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  • 1.
    Almqvist, Andreas
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Dasht, Johan
    Glavatskih, Sergei
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Persson, Lars-Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Sahlin, Fredrik
    Wall, Peter
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Homogenization of the Reynolds equation2005Report (Other academic)
  • 2.
    Almqvist, Andreas
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Glavatskih, Sergei
    Larsson, Roland
    Marklund, Pär
    Sahlin, Fredrik
    Dasht, Johan
    Persson, Lars-Erik
    Wall, Peter
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Homogenization of Reynolds equation2005Report (Other academic)
  • 3.
    Berg, Sven
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Häggblad, Hans-Åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Frictional behaviour of CaCO3 powder compacts2012In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 228, p. 429-434Article in journal (Refereed)
    Abstract [en]

    During powder compaction processes friction has an influence on the final shape and properties of components. It is therefore important to understand how the friction influences the compaction process. Since detailed friction measurements of the powder compact-tool interface are rare, simulation models of the powder compaction process often involve a more accurate description of the frictional behaviour. This limits the accuracy of the simulated results. More accurate numerical models can give improved results, especially in regards to the evolution of density and its distribution within the powder compacts.This study is as a step towards more advanced friction models for powder compaction simulations. A universal tribometer has been used to investigate the frictional behaviour of contact interfaces between a carbide counter surface and CaCO3 powder compacts with different densities. Both static and dynamic frictional properties were measured in a variety of conditions to build a fundamental foundation for friction modelling in powder compaction simulations.The results show that increasing the powder compact density decreases the dynamic friction coefficient but that the static friction coefficient remains fairly constant. The measured friction coefficient can be used to improve the simulation of a powder compact process. Also investigated is the change in friction coefficient that occurs in the compaction process when the surfaces are worn such that loose powder appears in the interface between the tool and the powder compact. This behaviour is important to take into account to accurately describe the compaction process.

  • 4. Berglund, Kim
    et al.
    Larsson, Roland
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Lubricant ageing effects on wet clutch friction characteristics2009Conference paper (Refereed)
  • 5.
    Berglund, Kim
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Marklund, Pär
    Larsson, Roland
    Lubricant ageing effects on the friction characteristics of wet clutches2010In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 224, no 7, p. 639-647Article in journal (Refereed)
    Abstract [en]

    The friction characteristics and performance of wet clutches have been investigated by several authors. Studies have also been made to understand the frictional performance during the service life of the clutch system. However, most lifetime studies have been conducted for systems with paper-based friction material so that systems using sintered bronze friction material remain largely unexplored. To study the friction performance of how these systems can vary over time, the friction characteristics for a clutch system using lubricants aged in three different ways were compared. The effects on friction characteristics resulting from oxidation of the lubricant, reduced additive concentration, and ageing under real operating conditions in a wet clutch test rig were studied. The oxidation effects on friction characteristics were examined using a modified waterless turbine oil oxidation stability test on a fully formulated lubricant. Five oxidation time periods from 48 to 408 h were investigated. For each period of oxidation, a friction performance test was run using a pin-on-disc machine. The ageing carried out in a wet clutch test rig is a standard test of a wet clutch systems manufacturer which is used in order to verify that an oil-friction disc combination will last the full service life of the specific application. This test gives a realistic ageing process similar to that in a wet clutch in a field test. Under boundary-lubricated conditions, additives are vital to the performance of wet clutches. Therefore, the effect of reducing the additive concentration in the oil was also studied, in the range of 10 to 100 per cent of the original additive package used in the fully formulated wet clutch lubricant. Results showed that a general friction increase can be observed for oxidation, additive reduction, and test rig ageing. It was also concluded that different methods of simulating the wet clutch ageing process differ and cannot be directly correlated with each other

  • 6.
    Berglund, Kim
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Olsson, Richard
    Borgwarner TTS.
    Evaluating lifetime performance of limited slip differentials2014In: Lubrication Science, ISSN 0954-0075, E-ISSN 1557-6833, Vol. 26, no 3, p. 189-201Article in journal (Refereed)
    Abstract [en]

