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  • 101.
    Hernandez, Sinuhe
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hardell, Jens
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Winkelmann, Horst
    AC²T research GmbH - Austrian Center of Competence for Tribology, Viktor-Kaplan-Straße 2 D, 2700 Wiener Neustadt.
    Ripoli, M. Rodriguez
    AC²T research GmbH - Austrian Center of Competence for Tribology, Viktor-Kaplan-Straße 2 D, 2700 Wiener Neustadt.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Influence of temperature on abrasive wear of boron steel and hot forming tool steels2015In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 338-339, p. 27-35Article in journal (Refereed)
    Abstract [en]

    In many industrial applications the occurrence of abrasive wear results in failure and replacement of components. Examples of these applications are found in mining, mineral handling, agriculture, forestry, process and metalworking industry. Some of these applications also involve operation of relatively moving surfaces at elevated temperatures which increases the severity of wear. A typical example of high temperature wear phenomena is that of tool steels during interaction with boron steel in hot forming. Some studies have been carried out regarding the high temperature tribological behaviour of these materials but results pertaining to their high temperature three body abrasive behaviour have not been published in the open literature. In this work, the high-temperature three body abrasive wear behaviour of boron steel and two different prehardened tool steels (Toolox33 and Toolox44) was investigated using a high temperature continuous abrasion machine (HT-CAT) at different temperatures ranging from 20 °C to 800 °C using a load of 45 N and a sliding speed of 1 ms-1. The wear results were correlated to the hot hardness of the different materials measured by means of a hot hardness tester (HHT) at a load of 10 kgf. Scanning electron microscopy and energy dispersive spectroscopy (SEM/EDS) techniques were used to characterise the worn surfaces. The hot hardness measurements of the three different materials showed a slight but continuous decrease of hardness from room temperature to 600 °C. At temperatures above 600 °C the hardness showed a sharp decrease. The wear rate of Toolox 44 was constant from 20 °C to 400 °C. On the other hand, Toolox33 and boron steel, showed a reduced wear rate from 20 °C to 400 °C attributed to an increased toughness and the formation of wear-protective tribolayers respectively. At higher temperatures (from 400 °C to 800 °C), the wear rate for these materials increased mainly due to a decrease in hardness and the occurrence of recrystallization processes.

  • 102.
    Hernandez, Sinuhe
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Leiro, Alejandro
    Ripoli, Manel Rodriguez
    AC²T research GmbH - Austrian Center of Competence for Tribology, Viktor-Kaplan-Straße 2 D, 2700 Wiener Neustadt.
    Vuorinen, Esa
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Sundin, Karl-Gustaf
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    High temperature three-body abrasive wear of 0.25C 1.42Si steel with carbide free bainitic (CFB) and martensitic microstructures2016In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 360-361, p. 21-28Article in journal (Refereed)
    Abstract [en]

    In the present work, the wear behaviour of different steels has been investigated under a three body abrasive environment at room and elevated temperatures. High-silicon steel (0.25C-1.42Si) was austempered at 300 and 320 ˚C in order to obtain two carbide-free bainitic steels with different mechanical properties. The same steel subjected to two different quench and temper heat treatments was used as a reference material for mechanical and wear testing. The steels were subjected to three-body abrasive wear by means of a high temperature continuous abrasion tester (HT-CAT). The tests were done at 25, 300 and 500 °C respectively. All samples showed similar wear rates at room temperature. At 500 °C, the material austempered at 320 ˚C showed the highest toughness and the lowest wear rate. High temperature hardness and impact toughness tests showed that abrasive wear is not only influenced by hardness but also by the toughness of the material. Owing to their good strength/toughness combination CFB steels could prove to be an important material for abrasive wear applications

  • 103. Hiensch, Martin
    et al.
    Larsson-Kråik, Per-Olof
    Nilsson, Olof
    Levy, Didier
    Kapoor, Ajay
    Franklin, Francis
    Nielsen, Jens
    Ringsberg, Jonas W.
    Josefsson, B. Lennart
    Two-material rail development: field test results regarding rolling contact fatigue and squeal behaviour2005In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 258, no 7-8, p. 964-972Article in journal (Refereed)
    Abstract [en]

    Results from the European 5th Framework project “InfraStar” are presented. The InfraStar project is developing a two-material rail to increase the productivity and reliability of rail infrastructure. The two-material rail aims to be rolling contact fatigue (RCF) resistant and to reduce squeal noise.The InfraStar consortium has built a high level of wheel–rail expertise and understanding regarding RCF initiation and development, level and position of wheel–rail contact forces, and new interface materials and has gained experience in both laboratory and field test operating conditions. Within the project a validated theoretical train–track interaction model and a fatigue design model for two-material rails have been developed.This paper focuses on the field test results of the two-material rail, and how the predictions and expectations from the selection process match with the results observed in track. Results are very promising. The two-material rail prototypes, now over 1 year in track, show no RCF damage where the non-treated rail shows clear RCF damage. The development of the application process and other objectives of the InfraStar project are discussed.

  • 104.
    Holgerson, Mikael
    Luleå tekniska universitet.
    Apparatus for measurement of engagement characteristics of a wet clutch1997In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 213, no 1-2, p. 140-147Article in journal (Refereed)
    Abstract [en]

    The problem of obtaining smooth gear changing whilst maintaining long life of wet clutches in automatic transmissions demands more knowledge about their behaviour. Experimental and theoretical studies on the engagement of a wet clutch have been carried out. A wet clutch test rig which can apply a drive torque during engagement was developed. The apparatus could also vary the sliding velocity, inertia, force rate, and lubrication. Measured output data included normal force, brake torque, sliding velocity and temperature over time. The input parameters and output characteristics obtained were similar to those in automatic transmissions used in cars. The friction characteristics as well as power and temperature were investigated. A simple model was developed to estimate the engagement performance which gave a good approximation of the performance measured in the tests. The friction is high in the beginning and end of the engagement cycle and lower inbetween. There is a torque peak just before the clutch stops owing to friction characteristics. The maximum developed power occurs at about half of the engagement time, while the maximum temperature is just before clutch stop

  • 105.
    Holmberg, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Andersson, Michael
    Hoganas AB, Bruksgatan 35, SE-26383 Hoganas, Sweden.
    Kassman Rudolphi, Åsa
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Rolling fatigue life of PM steel with different porosity and surface finish2019In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 426-427, no Part A, p. 454-461Article in journal (Refereed)
    Abstract [en]

