| 1. |
- Almqvist, Andreas, et al.
(författare)
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Simulation of piston ring : cylinder liner lubrication considering layered fluid films
- 2009
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Ingår i: Tribologia : Finnish Journal of Tribology. - 0780-2285. ; 28:3-4, s. 44-58
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Tidskriftsartikel (refereegranskat)abstract
- During the operation of hydrodynamically lubricated devices a fully formulated lubricant has the ability to form layers at the surfaces. A friction modifier's task is to adjust the interaction between lubricant and the surface so that friction is lowered. An antiwear additive creates a protective layer on the surface and this definitely influence the performance of the lubricated device. To gain fundamental understanding, models that address the modified liquid - solid interaction due to the formation of layers, but also models that may be used to study the effects of layers already formed on the contacting surfaces are required. In this paper, two non-Newtonian lubricant rheology models that may be used to simulate reacted layers resembling those created by lubricant additives are adopted for the simulation of the piston ring - cylinder liner lubrication problem. The possibility of layer to layer interaction, which is likely to occur in the convex conjunction between the ring and the liner, is considered and this extends the models found in the literature. The effects induced by this type of layering are studied by using a modified Reynolds' equation where the coefficients have been corrected with factors that accounts for the layer properties. This enables, effectively, studies of layers resembling those created by lubricant additives during the operation of the lubricated conjunction between a piston ring and a cylinder liner.
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| 2. |
- Almqvist, Andreas, et al.
(författare)
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The homogenization process of the time dependent Reynolds equation describing compressible liquid flow
- 2007
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Ingår i: Tribologia : Finnish Journal of Tribology. - 0780-2285. ; 26:4, s. 30-44
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Tidskriftsartikel (refereegranskat)abstract
- To increase the hydrodynamic performance in different machine elements during lubrication, e.g. journal bearings and thrust bearings, it is important to understand the influence of surface roughness. In this connection one encounters different approaches commonly based on some form of the Reynolds equation. They may generally be divided into deterministic- and averaging- techniques. The former regards all surface roughness information and provides a detailed understanding of the local effects that arise. The latter method is suitable when investigating how the surface roughness affects performance of the machine element as a whole. Homogenization is a rigorous mathematical concept that when applied to a certain problem may be thought of as an averaging technique also providing information about local effects. In this work the compressible time dependent Reynolds equation is homogenized. Related problems have recently been analyzed by homogenization techniques under various assumptions. In the present paper the compressibility is modeled assuming a constant lubricant bulk modulus. The formal method of multiple scale expansion is used to derive a so-called homogenized equation and a numerical solution method to solve both the deterministic problem and the homogenized problem is implemented. The numerical results clearly show that the solution of the homogenized equation is a suitable approximation to the solution of the deterministic problem. It is also demonstrated that for small values of the roughness wavelength, the homogenization technique is superior, since the solution of the deterministic problem requires an extremely fine discretization mesh. More over, the solution of the time dependent homogenized problem may in some cases be reduced to solve a stationary problem that facilitates the solution process and interpretation of results.
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| 3. |
- Andre, Benny, et al.
(författare)
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Nanoindentation on micro pillars for determination of intrinsic hardness and residual stress in coatings deposited on complex geometries
- 2012
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Ingår i: Tribologia. - 0780-2285. ; 31:1-2, s. 22-31
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Tidskriftsartikel (refereegranskat)abstract
- In this work a procedure to assess the local residual stress in coatings deposited on complex substrate geometries is described. A focused ion beam (FIB) is used to mill structures small enough to relax from residual stress. Nanoindentation is used to measure the change in mechanical properties, most importantly the hardness, in relaxed coating and in as-deposited coating. This change is then related to the residual stress in the coating. This relationship can then be used to calculate the residual stresses, at other positions or at other components, from changes in hardness as measured as before. The procedure is demonstrated on two different PVD coatings; one TiN coating and one nanocomposite TiNiC coating. On a large high speed steel substrate the TiN was measured to a hardness of 28 GPa using conventional techniques. Using this procedure, this could be divided into 23 GPa of intrinsic hardness and an extra 5 GPa induced by the known compressive residual stress of 3.9 GPa. When the same coating was deposited on a thin wire the full procedure allowed the residual stress to be determined to 3.5 GPa in compression.
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| 4. |
- Bodin, Anders
(författare)
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Tracked vehicles - the influence of design parameters on the tractive performance in deep snow
- 1999
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Ingår i: Tribologia : Finnish Journal of Tribology. - 0780-2285. ; 18:3, s. 6-12
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Tidskriftsartikel (refereegranskat)abstract
- A new tracked vehicle has been developed for studying the influence of different vehicle parameters on mobility in soft terrain, particularly on muskegs and in deep snow. The vehicle is skid steered with a hydrostatic transmission, driven by a five-cylinder diesel engine. The vehicle makes it possible to vary several design parameters in the field, and it is equipped with transducers to measure the vehicle trust, track motion resistance, belly resistance, drawbar pull, the trim angle of the vehicle and the slip between the tracks and snow.
