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  • 1.
    Abbasi, Saeed
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements.
    Jansson, Anders
    Stockholm University, Applied Environmental Science, Stockholm, Sweden.
    Olander, Lars
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Services Engineering.
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements.
    Sellgren, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements.
    A pin-on-disc study of the rate of airborne wear particle emissions from railway braking materials2012In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 284, p. 18-29Article in journal (Refereed)
    Abstract [en]

    The current study investigates the characteristics of particles generated from the wear of braking materials, and provides an applicable index for measuring and comparing wear particle emissions. A pin-on-disc tribometer equipped with particle measurement instruments was used. The number concentration, size, morphology, and mass concentration of generated particles were investigated and reported for particles 10 nm-32 mu m in diameter. The particles were also collected on filters and investigated using EDS and SEM. The effects of wear mechanisms on particle morphology and changes in particle concentration are discussed. A new index, the airborne wear particle emission rate (AWPER), is suggested that could be used in legislation to control non-exhaust emissions from transport modes, particularly rail transport.

  • 2.
    Abbasi, Saeed
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements. Department of Mechanical engineering, Golpayegan University of Technology.
    Teimourimanesh, Shahab
    Chalmers.
    Vernersson, Tore
    Chalmers.
    Sellgren, Ulf
    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 Elements.
    Lunden, Roger
    Chalmers.
    Temperature and Thermoelastic Instability at Tread Braking Using Cast Iron Friction Material2013In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 314, no 1–2, p. 171-180Article in journal (Refereed)
    Abstract [en]

    Braking events in railway traffic often induce high frictional heating and thermoelastic instability (TEI) at the interfacing surfaces. In the present paper, two approaches are adopted to analyse the thermomechanical interaction in a pin-on-disc experimental study of railway braking materials. In a first part, the thermal problem is studied to find the heat partitioning between pin and disc motivated by the fact that wear mechanisms can be explained with a better understanding of the prevailing thermal conditions. The numerical model is calibrated using the experimental results. In a second part, the frictionally induced thermoelastic instabilities at the pin-disc contact are studied using a numerical method and comparing them with the phenomena observed in the experiments. The effects of temperature on material properties and on material wear are considered. It is found from the thermal analysis that the pin temperature and the heat flux to the pin increase with increasing disc temperatures up to a transition stage. This agrees with the behaviour found in the experiments. Furthermore, the thermoelastic analysis displays calculated pressure and the temperature distributions at the contact interface that are in agreement with the hot spot behaviour observed in the experiments.

  • 3.
    Abbasi, Saeed
    et al.
    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.), Machine Elements.
    Olander, Lars
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Services Engineering.
    Larsson, Christina
    Bombardier Transportation Sweden AB, Västerås, Sweden.
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Sellgren, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements.
    A study of airborne wear particles generated from organic railway brake pads and brake discs2011In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 273, no 1, p. 93-99Article in journal (Refereed)
    Abstract [en]

    Brake pads on wheel-mounted disc brakes are often used in rail transport due to their good thermal properties and robustness. During braking, both the disc and the pads are worn. This wear process generates particles that may become airborne and thus affect human health. The long term purpose of ‘Airborne particles in Rail transport’ project is to gain knowledge on the wear mechanisms in order to find means of controlling the number and size distribution of airborne particles. In this regard, a series of full-scale field tests and laboratory tests with a pin-on-disc machine have been conducted. The morphology and the matter of particles, along with their size distribution and concentration, have been studied. The validity of results from the pin-on-disc simulation has been verified by the field test results. Results show an ultra-fine peak for particles with a diameter size around 100 nm in diameter, a dominant fine peak for particles with a size of around 350 nm in diameter, and a coarse peak with a size of 3-7 μm in diameter. Materials such as iron, copper, aluminium, chromium, cobalt, antimony, and zinc have been detected in the nano-sized particles.

  • 4. Alemani, Mattia
    et al.
    Gialanella, S.
    Straffelini, G.
    Ciudin, R.
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Perricone, G.
    Metinoz, I.
    Dry sliding of a low steel friction material against cast iron at different loads: Characterization of the friction layer and wear debris2017In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 376-377, p. 1450-1459Article in journal (Refereed)
    Abstract [en]

    Pin-on-disc testing was used to investigate the sliding behavior and the wear products of a low-steel friction material against a cast iron disc at different applied loads, to investigate the effect of the temperature rise induced by frictional heating. The testing rig was operated in a clean chamber with a purified incoming air flux. The outgoing flux carries the wear particles to an impactor that counted and sorted them by average diameter and weight. At increasing applied loads, corresponding to a proportional increase of the pin-disc contact temperature, the coverage of both the pin and disc surface by a friction layer was found to increase too. The relevant X-Ray diffraction patterns revealed the presence of a large amount of graphite and different compounds originating from the friction material and from the counterface disc, mainly iron oxides, as concerns this latter. After the test at the lowest investigated load, i.e., 1 kg, the disc worn surface exhibited abrasive grooves and a discontinuous friction layer mainly made of compacted iron oxide particles. After the test at higher loads, i.e., 5 and 7 kg, the disc surface was covered by a compact friction layer. As concerns the friction layer on the pins, most of the ingredients from the friction material were detected, in association with the iron oxides from the disc. These results can be interpreted in terms of the temperature stability range of the phenolic resin used as a binder of the friction material. The characterization of the collected airborne wear debris showed that the particles produced by the low temperature (i.e., low load) test were mostly equiaxed; whereas those produced by the high temperature (i.e., high loads) tests, predominantly displayed a plate-like morphology. The mechanisms of their formation in relation to the characteristics of the friction layers are illustrated and discussed.

  • 5.
    Alemani, Mattia
    et al.
    KTH.
    Wahlström, Jens
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.). KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements. KTH, School of Industrial Engineering and Management (ITM), Applied Mechanical Engineering (KTH Södertälje). 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.
    On the influence of car brake system parameters on particulate matter emissions2018In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 396, p. 67-74Article in journal (Refereed)
    Abstract [en]

    The influence of car brake system parameters on particulate matter emissions was investigated using a pin-on-disc tribometer. Samples from a low-steel friction material and a cast iron disc were tested for different sliding velocities, nominal contact pressures and frictional powers. Disc temperatures were also measured. Their impact on total concentration, size distribution, particle coefficient and transition temperature was analysed. Results show that frictional power is the most significant brake system parameter. However, temperature, as a response parameter, is the most influential, inducing a shift towards the ultrafine particulate fraction and raising emissions. A transition temperature, independent of the system parameters, was identified.

