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  • 1.
    Abbasi, Saeed
    et al.
    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.
    Zhu, Yi
    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.
    Pin-on-disc study of the effects of railway friction modifiers on airborne wear particles from wheel-rail contact2013In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 60, p. 136-139Article in journal (Refereed)
    Abstract [en]

    Knowledge of wheel–rail interaction is crucial to wheel and rail maintenance. In this interaction, some of theworn-off material is transformed into airborne particles. Although such wear is well understood, few studiestreat the particles generated. We investigated friction modifiers' effects on airborne particles characteristicsgenerated in wheel-rail contacts in laboratory conditions. Pin-on-disc machine testing with a round-head pinloaded by a dead weight load 40 N simulated maximum contact pressure over 550 MPa. Airborne particlecharacteristics were investigated in dry contacts and in ones lubricated with biodegradable rail grease andwater- and oil-based friction modifiers. The number of particles declined with the grease; the number ofultrafine particles increased with the water-based friction modifier, mainly due to water vaporization.

  • 2. Almqvist, Andreas
    et al.
    Sahlin, Fredrik
    Larsson, Roland
    Glavatskikh, Sergei
    Luleå University of Technology, Division of Machine Elements.
    On the dry elasto-plastic contact of nominally flat surfaces2007In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 40, no 4, p. 574-579Article in journal (Refereed)
    Abstract [en]

    A model to be used for numerical simulation of the contact of linear elastic perfectly plastic rough surfaces was developed. Energy dissipation due to plastic deformation is taken into account. Spectral theory and an FFT-techique are used to facilitate the numerical solution process. Results of simulations using four two-dimensional profiles with different topographies in contact with a rigid plane for a number loads are reported. From the results it is clear that the real area of contact (Ar) changes almost linearly with load and is only slightly affected by the difference in topography. A plasticity index is defined as the ratio of plastically deformed area (Ap) and Ar. Plastic deformation occurs even at low loads and there is a significant difference in plasticity index between the surface profiles considered. An investigation on how the spectral content of the surface profile influences the results presented is also performed. This is to ensure that the metrological limitations of the optical profilerused to measure the surfaces do not have a significant influence. It is concluded that the highest frequencies of the measured profile have a negligible influence on the real area of contact.

  • 3.
    Andersson, Martin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Sosa, Mario
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    The effect of running-in on the efficiency of superfinished gears2016In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 93, p. 71-77Article in journal (Refereed)
    Abstract [en]

    Reduced gear contact losses are necessary to keep operating temperatures, as well as fuel consumption low. In this work, an FZG gear test rig was used to investigate the effect of running-in on superfinished gears with respect to efficiency. This was compared to ground gears where a higher contact pressure yielded higher efficiency. No difference was found between the two running-in procedures when analysing superfinished gears. The effect of running-in on gears decreased when the initial surface roughness was reduced, which initially had an Ra, Rz and Rpk value of 0.08, 0.75 and 0.08 μm respectively. Superfinished gears showed an overall higher efficiency; however, a distinctly lower efficiency was present below 2 m/s when compared to ground gears.

  • 4.
    Andersson, Sören
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements.
    Björklund, Stefan
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements.
    Söderberg, Anders
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements.
    Frictions models for sliding dry, boundary and mixed lubricated contacts2007In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 40, p. 580-587Article in journal (Refereed)
    Abstract [en]

    Friction, lubrication, and wear have a strong influence on the performance and behavior of mechanical systems. This paper deals with different friction models for sliding contacts running under different conditions. The models presented are suited to different situations, depending on the type of contact, running conditions, and the behavior of interest. The models will be discussed from simulation and tribological points of view. The different types of friction models considered are:

    center dot friction models for transient sliding under dry, boundary and mixed lubrication conditions,

    center dot friction models for micro-displacements of engineering surfaces subjected to transient sliding,

    center dot friction models often used in the simulation and control of technical systems,

    center dot combined friction models that represent physical behaviors fairly well but are also suitable for use in simulating systems,

    center dot friction models that take into account the stochastic nature of interacting surface asperities

  • 5.
    Bergseth, Ellen
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements.
    Sjöberg, Sören
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements.
    Björklund, Stefan
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements.
    Influence of real surface topography on the contact area ratio in differently manufactured spur gears2012In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 56, p. 72-80Article in journal (Refereed)
    Abstract [en]

    Surface topography measurements from spur gears produced using four different manufacturing methods were used as input to a contact analysis programme. All test gears were case-hardened, two gears were machined in the hardened state using honing and grinding respectively, and two gears were machined in the non-hardened state using hobbing and hobbing followed by green-shaving respectively. The results show that the surface topography caused by the manufacturing methods has a large influence on the real contact area in the early life of the gear. The green-shaved gear surfaces and the honed gear surfaces have the highest contact area ratio after manufacturing (as-manufactured), which could be advantageous for future gear life with respect to e.g. the running-in process.