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| 5. |
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| 6. |
- Ekerfors, L.
(författare)
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Screw-Nut Transmission
- 1984
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Ingår i: Tribologia : Finnish Journal of Tribology. - 0780-2285. ; 3:3, s. 35-41
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Tidskriftsartikel (refereegranskat)
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| 7. |
- Gerth, Julia, et al.
(författare)
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Survey of damage mechanisms on PVD coated HSS hobs used in Swedish gear manufacturing industry
- 2011
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Ingår i: Tribologia. - 0780-2285. ; 30:1-2, s. 37-50
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Tidskriftsartikel (refereegranskat)abstract
- Gear hobbing is widely used for production of cylindrical gears in the Swedish transmission industry. The hob, usually consisting of a homogenous HSS (High Speed Steel) body coated with a ceramic PVD (Physical Vapour Deposition) coating, is designed for regrinding and recoating several times without affecting its cutting geometries. Efficient usage of the tool, considering production costs and gear quality, requires reconditioning before wear starts to affect the gear quality negatively and certainly before tool wear renders reconditioning impossible. Hobs of today generally lack in reliability, making it difficult to judge when they have to be taken out for reconditioning. This work presents a survey of wear as observed on today’s state of the art hobs used by Swedish gear manufactures. It aims to identify damage mechanisms and the common problems in order to enable future production of more reliable hobs. The tools were temporarily borrowed from the production and the analyses were made non-destructively using optical microscopes. This was complemented by destructive cross-sectional analysis on two of the hobs. Wear was most commonly located on the rake faces and the cutting edges of the cutting teeth. It mainly propagates by discrete fractures which appear to originate at local defects in the coating or at the interface. High intrinsic stress in the coating likely promotes coating spallation and accelerates the wear of the cutting edge.
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| 8. |
- Glavatskih, Sergei, et al.
(författare)
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Hydrodynamic thrust bearing experimental apparatus for testing environmentally adapted oils
- 1998
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Ingår i: Tribologia : Finnish Journal of Tribology. - 0780-2285. ; 17:2, s. 27-30
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Tidskriftsartikel (refereegranskat)abstract
- There are indications that some environmentally friendly oils provide performance advantages in hydrodynamic bearings compared to mineral oils. To verify and to quantify the advantages of the synthetic oils in hydrodynamic lubrication in terms of operating film thickness, bearing power loss and operating temperature, a test rig for laboratory experiments has been designed and manufactured. At the first stage of the project temperature and pressure distributions, power loss and oil film thickness for ISO VG46 and VG68 mineral and synthetic oils will be measured at different loads and rotational speeds. At the next stage several other lubricants will be tested. Among them rape seed oil and pine tree oil can be mentioned.
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| 9. |
- Hogmark, Sture, et al.
(författare)
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On adhesion in tribological contacts-Causes and consequences
- 2007
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Ingår i: Tribologia. - 0780-2285. ; 26:1, s. 3-16
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Tidskriftsartikel (refereegranskat)abstract
- This paper is focused to the metallurgical consequences of severe adhesive wear of metallicmaterials. Early examples from the late 70:ies from sliding wear tests of different steels areshown together with some high-resolution TEM micrographs of a cemented carbide cutting tooledge, prepared by using a Focused Ion Beam.Irrespective of sliding conditions, severe metallic wear of the adhesive type results in a surfacelayer, the structure of which is totally different from that of the original bulk material. Theoutermost surface layer displays a nano-crystalline structure followed by a textured layer inwhich the original grains are heavily deformed. For carbon steels, the nano-crystalline layeroften represents untempered martensite.During the wear process, oxide fragments and wear particles from the counter-material may alsobe mixed into the surface layer.The consequence for all metallic materials is that severe wear generates a hard superficial layer.For carbon steels, the hardness of the outermost layer may well exceed 1000 HV. The hardeningmechanisms are well known to a metallurgist and consist of grain refinement, deformationhardening through dislocation generation and tangling, solute hardening (martensite in carbonsteels) and second phase or particle strengthening through intermixing.Consequently, the wear process generates a surface layer on metallic materials that has a muchhigher wear resistance than the original material. This was also demonstrated in one of theexperiments.
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| 10. |
- Holgerson, Mikael
(författare)
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Wet clutch engagement characteristics
- 1999
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Ingår i: Tribologia : Finnish Journal of Tribology. - 0780-2285. ; 18:3, s. 4-5
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Tidskriftsartikel (refereegranskat)abstract
- A wet clutch test rig has been built to examine the characteristics of engagements of wet clutch plates. Results show that the drive torque has a major effect on the engagement and should therefore be taken into consideration when investigating wet clutch characteristics. Furthermore, it was found that the temperature rise is approximately a linear function of the developed energy, and that the friction coefficient is mainly independent of the operating conditions
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