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  • 201.
    Marklund, Pär
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Permeability of sinter bronze friction material for wet clutches2008In: Tribology & Lubrication Technology, ISSN 1545-858X, Vol. 64, no 12, p. 34-41Article in journal (Refereed)
    Abstract [en]

    The characteristics of wet clutches are of great importance for the overall behavior of the drive trains of many modern vehicles. It is considered that the clutch characteristic is affected by the permeability of the friction material. The permeability is considered to influence both the time of engagement and the temperature in the clutch due to the lubricant flow in the permeable material. In this work, a permeability measurement method suitable for wet clutch friction materials is thus used to measure the permeability of a friction material made of sintered bronze. This friction material is suitable for applications such as limited slip differentials or other wet clutches that have to withstand high temperature and high torque transfer. The permeability is also investigated for friction materials with pressed groove patterns. Wet clutch friction material permeability is often accounted for in simulations but the method used to measure the permeability is seldom described. The permeability of the investigated friction material is shown to be so small that it hardly will affect the temperature in the material due to cooling oil flow inside the material. However, the engagement time can be influenced by the permeability. It is also shown that pressed groove patterns can seal the friction material so that it becomes almost impermeable.

  • 202. Marklund, Pär
    et al.
    Mäki, Rikard
    Larsson, Roland
    Höglund, Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Khonsari, Michael. M.
    Louisiana State University.
    Jang, Joonyoung
    Louisiana State University.
    Ganemi, Bager
    Statoil Lubricants.
    Ohlsson, Richard
    Haldex Traction AB.
    Thermal influence on torque transfer of wet clutches in limited slip differential applications2005In: Proceedings of the World tribology congress III: presented at ..., September 12 - 16, 2005, Washington, DC, New York: American Society of Mechanical Engineers , 2005, p. 245-246Conference paper (Other academic)
    Abstract [en]

    Wet clutches operating under low velocity and high load are studied with the aim of obtaining reliable models for the torque transfer during boundary lubrication conditions.

  • 203.
    Marklund, Pär
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Mäki, Rikard
    Larsson, Roland
    Höglund, Erik
    Khonsari, M.M.
    Louisiana State University.
    Jang, Joonyoung
    Louisiana State University.
    Thermal influence on torque transfer of wet clutches in limited slip differential applications2007In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 40, no 5, p. 876-884Article in journal (Refereed)
    Abstract [en]

    Wet clutches operating under low velocity and high load are studied with the aim of obtaining reliable models for the torque transfer during boundary lubrication conditions. A friction model which takes temperature, speed and nominal pressure into account is developed and used with temperature calculations to be able to simulate behavior of a wet clutch working in boundary lubrication regime. Predicted torque and temperatures from the model agree well with experimental data.

  • 204. Marklund, Pär
    et al.
    Sahlin, Fredrik
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Modelling and simulation of thermal effects in wet clutches operating under boundary lubrication conditions2009In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 223, no 8, p. 1129-1141Article in journal (Refereed)
    Abstract [en]

    Wet clutches are frequently used in the drive trains of many modern vehicles. The behaviour of the clutches influences the behaviour of the whole drive train and therefore of the whole vehicle. The design of the clutch is very important because it operates in cooperation with the other parts of the drive train. The clutch also often has to work in the lubricant present in the transmission. To optimize the clutch for an application, properties such as disc geometry, materials, friction disc surface, and engagement axial force can be varied when designing the clutch. Today, the design process involves much testing, which is expensive and time consuming. There are no good hand-book solutions or engineering tools available, hence the designer has to be very experienced and often use trial and error methods in order to end up with a working clutch for an application.A simulation model is developed in this article, which in combination with a simple measurement technique for measuring the boundary lubrication friction coefficient is used to estimate temperature and torque transfer for a wet clutch working under limited slip conditions. The developed simulation model can be used as a design tool for wet clutches. The approach developed in this article can be used to investigate torque behaviour for wet clutches that have not been designed and is, therefore, suitable to use when optimizing the performance of a new clutch. The model includes fluid dynamics, contact mechanics, and temperature computations in the fluid film between the friction disc and the separator disc. Temperature computations in the clutch discs are also included in the model. The fluid dynamics calculations use homogenized flow factors to enable simulations of flow on a coarser grid and still include all surface roughness effects. The temperature distribution in the film in the sliding interface is approximated as a polynomial of the second order. The heat transfer in the grooves of the friction discs is solved by means of an equilibrium equation that includes radial cooling flow effects because of centrifugal flows. The temperature in the friction disc and separator disc is obtained from the solution of the full three-dimensional energy equation in polar cylindrical coordinates.The model is validated by measurements made in a test rig and good agreement between measurements and simulations is obtained, both with regard to temperature and transfered torque.The use of this model can reduce the time needed to develop a limited slip wet clutch application since the systematic way of finding the optimal clutch design will be more efficient than the often used Edisonian trial and error approach.

  • 205. Nybacka, Mikael
    et al.
    Larsson, Tobias
    Jeppsson, Peter
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Ågren, Anders
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Karlsson, Lennart
    Rantatalo, Matti
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Lindgren, Per
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Andren, Henrik
    Engström, Niclas
    Larsson, Roland
    Fransson, Lennart
    Hyyppä, Kalevi
    Fredriksson, Håkan
    Eriksson, Johan
    van Deventer, Jan
    Tingvall, Bror
    Project: CASTT - Centre for Automotive Systems Technologies and Testing2007Other (Other (popular science, discussion, etc.))
    Abstract [sv]

    Through the Centre for Automotive Systems Technologies and Testing, Luleå University of Technology aims to first of all support automotive winter testing in Northern Sweden. This means to support the local automotive test entrepreneurs and through them their customers: the car manufacturers and their suppliers. To succeed in this task, the center relies on the university's areas of leading research and most importantly on the cooperation between those areas.

