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  • 51.
    Cha, Yingying
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Tu, Minghui
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Elmgren, Max
    Silvergren, Sanna
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Variation in Airborne Particulate Levels at a Newly Opened Underground Railway Station2019In: Aerosol and Air Quality Research, ISSN 1680-8584, E-ISSN 2071-1409, Vol. 19, no 4, p. 737-748Article in journal (Refereed)
    Abstract [en]

    The construction of a new railway tunnel for commuter trains in Stockholm was completed in 2017. It included two modern stations (Odenplan and Stockholm City) with platform screen doors (PSD) and one old station (Stockholm Sodra) without PSDs. This study evaluates the concentrations of airborne particulates at the new Odenplan station, focusing on the effects of traffic operation, system age and train movement. For comparison, the other two stations in the tunnel and an above-ground railway station (Solna) were also investigated. The new platform was clean prior to opening for traffic (the average concentration of PM10 and PM2.5 was 12 and 2 mu g m(-3), respectively). Substantial increases in the PM10 and PM2.5 levels were observed after it came into service, with the average concentrations increasing to 120 and 30 mu g m(-3) after 1 week and then to 175 and 35 mu g m(-3) after 3 months of operation. The train movement factor (traffic frequency and train stopping period) was found to have a strong effect on the coarse-sized particle concentrations (0.3-10 mu m). Comparable levels of PM10 and PM2.5 were measured at both the new Odenplan station and the old station, where the amount of traffic was similar. For the other new station, Stockholm City, where traffic was only half as frequent, the PM10 and PM2.5 levels were substantially lower.

  • 52.
    Cha, Yingying
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Tu, Minghui
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Elmgren, Max
    SLB-analys, Environment and Health Administration, Stockholm, Sweden.
    Silvergren, Sanna
    SLB-analys, Environment and Health Administration, Stockholm, Sweden.
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Variation of airborne particulate levels in a newly built railway tunnel2018In: Aerosol and Air Quality Research, ISSN 1680-8584, E-ISSN 2071-1409Article in journal (Other academic)
    Abstract [en]

    The construction of a new railway tunnel for commuter trains in Stockholm was completed in 2017. It included two modern stations (Odenplan and Stockholm City) with platform screen doors (PSD) and one old station (Stockholm Södra) without PSDs. This study evaluates the concentrations of airborne particulates for the new stations, focussing on the effects of traffic operation, system age and train movement. For comparison, the other old station in the tunnel and an above-ground railway station (Solna) were also investigated. The new Odenplan platform was clean before its opening for traffic (12 and 2 μg/m3 for average PM10 and PM2.5, respectively). Substantial increases in the PM10 and PM2.5 concentrations were observed after it came into service. The average levels of PM10 and PM2.5 increased to 120 and 30 μg/m3 after one week of operation, and increased again to 175 and 35 μg/m3 after 3 months. The train movement factor (traffic frequency and train stop period) was found to have a strong effect on the particle concentrations of coarse sizes (0.3–10 μm). Comparable levels of PM10 and PM2.5 were measured at both the new station and the old station where the traffic frequency was similar. For the other new station, which had half the traffic frequency due to the station design with two separate platforms, the PM10 and PM2.5 levels were substantially lower.

  • 53.
    Duvefelt, Kenneth B. K.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Olofsson, Ulf L-O
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Johannesson, Carl Michael J.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Towards simultaneous measurements of skin friction and contact area: Results and experiences2015In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 229, no 3, p. 230-242Article in journal (Refereed)
    Abstract [en]

    This article investigates one of the important parameters when designing for feel, namely the friction coefficient. An experiment was performed to evaluate how fringe projection could be used to investigate the topography of the fingertip, especially while in contact and sliding on a smooth surface. By allowing this smooth surface to be a small sheet of glass, a topographic camera could take pictures through it. The glass was also connected to a universal force gauge to measure normal and tangential forces from which the coefficient of friction could be calculated. The intention was to get dependable data on the forces, coefficient of friction, apparent contact area and actual contact area. This set-up was tested using 66 students who used one and three fingers in both dry and wet conditions and with a rubber glove. In order to measure natural everyday friction, they were not given any particular instructions on how to clean or slide their fingers. This method resulted in a much higher variation in friction coefficients than has been found in previous research. In particular, many higher values were noticed. This illustrates that the friction coefficient is a very hard parameter to rely on when it comes to designing surfaces for feel.

  • 54.
    Duvefelt, Kenneth
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Four similar surfaces with different feel – a tactile study on adhesion, friction, Young’s modulus and thermal conductivity2016Manuscript (preprint) (Other academic)
    Abstract [en]

    Even surfaces that look the same and have the same topography have a different feel to them. How is this difference related to material properties? In this paper four surfaces (aluminosilicate glass, soda‑lime glass, polycarbonate and polyurethane) were evaluated by a test panel. The purpose was to study whether the panel could distinguish different material parameters, in particular the adhesion. Results showed that the test panel could sense differences in thermal conductivity, Young’s modulus and adhesion. The results also showed that the measured friction coefficients did not correspond to the test panels’ subjective opinion, unlike the perceived and measured adhesion force.

  • 55.
    Duvefelt, Kenneth
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Friction and adhesion on smooth surfaces in different climates – an evaluation of a polymer bioskin for tactile measurements2016Manuscript (preprint) (Other academic)
    Abstract [sv]

    Whether a surface feels good or not is obviously up to personal preference but the physical interaction between finger and surface can be measured and explained. For a smooth surface the sensation of touching is mainly determined by perceived friction and stickiness. Therefor would it be useful with an easy way to measure these properties and being able to specify the tactile properties of a surface without measuring finger friction and doing subjective tests with a test panel. For this have a polymer bioskin probe been tested in friction and adhesion measure­ments in three different climates. Results showed that tests with bioskin correlated better for tests on glass than on polymer surfaces and better in dry conditions than warm and humid. This means that in the right environment even a simple adhesion test can be used to grade tactile properties of smooth surfaces.

  • 56.
    Duvefelt, Kenneth
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Johannesson, Carl Michael
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Skedung, Lisa
    Model for contact between finger and sinusoidal plane to evaluate adhesion and deformation component of friction2016In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 96, p. 389-394Article in journal (Refereed)
    Abstract [en]

    One of the main parameters affecting finger friction, friction-induced vibrations in the finger, and consequently tactility is surface topography. Recently Skedung et al. performed finger friction measurements on fine controlled surfaces. These surfaces were sinusoidal with wavelengths from 0.27 to 8.8 mu m and amplitudes from 0.007 to 6 mu m. Building on those tests an analytical model for the contact was developed to explain the differences in friction coefficient. The contact was modelled as trapezoids in a circular pattern pressed against a sinusoidal plane. Results showed that the calculated contact area and therefore friction coefficient corresponded well with the measurements. This model can be used to see how the different surface parameters influence friction.