  • 6.
    Alfredsson, Bo
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Dahlberg, Johan
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Olsson, Mårten
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    The role of a single surface asperity in rolling contact fatigue2008In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 264, no 9-10, p. 757-762Article in journal (Refereed)
    Abstract [en]

    The effect of contact loading of single surface irregularities, i.e. asperities, as an underlying mechanism for surface initiated rolling contact fatigue was investigated numerically using FEM. Spalls in the teeth flanks of driving gear wheels were investigated for typical spalling crack initiation properties. The spalling entry angle was documented and some spalls with a convex entry tip were found. The residual surface stresses of the used teeth, with spalls, were measured with the hole drilling technique. The gear contact close to the rolling circle was modelled as two rolling cylinders. A single asperity was introduced into the contact surface of one of them. Due to the presence of the asperity a three dimensional contact model was required. The material description included J(2)-plasticity with isotropic and linear hardening. The simulation included residual stresses from material heat treatment. The first roll cycle introduced plastic deformation which altered the residual stresses. Thus, the stress results were captured during a second roll cycle. The most important result was that asperities will serve as local stress raisers in the contact surfaces. The computed stress cycle at the asperity was compared to stress cycles that gave ring/cone cracks at point loaded experiments. The principal stress trajectory into the material was compared to the cross-section profiles of the spalling entry and ring/cone crack. The surface stress profile at the asperity was compared to the convex surface profiles of the spalling tip and ring/cone crack. The asperity deformation and change in residual surface stresses from moderate plastic deformation during rolling were estimated.

  • 7.
    Alonso, Asier
    et al.
    CAF I D, Beasain, Spain.;Univ Navarra, TECNUN, Donostia San Sebastian, Spain..
    Casanueva, Carlos
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Perez, Javier
    CAF SA, Beasain, Spain..
    Stichel, Sebastian
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Modelling of rough wheel-rail contact for physical damage calculations2019In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 436, article id 202957Article in journal (Refereed)
    Abstract [en]

    This work presents the initial steps given in order to obtain a comprehensive physical damage model for the specific case of wheel rail contact wear, which would be able to relate contact conditions, material properties and wear rates. The main advantage of a physical damage wear model is that wheelset and rail manufacturers can perform simulations in order to improve and optimise material properties for different operational cases. The work in this paper focuses on delaminative wear, starting with the importance and modelling of rough contact, and a comparison against classic smooth contact models.

  • 8.
    Andersson, Sören
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Söderberg, Anders
    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.), Tribologi.
    A random wear model for the interaction between a rough and a smooth surface2008In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 264, no 9-10, p. 763-769Article in journal (Refereed)
    Abstract [en]

    Contact surfaces in many applications change form due to plastic and elastic deformation and to wear. This study focused on the plastic deformation and wear of the asperities on a rough surface rubbing against an opposite smooth, hard and wear-resistant surface. A stochastic model for the prediction of plastic deformations and wear of a rough surface is proposed. The surface roughness and the interaction between the surfaces are also represented by stochastic models. A single asperity is studied as it comes into contact and interacts with the opposite surface. Since the wear process is simulated as an initial-value problem, the proposed general wear model is formulated as a first order differential equation system representing events during the rubbing process at all of the asperities considered on a surface.

  • 9.
    Berggren, Eric
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    A new approach to the analysis and presentation of vertical track geometry quality and rail roughness2008In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 265, p. 1400-1496Article in journal (Refereed)
    Abstract [en]

    A new approach on enhancing the assessment of track geometry quality and rail roughness by means of train–track interaction simulation and wavelength content analysis is presented. The dynamic model includes vehicle, track and linearized wheel–rail contact with moving irregularities and can be simulated either in the frequency domain by using FFT or in the time domain by constructing a filter function based on system identification technique. The system is suitable to calculate wheel–rail forces for very long track sections and for several vehicle types under a wide range of travelling speeds since the computational scheme is very efficient (300 km/s on a standard computer). With numerical results we demonstrate the potential benefits of improving conventional track geometry inspection methods and highlight short defects (0.5–2 m) as a cause of high dynamic wheel–rail interaction forces. By using a wavelength weighting of measured rail roughness a new improved way of analyzing rail roughness data is also presented. This improves condition assessment of tracks and rails and will enable the track engineer to monitor the track in a better way.

  • 10.
    Bergseth, Ellen
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Henriksson, Mats
    Scania CV .
    Dizdar, Senad
    Höganäs AB.
    Sellgren, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Effects of thrust washer bearing surface characteristics on planetary gear train wear2019In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 432-433, article id 202933Article in journal (Refereed)
    Abstract [en]

    Thrust washers in spur planetary gears are placed between the planet wheel and planet carrier and act as spacers and wear pads. Metal to metal sliding contact between the planet wheel – washer – carrier causes frictional power losses that, combined with starved lubrication, may cause high contact temperatures and thermo-mechanical effects that potentially trigger thermo-elastic instabilities and excessive local wear. The planetary gear system would benefit from a low-friction interface between the washer and the planet wheel. Five washers with different surface treatments were tested in a full-scale gear rig. These tests were also replicated as closely as possible in a pin-on-disc tribometer. The following types of finishing material treatments were studied: a chemical nickel coating plus polymer on a nitro-carburised surface, a combination of nitro-carburization and solid lubricant layers, electroless deposited chemical nickel coating plus polymer, nitro-carburizing, and manganese phosphating. The frictional results indicate that tribometer tests can be used to compare and classify new washer materials. Lab scale tests show that a new experimental self-lubricating tribomaterial that was applied with laser cladding has a promising potential to increase planetary gear train robustness and service life, especially if the surface is fine grinded.