  • 6.
    Björklund, Stefan
    KTH, Superseded Departments, Machine Design.
    The influence of surface roughness in elliptical contacts2001In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 34, no 12, p. 841-845Article in journal (Refereed)
    Abstract [en]

    The influence of surface roughness on contact behaviour is of great importance in many tribological situations. In the last decade several methods to calculate the pressure distribution and the real contact area in contacts between rough surfaces have been described. A problem arising for slender elliptical contacts, such as between gear teeth, roller and raceway, cam and follower, etc., is that the size of the contact is much greater than the size of the asperities. Accordingly the number of contact nodes necessary for an accurate solution to the problem becomes excessively large. This paper describes a method to calculate the influence of three-dimensional surface roughness in contacts that are very long in one direction. The method is based on restricting the calculations to a subpart of the real contact area, while the rest of the contact is taken into account by mirroring techniques. The results show that the real contact area is very sensitive to the amplitude of the roughness, while the waviness is less important. An equation is suggested from which the real area can be calculated if the smooth case contact parameters and two roughness parameters are known.

  • 7. Boschkova, K.
    et al.
    Kronberg, B.
    Rutland, Mark W
    KTH, Superseded Departments, Chemistry.
    Imae, T.
    Study of thin surfactant films under shear using the tribological surface force apparatus2001In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 34, no 12, p. 815-822Article in journal (Refereed)
    Abstract [en]

    Static and dynamic behaviour of thin surfactant films in aqueous solution of hexadecyltrimethylammonium salicylate (C16TASal) were investigated using the tribological surface force apparatus. Normal force measurements show that 0.15 mM C16TASal builds up an innermost film of approximately 8-11 Angstrom thickness at each mica surface, indicating that the surfactant adsorbs in a flat conformation. Furthermore, the height of the force barrier at approximately 60 Angstrom is low (ca 2 mN/m) indicating that the second adsorbed layer is easily pushed out. Addition of salicylate salt to 0.15 mM C16TASal give rise to a more close packed structure, with a total thickness of 62-65 Angstrom. indicative of a micellar or bilayer arrangement at the surfaces. Furthermore, the frequency dependence of the shear modulus was investigated both at close separation at the innermost force barrier and at larger separations (up to 300-400 Angstrom). The visco-elastic measurements show that the elasticity modulus, G ', dominates over the loss modulus, G , for all studied cases, indicative of a more solid-like than liquid-like film. Finally, it is shown that shear at high contact pressures induces new aggregate structures at the surface.

  • 8.
    Cadario, Alessandro
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Alfredsson, Bo
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Fretting fatigue experiments and analyses with a spherical contact in combination with constant bulk stress2006In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 39, no 10, p. 1248-1254Article in journal (Refereed)
    Abstract [en]

    A fretting experiment with separate control of bulk stress, normal and tangential contact loads is presented. For the initial test series, constant normal and bulk loads were combined with a cyclic tangential load. Both the spherical indenter and the plane specimen were manufactured from alpha + beta titanium alloys. Strain gauges and acoustic emission measurements were employed for the determination of the time to crack initiation and the propagation life. The fretting cracks always initiated inside the slip zone at positions that were spread over the whole slip zone. Crack nucleation was investigated with five multiaxial fatigue criteria. It was concluded that macroscale stresses from the contact and bulk load alone could not explain all aspects of crack initiation. A possible explanation was found in the fretting-induced roughness. The growth of the fretting crack was simulated numerically by a parametrical description. It was noted that a cyclic bulk load was required to drive the crack growth through the specimen to final failure.

  • 9.
    Cha, Matthew
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.). Waukesha Bearings, United Kingdom .
    Glavatskih, Sergei
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.). Ghent University, Belgium .
    Nonlinear dynamic behaviour of vertical and horizontal rotors in compliant liner tilting pad journal bearings: Some design considerations2015In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 82, p. 142-152Article in journal (Refereed)
    Abstract [en]

    Dynamic behaviour of vertical and horizontal rotors in journal bearings with line pivot pads is investigated. Two bearing designs are compared: one with white metal pads and another with compliant liner pads. The influence of elasticity of the liner on the journal orbits is investigated. Some practical aspects of the compliant liner pad design are discussed. Compliant bearing design parameters such as preload factor, pivot offset, radial clearance, viscoelasticity, and pad inclination to control the size of the journal orbit are considered.

