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  • 101. Marshall, M. B.
    et al.
    Lewis, R.
    Dwyer-Joyce, R. S.
    Olofsson, Ulf
    KTH, Superseded Departments, Machine Design.
    Björklund, Stefan
    KTH, Superseded Departments, Machine Design.
    Ultrasonic characterisation of a wheel/rail contact2004In: Transient Processes in Tribology, 2004, Vol. 43, p. 151-158Conference paper (Refereed)
    Abstract [en]

    A quantification of stress in a wheel/rail contact is essential information required in fatigue and wear calculations for determining design life, regrinding and maintenance schedules. The aim of this work was to use ultrasound to non-destructively determine wheel/rail contact pressures. A wheel/rail interface behaves like a spring. If the pressure is high there are few air gaps; so it is very stiff and allows transmission of an ultrasonic wave. If the pressure is low then interface stiffness is lower and most ultrasound is reflected. A spring model was used to determine maps of contact stiffness from wheel/rail contact ultrasonic reflection data. A calibration procedure was then used to determine the pressure. Measured contact pressure contours are compared with those predicted by various contact theories.

  • 102.
    Nilsson, Rickard
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Dwyer-Joyce, R.S.
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    The abrasive wear of rolling bearings by lubricant borne particles2006In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 220, no J5, p. 429-439Article in journal (Refereed)
    Abstract [en]

    Damage caused by lubricant borne particles in rolling/sliding contacts can severely reduce the operational life of machine elements such as cam mechanisms, roller bearings, gears, and pumps. Lubricant supplies frequently contain such contaminating particles, either generated from within the machinery itself or entrained from the surroundings. The particle can be entrained into a lubricated contact and damage the bearing surfaces. Many such individual abrasive actions can lead to significant change in the surface profile of the rolling elements.

    In this work, a series of experiments has been carried out to investigate the mechanism of this surface damage and abrasion process when the contaminating particles are small and hard. The tests show, how particles are entrained into the contacts, the form of the scratches they produce, and the resulting surface profile changes. On the basis of these observations, a model of the abrasive wear process has been developed. The prediction of abrasive wear compares qualitatively well with observed form change on the bearing surface.

  • 103.
    Nilsson, Rickard
    et al.
    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.), Tribologi.
    Sundvall, Krister
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Filtration and coating effects on self-generated particle wear in boundary lubricated roller bearings2005In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 38, no 2, p. 145-150Article in journal (Refereed)
    Abstract [en]

    A specially designed test system involving boundary lubricated roller bearings was used to study wear at low particle concentration levels. A separate oil system circulated the oil through the test bearings. The effects of self-generated contaminants from the system were studied. Even at very low concentration levels, self-generated contaminants can cause significant wear. The concentration of self-generated particles was very high during the running-in period. It is therefore important that the filtration be very efficient during this period. The experimental results show that filtration during run-in for 1 h with a 3 μm filter can reduce both the mass loss and the number of self-generated particles by a factor of 10. Furthermore, the results also show that while the bearings with standard rollers can have significant wear, those with coated rollers are at the same time almost unaffected by wear. Also, the number of particles generated in the contact was significantly less when using coated rollers. There were twice as many self-generated particles when using a standard bearing as those compared with a coated bearing.

  • 104.
    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.

  • 105.
    Nosko, Oleksii
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Alemani, Mattia
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Temperature effect on emission of airborne wear particles from car brakes2015In: Europe's Braking Conference and Exhibition 2015, 2015, Vol. EB2015-TEF-014Conference paper (Refereed)
  • 106.
    Nosko, Oleksii
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Borrajo-Pelaez, Rafael
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Hedström, Peter
    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.).
    Porosity and shape of airborne wear microparticles generated by sliding contact between a low-metallic friction material and a cast iron2017In: Journal of Aerosol Science, ISSN 0021-8502, E-ISSN 1879-1964, Vol. 113, p. 130-140Article in journal (Refereed)
    Abstract [en]

    The wear of brakes in transport vehicles is one of the main anthropogenic sources of airborne particulate matter in urban environments. The present study deals with the characterisation of airborne wear microparticles from a low-metallic friction material / cast iron pair used in car brakes. Particles were generated by a pin-on-disc machine in a sealed chamber at sliding velocity of 1.3 m/s and contact pressure of 1.5 MPa. They were collected on filters in an electrical low pressure impactor, and an investigation was conducted to quantify their shape and porosity. Scanning electron microscopy revealed that most of the 0.1−0.9 µm particles are flakes and have a breadth-to-length aspect ratio of 0.7 ± 0.2. Particle porosity was determined by milling particles with a focused ion beam and subsequent analysis of the exposed particle cross-sections. Most of the 0.3–6.2 µm particles were revealed to have porosity of 9 ± 6%. Analysis of the relationship between effective particle density, particle material density, dynamic shape factor and porosity showed that the shape factor has a stronger influence on the effective density of airborne wear particles than the porosity factor. The obtained results are useful for accurate prediction of particle behaviour in the atmosphere and in the human respiratory system.