    Extensive research has been performed regarding wet clutch function and performance. Although wet clutches are used in both automatic transmissions and limited slip differentials in cars, most research has been performed for wet clutches incorporated in automatic transmissions. The operating conditions of wet clutches in automatic transmissions differ from the operating conditions of the wet clutches used in limited slip differentials. Therefore, a method and a test bench to use in the investigation of the degradation of limited slip differentials were developed in this work. The typical operating conditions of the limited slip differential and the differences compared with wet clutches incorporated in automatic transmissions were also addressed. Tests performed showed that the developed test bench and method can be used to address differences in frictional response over time for different types of operating condition

  • 7.
    Berglund, Kim
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Olsson, Richard
    Haldex Traction Systems AB, Borgwarner TTS.
    Predicting boundary friction of aging limited slip differentials2014In: Journal of tribology, ISSN 0742-4787, E-ISSN 1528-8897, Vol. 137, no 1, article id 12101Article in journal (Refereed)
    Abstract [en]

    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.

  • 8.
    Berglund, Kim
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Marklund, Pär
    Larsson, Roland
    Pach, Mayte
    Statoil Lubricants R&D.
    Olsson, Richard
    Haldex Traction AB.
    Wet clutch degradation monitored by lubricant analysis2010In: SAE technical paper series, ISSN 0148-7191, no 2010-01-2232Article in journal (Refereed)
    Abstract [en]

    In the competitive market of the car industry today, companies need to continuously strive to optimize the performance, price and environmental properties of their products in order to survive. Wet clutches, as parts of transmission components of passenger cars are no exception. An understanding of how the wet clutch system functions and fails is necessary to optimize price and service life. The friction characteristics of the wet clutch system are determined by lubricant-surface interactions in the contact between the friction discs. Wet clutch failure can often be associated with the deterioration of friction characteristics which eventually leads to stick-slip or shudder. Consequently, knowledge of why and of how friction characteristics change over time is of the outermost significance to enable the understanding and prediction of wet clutch performance. As the lubricant is an essential component of the wet clutch system, lubricant ageing is a factor of importance. Oxidation, thermal degradation, shearing, additive degradation and water contamination could all be considered to influence lubricant ageing. The aim of this work was therefore to find suitable ways of measuring the remaining useful life of wet clutch lubricants and to correlate changes in friction characteristics with changes in lubricant properties. Both field trials and measurements in a wet clutch test rig were performed. Viscosity, acid number, additive degradation, water contamination, particle content and metal content were measured for the lubricant as it degraded. Particle content results showed a rapid increase early in the ageing process. However, as ageing progressed particle levels actually decreased and this was probably a result of particles slowly grinded between contacting surfaces. On the other hand, metal content increased as ageing progressed, which could indicate slowly progressing wear. Water levels were found to be higher in field trials than in lubricants used in wet clutch test rigs. It is concluded that this was due to the severe and accelerated operating conditions of the wet clutch test rig.

  • 9.
    Berglund, Kim
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Marklund, Pär
    Larsson, Roland
    Pach, Mayte
    Statoil Lubricants R&D.
    Olsson, Richard
    Haldex Traction AB.
    Wet clutch degradation monitored by lubricant analysis2010In: SAE 2010 Powertrains, Fuels and Lubricants Meeting: October 25 - 27, 2010, San Diego, California, USA ; [papers], Warrendale, Pa: Society of Automotive Engineers, Incorporated , 2010Conference paper (Other academic)
    Abstract [en]