  • 11.
    Dahlberg, Johan
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Alfredsson, Bo
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Transient rolling of cylindrical contacts with constant and linearly increasing applied slip2009In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 266, no 1-2, p. 316-326Article in journal (Refereed)
    Abstract [en]

    The transient start problem of a rolling cylindrical contact has been studied. The transient conditions were controlled by the applied relative slip. Two cases with start of rolling from stationary contact were investigated, with constant and with linearly increasing applied slip. At each instant during the transition stage, it was assumed that the traction distribution could be approximated with the Carter traction for steady-state tractive rolling. Based on this distribution, approximate expressions were derived for the transient rolling distance and transient behaviour of the tangential load. The transient period could end in gross sliding or steady-state creep with the Carter traction distribution and stick-slip regions in the contact. The expressions and the transient traction distributions were validated numerically using FEM. Simulations with constant applied slip showed that when rolling started from a tangentially unloaded and unstrained position, the steady-state traction distribution by Carter was a good approximation of the actual transient traction distribution. The solution was accurate for transient rolling lengths longer than a quarter of the contact width. The transient behaviour depended on the bulk geometry of the structures. For the relatively stiff structure with two elastic steel cylinders, small amounts of relative slip and high coefficients of friction, the transient rolling distance, L-0, could become large. In the present study, examples with L-0 approximate to 40 . a were identified. Thus, situations exist for which the transient conditions might be important. The transient distance increased with smaller slip, larger coefficient of friction, lower bulk stiffness, higher contact normal loads and for more compliant materials. The spur gear contact interaction with varying slip was considered as a case study.

  • 12.
    Dirks, Babette
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles.
    Enblom, Roger
    Bombardier Transportation, Passengers Division - Specialist Engineering, Västerås, Sweden.
    Prediction model for wheel profile wear and rolling contact fatigue2011In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 271, no 1-2, p. 210-217Article in journal (Refereed)
    Abstract [en]

    A lifetime prediction tool for railway wheels and rails should be able to predict both wear and rolling contact fatigue (RCF), which are the two main deterioration phenomena. Several models exist to predict wear or RCF, but not many models exist which can predict both. In this study, two of these RCF prediction models have been extended. The performance of these models has been studied through a parametric study where multi-body simulations (MBS) provided the input to the models. The influences of several parameters which can have an effect on the wheel/rail life have been studied in order to find the behaviour of the different models. These parameters are: curve radius, worn wheel and rail profiles, coefficient of friction, primary stiffness, track irregularities, and cant deficiency. This paper describes the differences between the two models and shows that the adjustments of the models have a significant influence on RCF prediction.

  • 13.
    Dirks, Babette
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles.
    Enblom, Roger
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles. Bombardier Transportation, Sweden .
    Berg, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles.
    Prediction of wheel profile wear and crack growth - comparisons with measurements2016In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 366, p. 84-94Article in journal (Refereed)
    Abstract [en]

    A model which can predict the length of the surface crack and crack depth in rails was developed in a previous study by the authors B. Dirks, R. Enblom, A. Ekberg, M. Berg (2015) []. In the present study, verification of this crack prediction model in combination with a wear prediction model was done against wheel measurements. For a period of 15 months, the wheels of three units of a Stockholm commuter train were measured with respect to wear and crack development for verification of the wheel life prediction tool. Vehicle-track dynamics simulations were used to calculate the forces and contact positions for the wear and crack prediction models. It can be concluded that the wear prediction model gives reasonable results, especially considering the large scatter in the wheel profile measurements. Although the wheel life prediction tool could not be verified, since the crack prediction model had to be recalibrated for the current wheel application, the results appear promising.

  • 14.
    Enblom, Roger
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles. KTH, School of Engineering Sciences (SCI), Centres, The KTH Railway Group.
    Berg, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles.
    Impact of non-elliptic contact modelling in wheel wear simulation2008In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 265, no 9-10, p. 1532-1541Article in journal (Refereed)
    Abstract [en]

    Advances in simulation of railway wheel wear in the sense of material removal have drawn the attention to the importance of wheel–rail contact modelling. As a further step of enhancing the used simulation procedure in direction of increased generality and reduced need for application-dependent calibration, the focus of this investigation is the influence of non-elliptic contact models on the wheel wear rate and profile shape. To facilitate evaluation the semi-Hertzian contact procedure Stripes, developed by INRETS in France, has been implemented.

    To investigate the capabilities of Stripes to assess the contact area and pressure, shape comparisons have been made with other numerical methods for a set of wheel–rail contact situations. The referenced results are based on the linear elastic half-space assumption, elastic finite element analysis, and elastic–plastic finite element analysis. For reference also the elliptic contact area according to Hertz is shown as given by the contact data table of the multi-body simulation code.

    After exploring the properties of the Stripes procedure with respect to contact area estimation and pressure distribution, the focus is moved to the influence on wear rate, being the principal objective of this investigation. First the wear distribution over the contact patch is studied and compared to results using the elliptic model from the MBS code Gensys and the non-elliptic approach with Kalker's code Contact. Finally the evolution of the wheel profile is simulated for a few typical cases.

    This investigation of wear distributions over non-elliptic patches under different operating conditions indicates significant differences compared to both Contact and the applied Hertzian approach. The expansion from single contact occasions to complete simulations indicates comparable material removal rates but relocation towards the flange side. This tendency is apparent in all of the cases shown, however limited to initial wear in tangent run or reasonably mild curve negotiation.

  • 15.
    Enblom, Roger
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Berg, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Simulation of railway wheel profile development due to wear: influence of disc braking and contact environment2005In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 258, no 7-8, p. 1055-1063Article in journal (Refereed)
    Abstract [en]

    This paper addresses issues related to braking and wheel-rail contact conditions in the context of wheel wear simulation. The KTH approach to the topic includes Archard's wear model with associated wear maps, vehicle dynamics simulation and railway network definition. In previous work at KTH certain variations in operating conditions have been accounted for through empirically estimated average scaling factors. The objective of the current research is to be able to include such variations in the set of simulations. In particular the influence of disc braking as well as varying friction and lubrication conditions are investigated. Both environmental factors like moist and contamination and deliberate lubrication need to be considered. As part of the associated contact analysis the influence of local elastic deformation on the sliding velocity has been separately investigated.

