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Sahlin, Fredrik
Publications (10 of 16) Show all publications
Sahlin, F., Larsson, R., Almqvist, A., Lugt, P. & Marklund, P. (2010). A mixed lubrication model incorporating measured surface topography: Part 1: theory of flow factors (ed.). Paper presented at . Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, 224(4), 335-351
Open this publication in new window or tab >>A mixed lubrication model incorporating measured surface topography: Part 1: theory of flow factors
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2010 (English)In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 224, no 4, p. 335-351Article in journal (Refereed) Published
Abstract [en]

A mixed lubrication model that permits real three-dimensional surface topography as input is developed. The theory of computing flow factors within the model is presented, and with a following paper (Part 2) the method of measuring and adapting the surface roughness, and model validation through flow measurements and application to a bearing is shown. A contact mechanics model is used to calculate the elastoplastic displacement of a periodic topography signal. A method based on homogenization is used to calculate flow factors for all lubrication regimes. The flow factors are compared with the Patir and Cheng method. Results indicate that the two methods compare well for longitudinal roughness lay, but differ significantly for a cross-patterned surface roughness due to the more complete flow description of the current model.

Keywords
Engineering mechanics - Fluid mechanics, Teknisk mekanik - Strömningsmekanik
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-8575 (URN)10.1243/13506501JET658 (DOI)000277675800003 ()2-s2.0-77951134519 (Scopus ID)71772350-4677-11df-a0f4-000ea68e967b (Local ID)71772350-4677-11df-a0f4-000ea68e967b (Archive number)71772350-4677-11df-a0f4-000ea68e967b (OAI)
Note
Validerad; 2010; Bibliografisk uppgift: SAGE Best Paper Award, 2010; 20100412 (rola)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Sahlin, F., Larsson, R., Marklund, P., Almqvist, A. & Lugt, P. (2010). A mixed lubrication model incorporating measured surface topography: Part 2: roughness treatment, model validation, and simulation (ed.). Paper presented at . Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, 224(4), 353-365
Open this publication in new window or tab >>A mixed lubrication model incorporating measured surface topography: Part 2: roughness treatment, model validation, and simulation
Show others...
2010 (English)In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 224, no 4, p. 353-365Article in journal (Refereed) Published
Abstract [en]

A mixed lubrication flow factor model that permits real three-dimensional surface topography as input has been developed. Part 1 gives the theory of computing flow factors within the model. In this article, a method of adapting the measured surface topography signal to suit the numerical models is developed and presented in detail. The mixed lubrication model is validated through flow measurements for three different rough surface test specimens. Simulation of a hydrodynamic bearing was conducted and the results are presented in terms of pressure distributions and Stribeck curves covering all lubrication regimes. The results indicate that the model may be an efficient and accurate engineering design and research tool for tribological devices operating in all lubrication regimes.

Keywords
Engineering mechanics - Fluid mechanics, Teknisk mekanik - Strömningsmekanik
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-12178 (URN)10.1243/13506501JET659 (DOI)000277675800004 ()2-s2.0-77951115678 (Scopus ID)b4562ad0-4678-11df-a0f4-000ea68e967b (Local ID)b4562ad0-4678-11df-a0f4-000ea68e967b (Archive number)b4562ad0-4678-11df-a0f4-000ea68e967b (OAI)
Note
Validerad; 2010; Bibliografisk uppgift: SAGE Best Paper Award, 2010; 20100412 (rola)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Almqvist, A., Larsson, R. & Sahlin, F. (2009). Development of a lubrication simulation model (ed.). In: (Ed.), (Ed.), Svenska mekanikdagarna: Södertälje 2009. Paper presented at Svenska mekanikdagar 2009 : 15/06/2009 - 17/06/2009 (pp. 74). Stockholm: Svenska nationalkommittén för mekanik
Open this publication in new window or tab >>Development of a lubrication simulation model
2009 (English)In: Svenska mekanikdagarna: Södertälje 2009, Stockholm: Svenska nationalkommittén för mekanik , 2009, p. 74-Conference paper, Meeting abstract (Other academic)
Place, publisher, year, edition, pages
Stockholm: Svenska nationalkommittén för mekanik, 2009
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-40554 (URN)fbad3170-9dfa-11de-a77c-000ea68e967b (Local ID)fbad3170-9dfa-11de-a77c-000ea68e967b (Archive number)fbad3170-9dfa-11de-a77c-000ea68e967b (OAI)
Conference
Svenska mekanikdagar 2009 : 15/06/2009 - 17/06/2009
Note
Godkänd; 2009; 20090910 (ysko)Available from: 2016-10-03 Created: 2016-10-03 Last updated: 2018-01-14Bibliographically approved
Marklund, P., Sahlin, F. & Larsson, R. (2009). Modelling and simulation of thermal effects in wet clutches operating under boundary lubrication conditions (ed.). Paper presented at . Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, 223(8), 1129-1141
Open this publication in new window or tab >>Modelling and simulation of thermal effects in wet clutches operating under boundary lubrication conditions
2009 (English)In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 223, no 8, p. 1129-1141Article in journal (Refereed) Published
Abstract [en]