  • 107.
    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.).
    Effective density of airborne wear particles from car brake materials2017In: Journal of Aerosol Science, ISSN 0021-8502, E-ISSN 1879-1964, Vol. 107, p. 94-106Article in journal (Refereed)
    Abstract [en]

    People living in urban environments are subject to high health risks due to various anthropogenicsources of airborne particulate matter, including wear of transport vehicle brakes. Studies ofairborne particles often require an estimate of the effective particle density, a property thatallows correct matching of mass and size characteristics measured by different aerosolinstruments. In this study we investigated the effective density of airborne wear particles emittedfrom car brake materials. The particles were generated by a pin-on-disc machine located in asealed chamber. Two methods were used to determine the effective density. The first method isbased on measurements of PM10 and particle size distribution. The second method involvesmeasurements and subsequent fitting of the mobility size distribution and aerodynamic sizedistribution. Results from the two methods showed good agreement. It was found that theeffective density is 0.75±0.2 g/cm3. The particle emission, size distribution and effectivedensity are sensitive to temperature variations. An intensive emission of ultrafine particles isinitiated at the disc temperature of 185±16 °C. The effective density decreases with thetemperature in the interval 110–360 °C. There is a large difference between the effective densityand the density of the particle material, which suggests that the particles are porous.

  • 108.
    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.

  • 109.
    Nosko, Oleksii
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Vanhanen, Joonas
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Emission of 1.3–10 nm airborne particles from brake materials2017In: Aerosol Science and Technology, ISSN 0278-6826, E-ISSN 1521-7388, Vol. 51, no 1, p. 91-96Article in journal (Refereed)
    Abstract [en]

    Operation of transport vehicle brakes makes a significant contribution to airborne particulate matter in urban areas, which is subject of numerous studies due to the environmental concerns. We investigated the presence and number fractions of 1.3–10 nm airborne particles emitted from a low-metallic car brake material (LM), a non-asbestos organic car brake material (NAO) and a train brake cast iron against a cast iron. Particles were generated by a pin-on-disc machine in a sealed chamber and analyzed using a nano condensation nucleus counter, a CPC, and an FMPS. It was found that 1.3–4.4 nm particles are emitted during the friction. For the pairs with the LM and NAO, 1.3–4.4 nm particles predominate in number at temperatures above 160°C. The emission of the 1.3–4.4 nm particles precedes the emission of above 4.4 nm particles. For the cast iron pair, the number of 1.3–4.4 nm particles is smaller than the number of 4.4–10 nm particles. The findings suggest that brake materials produce a significant number of 1.3–4.4 nm airborne particles, and these particles should not be neglected in environmental and tribological studies.

  • 110.
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    A multi-layer model of low adhesion between railway wheel and rail2007In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 221, no 3, p. 385-389Article in journal (Refereed)
    Abstract [en]

    The current paper presents a new multi-layer model of low adhesion between railway wheel and rail. The model proposes that when leaves are crushed between railway wheels and rail, both a coated slippery layer and a chemically reacted, easily sheared surface layer are formed. Elemental depth profiling reveals that the chemically reacted, easily sheared surface layer contains substances such as P and Ca. Both the coated slippery layer and the chemically reacted, easily sheared surface layer must be removed to get proper adhesion between railway wheel and rail.

  • 111.
    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.

  • 112.
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Adhesion and friction modification2009In: Wheel-Rail Interface Handbook / [ed] Lewis, Roger; Olofsson, Ulf, Woodhead Publishing Limited, 2009, p. 510-527Chapter in book (Refereed)
    Abstract [en]

    Trains operate within the limitations imposed by the friction between the railway wheel and rail surfaces. Inadequate friction causes poor adhesion during braking, which is a safety issue as it leads to extended stopping distances. Inadequate friction is also a performance issue as it affects traction and thus limits the tangential force that can be developed in curving. Delays occur if a train passes over areas of poor adhesion while in service. In this chapter are models and methods to analyse and control the adhesion between railway wheel and rail discussed. Furthermore, recent research results are also presented and discussed.

  • 113.
    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.