    In the competitive market of the car industry today, companies need to continuously strive to optimize the performance, price and environmental properties of their products in order to survive. Wet clutches, as parts of transmission components of passenger cars are no exception. An understanding of how the wet clutch system functions and fails is necessary to optimize price and service life. The friction characteristics of the wet clutch system are determined by lubricant-surface interactions in the contact between the friction discs. Wet clutch failure can often be associated with the deterioration of friction characteristics which eventually leads to stick-slip or shudder. Consequently, knowledge of why and of how friction characteristics change over time is of the outermost significance to enable the understanding and prediction of wet clutch performance. As the lubricant is an essential component of the wet clutch system, lubricant ageing is a factor of importance. Oxidation, thermal degradation, shearing, additive degradation and water contamination could all be considered to influence lubricant ageing. The aim of this work was therefore to find suitable ways of measuring the remaining useful life of wet clutch lubricants and to correlate changes in friction characteristics with changes in lubricant properties. Both field trials and measurements in a wet clutch test rig were performed. Viscosity, acid number, additive degradation, water contamination, particle content and metal content were measured for the lubricant as it degraded. Particle content results showed a rapid increase early in the ageing process. However, as ageing progressed particle levels actually decreased and this was probably a result of particles slowly grinded between contacting surfaces. On the other hand, metal content increased as ageing progressed, which could indicate slowly progressing wear. Water levels were found to be higher in field trials than in lubricants used in wet clutch test rigs. It is concluded that this was due to the severe and accelerated operating conditions of the wet clutch test rig.

  • 10.
    Berglund, Kim
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Lundh, Henrik
    BorgWarner TorqTransfer Systems, Landskrona.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Prediction of driveline vibrations caused by ageing the limited slip coupling2016In: Proceedings of the Institution of mechanical engineers. Part D, journal of automobile engineering, ISSN 0954-4070, E-ISSN 2041-2991, Vol. 230, no 12, p. 1687-1698Article in journal (Refereed)
    Abstract [en]

    The prediction of the wet-clutch service life still remains a challenge for scientists and engineers. Previous research has shown the significance of the wet-clutch friction characteristics on the driveline dynamics. To avoid driveline vibrations an increasing friction coefficient with increasing sliding speed is desirable. Consequently, prediction of the occurrence of driveline vibrations relies on a detailed knowledge of how the friction characteristics are affected by wet-clutch degradation, as well as an understanding of the driveline dynamics. Wet clutches are used in both automatic transmissions and all-wheel-drive systems in cars, where they are referred to as limited slip couplings by manufacturers. Wet clutches used in automatic transmissions are subjected to high slip levels, but for very limited time periods. In all-wheel-drive systems, where the limited slip coupling can be used to control the torque transfer to, for example, the rear wheels, the slip levels are low but continuous. Most wet-clutch research has been performed for clutches in automatic transmissions and not for clutches used in all-wheel-drive systems. Thus, a simulation model was developed to evaluate how different operating conditions of the limited slip coupling influence degradation of the friction characteristics and the tendencies towards driveline vibrations. First, the changes in the friction characteristics with the time of ageing are simulated. The friction characteristics after ageing are used as the input to a simplified driveline model, which is used to evaluate the occurrence of vibrations. It is shown how the developed simulation model can be used as an efficient tool for engineers. The developed simulation model can be used to predict how the operating conditions for the limited slip coupling influence degradation of the friction characteristics.

  • 11.
    Björling, Marcus
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Habchi, W.
    Lebanese American University, Department of Industrial and Mechanical Engineering, Byblos.
    Bair, S.
    G.W. Woodruff School of Mechanical Engineering, Centre for High Pressure Rheology, Georgia Institute of Technology, Atlanta.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Towards the true prediction of EHL friction2013In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 66, p. 19-26Article in journal (Refereed)
    Abstract [en]

    The capability to predict elastohydrodynamic film-thickness and friction from primary measurements of transport properties of liquid has been an elusive goal for tribologists for 50 years. Most comparisons between predictions and experiments involve some amount of tuning of the model in order to match the experimental results. In true prediction, this cannot be done since there are normally no experimental results to compare to. Primary measurements of lubricant transport properties of Squalane were performed, and used in a numerical friction prediction model. Afterwards, friction was measured in a ball-on-disc tribotester. No tuning of the lubricant properties, model or test setup were applied. The current work on EHL-friction is therefore a true representation of the current level of EHL-friction prediction.