  • 57.
    Gustafsson, Mats
    et al.
    VTI - Swedish National Road and Transport Research Institute, Linköping, SE 581 95, Sweden.
    Abbasi, Saeed
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements.
    Blomqvist, Göran
    VTI - Swedish National Road and Transport Research Institute, Linköping, SE 581 95, Sweden.
    Gudmundsson, Anders
    Division of Ergonomics and Aerosol Technology, Lund University, SE 221 00, Lund, Sweden.
    Janhäll, Sara
    VTI - Swedish National Road and Transport Research Institute, Linköping, SE 581 95, Sweden.
    Johansson, Christian
    Department of Applied Environmental Science, Stockholm University, SE 106 91, Stockholm, Sweden.
    Norman, Micheal
    Stockholm Environment and Health Administration, SLB-analys, SE 104 20, Stockholm, Sweden.
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements.
    Sjövall, Bill
    Stockholm Environment and Health Administration, SLB-analys, SE 104 20, Stockholm, Sweden.
    Wilhelmsson, H
    VTI - Swedish National Road and Transport Research Institute, Linköping, SE 581 95, Sweden.
    Particles in road and railroad tunnel air: properties, sources and abatement possibilities2013Conference paper (Refereed)
  • 58.
    Hailong, Liu
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Jonsson, Lage
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy. FOI, Swedish Defence Research Agency, Division of CBRN Defence and Security, Umeå, Sweden ..
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Jönsson, Pär
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    A simulation study of particles generated from pellet wear contacts during a laboratory testManuscript (preprint) (Other academic)
    Abstract [en]

    In the blast furnace process, material losses occur due to mechanical wear between charged iron ore pellets and are exhausted in the form of dust in the off-gases. A redesigned tribometer combined with a ventilation chamber was developed to identify the dust emission from the mechanical wear contact of pellets. In order to obtain a better understanding of the measurement results, a coupled drift flux with a unified Eulerian deposition model was adopted to investigate particle dispersion and deposition during tests. Two influential factors, namely the air condition (5-20 l/min) and particle size (1-20 µm) were examined. The predicted results were presented by introducing two parameters, namely the measurable fraction and the deposition fraction. For each air condition, the measurable fraction declines while the deposition fraction rises as particle size grows. The critical size of the particles that becomes airborne and captured at the outlet was identified to be around 20 µm. In addition, a high airflow rate supplied at the inlet was observed to be favorable for improving the measurable fraction. Nevertheless, the results show that nearly 50 % of emitted particles (1-20 µm) that failed to be captured during tests. Thus it could be expected that these generated particles would be transported deeply in a blast furnace if they are not efficiently removed from the off-gas. As a consequence, they may influence the quality of the products. Furthermore, the validation of the simulation results against the experimental data was achieved by using the predicted measurable fraction.

  • 59. Hardwick, C.
    et al.
    Lewis, R.
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM).
    Low adhesion due to oxide formation in the presence of NaCl2012In: 9th International Conference on Contact Mechanics and Wear of Rail/Wheel Systems, CM 2012, 2012, p. 309-317Conference paper (Refereed)
    Abstract [en]

    This paper outlines work carried out to assess how adhesion may be influenced by contamination of the rail head with salt/grit from level crossings during winter months when they are applied to the road surfaces as a preventative method to stop ice formation. Twin-disc testing was carried out in which a mechanically formed oxide layer was produced on the disc specimens prior to assessing adhesion levels under realistic contact pressures and slips in the following conditions: dry, wet, dry salt, and two salt-water solutions. Under dry conditions adhesion levels differ little from reference tests without an oxide layer, however, the presence of an oxide layer under wet conditions can be seen to further reduce adhesion from a reference level (0.2) to below 0.1. When NaCl is entrained into the contact it increases adhesion levels above that seen under wet conditions in the presence of an oxide layer, however, the presence of NaCl is most likely to affect the generation of rail head oxides in the first place and in turn influence adhesion.

  • 60. Hardwick, Christopher
    et al.
    Lewis, Roger
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Low adhesion due to oxide formation in the presence of salt2014In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 228, no 8, p. 887-897Article in journal (Refereed)
    Abstract [en]

    This paper outlines work carried out to assess how, during winter months, adhesion may be influenced by contamination of the rail head by the salt/grit that is applied to road surfaces as a preventative method to stop ice formation. Twin-disc testing was carried out in which a mechanically formed oxide layer was produced on the disc specimens prior to assessing adhesion levels under realistic contact pressures and slips in the following conditions: dry, wet, dry salt and two salt/water solutions. Under dry conditions adhesion levels differ little from reference tests without an oxide layer, however, the presence of an oxide layer under wet conditions can be seen to further reduce adhesion from a reference level (0.2) to below 0.1. When salt is entrained into the contact it increases adhesion levels above that seen under wet conditions in the presence of an oxide layer, however, the presence of salt is most likely to affect the generation of rail head oxides in the first place and in turn influence adhesion.

  • 61. Harper, P.
    et al.
    Dwyer-Joyce, R.S.
    Sjödin, Ulf
    University of Sheffield, United Kingdom .
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Evaluation of an ultrasonic method for measurement of oil film thickness in a hydraulic motor piston ring2005In: Life Cycle Tribology, Elsevier, 2005, p. 305-312Chapter in book (Refereed)
    Abstract [en]

    The efficiency of a hydraulic motor depends on the lubrication performance of the piston ring. If the film is too thin then wear occurs quickly, if it is too thick then oil is lost into the cylinder and efficiency is reduced. In this paper a technique for oil film measurement based on ultrasonic reflection is investigated. This has the potential to be used non-invasively on real components. An ultrasonic pulse will reflect from a thin film interposed between two solids. The proportion of the pulse that is reflected depends on the stiffness of the intermediate layer. If the acoustic properties of the film material are known, then the stiffness can readily be used to determine the film thickness. This principle has been employed for the piston ring lubrication case. A piston/cylinder test bench has been used to evaluate the ultrasonic method. A focusing piezo-electric transducer is mounted outside the cylinder and ultrasonic pulses reflected back from the inner bore. The variation of these pulses as the piston ring passes underneath is investigated and used to determine oil film thickness. Films in the range 0.7 to 1.3 μm were measured; the thickness did not depend strongly on either ring speed or sealed pressure. Several practical aspects were investigated such as, attenuation in the cylinder material, response time, and transducer resolution. Whilst this study demonstrated that film thickness measurement is feasible, there are a number of practical considerations that require further work, principally the focusing and coupling of the ultrasonic transducer and the response time.

  • 62. Houghton, A.
    et al.
    Lewis, R.
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Sundh, Jon
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Characterising and reducing seizure wear of inconel and incoloy superalloys in a sliding contact2011In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 271, no 9-10, p. 1671-1680Article in journal (Refereed)
    Abstract [en]

    Superalloys, such as Inconels and Incoloys, are extensively used where high strength is a requirement. However, where these materials are required to slide against one another, particularly with poor or no lubrication, high friction levels and seizure are commonly seen to occur, which can cause component failure. In this work seizure characteristics of three superalloys (Inconel 718 and Incoloys 945 and 945X) were investigated, uncoated, coated with Armoloy (a hard, thin, dense chrome coating with a micro-nodular surface texture) and plasma nitrided in dry sliding conditions. A rig purpose built for initiating seizure was used. It involves sliding a ball against a disc at constant speed while the load is increased. Tests are designed to last less than one rotation so that the wear scar can be analysed, along with friction data, to establish at which load seizure occurred. Balls made from Inconel 718 were used along with sliding velocities ranging between 0.1 and 0.25 m/s with a load range of 0-1400 N. Tests were repeated twice. Repeatable behaviour was achieved in the tests and from the results obtained, zones/points corresponding to "seizing", "seizure" and "seized" were identified based on previous definition from the literature. Friction coefficients behaviour was also characterised. It was found that Inconel 718 and Incoloy 945 performed better than Incoloy 945X. Applying an Armoloy coating increased the seizure load and led to lower friction rates. The application of plasma nitriding led to a more consistent (although high) friction coefficient, but less surface damage occurring.

