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  • 101.
    Hultqvist, Tobias
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Vrček, Aleks
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Marklund, Pär
    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.
    Influence of lubricant pressure response on sub-surface stress in elastohydrodynamically lubricated finite line contacts2019In: Journal of tribology, ISSN 0742-4787, E-ISSN 1528-8897, Vol. 141, no 3, article id 031502Article in journal (Refereed)
    Abstract [en]

    In order to adapt to increasingly stringent CO2 regulations, the automotive industry must develop and evaluate low cost, low emission solutions in the powertrain technology. This often implies increased power density and the use of low viscosity oils, leading to additional challenges related to the durability of various machine elements. Therefore, an increased understanding of lubricated contacts becomes important where oil viscosity-pressure and compressibility-pressure behaviour have been shown to influence the film thickness and pressure distribution in EHL contacts, further influencing the durability. In this work, a finite line EHL contact is analysed with focus on the oil compressibility- and viscositypressure response, comparing two oils with relatively different behaviour and its influence on subsurface stress concentrations in the contacting bodies. Results indicate that increased pressure gradients and pressure spikes, and therefore increased localized stress concentrations, can be expected for stiffer, less compressible oils, which under transient loading conditions not only affect the outlet but also the edges of the roller

  • 102. Innings, Fredrik
    et al.
    Hultman, Erik
    Forsberg, Fredrik
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Understanding and analysis of wear in homogenizers for processing liquid food2011In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 271, no 9-10, p. 2588-2598Article in journal (Refereed)
    Abstract [en]

    The tribological research pertaining to homogenizers in processing liquid food has received much less attention compared to its potential in enhancing the efficiency and durability of the homogenization process equipment. Homogenization is a process used to disrupt fat globules in dairy products to reduce the formation of creamy layer (separation) and also to enhance the viscosity of certain products. This process takes place in a narrow gap in the homogenizer machine and this region is highly prone to wear. The occurrence of wear during processing not only impairs the homogenization effect but also leads to increased downtime of the machine. The aim of this work is to understand the occurrence of wear and wear mechanisms in the homogenization gap using both experimental and analytical approaches. Two experimental test rigs were used to study the differences in wear during operation, i.e. with and without particles. The trajectories of the particles have been simulated without the influence of cavitation using a CFD-code to investigate whether the particles are the cause of wear. The homogenizer gap has been simulated for a worn geometry to see how the occurrence of wear changes the particles trajectories. The results have shown that the presence of particles accelerates wear and most important parameters are the particle hardness and mass. When cavitation and particles are combined they create a synergistic effect on wear. This can be explained by the fact that cavitation can accelerate particles in random directions through the imploding action of cavities. A change in impact angle and increased velocity increases the amount of wear significantly. CFD-simulations and calculations show that the particles do not fully follow the streamlines and therefore create wear on the gap surfaces.

  • 103.
    Isokane, Mariko
    et al.
    Department of Mechanical Engineering, Graduate School of Tokyo University of Science.
    Tadokoro, Chiharu
    Department of Mechanical Engineering, Saitama University.
    Sasaki, Shinya
    Department of Mechanical Engineering, Tokyo University of Science.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Influence of ink composition on tribological properties of ballpoint pen2017In: Tribology online, ISSN 1881-218X, Vol. 12, no 5, p. 257-261Article in journal (Refereed)
    Abstract [en]

    In this work, the influence of ink composition on the tribological properties of ballpoint pens has been examined with a view to improve writing smoothness and pen lifetime. Friction experiments were performed using a ball on plate tribometer in order to simulate the sliding contact of a ballpoint pen. Ballpoint pen ink is composed of various solvents, resins, friction modifiers, colorants. To determine the basic tribological properties of ballpoint pen ink, this study focuses on the investigating the influence of different ink compositions: solvents, resins, and phosphate on the tribological behavior. The worn surfaces of specimens from tribological tests using different ink compositions were analyzed by using Fourier-transform infrared spectroscopi. Tribological tests were performed on eight different lubricant compositions including: i) the solvents without additives ii) the solvents with the resins and iii) the solvents with the friction modifiers. The results showed that for Oil A the tribological properties were affected by the molecular weight of the resin and the addition of phosphate reduced the coefficients of friction. Similar results were not observed for Oil B. In addition, it was found that the ratio of the components of the base oil affects the tribological properties of ballpoint pen ink

  • 104.
    Johansson, Jens
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Devlin, Mark
    Afton Chemical Corporation, Richmond, VA.
    Guevremont, Jeffrey
    Afton Chemical Corporation, Richmond, VA.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Investigations into the pitting behaviour of different gear lubricants by using a rolling four ball test configuration2011Conference paper (Refereed)
    Abstract [en]

    Vehicle manufacturers today face increasing demands to produce fuel efficient vehicles. If this is to be successfully achieved, the reduction of energy losses is vital [1]. One approach to loss reduction is to use lower viscosity trans mission fluids to reduce splash (churning) losses in the drive-train. However, this introduces potential problems in regard to the durability of machine components due to reduction in oil film thickness [2 ]. As regards gear transmission, the durability is mainly related to the formation of micropits on parts of gears where sliding is high, which later lead to pitting damage. The formation of micropits is due to surface stress which can be reduced by fluids that form thick EHD films or reduce sliding friction. In order to determine if these same lubricant properties as well as other parameters, known to influence the fuel efficiency of axle lubricants, also affect contact fatigue damage in rolling contacts, an extensive experimental study using a rolling four ball test was performed. The tests were performed with a series of fluids that form thin and thick EHD films and have low and high sliding friction. Additionally, these fluids have been formulated to hav e high and low hydrodynamic friction. All these fluids contai ned additive packages that meet the API GL-5 gear oil specifications. The different properties of the lubricating fluids were controlled by changes to the base oils as well as addition of friction modifiers. The results have shown that it is possible do distinguish the pitting properties of the different lubricants by using rolling four ball tests. A multiple linear regression statistical analysis was performed with the use of Matlab for evaluating the results obtained from rolling four ball tests. The statistical model developed, showed that some of the physical properties of fluids that a ffect fuel efficiency have an impact on pitting performance of the lubricants. The ball test specimens from rolling four ball tests have been analyzed by using SEM/ EDS and XPS in order to characterize the tribochemical films and understand the damage mechanisms.

