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Numrering	Referens	Omslagsbild	Hitta
1.	Brewe, David E., et al. (författare) The effect of vibration amplitude on vapour cavitation in journal bearings 1987 Ingår i: Wear. - : Elsevier BV. - 0043-1648 .- 1873-2577. ; 115:1-2, s. 63-73 Tidskriftsartikel (refereegranskat)abstract Computational movies were used to analyse the formation and collapse of vapour cavitation bubbles in a submerged journal bearing. The effect of vibration amplitude on vapour cavitation was studied for a journal undergoing circular whirl. The boundary conditions were implemented using Elrod's algorithm which conserves mass flow through the cavitation bubble as well as the oil film region of the bearing. In the calculations, 0.1 ε εmax, where ε is the instantaneous eccentricity and 0.4 εmax 0.9 for the different cases studied. For the case 0.1 ε 0.4, no vapour cavitation occurred. For the case in which 0.1 ε < 0.9, vapour cavitation was present for 76% of the total time
2.	Broitman, E., et al. (författare) Mechanical and tribological properties of CNx films deposited by reactive magnetron sputtering 2001 Ingår i: Wear. - 0043-1648 .- 1873-2577. ; 248:1-2, s. 55-64 Tidskriftsartikel (refereegranskat)abstract The hardness, elasticity, wear rate and friction coefficient of carbon nitride (CNx) films of defined microstructure and composition are presented. CNx films were deposited by dc reactive magnetron sputtering from a C target in N2/Ar plasma. Films were grown on Si (001), Ni, and HSS substrates to thickness of ~0.5 µm at a total pressure of 3 mTorr with the N2 fraction varied from 0 to 1, and the substrate temperature Ts, varied from ambient to 350°C. The mechanical and tribological properties of the coatings were evaluated by nanoindentation and dry ball-on-disk test. For CNx (0 = x = 0.35) films deposited below 200°C (amorphous structure), the elastic recovery and hardness do not change significantly with increasing N concentration, however, the friction coefficient increases from 0.19 to 0.45, while the coating wear rate is low. For CNx (0 = x = 0.15) films grown at Ts = 350°C, where a transition from a graphite-like to a "fullerene-like" phase occurs, a dramatic increase in hardness and elasticity is observed. Furthermore, the rms surface roughness decreases from 15.0 to 0.4 nm. For 0.15 = x = 0.20, CNx films deposited at Ts = 350°C (fullerene-like phase) exhibit a smooth surface, high hardness and elasticity (~90% recovery), and a coefficient of friction against hard steel of ~0.25. For all substrates, film friction coefficient tends to increase as the nitrogen content in the film is increased. Results also indicate the formation of a transfer layer which improves the tribological properties of the films. © 2001 Elsevier Science B.V. All rights reserved.
3.	Del Din, Massimo, et al. (författare) Wear characteristics with mixed lubrication conditions in a full scale journal bearing 1999 Ingår i: Wear. - 0043-1648 .- 1873-2577. ; 232:2, s. 192-198 Tidskriftsartikel (refereegranskat)abstract 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.
4.	Eriksson, Mikael, et al. (författare) Wear and contact conditions of brake pads: dynamical in situ studies of pad on glass 2001 Ingår i: Wear. - 0043-1648 .- 1873-2577. ; 249:3-4, s. 272-278 Tidskriftsartikel (refereegranskat)abstract A pin-on-disc machine has been used to make in situ observations of the dynamics of the contact between brake pad materials and a glass disc, while simultaneously monitoring the friction force. The machine, that is normally used to study elastohydrodynamical film formation, has been slightly modified and fitted with a brake pad material sample instead of a rolling ball. The glass disc facilitates direct microscopy and video recording of the dynamic contact situation using a microscope equipped with a CCD-camera. The most obvious features of the topography of a brake pad are the contact plateaus, small flat islands rising typically a few microns above the rest of the surface. These plateaus are based on the more wear resistant constituents of the pad such as fibres and abrasive particles, but also include softer ingredients. The study shows that the softer and more porous areas surrounding the contact plateaus are worn mainly through three-body abrasion. When the disc is sliding against the plateaus, a large number of small particles (wear debris) are transported through the narrow labyrinth between the surfaces, milling down the weaker constituents. The wear debris can also form very small particles or a continous friction film that may become compacted in front of the initial contact plateaus based on, e.g. a metal fibre. In this way larger but softer plateaus form. The investigation elucidates the rapid changes of the contact situation on a microscale.