  • 206.
    Nyqvist, Jari
    et al.
    ABB Stal AB, Finspång.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Solution to stability problems in steam turbines by optimisation of a squeeze film damper1996In: Sixth international conference on vibrations in rotating machinery: 9 - 12 September 1996, Bury St. Edmunds: Mechanical engineering publications for the Institution of mechanical engineers , 1996Conference paper (Other academic)
  • 207. Pettersson, Anders
    et al.
    Carlevi, Jens
    Kassfeldt, Elisabet
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Running-in studies of a hydraulic rotator2006In: Automotive and industrial lubrication: 15th International Colloquium Tribology, January 17 - 19, 2006 ; [book of synopses 2006] / [ed] Wilfried J. Bartz, Ostfildern: Techn. Akad. Esslingen , 2006Conference paper (Refereed)
  • 208. Pettersson, Anders
    et al.
    Carlevi, Jens
    Kassfeldt, Elisabet
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Larker, R.
    Running-in studies of a hydraulic rotator2007In: Tribologia : Finnish Journal of Tribology, ISSN 0780-2285, Vol. 26, no 3, p. 3-8Article in journal (Refereed)
    Abstract [en]

    The running-in properties of a hydraulic rotator of vane type for angular positioning of crane tools has been studied. The sliding contact between the vane nose and the stator ring was studied in detail. A pin-on-disc configuration tribometer was used for the tribotests. The pin was made out of a slice from a real vane and the disc was manufactured of the same material and with the same machining process as the real stator ring. Collected data included friction, wear and electric contact resistance. A new method was used to enable measurements of changes in surface topography at a specific location during the test. The results show that the relocation method is useful for monitoring small changes in surface topography under running-in, but the most significant parameter for detection of running-in for this application is electric contact resistance. Significant changes in friction and contact resistance were observed during the running-in period. The main reason for the changes is the build-up of a non-conducting tribofilm. The change in surface topography alone is too small to change the lubricating regime. The tribofilm is formed after a short distance but can not grow until the steepest asperities have been worn off. The results show that the plane milled surface has better running-in properties than the turned surface

  • 209. Pettersson, Anders
    et al.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Norrby, Thomas
    Andersson, O.
    Properties of base fluids for environmentally adapted lubricants2001In: Tribology 2001 : scientific achievements, industrial applications, future challenges: plenary and session key papers from the 2nd World Tribology Congress, Vienna, Austria, 3 - 7 September / [ed] Friedrich Franek, Wien: ÖTG , 2001Conference paper (Refereed)
  • 210. Pettersson, Anders
    et al.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Norrby, Thomas
    Andersson, Ove
    Umeå university.
    Properties of base fluids for environmentally adapted lubricants2002In: Handbook of Tribology and Lubrication, Renningen: Expert Verlag , 2002, p. 52-55Chapter in book (Other academic)
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  • 211.
    Pérez-Ràfols, Francesc
    et al.
    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.
    van Riet, Egbert J.
    Shell Global Solutions International BV, Innovation, Research and Development.
    Almqvist, Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    On the flow through plastically deformed surfaces under unloading: A spectral approach2018In: Proceedings of the Institution of mechanical engineers. Part C, journal of mechanical engineering science, ISSN 0954-4062, E-ISSN 2041-2983, Vol. 232, no 5, p. 908-918Article in journal (Refereed)
    Abstract [en]

    This study considers flow through the gap left between two surfaces during unloading, in other words, when an applied load is gradually reduced after loading to a state where plastic deformation occurs. In particular, the permeability of the gap is studied. It was found that a substantial reduction of the applied load is required before the permeability starts to increase significantly. The explanation for this phenomenon is given by the combination of components with different wavelengths present in the surface. Components with long wavelengths deform elastically and those with shorter wavelengths may also deform plastically. We found that plastic deformation acts to keep the permeability nearly constant at the beginning of the unloading and elastic spring-back is responsible for the rapid increase at lower loads. This principle constitutes a basis for the strategy that was developed in order to predict the load at which the rapid increase of permeability starts.

  • 212.
    Pérez-Ràfols, Francesc
    et al.
    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.
    Van Riet, Egbert J.
    Almqvist, Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    On the loading and unloading of metal-to-metal seals: A two scale stochastic approachManuscript (preprint) (Other academic)
  • 213.
    Rafols, Francesc Perez
    et al.
    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.
    Almqvist, Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Modelling of leakage on metal-to-metal seals2016In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 94, p. 421-427Article in journal (Refereed)
    Abstract [en]

    Surfaces in a typical seal exhibit both waviness and roughness. The influence of the interaction between these two scales on the leakage behaviour is expected to be relevant. Therefore, a model, which can study it, is developed here. The model is composed of state-of-the-art models for the contact mechanics between rough metal surfaces and for the liquid flow through the rough aperture in-between them. Correlation between percentage real contact area and actual contact topology and leak rate was confirmed through numerical analysis. Small changes in relative position between the contacting surfaces showed large deviation in leak rate. The validity of the model was justified by comparing results from numerical simulations using the model and experimental results found in literature qualitatively.

  • 214.
    Rafols, Francesc Perez
    et al.
    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.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Wall, Peter
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Almqvist, Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    A stochastic two-scale model for pressure-driven flow between rough surfaces2016In: Proceedings of the Royal Society. Mathematical, Physical and Engineering Sciences, ISSN 1364-5021, E-ISSN 1471-2946, Vol. 472, no 2190, article id 20160069Article in journal (Refereed)
    Abstract [en]

    Seal surface topography typically consists of global-scale geometric features as well as local-scale roughness details and homogenization-based approaches are, therefore, readily applied. These provide for resolving the global scale (large domain) with a relatively coarse mesh, while resolving the local scale (small domain) in high detail. As the total flow decreases, however, the flow pattern becomes tortuous and this requires a larger local-scale domain to obtain a converged solution. Therefore, a classical homogenization-based approach might not be feasible for simulation of very small flows. In order to study small flows, a model allowing feasibly-sized local domains, for really small flow rates, is developed. Realization was made possible by coupling the two scales with a stochastic element. Results from numerical experiments, show that the present model is in better agreement with the direct deterministic one than the conventional homogenization type of model, both quantitatively in terms of flow rate and qualitatively in reflecting the flow pattern.