  • 114.
    Olofsson, Ulf
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Lewis, Roger
    Tribology of the wheel-rail contact2006In: Handbook of Railway Vehicle Dynamics / [ed] Iwnicki, Simon, CRC Press, 2006, p. 121-141Chapter in book (Other academic)
  • 115.
    Olofsson, Ulf
    et al.
    KTH, Superseded Departments, Machine Design.
    Nilsson, Rickard
    KTH, Superseded Departments, Machine Design.
    Surface cracks and wear of rail: a full-scale test on a commuter train track2002In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 216, no 4, p. 249-264Article in journal (Refereed)
    Abstract [en]

    Damage mechanisms such as surface cracks and wear on a rail can reduce the service life of a railway track. The purpose of this investigation was to study the development of these two damage mechanisms on new and 3-year-old rails in a commuter railway track over a period of 2 years. Four curves were studied with radius between 303 and 616 m. In two of the curves, two different kinds of rail steel grade (UIC 900A grade with ultimate strength 900 N/mm2 and UIC 1100 grade with ultimate strength 1100 N/mm2) were used in each curve. In the other two curves, only the lower-strength rail was used. Four pieces of new rail, each 20 m long, were inserted in the two curves with both UIC 900A and UIC 1100 grade rail. Lubrication was applied on the high rail of one of the curves with both UIC 900A and UIC 1100 grade rail and on one of the curves with only UIC 900A grade rail. The two remaining curves were not lubricated. Surface cracks in the form of headchecks could be noted on the surface of the new 1100 grade rails after 1 month of traffic. By contrast, the surface of the UIC 900A grade rails showed visible surface cracks in only two of four curves and that after approximately 2 years of traffic. Both materials seemed to be similarly sensitive to crack initiation but the 1100 grade rail was more sensitive to crack propagation and also more sensitive to the formation of headcheck cracks. Lubrication, as expected, reduced the profile change. A less expected outcome was that lubrication also reduced the rate of crack propagation; however, the lubricated UIC 1100 grade rail was as sensitive to crack initiation as the unlubricated UIC 1100 grade rail. By comparing the wear depth in the headcheck zone with the crack length, equilibrium between these two damage mechanisms was found for the lubricated UIC 1100 grade rail. Both the crack length and the wear depth showed low values. By using a lubricant with friction modifiers the stresses was low enough to prevent crack propagation; at the same time, the rail was hard enough to reduce the wear rate. This is probably the most favourable state in terms of rail maintenance cost.

  • 116.
    Olofsson, Ulf
    et al.
    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.
    On the identification of wear modes and transitions using airborne wear particles2013In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 59, no SI, p. 104-113Article in journal (Refereed)
    Abstract [en]

    A novel test method was used to identify how contact conditions influence the wear modes and transitions for sliding steel-on-steel contacts. The test equipment was a pin-on-disc tribometer equipped with instruments for counting airborne particles. The results show that the dominant wear mode significantly influences the number of airborne particles generated from the contact. During mild wear few or no measurable airborne particles were generated. The transitional running-in process could also be identified by airborne particle measurement analysis.

  • 117.
    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
    A Study of Airborne Wear Particles Generated From a Sliding Contact2009In: Journal of tribology, ISSN 0742-4787, E-ISSN 1528-8897, Vol. 131, no 4Article in journal (Refereed)
    Abstract [en]

    Recently, much attention has been paid to the influence of airborne particles in the atmosphere on human health. Sliding contacts are a significant source of airborne particles in urban environments. In this study airborne particles generated from a sliding steel-on-steel combination are studied using a pin-on-disk tribometer equipped with airborne-particle counting instrumentation. The instrumentation measured particles in size intervals from 0.01 mu m to 32 mu m. The result shows three particle size regimes with distinct number peaks: ultrafine particles with a size distribution peak around 0.08 mu m, fine particles with a peak around 0.35 mu m, and coarse particles with a peak around 2 or 4 mu m. Both the particle generation rate and the wear rate increase with increasing sliding velocity and contact pressure.

  • 118.
    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.

  • 119.
    Olofsson, Ulf
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Piyush, Chandra
    Alemani, Mattia
    Gialannela, Stefano
    Straffelini, Giovanni
    Characterisation of wear particles and tracks from disc brake materials: a multianalytical approach2015In: Eurobrake 2015, 2015Conference paper (Refereed)
  • 120.
    Olofsson, Ulf
    et al.
    KTH, Superseded Departments, Machine Design.
    Sjostrom, H.
    Sjodin, U.
    Increased wear resistance of roller bearings using Me-C: H coated rollers2000In: Journal of tribology, ISSN 0742-4787, E-ISSN 1528-8897, Vol. 122, no 4, p. 682-688Article in journal (Refereed)
    Abstract [en]

    The contact surfaces bz a boundary lubricated spherical roller thrust bearing can change form due to sliding and particle generated wear. These form changes can seriously reduce the fatigue life of the bearings. An experimental test series has been performed where this effect was investigated in bearings with metal mixed amorphous carbon, Me-C: H, coated rollers that were tested against bearings with standard rollers. The experimental results show that while the bearings with standard rollers can fail due to wear, the bearings with coated rollers are at the same time almost unaffected by wear. Also the number of particles generated in the contact was significantly less when using coated rollers. There were twice as many self-generated particles when using a standard bearing compared with a coated bearing. The effect of the coating is discussed in terms of surface hardness, coefficient of friction and tribochemical phenomena. [S0742-4787(00)02004-X].