  • 105.
    Johansson, Jens
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Devlin, Mark T.
    Afton Chemical Corporation, Richmond, VA.
    Guevremont, Jeffrey M.
    Afton Chemical Corporation, Richmond, VA.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Effects of gear oil properties on pitting life in rolling four-ball test configuration2013In: Tribology Transactions, ISSN 1040-2004, E-ISSN 1547-397X, Vol. 57, no 1, p. 104-113Article in journal (Refereed)
    Abstract [en]

    There is a connection between the efficiency of oils and their wear and/or surface damage protective properties, an area not so well described in the literature. One such damage mode is macroscale contact fatigue on gear tooth flank surfaces, also called pitting. The present study is aimed at investigating the correlation between gear oils' physical properties, important in terms of gear transmission losses, and pitting life. Eight gear oils were formulated giving different combinations of base oil, viscosity, and concentration of friction modifiers. All eight oils also contained an additive package designed to meet GL-5 specifications. This study consists of three parts. In the first, the oils' physical properties were measured using a set of bench tests. In the second, the pitting lives of the oils were evaluated using rolling four-ball tests. The third part deals with the correlation between the measured physical properties of the oils and their pitting lives. This is achieved through multiple linear regression, with a view to finding the salient properties that have a significant influence on pitting life. The results show that gear oils' physical properties do have a large influence on the pitting lives. Oil properties that lower interfacial tangential stresses are beneficial in enhancing pitting life.

  • 106.
    Johansson, Jens
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Devlin, Mark T.
    Fundamental Research, Afton Chemical Corporation, Richmond, VA, USA.
    Guevremont, Jeffrey M.
    Fundamental Research, Afton Chemical Corporation, Richmond, VA, USA.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Improving Hypoid Gear Oil Pitting Performance through Friction Reduction2019In: Tribology Transactions, ISSN 1040-2004, E-ISSN 1547-397XArticle in journal (Refereed)
    Abstract [en]

    Earlier studies have shown that the load-dependent friction behavior of various gear oils can affect their pitting performance; that is, low friction resulted in a long pitting life. These studies were limited, however, to test methods and running conditions quite different from those occurring in actual gear transmissions. In the present study, a more gear-like twin-disc machine with test specimens and running conditions relevant for gear contacts was used to investigate whether the same trends could be found. To analyze this possible correlation, the first step was to prepare a set of hypoid gear oils and to test their friction performance to compare various ways of improving friction behavior but also to form an understanding of why their friction performance varied. The second step was to test the pitting performance of the oils. The pitting results could then be compared to the friction properties of the oils to analyze the correlation. Other possible mechanisms behind the formation of pits are also discussed. The results show that for the oils included, the antiwear and extreme-pressure additive package and the base oil type affect friction. The results further show that additive combinations and/or base oils that result in low friction lead to enhanced pitting performance.

  • 107.
    Johansson, Jens
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Devlin, Mark T.
    Afton Chemical Corporation, Richmond, VA.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Lubricant additives for improved pitting performance through a reduction of thin-film friction2014In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 80, p. 122-130Article in journal (Refereed)
    Abstract [en]

    This paper describes an investigation into possibilities of enhancement of pitting lives of rolling components by using additive combinations with low thin-film friction. Various viscosity index improvers, anti-wear and extreme-pressure additive combinations were analysed in terms of their frictional behaviour, which in turn was compared to the oils pitting lives. For the pitting studies, a rolling four-ball test was employed. Friction was measured using a ball on disc machine as well as indirectly through “near contact” temperature measurements performed during rolling four-ball tests. The results show that additive combinations that result in low friction at the specific running condition can enhance pitting performance

  • 108.
    Johansson, Jens
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Devlin, M.T.
    Afton Chemical Corporation, Richmond, VA.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Additive technology for improved pitting performande of mineral gear oils2014Conference paper (Refereed)
  • 109.
    Johansson, Jens
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Devlin, M.T.
    Afton Chemical Corporation, Richmond, VA.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Investigations into the occurrence of pitting in lubricated rolling four-ball tests2015In: Lubrication Science, ISSN 0954-0075, E-ISSN 1557-6833, Vol. 27, no 2, p. 103-126Article in journal (Refereed)
    Abstract [en]

    Pitting, a form of rolling contact fatigue, is a complex phenomenon and several factors influence its occurrence, particularly under lubricated conditions. In this work, studies have been conducted to observe the events that occur during lubricated rolling four-ball tests that may affect or eventually lead to the formation of pits. This is performed to form an understanding of the pit formation process. Included is tribofilm formation, surface degradation, wear mode, material changes and crack initiation sites. These investigations have been performed on the ball samples from rolling four-ball tests, conducted using two API GL-5 gear oils. The analyses revealed the formation of a low hardness region beneath the surface of the running track due to martensite decay. The formation rate and expansion of this region was found to differ for the two lubricating oils. The pitted balls also indicated that the initial fatigue cracks were initiated at or close to the surface

  • 110.
    Johansson, Jens
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Devlin, M.T.
    Afton Chemical Corporation, Richmond, VA.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Pit formation mechanisms in lubricated rolling four-ball tests2012In: 15th Nordic Symposium on Tribology - NordTrib 2012: 12 - 15 June 2012 - Trondheim, Norway, Trondheim: Department of Geography, Norwegian University of Science and Technology, 2012Conference paper (Refereed)
    Abstract [en]

    Pitting due to rolling contact fatigue is a complex phenomenon and several factors influence its occurrence, particularly under lubricated conditions. A deeper understanding of pit formation mechanisms is needed in order to effectively evaluate the pitting behaviour of different lubricants. The present work focuses on investigating the events that lead to pit formation in the lubricated rolling four -ball test by analysing surface degradation, wear mode, material changes and crack initiation sites etc. These investigations have been conducted using two API - GL5 gear oils. These analyses of pitted balls revealed the formation of a low hardness region beneath the surface of the rolling track due to martensite decay. The formation rate and expans ion of this region was found to differ for the two lubricating oils. Examination of the pitted ball has also indicated that the initial rolling contact fatigue cracks were initiated at or close to the surface.

  • 111.
    Kankanala, Anusha
    et al.
    Luleå tekniska universitet.
    Leiro, Alejandro
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Vuorinen, Esa
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    The tribological behaviour under rolling/sliding conditions of carbide-free bainitic steel austempered at different temperatures2010In: 14th Nordic Symposium on Tribology: NORDTRIB 2010 : Storforsen, Sweden, June 8-11, 2010, Luleå: Luleå tekniska universitet, 2010Conference paper (Refereed)
    Abstract [en]

    The dry rolling/sliding wear behaviour of Si alloyed carbide free bainitic steel austempered at different temperatures and sliding distances has been evaluated. Three different batches of samples were austempered in a salt bath maintained at 250, 300 and 350 °C respectively for 1h. Rolling with 5% sliding wear tests were performed with each batch of samples for different test cycles, namely 6000, 18000 and 30000 cycles respectively, in order to study the wear performance of these specific steels. An in-depth microstructural characterization has been carried out before and after the wear tests in order to link the wear behaviour to the microstructure of each sample. The wear resistance has been expressed by means of the specific wear calculated from the mass loss after the tests. The worn surfaces were analyzed by the scanning electron microscopy and X-ray diffraction techniques. Micro-hardness profiles were also obtained to analyze strainhardening effects beneath the contact surfaces. The results indicate that the harder material exhibited overall lower wear rates for all test cycles studied i.e., the one austempered at 250°C showed superior rolling/sliding wear resistance than the rest. It is also interesting to note that the hardness increment and thickness of the hardened layer increases with increasing the austempering temperature and number of test cycles.Furthermore the results appear to indicate that the initial roughness of the samples has no major effect on the outcome of the results. The higher wear performance of the sample austempered at 250°C has been attributed to its superior mechanical properties provided by its finer microstructure. It has been evidenced that all samples suffer the TRIP phenomenon since, after wear, no retained austenite could be detected by XRD.