  • 215. Rapetto, Marco
    et al.
    Almqvist, Andreas
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Lugt, Piet
    On the influence of surface roughness on real area of contact in normal, dry, friction free, rough contact by using a neural network2009In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 266, no 5-6, p. 592-595Article in journal (Refereed)
    Abstract [en]

    A model previously developed at LTU was used in order to perform numerical simulations of normal, dry, friction free, linear elastic contact of rough surfaces. A variational approach was followed and the FFT-technique was used to speed up the numerical solution process. Five different steel surfaces were measured using a Wyko optical profilometer and several 2D profiles were taken. The real area of contact and the pressure distribution over the contact length were calculated for all the 2D profiles. A new slope parameter was defined. An artificial neural network was applied to determine the relationship between the roughness parameters and the real area of contact. The trained model was able to capture the dependence of the real area of contact on the roughness parameters. The ability of the neural network to generalize on unseen data was tested. The neural network was able to prove the correlation between the roughness parameters and the real area of contact.

  • 216. Rapetto, Marco
    et al.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Almqvist, Andreas
    Lugt, Piet
    On the influence of surface roughness on real area of contact in normal, dry, friction free, rough contact by using a neural network2007In: Proceedings of the 11th International Conference on Metrology and Properties of Engineering Surfaces: Huddersfield, U.K., 17th - 20th July 2007 / [ed] Liam Blunt, Huddersfield: University of Huddersfield , 2007Conference paper (Refereed)
  • 217. Rapetto, Marco
    et al.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Almqvist, Andreas
    Lugt, Piet
    On the influence of surface roughness on real area of contact in normal, dry, friction free, rough contact by using a neural network2007In: Svenska Mekanikdagar 2007: Program och abstracts / [ed] Niklas Davidsson; Elianne Wassvik, Luleå: Luleå tekniska universitet, 2007, p. 32-Conference paper (Other academic)
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    FULLTEXT01
  • 218.
    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)
  • 219.
    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.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Influence of counter surface roughness and orientation on the tribological behavior of self-lubricating bearing materials in dry sliding conditions2018Conference paper (Refereed)
    Abstract [en]

    Bearing failures account for a significant share of the operational economical losses in hydropower plants. In Kaplan turbines, the most critical components are the self-lubricating polymer composite bearings used for regulation of the guide vanes and the turbine blades as they operate at high loads, low sliding speeds and small oscillatory movements. Reducing the sliding wear and friction of these bearings would offer a positive impact on both the economy and environment including longer useful life, lower operational costs and higher efficiency.

    In this study, influence of counter surface roughness and orientation on the tribological behavior of bearing materials used in hydropower applications are investigated using a linear reciprocating block-on-block configuration under high pressure and low sliding speed. Surface roughness was measured using white light interferometry. SEM and EDS analysis were used to investigate the polymer surfaces and the transfer film formation.

    Results from this study indicates that too smooth surfaces result in higher friction and wear of the counter surface while rougher surfaces have a negative effect on the wear of the polymers. It can be concluded that counter surface topography has a significant influence on the tribological behavior of these bearings and the effect differs between materials.

  • 220.
    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.
    Mouzon, Johanne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Forsberg, Fredrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Shah, Faiz Ullah
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Rodushkin, Ilia
    ALS Laboratory Group, ALS Scandinavia AB.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Material Characterization and Influence of Sliding Speed and Pressure on Friction and Wear Behavior of Self-Lubricating Bearing Materials for Hydropower Applications2018In: Lubricants, ISSN 2075-4442, Vol. 6, no 2, article id 39Article in journal (Refereed)
    Abstract [en]

    Nowadays, hydropower plants are forced to have more frequent power control and the self-lubricated bearings used in the applications are one of the most critical components affected by the continuously changing operating conditions. In this study, microstructure and composition of two commercially available bearing materials (Orkot TXM Marine and Thordon ThorPlas) used in hydropower turbines were studied. In addition, the influence of sliding speed and applied pressure on the friction and wear behavior of the materials was investigated systematically for dry sliding conditions. The bearing materials were characterized using X-ray microtomography, Nuclear Magnetic Resonance (NMR) spectroscopy and Inductively Coupled Plasma–Sector Field Mass Spectrometry (ICP-SFMS) techniques. Friction and wear tests were carried out with a polymer pin sliding against a stainless steel (SS2333) plate with a linear reciprocating motion. Test conditions were: room temperature, 9–28 MPa pressure and 10–40 mm/s sliding speed ranges. Surface analysis of the polymer pins and the wear tracks were performed by optical profilometry, Scanning Electron Microscope (SEM) and Energy Dispersive Spectroscopy (EDS) techniques. Test results show that, for both materials, the coefficient of friction (COF) is decreasing at higher pressures. Surface analysis reveals higher concentrations of solid lubricants in the transfer layers formed at higher pressures, explaining the decrease in COF. Furthermore, the specific wear rate coefficients are increasing at higher sliding speeds, especially at lower pressures. Results of this study demonstrate that, under dry sliding conditions, changes in sliding speed and pressure have a significant influence on the tribological behavior of these bearing materials.