  • 16.
    Enblom, Roger
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles.
    Stichel, Sebastian
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles.
    Industrial implementation of novel procedures for the prediction of railway wheel surface deterioration2011In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 271, no 1-2, p. 203-209Article in journal (Refereed)
    Abstract [en]

    Adequate performance of the wheel-rail interface is essential for satisfactory operation of a railway system in terms of quality of service and maintenance effort. Pertinent requirements on efficiency tend to push the operation conditions towards higher loads and increased speed while the wheel-rail contact remains a small and highly stressed area. Dominating modes of deterioration due to high normal and tangential stresses are wear and rolling contact fatigue. Both kinds lead to surface material loss, in the former case as a slow rate profile geometry change with consequences to the dynamic performance and in the latter case different crack patterns and eventually spalling or shelling requiring reprofiling. In this paper the implementation of emerging technologies for the prediction of wheel surface deterioration in an engineering environment is summarised. Methods for the prediction of wear and profile geometry evolution as well as for the assessment of the risk for the onset of rolling contact fatigue are described. Example results from recent applications are given. In general it may be concluded that the implemented methods are becoming useful for the prediction of profile alterations, for instance hollow wear linked to conicity increase, and flange wear. The fatigue assessment methods are less mature and need further calibration but are still capable of indicating location and significance of risk for damage.

  • 17. Furustig, J.
    et al.
    Dobryden, Illia
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science. Luleå University, Sweden.
    Almqvist, A.
    Almqvist, N.
    Larsson, R.
    The measurement of wear using AFM and wear interpretation using a contact mechanics coupled wear model2016In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 350-351, p. 74-81Article in journal (Refereed)
    Abstract [en]

    Detailed understanding of wear processes is required to improve the wear resistance and lifetime of machine components. Atomic force microscopy (AFM) is used to measure surface height profiles with high precision, before and after a wear experiment. The distribution and depth of wear on steel surfaces is then calculated using a relocation method. A numerical investigation of wear based on Archard's equation is conducted on the same measured surfaces. A good correlation was found between the model and experiment for wear larger than a hundred nm. The wear mechanisms considered in the numerical simulation was thus found to be the cause of the majority of the wear. On the scale of tens of nm the correlation was limited, but the measured wear was still analysed in detail.

  • 18.
    Gebretsadik, Elias Kassa
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Johansson, Anders
    Chalmers University of technology.
    Pålsson, Björn
    Chalmers University of technology.
    Ekh, Magnus
    Chalmers University of technology.
    Nielsen, Jens
    Chalmers University of technology.
    Ander, Mats
    Chalmers University of technology.
    Brouzoulis, Jim
    Chalmers University of technology.
    Simulation of wheel-rail contact and damage in switches & crossings2011In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 271, no 1, p. 472-481Article in journal (Refereed)
    Abstract [en]

    A methodology for the simulation of degradation of rail profiles in switches & crossings (S&C) is presented. The methodology includes: simulation of dynamic vehicle-track interaction considering stochastic variations in input data (such as wheel profile, train speed and wheel-rail friction coefficient), simulation of wheel-rail contacts accounting for non-linear material properties and plasticity, and simulation of wear and plastic deformation in the rail during the life of the S&C component. The methodology is demonstrated by predicting the damage of a switch rail profile, manufactured from R260 steel, when exposed to freight traffic in the diverging route (facing move). In particular, the consequences of increasing the axle load from 25 tonnes to 30 tonnes are studied.

  • 19. Gerth, J.
    et al.
    Werner, Mathias
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Machine and Process Technology.
    Larsson, M.
    Wiklund, U.
    Reproducing wear mechanisms in gear hobbing: Evaluation of a single insert milling test2009In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 267, no 12, p. 2257-2268Article in journal (Refereed)
    Abstract [en]

    Gear hobbing is a widely used method in industrial gear manufacturing. The most common type of hob is made of homogenous HSS and protected by a PVD coating. In order to increase the reliability and tool life of these milling tools, further developments of the tool surfaces and cutting edges are necessary. A single tooth milling test, using a HSS insert in a conventional milling machine, has been developed with the aim to reproduce the wear mechanisms seen on real HSS gear hobbing teeth. The benefits of such a test, compared to actual gear hobbing tests, are primarily accessibility and reduced costs for both design and production of test specimens (inserts). The main goal of this study was to verify that the wear mechanisms in the developed test correspond with the wear mechanisms obtained in real gear hobbing. Once this was verified, the influence of surfaces roughness on the performance of TiAlN coated HSS inserts was evaluated by using the tool as delivered or after polishing the tool surfaces. Parameters considered were tool wear, cutting forces and the quality of machined surfaces. The polished inserts, yielded less adhered work material and reduced flank wear but no significant difference in cutting forces as compared to the unpolished inserts.

  • 20. Gola, A. M.
    et al.
    Ghadamgahi, Mersedeh
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Ovako Sweden AB, Sweden.
    Ooi, S. W.
    Microstructure evolution of carbide-free bainitic steels under abrasive wear conditions2017In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 376-377, p. 975-982Article in journal (Refereed)
    Abstract [en]

    The idea of carbide-free bainitic (CFB) microstructure, a mixture of bainitic ferrite and retained austenite (RA), in high-silicon steels has been recently thoroughly investigated by numerous researchers. In this research, two medium-carbon steel grades were tested in a wear tumbling machine to investigate microstructural changes under wet sliding abrasive wear conditions and to benchmark their performance against conventional tempered martensitic steels. The nature and type of defects responsible for material removal were analysed using scanning electron microscopy. To observe microstructural evolution of heavily deformed top layers of test specimens, special layer-by-layer X-ray diffraction methodology was applied. This technique allows accurate quantification of the volume fraction of RA transformed into untempered martensite at different depths from the worn surface. The results suggest that better performance is achieved in specimens heat treated to carbide-free bainitic microstructure containing higher volume fraction of RA, however with blocks of RA thermally stable at room temperature. The improved wear resistance is due to the increased surface hardness caused by stress-induced transformation of RA into untempered martensite during wear, while maintaining good toughness in the subsurface zones, which prevent brittle cracking.