5.	Gåhlin, Rickard, et al. (författare) Wear volume and wear distribution of hydraulic motor cam rollers studied by a novel atomic force microscope technique 1998 Ingår i: Wear. - 0043-1648 .- 1873-2577. ; 220:1, s. 1-8 Tidskriftsartikel (refereegranskat)abstract The wear volume and wear distribution of chromium steel cam rollers in a high-torque hydraulic motor has been investigated. The cam roller is a part of a novel silicon nitride/chromium steel journal bearing system. An atomic force microscope (AFM) was used to obtain topographical images of the cam roller surfaces before and after use in a full-scale test of the hydraulic motor. The surfaces were marked with small Vickers indentations to make it possible to reposition the AFM to the same locations. To measure the microscopical wear and produce high resolution maps of the local distribution of wear, a recently developed method was utilised. The method is based on two techniques to treat digital topographical images. To map the distribution of wear, the image of the unworn surface is substracted by the image of the worn surface. To measure the wear volume, the bearing histogram is used to calculate a volume relative to a fixed depth. The calculated volume of the unworn surface is then subtracted by the volume of the worn surface. The ceramic/metal system displayed an extremely low wear rate. corresponding to a typical total mean wear depth of about 30 nm. The surface topography showed very limited changes with the minute wear mainly localised to the uppermost part of the surface ridges. The adopted method thus allowed a unique high resolution mapping and volumetric measurement of the initial stages of wear (1 mg lost out of 600 g) on a real machine element. This high resolution analysis is promising for improving tribological testing of real machine elements with long expected wear lives, by reducing the need for excessively accelerated tests or extremely long and costly test durations.
6.	Holgerson, Mikael (författare) Apparatus for measurement of engagement characteristics of a wet clutch 1997 Ingår i: Wear. - 0043-1648 .- 1873-2577. ; 213:1-2, s. 140-147 Tidskriftsartikel (refereegranskat)abstract 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
7.	Höglund, Erik, et al. (författare) Effect of pressurised gases on the viscosity of polyalkylene glycols 1997 Ingår i: Wear. - 0043-1648 .- 1873-2577. ; 207:1-2, s. 24-28 Tidskriftsartikel (refereegranskat)abstract 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.
8.	Höglund, Erik (författare) EHL and the use of image analysis 1994 Ingår i: Wear. - : Elsevier BV. - 0043-1648 .- 1873-2577. ; 179:1-2, s. 49-56 Tidskriftsartikel (refereegranskat)abstract 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
9.	Höglund, Erik (författare) Influence of lubricant properties on elastohydrodynamic lubrication 1999 Ingår i: Wear. - 0043-1648 .- 1873-2577. ; 232:2, s. 176-184 Tidskriftsartikel (refereegranskat)abstract 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
10.	Höglund, Erik (författare) Influence of polyalkylmethacrylate and sulphurized ester on oil film thickness in an elastohydrodynamic point contact 1987 Ingår i: Wear. - : Elsevier BV. - 0043-1648 .- 1873-2577. ; 115:1-2, s. 223-234 Tidskriftsartikel (refereegranskat)abstract 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
11.	Höglund, Erik (författare) Relationship between lubricant shear strength and chemical composition of the base oil 1989 Ingår i: Wear. - : Elsevier BV. - 0043-1648 .- 1873-2577. ; 130:1, s. 213-224 Tidskriftsartikel (refereegranskat)abstract 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.
12.	Isaksson, Ove (författare) Rheology for water-based hydraulic fluids 1987 Ingår i: Wear. - : Elsevier BV. - 0043-1648 .- 1873-2577. ; 115:1-2, s. 3-17 Tidskriftsartikel (refereegranskat)abstract 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 103 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.
13.	Johannesson, Hans L., et al. (författare) Calculation of the pressure distribution in an arbitrary elastomeric seal contact 1989 Ingår i: Wear. - : Elsevier BV. - 0043-1648 .- 1873-2577. ; 130:1, s. 3-15 Tidskriftsartikel (refereegranskat)abstract 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.
14.	Jonsson, Ulf J. (författare) Lubrication of rolling element bearings with HFC-polyolester mixtures 1999 Ingår i: Wear. - 0043-1648 .- 1873-2577. ; 232:2, s. 185-191 Tidskriftsartikel (refereegranskat)abstract 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
15.	Kassfeldt, Elisabet, et al. (författare) Environmentally adapted hydraulic oils 1997 Ingår i: Wear. - 0043-1648 .- 1873-2577. ; 207:1-2, s. 41-45 Tidskriftsartikel (refereegranskat)abstract 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.
16.	Kassman Rudolphi, Åsa, et al. (författare) Gross plastic fretting - examination of the gross weld regime. 1996 Ingår i: Wear. - 0043-1648 .- 1873-2577. ; 201:1-2, s. 255-264 Tidskriftsartikel (refereegranskat)
17.	Kassman Rudolphi, Åsa, et al. (författare) Gross plastic fretting - mechanical deterioration of silver coated electrical contacts. 1996 Ingår i: Wear. - 0043-1648 .- 1873-2577. ; 201:1-2, s. 244-254 Tidskriftsartikel (refereegranskat)
18.	Kassman, Åsa, et al. (författare) Surface damage, adhesion and contact resistance of siler coated plated copper contacts subjected to fretting motion 1993 Ingår i: Wear. - 0043-1648 .- 1873-2577. ; 165:2, s. 227-230 Tidskriftsartikel (refereegranskat)
19.	Kumar, Rajesh, et al. (författare) A systematic methodology to characterise the running-in and steady-state wear processes 2002 Ingår i: Wear. - 0043-1648 .- 1873-2577. ; 252:5-6, s. 445-453 Tidskriftsartikel (refereegranskat)abstract 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.
20.	Kumar, Rajesh, et al. (författare) Assessment of engine liner wear from bearing area curves 2000 Ingår i: Wear. - 0043-1648 .- 1873-2577. ; 239:2, s. 282-286 Tidskriftsartikel (refereegranskat)abstract 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.