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    fulltext
  • 221.
    Rodiouchkina, Maria
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Pelcastre, Leonardo
    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.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Lind, Jonna
    Uppsala University, Uppsala, Sweden.
    Kassman Rudolphi, Åsa
    Uppsala University, Uppsala, Sweden.
    Tribological behaviour of self-lubricating polymercomposite bearing materials during long-time dry sliding2019In: 74th STLE Annual Meeting and Exhibition, Society of Tribologists and Lubrication Engineers (STLE) , 2019, p. 140-140Conference paper (Refereed)
    Abstract [en]

    Thermosets and thermoplastics containing PTFE are used in marine and hydropower applications due to their long service life and self-lubricity in dry and water-lubricated contacts. Their tribological performance is usually extrapolated from short, accelerated tests, which induces risks of inaccurate or incorrect interpretation.

    The aim of this study is to investigate the tribological behaviour and development of transfer layers during long sliding tests (160 hours), corresponding to years of operation. To mimic operational shutdowns, the tests were stopped every 20 hours to study the evolution of the surface topography and transfer layers.

    The wear rates of both materials decreased significantly with time. For the thermoplastic, COF decreased due to accelerated material transfer after 80 hours, highlighting the importance of long duration tests. The thermoset showed the highest transfer amount after 20 h and cause severe abrasive wear on the counter surface accompanied by a COF increase.

  • 222.
    Rudnytskyj, André
    et al.
    AC2T research GmbH, Viktor-Kaplan-Straße 2/C, 2700 Wiener Neustadt, Austria; TU Wien, Institute of Engineering Design and Product Development, Lehárgasse 6, BA Building 9th Floor, 1060 Wien, Austria.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Gachot, Carsten
    TU Wien, Institute of Engineering Design and Product Development, Lehárgasse 6, BA Building 9th Floor, 1060 Wien, Austria.
    A Closer Look at the Contact Conditions of a Block-on-Flat Wear Experiment2022In: Lubricants, E-ISSN 2075-4442, Vol. 10, no 7, article id 131Article in journal (Refereed)
    Abstract [en]

    Specific wear rates of tribosystems always rely on the data obtained from wear experiments. Nonetheless, the events taking place during an experiment may often lead to wide variations and low repeatability of the results. In this work, the authors attempt to take a closer look into the dynamic contact conditions of a dry linearly reciprocating block-on-flat wear experiment. The finite element method and Archard’s wear model are used through COMSOL Multiphysics® 5.2a and LiveLink™ for MATLAB® software to model the wear and study the influence of different conditions of the block surface and alignment of the sample. Changes of the geometry of the block and the contact pressure are quantified for several back and forth motions, using an extrapolation scheme in the wear modelling methodology. The tracking of such changes allow a dynamic overview of how the block contact area and the contact pressure distribution change throughout time. The results show how the assumption of a constant contact area and use of a nominal contact pressure in calculating the wear rate in such experiments can be inappropriate, especially in the presence of roughness and misalignments of the block.

  • 223.
    Rudnytskyj, André
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Rodiouchkina, Maria
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hultqvist, Tobias
    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.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Contact mechanics and wear of self-lubricating polymer bearings used in hydropower applications2018Conference paper (Refereed)
    Abstract [en]

    Hydropower plants are today subjected to more frequent transient operating conditions due to the increased use of intermittent energy production sources, such as solar and wind. The changes arise from the need to regulate the power input to the electrical grid, posing questions on the reliability of the self-lubricated bearings used in hydropower applications. Aiming to study the effects of the transient conditions on wear and lifetime of these bearings, modelling and simulation have been employed to systematically investigate how different parameters influence the sliding contact. A simplified model developed using COMSOL Multiphysics 5.3 and LiveLink™ for MATLAB® of polymer composite bearing materials and stainless steel counter surface is presented and evaluated under different tribological conditions in terms of properties such as pressure, sliding speed, temperature and wear. Roughness of real surfaces is measured by white light interferometry and integrated in the model. Experimental results on the influence of important parameters on the behavior of such bearings are also presented, not only to validate the model, but also to provide input data to the simulation. The results of this study show that the simulation model can be used to identify critical operating conditions for self-lubricating bearings used in hydropower applications.

  • 224.
    Ràfols, Francesc Pérez
    et al.
    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.
    Van Riet, Egbert J.
    Shell Global Solutions International BV, Innovation, Research and Development, Rijswijk, The Netherlands.
    Almqvist, Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    On the loading and unloading of metal-to-metal seals: A two-scale stochastic approach2018In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 232, no 12, p. 1525-1537Article in journal (Refereed)
    Abstract [en]

    During operation, the mating surfaces of a metal-to-metal seal typically undergo significant plastic deformation, which in turn can have beneficial effect on its performance. In previous studies, it has, for instance, been shown that plastic deformation can provide for better sealing during unloading. Those studies did, however, only consider flow through unrealistically small domains. Therefore, it is possible that this might be a size effect, which would not be apparent in a real situation with a much larger domain. In this paper, we develop a model which can handle real-sized seal domains at the same time as fine details of the surface topography. More precisely, we construct a two-scale model, in which the global scale represents the seal domain and where the influence of the fine details at the local scale are represented by a stochastic element. By means of this stochastic two-scale model, we show that the beneficial effect associated with the plastic deformation persists also when real-sized seal domains are considered.

  • 225. Sahlin, Fredrik
    et al.
    Almqvist, Andreas
    Glavatskih, Sergei
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    A cavitation algorithm for arbitrary lubricant compressibility2005In: Proceedings of the World Tribology Congress III - 2005: presented at ..., September 12 - 16, 2005, Washington, DC, New York: American Society of Mechanical Engineers , 2005, Vol. Paper no 63940, p. 541-542Conference paper (Refereed)
    Abstract [en]

    A general cavitation algorithm is presented that accommodates for an arbitrary density-pressure relation. Here it is possible to model the compressibility of the lubricant in such way the density-pressure relation is realistic from sub-cavity to high pressure regions respectively. The algorithm preserves mass continuity which is of importance when inter-asperity cavitation of rough surfaces is considered. Results with this algorithm for different density-pressure relations are presented and discussed.