  • 21.
    Hannes, Dave
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Alfredsson, Bo
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Surface initiated rolling contact fatigue based on the asperity point load mechanism-A parameter study2012In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 294, p. 457-468Article in journal (Refereed)
    Abstract [en]

    The influence of asperity size, friction and residual surface stress on surface initiated rolling contact fatigue damage was investigated using the asperity point load mechanism. A parametric study was performed in two steps, first with a classic one-parameter-at-a-time approach, then as a 2-level full factorial design. The effect on fatigue initiation, damage size and spalling life for both early and developed spalling damage was examined for a gear application. Simplified response surfaces were derived as an engineering design tool for improved spalling resistance. The parametric investigation suggested that among the investigated parameters, reduced asperity height and local asperity friction will have the largest effect on the crack initiation risk. The simulations agreed with the engineering experiences that reduced surface roughness improves rolling contact fatigue resistance and that improved lubrication lengthens spalling lives and decreases fatigue risk. With compressive residual surface stresses the predictions suggested reduced fatigue risk and substantially decreased depth of individual spalls. Finally, predictions of experimentally observed effects of changing asperity size, friction and residual surface stress on spalling further motivates the asperity point load mechanism as the source behind surface initiated rolling contact fatigue.

  • 22.
    Hoseini, Mohammed
    et al.
    SP Swedish National Testing and Research Institute, Transport and Vehicle Technology, Building Technology and Mechanics, Borås.
    Jedenmalm, Anneli
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    Boldizar, Antal
    Department of Materials and Manufacturing Technology, Chalmers University of Technology, Göteborg.
    Tribological investigation of coatings for artificial joints2008In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 264, no 11-12, p. 958-966Article in journal (Refereed)
    Abstract [en]

    A modified pin-on-disc machine was used for the tribological investigation of ultrahigh molecular weight polyethylene (UHMWPE) sliding on stainless steel or stainless steel coated with diamond-like carbon, titanium nitride or Micronite. Micronite is a new type of coating applied by a physical vapour deposition technique combined with a very low friction coating material giving improved tribological properties. The tribological parameters used were chosen to mimic the conditions prevailing in the human body. The wear debris and the counter-surfaces were analysed. The surface analysis showed that the coating changed the roughness of the counter-surfaces. The diamond-like carbon and Micronite coatings had a much higher surface roughness than the titanium nitride coating. The results indicated that the enhanced tribological behaviour of the Micronite/UHMWPE sliding pair might be used as a material combination in artificial joints. Further studies are however required in order to support this.

  • 23.
    Hossein Nia, Saeed
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles.
    Stichel, Sebastian
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles.
    Casanueva, Carlos
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles.
    Prediction of RCF and Wear Evolution of Iron-Ore Locomotive wheels2015In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 338-339, p. 62-72Article in journal (Refereed)
    Abstract [en]

    Locomotives for the iron ore line in northern Sweden and Norway have a short wheel life. The average running distance between two consecutive wheel turnings is around 40,000 km which makes the total life of a wheel around 400,000 km. The main reason of the short wheel life is the severe rolling contact fatigue (RCF). The train operator (LKAB) has decided to change the wheel profiles to get a better match with the rail shapes in order to decrease the creep forces leading to RCF. Two wheel profiles optimised via a genetic algorithm were proposed. They have, however, not been analysed for long term wear development. There is a risk that the optimised profiles might wear in an unfavourable way and after a while cause even higher RCF or wear than the original one. This study predicts wheel profile evolution using the uniform wear prediction tool based on Archard’s wear law. RCF evolution on the surface of the wheel profiles is also investigated. The impact of wear on polishing the wheel surface and avoiding the RCF cracks to propagate is considered via introducing a correction factor to the calculated RCF index. Traction and braking are also considered in the dynamic simulation model, where a PID control system keeps the speed of the vehicle constant by applying a torque on the loco wheels. The locomotives are also equipped with a flange lubrication system, therefore the calculations are performed both for lubricated and non-lubricated wheels. The simulation results for the wheel profiles currently in use, which are performed to validate the model and the simulation procedure, show a good agreement with the measurements. It is also concluded that the lubrication system partly does not perform as expected. Comparison between the proposed optimised profiles for their long term behaviour suggests that one of them produces less RCF and wear compared to the other one.

  • 24. 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.

  • 25.
    Jelagin, Denis
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Larsson, Per-Lennart
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Hertzian Fracture at Finite Friction: A Parametric Study2008In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 265, no 5-6, p. 840-848Article in journal (Refereed)
    Abstract [en]

    Friction has a profound influence on Hertzian fracture initiation when dissimilar materials are involved. Experimental studies show that the presence of friction results in higher fracture loads and fracture radii as compared to the frictionless case. It has also been shown recently that the experimental observations concerning Hertzian fracture initiation at unloading may be explained by the effect friction has on a surface tensile stress distribution. Presently a contact cycle between two dissimilar elastic bodies at finite Coulomb friction has been investigated numerically for a wide range of material parameters and contact geometries. Emphasis has been given to the surface tensile stress distribution which is assumed to be a governing parameter for Hertzian fracture initiation. In particular it was found that during loading the contact region divides into invariant stick and inward slip regions and the presence of outward frictional shear tractions reduces the maximum surface tensile stress and shifts it away from the contact contour as compared to the frictionless case. At unloading, the distributions of stick-slip zones were found to be severely history- and geometry-dependent and shear tractions reversed their direction over part of the contact area. Consequently, tensile stresses were found to grow at unloading. Results concerning the influence of the friction coefficient, Dundur's parameter and the specimen's Poisson's ratio on the absolute maximum surface tensile stress obtained at a frictional contact cycle are reported along with the magnitudes of the relative increase of maximum tensile stresses at unloading. Based on a critical stress fracture criterion it is discussed how the predicted increases will influence the critical loads required for crack initiation.

  • 26. Kabo, Elena
    et al.
    Enblom, Roger
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles.
    Ekberg, Anders
    A simplified index for evaluating subsurface initiated rolling contact fatigue from field measurements2011In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 271, no 1-2, p. 120-124Article in journal (Refereed)
    Abstract [en]

    A previous simplification of the Dang Van equivalent stress measure for assessment of subsurface initiated rolling contact fatigue (RCF) related to wheel-rail contact is modified. The new criterion is intended for real-time assessment of subsurface RCF from measured wheel-rail contact forces. The only needed parameters in the new expression for the equivalent stress are the vertical force and the wheel and rail radii. Comparisons between the new and the original criterion are carried out and show good agreement for the studied cases of tangent track operations. By employing principles of vehicle dynamics the criterion is further extended to the case of operations in curves. Reasonable consistency was found for curve radii down to approximately 2000 m.

