UHMWPE) sliding against a cobalt chromium molybdenum (CoCrMo) counter surface with different lubricants, where the effects of hyaluronic acid (HA) and protein content in the lubricants were also investigated. The results suggested that although the dynamic loading did not affect the friction evolution for any of the lubricants, the friction value decreased for the lubricants that did not contain HA. The results showed that higher protein content in the lubricant increased the friction coefficient, however, it provided the highest protection against wear for sliding surfaces.

  • 117.
    Safari, Alaleh
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Ginebra, Maria Pau
    Biomaterials, Biomechanics and Tissue Engineering Group, Department of Materials Science and Metallurgy, Technical University of Catalonia.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Cervantes, Michel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Studying Water Based Lubricant Behavior in Mini-Channel2014Conference paper (Refereed)
    Abstract [en]

    One of the most common causes of failures in total joint replacements is the generation of wear particles within the joint that leads to the micro separation at the implant-bone interface. This contributes to bone lost aseptic loosening of the implant, requiring eventually its replacement.Many studies have been carried out to improve the wear characteristics of bearing surfaces in total joint replacement (TJR). From lubrication point of view the friction behavior of surfaces and rheology of the joint lubricant (Synovial fluid) were extensively studied. However, not much attention was paid to the interaction between the lubricant and the bearing surfaces. The aim of this study is to develop a methodology for studying the behavior of water based lubricant in a micro-channel. For this purpose, Micro-PIV (Particle Image velocimetry) was used in order to characterize the lubricant behavior. Experimental models made of relevant materials such as ultra high molecular weight polyethylene, Cobalt-Chromium-Molybdenum alloy and Titanium-Aluminum-Vanadium alloy with 1 and 1.5 mm width, 45 mm length and 2 mm depth experimentally investigated.

  • 118.
    Saravanan, Prabakaran
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Sustainable tribology: Processing and characterization of multiscale thermoplastic composites within hydropower applications2021In: Tribology of Polymer Composites: Characterization, Properties, and Applications / [ed] Sanjay Mavinkere Rangappa, Suchart Siengchin, Jyotishkumar Parameswaranpillai, Klaus Friedrich, Elsevier, 2021, p. 241-277Chapter in book (Other academic)
    Abstract [en]

    This chapter presents an overview of the demanding conditions of sliding bearing applications within hydropower plants, where the use of novel complex multiscale thermoplastic polymer composites is desired to combat the friction and wear issues. The three unique challenges of this application originate from its extreme contact pressure during operation (~  30 MPa), the longevity of operation (~  40 years) as the maintenance is significantly costly and complicated, and particularly the realization of oil-free or water lubrication from a sustainability perspective.

    Green or sustainable tribology in hydropower applications is an emerging concept that emphasizes environmental adaptive lubrication (EAL) or fossil-fuel free lubrication with an improved or similar tribological performance. Polymers are the most promising materials for EAL lubrication compared to metal, as the corrosion becomes an important issue.

    Recent investigations of several commercial and in-house made high-performance thermoplastic based multiscale polymer composite materials to solve the tribological issues in hydropower applications are presented in this chapter. Furthermore, various pre- and posttribological characterizations, detailed multiscale composite manufacturing processes, an important results are also described in detail.

  • 119.
    Saravanan, Prabakaran
    et al.
    Department of Mechanical Engineering, BITS-Pilani, Hyderabad, Telangana, India.
    Melk, Latifa
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Mechanical and thermal properties of vitamin E-doped UHMWPE reinforced with hydroxyapatite2021In: Tribology - Materials, Surfaces & Interfaces, ISSN 1751-5831, E-ISSN 1751-584X, Vol. 15, no 3, p. 193-200Article in journal (Refereed)
    Abstract [en]