  • 226. Sahlin, Fredrik
    et al.
    Almqvist, Andreas
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Glavatskih, Sergei
    A cavitation algorithm for arbitrary lubricant compressibility2007In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 40, no 8, p. 1294-1300Article in journal (Refereed)
    Abstract [en]

    A general cavitation algorithm that accommodates for an arbitrary density-pressure relation is presented. It is now possible to model the compressibility of the lubricant in such a way that the density-pressure relation is realistic throughout the contact. The algorithm preserves mass continuity for cavitation caused by bearing geometry and surface topography. It is a commonly accepted physical assumption that the contribution of the pressure driven flow is negligible in the cavitated region. This phenomenon is adopted in the present algorithm, which is similar to that of Elrod, and is modeled by a switch function that terminates the pressure gradient at the cavitation regions. Results with this algorithm for different density-pressure relations are presented and discussed. The effects of inlet conditions, such as surface roughness and starvation, on the load carrying capacity of the contact are analyzed.

  • 227.
    Sahlin, Fredrik
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Almqvist, Andreas
    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.
    Glavatskih, Sergei
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Rough surface flow factors in full film lubrication based on a homogenization technique2007In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 40, no 7, p. 1025-1034Article in journal (Refereed)
    Abstract [en]

    This paper describes a method to compute the flow factors that compensate for an arbitrary surface roughness in a compressible hydrodynamic lubrication based on a homogenization technique. The Reynolds equation is used as the governing equation and the two-scale expansion involved in the homogenization process enables the local roughness scale to be treated separately from the global geometry scale. With this method, it is possible to compute the flow factors for any deterministic roughness. Measured two-dimensional surface profiles are used as examples. Profiles having the same Abbot curve are also shown to have the same flow factors, providing an efficient classification of surfaces in hydrodynamic two-dimensional contacts. Flow factors are computed for the rough surface profiles, and solutions for global bearing geometry are obtained and compared with the corresponding solutions from a smooth geometry.

  • 228. Sahlin, Fredrik
    et al.
    Glavatskih, Sergei
    Almqvist, Torbjörn
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    2D CFD-analysis of micro-patterned surfaces in hydrodynamic lubrication2004In: Proceedings of the ASME/STLE international joint tribology conference 2004: October 24 - 27, 2004, Long Beach, California, USA, New York, 2004, Vol. Paper no 64009, p. 1637-1645Conference paper (Refereed)
    Abstract [en]

    Results of a numerical study of the influence of micro-patterned surfaces in hydrodynamic lubrication of two parallel walls are reported. Two types of parameterized grooves with the same order of depth as the film thickness are used on one stationary wall. The other wall is smooth and is sliding with a specified tangential velocity. Isothermal incompressible two dimensional full film fluid flow mechanics is solved using a Computational Fluid Dynamics method. It is shown that, by introducing a micro-pattern on one of two parallel walls, a net pressure rise in the fluid domain is achieved. This produces a load carrying capacity on the walls which is mainly contributed by fluid inertia. The load carrying capacity increases with Reynolds number. The load carrying capacity is reported to increase with groove width and depth. However, at a certain depth a vortex appears in the groove and near this value the maximum load carrying capacity is achieved. It is shown that the friction force decreases with deeper and wider grooves. Among all geometries studied, optimum geometry shapes in terms of hydrodynamic performance are reported.

  • 229. Sahlin, Fredrik
    et al.
    Glavatskih, Sergei
    Almqvist, Torbjörn
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Two-dimensional CFD-analysis of micro-patterned surfaces in hydrodynamic lubrication2005In: Journal of tribology, ISSN 0742-4787, E-ISSN 1528-8897, Vol. 127, no 1, p. 96-102Article in journal (Refereed)
    Abstract [en]

    Results of a numerical study of the influence of micro-patterned surfaces in hydrodynamic lubrication of two parallel walls are reported. Two types of parameterized grooves with the same order of depth as the film thickness are used on one stationary wall. The other wall is smooth and is sliding with a specified tangential velocity. Isothermal incompressible two dimensional full film fluid flow mechanics is solved using a Computational Fluid Dynamics method. It is shown that, by introducing a micro-pattern on one of two parallel walls, a net pressure rise in the fluid domain is achieved. This produces a load carrying capacity on the walls which is mainly contributed by fluid inertia. The load carrying capacity increases with Reynolds number. The load carrying capacity is reported to increase with groove width and depth. However, at a certain depth a vortex appears in the groove and near this value the maximum load carrying capacity is achieved. It is shown that the friction force decreases with deeper and wider grooves. Among all geometries studied, optimum geometry shapes in terms of hydrodynamic performance are reported

  • 230.
    Sahlin, Fredrik
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements. Siemens Industrial Turbomachinery, Finspong, Sweden.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Almqvist, Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Lugt, Piet M.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements. SKF Engineering & Research Centre, Nieuwegein, The Netherlands.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    A mixed lubrication model incorporating measured surface topography. Part 1: Theory of flow factors2010In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 224, no 4, p. 335-351Article in journal (Refereed)
    Abstract [en]

    A mixed lubrication model that permits real three-dimensional surface topography as input is developed. The theory of computing flow factors within the model is presented, and with a following paper (Part 2) the method of measuring and adapting the surface roughness, and model validation through flow measurements and application to a bearing is shown. A contact mechanics model is used to calculate the elastoplastic displacement of a periodic topography signal. A method based on homogenization is used to calculate flow factors for all lubrication regimes. The flow factors are compared with the Patir and Cheng method. Results indicate that the two methods compare well for longitudinal roughness lay, but differ significantly for a cross-patterned surface roughness due to the more complete flow description of the current model.