  • 10.
    Cha, Matthew
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Isaksson, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Glavatskih, Sergei
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Influence of pad compliance on nonlinear dynamic characteristics of tilting pad journal bearings2013In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 57, p. 46-53Article in journal (Refereed)
    Abstract [en]

    The effect of pad compliance on the dynamic response of tilting pad journal bearings is investigated. Pad compliance is varied by changing pivot geometry and Young's modulus of pad backing and pad liner. Two pad support configurations are considered: one that allows only circumferential tilt and another one that allows both circumferential and axial tilts. Journal orbits, oil film pressure and oil film thickness are compared and discussed. It is shown that higher pad backing compliance significantly increases the journal orbit size and results in an increase in oil film pressure while oil film thickness is decreased. With a compliant liner, oil film pressure is decreased while oil film thickness is increased. Tapers at the pad edges are essential to increase the global minimum oil film thickness in compliant liner bearings.

  • 11. Cupillard, Samuel
    et al.
    Glavatskih, Sergei
    Luleå University of Technology, Division of Machine Elements.
    Cervantes, Michel
    3D thermohydrodynamic analysis of a textured slider2009In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 42, no 10, p. 1487-1495Article in journal (Refereed)
    Abstract [en]

    Analysis of a 3D inlet textured slider bearing with a temperature dependent fluid is performed. Numerical simulations are carried out for a laminar and steady flow. Hot and cold lubricant mixing in the groove is modelled and examined for different operating conditions. Thermohydrodynamic performance of the bearing is analysed for different texture lengths. Results show that texture has a stronger and positive influence on load carrying capacity when thermal effects are considered. This beneficial effect is at a maximum for the longest dimples with a length shorter than the pad length. Texture is also beneficial for the load carrying capacity when the sliding speed and inlet flow rate are varied. The load carrying capacity of the slider can be increased by up to 16% in severe operating conditions (high sliding speed).

  • 12.
    Duvefelt, Kenneth
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Johannesson, Carl Michael
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Skedung, Lisa
    Model for contact between finger and sinusoidal plane to evaluate adhesion and deformation component of friction2016In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 96, p. 389-394Article in journal (Refereed)
    Abstract [en]

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

  • 13.
    Everitt, Carl-Magnus
    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.).
    Contact fatigue initiation and tensile surface stresses at a point asperity which passes an elastohydrodynamic contact2018In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 123, p. 234-255Article in journal (Other academic)
    Abstract [en]

    Contact mechanics and tribology was combined with fundamental fatigue and fracture mechanics to form a new mechanism for surface initiated rolling contact fatigue. Following, fatigue was investigated numerically for single asperities and craters in lubricated rolling contact surfaces. The hypothesis suggests that asperity point contacts can create sufficiently large tensile stresses for fatigue. The investigated case corresponded to a heavily loaded truck gear with ground surfaces. Reynolds equation resolved the elastohydrodynamic effect of the asperity in the transient three dimensional contacts. The Findley critical plane criterion was used for multiaxial and non-proportional fatigue evaluation. The simulations confirmed the new mechanism for rolling contact fatigue and showed how asperities can create contact fatigue in the lubricated contacts even without slip.

  • 14.
    Everitt, Carl-Magnus
    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 initiation of rolling contact fatigue at asperities considering slip, shear limit and thermal elastohydrodynamic lubrication2019In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 137, p. 76-93Article in journal (Refereed)
    Abstract [en]

    A numerical investigation was performed, with single axisymmetric asperities passing through lubricated rolling contacts at different slip. Two explanatory and cooperating phenomena were found as to why the damage develops more frequently at negative than positive slip. Metal contact occurred in the inlet, where tractive asperity contacts at negative slip provided a large tensile surface stress outside the contact. As the asperity moved through the contact, sliding supplied it with lubricant and heated the lubricant along the contact. The shear tractions were thus higher near the inlet than the outlet, making them more detrimental for negative than positive slip.

  • 15. Fillon, M.
    et al.
    Glavatskih, Sergei
    Luleå University of Technology, Division of Machine Elements.
    PTFE-faced centre pivot thrust pad bearings factors affecting TEHD performance2008In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 41, no 12, p. 1219-1225Article in journal (Refereed)
    Abstract [en]

    The paper presents a thermoelastohydrodynamic (TEHD) analysis of thrust bearings with polytetrafluoroethylene (PTFE) faced pads. The influence of pad active surface geometry on main characteristics such as temperature profile, film thickness and pressure field are investigated. Due to the high compliance of the PTFE layer, deformations of the active surface due to pressure are quite large and have to be taken into account. The initial geometry of the pad is also of great importance; a parametric study on the pad geometry permits clarification of both geometry and deformation effects. The geometry of the pad, particularly for centrally pivoted pads, has to be considered in order to accurately predict performance of PTFE-faced tilting-pad thrust bearings.