    The unique biocompatible and wear resistant nature of ultrahigh molecular weight polyethylene (UHMWPE) makes it a suitable material for load bearing applications in total joint replacements (TJR). However, oxidation induced wear is a common cause limiting the life span of implants. Hence, Vitamin-E, a common antioxidant, is added to prevent the wear loss due to oxidation of UHMWPE. In addition, Hydroxyapatite does improve the toughening mechanisms occurring in the polymer matrices. Hence, in this study, a novel hydroxyapatite (HA) nanoparticles reinforced Vitamin-E doped UHMWPE nanocomposites (UHMWPE-E/HA) were developed here in this work. The HA concentration was varied between 0.5 - 3 wt.% and optimum wt% is reported. The mechanical and thermal properties were investigated thoroughly using an array of characterizations. Particularly, a considerable improvement in fracture toughness (KIC) was obtained. Detailed examination of fractured surfaces was performed to understand the effect of HA reinforcement on fracture toughness of UHMWPE-E/HA nanocomposites.

  • 120.
    Sin, Jorge Rituerto
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hu, Xianming
    School of Mechanical Engineering, University of Leeds.
    Neville, Anne
    School of Mechanical Engineering, University of Leeds.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Tribology, Corrosion and Tribocorrosion of Metal on Metal Hip Implants: a review2013Conference paper (Refereed)
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  • 121.
    Sin, Jorge Rituerto
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hu, Xinming
    School of Mechanical Engineering, University of Leeds.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Tribology, corrosion and tribocorrosion of metal on metal implants2013In: Tribology - Materials, Surfaces & Interfaces, ISSN 1751-5831, E-ISSN 1751-584X, Vol. 7, no 1, p. 1-12Article in journal (Refereed)
    Abstract [en]

    Metal-on-metal joint replacements are considered as an alternative to metal-onpolyethylene implants, specially in case of young patients who require a safe and long-term performance of the device. The reduction of wear particles is a key factor in order to improve the life time of the implant in the human body. Metals have excellent properties that may increase the long-term success of the artificial joint replacement. However, corrosion of the metallic implant leads to an increase of the ion levels in the body of the patient. Metallic ions may produce a host response that can induce a catastrophic failure of the implant. This review initially focuses on the consequences that the degradation of the metals used in orthopaedic implants have for the health of the patient, and the different biological reactions that lead to the failure of the implant. Parameters that affect the release of particles and ions into the body are discussed as well. Special ttention is given to the tribology, corrosion and tribocorrosion behaviour of metal-on-metal implants. Finally, an overview of mathematical models that have been used to model the behaviour of the implants are also presented.

  • 122.
    Sin, Jorge Rituerto
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hu, Xinming
    Institute of Engineering Thermofluids, Surfaces and Interfaces, School of Mechanical Engineering, Universiy of Leeds.
    Neville, Anne
    Institute of Engineering Thermofluids, Surfaces and Interfaces, School of Mechanical Engineering, Universiy of Leeds.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Past, present and the future of metal on metal implants2011Conference paper (Refereed)
    Abstract [en]

    Metal on Metal joint replacements are considered as an alternative to Metal on Polyethylene implants, specially in case of young patients who require a safe and long-term performance of the device. The reduction of wear particles is a key factor in order to improve the life time of the implant in the human body. Metals have excellent properties that can increase the long-term success of the artificial joint replacement.However, corrosion of the metallic implant leads to an increase of the ion levels into the urine and blood of the patient. Metallic ions may produce a host response that can induce a catastrophic failure of the implant.The study of tribology and corrosion in biological environments (biotribocorrosion) will lead to a better understanding of the mechanisms that affect the degradation of the implant and the release of both particles and ions.The present paper reviews a number of medical results that show the increase of ions present in the body of patients. Different types of body response such as hypersensitivity and pseudotumours are also presented.The tribological performance of hip implants is explained as well as the corrosive behaviour of the most commonly used metallic materials. Biotribocorrosion studies are reviewed and the mechanisms of degradation of implants in biological environments are explained. Finally, some models of the performance of artificial joints are reported.