  • 112.
    Kassfeldt, Elisabet
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Lundmark, Jonas
    Prakash, Braham
    Sundgren, Anders
    Gleim AB.
    Wear properties of hardened high strength boron steel for rail cover2007In: High tech in heavy haul: Proceedings. International Heavy Haul Conference / [ed] Thomas Nordmark; Per-Olof Larsson-Kråik, Luleå: Luleå tekniska universitet, 2007, p. 539-546Conference paper (Refereed)
  • 113.
    Kawada, Shouhei
    et al.
    Graduate School of Tokyo University of Science, Tokyo, Japan.
    Watanabe, Seiya
    Graduate School of Tokyo University of Science, Tokyo, Japan.
    Tsuboi, Ryo
    Daido University, Nagoya, Japan.
    Sasaki, Shinya
    Tokyo University of Science, Tokyo, Japan.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Lubrication mechanism of halogen-free ionic liquids2017In: Tribology Online, ISSN 1881-2198, Vol. 12, no 4, p. 155-161Article in journal (Refereed)
    Abstract [en]

    Ionic liquids have potential for use as novel high-performance lubricants because of their attractive characteristics such as low volatility, high-thermal stability, and oxidation stability. It is known that ionic liquids exhibit excellent lubricity for metals because of halogen constituents in their molecular structure. However, occurrence of corrosive damage on the contacting surfaces lubricated with the ionic liquids has also been reported. To prevent damage due to corrosion, it is necessary to use halogen-free ionic liquids whose lubricity may be inferior compared with that of halogen-containing ionic liquids. In this study, the lubricity of halogen-free ionic liquids 1-butyl-3-methylimidazolium dicyanamide ([BMIM][DCN]) and 1-butyl-3-methylimidazolium tricyanomethane ([BMIM][TCC]) was evaluated by using a reciprocating sliding friction and wear tester (SRV Optimol)) using an oscillating steel cylinder on H-free DLC disk test configuration under boundary lubrication conditions. The SRV test results showed that H-free DLC with [BMIM][TCC] at 50N exhibited superior lubricity than that with [BMIM][DCN] at the same load. In order to understand the observed, the worn surfaces of test specimens were analyzed by using Raman spectroscopy, the friction coefficient of the film by atomic force microscopy (AFM), and the chemical composition by time of flight secondary ion mass spectrometry (TOF-SIMS). From Raman spectroscopic analysis results, graphitization of the transfer films of both [BMIM][DCN] and [BMIM][TCC] did not occur. From AFM results, the topography of [BMIM][TCC] was smooth as compared with that of [BMIM][DCN]. Thus, it was considered that the surface roughness affected the lubricity. In addition, the tribofilm derived from [BMIM][TCC] also affected the lubricity because it showed low friction coefficient on the flat position. From ToF-SIMS results, it was considered that [BMIM][DCN] itself adsorbed on H-free DLC surface. On the other hand, [BMIM][TCC] is thermally decomposed by friction and generated isolated CN and covering the H-free DLC surface. The tribofilm formed by [BMIM][TCC] exhibited lower friction coefficient than that by [BMIM][DCN].

  • 114.
    Kohli, A. K.
    et al.
    Bhabha Atomic Research Centre, Trombay, Mumbai.
    Prakash, Braham
    Contact pressure dependency in frictional behaviour of burnished molybdenum disulphide coatings2001In: Tribology Transactions, ISSN 1040-2004, E-ISSN 1547-397X, Vol. 44, no 1, p. 147-151Article in journal (Refereed)
    Abstract [en]

    The drop of coefficient of friction of MoS2 coatings with increase in contact pressure has been reported by various earlier researchers. Different hypothesis have been put forward to explain this phenomenon. This paper covers details of experiments carried out to investigate this further. Experiments have been carried out on reciprocating sliding wear and friction machine to bring out the influence of different parameters on the tribological behavior of MoS2 films. Role of frictional heating in this behavior has also been brought out. It is concluded that frictional properties of MoS2 are dependent on prevalent humidity as well as contact pressure and the drop of μ with contact pressure is independent of frictional heating.

  • 115.
    Kohli, A. K.
    et al.
    Board of Radiation and Isotope Technology, Mumbai.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Frictional behaviour of graphite in dry and water submerged sliding conditions2005In: Book of Abstracts: International Tribology Conference KOBE / [ed] N. Ohmae; H. Ishigaki, Tokyo: Japan Society of Tribologists , 2005, p. 169-Conference paper (Other academic)
  • 116.
    Kohli, A. K.
    et al.
    Bhabha Atomic Research Centre, Trombay, Mumbai.
    Prakash, Braham
    Tribological performance of molybdenum disulphide films1998In: Journal of Tribology India Limited, Vol. 3, no 1, p. 13-17Article in journal (Refereed)
  • 117.
    Kohli, A. K.
    et al.
    Bhabha Atomic Research Centre, Trombay, Mumbai.
    Prakash, Braham
    Tribological performance of molybdenum disulphide films1998In: Advances in Industrial Tribology / [ed] J. Bhatia, New Dehli: Tata McGraw Hill , 1998, p. 88-99Conference paper (Refereed)
  • 118.
    Kumar, R.
    et al.
    Indian Institute of Technology, New Delhi.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Sethuramiah, A.
    Indian Institute of Technology, New Delhi.
    Running-in and steady state wear studies on cast iron cylinder liner2002Conference paper (Refereed)
  • 119.
    Kumar, Rajesh
    et al.
    Indian Institute of Technology, New Delhi.
    Kumar, Salil
    Eicher Tractor Engineering Centre, Ballabgarh.
    Prakash, Braham
    Sethuramiah, A.
    Indian Institute of Technology, New Delhi.
    Assessment of engine liner wear from bearing area curves2000In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 239, no 2, p. 282-286Article in journal (Refereed)
    Abstract [en]

    This paper proposes a new procedure to evaluate engine liner wear volume and wear depth particularly for short duration engine tests. The method is based on the fact that honing depth is not removed when small amount of wear occurs. It was considered that 90% point of the bearing area curve is the same before and after wear. Then, the bearing area curve for the used liner was transformed by the depth differences at 90% and the area between the two curves was calculated by numerical procedure. As the diameter of the liner is known, the wear volume was calculated for the various zones selected at different points from TDC and BDC. The methodology involved has been programmed in C++. The wear depth is obtained by the projection on the depth axis of the two bearing area curves, and then finding their difference. This method is considered superior to the usual method of gauging the changes in diameter as such determinations are influenced by the distortions that occur in the liner. The new procedure needs to be applied more extensively to improve confidence in repeatability and reproducibility and to determine the limits of applicability. Controlled laboratory wear tests and further measurements on cylinders from field engines are therefore proposed.