21.	Larsson, Per-Olof, et al. (författare) Oil drops leaving an EHD contact 1994 Ingår i: Wear. - : Elsevier BV. - 0043-1648 .- 1873-2577. ; 179:1-2, s. 23-28 Tidskriftsartikel (refereegranskat)abstract 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.
22.	Larsson, Roland, et al. (författare) Elastohydrodynamic lubrication at pure squeeze motion 1994 Ingår i: Wear. - 0043-1648 .- 1873-2577. ; 179:1-2, s. 39-43 Tidskriftsartikel (refereegranskat)abstract 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
23.	Larsson, Roland, et al. (författare) Simplified solution to the combined squeeze-sliding lubrication problem 1994 Ingår i: Wear. - : Elsevier BV. - 0043-1648 .- 1873-2577. ; 173:1-2, s. 85-94 Tidskriftsartikel (refereegranskat)abstract 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
24.	Larsson, Roland, et al. (författare) Study of lubricated impact using optical interferometry 1995 Ingår i: Wear. - : Elsevier BV. - 0043-1648 .- 1873-2577. ; 190:2, s. 184-189 Tidskriftsartikel (refereegranskat)abstract 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.
25.	Larsson, Roland (författare) Transient non-Newtonian elastohydrodynamic lubrication analysis of an involute spur gear 1997 Ingår i: Wear. - 0043-1648 .- 1873-2577. ; 207:1, s. 67-73 Tidskriftsartikel (refereegranskat)abstract 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.
26.	Lundberg, Jan, et al. (författare) High-speed video photographs of lubrication breakdown in squeeze-sliding contact 1992 Ingår i: Wear. - 0043-1648 .- 1873-2577. ; 157:2, s. 427-433 Tidskriftsartikel (refereegranskat)abstract Using photographs from a high-speed video camera it was confirmed that the main part of breakdown of a lubricating film will appear at the end of the contact time for a contact simultaneously subjected to squeeze and sliding motion. This corresponds with earlier findings using totally different equipment for electric detection of the asperity contact. The present investigation used glass and steel as the lubricated surfaces, instead of steel and steel as was the case in the earlier investigation. In combination with far less stiff equipment, the new materials gave longer contact time and larger elastic deformations of the contact bodies. It was also verified that increased surface roughness, increased sliding velocity and decreased viscosity increase the risk of oil film breakdown
27.	Lundberg, Jan (författare) Lubrication of a rotating ball in normal approach 1989 Ingår i: Wear. - : Elsevier BV. - 0043-1648 .- 1873-2577. ; 130:1, s. 203-212 Tidskriftsartikel (refereegranskat)abstract An experimental study has been made of the degree of lubrication, which is defined as the number of interacting asperities, when a rotating spherical body approaches a plane during rotation. The normal velocity was varied between 0.1 and 0.5 m s-1 and the sliding velocity between 0 and 9.2 m s-1. The experiments show that the oil viscosity is the most important lubricant parameter. The degree of lubrication is not affected by either the normal velocity, the pressure viscosity coefficient or the shear strength proportionality constant. An increase in the sliding velocity gives a decrease in lubrication of between 25% and 65% depending on the surface roughness and type of lubricant. The surface roughness is also a most important factor impeding good lubrication. To avoid wear one has to increase the viscosity from 8 to 145 mm2 s-1 if the mean surface roughness Ra is increased from 0.01 to 0.14.
28.	Lundberg, Jan (författare) Lubrication of machine elements during combined squeeze and sliding motion 1993 Ingår i: Wear. - 0043-1648 .- 1873-2577. ; 169:2, s. 161-166 Tidskriftsartikel (refereegranskat)abstract The motion when two parts in a machine come into contact can be a normal, sliding or rolling approach, or a combination of the three. The case of combined normal and sliding motion can be very unfavourable from the point of view of lubrication. Nevertheless, this situation does occur, for example in a gear mesh and in heavily loaded rolling-element bearings.The following factors in the case of lubrication of machine elements during combined normal and sliding motion were studied experimentally: oil viscosity, surface texture, shear strength of oil and maximum pressure. The pressure also involves the parameters normal force, Young's modulus, Poisson's ratio and surface curvature.Based on the experimental results, an equation has been deduced which describes how the above-mentioned factors influence the permissible limiting sliding velocity Vsl without oil film breakdown: Vsl=0.127×10-6(v0.1-1.575)(ψ-13.1-1.707)(3840-pmax)This equation agrees well with results from experiments carried out by other authors, and is valid if combined sliding and impact between the machine elements, resulting in a limited contact time, are present.
29.	Lundberg, Jan (författare) Viscosity dependence of squeeze/sliding lubrication 1992 Ingår i: Wear. - 0043-1648 .- 1873-2577. ; 155:1, s. 31-36 Tidskriftsartikel (refereegranskat)abstract It has been found experimentally that increased lubricant viscosity will increase the permissible sliding speed without leading to breakdown of the lubricant film while the normal velocity is held at a constant level. The dependence approaches a square root function. It is also apparent that with a squeeze velocity present, increased sliding velocity will decrease the oil-film thickness. An initial attempt at an explanation is given in terms of a combination of Reynolds' equation and further experimental results.