  • 123.
    Sin, Jorge Rituerto
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hu, Xinming
    School of Mechanical Engineering, University of Leeds.
    Neville, Anne
    School of Mechanical Engineering, University of Leeds.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Tribocorrosion behaviour of Hf in Simulated Body Fluids2013Conference paper (Refereed)
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    FULLTEXT01
  • 124.
    Sin, Jorge Rituerto
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hu, Xinming
    School of Mechanical Engineering, University of Leeds.
    Neville, Anne
    School of Mechanical Engineering, University of Leeds.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Tribology, Corrosion and Tribocorrosion of Metal on Metal Hip Implants2012Conference paper (Refereed)
    Download full text (pdf)
    FULLTEXT01
  • 125.
    Sin, Jorge Rituerto
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Neville, A.
    Institute of Engineering Thermofluids, Surfaces and Interfaces, School of Mechanical Engineering, Universiy of Leeds.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Corrosion and tribocorrosion of hafnium in simulated body fluids2014In: Journal of Biomedical Materials Research. Part B - Applied biomaterials, ISSN 1552-4973, E-ISSN 1552-4981, Vol. 102, no 6, p. 1157-1164Article in journal (Refereed)
    Abstract [en]

    Hafnium is a passive metal with good biocompatibility and osteogenesis, however, little is known about its resistance to wear and corrosion in biological environments. The corrosion and tribocorrosion behavior of hafnium and commercially pure (CP) titanium in simulated body fluids were investigated using electrochemical techniques. Cyclic polarization scans and open circuit potential measurements were performed in 0.9% NaCl solution and 25% bovine calf serum solution to assess the effect of organic species on the corrosion behavior of the metal. A pin-on-plate configuration tribometer and a three electrode electrochemical cell were integrated to investigate the tribocorrosion performance of the studied materials. The results showed that hafnium has good corrosion resistance. The corrosion density currents measured in its passive state were lower than those measured in the case of CP titanium; however, it showed a higher tendency to suffer from localized corrosion, which was more acute when imperfections were present on the surface. The electrochemical breakdown of the oxide layer was retarded in the presence of proteins. Tribocorrosion tests showed that hafnium has the ability to quickly repassivate after the oxide layer was damaged; however, it showed higher volumetric loss than CP titanium in equivalent wear-corrosion conditions

  • 126.
    Sin, Jorge Rituerto
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Neville, Anne
    Institute of Engineering Thermofluids, Surfaces and Interfaces, School of Mechanical Engineering, Universiy of Leeds.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Investigation of hafnium as a candidate for orthopaedic applications2014Conference paper (Refereed)
    Abstract [en]

    Hafnium has been suggested as an interesting candidate for orthopaedic applicationsdue to its good biocompatibility and osteogenesis. However, there is a need to further investigate its resistance to wear and corrosion in biological environments if hafnium is to be considered for such applications.The corrosion and tribocorrosion behaviour of hafnium and commercially pure titanium in simulated body fluids were investigated using electrochemical techniques. A ball-on- plate configuration tribometer and a three electrode electrochemical cell were integrated to investigate the tribocorrosion performance of the studied materials. In addition, the effect of micro-motions on the corrosion resistance of the material was also studied. Cyclic polarisation scans, open circuit potential measurements and potentiostatic tests were performed in 0.9% NaCl solution and 25% bovine calf serum solution in order to assess the effect of organic species on the corrosion behaviour of the metal.The results showed that hafnium has a good corrosion resistance due to its passive state in the studied solutions. A tendency to suffer from localised corrosion was observed, but the electrochemical breakdown of the oxide layer was retarded in the presence of proteins. However, the pit formation was enhanced due to the presence of surface imperfections and when the surface was subjected to micro-motions. Tribocorrosion tests showed that hafnium has the ability to quickly repassivate after the oxide layer was damaged; however, it showed higher volumetric loss than CP titanium in the studied wear-corrosion conditions.This study provides an insight into the potential of hafnium for orthopaedic applications.