  • 120.
    Kumar, Rajesh
    et al.
    Institute of Technology, BHU.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Sethuramiah, A
    A methodology to estimate the wear coefficient of engine liner under lubricated conditions2006In: International Conference on Industrial Tribology - ICIT 2006: Bangalore, 30 Nov. - 2 Dec. 2006, Bangalore: Indian Institute of Science, Department of Mechanical Engineering , 2006, p. 109-113Conference paper (Refereed)
  • 121.
    Kumar, Rajesh
    et al.
    Indian Institute of Technology, New Delhi.
    Prakash, Braham
    Sethuramiah, A.
    Indian Institute of Technology, New Delhi.
    A systematic methodology to characterise the running-in and steady-state wear processes2002In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 252, no 5-6, p. 445-453Article in journal (Refereed)
    Abstract [en]

    An improved methodology has been developed to characterise running-in and steady-state wear processes. The experimental study was conducted with En 31 steel specimens on reciprocating tester with ball-on-flat geometry under lubricated sliding conditions. The tests were conducted according to a factorial design. The variables selected were the load, temperature and surface roughness. The wear behaviour for a given set of operating conditions has been characterised on the basis of developed methodology. The parametric influence of operating conditions was then analysed on the basis of polynomial relationships. The steady-state wear was found to be significantly influenced by the initial roughness.

  • 122.
    Kumar, Rajesh
    et al.
    Indian Institute of Technology, New Delhi.
    Prakash, Braham
    Sethuramiah, A.
    Indian Institute of Technology, New Delhi.
    Theoretical modelling of surface contact for honed surfaces1998In: Advances in Industrial Tribology / [ed] J. Bhatia, New Dehli: Tata McGraw Hill , 1998, p. 100-107Conference paper (Refereed)
  • 123.
    Larsson, Roland
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Special issue on tribology research in Scandinavia: Guest editorial2011In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 225, no J10, p. 973-974Article in journal (Other academic)
  • 124.
    Leiro, Alejandro
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Kankanala, Anusha
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Vuorinen, Esa
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Tribological behaviour of carbide-free bainitic steel under dry rolling/sliding conditions2011In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 273, no 1, p. 2-8Article in journal (Refereed)
    Abstract [en]

    The dry rolling/sliding wear behaviour of Si alloyed carbide free bainitic steel austempered at different temperatures and sliding distances has been evaluated. 60SiCr7 spring steel samples were austempered in a salt bath maintained at 250, 300 and 350 °C respectively for 1 h. Rolling with 5% sliding wear tests were performed using self mated discs for three different test cycles, namely 6000, 18000 and 30000 cycles. The aim was to study the wear performance of the 60SiCr7 steel with a carbide-free microstructure containing different amounts of retained austenite. An in-depth microstructural characterization has been carried out before and after the wear tests in order to link the wear behaviour to the microstructure of each sample. The wear resistance has been expressed by means of the specific wear calculated from the mass loss after the tests. The worn surfaces were analyzed by scanning electron microscopy and X-ray diffraction. Micro-hardness profiles were also obtained in order to analyze strain-hardening effects beneath the contact surfaces. The results indicate that the material with highest hardness—the one austempered at 250 °C—exhibited the lowest wear rate in every case. It was also observed that the hardness increment and thickness of the hardened layer increases with increasing the austempering temperature and number of test cycles. Finally, the results appear to indicate that the initial roughness of the samples has no major effect in the wear rate of the samples above 2500 cycles. The higher wear performance of the sample austempered at 250 °C has been attributed to its superior mechanical properties provided by its finer microstructure. It has been evidenced that all samples undergo the TRIP phenomenon since, after wear; no retained austenite could be detected by XRD.

  • 125.
    Leiro, Alejandro
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Roshan, Arash
    Luleå tekniska universitet.
    Sundin, Karl-Gustaf
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Vuorinen, Esa
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Fatigue of 0.55C-1.72Si Steel with Tempered Martensitic and Carbide-Free Bainitic Microstructures2014In: Acta Metallurgica Sinica (English Letters), ISSN 1006-7191, E-ISSN 2194-1289, Vol. 27, no 1, p. 55-62Article in journal (Refereed)
    Abstract [en]

    High-Si spring steel was heat treated in three different ways: Quenching and tempering at 460 °C to obtain a tempered martensite microstructure, and austempering at 300 and 350 °C, respectively, to obtain two different carbide-free bainitic microstructures. In the steel austempered at 350 °C, both the bainite lath thickness and retained austenite content were higher than those of the steel austempered at 300 °C. Rotating-bending fatigue tests were done in order to evaluate the effect of each heat treatment on the high-cycle fatigue behavior of the steel. When the austempering temperature was 300 °C, the endurance limit was increased by 25% despite a 5% reduction in tensile strength when compared with that of the quenched and tempered steel. The relationship between endurance limit [Rfat (50%)] and ultimate tensile strength (Rm) was higher for the austempered samples in comparison with that of the quenched and tempered material. Therefore, it is believed that the presence of retained austenite affects the relationship between endurance limit and tensile strength.

  • 126.
    Leiro, Alejandro
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Vuorinen, Esa
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Sundin, Karl-Gustaf
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Sourmail, T.
    ASCOMETAL-CREAS.
    Samanio, V.
    ASCOMETAL-CREAS.
    Caballero, F.C.
    National Center for Metallurgical Research (CENIM-CSIC), Madrid.
    Garcia-Mateo, C.
    National Center for Metallurgical Research (CENIM-CSIC), Madrid.
    Elvira, Roberto
    Gerdau Sidenor I+D.
    Wear of nano-structured carbide-free bainitic steels under dry rolling-sliding conditions2013In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 298-299, no 1, p. 42-47Article in journal (Refereed)
    Abstract [en]

    Specially designed steels with carbon contents from 0.6 to 1.0 wt.% were isothermally transformed at very low temperatures, between 220 and 270 °C, in order to obtain a nano-structured bainitic microstructure. It is shown that the wear resistance in dry rolling-sliding of these nano-structured steels is significantly superior to that ofbainitic steels transformed at higher temperatures with similar hardness values.In addition to the highly refined microstructure, the transformation under strain to martensite (TRIP effect), contributes to the plasticity of the nano-scaled steels, increasing surface hardness during testing, thus reducing the wear rate.