    Gears made of PM steel are of interest for the automotive industry because they can be produced to near net shape with only a few processing steps. Automotive gears experience a complex contact situation with rolling as well as combined rolling and sliding. They also have to be able to withstand high loads and fairly high temperature variations. Earlier work show that the main limiting parameter of the contact fatigue life of PM steel is the porosity. A higher porosity/lower density will decrease the fatigue life of the PM component. In the present study, the pure rolling contact fatigue life of PM steel with different density and surface finish has been investigated. A rolling contact fatigue test rig, where rods of the tested material are mounted between two rolling wheels, was used. Two densities of PM steel, 6.8 and 7.15 g/cm(3) and a full density reference steel with two different surface finishes, centerless grinded and superfinished, were tested. The tests were run for a given number of load cycles or until failure (fatigue life). SEM was used to study the surfaces and cross-sections to reveal the mechanisms of crack initiation and propagation. The higher density PM steel (7.15 g/cm(3)) outperformed the lower density steel (6.18 g/cm(3)) by a factor of around 4 in fatigue life at the same surface pressure, regardless of surface finish. Cracks are initiated at a depth of around 100 mu m. These cracks propagate and eventually they reach the surface, causing surface damage and failure. For the low density PM steel, both sub surface crack initiation and failure occurred earlier (at a lower number of load cycles) than for the higher density PM steel. Severe surface damage or wear were not found until failure occurred. Still, some initial alteration of the surfaces was seen already after 0.5 million load cycles, in the form of removal of the highest asperity peaks on the centerless grinded surfaces, and opening of the surface pores on the superfinished surface. No effect of surface finish was found on the fatigue life. The difference in surface roughness could induce a difference in local stress concentrations at the surface, but in this test the cracks causing fatigue failure are initiated at a depth where the stress distribution is not affected by local surface stress concentrations. This means that for fairly smooth surfaces roughness, the surface of PM steel is not important when it comes to pure rolling fatigue life.

  • 106.
    Holmberg, Kenneth
    et al.
    VTT, Finland.
    Ronkainen, Helena
    Laukkanen, Anssi
    Wallin, Kim
    Hogmark, Sture
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Jacobson, Staffan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Wiklund, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Souza, M.
    Stahle, Per
    Residual stresses in TiN, DLC and MoS2 coated surfaces with regard to their tribological fracture behaviour2009In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 267, no 12, p. 2142-2156Article in journal (Refereed)
    Abstract [en]

    Thin hard coatings on components and tools are used increasingly due to the rapid development in deposition techniques, tribological performance and application skills. The residual stresses in a coated surface are crucial for its tribological performance. Compressive residual stresses in PVD deposited TiN and DLC coatings were measured to be in the range of 0.03-4 GPa on steel substrate and 0.1-1.3 GPa on silicon. MoS2 coatings had tensional stresses in the range of 0.8-1.3 on steel and 0.16 GPa compressive stresses on silicon. The fracture pattern of coatings deposited on steel substrate were analysed both in bend testing and scratch testing. A micro-scale finite element method (FEM) modelling and stress simulation of a 2 m TiN-coated steel surface was carried out and showed a reduction of the generated tensile buckling stresses in front of the sliding tip when compressive residual stresses of 1 GPa were included in the model. However, this reduction is not similarly observed in the scratch groove behind the tip, possibly due to sliding contact-induced stress relaxation. Scratch and bending tests allowed calculation of the fracture toughness of the three coated surfaces, based on both empirical crack pattern observations and FEM stress calculation, which resulted in highest values for TiN coating followed by MoS2 and DLC coatings, being KC = 4-11, about 2, and 1-2 MPa m1/2, respectively. Higher compressive residual stresses in the coating and higher elastic modulus of the coating correlated to increased fracture toughness of the coated surface.

  • 107.
    Hoseini, Mohammed
    Hållfasthet (BMh).
    Tribological Investigation of Coatings for Artificial Joints2008In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 264, no 11-12, p. 958–966-Article in journal (Refereed)
  • 108.
    Hoseini, Mohammed
    et al.
    SP Swedish National Testing and Research Institute, Transport and Vehicle Technology, Building Technology and Mechanics, Borås.
    Jedenmalm, Anneli
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Mechanical Metallurgy.
    Boldizar, Antal
    Department of Materials and Manufacturing Technology, Chalmers University of Technology, Göteborg.
    Tribological investigation of coatings for artificial joints2008In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 264, no 11-12, p. 958-966Article in journal (Refereed)
    Abstract [en]

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

  • 109.
    Hossein Nia, Saeed
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles.
    Stichel, Sebastian
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles.
    Casanueva, Carlos
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles.
    Prediction of RCF and Wear Evolution of Iron-Ore Locomotive wheels2015In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 338-339, p. 62-72Article in journal (Refereed)
    Abstract [en]

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

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

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

  • 111.
    Höglund, Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    EHL and the use of image analysis1994In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 179, no 1-2, p. 49-56Article in journal (Refereed)
    Abstract [en]

    This paper describes three cases where image analysis has been used to evaluate transient phenomena in elastohydrodynamic lubrication (EHL). In the first case, a CCD camera and image analysis are used to evaluate the ball trajectory after impact in the "jumping ball apparatus" for subsequent calculation of the limiting shear stress-pressure coefficient. The error of the method is < 1%. In the second case, the motion of the rollers in a roller bearing is traced with a video camera and image analysis. The rolling and sliding motion in the loaded and unloaded parts of the bearing was clearly visible. Although the shaft speed was only 23.6 rpm, the method can easily be used up to 1500 rpm using a conventional high speed video and up to 27 000 rpm with a 6000 pictures per second video camera. In the third case, the method was applied to interferograms of an EHL point contact to investigate lubricant film thickness. The method uses hue, saturation and intensity values from digitized colour interferometric images together with calibration vales. It can be used to evaluate transient as well as quasistatic phenomena in the contact. The method makes it possible to determine absolute values of film thickness without prior knowledge about the fringe order in the interferogram. The method has been shown to work well in the range 140-700 nm with white light but preliminary tests for considerably thicker films are very promising

  • 112.
    Höglund, Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Influence of lubricant properties on elastohydrodynamic lubrication1999In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 232, no 2, p. 176-184Article in journal (Refereed)
    Abstract [en]

    In hard EHL, encountered in, e.g., gears, rolling element bearings etc. the properties of the lubricant play a significant role in the forming of a lubricating film and reducing friction between the contacting surfaces. The influence of pressure and temperature on viscosity, limiting shear stress and density, has to be taken into account when creating lubricant models to be used in numerical calculations of film thickness and friction. This paper describes some experimental methods to determine these properties of a number of different lubricating oils, both from mineral, vegetable and synthetic origin. The results show that, apart from 5P4E, naphthenic mineral oil has the highest values of pressure-viscosity as well as limiting shear stress-pressure coefficients. It also exhibits the highest density increase with pressure. Rapeseed oil has a rather high pressure-viscosity coefficient but a low limiting shear stress-pressure coefficient as well as a low density increase with pressure. Thus, rapeseed oil is a strong alternative to naphthenic (and also paraffinic) oil since it has the ability to form a relatively thick oil film and at the same time give a low coefficient of friction. Ester, polyglycol and polyalphaolefin oils also exhibit low values of friction but are not equally good as rapeseed oil to form a lubricant film as a result of their lower pressure-viscosity coefficients

