| 1. |
- Olofsson, Ulf, et al.
(författare)
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Increased wear resistance of roller bearings using Me-C : H coated rollers
- 2000
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Ingår i: Journal of tribology. - : ASME International. - 0742-4787 .- 1528-8897. ; 122:4, s. 682-688
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Tidskriftsartikel (refereegranskat)abstract
- The contact surfaces bz a boundary lubricated spherical roller thrust bearing can change form due to sliding and particle generated wear. These form changes can seriously reduce the fatigue life of the bearings. An experimental test series has been performed where this effect was investigated in bearings with metal mixed amorphous carbon, Me-C: H, coated rollers that were tested against bearings with standard rollers. The experimental results show that while the bearings with standard rollers can fail due to wear, the bearings with coated rollers are at the same time almost unaffected by wear. Also the number of particles generated in the contact was significantly less when using coated rollers. There were twice as many self-generated particles when using a standard bearing compared with a coated bearing. The effect of the coating is discussed in terms of surface hardness, coefficient of friction and tribochemical phenomena. [S0742-4787(00)02004-X].
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| 2. |
- Almqvist, Andreas, et al.
(författare)
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A new approach for studying cavitation in lubrication
- 2014
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Ingår i: Journal of tribology. - : ASME International. - 0742-4787 .- 1528-8897. ; 136:1
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Tidskriftsartikel (refereegranskat)abstract
- The underlying theory, in this paper, is based on clear physical arguments related to conservation of mass flow and considers both incompressible and compressible fluids. The result of the mathematical modeling is a system of equations with two unknowns, which are related to the hydrodynamic pressure and the degree of saturation of the fluid. Discretization of the system leads to a linear complementarity problem (LCP), which easily can be solved numerically with readily available standard methods and an implementation of a model problem in matlab code is made available for the reader of the paper. The model and the associated numerical solution method have significant advantages over today's most frequently used cavitation algorithms, which are based on Elrod-Adams pioneering work
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| 3. |
- Almqvist, Andreas
(författare)
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Homogenization of the Reynolds equation governing hydrodynamic flow in a rotating device
- 2011
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Ingår i: Journal of tribology. - : ASME International. - 0742-4787 .- 1528-8897. ; 133:2, s. 021705-1
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, a method facilitating the analysis of the effects of surface roughness on the lubrication of a rotating device is presented. The analysis utilizes homogenization—a suitable technique for averaging the effects of roughness as modeled by the Reynolds equation. The originality of this work lies in a novel way of deriving the so called local problems, also known as microbearing problems. It is clearly shown how this increases the computational efficiency by eliminating the dependence of the global coordinates on the formulation of these local problems. This does not only speed up the computation, it also means that the derived flow factors or flow tensors require less storage space. To provide for good usability, alongside the flow factors for the averaged Reynolds equation, the correction factors for the averaged friction torque (and force) and the expression for averaged load carrying capacity are presented here.
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| 4. |
- Almqvist, Andreas, et al.
(författare)
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Similarities and differences between the flow factor method by Patir and Cheng and homogenization
- 2011
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Ingår i: Journal of tribology. - : ASME International. - 0742-4787 .- 1528-8897. ; 133:3, s. 031702-1
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Tidskriftsartikel (refereegranskat)abstract
- Different averaging techniques have proved to be useful for analyzing the effects of surface roughness in hydrodynamic lubrication. This paper compares two of these averaging techniques, namely the flow factor method by Patir and Cheng (P&C) and homogenization. It has been rigorously proved by many authors that the homogenization method provides a correct solution for arbitrary roughness. In this work it is shown that the two methods coincide if and only if the roughness exhibits certain symmetries. Hence, homogenization is always the preferred method.
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| 5. |
- Almqvist, Torbjörn, et al.
(författare)
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Some remarks on the validity of Reynolds equation in the modeling of lubricant film flows on the surface roughness scale
- 2004
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Ingår i: Journal of tribology. - : ASME International. - 0742-4787 .- 1528-8897. ; 126:4, s. 703-710
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Tidskriftsartikel (refereegranskat)abstract
- The objective of this paper is to investigate the flow in a lubricant film on the surface roughness scale and to compare the numerical solutions obtained by two different solution approaches. This is accomplished firstly by the CFD-approach (computational fluid dynamic approach) where the momentum and continuity equations are solved separately, and secondly the Reynolds equation approach, which is a combination and a simplification of the above equations. The rheology is assumed to be both Newtonian and non-Newtonian. An Eyring model is used in the non-Newtonian case. The result shows that discrepancies between the two approaches may occur, primarily due to a singularity which appears in the momentum equations when the stresses in the lubricant attain magnitudes that are common in EHL. This singularity is not represented by the Reynolds equation. If, however, the rheology is shifted to a non-Newtonian Eyring model the deviations between the two solution approaches is removed or reduced. The second source of discrepancies between the two approaches is the film thickness to wavelength scale ω. It will be shown that the Reynolds equation is valid until this ratio is approximately O(10-2).
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| 6. |
- Almqvist, Torbjörn, et al.
(författare)
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THD analysis of tilting pad thrust bearings : comparison between theory and experiments
- 2000
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Ingår i: Journal of tribology. - : ASME International. - 0742-4787 .- 1528-8897. ; 122:2, s. 412-417
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Tidskriftsartikel (refereegranskat)abstract
- The objective of the present research is to verify a THD model of hydrodynamic thrust bearings. The developed model of a pivoted pad bearing, which can tilt both radially and circumferentially, allows for three-dimensional temperature distribution in the oil film and in the pad, as well as two-dimensional temperature variation in the runner. Viscosity and density are treated as functions of both temperature and pressure. Experiments have been performed on a test rig, containing two identical equalizing pivoted pad thrust bearings. Power loss, runner temperature, and pressure profiles as a function of load and rotational speed are compared for both theoretical and experimental investigations. Fairly good agreement has been found when the oil inlet temperature and heat transfer coefficients have been estimated in order to get the same runner temperature in both theory and experiment.