  • 127. Lundmark, Jonas
    et al.
    Höglund, Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Prakash, Braham
    Running-in behaviour of rail and wheel contacting surfaces2006In: AITC-AIT 2006: 5th International Conference on Tribology ; 20 - 22 September 2006, Parma, Italy, 2006, p. 33-Conference paper (Refereed)
  • 128. Lundmark, Jonas
    et al.
    Kassfeldt, Elisabet
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hardell, Jens
    Prakash, Braham
    Influence of initial surface topography on tribological performance of the wheel/rail interface during rolling/sliding conditions2007In: High tech in heavy haul: Proceedings. International Heavy Haul Conference. Specialist Technical Session / [ed] Thomas Nordmark; Per-Olof Larsson-Kråik, Luleå: Luleå tekniska universitet, 2007, p. 673-680Conference paper (Refereed)
  • 129. Lundmark, Jonas
    et al.
    Kassfeldt, Elisabet
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hardell, Jens
    Prakash, Braham
    The influence of initial surface topography on tribological performance of the wheel/rail interface during rolling/sliding conditions2009In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 223, no 2, p. 181-187Article in journal (Refereed)
    Abstract [en]

    The influence of surface roughness in a rail/wheel contact has been a concern for railway owners since the introduction of ‘rail grinding' as a maintenance strategy. Presently, there are no well-defined guidelines regarding the surface topographies of ground rails and re-turned wheels. There is thus a need to establish scientific guidelines regarding the surface topographies for the rails and wheels in order to minimize grinding costs/time and to improve rail/wheel performance. This study is aimed at investigating the influence of surface topographies of wheels and rails on running-in behaviour, wear, friction, and the resultant surface damage through experimental simulation in the laboratory. A two-disc rolling/sliding test machine has been used in this experimental work. Two different roughness values were produced on both the rail and wheel test specimens. A design of experiment approach has been used to conduct experiments and to analyse the results. The results show that the surface roughness values of the specimens in some material pairs do influence wear, friction, and resulting surface damage.

  • 130.
    Mann, B. S.
    et al.
    BHEL, Corporate R&D Division, Vikasnagar, Hyderabad.
    Prakash, Braham
    High temperature friction and wear characteristics of various coating materials for steam valve spindle application2000In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 240, no 1-2, p. 223-230Article in journal (Refereed)
    Abstract [en]

    Various coatings such as chromium carbide (deposited by plasma spraying and detonation gun techniques), chromium oxide, chromium oxide + titania + silica, NiCrAlY, and Al2O3 + Ni all deposited by plasma spraying; stelliting, and surface nitriding have been applied on X20CrMo V121 steel. This steel is used for high temperature applications such as steam turbine valve spindle. Friction and wear behavior of the surface coated and treated materials have been studied at an elevated temperature of 550°C while rubbing against graphite-filled stellited steel. These studies have been carried out on SRV optimol reciprocating tribometer. Test parameters for tribological studies have been selected with a view to simulate operating conditions encountered in operation. Additionally, the structure, porosity, hardness, bond strength, and thermal cycling behaviour of these surface coated/treated materials have been characterised. Based on these laboratory investigations, chromium carbide coating deposited by plasma spraying technique has been identified as the most suitable coating for steam turbine valve spindle application. Process parameters have been established for deposition of chromium carbide coating by plasma spraying technique on actual valve spindles. The field results obtained are found to be commensurate with the laboratory findings.

  • 131.
    Minami, Ichiro
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    He, Xin
    Luleå University of Technology.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Coating-lubricant combination for improving tribo-system performance2014In: Lubrication Science, ISSN 0954-0075, E-ISSN 1557-6833, Vol. 26, no 5, p. 375-386Article in journal (Refereed)
    Abstract [en]

    New tribo-systems composed of green chemicals have been investigated. Compatibility of friction modifiers with DLC was evaluated by using SRV test machine. A Zn-free lubricant formulation showed a steady-state friction coefficient of 0.15 for steel/steel contact. Hydrogenated DLC coating showed similar tribological properties when slid against steel. Interestingly, this lubricant showed low friction coefficient of 0.02 for hydrogen-free amorphous DLC when slid against steel. A model friction modifier improved the running-in performance and reduced wear for hydrogen-free DLC, while it marginally increased steady-state friction coefficient up to 0.04. The importance of material–lubricant combination and lubrication model has been highlighted

  • 132.
    Mishra, Tanmaya
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Nordin, Björn
    Bosch Rexroth Mellansel AB, Mellansel, Sweden.
    Svanbäck, Daniel
    Bosch Rexroth Mellansel AB, Mellansel, Sweden.
    Tervakangas, Sanna
    DIARC-Technology Oy, Espoo, Finland.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    The effects of contact configuration and coating morphology on the tribological behaviour of tetrahedral amorphous diamond-like carbon (ta-C DLC) coatings under boundary lubrication2019In: Tribology - Materials, Surfaces & Interfaces, ISSN 1751-5831, E-ISSN 1751-584X, Vol. 13, no 2, p. 120-129Article in journal (Refereed)
    Abstract [en]

    Tribological studies were carried out with tetrahedral amorphous diamond-like carbon (ta-C DLC) coatings, varying in thickness and roughness, using two different contact configurations lubricated with seven types of hydraulic oils. Tribopair of cast iron and ta-C coated steel were tested in both non-conformal and conformal, unidirectional sliding contacts. The friction and wear results were mainly affected by the thickness of the coating in the non-conformal contact and the surface roughness of the coating in the conformal contact. Tests done with mineral base oil containing rust inhibitor in the non-conformal contact and with Polyalphaolefins and synthetic ester base oils in the conformal contact resulted in the lowest friction while that with mineral base oil containing zinc resulted in high friction and counterface wear. The results highlight the interdependence of contact configuration, lubricant chemistry, coating’s surface morphology and coating’s thickness in determining the tribological behaviour of ta-C coatings under boundary lubrication.

  • 133.
    Mofidi, M.
    et al.
    Department of Mechanical Engineering, Sirjan University of Technology.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Frictional behaviour of some sealing elastomers in lubricated sliding2012In: 15th Nordic Symposium on Tribology - NordTrib 2012: 12 - 15 June 2012 - Trondheim, Norway, Trondheim: Department of Geography, Norwegian University of Science and Technology, 2012Conference paper (Refereed)
    Abstract [en]

    Frictional behaviour of four sealing elastomers, including an acrylonitrile butadienerubber (NBR), a hydrogenated acrylonitrile butadiene rubber (HNBR), an acrylate rubber(ACM) and a fluoroelastomer (FKM), sliding against a steel surface under unidirectionallubricated conditions have been studied. The lubricant used in this study was paraffinic oilwith no additive and the experiments were conducted under a block-on-ring testconfiguration. The friction coefficients of the elastomers have been measured at differentsliding velocities in boundary and fluid film lubrication regimes. In the first part of each test,the sliding velocity varied from low to high values and then, in the second part, the slidingvelocity varied from high to low values repeating the same conditions in reverse order. Theresults show that the friction coefficients at low speeds are different for the two parts whichcan be due to the oil absorption or possibly dissolution of some elastomer constituents in theoil. The NBR and the ACM were the least and the most affected elastomer by the lubricantrespectively. The friction coefficients of NBR and ACM at low speeds decreased in thesecond part of the tests (in which the interaction of oil and elastomer was for longerdurations) but the friction coefficient of HNBR and FKM increased in the second part of thetests.