30.	Mann, B. S., et al. (författare) High temperature friction and wear characteristics of various coating materials for steam valve spindle application 2000 Ingår i: Wear. - 0043-1648 .- 1873-2577. ; 240:1-2, s. 223-230 Tidskriftsartikel (refereegranskat)abstract Various coatings such as chromium carbide (deposited by plasma spraying and detonation gun techniques), chromium oxide, chromium oxide + titania + silica, NiCrAlY, and Al2O3 + Ni all deposited by plasma spraying; stelliting, and surface nitriding have been applied on X20CrMo V121 steel. This steel is used for high temperature applications such as steam turbine valve spindle. Friction and wear behavior of the surface coated and treated materials have been studied at an elevated temperature of 550°C while rubbing against graphite-filled stellited steel. These studies have been carried out on SRV optimol reciprocating tribometer. Test parameters for tribological studies have been selected with a view to simulate operating conditions encountered in operation. Additionally, the structure, porosity, hardness, bond strength, and thermal cycling behaviour of these surface coated/treated materials have been characterised. Based on these laboratory investigations, chromium carbide coating deposited by plasma spraying technique has been identified as the most suitable coating for steam turbine valve spindle application. Process parameters have been established for deposition of chromium carbide coating by plasma spraying technique on actual valve spindles. The field results obtained are found to be commensurate with the laboratory findings.
31.	Olofsson, Ulf, et al. (författare) Simulation of mild wear in boundary lubricated spherical roller thrust bearings 2000 Ingår i: Wear. - 0043-1648 .- 1873-2577. ; 241:2, s. 180-185 Tidskriftsartikel (refereegranskat)abstract Owing to the curved contact surfaces in a spherical roller thrust beating, the rollers will undergo sliding. For an unskewed roller there will be two points along each contact where the sliding velocity is zero. At all other points along the contact, sliding is present. Under boundary lubricated conditions the sliding can give rise to mild wear. Experimental results show that this wear can cause a significant change in the surface profile outside the zero sliding points. The mild wear in the contact was simulated using Archard's wear law. An iterative wear model is described in which the normal load distribution, the tangential tractions and the sliding distances are repeatedly calculated to simulate the changes in surface geometry due to wear. Good qualitative agreement was achieved between the simulation results and the previously presented experimental results.
32.	Olofsson, Ulf, et al. (författare) Wear, plastic deformation and friction of two rail steels-€”a full-scale test and a laboratory study 2003 Ingår i: Wear. - 0043-1648 .- 1873-2577. ; 254:1â€“2, s. 80-93 Tidskriftsartikel (refereegranskat)abstract Form change due to wear and plastic deformation on a rail can reduce the service life of a track. The purpose of this investigation was to study the development of these damage mechanisms on new and 3-year-old rails in a commuter track over a period of 2 years. The experimental results from the form measurements show that there was a significant change in rail profile due to wear as well as to plastic deformation. Plastic deformation and wear was a continuing process even for rail that had been in service for 5 years. The plastic deformation mechanism was plastic ratchetting. Compared with the UIC 900A grade rail, the form change was less for the UIC 1100 grade rail. However, the contact situation in terms of sliding velocity and contact pressure had more influence on form change than the change of material. The results from 3D surface measurement showed that there were different wear mechanisms involved at different parts of the rail. Mild wear dominated at the rail head, but at the rail edge severe wear clearly influenced the amount of wear. The severe wear showed traces of seizure. Material tests were performed on two different testing machines: a two-roller and a pin-on-disk machine. On the basis of results from the material testing, a simple wear map was constructed. In the wear map, the wear coefficient is presented as a function of sliding velocity and contact pressure. The results from laboratory tests showed that wear coefficient depended strongly on sliding velocity. The increase in the wear coefficient when increasing sliding velocity was due to a change of wear mechanism from mild wear to severe wear.
33.	Sellgren, U., et al. (författare) A finite element-based model of normal contact between rough surfaces 2003 Ingår i: Wear. - 0043-1648 .- 1873-2577. ; 254:11, s. 1180-1188 Tidskriftsartikel (refereegranskat)abstract Engineering surfaces can be characterized as more or less randomly rough. Contact between engineering surfaces is thus discontinuous and the real area of contact is a small fraction of the nominal contact area. The stiffness of a rough surface layer thus influences the contact state as well as the behavior of the surrounding system. A contact model that takes the properties of engineering surfaces into account has been developed and implemented using finite element software. The results obtained with the model have been verified by comparison with results from an independent numerical method. The results show that the height distribution of the topography has a significant influence on the contact stiffness but that the curvature of the roughness is of minor importance. The contact model that was developed for determining the apparent contact area and the distribution of the mean contact pressure could thus be based on a limited set of height parameters that describe the surface topography. By operating on the calculated apparent pressure distribution with a transformation function that is based on both height and curvature parameters, the real contact area can be estimated when the apparent contact state is known. The model presented is also valid for cases with local plastic flow in the bulk material.