  • 121.
    Olofsson, Ulf
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Sundh, Jon
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Bik, Ulf
    Nilsson, Ricard
    The influence of snow on the tread braking performance of a train: A pin-on-disc simulation performed in a climate chamber2016In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 230, no 6, p. 1521-1530Article in journal (Refereed)
    Abstract [en]

    In trains with tread brakes, the coefficient of friction between the brake block and the railway wheel determines the stopping distance. The blocks have traditionally been manufactured from cast iron. Although these blocks have good braking capacity, their use is often restricted due to the squealing noise they emit. Tests of alternative composite block materials have been successful under summer conditions; however, in regions with snowy winters the use of such materials has been limited due to problems with braking capacity under snowy conditions. This research aims to develop a laboratory-scale test methodology for evaluating the braking capacity of tread brake materials under winter and snowy conditions. A pin-on-disc machine placed in a climate chamber was used for testing, and a block of standard cast iron was compared with blocks of standard composite materials. The results indicated that the blocks of standard composite materials generate a much smoother surface on the counter wheel and a significantly lower friction coefficient under snowy conditions. A second test series evaluated blocks of alternative composite materials, and a candidate material with low noise and a sufficiently high sliding friction coefficient was selected for further study. A third test series examining geometrical changes in the contact surface in terms of milled parallel tracks was performed; it revealed that the braking capacity under winter conditions can be increased by milling actions if the parallel tracks are properly oriented - in this case, at an angle of 45 degrees to the sliding direction.

  • 122.
    Olofsson, Ulf
    et al.
    KTH, Superseded Departments, Machine Design.
    Sundvall, Krister
    KTH, Superseded Departments, Machine Design.
    Influence of leaf, humidity and applied lubrication on friction in the wheel-rail contact: pin-on-disc experiments2004In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 218, no 3, p. 235-242Article in journal (Refereed)
    Abstract [en]

    A novel test method has been used to study how applied and natural lubrication (leaf and humidity) influences the coefficient of friction in the wheel-rail contact. A pin-on-disc tribometer placed in a climate chamber was used as the test equipment. The pin-on-disc contact simulates the wheel-rail contact caused by commuter train traffic on straight track. The results show that the coefficient of friction decreases when the relative humidity increases and decreases even more when a leaf is used as a lubricant. By using an elm leaf as the lubricant, the coefficient of friction is reduced by a factor of four compared with the unlubricated case. However, the coefficient of friction decreases even more when a rail lubricant is used.

  • 123.
    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.

  • 124.
    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. 

  • 125.
    Olofsson, Ulf
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Wahlström, Jens
    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.
    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).
    Jansson, Anders
    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).
    Airborne Wear Particles from Disc Brakes: A Comparison of Measurements from Cars, Test Stands and Material Tests2008Conference paper (Other academic)
  • 126.
    Olofsson, Ulf
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements. KTH, School of Engineering Sciences (SCI), Centres, The KTH Railway Group.
    Zhu, Yi
    KTH, School of Engineering Sciences (SCI), Centres, The KTH Railway Group. KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements.
    Abbasi, Saeed
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements. KTH, School of Engineering Sciences (SCI), Centres, The KTH Railway Group.
    Lewis, Roger
    Lewis, Steve
    Tribology of the wheel rail contact: aspects of wear, particle emission and adhesion2013In: Vehicle System Dynamics, ISSN 0042-3114, E-ISSN 1744-5159, Vol. 51, no 7, p. 1091-1120Article in journal (Refereed)
    Abstract [en]

    The wheel−rail contact is a safety critical interface. Wear, particle emission and adhesion are all wheel−rail contact phenomena and are discussed here. All three phenomena are material and system parameters and are linked together. Different countermeasures to one phenomenon such as adhesion enhancement with a friction modifier can increase the wear in the contacting bodies. The wear of railway wheel and rail is linked to the number of airborne particles generated, but the exact number and size distribution of the aerosols particles are unknown. The main objective of this study is to review recent work in this field and to discuss future trends.