  • 127.
    Sin, Jorge Rituerto
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Suñer, Silvia
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Neville, A.
    Institute of Engineering Thermofluids, Surfaces and Interfaces, School of Mechanical Engineering, University of Leeds, LS2 9JT Leeds, UK.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Fretting corrosion of Hafnium in Simulated Body Fluids2014In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 75, p. 10-15Article in journal (Refereed)
    Abstract [en]

    Hafnium has been suggested as an interesting material for biomedical applications due to its good biocompatibility and osteogenesis. However, its behaviour under fretting corrosion conditions, found in applications such as dental and joint implants, has not been studied in depth. A three-electrode electrochemical cell integrated with a ball-on-flat reciprocating tribometer was used to investigate the corrosion of hafnium and commercially pure (CP) titanium in simulated body fluids. An increased susceptibility to pitting corrosion was observed when hafnium was subjected to fretting. Open circuit potential measurements showed a more severe mechanical depassivation due to fretting in the case of CP titanium in comparison to hafnium. In addition, the anodic currents measured during potentiostatic tests were also higher for CP titanium.

  • 128.
    Somberg, Julian
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Gonçalves, Gil
    Aveiro University.
    Exploring surface-functionalized chemically expanded graphite as solid lubricant in UHMWPE compositesManuscript (preprint) (Other academic)
  • 129.
    Somberg, Julian
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Gonçalves, Gil
    Centre for Mechanical Technology and Automation (TEMA), University of Aveiro, Portugal; Intelligent Systems Associate Laboratory (LASI), Portugal.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Graphene oxide versus graphite and chemically expanded graphite as solid lubricant in ultrahigh molecular weight polyethylene composites2023In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 187, article id 108643Article in journal (Refereed)
    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.

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  • 130.
    Somberg, Julian
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Gonçalves, Gil
    Centre for Mechanical Technology and Automation (TEMA), University of Aveiro, Portugal.
    Sánchez, María Soria
    Institute of Material Science of Barcelona, Spain.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Chemically expanded graphite-based ultra-high molecular weight polyethylene nanocomposites with enhanced mechanical properties2022In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 224, article id 111304Article in journal (Refereed)
    Abstract [en]

    Chemically expanded graphite (CEG) has recently been identified as promising reinforcement for polymer composites with the ability for commercial up-scaling. In this work, silane and polydopamine functionalized CEG were successfully synthesized and employed to prepare ultra-high molecular weight polyethylene (UHMWPE) nanocomposites with an enhanced interfacial compatibility. Characterisation of the functionalized CEG indicated a significant oxygen reduction, which gave rise to a restoration of the graphitic structure. The polydopamine functionalized CEG showed an enhanced exfoliation and dispersion in organic solvents and the polymer matrix with respect to the non-modified CEG. The silane functionalized CEG provided a higher affinity towards the matrix with polymer chains covering the CEG sheets on the fracture surfaces. The addition of functionalized CEG enhanced the mechanical properties of the UHMWPE matrix with an increase in micro-hardness of up to 25% and storage modulus of up to 58%. Furthermore, the hydrophobicity of the composites was significantly enhanced with an increase in water contact angle from 98.6° for the pure polymer to 119° for 5 wt% silane functionalized CEG. Preliminary wear experiments indicated the potential of the composites for tribological applications with a decrease in wear rate of up to 99% under water lubricated conditions.

  • 131.
    Somberg, Julian
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Jain, Ayush
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Lagrama, Kimberly Rose
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    High Performance PPS Composites for Tribological Applications2019Conference paper (Refereed)
    Abstract [en]