34.	Sjödin, Ulf, et al. (författare) Initial sliding wear on piston rings in a radial piston hydraulic motor 2003 Ingår i: Wear. - 0043-1648 .- 1873-2577. ; 254:11, s. 1208-1215 Tidskriftsartikel (refereegranskat)abstract The initial sliding wear of boundary lubricated piston rings used in a hydraulic motor is studied in terms of the changes in mass, form and surface toughness. The piston ring in a hydraulic motor makes an important contribution to high volumetric efficiency by properly sealing the cylinder bore and piston. The results show that the wear on the piston ring in this particular test rig takes place at the top of the asymmetric crowning at the outer surface contacting the cylinder bore. Initially, the roughness amplitude decreased rapidly, and had decreased by one-third after sliding 10 m. The dominant wear mechanism was mild wear. Abrasive wear also clearly influences the amount of wear.
35.	Spiegelberg, Christer, et al. (författare) Simulation of transient friction of a cylinder between two planes 2003 Ingår i: Wear. - 0043-1648 .- 1873-2577. ; 254:11, s. 1170-1179 Tidskriftsartikel (refereegranskat)abstract The need for good friction models for transient motions has increased as a consequence of the increased use of mechatronics and control engineering principles in precision mechanics. The machine elements in such equipment often involve rolling and sliding contacts. Most studies of friction in rolling and sliding contacts running under dry or boundary lubricated conditions have examined steady-state conditions. This paper describes simulations of the motion of a cylinder between two planes, first with a step change in velocity and then with an oscillating motion of the upper plane. The motion of the cylinder is determined by the friction in the contacts and the inertia. The friction in the rolling and sliding contacts is simulated with a brush model. The surfaces are assumed to be ideally smooth. For the step change in velocity, there is initially a period of complete sliding in the upper contact. During the sliding period, the friction force is the maximum possible, but it decreases as the complete sliding ends. The simulations show heavily damped oscillations, with frequencies corresponding to the natural translatory and torsional frequencies of the system. For the oscillating motions the sliding increases with the frequency of the motion, as expected.
36.	Svahn, Fredrik, et al. (författare) The influence of surface roughness on friction and wear of machine element coatings 2003 Ingår i: Wear. - 0043-1648 .- 1873-2577. ; 254:11, s. 1092-1098 Tidskriftsartikel (refereegranskat)abstract The use of low frictioncoatings like amorphous carbon or metal-doped carbon coatings on machineelements is constantly increasing. Most often, a surface treatment, e.g. grinding and polishing or honing, is required for optimal performance of the coated machineelement. This can be time consuming and costly. In this study, the effect of surfaceroughness on friction and sliding wear of two different coatings, one tungsten containing and one chromium containing coating, were examined using a ball-on-disc test. Ball bearing steel plates were grinded to different surfaceroughnesses and coated with the two different coatings. The friction was found to depend on surfaceroughness where the rougher surfaces gave higher friction coefficients. The wear rate for the a-C:W coating was found to be independent of the roughness, whereas the roughness had a strong influence on the wear rate for the a-C:Cr coating. This could partly be explained by a difference in wear mechanism, where fatigue wear was observed for the a-C:Cr coating but not for the a-C:W coating.
37.	Telliskivi, Tanel (författare) Simulation of wear in a rolling-sliding contact by a semi-Winkler model and the Archard's wear law 2004 Ingår i: Wear. - 0043-1648 .- 1873-2577. ; 256:7-8, s. 817-831 Tidskriftsartikel (refereegranskat)abstract The purpose of this work is to develop a method of controlling the friction and wear affecting the contact pair in rolling-sliding contact. The scope is in small-scale tribology by which mechanism of wear would be clarified on first hand by Archard's law. The prerequisite for using Archard's wear law in a simulation is proper piecewise linear modelling of contact at the substructural level, including prediction of deformations and relative motions for every part of the contact. The deformation level at the real contact depends on such parameters as normal forces. relative motions, geometry, surface tractions, etc. There is a need for a simulation tool that explains the role of these parameters. The present work simulates the well-known disc-on-disc test for dry wear. The deformation field due to normal load is solved by the Winkler mattress method. The tangential stress field is subsequently calculated knowing the normal pressure field, the penetration and the general rigid body movement for every subregion. The influence functions from potential theory are used to model the tangential traction and displacement field in the contact. The special computing excludes the need for the creep constants that depend on the Poisson's ratio and the result is not dependent on the shape of the contact area. Every rectangular cell is tested whether it is subject to sliding. The sliding distance is calculated by subtracting elastic displacements from the relative motion of the rigid body. The elastic deflections are reversible and exist both under the sticking region in contact and also in the sliding region. A comparison of the results of a simulation and a disc-on-disc test is presented. Good agreement was found for both wear and rolling friction at different load and creep levels.