  • 127.
    Olofsson, Ulf
    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.).
    Löfving, S.
    Casselgren, J.
    Mayer, L.
    Nilsson, R.
    An optical sensor for the identification of low adhesion in the wheel rail contact2012In: 9th International Conference on Contact Mechanics and Wear of Rail/Wheel Systems, CM 2012, Southwest Jiaotong University , 2012, p. 318-323Conference paper (Refereed)
    Abstract [en]

    Low adhesion between railway wheel and rail, which is usually induced by contaminants such as water, oil, leaves etc., affects railway operation in terms of performance and safety. This study uses an optical sensor to identify different surface layers which cause low adhesion. A laboratory set up and field tests under various conditions were subject to the surface layer identification by the optical sensor. In addition, the friction coefficient was measured on the same surface layers. The results show that the sensor can distinguish between different surface layers. This information further linked to the levels of the friction coefficient, which can be used in the prediction system for the railway operator.

  • 128.
    Olofsson, Ulf
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Zhu, Yi
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Löving, S
    Casselgren, J
    Mayer, L
    Nilsson, R
    An optical sensor for the identification of low adhesion in the wheel/rail contact2012In: The international Journal of railway technology, ISSN 2049-5358, E-ISSN 2053-602X, no 3, p. 97-110Article in journal (Refereed)
  • 129.
    Perricone, Guido
    et al.
    Brembo S.p.A., Stezzano, Italy.
    Alemani, Mattia
    Brembo S.p.A., Stezzano, Italy.
    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), Machine Design (Dept.), Tribologi.
    Olofsson, Ulf
    KTH, Superseded Departments (pre-2005), Machine Design. KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi. KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements. KTH, School of Engineering Sciences (SCI), Centres, The KTH Railway Group. KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    A proposed driving cycle for brake emissions investigation for test stand2019In: Proceedings of the Institution of mechanical engineers. Part D, journal of automobile engineering, ISSN 0954-4070, E-ISSN 2041-2991Article in journal (Refereed)
    Abstract [en]

    Particulate matter emission factors from vehicle brakes are difficult to assess directly from the field. Moreover, there is a lack of a standardized cycle and test stand for evaluating brake emissions. For these reasons, a test cycle was developed from real driving data collected from a car. This new test cycle was implemented on an inertia disc brake dynamometer appositely designed for brake particle emission studies. Results reveal that, for the brake system used as an example, the obtained emission factors for the urban driving conditions studied are comparable to EURO 6 regulations in terms of particle number and comparable to EURO 4 levels in terms of mass with brake emission factors equal to 4.37–6.46 × 1011 particles/km and 44–48 mg/km, respectively.

  • 130.
    Perricone, Guido
    et al.
    Brembo S.p.A., 24040 Stezzano (BG), Italy.
    Matĕjka, Vlastimil
    Department of Chemistry, Faculty of Materials Science and Technology, VSB-Technical University of Ostrava, 708 00 Ostrava, Czech Republic.
    Alemani, Mattia
    Brembo S.p.A., 24040 Stezzano (BG), Italy.
    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), Machine Design (Dept.), Tribologi.
    Olofsson, Ulf
    KTH, Superseded Departments (pre-2005), Machine Design. KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi. KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements. KTH, School of Engineering Sciences (SCI), Centres, The KTH Railway Group. KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    A Test Stand Study on the Volatile Emissions of a Passenger Car Brake Assembly2019In: Atmosphere, ISSN 2073-4433, E-ISSN 2073-4433, Vol. 10, no 5, article id 263Article in journal (Refereed)
    Abstract [en]

    Brake-related airborne particulate matter contributes to urban emissions in the transport sector. Recent research demonstrated a clear dependence of the number of ultra-fine particles on the disc brake temperature. Above the so-called transition temperature, the number of ultra-fine particles increases dramatically (several magnitudes). As for exhaust emissions, part of the emissions released during braking can be in the volatile fraction. For this reason, a disc brake test stand specifically designed for aerosol research was equipped with three different aerosol sampling instruments: (i) a standard cascade impactor, (ii) a cascade impactor operating at high temperature with a heated sampling line, and (iii) a standard cascade impactor with a thermodenuder. Tests with a brake assembly representative of European passenger vehicles were executed, and the concentration of released airborne particles was determined. The results showed a decrease by several magnitudes in the concentration (in the size range of below 200 nm) using the cascade impactor operating at 180 °C with the sampling line heated to 200 °C. A further decrease in the concentration of airborne particles with size fractions below 200 nm was measured using a standard cascade impactor with a thermodenuder heated to 300 °C.