  • 134. Mofidi, Mohammad
    et al.
    Kassfeldt, Elisabet
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Prakash, Braham
    Influence of ageing an elastomer lubricating fluids on its tribological behavior2006In: 12th Nordic Symposium on Tribology, NORDTRIB 2006: LO-skolen, Helsingør, Denmark, June 7-9 2006, Kongens Lyngby: Technical University of Denmark , 2006Conference paper (Refereed)
  • 135. Mofidi, Mohammad
    et al.
    Kassfeldt, Elisabet
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Prakash, Braham
    Tribological behaviour of an elastomer aged in different oils2008In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 41, no 9-10, p. 860-866Article in journal (Refereed)
    Abstract [en]

    This paper presents the influence of aging the nitrile rubber, the most popular seal material, in various base fluids on sliding friction and abrasive wear. The lubricants used are synthetic esters, natural esters, different types of mineral base oils, poly-*-olefins and very high viscosity index oils. Friction has been studied for two directions of motion with respect to lay on the elastomer sample by using the SRV Optimol test machine. These findings show that as compared to all other lubricant formulations, ageing the elastomer in polyol ester leads to the maximum reduction of friction coefficient especially in perpendicular sliding to the initial lay on the surface. The abrasive wear studies were carried out by using a two-body abrasive wear tester against dry and lubricated elastomer. It was interesting to note that two-body abrasive wear of elastomeric material was higher during rubbing in presence of the fluids as compared to that in dry condition. Further, aging the elastomer in these base fluids especially in ester base fluids, results in more abrasive wear.

  • 136. Mofidi, Mohammad
    et al.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Influence of counterface topography on sliding friction and wear of some elastomers under dry sliding conditions2008In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 222, no 5, p. 667-673Article in journal (Refereed)
    Abstract [en]

    In this work, the friction and wear behaviour of acrylonitrile butadiene rubber (NBR), hydrogenated acrylonitrile butadiene rubber (HNBR), acrylate rubber (ACM), and fluoroelastomer (FKM) against steel surfaces under unidirectional dry sliding conditions have been studied. The influence of surface roughness of the steel counterface on friction and wear was studied using a block-on-ring test configuration. At low load, the friction coefficient decreased after a running-in period and the wear was insignificant, especially for the ACM and FKM. The running-in time in terms of achieving a stable dry friction for the different elastomers, from longest to shortest, is in the order HNBR, NBR, FKM, and ACM, with an exception in case of FKM sliding against a smooth steel counterface. At higher contact pressure, powdery worn particles on the ACM and a decrease in friction coefficient were observed, but for FKM and HNBR, worn particles with roll shapes were produced. The worn particles of FKM were significantly larger than those of the other tested materials, and a considerably higher wear in FKM was observed.

  • 137. Mofidi, Mohammad
    et al.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    The influence of lubrication on two body abrasive wear of sealing elastomers2008In: Proceedings of NORDTRIB 2008, 13th Nordic Symposium on Tribology: Scandic Rosendahl Hotel, Tampere, Finland, June 10 - 13, 2008 / [ed] Jaakko Kleemola; Arto Lehtovaara, Tampere: Tampere University of Technology, 2008Conference paper (Refereed)
    Abstract [en]

    Elastomeric seals are prone to failure caused by abrasion during sliding against rough surfaces. In this research, the two body abrasive wear of sealing elastomers in dry and lubricated conditions has been studied. A two body abrasive wear tester has been used to investigate the abrasive wear of the elastomers under varying test parameters. This test aparatus reciprocates a rectangular elastomeric sample against an abrasive paper wrapped around the circumferential surface of a wheel. The samples were weighed using an accurate scale before and after the tests to quantify the abrasive wear. The experiments have been carried out at varying normal load and abrasive size in dry and lubricated conditions. The influence of two different lubricants, including a synthetic ester and a mineral oil, together with the test parameters on the abrasive wear has been studied. The results show that, depending on the material, lubricant, abrasive size, normal load and test duration, the abrasive wear of elastomers may increase or decrease in the presence of lubricants, however, in most cases, the abrasive wear in the lubricated condition is higher than that in the dry condition. The influence of lubricant on the increase in abrasive wear is more significant when a fine abrasive is used. Increase in the abrasive wear in presence of the synthetic ester is more pronounced than in presence of the mineral oil.

  • 138. Mofidi, Mohammad
    et al.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Two body abrasive wear and frictional characteristics of sealing elastomers under unidirectional lubricated sliding conditions2010In: Tribology - Materials, Surfaces & Interfaces, ISSN 1751-5831, E-ISSN 1751-584X, Vol. 4, no 1, p. 26-37Article in journal (Refereed)
    Abstract [en]

    Since abrasion is a common cause of seal failures, understanding the mechanisms of abrasion of an elastomer in the presence of lubricants is of importance in sealing applications. In this research a block on ring configuration was used to study the influence of lubrication on the two body abrasion of several commonly used sealing elastomers (two acrylonitrile butadiene rubbers, an acrylic rubber and a fluoro rubber). The friction force and the abrasive wear of the samples were measured and the worn surfaces and wear particles were investigated using an optical microscope. The tear strength of the elastomers before and after immersion in monoester oil as well as the oil absorption has been measured. Both scratches (parallel to the direction of sliding) and ridges (perpendicular to the direction of sliding) were observed on the worn surfaces of nitrile rubbers but the surfaces of acrylic and fluoro rubber were characterised by scratches only. The worn surfaces of nitrile rubbers were defined with more continuous ridges at lower sliding velocity and the presence of a lubricant in the contact reduced the continuous ridges. Examination of the wear particles shows that the wear particles (particularly for acrylic rubber) under dry sliding condition were aggregated, but the lubricant dispersed the wear particles and prevented aggregation. In most cases, abrasive wear of the elastomers under lubricated condition is higher than that under dry condition. The results show that the friction coefficient increased with increasing sliding velocity and decreased with contact pressure. Apart from the fluoro rubber, the friction coefficient as well as the tear strength of the elastomers decreased significantly in the presence of lubricant, particularly for acrylic rubber.

  • 139. Mofidi, Mohammad
    et al.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Persson, B.N.J.
    IFF, Jülich.
    Albohr, O.
    Pirelli Deutschland AG, Höchst/Odenwald.
    Rubber friction on (apparently) smooth lubricated surfaces2008In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 20, no 8Article in journal (Refereed)
    Abstract [en]

    We study rubber sliding friction on hard lubricated surfaces. We show that even if the hard surface appears smooth to the naked eye, it may exhibit short-wavelength roughness, which may make the dominant contribution to rubber friction. That is, the observed sliding friction is mainly due to the viscoelastic deformations of the rubber by the counterface surface asperities. The results presented are of great importance for rubber sealing and other rubber applications involving ( apparently) smooth surfaces.