  • 16.
    Glavatskih, Sergei
    Luleå University of Technology, Division of Machine Elements.
    A method of temperature monitoring in fluid film bearings2004In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 37, no 2, p. 143-148Article in journal (Refereed)
    Abstract [en]

    In the present paper a method to improve temperature monitoring of fluid film bearings is described. The method is tested in an industrial tilting pad thrust bearing. Test results for steady state and transient operating conditions are reported. Temperatures monitored by a thermocouple through the utilisation of the proposed method are compared to those measured by thermocouples in the pad backing and in the collar. The method is also tested on a PTFE-faced bearing. Test results show that the proposed method improves sensitivity to thermal transients in conventional babbitted bearings and provides adequate means of temperature monitoring in the PTFE-faced bearings.

  • 17.
    Glavatskih, Sergei
    et al.
    Luleå University of Technology, Division of Machine Elements.
    Höglund, Erik
    Tribotronics: towards active tribology2008In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 41, no 9-10, p. 934-939Article in journal (Refereed)
    Abstract [en]

    A constant trend towards more compact mechanical systems with higher power densities and increased thermo-mechanical loads emphasises the importance of the development of new design approaches and novel tribological systems. Ignoring this may cause a significant slow down in technological and industrial development. Tribotronics or active tribology based on adaptive performance is thought of as being critical in the implementation of smart machine concepts. Recognition of the importance of tribotronics, or active control of system loss outputs, such as those through friction and wear will have significant beneficial economic consequences as a result of the associated accelerated rate of technological progress. These smart tribotronic systems can be embedded in a great variety of machines and mechanisms. If this integration is made at the design stage, products that are more flexible, efficient and reliable can be produced. The concept of tribotronics is presented and discussed in this paper. Some illustrativeexamples that show the feasibility of an “active” approach are given. In addition, various possibilities already reported in literature are discussed.

  • 18. Golchin, Arash
    et al.
    Simmons, Gregory F.
    Glavatskih, Sergei
    Luleå University of Technology, Division of Machine Elements.
    Break-away friction of PTFE materials in lubricated conditions2011In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 48, p. 54-62Article in journal (Refereed)
    Abstract [en]

    This study investigates the tribological characteristics at initiation of sliding (break-away friction) of several polytetrafluoroethylene based materials. Four PTFE composites, pure PTFE, and white metal were tested in a reciprocating tribo-meter with the block on plate configuration against a steel counter-surface. Apparent contact pressure and oil temperature were varied from 1 to 8 MPa and 25 to 85 Â°C respectively. SEM investigations revealed wear patterns of the PTFE materials and the abrasive nature of hard fillers. Bronze filled, carbon filled, and pure PTFE were found to provide lower break-away friction and less variation over the course of testing and generally superior properties.

  • 19.
    Häggström, Daniel
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.). Scania CV AB, Sweden.
    Nyman, Pär
    Sellgren, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Björklund, Stefan
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Predicting friction in synchronizer systems2016In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 97, p. 89-96Article in journal (Refereed)
    Abstract [en]

    The coefficient of friction in synchronizers is important from both a performance and a functional point of view. The synchronization process is highly transient, and the parameters affecting the coefficient of friction have strong mutual dependences, making analysis highly complex. A new friction model for a lubricated molybdenum-steel contact has been developed based on integrating results from physical rig tests and FEM simulations. A simplified thermal model has also been developed, with the purpose to quickly assess the coefficient of friction based on transient force and synchronizer dimensions. The results show good correlation with measured data except at very low sliding speed.

  • 20. Kawada, S.
    et al.
    Watanabe, Seiya
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Surface and Corrosion Science.
    Tadokoro, C.
    Tsuboi, R.
    Sasaki, S.
    Lubricating mechanism of cyano-based ionic liquids on nascent steel surface2018In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 119, p. 474-480Article in journal (Refereed)
    Abstract [en]

    This study investigates the lubricating mechanism of cyano-based ionic liquids on steel surfaces using Q-MS, ToF-SIMS, and TGA. [EMIM][DCN], [EMIM][TCC], [EMIM][TCB], [BMPL][DCN], [BMPL][TCC], and [BMPL][TCB] were selected as lubricants. [EMIM][TCB] exhibited the highest friction coefficient. The others exhibited very low friction coefficients of less than 0.08. Q-MS analysis indicated that the cation components were detected in outgassing during sliding tests. However, anion components were not detected. ToF-SIMS results showed that the anions remained on the worn surfaces which would lead low friction coefficients. To achieve low friction coefficient, the tribo-decomposition of the ionic liquids and adsorption of anion were required. TGA indicated thermal stability was an index for tribo-decomposition on the nascent steel surface.