  • 131. Perricone, Guido
    et al.
    Wahlström, Jens
    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.).
    Towards a test stand for standardized measurements of the brake emissions2016In: Proceedings of the Institution of mechanical engineers. Part D, journal of automobile engineering, ISSN 0954-4070, E-ISSN 2041-2991, Vol. 230, no 11, p. 1521-1528Article in journal (Refereed)
    Abstract [en]

    Brake-related particulate matter contributes considerably to the non-exhaust emissions of the transport sector in urban areas of the world. The airborne particle emissions from automotive brakes currently lack any proper regulations. Future regulations require test stands, test cycles and particle instruments to be suitable for measuring the brake emissions. This present work focuses on the design of a novel test stand for reliable measurements of the brake emissions with a high sampling efficiency. A test stand in the form of an inertial disc brake dynamometer was redesigned to allow control of the cleanness of the incoming air and to assure isokinetic sampling. The cleanness of the incoming air, together with an over-pressurized chamber around the brake assembly, ensures that all the particles measured originate from the brake materials. In order to evaluate the novel design, the number and size distributions of the brake emissions are measured online with and without control of the cleanness of the intake air. The results reveal that this test stand can be proposed as a standard test stand to assess objectively the emissions of airborne brake particles in future regulations.

  • 132. Perricone, Guido
    et al.
    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.), Tribologi.
    Alemani, Mattia
    Ciotti, Alessandro
    A Novel Dyno Bench Design Focussing on Measurements in Controlled Air of Particle Emission from Brakes2015Conference paper (Refereed)
  • 133.
    Renberg, Ulrica
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Ångström, Hans-Erik
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Instantaneous On-Engine Turbine Efficiency for an SI Engine in the Closed Waste Gate Region for 2 Different Turbochargers2006In: SAE Technical Papers, 2006, no 01-3389Conference paper (Refereed)
    Abstract [en]

    1D engine simulations of turbocharged engines are difficult to perform with good accuracy. Calculations of turbine performance are based on performance maps. These are measured under steady flow conditions using air at moderate temperatures, not very representative of the very hot and pulsating gas flow the on-engine turbine is exposed to. To improve the predictivity of today's 1D engine calculations or the limiting factors of the turbocharger itself, it is most important to gain deeper understanding of how the turbine behaves under on-engine conditions.

    The objective of this paper is to compare calculated instantaneous on-engine turbine efficiency based on measurements with results from using steady-flow efficiency performance maps. The work is performed using two different turbochargers at two operating points with closed waste gate.

    It is shown that the turbine efficiency characteristic derived from measurements and that from using steady-flow efficiency performance maps describe a quite different behavior of the turbine. The on-engine turbine efficiency has systematically shown to be asymmetric over an exhaust pulse. It is considerably higher during the “downhill side” of the pulse, a phenomenon not captured by the 1D quasi steady calculations.

    An error estimation is made for the measurement-based efficiency. The cumulative error results from individual measurement errors of its constituent parameters. The efficiency uncertainty is most governed and very sensitive to the measurement error of the turbine shaft speed. The pressure before and after the turbine are also important to measure correctly.

  • 134.
    Riva, Gabriele
    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.), Machine Elements.
    Alemani, Mattia
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements.
    A CFD study of a pin-on-disc tribometer setup focusing on airborne particle sampling efficiency2017In: ECOTRIB 2017, 2017Conference paper (Refereed)
    Abstract [en]

    One of the most important measures to evaluate air quality is the presence of particles. Pin-on-disc tribometers are used to study airborne wear particles originating from different sliding contacts in a controlled laboratory environment. One important aspect when measuring airborne particles is to ensure isokinetic sampling conditions. Another important aspect is that the concentration and the particles distribution entering the sampling probe are representative for the emissions generated. It is therefore important to have an estimation of the sampling efficiency of the test system. The aim of this paper is to investigate the particle sampling efficiency of a pin-on-disc tribometer setup. In addition, a modified sampling setup that allows isokinetic sampling is investigated. CFD simulations to investigate air and particle motion were performed for both the existing and the modified configuration. The results show that the velocity field at the outlet does not allow isokinetic sampling for the existing configuration. In the modified configuration a sampling pipe is used to make isokinetic sampling possible. A comparison between the two configurations show that the modified configuration increases the sampling efficiency with almost 40% for ultrafine particles and about 20% for fine and coarse particles. It remains to validate the CFD simulations with experiments.

  • 135.
    Sellgren, Ulf
    et al.
    KTH, Superseded Departments, Machine Design.
    Olofsson, Ulf
    KTH, Superseded Departments, Machine Design.
    Application of a constitutive model for micro-slip in finite element analysis1999In: Computer Methods in Applied Mechanics and Engineering, ISSN 0045-7825, E-ISSN 1879-2138, Vol. 170, no 1-2, p. 65-77Article in journal (Refereed)
    Abstract [en]

    Micro-slip is a phenomenon that occurs between contacting surfaces when a frictional load, less than that necessary to produce macro-slip, is applied to the contacting surfaces. Micro-slip is an elastoplastic physical behavior that is important for fretting fatigue, control engineering, the damping and stiffness of connections and joints. A micro-slip friction lau, suitable for finite element (FE) analysis of systems of interacting bodies where micro-slip effects are of importance has been implemented in a commercial FE software. Physical arguments for a micro-slip friction law are presented. The friction law is based on asperity deformation and is capable of simulating oscillating movements. An important feature of the frictional model is that it decouples the parameters that are related to shape, material and surface topography, respectively. Two examples are chosen to illustrate the applicability of the model. Significant differences in friction force distribution between an elastic Coulomb friction law and the micro-slip friction law are detected on local level as well as on global level.