  • 231.
    Sahlin, Fredrik
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements. Siemens Industrial Turbomachinery, Finspong, Sweden.
    Larsson, Roland
    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.
    Almqvist, Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Lugt, Piet M.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements. SKF Engineering and Research Centre, Nieuwegein, The Netherlands.
    A mixed lubrication model incorporating measured surface topography. Part 2: Roughness treatment, model validation, and simulation2010In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 224, no 4, p. 353-365Article in journal (Refereed)
    Abstract [en]

    A mixed lubrication flow factor model that permits real three-dimensional surface topography as input has been developed. Part 1 gives the theory of computing flow factors within the model. In this article, a method of adapting the measured surface topography signal to suit the numerical models is developed and presented in detail. The mixed lubrication model is validated through flow measurements for three different rough surface test specimens. Simulation of a hydrodynamic bearing was conducted and the results are presented in terms of pressure distributions and Stribeck curves covering all lubrication regimes. The results indicate that the model may be an efficient and accurate engineering design and research tool for tribological devices operating in all lubrication regimes.

  • 232.
    Sandberg, Joakim
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Kalliorinne, Kalle
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hindér, Gustav
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Holmberg, Hans-Christer
    Luleå University of Technology, Department of Health, Education and Technology, Health, Medicine and Rehabilitation.
    Almqvist, Andreas
    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.
    A Novel Free-Gliding Ski Tribometer for Quantification of Ski–Snow Friction with High Precision2023In: Tribology letters, ISSN 1023-8883, E-ISSN 1573-2711, Vol. 71, no 4, article id 111Article in journal (Refereed)
    Abstract [en]

    The nature of snow and the ever-changing environment makes measuring friction on snow and ice challenging. Additionally, due to the low friction involved, the equipment used must exhibit high sensitivity. Previous investigations of ski–snow friction have ranged from small-scale model experiments performed in the laboratory to experiments with full-sized skis outdoors. However, few have been conducted under conditions similar to those encountered during actual skiing. Here, we present a novel sled tribometer which provides highly reproducible coefficient of friction (COF) values for full-sized skis gliding at relevant speeds (approximately 5.9 m/s) in a controlled indoor environment. The relative standard deviation (RSD) of the COF is as low as 0.5%. The continuous recording of velocity allows for innovative investigations into COF variations when skis are permitted to free-glide in a natural setting. Different methods of analysing the results are presented which shows that the precision is not a single number, but a function of the range of velocities over which the average COF is calculated.

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    fulltext
  • 233.
    Schnabel, Stephan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Golling, Stefan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    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.
    Absolute Measurement of Elastic Waves Excited by Hertzian Contacts in Boundary Restricted Systems2017In: Tribology letters, ISSN 1023-8883, E-ISSN 1573-2711, Vol. 65, no 1, article id 7Article in journal (Refereed)
    Abstract [en]

    In most applied monitoring investigations using acoustic emission, measurements are carried out relatively, even though that limits the use of the extracted information. The authors believe acoustic emission monitoring can be improved by instead using absolute measurements. However, knowledge about absolute measurement in boundary restricted systems is limited. This article evaluates a method for absolute calibration of acoustic emission transducers and evaluates its performance in a boundary restricted system. Absolute measured signals of Hertzian contact excited elastic waves in boundary restricted systems were studied with respect to contact time and excitation energy. Good agreement is shown between measured and calculated signals. For contact times short enough to avoid interaction between elastic waves and initiating forces, the signals contain both resonances and zero frequencies, whereas for longer contact times the signals exclusively contained resonances. For both cases, a Green’s function model and measured signals showed good agreement.

  • 234.
    Schnabel, Stephan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Golling, Stefan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    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.
    The influence of contact time and event frequency on acoustic emission signals2017In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 231, no 10, p. 1341-1349Article in journal (Refereed)
    Abstract [en]

    Studies of acoustic emissions (AE) of rotating machine elements is often performed under a constant speed. There are few investigations on speed and contact time dependency of acoustic emission signals, even though some investigations have reported difficulties at elevated rotational speeds. Simplified experiments are, therefore, presented in this article to increase the understanding of the time dependency of acoustic emission signals. Hertzian impacts and tensile tests are used to study contact time, the time duration of an event and offset time, the time between events and accordingly the event frequency. The results of these model experiments indicate an indirect quadratic proportionality of acoustic emission amplitudes and contact time (umax∝1/(tc2)">u max ∝1/(t 2 c ) umax∝1/(tc2) ), as well as a proportional relationship between the root mean square and event frequency (RMS∝fevent∝1/toffset">RMS∝f event ∝1/t offset  RMS∝fevent∝1/toffset ). The relationship between contact time and the root mean square of acoustic emission signals is strongly dependent on the damping of the system

  • 235.
    Schnabel, Stephan
    et al.
    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.
    Contact resistance measurements as a monitoring tool for running in processes of point contacts2013Conference paper (Refereed)
  • 236.
    Schnabel, Stephan
    et al.
    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.
    Elastic Waves of a Single Elasto-Hydrodynamically Lubricated Contact2017In: Tribology letters, ISSN 1023-8883, E-ISSN 1573-2711, Vol. 65, no 1, article id 5Article in journal (Refereed)
    Abstract [en]

    Elastic waves are widely used for condition monitoring of rolling element bearings through vibration or acoustic emission measurements . While vibration signals are understood to a high degree due to many scientific investigations as well as a long history of usage in the field, acoustic emission signals of rolling element bearings are poorly understood. Therefore, this investigation presents simulation studies and measurements of a single elasto-hydrodynamically lubricated (EHL) contact. In this investigation the EHL contact is a ball bouncing on a lubricated plate. The simulation based on Green’s function and the measurements based on a accelerometer to some extent agree. A shift of zero frequencies towards higher frequencies when compared to Hertzian reference measurements was determined for an infinite plate setup. Taking boundary restrictions into account, elastic waves of a Hertzian contact and an EHL contact only differ by a damping of higher resonances which is most likely caused by the EHL film.