  • 21.
    Kuznetsov, Evgeny
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.). COMSOL LLC, Russian Federation.
    Glavatskih, Sergei
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.). Ghent University, Belgium .
    Dynamic characteristics of compliant journal bearings considering thermal effects2016In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 94, p. 288-305Article in journal (Refereed)
    Abstract [en]

    A numerical THD model that takes into account mechanical and thermal deformations of a compliant lining is used to investigate the influence of compliance on dynamic characteristics of a two axial groove bearing. A detailed study on the contribution of mechanical and thermal deformation components of the compliant lining to the non-dimensional bearing stiffness and damping is carried out. Thermal deformation is found to increase horizontal stiffness K<inf>yy</inf> and cross-coupled stiffness K<inf>xy</inf> and slightly reduce journal critical mass. Mechanical deformation of the compliant lining is found to decrease damping, reduce vertical and cross-coupled K<inf>xy</inf> stiffness. Radial clearance is found to increase stiffness, except its horizontal component, and decrease horizontal damping. Compliant lining is found to improve bearing stability.

  • 22. Kuznetsov, Evgeny
    et al.
    Glavatskih, Sergei
    Luleå University of Technology, Division of Machine Elements.
    Fillon, Michel
    THD analysis of compliant journal bearings considering liner deformation2011In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 44, no 12, p. 1629-1641Article in journal (Refereed)
    Abstract [en]

    A numerical THD model is developed to investigate the effect of lining compliance on the bearing characteristics. The analysis shows increased load carrying capacity, significantly reduced peak pressures and thicker oil film in the loaded zone compared to a white metal bearing. Slightly thinner oil films are predicted at the bearing edges. Temperature and power loss are found to be similar for some load–speed combinations but higher for other operating conditions. It is also shown that load carrying capacity is more sensitive to thermal expansion while pressure and oil film thickness profiles are more sensitive to elastic deformation.

  • 23.
    Li, Xinmin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    A study on friction and wear reduction due to porosity in powder metallurgic gear materials2017In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 110, p. 86-95Article in journal (Refereed)
    Abstract [en]

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

  • 24.
    Li, Xinmin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Sosa, Mario
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Andersson, Martin
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    A study of the efficiency of spur gears made of powder metallurgy materials - ground versus super-finished surfaces2016In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 95, no 1, p. 211-220Article in journal (Refereed)
    Abstract [en]

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

  • 25.
    Lyu, Yezhe
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Bergseth, Ellen
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Tu, Minghui
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Effect of humidity on the tribological behaviour and airborne particle emissions of railway brake block materials2018In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 118, p. 360-367Article in journal (Refereed)
    Abstract [en]

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

  • 26.
    Mallipeddi, D.
    et al.
    Chalmers Univ Technol, Ind & Mat Sci, SE-41296 Gothenburg, Sweden..
    Norell, M.
    Chalmers Univ Technol, Ind & Mat Sci, SE-41296 Gothenburg, Sweden..
    Sosa, M.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Nyborg, L.
    Chalmers Univ Technol, Ind & Mat Sci, SE-41296 Gothenburg, Sweden..
    The effect of manufacturing method and running-in load on the surface integrity of efficiency tested ground, honed and superfinished gears2019In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 131, p. 277-287Article in journal (Refereed)
    Abstract [en]

    This study compares gear surface characteristics generated by grinding, honing and superfinishing of casehardened steel, including the evolution during efficiency testing with two different prior running-in loads (0.9 GPa and 1.7 GPa). The most influential factor was surface roughness. Micro-pitting was associated with surface asperities and hence only seen in ground and honed gears, while being absent for super-finished gears. The micro-pitting was enhanced by running-in load, but only for rough surfaces. Deformation-induced localized microstructure impact was associated with cracks. Residual stresses reached similar levels after efficiency testing. Phosphorous content in the gear surface was connected to surface roughness and running-in load.

  • 27. Mallipeddi, D.
    et al.
    Norell, M.
    Sosa, Mario
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Nyborg, L.
    Influence of running-in on surface characteristics of efficiency tested ground gears2017In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 115, p. 45-58Article in journal (Refereed)
    Abstract [en]

    The effect of running-in load (0.9 or 1.7 GPa) on surface characteristics of ground spur gears, and on their development during subsequent efficiency testing (FZG rig), is examined. The effect was confined to less than 10 μm depth. Micropitting was associated with surface asperities and their plastic deformation; higher running-in load gave more micropitting, also after identical efficiency tests. Running-in increased unequal compressive residual stresses in both profile and axial directions, while after efficiency testing they approached equal levels. Deformation induced martensite is considered to form during running-in only at high load, still the amount after efficiency testing increased with running-in load. Higher surface content of phosphorous from extreme pressure additive (EP) occurred only after efficiency test following running-in at high load.

  • 28. Matějka, V.
    et al.
    Metinöz, I.
    Wahlström, Jens
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.). System- o Komponentdesign.
    Alemani, M.
    Perricone, G.
    On the running-in of brake pads and discs for dyno bench tests2017In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 115, p. 424-431Article in journal (Refereed)
    Abstract [en]

    Running-in process of low metallic brake pads and cast iron discs are investigated using full scale inertia brake dynamometer designed for particle emission studies. The airborne particles are measured using ELPI+ and collected on filters. The pads and disc contact surfaces are studied using microscopy techniques. It is observed that the particle emissions from the new pads and discs are significantly higher compared with the used ones and indicates importance of proper running-in of the pads and disc for wear particle emission tests. The results also indicate that pads and disc pairs which are able to stabilize friction behavior faster will produce less particle emissions which could influence the strategies of brake material formulations or steps during their production.