  • 27. 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.

  • 28. 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.

  • 29.
    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.

  • 30.
    Lindholm, Per
    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.), Machine Elements.
    Svahn, Fredrik
    Method and surface roughness aspects for the design of DLC coatings2006In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 261, no 1, p. 107-111Article in journal (Refereed)
    Abstract [en]

    The design of coatings for highly loaded component contacts, such as bearings, gears and valve train components involves several important factors, including load, friction, lubrication, surface characteristics and material parameters. This paper presents an investigation of the influence of the material, coating thickness and surface roughness on tensional stress levels for coatings that are more compliant than the substrate material. Specifically the effect of multiple asperity contact is studied in three dimensions. The simulation is based on a finite element model where the load is applied as several interacting Hertzian pressure distributions. The results show that the surface structure, in combination with the elastic properties of the coating, has a large influence on the tensional stress level in the coating. The highest tensional stress level in the coating occurs when contact spots almost overlap neighbouring cells and at the same time the size of the contact spots is in the same order of magnitude as the coating thickness.

  • 31.
    Lindholm, Per
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Svahn, Fredrik
    Study of thickness dependence of sputtered-carbon coating for low friction valve lifters2006In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 261, no 3-4, p. 241-250Article in journal (Refereed)
    Abstract [en]

    This paper presents test and stress calculation results of two thicknesses (0.7 and 1.7 mu m) of amorphous a-C:Cr-coated standard rollers for a cam roller follower valve train mechanism in a diesel truck engine. The coated rollers were tested for 100 h on equipment simulating near-normal engine running conditions. For the thicker coating, the results show mainly polishing wear and low wear on the cam surface. The thinner coating delaminates and the cam shows higher wear. The delamination may be the product of high tensional stresses in the thinner coating, as determined by finite element calculations. These tensions allow surface cracks to propagate down to the chromium interlayer and vice versa.

  • 32.
    Lundgren, Sarah M.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Persson, Karin
    Clarke, Jim
    Brewer, Mark
    Claesson, Per M.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Friction and wear of unsaturated fatty acids in alkane solution under boundary conditions2007In: Wear, ISSN 0043-1648, E-ISSN 1873-2577Article in journal (Other academic)
  • 33. Lundén, Roger
    et al.
    Ekberg, Anders
    Berg, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Centres, The KTH Railway Group.
    Stichel, Sebastian
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Centres, The KTH Railway Group.
    Grassie, Stuart
    Special edition of "Wear" to contain CM2015 proceedings2016In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 366, p. 1-2Article in journal (Refereed)
  • 34.
    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. 

  • 35.
    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.

  • 36.
    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.

  • 37.
    Nilsson, Rickard
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Svahn, F.
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Relating contact conditions to abrasive wear2006In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 261, no 1, p. 74-78Article in journal (Refereed)
    Abstract [en]

    Damage caused by particles within rolling/sliding contacts can severely reduce the operational life of machinery such as roller bearings, gears and pumps. Abrasive wear of spherical roller thrust bearings has been studied using a stylus apparatus and scanning electron microscopy (SEM). Both a standard bearing and a bearing with rollers coated with metal mixed amorphous carbon (Me-C:H) were studied. The SEM measurements were performed systematically across the contact surfaces so that surfaces with gradually different contact situations could be examined. These measurements were compared to the measured wear depth of the components of the roller bearing. Also, the calculated contact conditions in terms of creep, contact size and surface separation have been related to the observed wear pattern at various locations. To attempt to understand the wear behaviour of the bearing with coated rollers, the coating as well as the material content of the surfaces were examined using both SEM and energy dispersive X-ray spectrometry (EDS). This revealed that the coating did not flake off but rather was scratched off. It is possible to link the abrasive wear behaviour to the contact conditions. It is crucial to understand this relationship when building a simulation model of abrasive wear.

  • 38.
    Nosko, Oleksii
    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.).
    Quantification of ultrafine airborne particulate matter generated by the wear of car brake materials2017In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 374-375, p. 92-96Article in journal (Refereed)
    Abstract [en]

    The wear of car brakes is one of the main sources of airborne particulate matter in urban environments. Ultrafine wear particles are of special environmental interest since they can easily penetrate the human body through inhalation and cause various diseases. In the present study, the contribution of ultrafine particles to airborne particulate matter emitted from car brake materials was investigated under different friction conditions. Particles were generated using a pin-on-disc machine located in a sealed chamber and analysed in terms of number, volume and mass concentrations. It was found that temperature has a strong influence on the size distribution of the emitted particles. At temperatures below 200 °C, the ultrafine particles make no measurable contribution to the mass concentration of airborne particles with diameters smaller than 10 µm (PM10). However, at temperatures above 200 °C, the mass fraction of the ultrafine particles in PM10 reaches tens of percent. In general, this fraction increases with the temperature and decreases with the sliding duration. The mass contribution of ultrafine wear particles to PM10 is substantial, and it should not be neglected in environmental and tribological studies.

  • 39.
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    A study of airborne wear particles generated from the train traffic-Block braking simulation in a pin-on-disc machine2011In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 271, no 1-2, p. 86-91Article in journal (Refereed)
    Abstract [en]

    Recently, much attention has been given to the influence of airborne particles in the atmosphere on human health. Sliding contacts are a significant source of airborne particles. In this study airborne particles from railway block brakes are studied using cast iron and composite block material on railway wheel steel. A pin-on-disc tribometer equipped with airborne particle counting instrumentation was used as experimental set-up. The result shows differences for the two tested block brake material combinations in particle size distribution, morphology and elemental content.