  • 237.
    Schnabel, Stephan
    et al.
    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.
    Study of the short term effect of Fe3O4 particles in rolling element bearings: Observation of vibration, friction and change of surface topography of contaminated angular contact ball bearings2013Conference paper (Refereed)
    Download full text (pdf)
    FULLTEXT01
  • 238.
    Schnabel, Stephan
    et al.
    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.
    Study of the short-term effect of Fe3O4 particles in rolling element bearings: Observation of vibration, friction and change of surface topography of contaminated angular contact ball bearings2014In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 228, no 10, p. 1063-1070Article in journal (Refereed)
    Abstract [en]

    The harsh environment rolling element bearings are exposed to in iron-mining industries is replicated in a laboratory scale in this work. Bearings (SKF 7204BEP) were tested both with and without magnetite oxide (Fe3O4) contamination. In order to study the interaction between contaminants and extreme pressure additives, the rolling element bearings were lubricated with two different greases: Grease without extreme pressure and grease containing sulphur-based extreme pressure additives. Further, the effect of the contamination–additive interaction on rolling bearing performance and monitoring signals (vibration and acoustic emission) was investigated. The obtained results indicate an advantage of extreme pressure additive in case of the investigated operating conditions. Furthermore, the use of extreme pressure additives decreased wear, surface roughness, vibration and acoustic emission for both test durations of 24 h and 168 h. The decrease of the acoustic emissions and the surface roughness parameter Rq in case of the tests with a duration of 168 h as high as 70% and 60%, respectively using extreme pressure additives in comparison with the plain grease was observed. The major cause for this reduction seems to be the interaction between contaminants and extreme pressure additives.

  • 239.
    Schnabel, Stephan
    et al.
    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.
    Golling, Stefan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    The Detection of Plastic Deformation in Rolling Element Bearings by Acoustic Emission2017In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 110, p. 209-215Article in journal (Refereed)
    Abstract [en]

    The detection of plastic deformation caused by particle contamination in rolling element bearings using acoustic emission is reliable at low speeds as shown in several studies. However, there are no studies at greater speeds of the detection of plastic deformation by acoustic emission in rolling element bearings. The acoustic emission signals of rolling element bearings have, however, been shown to be dominated by transient force signals which are elastic waves caused by transient forces acting at the raceway surface. The results of the test showed a dominance of transient force signals at elevated speeds, which masks signals caused by plastic deformation and prohibits the detection of particle contamination, while at low rotational speed plastic deformation is detected by acoustic emission.

  • 240.
    Schnabel, Stephan
    et al.
    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.
    Minami, Ichiro
    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.
    Monitoring of Running-in of an EHL contact using Contact Impedance2016In: Tribology letters, ISSN 1023-8883, E-ISSN 1573-2711, Vol. 63, no 3, article id 35Article in journal (Refereed)
    Abstract [en]

    Running-in is an important process for elasto-hydrodynamic lubricated contacts, which affect both service life and operating performance. However, the possibilities of monitoring running-in are still poor. Therefore, the properties of electrical contact impedance as a monitoring tool were studied by using an in-house made ball on disc apparatus. The contact impedance was monitored during run-in experiments with different initial surface roughness of the discs, different slide-to-roll ratios and with pure or additive containing paraffinic oil. The relationship between surface roughness parameters, contact resistance and contact capacitance was investigated. While the contact resistance seems to be affected by the parameter Rz, the contact capacitance seems more dependent on Rq. In addition, the experiments showed that surface active additives do not necessarily need to influence the contact impedance.

  • 241.
    Shi, Yijun
    et al.
    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.
    Non-corrosive and Biomaterials Protic Ionic Liquids with High Lubricating Performance2016In: Tribology letters, ISSN 1023-8883, E-ISSN 1573-2711, Vol. 63, no 1, article id 1Article in journal (Refereed)
    Abstract [en]

    Achieving non-corrosive and green ionic liquids is a big challenge for the tribologist. A kind of biomaterials-based protic ionic liquids (PILs) was synthesized in this paper. Rapeseed oil, group 1 mineral oil and one commercially available fully formulated gear oil were as used reference to study the property of the synthesized PILs. The copper strip standard corrosion test was employed to study the anti-corrosion property. The boundary lubrication and elastohydrodynamic lubrication performance of the lubricants was studied on an Optimol SRV-III oscillating friction and wear tester, and a WAM (model 11) ball-on-disk test rig, respectively. The lubricating mechanism of the synthesized PILs was also discussed in this paper

  • 242.
    Shi, Yijun
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Minami, Ichiro
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Grahn, Mattias
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Björling, Marcus
    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.
    Boundary and elastohydrodynamic lubrication studies of glycerol aqueous solutions as green lubricants2014In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 69, p. 39-45Article in journal (Refereed)
    Abstract [en]

    In this paper, the boundary and elastohydrodynamic lubricating behaviour of glycerol and its aqueous solutions are discussed in both rolling and sliding contacts with a view on assessing the use of glycerol as a green lubricant. To understand the lubricating mechanism, the film thickness of glycerol and its aqueous solutions were studied at different velocities. The results show that the viscosity of glycerol can be controlled for a wide range by adding different amounts of water. The lubricating behaviour of glycerol in all lubricating regimes can be improved by adding water. The results suggest that glycerol aqueous solutions have great potential to replace rapeseed oils as environmentally friendly base oils in several applications.

