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  • 1.
    Nilsson, Rickard
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Maskinkonstruktion (Avd.).
    On wear in rolling/sliding contacts2005Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The aim of this thesis is to increase the understanding of wear in rolling/sliding contacts such as the wheel-rail contact for railroads and the roller-washer contact for roller bearings.

    The Stockholm commuter train network has been the subject of papers A and B in this thesis in which the wear and surface cracks on rails has been observed for a period of three years. By comparing the wear depth with the crack length, equilibrium between these two damage mechanisms was found for a lubricated rail. 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.

    Roller bearings subjected to lubricant borne particles have been the subject of papers C, D and E in this thesis. Particles in the lubricating oil can have a significant impact on the wear in lubricated contacts. Even at low concentration levels can self-generated particles cause significant wear. The here presented results shows that filtration during run-in can significantly reduce both the mass loss and the number of self generated particles. A series of experiments has been carried out to study the wear of roller bearings by ingested lubricant borne hard particles. The form of the worn profile and the length of wear scratches correspond closely to the sliding within the contact. A count of the number of wear scratches on the rolling element surface indicates that the contact concentrates particles. A novel wear model based on the observation of a single point on the contacting surface when a concentration of particles passes through it has been developed and the necessary data for the model has been determined from the experiments. Comparison of the simulation results with the experimental results shows good qualitative agreement for the form change of the washer surfaces.

  • 2.
    Nilsson, Rickard
    KTH, Tidigare Institutioner                               , Maskinkonstruktion.
    Rail wear development: measurements and evaluation2002Rapport (Annet vitenskapelig)
  • 3.
    Nilsson, Rickard
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.).
    Dwyer-Joyce, R.S.
    Olofsson, Ulf
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Tribologi.
    The abrasive wear of rolling bearings by lubricant borne particles2006Inngår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 220, nr J5, s. 429-439Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 4.
    Nilsson, Rickard
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Maskinkonstruktion (Avd.).
    Olofsson, Ulf
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Tribologi.
    Sundvall, Krister
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.).
    Filtration and coating effects on self-generated particle wear in boundary lubricated roller bearings2005Inngår i: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 38, nr 2, s. 145-150Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 5.
    Nilsson, Rickard
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.).
    Svahn, F.
    Olofsson, Ulf
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Tribologi.
    Relating contact conditions to abrasive wear2006Inngår i: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 261, nr 1, s. 74-78Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 6.
    Olofsson, Ulf
    et al.
    KTH, Tidigare Institutioner                               , Maskinkonstruktion.
    Nilsson, Rickard
    KTH, Tidigare Institutioner                               , Maskinkonstruktion.
    Surface cracks and wear of rail: a full-scale test on a commuter train track2002Inngår i: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 216, nr 4, s. 249-264Artikkel i tidsskrift (Fagfellevurdert)
    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.

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