  • 113.
    Höglund, Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Influence of polyalkylmethacrylate and sulphurized ester on oil film thickness in an elastohydrodynamic point contact1987In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 115, no 1-2, p. 223-234Article in journal (Refereed)
    Abstract [en]

    The aim of this investigation is to determine how additives in a base oil affect the central oil film thickness in an elastohydrodynamic rolling point contact. The experiments have been carried out using a sapphire disc and a steel ball and the film thickness has been measured by means of optical interferometry. A detailed description of the apparatus is given.Two different additives have been used, polyalkylmethacrylate (PMA) and sulphurized ester (SE). Each of them have been mixed in a superrefined naphthenic base oil at five different concentrations.The results show that the central oil film thickness increases with increasing concentration of additive. This is because the additives increase the oil viscosity. If this effect is compensated for, 0.1 wt.% PMA or 0.63-2.5 wt.% SE give the best relative oil film build-up. There is consequently no reason to use more additive in the base oil unless one wants to have a thicker oil film because of the viscosity-increasing effect

  • 114.
    Höglund, Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Relationship between lubricant shear strength and chemical composition of the base oil1989In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 130, no 1, p. 213-224Article in journal (Refereed)
    Abstract [en]

    A new method for the experimental evaluation of the shear strength of lubricants at high pressures and temperatures is presented. The main parts of the experimental apparatus are a lubricated sintered-carbide surface and an impacting steel ball. A picture-processing system is used to examine the ball trajectory after impact and to calculate the limiting shear strengthpressure coefficient of the lubricant. Using this apparatus the influence of the chemical composition of the base oil on the limiting shear strengthpressure coefficient has been investigated. It was found that the chemical structure of the oil is of major importance in determining the shear strength. Additives have no significant effect on the shear strength.

  • 115.
    Höglund, Erik
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Jonsson, Ulf
    Luleå tekniska universitet.
    Uusitalo, Östen
    Luleå tekniska universitet.
    Effect of pressurised gases on the viscosity of polyalkylene glycols1997In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 207, no 1-2, p. 24-28Article in journal (Refereed)
    Abstract [en]

    Experiments have been conducted into the effect of pressurised hydrocarbons on the viscosity of a polyalkylene glycol. This lubricant is intended to be used in a sub-sea compressor/pump unit and the risk of diluting the lubricant by the surrounding natural gas, thus reducing the lubricant's viscosity, was to be investigated. Dilution can cause insufficient lubrication of the compressor's moving parts. A pressurised Höppler type viscometer was used for the tests which were conducted at 50 °C with a methane based hydrocarbon mixture and with pure nitrogen. The viscosity of the lubricant was reduced to 24% after 24 h exposure at 100 bar with the hydrocarbon mixture. A gas analysis was performed which indicates that the heavier hydrocarbons used are relatively soluble in the lubricant even at relatively low pressures. Nitrogen was found to have a very limited effect on the viscosity even if some was dissolved in the oil. A long duration test of 11 days was also made with nitrogen. This test did not show any significant reduction of the viscosity.

  • 116. Innings, Fredrik
    et al.
    Hultman, Erik
    Forsberg, Fredrik
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Understanding and analysis of wear in homogenizers for processing liquid food2011In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 271, no 9-10, p. 2588-2598Article in journal (Refereed)
    Abstract [en]

    The tribological research pertaining to homogenizers in processing liquid food has received much less attention compared to its potential in enhancing the efficiency and durability of the homogenization process equipment. Homogenization is a process used to disrupt fat globules in dairy products to reduce the formation of creamy layer (separation) and also to enhance the viscosity of certain products. This process takes place in a narrow gap in the homogenizer machine and this region is highly prone to wear. The occurrence of wear during processing not only impairs the homogenization effect but also leads to increased downtime of the machine. The aim of this work is to understand the occurrence of wear and wear mechanisms in the homogenization gap using both experimental and analytical approaches. Two experimental test rigs were used to study the differences in wear during operation, i.e. with and without particles. The trajectories of the particles have been simulated without the influence of cavitation using a CFD-code to investigate whether the particles are the cause of wear. The homogenizer gap has been simulated for a worn geometry to see how the occurrence of wear changes the particles trajectories. The results have shown that the presence of particles accelerates wear and most important parameters are the particle hardness and mass. When cavitation and particles are combined they create a synergistic effect on wear. This can be explained by the fact that cavitation can accelerate particles in random directions through the imploding action of cavities. A change in impact angle and increased velocity increases the amount of wear significantly. CFD-simulations and calculations show that the particles do not fully follow the streamlines and therefore create wear on the gap surfaces.

  • 117.
    Isaksson, Ove
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Rheology for water-based hydraulic fluids1987In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 115, no 1-2, p. 3-17Article in journal (Refereed)
    Abstract [en]

    High water-based hydraulic fluids with slightly higher viscosities than water, for instance 95-5 emulsions and micro-emulsions, do not show any significant deviation from a Newtonian fluid. Adding polymeric viscosity improvers for the purpose of increasing the viscosity will be successful as long as the shear rate is low. However, as the shear rate is increased, higher than about 10**3 s** minus **1, the viscosity will decrease and the advantage of the improver will vanish. The shear rate available was too low to break down the viscosity improvers. This is shown by the fact that the shear stress curve is reversible. Non-Newtonian fluids approach a more Newtonian behavior when the temperature is increased. The viscosity increase with pressure is much lower for water-based fluids than for a mineral oil. The pressure coefficient is about 10 times higher for mineral oils. The pressure coefficient increases if the water content of a water-based fluid is reduced.

  • 118. Iwai, Y.
    et al.
    Miyajima, T.
    Mizuno, A.
    Honda, T.
    Itou, T.
    Hogmark, Sture
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Micro-Slurry-jet Erosion (MSE) testing of CVD TiC/TiN and TiC coatings2009In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 267, no 1-4, p. 264-269Article in journal (Refereed)
    Abstract [en]

    Several different experimental techniques are normally used to evaluate tribological properties of thin hard coatings. However, most of the tests cannot assess properties of coating, substrate and interface independently. In this study, the potential of a Micro-Slurry-jet Erosion (MSE) test to swiftly evaluate the intrinsic wear properties of thin single layered and multilayered coatings is demonstrated. A slurry containing 1.2 mu m alumina particles was impacted at high velocity perpendicular to CVD TiC/TiN (TiN on top of TiC) and Tic coatings deposited on cemented carbide. In addition, nano-indentation and XRD, GDOES, AFM analyses were done for the original and worn surfaces. For the TiC/TiN coating, the wear depth of the TiN layer increased linearly until the Tic layer was reached. There after the wear occurred at a lower rate but tended to increase towards the TiC/substrate interlayer. The single layered Tic coating showed the same wear behaviour as the TiC layer of the TiC/TiN coating. The wear rate was constant within the individual TiN and Tic layers, but changed near the interfaces. The micro-topographies of the worn surfaces observed by AFM correlated to the difference in the wear rate of the individual layers and the change in wear rate at the interface to the substrate. The Tic layer proved to have about two times higher wear resistance than the TiN layer. Consequently, the MSE test can distinguish between small differences in the properties of the coatings and of the interlayer zones, and can be used as a screening test when evaluating multilayered as well as single layered coatings.