  • 63. Höjer, M.
    et al.
    Bergseth, Ellen
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Nilsson, R.
    Lyu, Yezhe
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    A noise related track maintenance tool for severe wear detection of wheel-rail contact2016In: Civil-Comp Proceedings, ISSN 1759-3433, Vol. 110Article in journal (Refereed)
    Abstract [en]

    An on-board measurement system has been developed that in real time identifies the probability for occurrence and also the exact location of severe wear in the wheelrail contact. Noise generated by the wheel-rail contact is a troublesome side effect both when railway vehicles negotiate curves and run on straight tracks. The concept behind this project is to use this noise as an indicator of the transition from the mild wear regime to the severe/catastrophic wear regime that implies high maintenance cost. At first tribometers were used in a laboratory study to investigate the relationships between wear and the emitted noise. Wear transitions from mild to severe wear were always accompanied by an increase in sound pressure of about 10 dB. The transitions also changed the sound pressure amplitude distribution from a narrow banded to a broader banded distribution. Secondly a full scale test in a small radius curve in a depot was carried out using a metro train, type C20. In agreement with the laboratory tests, the same kind of transfer from mild to severe wear was identified on the full scale tests in the depot. In addition, the sound pressure changed significantly, both in amplitude and in distribution, when transferring from mild to severe wear. By comparing the noise from the inner wheel-rail contact to noise from the outer wheel-rail contact a wear detection parameter for the outer wheel-rail contact is suggested. The third part of this project involves validation of the maintenance tool by operating the instrumented train in normal metro traffic, while at the same time collecting wear particles and making replicate casts of the rail at critical locations in the metro. Further comparison with weather data and a maintenance log has also been performed. © Civil-Comp Press, 2016.

  • 64.
    Janhäll, Sara
    et al.
    VTI - Swedish National Road and Transport Research Institute, Linköping, SE 581 95, Sweden.
    Mats, Gustafsson
    VTI - Swedish National Road and Transport Research Institute, Linköping, SE 581 95, Sweden.
    Abbasi, Saeed
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements.
    Blomqvist, Göran
    VTI - Swedish National Road and Transport Research Institute, Linköping, SE 581 95, Sweden.
    Gudmundsson, Anders
    Division of Ergonomics and Aerosol Technology, Lund University, Lund, SE 221 00, Sweden.
    Johansson, Christian
    Department of Applied Environmental Science, Stockholm University, Stockholm, SE 106 91, Sweden.
    Norman, Michael
    Stockholm Environment and Health Administration, SLB-analysis, Stockholm, SE 104 20, Sweden.
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements.
    Sjövall, Bill
    Stockholm Environment and Health Administration, SLB-analysis, Stockholm, SE 104 20, Sweden.
    Road tunnels - particle properties, wet and dry conditions2013Conference paper (Refereed)
  • 65. Jansson, Anders
    et al.
    Olander, Lars
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Services Engineering (name changed to Building Service and Energy Systems 2012-03-01).
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements.
    Sundh, Jon
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements.
    Söderberg, Anders
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements.
    Wahlström, Jens
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Ultrafine Particle Formation from Wear2010In: The International Journal of Ventilation, ISSN 1473-3315, E-ISSN 2044-4044, Vol. 9, no 1, p. 83-88Article in journal (Refereed)
    Abstract [en]

    Much attention is given to the consequences of airborne particles on human health and well-being. Wear is one source of airborne particles and contributions in the urban environments from wheel-to-rail contacts and disc brakes cannot be neglected. Traditionally, mechanical wear has been associated with the generation of particles of diameters of some microns. However, the research described has found ultrafine particle generation from wear processes. Particle generation from wear was measured under controlled laboratory conditions. The wear was created through sliding contact in a tribometer (type "pin-on-disc") with different materials and with different sliding velocities and pressures, to represent rail traffic and automobile disc braking. Particle concentrations and size distributions in the air were determined for particle diameters from 10 nm up to more than 10 mu m. For most materials and conditions three particle size modes were found: one at 50-100 nm, one at a few hundred nm and one at a few mu m particle diameter.

  • 66. Karpov, Oleksii
    et al.
    Nosko, Pavlo
    Fil, Pavlo
    Nosko, Oleksii
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Prevention of resonance oscillations in gear mechanisms using non-circular gears2017In: Mechanism and machine theory, ISSN 0094-114X, E-ISSN 1873-3999, Vol. 114, p. 1-10Article in journal (Refereed)
    Abstract [en]

    One of the main disadvantages of gear mechanisms is the occurrence of noise and vibrations. This study investigated the applicability of non-circular gears for preventing resonance oscillations in gear mechanisms. The influence of a small deviation of the gear centrodes from the nominal circles on kinematic and oscillatory characteristics was analysed. It was shown that a larger deviation results in a smaller resonance amplitude due to mesh frequency variability and simultaneously in higher additional dynamic loads on the mechanism. The shape of the gear centrodes was determined which provides a relatively small resonance amplitude with minimum additional dynamic loads. A mechanical device was developed to enable cutting of slightly non-circular gears on a hobbing machine without numerical control.

  • 67. Kutelia, E. R.
    et al.
    Gventsadze, D. I.
    Eristavil, B. G.
    Maisuradze, N. I.
    Tsurtsumia, O. O.
    Gventsadze, L. D.
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Wahlström, Jens
    KTH, School of Industrial Engineering and Management (ITM), Applied Mechanical Engineering (KTH Södertälje).
    Olander, Lars
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Services Engineering (name changed to Building Service and Energy Systems 2012-03-01).
    The tribological efficiency and the mechanism of action of nano-porous composition base brake lining materials2011In: International Congress on Advances in Applied Physics and Materials Science, 2011, p. 546-554Conference paper (Refereed)
    Abstract [en]

    Based on the comparative analysis of the experimental values determined for the tribological parameters for the three novel nano-porous composition base and two conventional brake lining materials while friction with the grey cast iron disc, it was shown the considerable high tribological efficiency of the novel nano-porous composition base lining materials in comparison with the conventional (from EU and USA market) brake lining materials. The explanation is given to the action mechanism of nano-porous composition base brake lining material and its tribological efficiency basing on the "triple phase" tribo-pair model.

  • 68. Lewis, R.
    et al.
    Dwyer-Joyce, R. S.
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Pombo, J.
    Ambrosio, J.
    Pereira, M.
    Ariaudo, C.
    Kuka, N.
    Mapping railway wheel material wear mechanisms and transitions2010In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 224, no F3, p. 125-137Article in journal (Refereed)
    Abstract [en]

    In order to develop more durable wheel materials to cope with the new specifications being imposed on wheel wear, a greater understanding of the wear mechanisms and transitions occurring in wheel steels is needed, particularly at higher load and slip conditions. The aim of this work was to draw together current understanding of the wear mechanisms, regimes, and transitions (particularly with R8T wheel material) and new tests on R7T wheel material; to identify gaps in the knowledge; and to develop new tools for assessing wear of wheel materials, such as wear maps, that can be used to improve wear prediction. Wear assessment of wheel materials, as well as wear rates, regimes, and transitions, is discussed. Twin disc wear testing, used extensively for studying wear of wheel and rail materials, has indicated that three wear regimes exist for wheel materials: mild, severe, and catastrophic. These have been classified in terms of wear rate and features. Wear rates are seen to increase steadily initially and then level off, before increasing rapidly as the severity of the contact conditions is increased. Analysis of the contact conditions in terms of friction and slip has indicated that the levelling off of the wear rate observed at the first wear transition is caused by the change from partial slip to full slip conditions at the disc interface. Temperature calculations for the contact showed that the large increase in wear rates seen at the second wear transition may result from a thermally induced reduction in yield strength and other material properties. Comparisons made between discs and actual wheels have provided some support for the theories relating to the transitions observed. Wear maps have been produced using the test results to study how individual contact parameters such as load and sliding speed influence wear rates and transitions. The maps are also correlated to expected wheel-rail contact conditions. This improved understanding of wheel wear mechanisms and transitions will help in the aim of eventually attaining a wear modelling methodology reliant on material properties rather than on wear constants derived from testing.