38.	Wiklund, U, et al. (författare) Influence of residual stresses on fracture and delamination of thin hard coatings 1999 Ingår i: Wear. - : ELSEVIER SCIENCE SA. - 0043-1648 .- 1873-2577. ; 232:2, s. 262-269 Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract The risk of fracture and delamination of residually stressed coating systems is examined. Stress concentrations are generated at the interface of coated systems where the substrate deviates from bring perfectly smooth, flat and infinitely large. Using fin
39.	Wikström, Victoria, et al. (författare) Wear of bearing liners at low speed rotation of shafts with contaminated oil 1993 Ingår i: Wear. - : Elsevier BV. - 0043-1648 .- 1873-2577. ; 162-164:2, s. 996-1001 Tidskriftsartikel (refereegranskat)abstract An experimental and theoretical investigation was carried out to investigate the relationship between wear of bearing liners and low shaft speed, contamination, oil temperature, bearing load and time. Experimentally, it was found that oil with no external debris added produced only slight polishing of the liners. When the oil was contaminated with 0.02 wt.% iron or quartz particles of a known distribution (less than 32 μm diameter), increased wear was detected. Also, comparison of the results of the clean and iron-contaminated tests with those for quartz-contaminated oil show that the character of the worn liner area has changed from evenly rubbed zones to equally divided polished stripes in the circumferential direction. During the tests, the bearing friction was measured. In no test did the friction rise drastically, as would have been the case if severe wear and scoring had appeared. In actual applications, though, this sometimes occurs. This may be explained by severe contamination in industrial lubricating systems, with larger particles and higher debris concentration. A clean lubricating system is thus crucial in order to avoid heavy wear at low speeds. The experimental results were then compared with those indicated theoretically for film thickness at low speed. The theoretical minimum film thickness at low speed was much smaller than the size of the debris. The results indicate that if So-1 <=340, B/D >=0.73 and C>=0.18 mm, no severe wear will occur.
40.	Xiao, Li, et al. (författare) A study on the effect of surface topography on rough friction in roller contact 2003 Ingår i: Wear. - Amsterdam : Elsevier. - 0043-1648 .- 1873-2577. ; 254:11, s. 1162-1169 Tidskriftsartikel (refereegranskat)abstract The friction behaviour of gear teeth in the context of tribology can have a strong effect on housing vibration, noise and efficiency. One of the parameters that greatly influences the friction under certain running conditions is surface roughness. In this work, rough friction was studied in lubricated sliding of roller surfaces, which were manufactured to simulate the real gear surfaces. By examining 3D surface topography of two mating bodies, both surface roughness and its effect on friction behaviour can be studied. In a previous study, a rough-friction test rig has been designed, constructed and initially verified. The types of surfaces involved in this study are ground, shot-peened, phosphated and electrochemically deburred. These rollers were subjected to the same friction testing procedures. Roller surfaces were then examined, and correlation between the topography and the frictional behaviour was analysed. Friction behaviour was interpreted in terms of Stribeck curves (friction coefficient as the function of Hersey parameter (ην/p)). The results showed that electrochemically deburred and certain phosphated surfaces provide lower friction coefficient values which are competitive to fine-ground surfaces in lubricated rolling/sliding contact. © 2003 Elsevier Science B.V. All rights reserved.
41.	Öqvist, Mona (författare) Numerical simulations of mild wear using updated geometry with different step size approaches 2001 Ingår i: Wear. - 0043-1648 .- 1873-2577. ; 249:1, s. 6-11 Tidskriftsartikel (refereegranskat)abstract Wear of engineering components is often a critical factor influencing the product life. Prediction and simulation of wear is therefore an important matter in engineering. Numerical simulations of wear of a cylindrical steel roller oscillating against a steel plate are performed with a special version of the finite element program NIKE2D. The simulation was done in steps and the pressure and the sliding distance was recalculated as the surface geometry changed. The wear model used in the simulations is global. The global wear model gives an opportunity to predict the change in shape of the surfaces in a fast and efficient manner, it will however not incorporate information on how the wear occurs on molecular scale.Two different strategies in selecting the time step for the geometry update were used. In the first case a larger time step was used in the first wear steps and a smaller one in the final ones, and in the second a constant time step was used. To get information on the coefficient of friction an experiment was performed. This experiment was used to evaluate the simulation as well as give the proper input to the simulation. The simulated topography of the surfaces was compared with experimental results and the agreement was good. It can be concluded that allowing the time step to differ between the wear steps will speed up the wear simulation considerably. A large time step for the geometry update will cause some waviness of the cylindrical surface but when the smaller time steps have been used at the end of the computation this error will disappear.
42.	Abbasi, Saeed, et al. (författare) A pin-on-disc study of the rate of airborne wear particle emissions from railway braking materials 2012 Ingår i: Wear. - UK : Elsevier. - 0043-1648 .- 1873-2577. ; 284, s. 18-29 Tidskriftsartikel (refereegranskat)abstract The current study investigates the characteristics of particles generated from the wear of braking materials, and provides an applicable index for measuring and comparing wear particle emissions. A pin-on-disc tribometer equipped with particle measurement instruments was used. The number concentration, size, morphology, and mass concentration of generated particles were investigated and reported for particles 10 nm-32 mu m in diameter. The particles were also collected on filters and investigated using EDS and SEM. The effects of wear mechanisms on particle morphology and changes in particle concentration are discussed. A new index, the airborne wear particle emission rate (AWPER), is suggested that could be used in legislation to control non-exhaust emissions from transport modes, particularly rail transport.