  • 40.
    Olofsson, Ulf
    et al.
    KTH, Superseded Departments, Machine Design.
    Andersson, S.
    Björklund, Stefan
    KTH, Superseded Departments, Machine Design.
    Simulation of mild wear in boundary lubricated spherical roller thrust bearings2000In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 241, no 2, p. 180-185Article in journal (Refereed)
    Abstract [en]

    Owing to the curved contact surfaces in a spherical roller thrust beating, the rollers will undergo sliding. For an unskewed roller there will be two points along each contact where the sliding velocity is zero. At all other points along the contact, sliding is present. Under boundary lubricated conditions the sliding can give rise to mild wear. Experimental results show that this wear can cause a significant change in the surface profile outside the zero sliding points. The mild wear in the contact was simulated using Archard's wear law. An iterative wear model is described in which the normal load distribution, the tangential tractions and the sliding distances are repeatedly calculated to simulate the changes in surface geometry due to wear. Good qualitative agreement was achieved between the simulation results and the previously presented experimental results.

  • 41.
    Olofsson, Ulf
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Olander, Lars
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Services Engineering.
    Jansson, Anders
    Towards a model for the number of airborne particles generated from a sliding contact2009In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 267, no 12, p. 2252-2256Article in journal (Refereed)
    Abstract [en]

    Recently, much attention has been given to the influence of airborne particles in the atmosphere on human health. Sliding contacts are a significant source of airborne particles in urban environments. Airborne particles may be generated by disc brakes and wheel-rail contacts. This paper presents a new model for determining the number of airborne particles generated by a sliding contact. Previously presented data from a pin-on-disc tribometer equipped with airborne particle counting instrumentation was used to verify the model. The derived particle rate is proportional to the load for the ball bearing steel material evaluated. Furthermore, the model incorporates three particle regimes with distinct number peaks; one with ultra fine particles with a peak around 0.08 mu m, one with fine particles with a peak around 0.35 mu m and one with coarse particles with a peak around 2 mu m, that can be used to rank the number of generated particles from different material combinations and contact conditions.

  • 42.
    Olofsson, Ulf
    et al.
    KTH, Superseded Departments, Machine Design.
    Telliskivi, Tanel
    KTH, Superseded Departments, Machine Design.
    Wear, plastic deformation and friction of two rail steels-€”a full-scale test and a laboratory study2003In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 254, no 1–2, p. 80-93Article in journal (Refereed)
    Abstract [en]

    Form change due to wear and plastic deformation on a rail can reduce the service life of a track. The purpose of this investigation was to study the development of these damage mechanisms on new and 3-year-old rails in a commuter track over a period of 2 years. The experimental results from the form measurements show that there was a significant change in rail profile due to wear as well as to plastic deformation. Plastic deformation and wear was a continuing process even for rail that had been in service for 5 years. The plastic deformation mechanism was plastic ratchetting. Compared with the UIC 900A grade rail, the form change was less for the UIC 1100 grade rail. However, the contact situation in terms of sliding velocity and contact pressure had more influence on form change than the change of material. The results from 3D surface measurement showed that there were different wear mechanisms involved at different parts of the rail. Mild wear dominated at the rail head, but at the rail edge severe wear clearly influenced the amount of wear. The severe wear showed traces of seizure. Material tests were performed on two different testing machines: a two-roller and a pin-on-disk machine. On the basis of results from the material testing, a simple wear map was constructed. In the wear map, the wear coefficient is presented as a function of sliding velocity and contact pressure. The results from laboratory tests showed that wear coefficient depended strongly on sliding velocity. The increase in the wear coefficient when increasing sliding velocity was due to a change of wear mechanism from mild wear to severe wear.

  • 43.
    Olofsson, Ulf
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Tu, Minghui
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Nosko, Oleksii
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Lyu, Yezhe
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Dizdar, Senad
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.). Höganäs AB, R&D, 263 83 Höganäs, Sweden.
    A pin-on-disc study of airborne wear particle emissions from studded tyre on concrete road contacts2018In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 410-411, p. 165-172Article in journal (Refereed)
    Abstract [en]

    Studded tyres wear surfaces of winter roads, generating inhalable airborne particles. In this study, four concrete road materials and two stud geometries were investigated in terms of wear, road material hardness and airborne particle concentration. The sliding contact between studded tyres and road materials was studied using a pin-on-disc machine in a clean chamber. The results show that the normal load and the stud size have a large influence on the wear and particle emission. It was found that the wear and particle concentration are inversely proportional to the hardness of the aggregate in the road material and proportional to the sliding distance. The particle size distribution has peaks at 0.2 µm, 1 µm and 2 µm. 

  • 44.
    Olsson, Erik
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Larsson, Per-Lennart
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    On the tangential contact behavior at elastic–plastic spherical contact problems2014In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 319, no 1/2, p. 110-117Article in journal (Refereed)
    Abstract [en]

    The problem of tangential contact between an elastic-plastic sphere and a rigid plane is studied analytically and numerically with the specific aim to derive force-displacement relations to be used in numerical simulations of granular materials. The simulations are performed for both ideal-plastic and strain hardening materials with different yield stresses and including large deformation effects in order to draw general conclusions. The results are correlated using normalized quantities pertinent to the correlation of indentation testing experiments leading to a general description of the tangential contact problem. Explicit formulas for the normal and tangential forces are presented as a function of the tangential displacement using data that are easily available from axi-symmetric analyses of spherical contact. The proposed model shows very good agreement when compared with the FE-simulations.

  • 45.
    Pecorari, Claudio
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Rokhlin, Stanislav I.
    Elasto-plastic micromechanical model for determination of dynamic stiffness and real contact area from ultrasonic measurements2007In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 262, no 7-8, p. 905-913Article in journal (Refereed)
    Abstract [en]

    The interaction of ultrasonic waves with rough surfaces in contact is sensitive to the micromechanics of the contacts and to the topography of the surfaces. A continuous effort to develop a link between ultrasonic measurements and interfacial properties has evolved to the extent that elasto-plasticity occurring during loading can now be taken into account. Here, a state-of-the-art model is critically revisited in light of recent results on the micromechanics of elasto-plastic asperities in contact during unloading. A new probability density function of the asperity height is derived, which takes into account plastic deformation. This function is used to evaluate the pressure during unloading as a function of the relative approach between the mean planes of the surfaces. It is also shown that this relation can be cast in terms of the probability density function prior deformation, provided that a suitable transformation variable is utilized. These results are used to obtain a new expression for the dynamic stiffness of the elasto-plastic interface which determines the response of the latter to an incident wave. Finally, some results illustrating the behavior of the static and dynamic interfacial stiffness during a complete loading-unloading cycle are presented.