  • 12.
    Björling, Marcus
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Habchi, Wassim
    Department of Industrial and Mechanical Engineering, Lebanese American University, Byblos, Lebanese American University, Department of Industrial and Mechanical Engineering, Byblos.
    Bair, Scott
    G.W. Woodruff School of Mechanical Engineering, Centre for High Pressure Rheology, Georgia Institute of Technology, Atlanta.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Friction reduction by thin-layer thermal insulation in elastohydrodynamic contacts2016Conference paper (Refereed)
  • 13.
    Björling, Marcus
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Habchi, Wassim
    Department of Industrial and Mechanical Engineering, Lebanese American University, Byblos.
    Bair, Scott
    Georgia Institute of Technology, Centre for High Pressure Rheology, G.W. Woodruff School of Mechanical Engineering, Atlanta.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Friction reduction in elastohydrodynamic contacts by thin-layer thermal insulation2014In: Tribology letters, ISSN 1023-8883, E-ISSN 1573-2711, Vol. 53, no 2, p. 477-486Article in journal (Refereed)
    Abstract [en]

    Reducing friction is of utmost importance to improve efficiency and lifetime of many products used in our daily lives. Thin hard coatings like diamond-like carbon (DLC) have been shown to reduce friction in full-film-lubricated contacts. In this work, it is shown that contrarily to common belief, the friction reduction stems mainly from a thermal phenomenon and not only a chemical/surface interaction one. It is shown that a few micrometer-thin DLC coating can significantly influence the thermal behavior in a lubricated mechanical system. The presented simulations, validated by experiments, show that applying a thin DLC coating to metal surfaces creates an insulating effect that due to the increased liquid lubricant film temperature at the center of the contact, locally reduces lubricant viscosity and thus friction. The results of the investigation show that the addition of thin insulating layers could lead to substantial performance increases in many applications. On a component level, the contact friction coefficient in some common machine components like gears, rolling element bearings, and cam followers can potentially be reduced by more than 40 %. This will most likely open up the way to new families of coatings with a focus on thermal properties that may be both cheaper and more suitable in certain applications than DLC coatings

  • 14.
    Björling, Marcus
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Habchi, Wassim
    Lebanese American University, Department of Industrial and Mechanical Engineering, Byblos.
    Bair, Scott
    G.W. Woodruff School of Mechanical Engineering, Centre for High Pressure Rheology, Georgia Institute of Technology, Atlanta.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Towards the true prediction of EHL friction2013Conference paper (Refereed)
  • 15.
    Björling, Marcus
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Habchi, Wassim
    Bair, Scott
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Warm carbon coat reduces friction2014In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 505, no 7483, p. 264-Article in journal (Other academic)
    Abstract [en]

    A coating material made of carbon reduces friction not just by providing a slippery surface, but also by keeping the points of contact warm. Marcus Björling at Luleå University of Technology in Sweden and his team coated steel balls with ``diamond-like-carbon'' - a material in which carbon atoms have a bonding pattern similar to that of diamond. They rolled the balls against a metal disk with an oil lubricant in between, and showed that the carbon coating acts as an insulator, lowering the viscosity of the lubricant and thus reducing the fricion between the ball and the disk. These findings could encourage the development of lubricant coatings made from insulating materials

  • 16.
    Björling, Marcus
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Isaksson, Patrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    The influence of DLC coating on EHL friction coefficient2012In: Tribology letters, ISSN 1023-8883, E-ISSN 1573-2711, Vol. 47, no 2, p. 285-294Article in journal (Refereed)
    Abstract [en]