  • 29.
    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.

  • 30.
    Nosko, Oleksii
    et al.
    Saitama University, Japan .
    Nagamine, T.
    Mori, H.
    Sato, Y.
    Theoretical study of thermofrictional oscillations due to negative friction-temperature characteristic2013In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 61, p. 235-243Article in journal (Refereed)
    Abstract [en]

    Analytical study on oscillations of a body on a moving counterbody has been done by assuming imperfect frictional thermal contact and friction that decreases with contact temperature. It has been shown that stick-slip oscillation occurs due to decrease of friction coefficient when the body moves in the opposite direction to the counterbody. Dynamical characteristics, such as conditions for stable sliding and limit cycles, have been studied. Normal force between the bodies has significant effect on sliding stability.

  • 31.
    Nosko, Oleksii
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Nagamine, T.
    Nosko, A. L.
    Romashko, A. M.
    Mori, H.
    Sato, Yuichi
    Measurement of temperature at sliding polymer surface by grindable thermocouples2015In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 88, p. 100-106Article in journal (Refereed)
    Abstract [en]

    This paper is devoted to experimental study of capabilities and limitations of grindable thermocouples as applied to polymer materials sliding on metal. Chromel-alumel and chromel-copel grindable thermocouples have been developed and tested for wide ranges of contact pressure and sliding velocity. The background temperature of the sliding surface can be determined as the lower envelope of the signal from the grindable thermocouple. Steady and unsteady regimes of sliding have been investigated. For steady sliding, the accuracy of the temperature determination increases with measurement duration. In the case of unsteady sliding, accurate temperature determination requires multiple tests under the same conditions. The thickness of the thermocouple junction has been analyzed for correct comparison of experimental and calculated temperatures.

  • 32.
    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.

  • 33.
    Olsson, Erik
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Larsson, Per Lennart
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    A unified correlation model describing global properties at elastoplastic sharp indentation contact2016In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 103, p. 252-260Article in journal (Refereed)
    Abstract [en]

    The correlation of sharp indentation testing is analyzed and discussed based on present and previous numerical findings. In particular, correlation of two global indentation properties, hardness and relative contact area, at sharp indentation of classical elastic-plastic materials is discussed in detail. It is shown that the results cannot in general, and in particular at high strain hardening, be correlated accurately using a single parameter, comprising both geometrical and mechanical properties, with the uniaxial stress-strain curve represented by the flow stress at a representative value on the effective plastic strain. Instead, also the level of the plastic hardening must be considered. Based on this finding, a unified model for correlation of global properties is presented for cone indentation of elastoplastic materials.

  • 34.
    Riva, Gabriele
    et al.
    Brembo S.p.A., Stezzano, BG, Italy.
    Valota, Giorgio
    Brembo S.p.A., Stezzano, BG, Italy.
    Perricone, Guido
    Brembo S.p.A., 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.
    An FEA approach to simulate disc brake wear and airborne particle emissions2019In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 138, p. 90-98Article in journal (Refereed)
    Abstract [en]

    Emissions from disc brake wear adversely affect the air quality in cities. Finite Element Analysis (FEA) approaches focussing on the macroscopic wear of pads and rotors can be found in the literature, but none of these take the wear and emission dependence of the local contact pressure and sliding speed into account. The aim of the present study is to further develop an FEA approach for simulation of macroscopic wear and airborne emission to include the dependences of local contact pressure and sliding speed by implementing wear and emission maps obtained by pin-on-disc tribometer tests. Results from a dyno bench test are compared with simulated results. The simulated rotor and pads wear, and airborne emissions are in line with the measured values.

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

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

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

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

  • 37.
    Shu, Ju
    et al.
    KTH, School of Industrial Engineering and Management (ITM).
    Harris, Kathryn
    KTH, School of Industrial Engineering and Management (ITM).
    Munavirov, B.
    Westbroek, R.
    Leckner, J.
    Glavatskih, Sergei
    KTH, School of Industrial Engineering and Management (ITM). Soete Laboratory, Ghent University, B-9000 Ghent, Belgium.
    Tribology of polypropylene and Li-complex greases with ZDDP and MoDTC additives2018In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 118, p. 189-195Article in journal (Refereed)
    Abstract [en]

    The influence of thickener and additive interactions on grease lubricating performance is examined. Polypropylene and lithium complex thickened (Li-complex) greases were tested both as neat greases and with a 2 wt% addition of ZDDP and/or MoDTC. A combination of ZDDP and MoDTC in the polypropylene grease provided the lowest friction with greater longevity compared to the Li-complex grease with the same additives, independent of sliding speed, contact pressure, temperature or type of sliding: continuous vs. reciprocating. The additive combination of ZDDP and MoDTC provided the best antiwear performance in both greases. Depending on the grease sample type, EDS revealed the presence of iron, zinc, phosphorous, sulfur, and molybdenum within the tribofilms.