Wet clutches are frequently used in the drive trains of many modern vehicles. The behaviour of the clutches influences the behaviour of the whole drive train and therefore of the whole vehicle. The design of the clutch is very important because it operates in cooperation with the other parts of the drive train. The clutch also often has to work in the lubricant present in the transmission. To optimize the clutch for an application, properties such as disc geometry, materials, friction disc surface, and engagement axial force can be varied when designing the clutch. Today, the design process involves much testing, which is expensive and time consuming. There are no good hand-book solutions or engineering tools available, hence the designer has to be very experienced and often use trial and error methods in order to end up with a working clutch for an application.A simulation model is developed in this article, which in combination with a simple measurement technique for measuring the boundary lubrication friction coefficient is used to estimate temperature and torque transfer for a wet clutch working under limited slip conditions. The developed simulation model can be used as a design tool for wet clutches. The approach developed in this article can be used to investigate torque behaviour for wet clutches that have not been designed and is, therefore, suitable to use when optimizing the performance of a new clutch. The model includes fluid dynamics, contact mechanics, and temperature computations in the fluid film between the friction disc and the separator disc. Temperature computations in the clutch discs are also included in the model. The fluid dynamics calculations use homogenized flow factors to enable simulations of flow on a coarser grid and still include all surface roughness effects. The temperature distribution in the film in the sliding interface is approximated as a polynomial of the second order. The heat transfer in the grooves of the friction discs is solved by means of an equilibrium equation that includes radial cooling flow effects because of centrifugal flows. The temperature in the friction disc and separator disc is obtained from the solution of the full three-dimensional energy equation in polar cylindrical coordinates.The model is validated by measurements made in a test rig and good agreement between measurements and simulations is obtained, both with regard to temperature and transfered torque.The use of this model can reduce the time needed to develop a limited slip wet clutch application since the systematic way of finding the optimal clutch design will be more efficient than the often used Edisonian trial and error approach.

National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-15103 (URN)10.1243/13506501JET563 (DOI)000272949400003 ()2-s2.0-77149125939 (Scopus ID)e908b530-d414-11de-bae5-000ea68e967b (Local ID)e908b530-d414-11de-bae5-000ea68e967b (Archive number)e908b530-d414-11de-bae5-000ea68e967b (OAI)
Note
Validerad; 2009; 20091118 (parmar)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Sahlin, F. (2008). Lubrication, contact mechanics and leakage between rough surfaces (ed.). (Doctoral dissertation). Paper presented at . Luleå: Luleå tekniska universitet
Open this publication in new window or tab >>Lubrication, contact mechanics and leakage between rough surfaces
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Mechanical components with interacting surfaces are central in everyday life. Interactions between surfaces, such as the sliding, rolling and bouncing, on one another may be found everywhere. These surfaces are often required to withstand severe conditions resulting in wear, which may ultimately lead to failure. To reduce the risk of failure, a lubricant is often added between the surfaces that partly or completely separates the surfaces from direct mechanical contact. The physical conditions existing between two interacting surfaces are complex, with parameters such as colliding surface asperities, mechanical deformations, lubricant flow transport and chemical reactions. A combination of all these parameters will affect the output parameters of interest for the consumer, e.g., friction, wear rate and leakage a.k.a. energy efficiency, service life and environmental impact in other terminologies. To design components with improved performance, more knowledge of the tribological (interacting surfaces) interface is needed both from experimental and theoretical viewpoint. In this work, various aspects of the lubrication between surfaces were theoretically simulated, to gain a greater understanding of tribological interfaces and to develop tribological design tools. When the interacting surfaces are separated by a thick fluid film, the influence from surface asperities is small and the surfaces can be treated as if they were smooth. For this type of lubrication condition, Computational Fluid Dynamics (CFD) is used to investigate the influence from a surface pattern applied onto one of the two interacting surfaces. It is shown that parallel surfaces generate a pressure increase originating from fluid inertia between the surfaces as a result of introducing the micro-pattern. In some lubricant films low pressures may occur at region of an expanding gap between the interacting surfaces. A liquid lubricant can only resist small tensile stresses until it cavitates into a mixture of gas and liquid. Hence, a cavitation model is presented that accommodates for an arbitrary lubricant compressibility. It was found that the geometry and lubricant starvation at the inlet of the tribological interface, as well as the compressibility model, are significant factors for load carrying capacity of the lubricant when cavitation is considered. For thin lubricant films, surface roughness becomes important in the performance of the tribological interface. Direct numerical simulations of the interface with measured surface roughness requires too many degrees of freedoms to be accounted for in computations. Therefore, a homogenization method is used, where the gap between the surfaces in the tribological interface may be modeled by two scales; a global geometry scale and a local surface roughness scale, where the method enables the two scales to be treated separately. A method to generate dimensionless flow factors to compensate for the surface roughness is developed. The flow factors, once solved for a particular surface, can be used to compensate for the surface roughness in any smooth global problem for any film thickness. It is shown that the cumulative distribution of heights of the surface roughness (bearing ratio) completely determines the lubricating conditions for two-dimensional roughness and that the effects of the roughness increase as the film thickness decreases. By further decreasing the film thickness, into the mixed lubrication regime, the surface asperities will start to collide and take over some of the load carried by the fluid. The surface roughness has a crucial influence on the performance in this regime. A model to simulate the linear elastic perfectly plastic deformation of rough surfaces is developed. The model is based on FFT to improve the computational efficiency. Thus, the model is suitable to accept periodic input, which is a demand for the homogenization method previously mentioned. To consider both the asperity collisions and the hydrodynamic effects, a mixed lubrication model is developed capable of using three-dimensional measured surface roughness as input. The model is based on computing flow factors that carry the effects of a specific surface roughness in all regimes from completely separated surfaces to dry contact and full asperity deformation. An efficient simulation procedure is described, from importing the roughness measurement data to the simulation of a complete application. Linear elastic perfectly plastic displacement is considered and a homogenization method for fluid transport is used. The mixed lubrication model is validated through experiments with good correlation. It is shown that real deterministic surface roughness measurements may be efficiently imported and used in the model. Also, any global geometry may be simulated in any regime once the rough surface flow factors have been calculated. An important property of a tribological interface, especially in seals, is the flow or leakage through the contact. In many applications, leakage is crucial in terms of environmental impact. By using the mixed lubrication model previously developed, leakage through a range of measured elastomer and seal surfaces is investigated (see cover figure). It is found that the mixed lubrication model permits an efficient analysis of the leakage, even though real measured surface roughness was used as input. Moreover, the valley roughness parameters are shown to be important in characterizing the leakage and the peak roughness parameters are important for the percolation threshold.