  • 119.
    Jacobson, Staffan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Hogmark, Sture
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Surface modifications in tribological contacts2009In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 266, no 3-4, p. 370-378Article in journal (Refereed)
    Abstract [en]

    A characteristic of almost any type of dry or boundary lubricated tribological contact is that the composition and tribological properties of the original interface will change during use. The modifications include topography changes (smoothening or roughing), formation of micro-cracks, phase transformations, deformation hardening, formation of oxides, formation of solid films by reactions with lubricant additives, transfer of material from the counter surface, and so on. The thickness of these layers and films range from atomic monolayers (e.g., hydrogen termination of diamond surfaces) to tens of mu m (e.g., plastic deformation of metals). Since the tribological properties of tools, wear parts and mechanical components then are determined by these modified surfaces rather than by the original, they deserve attention and careful assessment. Without the knowledge about how these surface layers are formed and how they modify the tribosystem, it is not possible to predict the friction and wear properties of a material in a given tribological situation. Thus, post-test evaluation including microscopy and analysis of both surfaces and cross-sections is required. A number of surface modifications selected from a wide variety of tribosystems is briefly presented. The corresponding surface modifications range from the most well known and simple to the more complex and relatively unexplored. Finally, the potential of designing materials and lubricants for improved surface modification is discussed and examples are given of current research projects on promoting formation of protecting low-friction tribofilms in boundary-lubricated systems.

  • 120.
    Jelagin, Denis
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Larsson, Per-Lennart
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Hertzian Fracture at Finite Friction: A Parametric Study2008In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 265, no 5-6, p. 840-848Article in journal (Refereed)
    Abstract [en]

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

  • 121.
    Johannesson, Hans L.
    et al.
    Chalmers University of Technology.
    Kassfeldt, Elisabet
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Calculation of the pressure distribution in an arbitrary elastomeric seal contact1989In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 130, no 1, p. 3-15Article in journal (Refereed)
    Abstract [en]

    When using the inverse hydrodynamic theory to calculate leakage flow and frictional force in an elastomeric seal contact, the pressure distribution is a necessary input. Up till now, assumed or measured pressure distributions usually have been used. One of the authors has earlier presented a semiempirical method for calculating the pressure distribution in an O-ring seal contact. The new calculation method, presented in this paper, is a generalization and an improvement of this earlier work. The method presented is mainly analytical and is based on calculations of the boundary strains in the contact zone and a model of the material behavior, which is based on the pressure dependence of the material compressibility. A computer program has been developed and two test examples are treated. A comparison with experiments is made.

  • 122.
    Johansson, S.
    et al.
    Volvo Technology AB, Chalmers Science Park, Gothenburg.
    Frennfelt, C.
    Volvo Technology AB, Chalmers Science Park, Gothenburg.
    Killinger, A.
    Universität Stuttgart, Institut für Fertigungstechnologie keramischer Bauteile (IFKB), Stuttgart.
    Nilsson, P.H.
    Volvo Technology AB, Chalmers Science Park, Gothenburg.
    Ohlsson, R.
    Volvo Powertrain AB, Gothenburg.
    Rosén, Bengt - Göran
    Halmstad University, School of Business and Engineering (SET), Mechanical Engineering and Industrial Design (MTEK), Functional Surfaces.
    Frictional evaluation of thermally sprayed coatings applied on the cylinder liner of a heavy duty diesel engine: pilot tribometer analysis and full scale engine test2011In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 273, no 1, p. 82-92Article in journal (Refereed)
    Abstract [en]

    The piston system accounts for roughly half of the mechanical friction of an internal combustion engine, thus it is important to optimize. Different thermally sprayed cylinder liners were investigated in order to optimize the frictional impact of the contact between cylinder liner and piston ring/piston. A novel tribometer test setup was used to scan through different materials at different running conditions. Based on these results a full-scale single cylinder test was performed to validate the results from the rig. A comparison of the results between the tribometer and the engine shows the importance of the ratio between viscous and mechanical friction losses.

  • 123.
    Johansson, Staffan
    et al.
    Volvo Technology AB.
    Nilsson, Per
    Volvo Technology AB.
    Ohlsson, Robert
    Volvo Powertrain AB.
    Rosén, Bengt-Göran
    Halmstad University, School of Business and Engineering (SET), Mechanical Engineering and Industrial Design (MTEK), Functional Surfaces.
    Experimental friction evaluation of cylinder liner/piston ring contact2011In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 271, no 3-4, p. 625-633Article in journal (Refereed)
    Abstract [en]

    Fuel consumption is an extremely important parameter for the automotive industry today. Anticipated emission legislative demands in combination with a rising oil price are true motivators. In engines the piston system is the largest source of frictional losses, accounting for about 50% of the total frictional losses, thus it is important to optimize. Apart from frictional losses the piston system is a large consumer of lubricating oil, a considerable contributor to the total amount of particulate emissions (PM). New materials, coatings and high-tech machining processes that previously were considered to be too expensive and therefore only used in complex applications are today becoming more affordable. It is important to develop reliable test methods to study these new concepts. The reciprocating tribometer at Volvo Technology has been updated to better evaluate the frictional difference between material combinations/surfaces; it is possible to evaluate a number of operational parameters in each experiment. The components that were studied were a piston ring running against a cylinder liner. Friction, wear and change in surface morphology were studied in the experiments. It is shown that for the introduced DoE based tribometer test the interaction of dynamic viscosity, velocity and contact pressure can be studied within one experiment. The results show differences in friction which could be explained as the surface creating beneficial contact conditions for oil film build-up. It is also apparent that surface roughness is important regardless of material properties. To better understand the correlations between friction and surface roughness a future study should include a study of similar materials with different roughness values.