  • 38. Simmons, Gregory F.
    et al.
    Glavatskih, Sergei
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Mueller, Michael
    Byheden, Åke
    Prakash, Braham
    Extending performance limits of turbine oils2014In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 69, p. 52-60Article in journal (Refereed)
    Abstract [en]

    New turbine oils providing both extremely high viscosity index (VI) and improved boundary/mixed lubrication performance are investigated. Comparisons are made in both laboratory scale testing using typical journal bearing sliding surfaces (steel and white metal) and full scale testing using a hydrodynamic journal bearing test machine. The results from these studies demonstrate the effectiveness of new, high VI, turbine oils for reducing friction at machine startup and improving performance during full film operation.

  • 39. Simmons, Gregory F.
    et al.
    Varela, Alejandro Cerda
    Santos, Ilmar Ferreira
    Glavatskih, Sergei
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Dynamic characteristics of polymer faced tilting pad journal bearings2014In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 74, p. 20-27Article in journal (Refereed)
    Abstract [en]

    Dynamic characteristics of polymer faced tilting pad journal bearings are presented. Investigations are conducted using a single pad, load on pad configuration over a range of shaft speeds and loads. Two polyether ether ketone (PEEK) faced pads, one polytetrafluoroethylene (PTFE) faced pad and two entirely PEEK pads are investigated to determine the effect of varying mean bearing pressure and pivot characteristics as well as different material properties of the polymer layer. Experimental results indicate increased damping and decreased stiffness and slightly increased oil film temperature for entirely PEEK pads compared to pads with a PEEK lining and steel backing. Similar effects were observed by using a softer (PTFE) pad liner with a steel backing.

  • 40.
    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.

  • 41.
    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.

  • 42.
    Sundh, Jon
    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.
    Seizure mechanisms of wheel–rail contacts under lubricated conditions using a transient ball-on-disc test method2008In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 41, p. 867-874Article in journal (Refereed)
    Abstract [en]

    This study focuses on the transition from mild to severe wear in the wheel and rail contact. Such a transition has been observed at increased loading (normal load, sliding velocity, or bulk temperature) which can be compared to a change from a wheel thread-rail head contact to a wheel flange-rail gauge contact. This transition was experimentally studied using a transient test method of ball-on-disc type at different sliding velocities, contact pressures, and lubricants. It can be seen in the results that different seizure mechanisms are active for different sliding velocities. Also the amount of applied lubricant clearly affects the transition to seizure.

  • 43.
    Söderberg, Anders
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements.
    Björklund, Stefan
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements.
    Validation of a simplified numerical contact model2008In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 41, no 9-10, p. 926-933Article in journal (Refereed)
    Abstract [en]

    Surface roughness tends to have a significant effect on how loads are transmitted at the contact interface between solid bodies. Most numerical contact models for analyzing rough surface contacts are computational demanding and more computationally efficient contact models are required. Depending on the purpose of the simulation, simplified and less accurate models can be preferable to more accurate, but also more complex, models. This paper discusses a simplified contact model called the elastic foundation model and its applicability to rough surfaces. The advantage of the model is that it is fast to evaluate, but its disadvantage is that it only gives an approximate solution to the contact problem. It is studied how surface roughness influences the errors in the elastic foundation solution in terms of predicted pressure distribution, real contact area, and normal and tangential contact stiffness. The results can be used to estimate the extent of error in the elastic foundation model, depending on the degree of surface roughness. The conclusion is that the elastic foundation model is not accurate enough to give a correct prediction of the actual contact stresses and contact areas, but it might be good enough for simulations where contact stiffness are of interest.

  • 44. Verma, P. C.
    et al.
    Alemani, M.
    Gialanella, S.
    Lutterotti, L.
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Straffelini, G.
    Wear debris from brake system materials: A multi-analytical characterization approach2016In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 94, p. 249-259Article in journal (Refereed)
    Abstract [en]

    In this work a streamline characterization protocol for debris coming from wear tests on materials used for disc brake assemblies is presented. An important aspect of the methodology concerns powder collection involving aluminum foil, for a gravitational collection, and polycarbonate filters of an impactor, on which particles are selectively trapped, according to their size. The protocol is based on the application of scanning and transmission electron microscopy, X-ray spectroscopy, X-ray and selected area electron diffraction. The aim of the study was to identify selection parameters, like specimen availability and average particle size, for an effective and smart application of the techniques.