    Polyphenylene Sulfide(PPS) is known to possess superior mechanical and chemical properties, making it a suitable polymer for application as bearing material. In the trend of replacing metallic bearing materials with polymeric based materials, PPS based composites have been prepared in an effort to enhance its mechanical and tribological properties. Results have previously shown significant improvements in friction and wear behaviour by the addition of carbon reinforcements in both micro and nano scale range, in the form of i.e. short carbon fibers (SCFs) and nano diamonds (NDs). Based on these results, novel composites were processed and consolidated using injection moulding in our lab. Furthermore, to reduce the polymer ́s brittleness and improve its self-lubricity, polytetrafluoroethylene (PTFE) was blended with PPS matrix in the second part of the project. To understand the fundamental wear mechanisms, different wt% of PTFE were blended with PPS (from 10% to 90%) using high speed dry blending method. In addition, SCFs, NDs were used as reinforcement in the PPS/PTFE blend. The surface and bulk properties of the newly prepared multiscale composites were investigated by several characterisation methods including contact angle measurements and dilatometry to determine the linear coefficient of thermal expansion. Wear and the coefficient of friction were measured by a pin on disk tribometer by emphasising on different contact pressures and lubrication conditions. Improvements were observed with the addition of different reinforcements with SCFs in particular. The friction coefficient was reduced by over 50% while the specific wear rate was lower by a factor in the region of 4*102. The PTFE provided a significant effect on the polymer matrix tribological behaviour (almost at all wt%) as wear and friction were reduced significantly with respect to virgin PPS. The surface and transfer film formation were characterised on both the pin and counter surfaces by means of Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) to determine the effect of the added reinforcements on the wear behaviour and transfer film formation.

  • 132.
    Somberg, Julian
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Rudnytskyj, André
    Andritz HYDRO GmbH.
    Berglund, Kim
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Ukonsaari, Jan
    Vattenfall R&D.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    The effect of lubrication on the tribological properties of polymer composites for high contact pressure hydropower bearingsManuscript (preprint) (Other academic)
  • 133.
    Somberg, Julian
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Saravanan, Prabakaran
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Vadivel, Hari Shankar
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Berglund, Kim
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements. Sustainalube AB, Sweden.
    Ukonsaari, Jan
    Vattenfall AB, R&D, Sweden.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Tribological characterisation of polymer composites for hydropower bearings: Experimentally developed versus commercial materials2021In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 162, article id 107101Article in journal (Refereed)
    Abstract [en]

    To mitigate the effects of downstream lubricant spillage from hydroelectric power plants, environmentally friendly lubricants are required. For the sustainable operation of oil-free bearings, the development of high performance bearing materials is crucial. In this study, the tribological performance of PPS and UHMWPE-based composites, incorporating various reinforcements, such as graphene oxide, is evaluated and compared with five commercial materials. Experiments were performed under different lubricating conditions; Dry, water, and using a glycerol-based environmentally adaptive lubricant (EAL). The use of water inhibited an adequate transfer film, which increased wear for most materials. EAL lubrication showed a significant reduction in friction (up to 98%) when compared to dry conditions. The experimentally developed PPS composite provided superior tribological properties, especially under water-lubricated conditions.

  • 134.
    Suñer, Silvia
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Bladen, Catherine L.
    Institute of Medical and Biological Engineering, Leeds, UK.
    Gowland, Nicholas
    Institute of Medical and Biological Engineering, Leeds, UK.
    Tipper, Joanne L.
    Institute of Medical and Biological Engineering, Leeds, UK.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Investigation of wear and wear Particles from a UHMWPE/multi-walled carbon nanotube nanocomposite for total joint replacements2014In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 317, no 1-2, p. 163-169Article in journal (Refereed)
    Abstract [en]

    Ultra high molecular weight polyethylene (UHMWPE) has been extensively used as a bearing surface in joint prostheses. However, wear debris generated from this material has been associated with osteolysis and implant loosening. Alternative materials, such as polymer composites, have been investigated due to their exceptional mechanical properties. The goal of the present work was to investigate the wear rate, size and volume distributions, bioactivity and biocompatibility of the wear debris generated from a UHMWPE/Multi-walled carbon nanotube (MWCNT) nanocomposite material compared with conventional UHMWPE. The results showed that the addition of MWCNTs led to a significant reduction in wear rate. Specific biological activity and functional biological activity predictions showed that wear particles from the UHMWPE/MWCNT nanocomposite had a reduced osteolytic potential compared to those produced from the conventional polyethylene. In addition, clinically relevant UHMWPE/MWCNT wear particles did not show any adverse effects on the L929 fibroblast cell viability at any of the concentrations tested over time. These findings suggest that UHMWPE/MWCNT nanocomposites represent an attractive alternative for orthopaedic applications.