  • 69. Lewis, R.
    et al.
    Magel, E.
    Wang, W. -J
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements.
    Lewis, S.
    Slatter, T.
    Beagles, A.
    Towards a standard approach for the wear testing of wheel and rail materials2017In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 231, no 7, p. 760-774Article in journal (Refereed)
    Abstract [en]

    An examination of the literature for the wear testing methodologies for wheel and rail materials reveals that while only a few different techniques have been used, there is a wide variety in exactly how the tests have been conducted and the resulting data reported. This makes comparison of the data very difficult. This work, carried out as part of the International Collaborative Research Initiative which is aiming to bring together the wheel–rail interface researchers from across the world to collate data and knowledge to try to solve some of the common problems that are faced, has examined the different approaches used and has attempted to pull together all the good practice used into a test specification for future twin-disc testing for wheel and rail materials. The adoption of the method will allow data to be compared reliably and eventually enable data to be compiled into wear maps to use as input, for example, to multi-body dynamics simulation wear prediction tools.

  • 70. Lewis, R.
    et al.
    Olofsson, Ulf
    KTH, Superseded Departments, Machine Design.
    Mapping rail wear regimes and transitions2004In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 257, no 08-jul, p. 721-729Article in journal (Refereed)
    Abstract [en]

    This paper outlines work carried out to produce maps of rail material wear coefficients taken from laboratory tests run on twin disc and pin-on-disc machines as well as those derived from measurements taken in the field. Wear regimes and transitions are identified using the maps and defined in terms of slip and contact pressure. Wear regimes are related to expected wheel/rail contact conditions and contact points (rail head/wheel tread and rail gauge/wheel flange). Surface morphologies are discussed and comparisons are made between field and laboratory data.

  • 71.
    Lewis, Roger
    et al.
    Department of Mechanical Engineering, University of Sheffield.
    Lewis, S.
    Department of Mechanical Engineering, University of Sheffield.
    Zhu, Yi
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi. KTH, School of Engineering Sciences (SCI), Centres, The KTH Railway Group.
    Abbasi, Saeed
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements. KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements. KTH, School of Engineering Sciences (SCI), Centres, The KTH Railway Group.
    The Modification of a Slip Resistance Meter for Measurement of Railhead Adhesion2013In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 227, no F2, p. 196-200Article in journal (Refereed)
    Abstract [en]

    The aim of this work was to find a quick, flexible and localised method for determining railhead adhesion. The proposed method is a pendulum rig, which has a rubber pad at the base of a swinging arm. The arm is released and as the rubber pad slides across the contact surface, energy is lost. This loss can be translated into a friction coefficient. Tests have been performed under dry and contaminated conditions, including water, oil and leaf layers both in the laboratory on extracted rail and in the field on live rail. Friction modifiers were also tested. The results of these tests are compared with data obtained using a hand-pushed tribometer. The performed study shows that the pendulum is a viable way to test adhesion levels in the field.

  • 72. Lewis, Roger
    et al.
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Basic tribology of the wheel-rail contact2009In: Wheel-Rail Interface Handbook, Woodhead Publishing Limited, 2009, p. 34-57Chapter in book (Refereed)
    Abstract [en]

    The aim of this chapter is to introduce some of the basics of wheel-rail tribology before the topics are dealt with in greater detail in the subsequent chapters. Wear, contact mechanics, fatigue and adhesion are covered. Great emphasis is placed on the need to consider these subjects together to optimise the management of the wheel-rail contact as they all interact with each other. Frequent references are made to chapters where further information on the issues being discussed can be found.

  • 73. Lewis, Roger
    et al.
    Olofsson, UlfKTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Wheel-Rail Interface Handbook2009Collection (editor) (Refereed)
    Abstract [en]

    Many of the engineering problems of particular importance to railways arise at interfaces and the safety-critical role of the wheel-rail interface is widely acknowledged. Thus better understanding of wheel-rail interfaces is critical to improving the capacity, reliability and safety of the railway system. This book is a one-stop reference for railway engineering practitioners and academic researchers. The first section provides the fundamentals of contact mechanics, wear, fatigue and lubrication as well as state-of-the-art research and emerging technologies related to the wheel-rail interface and its management. The second section offers an overview of industrial practice from several different regions of the world, thereby lending an international perspective.

  • 74. Lewis, S. R.
    et al.
    Lewis, R.
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    An alternative method for the assessment of railhead traction2011In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 271, no 1-2, p. 62-70Article in journal (Refereed)
    Abstract [en]

    Work has been carried out to develop a fast test method for the determining of railhead traction levels. Current methods used in the field are time consuming and offer relatively little control of external or test parameters. A pendulum rig has been used for this investigation and adapted to measure railhead friction levels under various states of contamination. The rig consists of an aluminium tubular pendulum; on the end of which is a spring mounted, rubber pad (slider pad). The rig functions on the same principles as used in a Charpy impact test, i.e. energy is lost as the slider pad comes into contact with a surface (in this case the rail head). This loss in kinetic energy is measured and can be translated into a friction coefficient. Tests have been carried out to validate the placing of the contaminants on the rail prior to testing and also to determine the setup of the rig. High speed video has also been used to determine the speed of the slider. The pendulum was also tested in the field and showed good correlation in comparison with a hand pushed Tribometer. Pendulum results have been compared to those from twin disk simulations of the wheel/rail contact and good correlation can also be found.

  • 75. Lewis, Stephen R.
    et al.
    Lewis, Roger
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Eadie, Don T.
    Cotter, John
    Lu, Xin
    Effect of humidity, temperature and railhead contamination on the performance of friction modifiers: Pin-on-disk study2013In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 227, no F2, p. 115-127Article in journal (Refereed)
    Abstract [en]

    Commercially available friction modifiers are used in many different countries that have widely different atmospheric conditions. These variations in atmospheric conditions lead to varying levels of railhead oxidation and debris build-up. Friction modifiers can be applied to the rail without any prior cleaning of the rail and this can lead to varying friction modifier/iron oxide ratios potentially affecting the performance of the friction modifier. This paper reports the results of an investigation that was performed to determine the effects of varying atmospheric and oxide conditions on the performance of friction modifiers. A pin-on-disk test rig with an attached environmental chamber was used for the study. Results show that relative humidity has a pronounced effect on the way in which the friction modifier affects friction levels, and also the amount of time it remains on the disk. This also depends on the concentration of oxide in the friction modifier. Glow discharge optical emission spectroscopy analysis was also carried out to assess the effect of the friction modifier and atmospheric conditions on the chemical composition of the surface of the disk. Results show that the depth of surface modification is vastly different depending on the conditions and level of railhead debris.