  • 124.
    Jonsson, Ulf J.
    Luleå tekniska universitet.
    Lubrication of rolling element bearings with HFC-polyolester mixtures1999In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 232, no 2, p. 185-191Article in journal (Refereed)
    Abstract [en]

    Manufacturers of refrigeration and air-conditioning compressors have had to re-evaluate their knowledge of compressor bearing lubrication following the introduction of hydrofluorocarbon (HFC) refrigerants and polyolester lubricants. The lack of anti wear protection in comparison to traditionally used refrigerants/lubricants makes the lubrication of bearings using these modern systems a much more difficult task than before. This paper presents results from ongoing research activities to develop methods and generate data that can be used to support engineers and chemists designing compressors and lubricants. Viscosity and pressure-viscosity data for three ISO VG 32 polyolester lubricants and also a film forming comparison between two ISO VG 68 polyolester lubricants are presented. This data shows that a high degree of branching has a negative effect on the performance of the lubricant in certain applications. Whilst a branched lubricant offers the benefit of a higher-pressure-viscosity coefficient under normal conditions, the reduction in viscosity and pressure-viscosity coefficient when diluted by refrigerant is far greater than for normal/linear lubricants. This characteristic results in a poorer film forming ability in applications where the lubricant is subjected to refrigerant gas with a low superheat

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

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

  • 126.
    Karlsson, Patrik
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Gåård, Anders
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Krakhmalev, Pavel
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Influence of tool steel microstructure on friction and initial material transfer2014In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 319, no 1-2, p. 12-18Article in journal (Refereed)
    Abstract [en]

    An investigation was conducted to study the influence of tool steel microstructure on initial material transfer and friction. Two different powder metallurgy tool steels and an ingot cast tool material were tested in dry sliding against 1.4301, 1.4162, Domex 355 MC and Domex 700 MC sheet materials. It was found that tool steel hard phase heights influence initial material transfer and friction. The coefficient of friction increased with decreasing tool steel hard phase heights at 50 N normal load and initial material transfer occurred around protruding hard phases. At higher load of 500 N the sheet material adhered to both the tool steel matrix and hard phases. Coefficient of friction decreased with increasing proof strength of the sheet material at 500 N normal load.

  • 127.
    Karlsson, Patrik
    et al.
    Department of Mechanical and Materials Engineering, Karlstad University, Karlstad, Sweden.
    Gåård, Anders
    Department of Mechanical and Materials Engineering, Karlstad University, Karlstad, Sweden.
    Krakhmalev, Pavel
    Department of Mechanical and Materials Engineering, Karlstad University, Karlstad, Sweden.
    Influence of tool steel microstructure on friction and initial material transfer2014In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 319, no 1-2, p. 12-18Article in journal (Refereed)
    Abstract [en]

    An investigation was conducted to study the influence of tool steel microstructure on initial material transfer and friction. Two different powder metallurgy tool steels and an ingot cast tool material were tested in dry sliding against 1.4301, 1.4162, Domex 355 MC and Domex 700 MC sheet materials. It was found that tool steel hard phase heights influence initial material transfer and friction. The coefficient of friction increased with decreasing tool steel hard phase heights at 50 N normal load and initial material transfer occurred around protruding hard phases. At higher load of 500 N the sheet material adhered to both the tool steel matrix and hard phases. Coefficient of friction decreased with increasing proof strength of the sheet material at 500 N normal load.

  • 128.
    Karlsson, Patrik
    et al.
    Department of Mechanical and Materials Engineering, Karlstad University, Karlstad, Sweden.
    Gåård, Anders
    Department of Mechanical and Materials Engineering, Karlstad University, Karlstad, Sweden.
    Krakhmalev, Pavel
    Department of Mechanical and Materials Engineering, Karlstad University, Karlstad, Sweden.
    Bergström, Jens
    Department of Mechanical and Materials Engineering, Karlstad University, Karlstad, Sweden.
    Galling resistance and wear mechanisms for cold-work tool steels in lubricated sliding against high strength stainless steel sheets2012In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 286-287, p. 92-97Article in journal (Refereed)
    Abstract [en]

    Tool damage in sheet metal forming of stainless steel is of high concern for the forming industry. In the present work, ingot cast AISI D2 and advanced powder metallurgy tool steel (PM) cold-work tool steels were evaluated and ranked regarding wear mechanisms and galling resistance. Wear tests were performed using a slider-on-flat-surface (SOFS) tribometer in sliding against austenitic–ferritic (duplex) stainless steel sheets at different contact pressures in lubricated conditions. The best galling resistance was observed for the nitrogen alloyed PM tool steels. Abrasive scratching of the tool surfaces and transfer of sheet material due to adhesive wear were the main metal forming tool surface damage mechanisms. By increasing the hardness of one PM sheet metal forming tool grade, the galling resistance was enhanced.

  • 129.
    Karlsson, Patrik
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Gåård, Anders
    Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Krakhmalev, Pavel
    Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Bergström, Jens
    Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Galling resistance and wear mechanisms for cold-work tool steels in lubricated sliding against high strength stainless steel sheets2012In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 286-287, p. 92-97Article in journal (Refereed)
    Abstract [en]

    Tool damage in sheet metal forming of stainless steel is of high concern for the forming industry. In the present work, ingot cast AISI D2 and advanced powder metallurgy tool steel (PM) cold-work tool steels were evaluated and ranked regarding wear mechanisms and galling resistance. Wear tests were performed using a slider-on-flat-surface (SOFS) tribometer in sliding against austenitic–ferritic (duplex) stainless steel sheets at different contact pressures in lubricated conditions. The best galling resistance was observed for the nitrogen alloyed PM tool steels. Abrasive scratching of the tool surfaces and transfer of sheet material due to adhesive wear were the main metal forming tool surface damage mechanisms. By increasing the hardness of one PM sheet metal forming tool grade, the galling resistance was enhanced.

  • 130.
    Kassfeldt, Elisabet
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Dave, Göran
    Göteborgs universitet.
    Environmentally adapted hydraulic oils1997In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 207, no 1-2, p. 41-45Article in journal (Refereed)
    Abstract [en]

    A comparison has been carried out between one mineral based hydraulic oil and three environmentally adapted hydraulic oils. Two of these are semi-synthetic oils, i.e. mixtures of vegetable base oil and synthetic esters, and the last is based on synthetic esters only. Technical properties such as viscosity, pour point etc., and chemical properties such as phosphorus and sulphur content etc. were documented using standard test methods. The lubricant capability properties were determined through measurements of the capability of each oil to build a film in an elastohydrodynamic contact. The oil film thickness is important to avoid wear and failure and to guarantee separation of surfaces. The results show that at 40°C the environmentally adapted oils give a thicker film than the mineral oil. At 80°C there is no significant difference between the different types of oil in their capability to build a lubricating film. The maximum shear strength was measured and these results are presented with the constant of proportionality γ, from the theoretical model τ approximately equals γp, which is valid at very high pressures. The measurements were carried out at contact pressures in the range 5-7 GPa. The results show that all environmentally adapted oils give a lower γ value than the mineral oil, which is an advantage since a low shear strength results in lower friction in highly loaded contacts. Measurements of toxicity to aquatic organisms (Daphnia magna) show very large differences between the tested oils, and this implies that a change from a mineral oil to an environmentally adapted oil can give important environmental advantages.