  • 135.
    Suñer, Silvia
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Investigation of graphene oxide as reinforcement for orthopaedic applications2014In: Tribology - Materials, Surfaces & Interfaces, ISSN 1751-5831, E-ISSN 1751-584X, Vol. 8, no 1, p. 1-6Article in journal (Refereed)
    Abstract [en]

    Carbon based polymer composites have been suggested as an alternative to conventional ultra high molecular weight polyethylene (UHMWPE) in total joint replacements. The aim of this study was to investigate the use of graphene oxide (GO) as reinforcement of UHMWPE. Under optimised mixing conditions, the prepared UHMWPE/GO composite showed an enhanced thermal stability compared to conventional UHMWPE. Also, the present study has shown the potential of ball milling as a processing method for synthesising UHMWPE/GO composites to be used in load bearing implants.

  • 136.
    Suñer, Silvia
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Gowland, N.
    Institute of Medical and Biological Engineering, University of Leeds, UK.
    Craven, R.
    Institute of Medical and Biological Engineering, University of Leeds, UK.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Tipper, J.L.
    Institute of Medical and Biological Engineering, University of Leeds, UK.
    Ultrahigh molecular weight polyethylene/graphene oxide nanocomposites: Wear characterization and biological response to wear particles2018In: Journal of Biomedical Materials Research. Part B - Applied biomaterials, ISSN 1552-4973, E-ISSN 1552-4981, Vol. 106, no 1, p. 183-190Article in journal (Refereed)
    Abstract [en]

    In the field of total joint replacements, polymer nanocomposites are being investigated as alternatives to ultrahigh molecular weight polyethylene (UHMWPE) for acetabular cup bearings. The objective of this study was to investigate the wear performance and biocompatibility of UHMWPE/graphene oxide (GO) nanocomposites. This study revealed that low concentrations of GO nanoparticles (0.5 wt %) do not significantly alter the wear performance of UHMWPE. In contrast, the addition of higher concentrations (2 wt %) led to a significant reduction in wear. In terms of biocompatibility, UHMWPE/GO wear particles did not show any adverse effects on L929 fibroblast and PBMNC viability at any of the concentrations tested over time. Moreover, the addition of GO to a UHMWPE matrix did not significantly affect the inflammatory response to wear particles. Further work is required to optimize the manufacturing processes to improve the mechanical properties of the nanocomposites and additional biocompatibility testing should be performed to understand the potential clinical application of these materials

  • 137.
    Suñer, Silvia
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Tipper, Joanne L.
    Institute of Medical and Biological Engineering, Leeds, UK.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Ultra high molecular weight polyethylene/graphene oxide nanocomposites: Thermal, mechanical and wettability characterisation2015In: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 78, p. 185-191Article in journal (Refereed)
    Abstract [en]

    Numerous carbon nanostructures have been investigated in the last years due to their excellent mechanical properties. In this work, the effect of the addition of graphene oxide (GO) nanoparticles to UHMWPE and the optimal %wt GO addition were investigated. UHMWPE/GO nanocomposites with different GO wt% contents were prepared and their mechanical, thermal, structural and wettability properties were investigated and compared with virgin UHMWPE. The results showed that the thermal stability, oxidative resistance, mechanical properties and wettability properties of UHMWPE were enhanced due to the addition of GO. UHMWPE/GO materials prepared with up to 0.5 wt% GO exhibited improved characteristics compared to virgin UHMWPE and nanocomposites prepared with higher GO contents.