  • 76.
    Li, Xinmin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    A study on friction and wear reduction due to porosity in powder metallurgic gear materials2017In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 110, p. 86-95Article in journal (Refereed)
    Abstract [en]

    It has been widely acknowledged that controlled texturing on a surface can contribute to friction and wear reduction at lubricated sliding contact interfaces. This paper investigates the influence on friction and wear of different pore size distributions of powder metallurgy gear materials. The pore sizes are controlled by different densities of the powder metallurgic materials. Two different kinds of powder metallurgy (PM) gear materials were applied and a standard gear material are used as a reference. The friction and wear coefficients of PM materials sliding on PM materials increase with increasing pore size. The friction and wear coefficients of regular steel sliding on PM materials decrease with increasing pore size. No matter what the material of the disc, peeling is one of the main damage mechanisms of powder metallurgy pins with the biggest porosity.

  • 77.
    LI, Xinmin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    FZG gear efficiency and pin-on-disc frictional study of sintered and wrought steel gear materials2015In: Tribology letters, ISSN 1023-8883, E-ISSN 1573-2711, Vol. 60, no 9Article in journal (Refereed)
    Abstract [en]

    Load-dependent power loss is a major contributor to power loss in gear transmission systems. In this study pin-on-disc frictional and FZG efficiency experiments were conducted with powder metallurgy (Distaloy AQ+0.2%C) and wrought material (16MnCr5) combinations. The gear mesh torque loss from gear efficiency tests and the friction coefficient from the pin-on-disc tests were then compared. The trend for both test series was the same. The combination of 16MnCr5 in contact with Distaloy AQ+0.2%C shows the lowest coefficient of friction and gear mesh torque loss, followed by the combination of Distaloy AQ+0.2%C in contact with itself, and finally the combination of 16MnCr5 in contact with itself.

  • 78.
    Li, Xinmin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Bergseth, Ellen
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Pin-on-Disc Study of Tribological Performance of Standard and Sintered Gear Materials Treated with Triboconditioning Process: Pre-treatment by Pressure-induced Tribo-film formation2017In: Tribology Transactions, ISSN 1040-2004, E-ISSN 1547-397X, Vol. 60, no 1, p. 47-57Article in journal (Refereed)
    Abstract [en]

    oating is one of the innovative approaches used to improve the wear resistance and load-carrying capacity of surfaces in rolling-sliding contact, such as gears and rolling element bearings. In this study, the tribological performance of standard gear material (16MnCr5) and two kinds of powder metallurgy (PM) gear material (Distaloy AQ + 0.2% C and Astoloy 85Mo +0.2% C) with and without tribofilms formed by a pre-treatment were evaluated. Specimens treated with the pre-treatment and the substrate is subjected to pin-on-disc tests under boundary lubrication conditions. The friction and wear performance of the two different PM gear materials with the pre-treatment formed tribo-film were compared to RS-RS (16MnCr5 material disc and pin combination) for reference. It was found that the pre-treatment lowers the friction coefficient and enhances the wear resistance of pins because of the tribo-film formed. The tribo-film caused good running-in due to the existing of  and Fe and W oxides. Mo-Mo (Astoloy 85Mo + 0.2% C material disc and pin combination) and Mo-RS (Astoloy 85Mo + 0.2% C disc and 16MnCr5 pin combination) showed statistically significant higher wear resistance.

  • 79.
    Li, Xinmin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Sosa, Mario
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Andersson, Martin
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    A study of the efficiency of spur gears made of powder metallurgy materials - ground versus super-finished surfaces2016In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 95, no 1, p. 211-220Article in journal (Refereed)
    Abstract [en]

    Power loss is one of the main concerns in gear transmission systems. In this study a recirculating power back-to-back FZG test rig was used to investigate the efficiency of spur gears made of powder metallurgy (PM) material using two different surface manufacturing methods (ground and super-finished). The results were compared with previously presented results of standard gear material from the same test rig. The influence of the material (Wrought steel or PM) and surface roughness on the gear mesh efficiency and the total efficiency of the gearbox were analyzed in detail. The Young's modulus for PM materials is lower than for conventional gear steel. This may influence gear tooth bending and the efficiency of the gear transmission. Gear contact simulation results showed that the influence of gear tooth bending on PM gear transmission efficiency can be ignored in the FZG gear geometry. Higher surface energy combined with a smoother surface led to a lower transmission efficiency for the super-finished powder metallurgy gear combination compared to the standard gear material.

  • 80.
    LI, XINMIN
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Sosa, Mario
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    A pin on disc study of the tribology characteristics of sintered versus standard gear materials2014Conference paper (Other (popular science, discussion, etc.))
    Abstract [en]

    Powder metallurgy allows complex component geometries which includes gears. There is however a lack of knowledge of the tribological performance of powder material gears compared to gears manufactured from standard gear materials. In this study, a pin on disc machine was used to simulate the sliding part of gear tooth contact both in boundary and mixed lubricated regions. A comparative study of the tribology characteristics of two kind of sintered gear materials with a standard gear material was performed. The comparison comprised of damage mechanisms, wear, friction and running-in between these materials in different pin on disc configuration (standard vs standard, sintered versus sintered and sintered versus standard). For the same gear materials combinations [RS-RS (16MnCr5), AQ-AQ (Distaloy AQ+0.2%C) and Mo-Mo (Astaloy 85Mo+0.2%C)], RS gear material has a lower friction coefficient. When it comes to PM and RS material combinations, both of the PM materials showed a lower friction coefficient, when the pins are made of PM materials in contrast if we have RS pin. Also for the wear rate, RS material always shows the lowest wear rate no matter the disc material. AQ and Mo gear materials have nearly the same wear rate. A distinct difference between different material combinations, both in friction and in wear rate, is observed during the running-in phase.

  • 81.
    Li, Xinmin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Sosa, Mario
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    A pin-on-disc study of the tribology characteristics of sintered versus standard steel gear materials2015In: Wear, ISSN 0043-1648, E-ISSN 1873-2577Article in journal (Other (popular science, discussion, etc.))
    Abstract [en]

    Though powder metallurgy (PM) allows manufacturing of complex components, including gears, we lack knowledge of the tribological performance of PM versus standard steel gear materials. Using a pin-on-disc machine, we simulate the sliding part of gear tooth contact in boundary and mixed lubricated regions, comparing the tribological characteristics of two sintered gear materials with those of a standard gear material. The comparison considered damage mechanisms, wear, and friction between these materials in different configurations (i.e., standard versus standard, sintered versus sintered, and sintered versus standard). The results indicate that, for pairings of the same gear materials, i.e., RS–RS (16MnCr5), AQ–AQ (Distaloy AQ+0.2% C), and Mo–Mo (Astaloy 85Mo+0.2% C), RS has a lower friction coefficient. For PM and RS combinations, both PM pins have lower friction coefficients with RS disc material than do RS pins with PM disc materials. For the wear coefficient, at low and high speeds, RS pins always display better wear resistance than do AQ or Mo pins because of their high hardness and compacted microstructure. For RS–PM combinations, Mo pins display higher wear resistance than do AQ pins because their larger and more numerous pores enable good lubrication. Pins in the Mo–RS combination displayed the highest wear resistance, mainly because the pores in Mo discs hold lubricant, lubricating the contact surface and preventing adhesive wear. For the RS pin in the Mo–RS combination and the AQ pin in RS–AQ, the damage mechanism is slight adhesive wear and scuffing. For pins in the PM–PM, RS–PM, AQ–RS, and RS–RS combinations, the damage mechanism is a heavier scuffing-type adhesive wear.