43.	Abbasi, Saeed, et al. (författare) A study of airborne wear particles generated from organic railway brake pads and brake discs 2011 Ingår i: Wear. - UK : Elsevier. - 0043-1648 .- 1873-2577. ; 273:1, s. 93-99 Tidskriftsartikel (refereegranskat)abstract Brake pads on wheel-mounted disc brakes are often used in rail transport due to their good thermal properties and robustness. During braking, both the disc and the pads are worn. This wear process generates particles that may become airborne and thus affect human health. The long term purpose of ‘Airborne particles in Rail transport’ project is to gain knowledge on the wear mechanisms in order to find means of controlling the number and size distribution of airborne particles. In this regard, a series of full-scale field tests and laboratory tests with a pin-on-disc machine have been conducted. The morphology and the matter of particles, along with their size distribution and concentration, have been studied. The validity of results from the pin-on-disc simulation has been verified by the field test results. Results show an ultra-fine peak for particles with a diameter size around 100 nm in diameter, a dominant fine peak for particles with a size of around 350 nm in diameter, and a coarse peak with a size of 3-7 μm in diameter. Materials such as iron, copper, aluminium, chromium, cobalt, antimony, and zinc have been detected in the nano-sized particles.
44.	Abbasi, Saeed, 1973-, et al. (författare) Temperature and Thermoelastic Instability at Tread Braking Using Cast Iron Friction Material 2013 Ingår i: Wear. - : Elsevier BV. - 0043-1648 .- 1873-2577. ; 314:1–2, s. 171-180 Tidskriftsartikel (refereegranskat)abstract Braking events in railway traffic often induce high frictional heating and thermoelastic instability (TEI) at the interfacing surfaces. In the present paper, two approaches are adopted to analyse the thermomechanical interaction in a pin-on-disc experimental study of railway braking materials. In a first part, the thermal problem is studied to find the heat partitioning between pin and disc motivated by the fact that wear mechanisms can be explained with a better understanding of the prevailing thermal conditions. The numerical model is calibrated using the experimental results. In a second part, the frictionally induced thermoelastic instabilities at the pin-disc contact are studied using a numerical method and comparing them with the phenomena observed in the experiments. The effects of temperature on material properties and on material wear are considered. It is found from the thermal analysis that the pin temperature and the heat flux to the pin increase with increasing disc temperatures up to a transition stage. This agrees with the behaviour found in the experiments. Furthermore, the thermoelastic analysis displays calculated pressure and the temperature distributions at the contact interface that are in agreement with the hot spot behaviour observed in the experiments.
45.	Aiso, Toshiharu, 1983-, et al. (författare) Effect of combined additions of Si, Mn, Cr and Al to carbon steel on material transfer in a steel/TiN coated tool sliding contact 2017 Ingår i: Wear. - : Elsevier BV. - 0043-1648 .- 1873-2577. ; 388-389, s. 9-17 Tidskriftsartikel (refereegranskat)abstract Material transferred from steel work materials onto the cutting tools largely affects tool life and machining performance. This material transfer is strongly influenced by the steel composition, and different alloying can have very different effects. Crossed cylinders sliding tests can be used to simulate the contact between the chip and the tool in machining. In this work such a test is used to evaluate material transfer and friction characteristics of a TiN coated tool sliding against five model steels. These model steels are especially designed to study the effects from specific combination of alloy elements, i.e. the steels, containing 0.55 mass% C and 1 mass% Si, are alloyed with one or more of 1 mass% Mn, Cr and Al. When using the steels alloyed without Al, Si-rich oxide layers are formed on the coating, resulting in a low friction coefficient. When using the steels alloyed with Al, almost pure Al–O layers are formed, resulting in a higher friction coefficient and rapid coating cracking. Essentially, the most easily oxidized alloy element is most strongly enriched in the oxide and decides the main mechanism of the material transfer and friction behavior.
46.	Aiso, Toshiharu, 1983-, et al. (författare) Effect of Si and Al additions to carbon steel on material transfer and coating damage mechanism in turning with CVD coated tools 2016 Ingår i: Wear. - : Elsevier BV. - 0043-1648 .- 1873-2577. ; 368-369, s. 379-389 Tidskriftsartikel (refereegranskat)abstract Material transfer from the work materials to the tools strongly influences machining performance and tool life. The influence of Si and Al additions to carbon steel on the material transfer and coating wear in turning with CVD coated carbide tools is investigated. Three model steels are specifically designed to separately study the effects of the individual alloying elements: one reference steel with C as the only alloying element (Base steel), and two steels alloyed also with 1 mass% Si or Al. In the region around the depth of cut on the rake face, where the outside edge of the chip passes over the tool surface, the coating is worn mainly by abrasion when cutting the Base steel. When cutting the Si alloyed steel, an almost pure Si–O transfer layer covers the coating surface, which protects it from wear. When cutting the Al alloyed steel, an almost pure Al–O transfer layer forms on the coating. This layer promotes steel transfer and associated adhesive wear of the coating, which rapidly results in coating detachment and eventually causes notch wear. In the crater region, only the Al alloyed steel results in a transfer layer, an AlN layer that reduces the crater wear.