    High hardness, high elastic modulus, low friction characteristics, high wear and corrosion resistance, chemical inertness, and thermal stability are factors that make diamond-like carbon (DLC) coatings the subject of many studies. For the same reasons they also seem suitable for use in, amongst others, machine components and cutting tools. While most studies in the literature focus on the influence of coatings on wear and friction in boundary lubrication and pure sliding contacts, few studies can be found concerning rolling and sliding elastohydrodynamic lubrication (EHL) friction, especially in the mixed and full film regime. In this article tests are carried out in a Wedeven Associates Machine tribotester where an uncoated ball and disc pair is compared to the case of coated ball against uncoated disc, coated disc against uncoated ball, and coated disc against coated ball. The tests are conducted at two different temperatures and over a broad range of slide-to-roll ratios and entrainment speeds. The results are presented as friction maps as introduced in previous work (Björling et al. in J Eng Tribol 225(7):671, 2011). Furthermore a numerical simulation model is developed to investigate if there is a possibility that the hard, thin DLC coating is affecting the friction coefficient in an EHL contact due to thermal effects caused by the different thermal properties of the coating compared to the substrate. The experimental results show a reduction in friction coefficient in the full film regime when DLC-coated surfaces are used. The biggest reduction is found when both surfaces are coated, followed by the case when either ball or disc is coated. The thermal simulation model shows a substantial increase of the lubricant film temperature compared to uncoated surfaces when both surfaces are coated with DLC. The reduction in friction coefficient when coating either only the ball or the disc are almost the same, lower than when coating both the surfaces but still higher than the uncoated case. The findings above indicate that it is reasonable to conclude that thermal effects are a likely cause for the decrease in coefficient of friction when operating under full film conditions, and in the mixed lubrication regime when DLC-coated surfaces are used

  • 17.
    Björling, Marcus
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    The effect of DLC coating thickness on elstohydrodynamic friction2014In: Tribology letters, ISSN 1023-8883, E-ISSN 1573-2711, Vol. 55, no 2, p. 353-362Article in journal (Refereed)
    Abstract [en]

    The application of surface coatings has been shown to reduce friction in elastohydrodynamic lubrication (EHL), not only in the mixed and boundary regime when asperity interactions occur, but also in the full film regime. Several studies suggest that the full film friction reduction is due to a violation of the no-slip boundary condition and thus slip is taking place between the solid and the liquid. Another hypothesis proposes that the full film friction reduction is due to the low thermal conductivity of diamond-like carbon (DLC) coatings. In this work, two DLC coatings with the same composition, but different thicknesses, are investigated with uncoated steel specimens as a reference, all with the same surface roughness. Friction tests in a ball-on-disk machine show that both coatings reduce friction compared to the uncoated reference case in full film EHL. The thicker coating is significantly more effective at reducing friction than the thinner one at a maximum friction reduction of 41 % compared to 29 % for the thinner coating. Moreover, contact angle measurements, surface energy measurements, and spreading parameter calculations show no statistically significant differences between the two coatings, suggesting that the friction reduction capabilities of coatings in full film EHL cannot be described by solid-liquid interactions alone. The difference in friction reduction between the specimens in this work is mainly attributed to different thermal properties.

  • 18. Björling, Marcus
    et al.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Marklund, Pär
    Kassfeldt, Elisabet
    EHL friction mapping: the influence of lubricant, roughness, speed and slide to roll ratio2010In: 14th Nordic Symposium on Tribology: NORDTRIB 2010 : Storforsen, Sweden, June 8-11, 2010, Luleå: Luleå tekniska universitet, 2010Conference paper (Refereed)
    Abstract [en]

    A friction test is conducted in a WAM ball on disc test rig. The output from the test is friction coefficient versus entrainment speed and slide-to-roll ratio presented as a 3D friction map. A number of parameters are varied while studying the friction coefficient; surface roughness, base oil viscosity and EP additive package. Entrainment speed, slide to roll ratio and oil temperature are also varied. The results show that the mapping is efficient in showing the different types of friction that may occur in an EHL contact. The results also show that the friction behaviour can be strongly influenced by changing surface roughness as well as base oil viscosity, EP additive content and operating temperature.