  • 140. Mofidi, Mohammad
    et al.
    Simmons, Gregory
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Friction and wear characteristics of elastomers in lubricated contact with EALs2008Conference paper (Other academic)
    Abstract [en]

    The friction and wear characteristics of several elastomers have been studied during reciprocating sliding conditions when lubricated with uncontaminated environmentally adapted lubricants and the same lubricants contaminated with moisture. The elastomers studied are Nitrile Butadiene Rubber (NBR), Hydrogenated Nitrile Butadiene Rubber (HNBR), and Fluorocarbon Rubber (FKM). The lubricants used are complex ester and polyol ester as well as both aged and non-aged polyol esters with 5% water content. Experiments were conducted using a Cameron-Plint test rig with a steel cylinder sliding in the longitudinal direction with a reciprocating motion against a curved elastomer specimen to avoid any edge contact. Sliding velocities were maintained low to reduce the thermal effects often associated with elastomer friction. In these tests, HNBR resulted in the lowest friction, with NBR the highest. The NBR specimens most often experienced wear, while FKM and HNBR experienced very little wear. The various oils, with some exceptions, had similar friction performance both at the higher and the lower loads. Experiments were also conducted using an SRV Optimol test rig at higher frequencies with a steel cylinder in contact with an elastomer mounted on a steel disc. The results from the SRV test rig differed significantly with those of the Cameron-Plint rig with FKM resulting the greatest wear and NBR producing minimal wear. This difference was primarily caused by the differences in contact geometry and the operating parameters between the tests.

  • 141.
    Mofidi, Mohammadreza
    et al.
    Sijan University of Technology.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    The influence of lubrication on two-body abrasive wear of sealing elastomers under reciprocating sliding conditions2011In: Journal of elastomers and plastics (Print), ISSN 0095-2443, E-ISSN 1530-8006, Vol. 43, no 1, p. 19-31Article in journal (Refereed)
    Abstract [en]

    Elastomeric seals are prone to failure caused by abrasion during sliding against rough surfaces. In this research, the two-body abrasive wear of some selected sealing elastomers (nitrile rubber, hydrogenated nitrile rubber, acrylic rubber, and fluoro rubber) in dry and lubricated conditions has been studied. The influence of three different oils (synthetic ester, polyalphaolefin, and mineral oil) on the abrasive wear of the elastomers, at varying normal load and abrasive particle size, has been studied. The results show that, depending on the material, lubricant, abrasive size, and normal load, the abrasive wear of elastomers may increase or decrease in the presence of lubricants, and in most cases, the abrasive wear in the lubricated condition is higher than that in the dry condition. The influence of lubricant on the increase in abrasive wear is more significant during sliding against fine abrasives. Apart from the acrylic rubber, increase in the abrasive wear in presence of the synthetic ester is higher than those in presence of the mineral oil and polyalphaolefin.

  • 142.
    Moghaddam, Pouria Valizadeh
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hardell, Jens
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Vuorinen, Esa
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Caballero, Francisca G.
    National Center for Metallurgical Research (CENIM-CSIC).
    Sourmail, Thomas
    ASCOMETAL, HAGONDANGE.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Corrigendum to: The role of retained austenite in dry rolling/sliding wear of nanostructured carbide-free bainitic steels, Wear 428–429 (2019) 193 - 2042020In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 446-447, article id 203072Article in journal (Refereed)
  • 143.
    Moghaddam, Pouria Valizadeh
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hardell, Jens
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Vuorinen, Esa
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    The role of retained austenite in dry rolling/sliding wear of nanostructured carbide-free bainitic steels2019In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 428-429, p. 193-204Article in journal (Refereed)
    Abstract [en]

    The dry rolling/sliding wear of nanostructured bainite has been investigated and compared with that of a conventional quenched and tempered bearing steel. In order to elucidate the role of retained austenite on the wear performance, high silicon hypereutectoid bearing steel with an identical alloy composition was heat treated to obtain different microstructures with similar hardness and different amounts of retained austenite. The results indicate that the nanostructured bainite can meet the minimum hardness requirements for bearing applications. Moreover, the nanostructured bainite outperformed the tempered martensitic steel in terms of wear resistance. The work hardening capacity and thus wear resistance increases due to the transformation of retained austenite into martensite. The results of XRD analyses show that the higher stability of retained austenite and strength of bainitic ferrite leads to better wear performance. It is demonstrated that the stability of retained austenite outweigh the influence of retained austenite content on wear resistance. Adhesion and oxidation were identified as the main wear mechanisms. In addition to microstructure, surface oxidation also plays a prominent role in determining the wear resistance. 

  • 144.
    Mozgovoy, Sergej
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Alik, Lotfi
    Luleå tekniska universitet.
    Hardell, Jens
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Material transfer during high temperature sliding of Al-Si coated 22MnB5 steel against PVD coatings with and without aluminium2019In: Wear of Materials, Elsevier, 2019, Vol. 426-427, p. 401-411Conference paper (Refereed)
    Abstract [en]

    Press hardening of Al-Si coated 22MnB5 steel is the dominant technology to enable light weight design in automotive applications. Transfer of the Al-Si coating onto the tool surface occurs during hot forming. This affects process economy and quality of produced components. The reported galling mechanisms are adhesion and compaction of wear debris. Surface engineering of forming tools has been proposed to minimise the transfer of Al-Si coating. Plasma nitriding of tool steel surfaces reduces adhesion but has poor abrasive wear resistance. PVD coatings have generally been found to promote galling due to higher chemical affinity but improve abrasive wear resistance. Most studied PVD coatings are transition metal nitrides containing aluminium. The aim of this study is to investigate the role of aluminium in PVD coatings and its effect on transfer of Al-Si coating material during sliding against coated tool steel at high temperatures. This work has focussed on PVD coatings (AlCrN and CrWN) deposited on plasma nitrided tool steel. Their tribological behaviour was studied using a hot strip-drawing tribometer capable of simulating the conditions prevalent in press hardening. The results showed that PVD coatings containing aluminium induce more material transfer. The material transfer is mainly related to chemical affinity since all coatings were polished to a low surface roughness (Sa =~120 nm) to minimise transfer initiated by surface defects. The hardness of the PVD coatings does not seem to influence the material transfer since the softer coating (CrWN, HV0.05 = ~1850) showed less transfer compared to AlCrN (HV0.05 = ~2100). The CrWN coating showed longer running-in compared to AlCrN due to reduced initial material transfer. Formation of thicker transfer layers governs the steady state friction mechanisms. Material transfer of Fe-Al intermetallic compounds occurs at the initial stages of sliding through direct adhesion to the PVD coating. The layers grow to > 5 µm thickness within a few decimetres of sliding.