Place, publisher, year, edition, pages
Luleå: Luleå tekniska universitet, 2008. p. 227
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544 ; 2008:26
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-17988 (URN)63abeb70-1dcf-11dd-8384-000ea68e967b (Local ID)63abeb70-1dcf-11dd-8384-000ea68e967b (Archive number)63abeb70-1dcf-11dd-8384-000ea68e967b (OAI)
Note

Godkänd; 2008; 20080509 (ysko)

Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-02-26Bibliographically approved
Sahlin, F., Almqvist, A., Larsson, R. & Glavatskih, S. (2007). A cavitation algorithm for arbitrary lubricant compressibility (ed.). Paper presented at . Tribology International, 40(8), 1294-1300
Open this publication in new window or tab >>A cavitation algorithm for arbitrary lubricant compressibility
2007 (English)In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 40, no 8, p. 1294-1300Article in journal (Refereed) Published
Abstract [en]

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

National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-15815 (URN)10.1016/j.triboint.2007.02.009 (DOI)000246751400009 ()2-s2.0-34247521904 (Scopus ID)f5fcfdb0-9f45-11dc-9810-000ea68e967b (Local ID)f5fcfdb0-9f45-11dc-9810-000ea68e967b (Archive number)f5fcfdb0-9f45-11dc-9810-000ea68e967b (OAI)
Note
Validerad; 2007; 20071130 (pirkko)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Almqvist, A., Sahlin, F., Larsson, R. & Glavatskikh, S. (2007). On the dry elasto-plastic contact of nominally flat surfaces (ed.). Paper presented at . Tribology International, 40(4), 574-579
Open this publication in new window or tab >>On the dry elasto-plastic contact of nominally flat surfaces
2007 (English)In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 40, no 4, p. 574-579Article in journal (Refereed) Published
Abstract [en]

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

National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-13243 (URN)10.1016/j.triboint.2005.11.008 (DOI)000243576700002 ()2-s2.0-33845202503 (Scopus ID)c6dcb050-8d55-11db-8975-000ea68e967b (Local ID)c6dcb050-8d55-11db-8975-000ea68e967b (Archive number)c6dcb050-8d55-11db-8975-000ea68e967b (OAI)
Note
Validerad; 2007; 20061216 (ysko)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Sahlin, F., Almqvist, A., Glavatskih, S. & Larsson, R. (2007). Rough surface flow factors in full film lubrication based on a homogenization technique (ed.). Paper presented at . Tribology International, 40(7), 1025-1034
Open this publication in new window or tab >>Rough surface flow factors in full film lubrication based on a homogenization technique
2007 (English)In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 40, no 7, p. 1025-1034Article in journal (Refereed) Published
Abstract [en]