  • 45. Verma, Piyush Chandra
    et al.
    Alemani, Mattia
    Gialanella, Stefano
    Lutterotti, Luca
    Olofsson, Ulf
    KTH.
    Straffelini, Giovanni
    Wear debris from brake system materials: A multi-analytical characterization approach (vol 94, pg 249, 2016)2016In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 97, p. 510-511Article in journal (Refereed)
  • 46.
    Wahlström, Jens
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    A comparison of measured and simulated friction, wear, and particle emission of disc brakes2015In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 92, p. 503-511Article in journal (Refereed)
    Abstract [en]

    Airborne wear particles originating from disc brakes are among the main contributors to non-exhaust emissions. The macroscopic wear behaviour of disc brakes can be explained by the growth and destruction of mesoscopic contact plateaus. The pad wear and temperature has earlier been simulated using a cellular automaton mesoscopic approach. The present paper seeks to refine the simulation approach to include disc wear and temperature, and to investigate the validity of this approach by comparing simulated brake events with a dyno bench test. The comparison shows a promising qualitative correlation between the simulated and the experimental results.

  • 47.
    Wahlström, Jens
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements.
    Gventsadze, D.
    Olander, Lars
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Services Engineering.
    Kutelia, E
    Gventsadze, L.
    Tsurtsumia, O.
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    A pin-on-disc investigation of nanoporous composite-based and conventional brake padmaterials focusing on airborne wear particles2011In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464Article in journal (Other academic)
  • 48.
    Wahlström, Jens
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements.
    Gventsadze, D.
    Olander, Lars
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Services Engineering.
    Kutelia, E.
    Gventsadze, L.
    Tsurtsumia, O.
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    A pin-on-disc investigation of novel nanoporous composite-based and conventional brake pad materials focussing on airborne wear particles2011In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 44, no 12, p. 1838-1843Article in journal (Refereed)
    Abstract [en]

    Wear particles originating from disc brakes contribute to particulate concentration in the urban atmosphere. In this work novel nanoporous composite-based and conventional brake materials were tested against cast-iron discs in a modified pin-on-disc machine. During testing airborne wear particles were measured online and collected on filters, which were analysed using SEM and EDX. The morphology of airborne wear particles containing elements such as iron, oxygen, and copper is presented. These results show that two of the nanoporous materials generated 3-7 times less airborne wear particles than the conventional materials. Both the conventional and nanoporous materials displayed a bimodal number distribution.

  • 49. Xiao, L.
    et al.
    Björklund, Stefan
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements.
    Rosen, B. G.
    The influence of surface roughness and the contact pressure distribution on friction in rolling/sliding contacts2007In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 40, no 4, p. 694-698Article in journal (Refereed)
    Abstract [en]

    A numerical contact model is used to study the influence of surface roughness and the pressure distribution on the frictional behaviour in rolling/sliding contacts. Double-crowned roller surfaces are measured and used as input for the contact analysis. The contact pressure distribution is calculated for dry static contacts and the results are compared with friction measurements in a lubricated rolling/sliding contact made with a rough friction test rig. The mean pressure is suggested as a parameter that can be used to predict the influence of surface roughness on the friction coefficient in such contacts. The results show two important properties of the friction coefficient for the friction regime studied in this paper: (1) there is a linear decrease in friction coefficient as a function of the slide-to-roll ratio, and (2) the friction coefficient increases linearly with increasing mean contact pressure up to a maximum limit above which the friction coefficient is constant. The absolute deviation of experimental results front the derived theory is for most cases within 0.005.

  • 50.
    Zhu, Yi
    et al.
    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.
    Söderberg, Anders
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Adhesion modeling in the wheel-rail contact under dry and lubricated conditions using measured 3D surfaces2013In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 61, p. 1-10Article in journal (Refereed)
    Abstract [en]

    Adhesion between wheels and rails plays an essential role in the safe, efficient, and reliable operation of a railway network. Particularly under lubricated conditions, which can be a natural lubricant as water and an applied lubricant as rail oil, trains can experience adhesion loss. This paper presents an adhesion model constructed using the measured 3D wheel-rail surfaces. The numerical model comprises of three parts: a normally loaded contact model; an interfacial fluid model; and a rolling-sliding contact model. Simulation examples use the numerical model to investigate how water or oil contamination might affect wheel-rail adhesion in contacts with different surface roughness levels. Simulation indicates that adhesion peaks are almost at the same creep on different surfaces. The fluid load capacity is inversely proportional to the adhesion coefficient, both of which are clearly dependent on vehicle speed. Oil reduces adhesion coefficient more than water does. The adhesion coefficient on the low roughness surfaces is higher than that on the generated smooth surfaces under oil-lubricated conditions while it is the opposite for water-lubricated contact.

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