  • 138.
    Suñer, Silvia
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Tipper, Joanne
    Institute of Medical and Biological Engineering, Faculty of Biological Sciences, University of Leeds, Leeds, UK.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Biological effects of wear particles generated in total joint replacements: trends and future prospects2012In: Tribology - Materials, Surfaces & Interfaces, ISSN 1751-5831, E-ISSN 1751-584X, Vol. 6, no 2, p. 39-52Article, review/survey (Refereed)
    Abstract [en]

    Joint replacements have considerably improved the quality of life of patients with joints damaged by disease or trauma. However, problems associated with wear particles generated due to the relative motion between the components of the bearing are still present and can lead to the eventual failure of the implant. The biological response to wear debris affects directly the longevity of the prosthesis. The identification of the mechanisms by which cells respond to wear debris and how particles distribute into the human body may provide valuable information for the long term success of artificial joints. During the last few decades, orthopaedic research has been focused on predicting the in vivo performance of joint replacements. However, the exact relationship between material physicochemical properties and inflammatory response has not been fully understood. Laboratory wear simulators provide an accurate prediction of implant wear performance. Though, particles generated from such wear simulators require validation to compare them with particles extracted from peri-implant tissues. This review focuses initially on the current status of total joint replacements (hard on soft and hard on hard bearings) as well as on the tribological behaviour of the potential materials currently under investigation. Then, the correspondence between particles observed in vivo and those generated in vitro to predict the cellular response to wear debris is discussed. Finally, the biological effects of the degradation products generated by wear and corrosion are described

  • 139.
    Vadivel, Hari
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Golchin, Arash
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Tribological behaviour of carbon filled hybrid UHMWPE composites in water2018In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 124, p. 169-177Article in journal (Refereed)
    Abstract [en]

    In this study, newly developed hybrid composites with Ultra High Molecular Weight Polyethylene (UHMWPE) as base polymer and Graphene Oxide (GO), Nano Diamonds (ND) and Short Carbon Fibres (SCF) as fillers were manufactured. The tribological performance of these composites in a water lubricated sliding contact and the effect of inclusion of the fillers on the mechanical and thermal properties of the composites were investigated. The resulting hybrid composite formed by using the fillers and the base polymer displayed low friction coefficient and high wear resistance. Compared to unfilled UHMWPE, composite with all the fillers incorporated had 21% smaller friction coefficient and 15% less wear.

  • 140.
    Vadivel, Hari Shankar
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Al-Maqdasi, Zainab
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Pupure, Liva
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Institue of Structural Engineering and Reconstruction, Riga Technical University, LV 1658, Riga, Latvia.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Kalin, Mitjan
    Laboratory for tribology and interface nanotechnology, University of Ljubljana, 1000, Ljubljana, Slovenia.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Time-dependent properties of newly developed multiscale UHMWPE composites2022In: Polymer testing, ISSN 0142-9418, E-ISSN 1873-2348, Vol. 105, article id 107400Article in journal (Refereed)
    Abstract [en]

    Ultra-high molecular-weight polyethylene (UHMWPE) composites reinforced with Graphene Oxide (GO), Nanodiamonds (ND), and Short Carbon Fibres (SCF) are characterised for their mechanical performance in tensile and short-term creep tests. A methodology to separate and analyse the materials’ viscoelastic (VE) and viscoplastic (VP) responses is applied and evaluated. The results show a clear dependence of the performance on size scale/morphology of the reinforcements. All composites show time-dependent VP responses that can be expressed by Zapas model and fit the experimental data with high accuracy. The analysed VE strains and creep compliance curves reveal the nonlinear stress-dependent VE behaviour of all composites at all tested creep stresses. Combining multiscale reinforcements results in an improvement that surpasses that of individual reinforcements. The results of this work offer valuable input for the design and selection of polymer-based materials in demanding applications where prolonged use under service conditions is critical to their performance.