  • 19.
    Björling, Marcus
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Kassfeldt, Elisabet
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Elastohydrodynamic lubrication friction mapping: The influence of lubricant, roughness, speed, and slide-to-roll ratio2011In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 225, no 7, p. 671-681Article in journal (Refereed)
    Abstract [en]

    A friction test is conducted in a Wedeven Associates Machine ball-on-disc test rig. The output from the test, friction coefficient versus entrainment speed and slide-to-roll ratio (SRR), is presented as a three-dimensional friction map. A number of parameters are varied while studying the friction coefficient; surface roughness, base oil viscosity, base oil type, and extreme pressure (EP) additive package. Entrainment speed, SRR, and oil temperature are also varied. The results show that the mapping is efficient in showing the different types of friction that may occur in an elasto-hydrodynamic lubrication contact. The results also show that the friction behaviour can be strongly influenced by changing surface roughness as well as base oil viscosity, base oil type, EP additive content, and operating temperature.

  • 20.
    Björling, Marcus
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    On the effect of DLC coating on full film EHL friction2013Conference paper (Refereed)
  • 21.
    Björling, Marcus
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Miettinen, J.
    Group of Tribology and Machine Elements, Department of Materials Science, Tampere University of Technology.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Lehtovaara, A.
    Group of Tribology and Machine Elements, Department of Materials Science, Tampere University of Technology.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    The correlation between gear contact friction and ball on disc friction measurements2015In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 83, p. 114-119Article in journal (Refereed)
    Abstract [en]

    Running experiments with full-size gearboxes from the actual application has the advantage of giving realistic results in terms of power losses. The drawback is extensive costs, lengthy testing, and the difficulty in differentiating between load dependent and load independent losses, and which losses are coming from the gears, seals, bearings or synchronizers. In this work, the correlation between friction measurements conducted in a ball-on-disc machine and friction measurements conducted in a back-to-back gear rig is investigated. The correlation between the gear tests and the ball-on-disc tests were reasonably good in terms of absolute values, and the shape of the friction curves were similar, indicating that the ball-on-disc measurements to a large extent are capturing the behavior of the gear contact

  • 22.
    Björling, Marcus
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Miettinen, Juha
    Group of Tribology and Machine Elements, Department of Materials Science, Tampere University of Technology.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Lehtovaara, Arto
    Group of Tribology and Machine Elements, Department of Materials Science, Tampere University of Technology.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    The correlation between gear contact friction and ball on disc friction measurements2016Conference paper (Refereed)
  • 23.
    Dittes, Nicholas
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Pettersson, Anders
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Mixing Grease with Water2015Conference paper (Other academic)
    Abstract [en]

    The purpose of this paper is to convey a simple and effective method to mix water with grease and verify the homogeneity of the mixture using Karl-Fischer (KF) titration as the analysis tool. This is required to better develop a future water in grease sensor for on-line condition monitoring. This paper will also attempt to investigate how well KF titration functions as a tool for measuring water content in grease. Additional investigations include how the water content varies with time in grease samples open to atmosphere at different temperature. This research verifies a simple grease mixing method and investigates the water transport in water contaminated grease samples.

  • 24.
    Dittes, Nicholas
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Pettersson, Anders
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Lang, Defeng
    SKF Engineering and Research Center, Nieuwegein.
    Lugt, Piet M.
    SKF Engineering and Research Center, Nieuwegein.
    Dielectric Thermoscopy Characterization of Water Contaminated Grease2018In: Tribology Transactions, ISSN 1040-2004, E-ISSN 1547-397X, Vol. 74, no 3, p. 60-73Article in journal (Refereed)
    Abstract [en]

    The temperature dependence on the dielectric properties of water-contaminated grease is investigated in this article. The purpose of this investigation was to identify the dielectric properties that could be measured to differentiate varying levels of water contamination in calcium sulfonate complex (CaS-X) grease with three different test cells with the purpose of eventually developing a grease condition sensor. Measuring the change in dielectric constant over a small temperature change yielded useful estimations of water content and amount of grease where the added water content ranged from 0.22% to about 5.5%. Additionally, other parameters such as incomplete fill/coverage of the sensors were investigated as a prestudy. The results from this set of experiments show that the measurement has potential to be developed into a condition monitoring sensor in the future.