  • 131.
    Kassfeldt, Elisabet
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Din, Massimo Del
    ABB Stal AB, Finspång.
    Wear characteristics with mixed lubrication conditions in a full scale journal bearing1999In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 232, no 2, p. 192-198Article in journal (Refereed)
    Abstract [en]

    Increased awareness of environmental problems has stressed the importance of switching from traditional lubricants to more environmentally friendly alternatives. Different investigations with standard test methods indicate that such a switch is possible without loss of lubricating power. The question arises if the statement above is true for industrial lubricating conditions, without laboratory cleanliness. This paper presents a study of friction and wear in a two grooved journal bearing at different shaft speeds, oil temperatures and contamination levels. A number of tests have been conducted combined with a theoretical analysis of film thickness and lubricating regime. The aim was to investigate whether an environmentally adapted rape seed-synthetic ester oil could replace a traditional mineral oil in a full scale application. The results show that the rape seed-synthetic ester oil gives significantly lower values of wear regardless of the operating conditions and there is also a tendency of lower values of frictional torque compared with the mineral oil. Mainly operating in the mixed lubrication regime, no signs of impending bearing failure have been registered, even though a large amount of silica particles added to the oil gave higher wear values than with uncontaminated oil.

  • 132.
    Kassfeldt, Elisabet
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Lundmark, Jonas
    Tribological properties of hardened high strength Boron steel at combined rolling and sliding condition2009In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 267, no 12, p. 2287-2293Article in journal (Refereed)
    Abstract [en]

    The use of hardened high strength steel is found in applications where high wear resistance is required. The wear properties of high strength Boron steel are well known in applications with abrasive wear from stones, ore and other hard material. A unique concept of wear protection of rails is newly presented, a wear resistant cap made of hardened high strength Boron steel.Reducing the wear of rails and wheels and controlling the frictional behavior in the wheel/rail contact are two key issues for railway owners in order to reduce the increasing costs related to higher axle loads, higher speeds, more frequent traffic, etc. Therefore, the aim of this work has been to investigate and compare the tribological properties of Boron steel and UIC 1100 rail steel in contact with Blue Light wheel steel (AAR Class C (69-JDG-8)) under dry and water lubricated conditions in a two-disc tribometer. Advanced analytical instruments including 3D optical surface profiler, micro-hardness indenter, light microscope and SEM/EDS were used to analyze the results.Results from the experiments show that the friction coefficient in tests with Boron steel is more stable both in dry and water lubricated conditions than tests including UIC 1100 rail steel used in todays application. Surface damages seen from water lubricated tests on UIC 1100 rail steel are not seen on the surface of the Boron steel discs. In all tests, the wear decreased when water was added in the contact and friction was slightly decreased.

  • 133.
    Kassman Rudolphi, Åsa
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Jacobson, Staffan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Gross plastic fretting - examination of the gross weld regime.1996In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 201, no 1-2, p. 255-264Article in journal (Refereed)
  • 134.
    Kassman Rudolphi, Åsa
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Jacobson, Staffan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Gross plastic fretting - mechanical deterioration of silver coated electrical contacts.1996In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 201, no 1-2, p. 244-254Article in journal (Refereed)
  • 135.
    Kassman, Åsa
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Jacobson, Staffan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Surface damage, adhesion and contact resistance of siler coated plated copper contacts subjected to fretting motion1993In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 165, no 2, p. 227-230Article in journal (Refereed)
  • 136.
    Khader, Iyas
    et al.
    Department of Industrial Engineering, German-Jordanian University.
    Renz, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Kailer, Andreas
    Fraunhofer Institute for Mechanics of Materials IWM.
    A wear model for silicon nitride in dry sliding contact against a nickel-base alloy2017In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 376-377, no Part A, p. 352-362Article in journal (Refereed)
    Abstract [en]

    The properties of silicon nitride ceramics allow their broad application in extreme tribological conditions. High-temperature sliding contact of Si3N4-base materials against metals will be found more often in future applications, in which the ceramic's wear resistance becomes clearly necessary.

    In this study, the dry sliding behavior of silicon nitride against Inconel 718 is investigated. Wear experiments were carried out at sliding velocities ranging from 1 to 20 m/s. A finite element wear simulation was constructed by relying on experimentally measured wear rates and COF. The simulations enabled quantifying localized temperature and contact stress fields as a function of geometrical changes due to progressive wear.

    The experiments showed a transition in wear mechanisms depending on the sliding velocity and frictional power. Cross-sectional analysis of the ceramic samples provided information on the tribochemical processes and the dominant wear mechanisms. Combining analytical and numerical results enabled proposing a schematic wear model. The agreement of this model with common theories of wear is discussed.

  • 137.
    Khan, Saad Ahmed
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Persson, Ingemar
    AB DEsolver, Östersund.
    Lundberg, Jan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Stenström, Christer
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Prediction of top-of-rail friction control effects on rail RCF suppressed by wear2017In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 380-381, p. 106-114Article in journal (Refereed)
    Abstract [en]

    Rolling contact fatigue (RCF) and wear, two major deterioration processes, limit the lifetime of rails. These deterioration processes are even more severe on the curves of tracks used by heavy haul trains. Because wear is a material removing process, it can suppress the formation of RCF (also known as surface initiated cracks). In railways, cracks have a higher risk of instigating a catastrophic failure than wear; hence, it is comparatively better to have wear than to have cracks. By controlling the top-of-rail friction, both of these deteriorating processes can be reduced to enhance the lifetime of rails. In order to achieve these possible advantages, the infrastructure manager of the Swedish railway is planning to implement a top-of-rail friction control technology on the iron ore line in northern Sweden wherein RCF is a major problem on the curves. The present study uses a damage index model in a multi-body simulation software and predicts the probability of RCF formation with suppressing effect of wear for different friction control values. The effect of friction control is simulated on curve radii ranging from 200 to 3,000 m and axle loads ranging from 30 to 40 t at a constant train speed of 60 km/h. Findings show that on a very sharp circular curve, radius < 300 m, RCF can be eliminated without friction control due to the high wear rate. On moderate curves, 300 < radius < 1,000 m, a friction coefficient (µ) of, at most, 0.3 with a Kalker's coefficient of, at most, 30% is required to avoid RCF

  • 138.
    Krakhmalev, Pavel
    et al.
    Karlstad University, Faculty of Technology and Science, Materials Science. Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Bergström, Jens
    Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering. Karlstad University, Faculty of Technology and Science, Materials Science.
    Tribological behavior and wear mechanisms of MoSi2-base composites sliding against AA6063 alloy at elevated temperature2006In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 260, no 4-5, p. 450-457Article in journal (Refereed)
  • 139.
    Krakhmalev, Pavel
    et al.
    Karlstad University, Faculty of Technology and Science, Materials Science. Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Rodil, Adeva
    Bergström, Jens
    Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering. Karlstad University, Faculty of Technology and Science, Materials Science.
    Influence of microstructure on the abrasive edge wear of WC–Co hardmetals2007In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 263, no 1-6, p. 240-245Article in journal (Refereed)
  • 140.
    Kumar, Rajesh
    et al.
    Indian Institute of Technology, New Delhi.
    Kumar, Salil
    Eicher Tractor Engineering Centre, Ballabgarh.
    Prakash, Braham
    Sethuramiah, A.
    Indian Institute of Technology, New Delhi.
    Assessment of engine liner wear from bearing area curves2000In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 239, no 2, p. 282-286Article in journal (Refereed)
    Abstract [en]