  • 141.
    Vadivel, Hari Shankar
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements. University of Ljubljana, 1000, Ljubljana, Slovenia.
    Bek, Marko
    University of Ljubljana, 1000, Ljubljana, Slovenia.
    Šebenik, Urška
    University of Ljubljana, 1000, Ljubljana, Slovenia.
    Slemenik Perše, Lidija
    University of Ljubljana, 1000, Ljubljana, Slovenia.
    Kádár, Roland
    Chalmers University of Technology, 41296, Sweden.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Kalin, Mitjan
    University of Ljubljana, 1000, Ljubljana, Slovenia.
    Do the particle size, molecular weight, and processing of UHMWPE affect its thermomechanical and tribological performance?2021In: Journal of Materials Research and Technology, ISSN 2238-7854, Vol. 12, p. 1728-1737Article in journal (Refereed)
    Abstract [en]

    UHMWPE has exhibited excellent performance when used as contact surfaces in tribological contacts. Traditionally, only UHMWPE grades, with narrow particle size and molecular weight distribution, have been deemed suitable for such applications. Now, various UHMWPE grades are available that are different from each other based on their particle size and molecular weight distribution. The question of whether the particle size of UHMWPE affects its performance and properties presents a research gap. The present study attempts to address this question. Additionally, the effect of processing of the UHMWPE is studied. It is observed that although minor differences were observed in the properties of the various grades of UHMWPE, they are inadequate to conclusively determine that the particle size and processing effect the properties and performance of the material.

  • 142.
    Vadivel, Hari Shankar
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements. Laboratory for Tribology and Interface Nanotechnology, University of Ljubljana, Ljubljana, 1000 Slovenia.
    Somberg, Julian
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Kalin, Mitjan
    Laboratory for Tribology and Interface Nanotechnology University of Ljubljana Ljubljana 1000 Slovenia.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Tribological performance of a UHMWPE-based multiscale composite under different lubrication and loads2022In: Lubrication Science, ISSN 0954-0075, E-ISSN 1557-6833, Vol. 34, no 7, p. 480-492Article in journal (Refereed)
    Abstract [en]

    An UHMWPE-based multiscale composite containing graphene oxide, nanodiamonds, and short carbon fibres has shown excellent performance under distilled water lubrication. However, it is crucial to evaluate its tribological performance under conditions which more accurately represent the final application. In this study, the tribological performance of the developed UHMWPE-based multiscale composite is evaluated and compared with neat UHMWPE under different lubricating conditions: no lubricant (dry), in seawater (SW) and in an environmentally acceptable lubricant (EAL). While neat UHMWPE displays a lower friction and wear in dry conditions, the multiscale composite performs better under SW and EAL lubrication. A maximum reduction in friction coefficient of 77% and specific wear rate of 88% are obtained in SW. Under EAL lubricated conditions, the multiscale composite has a maximum reduction in specific wear rate of up to 75%. 

  • 143.
    Ventura, Alejandra M.
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Kneissl, Lucas M.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Nunes, Stephanie
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Recycled carbon fibers as an alternative reinforcement in UHMWPE composite. Circular economy within polymer tribology2022In: Sustainable Materials and Technologies, ISSN 2214-9937, Vol. 34, article id e00510Article in journal (Refereed)
    Abstract [en]

    The increasing demand of carbon fiber reinforced polymers over the last few decades has brought attention to critical aspects such as disposal, environmental impact, and cost of production. Therefore, adopting a circular economy approach focused on improving efficiency is an enticing alternative nowadays. This investigation is focused on the mechanical and tribological characterization of ultra high molecular weight polyethylene (UHMWPE) composites reinforced with virgin (vCF) and recycled carbon fibers (rCF) under water lubricated conditions. An improvement of 208% in Young's modulus, 105% in ultimate tensile strength and 146% in hardness for the samples with 30%wt rCF, compared to pure UHMWPE, was observed. Reductions of up to 62% in coefficient of friction and 32% in wear rates for 10 wt% CF composites were obtained, facilitated through the formation of a transfer film, which was present on the countersurfaces. The results of this project show that the composites containing recycled fibers exhibit a comparable performance to their virgin counterparts. An economical evaluation estimated possible monetary savings of 910.2 M€ in a time span from 2022 to 2026 by using rCF in composite production, providing arguments for the use of rCF reducing the environmental impact and cost without compromising performance.

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