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| 7. |
- Baart, Pieter, et al.
(författare)
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Contaminant migration in the vicinity of a grease lubricated bearing seal contact
- 2011
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Ingår i: Journal of tribology. - : ASME International. - 0742-4787 .- 1528-8897. ; 133:4
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Tidskriftsartikel (refereegranskat)abstract
- Lubricating grease is commonly used for lubricating sealed and greased for life rolling element bearings. This grease also provides an additional sealing function to protect the bearing against ingress of contaminants. In this work the sealing function of lubricating grease in the vicinity of the seal lip contact has been studied experimentally by measuring the migration of spherical fluorescent contaminant particles in the vicinity of the contact, as a function of shaft speed and lubricant type. The experimental results reveal that in some greases contaminant particles migrate towards the sealing contact where the shear rate reaches its highest value. However, for other greases, Newtonian base oils, and elastic fluids, this is not necessarily the case and contaminant particles consistently migrate away from the sealing contact. Various physical phenomena have been investigated to explain the difference in migration behavior. It is concluded that migration towards the sealing contact is driven by the viscosity gradient and migration away from the sealing contact is related to the Weissenberg number. The sealing function of grease in the vicinity of the sealing contact is due to the migration of contaminant particles. The migration reduces the probability of particles to reach the sealing and bearing contacts.
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| 8. |
- Berglund, Kim, et al.
(författare)
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Predicting boundary friction of aging limited slip differentials
- 2014
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Ingår i: Journal of tribology. - : ASME International. - 0742-4787 .- 1528-8897. ; 137:1
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Tidskriftsartikel (refereegranskat)abstract
- The prediction of friction is a challenge for scientists and engineers in a wide variety of applications in industry today. One such an application is the limited slip differential. The friction characteristics of the wet clutch are central to the performance of the limited slip differential system. Frictional changes with aging of the limited slip differential affect both the torque transfer accuracy and the tendencies to vibrations and noise generation due to stick-slip or shudder. Therefore, the objective of this work is to establish a method to predict the frictional changes of aging limited slip differential systems. In this study, a number of experiments were performed to establish a method to predict the changes in boundary friction with time due to aging. Accelerated aging was performed for different sets of operating conditions. Results from the tests were used to establish and verify a model to predict friction increase in limited slip differentials. The method assumes that frictional changes with aging are caused by decreased concentrations of friction modifying additives. The decrease in concentration was assumed to depend on the lubricant bulk temperature according to the Arrhenius equation. The model agreed well with tests performed at operating conditions close to the real operating conditions of the limited slip differential. The developed method can be implemented in a vehicle where it can be used to compensate for frictional changes and to indicate when service should be made.
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| 9. |
- Broitman, Esteban, et al.
(författare)
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Tribological and Nanomechanical Behavior of Liquid Wood
- 2019
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Ingår i: Journal of tribology. - : ASME. - 0742-4787 .- 1528-8897. ; 141:2
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Tidskriftsartikel (refereegranskat)abstract
- During the last decades, there has been an increased interest in the use of lignin-based composites following the ideas of developing green materials for fossil-based raw materials substitution. The biopolymer Arboform is a mixture of lignin, plant fibers, and additives, which is nowadays successfully used in many applications. As a thermoplastic, it can be molded and is therefore also called "liquid wood." In this paper, we report a study comparing the nanomechanical and tribological properties of Arboform (AR), and Aramid-reinforced Arboform (AR-AF) composite biopolymers. The samples were produced in an industrial-scale injection molding machine. Nanoindentation experiments have revealed that, in both series of biopolymer samples, an increase in temperature or a change in the injection direction from 0 deg to 90 deg produces an increase in hardness. On the other hand, Youngs modulus is slightly affected by the increase in temperature, and not affected by the injection angle. Tribological characterization has shown that all samples, except the AR-AF injected at 175 degrees C, present noticeable wear and have a similar friction coefficients mu similar to 0.44-0.49 at Hertzian contact pressures p(0) between 90 and 130 MPa. Interestingly, the reinforced polymer produced at 175 degrees C shows no wear and low friction of mu similar to 0.19 at p(0)=90 MPa. Our results show that the reinforced Arboform biopolymers are a good candidate to replace other polymers in many mechanical and tribological applications.
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| 10. |
- Cabanettes, Frédéric, 1982-, et al.
(författare)
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Influence of Minimum Quantity Lubrication on Friction Characterizing Tool–Aluminum Alloy Contact
- 2016
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Ingår i: Journal of tribology. - New York : ASME Press. - 0742-4787 .- 1528-8897. ; 138:2
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Tidskriftsartikel (refereegranskat)abstract
- The possibility to reduce the amount of cutting fluids from machining processes is actively studied by the industrials and researchers. Minimum Quantity Lubrication (MQL) is a solution towards cutting fluids reduction. This article investigates the consequences on friction coefficient induced by the use of MQL. A tribometer is used in order to simulate experimentally the tribological conditions encountered during machining. As the cutting speed increases a lower amount of oil is deposited on the rough surfaces. Depending on the MQL operating conditions and sliding velocities it is plausible to reach starvation by leaving the real rough contact partly dry. A model computing a starvation percentage by filling an estimated oil amount in a deformed topography correlates with the experimental results. © 2015 by ASME
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