    This paper proposes a new procedure to evaluate engine liner wear volume and wear depth particularly for short duration engine tests. The method is based on the fact that honing depth is not removed when small amount of wear occurs. It was considered that 90% point of the bearing area curve is the same before and after wear. Then, the bearing area curve for the used liner was transformed by the depth differences at 90% and the area between the two curves was calculated by numerical procedure. As the diameter of the liner is known, the wear volume was calculated for the various zones selected at different points from TDC and BDC. The methodology involved has been programmed in C++. The wear depth is obtained by the projection on the depth axis of the two bearing area curves, and then finding their difference. This method is considered superior to the usual method of gauging the changes in diameter as such determinations are influenced by the distortions that occur in the liner. The new procedure needs to be applied more extensively to improve confidence in repeatability and reproducibility and to determine the limits of applicability. Controlled laboratory wear tests and further measurements on cylinders from field engines are therefore proposed.

  • 141.
    Kumar, Rajesh
    et al.
    Indian Institute of Technology, New Delhi.
    Prakash, Braham
    Sethuramiah, A.
    Indian Institute of Technology, New Delhi.
    A systematic methodology to characterise the running-in and steady-state wear processes2002In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 252, no 5-6, p. 445-453Article in journal (Refereed)
    Abstract [en]

    An improved methodology has been developed to characterise running-in and steady-state wear processes. The experimental study was conducted with En 31 steel specimens on reciprocating tester with ball-on-flat geometry under lubricated sliding conditions. The tests were conducted according to a factorial design. The variables selected were the load, temperature and surface roughness. The wear behaviour for a given set of operating conditions has been characterised on the basis of developed methodology. The parametric influence of operating conditions was then analysed on the basis of polynomial relationships. The steady-state wear was found to be significantly influenced by the initial roughness.

  • 142.
    Larsson, Elin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Andersson, Anna M.
    ABB Corporate Research, Västerås, Sweden.
    Kassman Rudolphi, Åsa
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Grease lubricated fretting of silver coated copper electrical contacts2017In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 376, p. 634-642Article in journal (Refereed)
    Abstract [en]

    Fretting of silver coated electrical contacts has been studied in a crossed cylinder contact model setup at varying displacement amplitude. The contacts have been tested dry (unlubricated) and lubricated with lithium complex (LiX) and polypropylene (PP) thickened greases. The same polyalphaolefin (PAO) base oil blend was used, hence the thickener is the only difference between the greases. At low displacement amplitude no large difference between dry and lubricated conditions was found. Contact welding occurs for all contacts, also the lubricated. The grease is ejected from the contact area after only a few fretting cycles and the contact welds. A positive effect of grease lubrication on friction and wear is primarily seen at high vibration amplitude, where gross slip is the prevailing fretting regime. For the LiX grease lubricated contacts, fretting at intermediate displacement amplitudes show to be the most critical and the wear marks show much surface damage. Here, the PP grease showed better lubricating effect than the LiX grease.

  • 143.
    Larsson, Elin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Olander, Petra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Jacobson, Staffan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Boric acid as a lubricating fuel additive - Simplified lab experiments to understand fuel consumption reduction in field test2017In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 376, p. 822-830Article in journal (Refereed)
    Abstract [en]

    In field tests, a boric acid based fuel additive has led to reduced fuel consumption. The reduction was substantial, an average of 6 and 10% in passenger cars and diesel generators respectively. Aiming towards improved understanding of mechanisms behind the fuel saving, three methods to mimic the effect of the additive in the piston-ring/cylinder contact have been evaluated. A reciprocating cylinder/flat configuration with ball bearing steel against grey cast iron was used, and it was lubricated with base oil. The different methods were as following: A) repeated spraying of a small amount of the boric acid solution onto the surfaces, B) predeposition of a boric acid layer on the flat surface and C) a combination of method A) and B). The three methods all showed effects of the additive, spanning from about 20% to 50% reductions (in the latter case, from roughly 0.1 to 0.05 in coefficient of friction averaged over the stroke). The greatest potential of the additive was seen with local coefficient of frictions lower than 0.020 in tests at room temperature with Method C. This means a reduction of around 75% compared to the lowest levels measured for the reference tests run without the additive. The most stable friction test was Method A, where a small amount of boric acid solution was repeatedly sprayed onto the lubricated sliding surfaces. In this type of test, friction reductions of roughly 20% and 40% were found at 100 C and room temperature respectively. The tribological and chemical mechanisms of boric acid in this test configuration are yet not fully understood and more studies are needed. However, the observed poor stability of the tribofilms containing boron and oxygen complicates such activities.

  • 144.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Transient non-Newtonian elastohydrodynamic lubrication analysis of an involute spur gear1997In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 207, no 1, p. 67-73Article in journal (Refereed)
    Abstract [en]

    The meshing of a gear is a typical example where non-stationary conditions exist. Load, velocities and curvature vary along the line of action. In this analysis, pressure and film thickness are computed at several points along the line of action by taking the transient effect into consideration. Isothermal full film lubrication is assumed and the fluid model is a non-Newtonian model which includes the effect of a limiting shear strength.The gear teeth are assumed to be rigid. The load is first assumed to be carried by either two pairs of gear teeth or by only one pair. This transition from two to one pair and vice versa is modelled as a step variation of the load.The results show that the transient effect is most pronounced at the load transitions where the previous pair of teeth goes out of action and where the next pair of teeth comes into action. Due to the squeeze effect, the minimum film thickness increases for a moment when the load is doubled. The opposite happens when the load is halved again, the film thickness decreases for a moment until it stabilises.The friction coefficient is computed at the different contact points and so are also the sub-surface stresses. Results are presented for two different lubricants, a paraffinic mineral oil and an oil of the poly-α-olefin type.