  • 82.
    Lin, Jiachun
    et al.
    Beijing Univ Technol, Dept Instrument Sci & Technol, Beijing, Peoples R China.;KTH Royal Inst Technol, Dept Machine Design, Stockholm, Sweden..
    Bergstedt, Edwin
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Lindholm, Per
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.). ABB AB Corp Res, Vasteras, Sweden..
    Shi, Zhaoyao
    Beijing Univ Technol, Dept Instrument Sci & Technol, Beijing, Peoples R China..
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    In situ measurement of gear tooth profile during FZG gear micropitting test2019In: SURFACE TOPOGRAPHY-METROLOGY AND PROPERTIES, ISSN 2051-672X, Vol. 7, no 1, article id 015018Article in journal (Refereed)
    Abstract [en]

    According to the GFKT-C/8.3/90 FZG gear micropitting test procedure, the average value of gear tooth profile deviation is used as the failure criterion. Typically, gear tooth profile deviation is measured using a gear measuring machine. In order to do that during the FZG gear test, the gears tested have to be disassembled from, and assembled to the test rig. This process is tedious, time-consuming and is likely to add uncertainty to the testing results. An in situ gear tooth profile measurement method has been developed and applied in FZG gear micropitting tests. The tooth profile of the tested gear was measured in-situ in the gearbox before, during and after each load stage of the gear micropitting test. An algorithm was developed to fit the measured profile to its theoretical shape. Furthermore, a tooth profile change evaluation algorithm was developed for monitoring the evolution of the tooth profile during the duration of the test. The whole methodology was exemplified with a wrought gear test case run to pitting damage.

  • 83.
    Lin, Jiachun
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Bergstedt, Edwin
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Lindholm, Per
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Shi, Zhaoyao
    Beijing Univ Technol, Dept Instrument Sci & Technol, Beijing, Peoples R China..
    Olofsson, Ulf
    KTH, Superseded Departments (pre-2005), Machine Design.
    In situ measurement of gear tooth profile during FZG gear micropitting test (vol 7, 015018, 2019)2019In: SURFACE TOPOGRAPHY-METROLOGY AND PROPERTIES, ISSN 2051-672X, Vol. 7, no 2, article id 029601Article in journal (Refereed)
  • 84.
    Lindholm, Per
    et al.
    KTH.
    Sosa, Mario
    KTH.
    Olofsson, Ulf
    KTH.
    The effect of elasticity in powder metal gears on tooth loading and mean coefficient of friction2018In: Proceedings of the Institution of mechanical engineers. Part C, journal of mechanical engineering science, ISSN 0954-4062, E-ISSN 2041-2983, Vol. 232, no 11, p. 2023-2031Article in journal (Refereed)
    Abstract [en]

    Powder metal gears have a lower density than conventional steel gears due to their intrinsic porosity from the manufacturing process. This also results in a lower elasticity leading to larger deformations and lower contact pressure in a gear contact. By using different modelling tools (namely FEA and available commercial software), the load behavior along the line of action is studied to compare the influence of lower elasticity with standard wrought steel elasticity for FZG-C type gears. A further step is taken analyzing this effect on the mean coefficient of friction through the recalculation of the gear mesh power loss factor. Conclusions observed are differences in load distribution and marginal differences in the gear mesh power loss factor when comparing sintered and wrought steel FZG-C type gears. Sintered steel showed a marginally longer line of action and simultaneously a decrease of the single tooth contact length when compared to wrought steel, while differences in the gear mesh power loss factor proved non-essential due to the spread in previously measured experimental data.

  • 85.
    Liu, Hailong
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Cha, Yingying
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Jonsson, Lage Tord Ingemar
    Jönsson, Pär
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Effect of the Sliding Velocity on the Size and Amount of Airborne Wear Particles Generated from Dry Sliding Wheel-Rail Contacts2016In: Tribology letters, ISSN 1023-8883, E-ISSN 1573-2711, Vol. 63, no 3, article id 30Article in journal (Refereed)
    Abstract [en]

    A set of frictional experiments have been conducted on a pin-on-disk apparatus to investigate the effect of the sliding velocity on airborne wear particles generated from dry sliding wheel-rail contacts. The size and the amount of generated particles were acquired by using particle counter instruments during the whole test period. After the completion of tests, the morphology and chemical compositions of pin worn surfaces and collected particles were analyzed by using scanning electron microscopy combined with an energy-dispersive X-ray analysis system. The results show that the total particle number concentration increases dramatically with an increased sliding velocity from 0.1 to 3.4 m/s. Moreover, the fine and ultrafine particles (<1 mu m) dominates the particle generation mode in the case of a high sliding velocity (1.2 and 3.4 m/s). The contact temperature variation is observed to be closely related to the size mode of the particle generation. In addition, the sliding velocity is found to influence the active wear. Correspondingly, an oxidative wear is identified as the predominant wear mechanisms for cases with high sliding velocities (1.2 and 3.4 m/s). This produces a substantial number of iron oxide-containing particles (<1 mu m) and reduces the wear rate to a relative low level (the wear rate for a 3.4 m/s sliding velocity is 4.5 % of that for a 0.4 m/s sliding velocity).

  • 86.
    Liu, Hailong
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Jonsson, Lage Tord Ingemar
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Swedish Def Res Agcy, Sweden.
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Jönsson, Pär Göran
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    A Simulation Study of Particles Generated from Pellet Wear Contacts during a Laboratory Test2016In: ISIJ INTERNATIONAL, ISSN 0915-1559, Vol. 56, no 11, p. 1910-1919Article in journal (Refereed)
    Abstract [en]

    In the blast furnace process, material losses occur due to mechanical wear between charged iron ore pellets and are exhausted in the form of dust in the off-gases. A redesigned tribometer combined with a ventilation chamber was developed to identify the dust emission from the mechanical wear contact of pellets. In order to obtain a better understanding of the measurement results, a coupled drift flux with a unified Eulerian deposition model was adopted to investigate particle dispersion and deposition during tests. Two influential factors, namely the air condition (5-20 L/min) and particle size (1-20 mu m) were examined. The predicted results were presented by introducing two parameters, namely the measurable fraction and the deposition fraction. For each air condition, the measurable fraction declines while the deposition fraction rises as particle size grows. The critical size of the particles that becomes airborne and captured at the outlet was identified to be around 20 mu m. In addition, a high airflow rate supplied at the inlet was observed to be favorable for improving the measurable fraction. Nevertheless, the results show that nearly 50% of emitted particles (1-20 mu m) that failed to be captured during tests. Thus it could be expected that these generated particles would be transported deeply in a blast furnace if they are not efficiently removed from the off-gas. As a consequence, they may influence the quality of the products. Furthermore, the validation of the simulation results against the experimental data was achieved by using the predicted measurable fraction.

  • 87.
    Liu, Hailong
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Jonsson, Lage Tord Ingemar
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy. FOI, Swedish Defence Research Agency, Division of CBRN Defence and Security, Umeå, Sweden..
    Jönsson, Pär Göran
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    A pin-on-disc study of airborne wear particles from dry sliding wheel-rail contacts2016In: Civil-Comp Proceedings, ISSN 1759-3433, Vol. 110Article in journal (Refereed)
    Abstract [en]

    Pin-on-disc laboratory tests were carried out to identify the generation of airborne wear particles in wheel-rail contacts under different sliding velocities. The results show that the sliding velocity significantly influences both the number and size distribution of airborne wear particles. A comparison of the contact temperature was obtained during tests. For tests with high sliding velocities (1.2 and 3.4 m/s), the particle number concentration level was related to the elevated contact temperature in selected time intervals. Moreover, morphological and elemental analyses of collected particles and pin worn surfaces were studied by using a scanning electron microscope and field emission-scanning electron microscope. The data suggests that the oxide layers were detected within the pin's worn surfaces and an abundant presence of iron-oxide containing particles was observed. Therefore, it can be concluded that abundant fine and ultrafine airborne particles are more likely to be produced from an oxidative wear process in a wheel-rail contact under high sliding velocities.