  • 46. Perricone, Guido
    et al.
    Matejka, Vlastimil
    Alemani, Mattia
    Valota, Giorgio
    Bonfanti, Andrea
    Ciotti, Alessandro
    Olofsson, Ulf
    Söderberg, Anders
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements. KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.). 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.), Machine Design (Div.). KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements. KTH, School of Industrial Engineering and Management (ITM), Applied Mechanical Engineering (KTH Södertälje). KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Nosko, Oleksii
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Straffelini, Giovanni
    Gialanella, Stefano
    Ibrahim, Metinoz
    A concept for reducing PM10 emissions for car brakes by 50%2018In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 396, p. 135-145Article in journal (Refereed)
    Abstract [en]

    With regard to airborne particles with an aerodynamic diameter of less than 10 mu m (PM10), in countries in the European Union, the mass of brake emissions equals approximately 8-27% of the total traffic-related emissions. Using a research methodology combining tests at different scale levels with contact mechanics simulations and PM10 chemical characterization, the REBRAKE EU-financed project had the following aims: i) to demonstrate the possibility of reducing the PM10 fraction of the airborne particulate from brake wear by 50 wt%; ii) to enhance the general understanding on the physical and chemical phenomena underlying the brake wear process. The results achieved so far indicate that it is possible to design a disc brake system for a European standard car affording at least a 32 wt% PM10 emission reduction using a standard European pad and a heat-treated rotor. A further reduction to 65 wt% PM10 emission could be achieved with NAO pad material and the same heat-treated disc.

  • 47. Sellgren, U.
    et al.
    Björklund, Stefan
    KTH, Superseded Departments, Machine Design.
    Andersson, S.
    A finite element-based model of normal contact between rough surfaces2003In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 254, no 11, p. 1180-1188Article in journal (Refereed)
    Abstract [en]

    Engineering surfaces can be characterized as more or less randomly rough. Contact between engineering surfaces is thus discontinuous and the real area of contact is a small fraction of the nominal contact area. The stiffness of a rough surface layer thus influences the contact state as well as the behavior of the surrounding system. A contact model that takes the properties of engineering surfaces into account has been developed and implemented using finite element software. The results obtained with the model have been verified by comparison with results from an independent numerical method. The results show that the height distribution of the topography has a significant influence on the contact stiffness but that the curvature of the roughness is of minor importance. The contact model that was developed for determining the apparent contact area and the distribution of the mean contact pressure could thus be based on a limited set of height parameters that describe the surface topography. By operating on the calculated apparent pressure distribution with a transformation function that is based on both height and curvature parameters, the real contact area can be estimated when the apparent contact state is known. The model presented is also valid for cases with local plastic flow in the bulk material.

  • 48.
    Sh. Sichani, Matin
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles. KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Railway Technology. KTH, School of Engineering Sciences (SCI), Centres, The KTH Railway Group.
    Enblom, Roger
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles. KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Railway Technology. KTH, School of Engineering Sciences (SCI), Centres, The KTH Railway Group.
    Berg, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles. KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Railway Technology. KTH, School of Engineering Sciences (SCI), Centres, The KTH Railway Group.
    Comparison of non-elliptic contact models: Towards fast and accurate modelling of wheel-rail contact2014In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 314, no 1-2, p. 111-117Article in journal (Refereed)
    Abstract [en]

    The demand to investigate and predict the surface deterioration phenomena in the wheel-rail interface necessitates fast and accurate contact modelling. During the past 20 years, there have been attempts to determine more realistic contact patch and stress distributions using fast simplified methods. The main aim of the present work is to compare some of these state-of-the-art, non-elliptic contact models available in the literature. This is considered as the first step to develop a fast and accurate non-elliptic contact model that can be used on-line with vehicle dynamics analysis. Three contact models, namely STRIPES, Kik-Piotrowski and Linder are implemented and compared in terms of contact patch prediction, as well as contact pressure and traction distributions. The evaluation of these models using CONTACT software indicate the need for improvement of contact patch and pressure estimation in certain contact cases.

  • 49.
    Sichani, Matin Sh.
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles.
    Enblom, Roger
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles. Bombardier Transportation, Sweden.
    Berg, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles.
    A fast wheel-rail contact model for application to damage analysis in vehicle dynamics simulation2016In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 366, p. 123-130Article in journal (Refereed)
    Abstract [en]

    A novel wheel-rail contact model is proposed to be implemented for multi-body dynamics simulation, in order to facilitate accurate online calculation of damage phenomena such as wear and rolling contact fatigue. The normal contact, i.e. contact patch and pressure distribution, is calculated using a fast non elliptic algorithm called ANALYN. The tangential contact, i.e. tangential stress distribution, stick-slip division and creep force calculation, is treated using an alternative to the FASTSIM algorithm that is based on a strip theory which extends the two-dimensional solution of rolling contact to three-dimensional contacts. The proposed contact model is compared to the Hertz+FASTSIM model and evaluated using the CONTACT code in terms of contact patch and stress distribution as well as creep force curves. The results show that the proposed model can significantly improve the estimation of the contact solution both in terms of creep force estimation and contact details, such as stress distribution, needed for damage predictions.

  • 50.
    Sjödin, Ulf
    et al.
    KTH, Superseded Departments, Machine Design.
    Olofsson, Ulf
    KTH, Superseded Departments, Machine Design.
    Experimental study of wear interaction between piston ring and piston groove in a radial piston hydraulic motor2004In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 257, no 12, p. 1281-1287Article in journal (Refereed)
    Abstract [en]

    The wear interaction between piston ring and piston groove in a radial piston hydraulic motor was studied in regard to mass loss and changes in form and surface roughness. A specially developed test rig that simulates the tilting movements of pistons at the end of strokes was used in the test. The results show that wear on the piston ring groove can be up to 10 times greater than the wear on the piston ring. For both interacting surfaces, the dominant wear mechanism was mild wear. The results from a factorial design show that the form of the piston groove significantly influences the amount of wear.

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