  • 136. Silvergren, Sanna
    et al.
    Olofsson, Ulf
    KTH, School of Engineering Sciences (SCI), Centres, The KTH Railway Group. KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Andersson, Martin
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Lyu, Yezhe
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi. KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Norman, Michael
    Sanchez, Gonzalo Garcia
    Sjövall, Billy
    Tu, Minghui
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Ombordmätningar av partiklar och koldioxid i X60B förarhytter2017Report (Other (popular science, discussion, etc.))
  • 137.
    Sjöberg, Sören
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi. KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Andersson, Martin
    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.
    Olofsson, Ulf
    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.
    Analysis of running-in using Stribeck curves, with application to gear meshManuscript (preprint) (Other academic)
  • 138.
    Sjöberg, Sören
    et al.
    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.), Tribologi.
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    The influence of manufacturing method on the running-in of gears2011In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 225, no 10, p. 999-1012Article in journal (Refereed)
    Abstract [en]

    Striving for higher gear transmission efficiency by using a low-viscosity transmission lubricant affects the lubricant film thickness. To keep the K-ratio (the ratio between the film thickness and the surface roughness) intact, more effort must be put on the surface topography. This paper presents a study of how running-in affects the dry elastic contact area ratio in spur gears using real surface topographies from three common manufacturing methods (green-shaving, honing, and grinding). The test gears were manufactured in case-hardened steel, similar to 20MnCrS5. Surface topography measurements were used as input to a contact analysis boundary element software program. An important hypothesis used in this work is that the dry elastic contact area ratio, i.e. the ratio between real and nominal contact area, can be used as a measure of the contact conditions in gears. It is concluded that running-in differs significantly for the studied manufacturing methods and that the dry elastic contact area ratio gives a consistent description of these changes. The shaved gears have the highest dry elastic contact area ratio after running in, where the ground gears have the lowest dry elastic contact area ratio. The increase in dry elastic contact area ratio is about 30 per cent for the shaved gears, 12 per cent for the honed gears and less than 5 per cent for the ground gears. Extreme value parameters, such as R(p) and R(z), showed relatively good correlation to dry elastic contact area ratio. However no genuine correlation could be found between dry elastic contact area ratio and two-dimensional (2D) surface roughness parameters. Furthermore, traditional gear metrology form parameters do not serve as a good measure on the changes occurring during the running-in.

  • 139.
    Sjöberg, Sören
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements.
    Sosa, Mario
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements.
    Andersson, Martin
    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.
    A study of the running-in and efficiency of ground gearsManuscript (preprint) (Other academic)
  • 140.
    Sjöberg, Sören
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    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.), Tribologi.
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Analysis of efficiency of spur ground gears and the influence of running-in2016In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 93, p. 172-181Article in journal (Refereed)
    Abstract [en]

    High-performing gear transmissions are needed to reduce CO2 emissions. In this paper an FZG gear test rig was used to investigate how two running-in loads affects the gear mesh efficiency for two different temperatures. The gear surface roughness was investigated in parallel with testing. Higher efficiency was observed for tests using a high running-in load, and for low lubricant temperatures. The running-in load had a larger effect on the mesh efficiency than temperature. The high running-in load also yielded higher gear mesh efficiency and had a larger impact on surface parameters.

  • 141.
    Sjöberg, Sören
    et al.
    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.
    Sundh, Jon
    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. KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Scuffing resistance of gear surfaces: influence of manganese phosphate and lubricantsManuscript (preprint) (Other academic)
  • 142.
    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.

  • 143.
    Sjödin, Ulf
    et al.
    KTH, Superseded Departments, Machine Design.
    Olofsson, Ulf
    KTH, Superseded Departments, Machine Design.
    Initial sliding wear on piston rings in a radial piston hydraulic motor2003In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 254, no 11, p. 1208-1215Article in journal (Refereed)
    Abstract [en]

    The initial sliding wear of boundary lubricated piston rings used in a hydraulic motor is studied in terms of the changes in mass, form and surface toughness. The piston ring in a hydraulic motor makes an important contribution to high volumetric efficiency by properly sealing the cylinder bore and piston. The results show that the wear on the piston ring in this particular test rig takes place at the top of the asymmetric crowning at the outer surface contacting the cylinder bore. Initially, the roughness amplitude decreased rapidly, and had decreased by one-third after sliding 10 m. The dominant wear mechanism was mild wear. Abrasive wear also clearly influences the amount of wear.