  • 243.
    Shirzadegan, Mohammad
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Almqvist, Andreas
    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.
    Fully coupled EHL model for simulation of finite length line cam-roller follower contacts2016In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 103, p. 584-598Article in journal (Refereed)
    Abstract [en]

    This paper presents a fully coupled multiphysics model developed for numerical simulation of the elastohydrodynamically lubricated contact between a cam and roller, typically found in cam mechanisms controlling fuel injection in an internal combustion engine. Special attention was focused on enabling systematic analyses of effects associated with, roller crowning and edge geometries, lubricant rheology as well as typical cam mechanism operating conditions. The interaction between the cam and roller follower result in high generated pressure and narrow film thickness that increase the risk of wear and fatigue. Furthermore, this article highlights the variation of pressure and film thickness under tilting conditions. The model was also validated against some particular model problems, found in the literature.

  • 244.
    Shirzadegan, Mohammad
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Björling, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Almqvist, Andreas
    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.
    Low degree of freedom approach for predicting friction in elastohydrodynamically lubricated contacts2016In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 94, p. 560-570Article in journal (Refereed)
    Abstract [en]

    A low degree of freedom, semi-analytical model for rapid estimation of the friction coefficient in elastohydrodynamically lubricated contacts was developed and tested. Its estimates are based on the shear rate dependent Carreau equation for the apparent viscosity, together with the hydrodynamic pressure and the temperature of the lubricant. To validate the approach, the model's predictions were compared to experimental coefficient of friction measurements acquired using a ball-on-disc test device at various applied loads, entrainment velocities, and slide to roll ratios. The model’s predictions were in good agreement with the experimental results, showing that it is suitable for use in multibody dynamics analyses where rapid computation of elastohydrodynamic friction is required to minimize computing time and resource consumption.

  • 245.
    Shirzadegan, Mohammad
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Björling, Marcus
    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.
    Almqvist, Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Low degree of freedom EHL friction: Through fast estimation2015In: 42nd Leeds-Lyon Symposium on Tribology, 2015Conference paper (Refereed)
  • 246.
    Shirzadegan, Mohammad
    et al.
    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.
    Almqvist, Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    A low degree of freedom approach for prediction of friction in finite EHL line contacts2017In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 115, p. 628-639Article in journal (Refereed)
    Abstract [en]

    A low degree of freedom (LDOF) approach for expedient prediction of friction in finite EHL line contact is presented. Friction prediction are in good agreement with existing results for all of the reference cases tested. With the present LDOF approach, friction predictions can be obtained thousands of times faster than if using a fully coupled FE-based model. It can, therefore be used to simulated the tribological contacts in multi-body dynamic (MBD) systems with millions of degrees of freedoms. The model was utilised to study edge stress concentrations due to roller tilt. The results confirmed that increasing the tilting angle increases the maximum pressure and shifts its location towards the edge of roller. An increase in total friction was also observed.

  • 247.
    Shirzadegan, Mohammad
    et al.
    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.
    Almqvist, Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Numerical analysis of EHL in cam mechanisms2016In: Nordic Symposium on Tribology - NORDTRIB 2016, 2016Conference paper (Refereed)
  • 248.
    Solimanjad, N.
    et al.
    Luleå University of Technology.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Die wall friction and influence of some process parameters on friction in iron powder compaction2003In: Materials Science and Technology, ISSN 0267-0836, E-ISSN 1743-2847, Vol. 19, no 12, p. 1777-1782Article in journal (Refereed)
    Abstract [en]

    The coefficient of friction is a system response parameter, which is affected by a number of parameters such as normal load and sliding distance. Experimental results describing the influence of these parameters are presented in this study. These parameters have a crucial role in the modelling of the compaction process and also provide an in depth understanding of the mechanism of friction in powder compaction. The powder surface characteristics change continuously during the pressing, making friction measurement quite difficult. An attempt has been made to identify and separate the powder behaviour during compaction. The experimental results show that the plastic deformation of the surface in contact with the die wall occurs at an early stage of the compacting. At densities above 5 g cm3 the plastic deformation is completed and the variation of the coefficient of friction is minimal. It has been observed that most changes of the powder surface occur at low densities. The nature of the friction has also been discussed.

  • 249. Solimanjad, N.
    et al.
    Wikström, H.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    A new device for measurement of friction during metal powder compaction2001In: Advances in powder metallurgy & particulate materials - 2001: proceedings of the 2001 International Conference on Powder Metallurgy & Particulate Materials ; May 13-17th, New Orleans / [ed] William B. Eisen, Princeton, NJ: Metal powder industries federation , 2001, p. 323-330Conference paper (Refereed)
    Abstract [en]

    In order to investigate friction behaviour of powder during the compaction, die pressing is often used. Compaction is a complicated process and direct and continuous measurement of coefficient of friction is not easy. The coefficient of friction varies due to changes in the pressure distributions during compaction. In this paper a new device for measuring the coefficient of friction between metal powder particles in contact with the die-wall during compaction is presented. The device is able to measure the friction coefficient between the powder particles and the die-wall directly and continuously. Sliding velocity, compaction velocity, normal load and temperature can be monitored and controlled. Measurement of the coefficient of friction at low densities is one of the advantages, and possible application, of this apparatus.

  • 250.
    Solimannezhad, Naghi
    et al.
    Luleå University of Technology.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Dependence of friction on various parameters in the metal powder compaction process1999In: Advances in powder metallurgy and parrticulate materials: proceedings of the 1999 International Conference on Powder Metallurgy & Particulate Materials, June 20-24, 1999 Vancouver / [ed] Charles L. Rose, Princeton, NJ: Metal powder industries federation , 1999Conference paper (Refereed)
234567 201 - 250 of 301
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