  • 25.
    Dittes, Nicholas
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Sjödahl, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Casselgren, Johan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lugt, Piet M.
    SKF Engineering and Research Center, Nieuwegein.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Pettersson, Anders
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Optical Attenuation Characterization of Water Contaminated Lubricating Grease2018In: Tribology Transactions, ISSN 1040-2004, E-ISSN 1547-397XArticle in journal (Refereed)
    Abstract [en]

    Water contaminated grease samples are investigated with attenuation spectra in the visible and near-infrared (NIR) region in this paper. The purpose of this investigation was to identify a model with optical attenuation spectra such that water content of grease samples could be characterized with a simple measurement setup using common methodology from the field of instrumental chemistry. The ratio between two chosen wavelengths of light appear to approximate water content of grease samples with an acceptable coefficient of determination using a methodology to show what can potentially be done to develop condition monitoring tools. To illustrate the outlined method, a prestudy of grease aging and oxidation levels are also investigated to show that other variables do not significantly change the measurement.

  • 26.
    Fatima, Nowshir
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Holmgren, Allan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Degradation mechanism of water contaminated automatic transmission fluid (ATF) in wet clutch system2013Conference paper (Refereed)
  • 27.
    Fatima, Nowshir
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Holmgren, Allan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Minami, Ichiro
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Degradation Mechanism of Automatic Transmission Fluid by Water as a Contaminant2015In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 229, no 1, p. 74-85Article in journal (Refereed)
    Abstract [en]

    The degradation mechanism of water contaminated Automatic Transmission Fluids (ATF) was experimentally investigated. Water contaminated ATF was tribotested in a full-scale wet clutch test rig to monitor the friction durability during clutch ageing, and was also statically aged in oven to evaluate the interaction of ATF with water. The bulk properties and chemical nature of the ATF were analysed using viscosity measurements, Fourier Transform Infrared Spectroscopy (FTIR) and Thermogravimetric Analysis (TGA). It was shown that water presence in the ATF can increase the mean friction coefficient over a short time period, though in the long term perspective there is a higher loss of mean friction. Phase separation of the water-in-oil emulsion by centrifugation at 20000 rpm made it possible to examine the water phase using infrared 2spectroscopy. The spectroscopic analysis revealed the hydrophilic nature of certain ATF constituents, although the impact of water on the bulk properties like lubricant viscosity and thermal stability was insignificant. The analysis of the tribotests showed that the friction increase for water contamination was a short-term effect and likely due to the interaction between polar surface active additives and water. Even though no significant change has been found for thermal degradation or in bulk properties of the lubricant, the initially changed action of the water soluble additives and generation of high friction resulted in a total deterioration of the clutch performance during long term use.

  • 28.
    Fatima, Nowshir
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Influence of clutch output shaft inertia and stiffness on the performance of the wet clutch2013In: Tribology Transactions, ISSN 1040-2004, E-ISSN 1547-397X, Vol. 56, no 2, p. 310-319Article in journal (Refereed)
    Abstract [en]

    Being a part of the complex mass, spring and damper system in a driveline, the choice of design factors like, output shaft stiffness and inertia of a wet clutch system can influence its performance. The effects of these parameters are experimentally evaluated in this paper. Widely used commercial paper based friction plates with standard steel reaction plates are tested with four different stiffness and inertia combinations in a recently developed wet clutch test rig. A low inertia system in general showed a faster degradation and shorter clutch life for high torsional oscillation. Besides the system becomes more shudder sensitive for lower natural frequency in case of less stiff system. The less stiff output shaft with low inertia showed the highest shudder tendency among the four conditions. The differences in performance for different output shaft conditions become noticeable for numerous clutch engagements or a degraded system. The effect of different shaft design conditions is also illuminated in the topographical analysis of the separators’ surfaces and morphological study of frictional surfaces. This study reveals the influence of both inertia and stiffness not only on shudder sensitivity of the system but also on the clutch frictional performance as well as the overall clutch life.