  • 144.
    Sjödin, Ulf
    et al.
    KTH, Superseded Departments, Machine Design.
    Pettersson, Ulf
    Olofsson, Ulf
    KTH, Superseded Departments, Machine Design.
    Influence of surface texture on friction and wearManuscript (preprint) (Other academic)
  • 145.
    Skedung, Lisa
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Danerlöv, Katrin
    Institute for Surface Chemistry (YTK), Stockholm, Sweden.
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Aikala, Maiju
    Oy Keskuslaboratorio - Centrallaboratorium Ab (KCL), Espoo, Finland.
    Niemi, Kari
    Oy Keskuslaboratorio - Centrallaboratorium Ab (KCL), Espoo, Finland.
    Kettle, John
    Oy Keskuslaboratorio - Centrallaboratorium Ab (KCL), Espoo, Finland.
    Rutland, Mark W.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Finger Friction Measurements on Coated and Uncoated Printing Papers2010In: Tribology letters, ISSN 1023-8883, E-ISSN 1573-2711, Vol. 37, no 2, p. 389-399Article in journal (Refereed)
    Abstract [en]

    A macroscopic finger friction device consisting of a piezoelectric force sensor was evaluated on 21 printing papers of different paper grades and grammage. Friction between a human finger and the 21 papers was measured and showed that measurements with the device can be used to discriminate a set of similar surfaces in terms of finger friction. When comparing the friction coefficients, the papers group according to paper grade and the emerging trend is that the rougher papers have a lower friction coefficient than smoother papers. This is interpreted in terms of a larger contact area in the latter case. Furthermore, a decrease in friction coefficient is noted for all papers on repeated stroking (15 cycles back and forth with the finger). Complementary experiments indicate that both mechanical and chemical modifications of the surface are responsible for this decrease: (1) X-ray photoelectron spectroscopy measurements show that lipid material is transferred from the finger to the paper surface, (2) repeated finger friction measurements on the same paper sample reveal that only partial recovery of the frictional behaviour occurs and (3) profilometry measurements before and after stroking indicate small topographical changes associated with repeated frictional contacts.

  • 146.
    Skedung, Lisa
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Danerlöv, Katrin
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    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.).
    Aikala, Maiju
    Kettle, John
    Arvidsson, Martin
    Berglund, Birgitta
    Rutland, Mark W.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Discriminating similar surfaces with friction: Finger friction measurements on coated and uncoated printing papers2010In: International Conference on Nanotechnology for the Forest Products Industry 2010, 2010, p. 121-144Conference paper (Refereed)
  • 147.
    Skedung, Lisa
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Danerlöv, Katrin
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Johannesson, Carl Michael
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements.
    Aikala, Maiju
    Kettle, John
    Arvidsson, Martin
    Berglund, Birgitta
    Rutland, Mark W.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Tactile perception: Finger friction, surface roughness and perceived coarseness2011In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 44, no 5, p. 505-512Article in journal (Refereed)
    Abstract [en]

    Finger friction measurements performed on a series of printing papers are evaluated to determine representativeness of a single individual. Results show occasionally large variations in friction coefficients. Noteworthy though is that the trends in friction coefficients are the same, where coated (smoother) papers display higher friction coefficients than uncoated (rougher) papers. The present study also examined the relationship between the measured friction coefficients and surface roughness to the perceived coarseness of the papers. It was found that both roughness and finger friction can be related to perceived coarseness, where group data show that perceived coarseness increases with increasing roughness.

  • 148.
    Skedung, Lisa
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Danerlöv, Katrin
    Institute for Surface Chemistry (YTK), Stockholm, Sweden.
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Johannesson, Carl Michael
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements.
    Aikala, Maiju
    Oy Keskuslaboratorio - Centrallaboratorium Ab (KCL), Espoo, Finland.
    Kettle, John
    Oy Keskuslaboratorio - Centrallaboratorium Ab (KCL), Espoo, Finland.
    Arvidsson, Martin
    Department of Psychology, Stockholm University, Sweden.
    Rutland, Mark W.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Reproducibility of finger friction, surface roughness and perception of printing papersArticle in journal (Other academic)
  • 149.
    Skytte af Sätra, Ulf
    et al.
    KTH, Superseded Departments, Machine Design.
    Olofsson, Ulf
    KTH, Superseded Departments, Machine Design.
    Experimental Study Of Piston Ring Wear In A Radial Piston Hydraulic Motor Influenced By Properties Of The Cylinder BoreManuscript (preprint) (Other academic)
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    Skytte af Sätra, Ulf
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