  • 88.
    Lyu, Yezhe
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Bergseth, Ellen
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Open System Tribology and Influence of Weather Condition2016In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 6, article id 32455Article in journal (Refereed)
    Abstract [en]

    The tribology of an open system at temperatures ranging between 3 degrees C and -35 degrees C, with and without snow, was investigated using a pin-on-disc tribometer mounted in a temperature-controlled environmental chamber. The relationship between the microstructure and ductility of the materials and the tribology at the contacting surfaces was investigated. The study shows that during continuous sliding, pressure causes snow particles to melt into a liquid-like layer, encouraging the generation of oxide flakes on the contact path. The friction coefficient and wear rate are dramatically reduced through an oxidative friction and wear mechanism. In the absence of snow, the tribological process is controlled by the low temperature brittleness of steel in the temperature range from 3 degrees C to -15 degrees C. At these temperatures, cracks are prone to form and extend on the worn surfaces, resulting in the spalling of bulk scraps, which are crushed into debris that increases the friction coefficient and wear rate due to strong abrasion. When the temperature falls to -25 degrees C, an ice layer condenses on the metal surfaces and relaxes the tribological process in the same way as the added snow particles, which significantly decreases the friction and wear.

  • 89.
    Lyu, Yezhe
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Bergseth, Ellen
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    The effect of Subzero temperature and snow on the tribology of wheel-rail contact2016In: Civil-Comp Proceedings, ISSN 1759-3433, Vol. 110Article in journal (Refereed)
    Abstract [en]

    The wheel-rail system operates in an open environment where the weather condition varies constantly. In this laboratory study, an investigation using a pin-on-disc tribometer placed in a temperature-controlled room was conducted to examine the effect of subzero temperature and snow on friction and wear at the wheel-rail contact. In temperature range from 3 to-15 °C (without snow) friction and wear were dominated by low temperature brittleness, which led to an increase in friction and wear. When temperature decreased down to-25 °C, an ice layer condensed on the pin and disc surfaces, which then melted during sliding and acted as a lubricant, leading to the sharp decrease of friction and wear. When snow crystals were added into the contact they melted into water droplets during sliding because of pressure melting and reduced the friction and wear following the boundary lubrication mechanism. With increasing temperature from-25 to 3 °C, friction performed monotonously decreasing because of the increasing thickness of the water layer. A large area of oxide flakes generated on the worn surfaces also significantly protected the contacting wheels and rails from severe wear. © Civil-Comp Press, 2016.

  • 90.
    Lyu, Yezhe
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Bergseth, Ellen
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements. KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    TRIBOLOGY OF THREE RAILWAY BRAKE BLOCK MATERIALS TESTED AGAINST RAILWAYWHEEL AT LOW TEMPERATURES2018Conference paper (Refereed)
    Abstract [en]

    Three railway brake block materials, i.e. cast iron, sintered and organic composite, were tested against railway wheel at10, 3, -10, -20 and -30 °C using a pin-on-disc tribometer with regards to the friction and wear performance. At -10 and -20 °C, cast iron tests yielded very high wear losses both on pin and disc samples and low friction coefficient. The largeamount of graphite worn off from the cast iron sample acted as a lubricant. Friction and wear of sintered material arenot sensitive to the change of temperature. Disc sample tested against organic composite at -30 °C showed negativewear loss, indicating that materials were added onto the surface.

  • 91.
    Lyu, Yezhe
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Bergseth, Ellen
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Lindgren, Anders
    Tyréns AB, Stockholm, Sweden.
    Höjer, Martin
    Tyréns AB, Sweden.
    On the relationships among wheel–rail surface topography, interface noise and tribological transitions2015In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 338-339, p. 36-46Article in journal (Refereed)
    Abstract [en]

    Noise from the wheel-rail interface is a troublesome side effect when railway vehicles negotiate rail curves and straight tracks. A laboratory study using two pin-on-disc tribometers to simulate the pure sliding process in a wheel-rail contact investigated the relationships between surface topographies, tribological aspects and emitted noise. The influence of five different initial surface topographies manufactured by polishing and grinding (transverse and circular) was studied. Polished samples yielded the highest friction coefficient and wear rate because of strong adhesion. Samples with manufacturing traces vertical to the sliding direction produced the lowest friction coefficient and wear rate, and were dominated by ploughing and abrasion. Samples with manufacturing marks parallel to the sliding direction exhibited a medium level in both fiction coefficient and wear rate; the wear mechanism was combined ploughing-adhesion. Noise emission followed the same pattern as the friction coefficients: the highest sound pressure levels occurred for the polished samples and the lowest for the samples with transverse manufacturing marks. Wear transitions from mild to severe wear were always accompanied by an increase in sound pressure of about 10 dB. The transitions also changed the sound pressure amplitude distribution from a narrow banded to a broader banded. 

  • 92.
    Lyu, Yezhe
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Bergseth, Ellen
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Tu, Minghui
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Effect of humidity on the tribological behaviour and airborne particle emissions of railway brake block materials2018In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 118, p. 360-367Article in journal (Refereed)
    Abstract [en]

    A pin-on-disc tribometer placed in a one-way ventilated chamber was used to investigate the effect of relative humidity on the tribology and airborne particle emission of three commercial railway brake block materials (grey cast iron, organic composite, and sintered). Cast iron showed the highest friction coefficient, particle emission and wear loss and organic composite exhibited the lowest. The generation of oxide layers on the worn cast iron surface resulted in a decrease in friction, particle emission and wear. Moisture adsorption by the organic composite leads to decreased friction coefficient and particle emission with increasing humidity. Relative humidity does not affect the friction coefficient of the sintered brake block, whose particle emission and wear loss significantly decline with increasing relative humidity.

  • 93.
    Lyu, Yezhe
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Bergseth, Ellen
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Wahlström, Jens
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    A pin-on-disc study on the tribology of cast iron, sinter and composite railway brake blocks at low temperatures2019In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, p. 48-52Article in journal (Refereed)
    Abstract [en]

    Most freight wagons in the EU use cast iron brake blocks. Cast iron brake blocks have a stable braking capability in different environmental conditions, but wear down the wheel tread quickly. Therefore, there is a need to understand the tribology of other brake block materials. A pin-on-disc tribometer placed in a temperature-controlled chamber is used to investigate the tribology of cast iron, sinter and composite railway brake blocks at low ambient temperatures. Pins made from different brake blocks are tested with discs made from steel wheels. Both friction coefficient and wear are evaluated at five different temperatures from + 10 to − 30 °C. The cast iron block demonstrated the greatest wear at − 10 and − 20 °C, due to the ductile-to-brittle transition at low temperatures. The worn graphite from cast iron is likely to become a solid lubricant, reducing the friction at − 10 and − 20 °C. For the composite brake block, a gradual decrease in friction with decreasing temperature was found. The sinter brake block was not sensitive to changes in ambient temperature. The sliding speed in the current study is relatively low and further study at higher speed is suggested in order to evaluate the tribological performance of different brake blocks.