  • 145.
    Mozgovoy, Sergej
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hardell, Jens
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Deng, Liang
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Oldenburg, Mats
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Effect of temperature on friction and wear of prehardened tool steel during sliding against 22MnB5 steel2013Conference paper (Refereed)
  • 146.
    Mozgovoy, Sergej
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hardell, Jens
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Deng, Liang
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Oldenburg, Mats
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Effect of temperature on friction and wear of prehardened tool steel during sliding against 22MnB5 steel2014In: Tribology - Materials, Surfaces & Interfaces, ISSN 1751-5831, E-ISSN 1751-584X, Vol. 8, no 2, p. 65-73Article in journal (Refereed)
    Abstract [en]

    Mechanical components in tribological systems exposed to elevated temperatures are gaining increased attention since more and more systems are designed to operate under extreme conditions. In hot metal forming, the effect of temperature on friction and wear is especially important since it is directly related to process economy (tool wear) and quality of the produced parts (friction between tool and workpiece). This study is therefore focused on fundamental understanding pertaining to the tribological characteristics of prehardened hot work tool steel during sliding against 22MnB5 boron steel. The tribological tests were carried out using a high temperature reciprocating sliding friction and wear tester under a normal load of 31 N (corresponding to a contact pressure of 10 MPa), a sliding speed of 0·2 m s−1 and temperatures ranging from 40°C to 800°C. It was found that friction coefficient and specific wear rate decreased at elevated temperature because of formation of compacted wear debris layers on the surfaces.

  • 147.
    Mozgovoy, Sergej
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hardell, Jens
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Deng, Liang
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Oldenburg, Mats
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Simulative High Temperature Friction and Wear Studies for Press Hardening Applications2015In: Hot Sheet Metal Forming of High-Performance Steel 5th International Conference: May 31-June 3, Toronto, Canada : Proceedings / [ed] Kurt Steinhoff; Mats Oldenburg; Braham Prakash, Auerbach: Verlag Wissenschaftliche Scripten , 2015, p. 167-175Conference paper (Refereed)
    Abstract [en]

    Press hardening is employed in automotive industry to produce advanced high-strength steel components for safety and structural applications. In this hot forming process, the dimensional accuracy of produced components relies not only on an optimum friction level for the deformation of the workpiece, but it also gets affected by wear of the forming tools, which reduces the service life of the tool as well. It is desirable to enhance the durability of the tools by understanding the influence of contact conditions on tool wear. However, this is difficult to achieve in conventional tribological testing equipment. With this in view, the tribological behaviour of tool-workpiece material pairs at elevated temperatures has been studied in a newly developed experimental set-up simulating the conditions prevalent during interaction of the hot workpiece with the tool surface. The coefficients of friction of uncoated and Al-Si coated 22MnB5 steel decreased when the normal load increased. The influence of sliding velocity on the coefficient of friction was negligible for uncoated and Al-Si coated 22MnB5 steel. In the case of Al-Si coated 22MnB5 steel, adhesive material transfer of the Al-Si coating onto the tool steel surface was the main wear mechanism and this was also the reason for the higher and unstable friction coefficient when compared to uncoated 22MnB5 steel. In the case of uncoated 22MnB5 steel, adhesion was the main wear mechanism.

  • 148.
    Mozgovoy, Sergej
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hardell, Jens
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Deng, Liang
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Oldenburg, Mats
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Tribological Behavior of Tool Steel under Press Hardening Conditions Using Simulative Tests2018In: Journal of tribology, ISSN 0742-4787, E-ISSN 1528-8897, Vol. 140, no 1, article id 011606Article in journal (Refereed)
    Abstract [en]

    Press hardening is employed in the automotive industry to produce advanced high-strength steel components for safety and structural applications. This hot forming process depends on friction as it controls the deformation of the sheet. However, friction is also associated with wear of the forming tools. Tool wear is a critical issue when it comes to the dimensional accuracy of the produced components and it reduces the service life of the tool. It is therefore desirable to enhance the durability of the tools by studying the influence of high contact pressures, cyclic thermal loading, and repetitive mechanical loading on tool wear. This is difficult to achieve in conventional tribological testing devices. Therefore, the tribological behavior of tool-workpiece material pairs at elevated temperatures was studied in a newly developed experimental setup simulating the conditions prevalent during interaction of the hot sheet with the tool surface. Uncoated 22MnB5 steel and aluminum-silicon (Al-Si)-coated 22MnB5 steel were tested at 750 °C and 920 °C, respectively. It was found that higher loads led to lower and more stable friction coefficients independent of sliding velocity or surface material. The influence of sliding velocity on the coefficient of friction was only marginal. In the case of Al-Si-coated 22MnB5, the friction coefficient was generally higher and unstable due to transfer of Al-Si coating material to the tool. Adhesion was the main wear mechanism in the case of uncoated 22MnB5

  • 149.
    Mozgovoy, Sergej
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hardell, Jens
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    High Temperature Friction and Wear Performance of PVD Coatings under Press Hardening Contact Conditions2019In: Advances in Tribology, ISSN 1687-5915, E-ISSN 1687-5923, Vol. 2019, article id 4981246Article in journal (Refereed)
    Abstract [en]

    Press hardening is widely employed to produce automotive structural and safety components from advanced high-strength steels. This process depends on friction between the forming tools and the work piece. Wear of the forming tools affects the dimensional accuracy of produced components and reduces their service life. It is therefore desirable to reduce wear of forming tools for press hardening applications. One way to achieve this is by applying hard physical vapour deposited (PVD) coatings on the tool. In this work, the tribological behaviour of PVD coated tool-work piece material pairs has been studied at elevated temperatures in an experimental set-up simulating the tribological conditions in press hardening. Four different PVD coatings deposited on tool steel and uncoated tools as reference were studied during sliding against uncoated and Al-Si coated 22MnB5 steel. Results show that uncoated tools exhibited the lowest coefficient of friction when sliding against uncoated 22MnB5 steel. A CrWN coating initially showed low coefficient of friction but it increased with increasing sliding distance. A TiAlN coating and one of two AlCrN coatings showed similar frictional behaviour when sliding against uncoated 22MnB5 steel. During sliding against uncoated 22MnB5 steel, adhesive wear has been found to be the dominant wear mechanism. Adhesive wear was considerably reduced in the case of hard PVD coated tools in comparison to that of uncoated tools. During sliding against Al-Si coated 22MnB5 steel, no clear advantage in terms of friction behaviour of uncoated or PVD coated tools was observed. However, the transfer of Al-Si coating material from the work piece to the tools was significantly reduced for PVD coated tools. Frictional instabilities in all cases involving Al-Si coated work piece material further confirmed the occurrence of adhesive material transfer.

  • 150.
    Mozgovoy, Sergej
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hardell, Jens
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    High Temperature Friction and Wear Studies on Tool Coatings under Press Hardening Contact Conditions2015Conference paper (Refereed)
12345 101 - 150 of 244
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