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

National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-11294 (URN)10.1016/j.triboint.2006.09.007 (DOI)000246054100002 ()2-s2.0-33947130619 (Scopus ID)a3b89940-7f44-11dc-965a-000ea68e967b (Local ID)a3b89940-7f44-11dc-965a-000ea68e967b (Archive number)a3b89940-7f44-11dc-965a-000ea68e967b (OAI)
Note
Validerad; 2007; 20071020 (rola)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Sahlin, F., Almqvist, A., Glavatskih, S. & Larsson, R. (2005). A cavitation algorithm for arbitrary lubricant compressibility (ed.). In: (Ed.), (Ed.), Proceedings of the World Tribology Congress III - 2005: presented at ..., September 12 - 16, 2005, Washington, DC. Paper presented at World Tribology Congress : 12/09/2005 - 16/09/2005 (pp. 541-542). New York: American Society of Mechanical Engineers, Paper no 63940
Open this publication in new window or tab >>A cavitation algorithm for arbitrary lubricant compressibility
2005 (English)In: Proceedings of the World Tribology Congress III - 2005: presented at ..., September 12 - 16, 2005, Washington, DC, New York: American Society of Mechanical Engineers , 2005, Vol. Paper no 63940, p. 541-542Conference paper, Published paper (Refereed)
Abstract [en]

A general cavitation algorithm is presented that accommodates for an arbitrary density-pressure relation. Here it is possible to model the compressibility of the lubricant in such way the density-pressure relation is realistic from sub-cavity to high pressure regions respectively. The algorithm preserves mass continuity which is of importance when inter-asperity cavitation of rough surfaces is considered. Results with this algorithm for different density-pressure relations are presented and discussed.

Place, publisher, year, edition, pages
New York: American Society of Mechanical Engineers, 2005
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-31413 (URN)10.1115/WTC2005-63940 (DOI)5965b160-c0d7-11db-834c-000ea68e967b (Local ID)5965b160-c0d7-11db-834c-000ea68e967b (Archive number)5965b160-c0d7-11db-834c-000ea68e967b (OAI)
Conference
World Tribology Congress : 12/09/2005 - 16/09/2005
Note
Godkänd; 2005; 20070217 (rola)Available from: 2016-09-30 Created: 2016-09-30 Last updated: 2018-01-14Bibliographically approved
Almqvist, A., Sahlin, F. & Larsson, R. (2005). An Abbott curve based rough surface contact mechanics approach (ed.). In: (Ed.), (Ed.), Proceedings of the World Tribology Congress III - 2005: presented at ..., September 12 - 16, 2005, Washington, DC. Paper presented at World Tribology Congress : 12/09/2005 - 16/09/2005 (pp. 397-398). New York: American Society of Mechanical Engineers, Paper no 64038
Open this publication in new window or tab >>An Abbott curve based rough surface contact mechanics approach
2005 (English)In: Proceedings of the World Tribology Congress III - 2005: presented at ..., September 12 - 16, 2005, Washington, DC, New York: American Society of Mechanical Engineers , 2005, Vol. Paper no 64038, p. 397-398Conference paper, Published paper (Refereed)
Abstract [en]

In this way all the height information of the surface profile is preserved and not only a few parameters, like Ra, Rq, Rz, Rsk, etc. The aim of this work is to investigate how classes of surfaces based on a single Abbott curve perform in terms of contact mechanical parameters like the real area of contact. The result shows that surfaces taken from a class of random surfaces generated from a specific Abbott curve behaves similar in a contact mechanics simulation. That is, the distribution of for example the real area of contact within such a class is compact, having a small deviation from its mean.This implies that it is possible to simulate classes of surfaces based on Abbott curves and to use the results to predict contact mechanical properties of real surface topographies.

Place, publisher, year, edition, pages
New York: American Society of Mechanical Engineers, 2005
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-35874 (URN)10.1115/WTC2005-64038 (DOI)32844468374 (Scopus ID)a949e030-65d6-11dc-8a3f-000ea68e967b (Local ID)a949e030-65d6-11dc-8a3f-000ea68e967b (Archive number)a949e030-65d6-11dc-8a3f-000ea68e967b (OAI)
Conference
World Tribology Congress : 12/09/2005 - 16/09/2005
Note
Godkänd; 2005; 20070918 (ysko)Available from: 2016-09-30 Created: 2016-09-30 Last updated: 2018-01-14Bibliographically approved
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