  • 145.
    Larsson, Roland
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Höglund, Erik
    Elastohydrodynamic lubrication at pure squeeze motion1994In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 179, no 1-2, p. 39-43Article in journal (Refereed)
    Abstract [en]

    Experimental and theoretical studies of elastohydrodynamically lubricated contacts normally assume static or quasi-static conditions. Non-steady conditions are, however, common. In this paper the case of a ball impacting a flat lubricated surface is investigated theoretically. This case implies transient conditions and the lubricating effect is due to pure squeeze action. Pressure and film thickness distributions are computed during impact and rebound. The results of the analysis show the effects of ball mass, initial impact velocity, lubricant properties and the thickness of the applied lubricant layer on the minimum film thickness. Increased impact velocity increases the minimum value of film thickness achieved during the bounce. The damping capacity of the lubricating film is very high at low impact velocity and small ball mass. In fact, the damping is so high that no rebound occurs if the velocity or the ball mass are smaller than certain critical values. The thickness of the lubricant layer has no influence on the results if it is greater than a certain value. If the pressure-viscosity coefficient is increased, the film becomes thicker

  • 146.
    Larsson, Roland
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Lundberg, Jan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Simplified solution to the combined squeeze-sliding lubrication problem1994In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 173, no 1-2, p. 85-94Article in journal (Refereed)
    Abstract [en]

    The unfavourable elastohydrodynamic lubrication situation in combined squeeze and sliding motion has been analysed both theoretically and experimentally. In experiments a rotating roller impacted and rebounded on a lubricated surface. It was found that oil film breakdown always occurs at the end of the impact time, when the contact force is low. It has also been found that there exists an upper limit for the sliding velocity. Below this limiting velocity no oil film breakdown occurs. This paper is an initial attempt to explain theoretically why oil film breakdown takes place towards the end of the impact, and why an increasing sliding velocity reduces the capability of the oil film to separate the lubricated surfaces. If the oil film's elastic and damping behaviour are taken into consideration it can be shown that a considerable phase shift between maximum contact force and oil film breakdown will arise. It has been found that the squeeze action dominates the pressure formation in the contact and thus the hydrodynamic effect of sliding motion is moderate. Furthermore, several effects, such as non-Newtonian behaviour, surface roughness, temperature rise, starvation and deformations, which are not included in the theoretical model, may decrease the oil film thickness if the sliding velocity increases

  • 147.
    Larsson, Roland
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Lundberg, Jan
    Study of lubricated impact using optical interferometry1995In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 190, no 2, p. 184-189Article in journal (Refereed)
    Abstract [en]

    An experimental study of lubricated impacts between a steel ball and a flat glass surface has been performed. The experimental set-up consists of a Ø70 mm ball mounted on a pendulum which impacts onto a lubricated glass disc. The contact region is studied by means of optical interferometry using a monochromatic light source, a microscope and a high-speed video recording equipment. The lubricants are of PAO type and the viscosity ranges from 27 to 2600 mm2 s-1 at the test temperature. The impact velocity is varied between 0.08 and 0.29 m s-1. A dimple occurs at the centre of the contact where the lubricant is trapped. The influence of viscosity and impact velocity on the dimple's depth and diameter is studied.

  • 148. Larsson-Kråik, Per-Olof
    et al.
    Jacobson, Bo
    Luleå tekniska universitet.
    Höglund, Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Oil drops leaving an EHD contact1994In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 179, no 1-2, p. 23-28Article in journal (Refereed)
    Abstract [en]

    Many machine elements are lubricated with oil or grease. The flow of lubricant depends on different parameters such as surface roughness, surface energy, temperature, etc. A known problem with rolling bearings is that lubricants have to be refilled more frequently if a gas stream passes through the bearing. It is therefore important to know the behaviour of the lubricant in order to predict, e.g. bearing fatigue life due to a gas stream. By studying the droplets thrown out into the air after passing an elastohydrodynamic contact, the most important parameters for oil drop formation have been determined. The analysis is based on picture processing and statistical methods. The experiments show that an increase in temperature, viscosity or surface velocity will increase the total drop volume. Decreased contact pressure and pure rolling also increase the total drop volume. The volume flow, passing the Hertzian contact area, varied between 18 and 30% of the air born oil-drop flow and it is reasonable to assume that increased flow of air-borne droplets will decrease the film thickness due to insufficient replenishment.

  • 149.
    Leiro, Alejandro
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Kankanala, Anusha
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Vuorinen, Esa
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Tribological behaviour of carbide-free bainitic steel under dry rolling/sliding conditions2011In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 273, no 1, p. 2-8Article in journal (Refereed)
    Abstract [en]

    The dry rolling/sliding wear behaviour of Si alloyed carbide free bainitic steel austempered at different temperatures and sliding distances has been evaluated. 60SiCr7 spring steel samples were austempered in a salt bath maintained at 250, 300 and 350 °C respectively for 1 h. Rolling with 5% sliding wear tests were performed using self mated discs for three different test cycles, namely 6000, 18000 and 30000 cycles. The aim was to study the wear performance of the 60SiCr7 steel with a carbide-free microstructure containing different amounts of retained austenite. An in-depth microstructural characterization has been carried out before and after the wear tests in order to link the wear behaviour to the microstructure of each sample. The wear resistance has been expressed by means of the specific wear calculated from the mass loss after the tests. The worn surfaces were analyzed by scanning electron microscopy and X-ray diffraction. Micro-hardness profiles were also obtained in order to analyze strain-hardening effects beneath the contact surfaces. The results indicate that the material with highest hardness—the one austempered at 250 °C—exhibited the lowest wear rate in every case. It was also observed that the hardness increment and thickness of the hardened layer increases with increasing the austempering temperature and number of test cycles. Finally, the results appear to indicate that the initial roughness of the samples has no major effect in the wear rate of the samples above 2500 cycles. The higher wear performance of the sample austempered at 250 °C has been attributed to its superior mechanical properties provided by its finer microstructure. It has been evidenced that all samples undergo the TRIP phenomenon since, after wear; no retained austenite could be detected by XRD.

  • 150.
    Leiro, Alejandro
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Vuorinen, Esa
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Sundin, Karl-Gustaf
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Sourmail, T.
    ASCOMETAL-CREAS.
    Samanio, V.
    ASCOMETAL-CREAS.
    Caballero, F.C.
    National Center for Metallurgical Research (CENIM-CSIC), Madrid.
    Garcia-Mateo, C.
    National Center for Metallurgical Research (CENIM-CSIC), Madrid.
    Elvira, Roberto
    Gerdau Sidenor I+D.
    Wear of nano-structured carbide-free bainitic steels under dry rolling-sliding conditions2013In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 298-299, no 1, p. 42-47Article in journal (Refereed)
    Abstract [en]

    Specially designed steels with carbon contents from 0.6 to 1.0 wt.% were isothermally transformed at very low temperatures, between 220 and 270 °C, in order to obtain a nano-structured bainitic microstructure. It is shown that the wear resistance in dry rolling-sliding of these nano-structured steels is significantly superior to that ofbainitic steels transformed at higher temperatures with similar hardness values.In addition to the highly refined microstructure, the transformation under strain to martensite (TRIP effect), contributes to the plasticity of the nano-scaled steels, increasing surface hardness during testing, thus reducing the wear rate.

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