47.	Alemani, Mattia, et al. (författare) Dry sliding of a low steel friction material against cast iron at different loads : Characterization of the friction layer and wear debris 2017 Ingår i: Wear. - : Elsevier. - 0043-1648 .- 1873-2577. ; 376-377, s. 1450-1459 Tidskriftsartikel (refereegranskat)abstract Pin-on-disc testing was used to investigate the sliding behavior and the wear products of a low-steel friction material against a cast iron disc at different applied loads, to investigate the effect of the temperature rise induced by frictional heating. The testing rig was operated in a clean chamber with a purified incoming air flux. The outgoing flux carries the wear particles to an impactor that counted and sorted them by average diameter and weight. At increasing applied loads, corresponding to a proportional increase of the pin-disc contact temperature, the coverage of both the pin and disc surface by a friction layer was found to increase too. The relevant X-Ray diffraction patterns revealed the presence of a large amount of graphite and different compounds originating from the friction material and from the counterface disc, mainly iron oxides, as concerns this latter. After the test at the lowest investigated load, i.e., 1 kg, the disc worn surface exhibited abrasive grooves and a discontinuous friction layer mainly made of compacted iron oxide particles. After the test at higher loads, i.e., 5 and 7 kg, the disc surface was covered by a compact friction layer. As concerns the friction layer on the pins, most of the ingredients from the friction material were detected, in association with the iron oxides from the disc. These results can be interpreted in terms of the temperature stability range of the phenolic resin used as a binder of the friction material. The characterization of the collected airborne wear debris showed that the particles produced by the low temperature (i.e., low load) test were mostly equiaxed; whereas those produced by the high temperature (i.e., high loads) tests, predominantly displayed a plate-like morphology. The mechanisms of their formation in relation to the characteristics of the friction layers are illustrated and discussed.
48.	Alemani, Mattia, et al. (författare) On the influence of car brake system parameters on particulate matter emissions 2018 Ingår i: Wear. - : ELSEVIER SCIENCE SA. - 0043-1648 .- 1873-2577. ; 396, s. 67-74 Tidskriftsartikel (refereegranskat)abstract The influence of car brake system parameters on particulate matter emissions was investigated using a pin-on-disc tribometer. Samples from a low-steel friction material and a cast iron disc were tested for different sliding velocities, nominal contact pressures and frictional powers. Disc temperatures were also measured. Their impact on total concentration, size distribution, particle coefficient and transition temperature was analysed. Results show that frictional power is the most significant brake system parameter. However, temperature, as a response parameter, is the most influential, inducing a shift towards the ultrafine particulate fraction and raising emissions. A transition temperature, independent of the system parameters, was identified.
49.	Alfredsson, Bo, et al. (författare) The role of a single surface asperity in rolling contact fatigue 2008 Ingår i: Wear. - : Elsevier BV. - 0043-1648 .- 1873-2577. ; 264:9-10, s. 757-762 Tidskriftsartikel (refereegranskat)abstract The effect of contact loading of single surface irregularities, i.e. asperities, as an underlying mechanism for surface initiated rolling contact fatigue was investigated numerically using FEM. Spalls in the teeth flanks of driving gear wheels were investigated for typical spalling crack initiation properties. The spalling entry angle was documented and some spalls with a convex entry tip were found. The residual surface stresses of the used teeth, with spalls, were measured with the hole drilling technique. The gear contact close to the rolling circle was modelled as two rolling cylinders. A single asperity was introduced into the contact surface of one of them. Due to the presence of the asperity a three dimensional contact model was required. The material description included J(2)-plasticity with isotropic and linear hardening. The simulation included residual stresses from material heat treatment. The first roll cycle introduced plastic deformation which altered the residual stresses. Thus, the stress results were captured during a second roll cycle. The most important result was that asperities will serve as local stress raisers in the contact surfaces. The computed stress cycle at the asperity was compared to stress cycles that gave ring/cone cracks at point loaded experiments. The principal stress trajectory into the material was compared to the cross-section profiles of the spalling entry and ring/cone crack. The surface stress profile at the asperity was compared to the convex surface profiles of the spalling tip and ring/cone crack. The asperity deformation and change in residual surface stresses from moderate plastic deformation during rolling were estimated.
50.	Ali, Nashit, et al. (författare) Friction, wear, and airborne particle emissions from rail-wheel contact with laser cladded overlays-A pin-disc tribometer simulation 2023 Ingår i: Wear. - Amsterdam : Elsevier BV. - 0043-1648 .- 1873-2577. ; 518 Tidskriftsartikel (refereegranskat)abstract The present study uses a pin-on-disc tribometer to evaluate friction, wear, and airborne particle emissions for a rail-wheel contact. Test pins from UIC60 900A rail carbon steels were in contact with three types of test discs surfaces: R7 wheel carbon steel, laser cladding overlayed martensitic stainless steel, and laser cladding overlayed Ni-based-8% MnS self-lubricating alloy. Test results show about halving of the coefficient of friction, 0.42 to 0.22, and one ten-power lower specific pin and disc wear of discs with self-lubricating overlay compared to standard railway carbon steel contacts. Using stainless-steel overlayed discs also resulted in one ten-power lower specific disc wear, but pin wear is unchanged. Particle emission for the tests with discs with self-lubricating overlay is constant at almost 200 particles/cm3 while running in the distance is needed for the other tests. Almost all generated airborne wear particles were in the sub-100 nm range. The use of laser-cladded (LC) overlay reduced the number of airborne wear particles in the sub-100 nm range by more than a factor of 10.

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