  • 94.
    Lyu, Yezhe
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Björklund, Stefan
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Bergseth, Ellen
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Nilsson, R.
    Lindgren, A.
    Höjer, M.
    Development of a noise related track maintenance tool2015In: 22nd International Congress on Sound and Vibration, ICSV 2015, International Institute of Acoustics and Vibrations , 2015Conference paper (Refereed)
    Abstract [en]

    The purpose of this work-package within the Quiet-track, FP7, is to develop a noise related track maintenance tool, in the form of an on-board measurement system. As a first step, lab scale tests using a pin-on-disc tribometer were used in order to distinguish how noise changes when the wear mechanism in a sliding contact shifts from normal wear to severe and catastrophic wear. Once the potential for using sound as an indication of severe wear transitions was established, full scale tests were carried out with a rapid transit (metro) train, type C20. The train was equipped with microphones that continuously measured the sound pressure near the wheel rail contact. In order to provoke severe/catastrophic wear, the test train was run in a curve with small radius, and the rails and wheels were carefully cleaned before the tests. The same kind of transfer from mild to severe/catastrophic wear was identified on the full scale test as in the laboratory scale test, confirmed by studying the surface topography and the morphology of the wear particles. Moreover, the full scale test results showed that the sound pressure changed significantly when transferring from mild to severe wear in agreement with the pin-on-disc test results. By comparing noise from the inner wheel/rail contact to noise form the outer wheel/rail contact a wear indication value for the outer wheel/rail contact is suggested in this study. This value can be seen as an advanced parameter from which the probability of severe wear, in the wheel flange/rail gauge face contact of the outer contact, can be estimated. At present, a real time condition monitoring system is set up in Stockholm (Metro line 1) in order to validate the results.

  • 95.
    Lyu, Yezhe
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Leonardi, Mara
    University of Trento, Italy.
    Ma, Jijie
    College of Engineering, Zhejiang Normal University, China.
    Wahlström, Jens
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Gialanella, Stefano
    University of Trento, Italy.
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    A PIN-ON-DISC STUDY ON THE FRICTION, WEAR AND AIRBORNE PARTICLE EMISSION FROM RECYCLED BRAKE PAD MATERIAL2019Conference paper (Refereed)
  • 96.
    Lyu, Yezhe
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Leonardi, Mara
    Trento University.
    Wahlström, Jens
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Gialanella, Stefano
    Trento University.
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Friction, wear and airborne particle emission from Cu-free brake materials2020In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 141, article id 105959Article in journal (Refereed)
    Abstract [en]

    Cu is required to be abated in brake pads due to its toxicity. There are on the market several Cu-free brake pads. These Cu-free brake pads are only evaluated regarding their friction and wear performance, whereas, their airborne particle emissions are not considered. A pin-on-disc tribometer is used to evaluate the friction, wear and airborne particle emission from two Cu-free commercial brake pads used in the Europe. Moreover, a commercial brake pad containing Cu is evaluated as a reference. The results indicate that Cu-free brake pads yield comparable coefficient of friction as the Cu-contained brake pad. All three brake materials result in similar wear to the mating brake rotor. Cu-free brake pads generate more airborne particles than Cu-contained brake pad.

  • 97.
    Lyu, Yezhe
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Wahlström, Jens
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Tu, Minghui
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    A Friction, Wear and Emission Tribometer Study of Non-Asbestos Organic Pins Sliding Against AlSiC MMC Discs2018In: Tribology in Industry, ISSN 0354-8996, Vol. 40, no 2, p. 274-282Article in journal (Refereed)
    Abstract [en]

    The friction, wear and particle emission from an AlSiC MMC brake disc/non-asbestos organic brake pad system is studied using a pin-on-disc tribometer. The results show that this unconventional AlSiC MMC brake disc system presents friction performance as good as a conventional cast iron brake disc system. During braking, brake pad materials are transferred to the brake disc surface to form a protective third body tribo-layer, resulting in a negative specific wear rate of the brake disc. A higher contact load is likely to make it easier to generate the tribo-layer. The tribo-layer also seems to depend on the disc surface grinding features and the contact temperature during braking. By reusing an AlSiC MMC disc where the tribo-layer is already formed, the airborne emission in terms of mass is about 50% lower and in terms of number about the same as the conventional brake contact pair under a similar braking condition. Further full-scale studies are suggested to determine the validity of the findings.

  • 98.
    Lyu, Yezhe
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Zhu, Yi
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.). Zhejiang University, China.
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Wear between wheel and rail:A pin-on-disc study of environmental conditions and iron oxides2015In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 328-329, p. 277-285Article in journal (Refereed)
    Abstract [en]

    Railways operate in an open environment where temperature, humidity, and the oxidation conditions are subjected to change. An experimental investigation used a pin-on-disc machine to examine the influence of environmental conditions and iron oxides on the wear performance of the wheel-rail contact. The wear mechanisms were analyzed using scanning electron microscopy and found to be highly dependent on the environmental conditions. On clean contacts, adhesive wear is predominant under low-moisture conditions, becoming more serious with decreasing temperature. With high moisture and at room temperature (i.e., 20. °C and 10. °C) oxide flakes would self-produce and protect the pins from severe wear, as oxidative wear is the main wear mechanism. Samples experienced a transformation of the wear mechanism from adhesive to oxidative with increasing humidity on clean contacts. Complex three-body wear in abrasion form has been determined to dominate oxidized contacts. Under dry conditions, pins underwent severe wear appearing as delamination at 20. °C and crushed wear debris at 3. °C. Raising the moisture level helps the pins to avoid severe wear.

  • 99.
    Ma, Jijie
    et al.
    College of Engineering, Zhejiang Normal University, China.
    Hedlund-Åström, Anna
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements.
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Lyu, Yezhe
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Leonardi, Mara
    Department of Industrial Engineering, University of Trento, Italy.
    Wahlström, Jens
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    ECO DESIGN OF BRAKE PADS WITH RECYCLED FRICTION MATERIALS2019Conference paper (Refereed)
  • 100. Marshall, M. B.
    et al.
    Lewis, R.
    Dwyer-Joyce, R. S.
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Björklund, Stefan
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements.
    Experimental characterization of wheel-rail contact patch evolution2006In: Journal of tribology, ISSN 0742-4787, E-ISSN 1528-8897, Vol. 128, no 3, p. 493-504Article in journal (Refereed)
    Abstract [en]

    The contact area and pressure distribution in a wheel/rail contact is essential information required in any fatigue or wear calculations to determine design life, re-grinding, and maintenance schedules. As wheel or rail wear or surface damage takes place the contact patch size and shape will change. This leads to a redistribution of the contact stresses. The aim of this work was to use ultrasound to nondestructively quantify the stress distribution in new, worn, and damaged wheel-rail contacts. The response of a wheel/rail interface to an ultrasonic wave can be modeled as a spring. If the contact pressure is high the interface is very stiff, with few air gaps, and allows the transmission of an ultrasonic sound wave. If the pressure is low, interfacial stiffness is lower and almost all the ultrasound is reflected. A quasistatic spring model was used to determine maps of contact stiffness from wheel/rail ultrasonic reflection data. Pressure was then determined using a parallel calibration experiment. Three different contacts were investigated; those resulting from unused, worn, and sand damaged wheel and rail specimens. Measured contact pressure distributions are compared to those determined using elastic analytical and numerical elastic-plastic solutions. Unused as-machined contact surfaces had similar contact areas to predicted elastic Hertzian solutions. However, within the contact patch, the numerical models better reproduced the stress distribution, as they incorporated real surface roughness effects. The worn surfaces were smoother and more conformal, resulting in a larger contact patch and lower contact stress. Sand damaged surfaces were extremely rough and resulted in highly fragmented contact regions and high local contact stress.

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