  • 29.
    Fatima, Nowshir
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Study on the wet clutch friction interfaces for humid lubrication condition2013Conference paper (Refereed)
    Abstract [en]

    The friction influencing parameters also influence the wet clutch sliding surface conditions. The tribofilm formations as well as the chemical and mechanical degradation for frictional interfaces can be different for the choice of the lubricant conditions. The present investigations revealed the effects of water contamination in automatic transmission fluid (ATF) not only on the frictional performance, but also on the friction interfaces. The surface profiles of the tested separator plates, the EDS-SEM (Scanning Electron Microscopy-Energy-dispersive X-ray spectroscopy) analysis of the friction interfaces and optical microscopy for the used friction liners showed the difference in surface morphology, adsorption of additive elements, permeability and porosity for a humid clutch environment.

  • 30.
    Fatima, Nowshir
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Water contamination effect in wet clutch system2013In: Proceedings of the Institution of mechanical engineers. Part D, journal of automobile engineering, ISSN 0954-4070, E-ISSN 2041-2991, Vol. 227, no 3, p. 376-389Article in journal (Refereed)
    Abstract [en]

    Water contamination in wet clutch systems can be a problem since both torque characteristics and wear resistance can be influenced by water presence. The present paper reveals the effect of externally added water on the wet clutch frictional performance. Commercially available standard paper based friction plates and steel separator plates lubricated in commercially available automatic transmission fluid were investigated in a recently developed automated test rig implementing a well confined experimental approach. Frictional response was observed for three different situations with different water amount and water exposure time. There is observed undesirable friction increase with increasing water amount in the system. The rate of increase in friction coefficient does not linearly depend on the amount of added water and this is a noticeable outcome from the common possible water contamination effects like change in lubricant viscosity, inadequate additive performance and weakening of friction material. The more reduced separator plates’ surface roughness (Ra) in a water contaminated clutch system compared to an uncontaminated one can be a reason for the change in friction. It is also shown that different water exposure time has no large impact on the change in friction level and separator plate’s roughness.

  • 31. Fatima, Nowshir
    et al.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Wet Clutch Friction Interfaces under Water Contaminated Lubricant Conditions2016In: Tribology Transactions, ISSN 1040-2004, E-ISSN 1547-397X, Vol. 59, no 3, p. 441-450Article in journal (Refereed)
    Abstract [en]

    The performance of wet clutches used for automatic transmissions or other applications usually includes the desired positive friction characteristics and a shudder-free torque generation. Changes in the operating variables such as the lubricant conditions influence the formation of tribofilm, friction characteristics and can alter the degradation of the friction interfaces. In this work, the friction characteristics and degradation of the paper-steel friction interfaces were monitored when a commercial fully-formulated automatic transmission fluid (ATF) was contaminated with water. It was found that water in ATF influenced the clutch stability by increasing the mean coefficient of friction (µ) and the negative friction-velocity slope. Surface studies of the post-test friction interfaces clearly indicated reduced surface porosity and permeability, increased wettability and changed elemental composition on the contacting surfaces after tested with water- contaminated ATF. Moreover, water-contaminated paper-liners’ thermal decomposition shifted to a lower temperature compared to an uncontaminated liner during thermal analyses. These results displayed faster degradation and reduced service life of the clutch friction interfaces for water contamination. The resultant surface condition can be associated with the observed unstable friction and negative friction-velocity slopes.

  • 32. Fatima, Nowshir
    et al.
    Minami, Ichiro
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Holmgren, Allan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Berglund, Kim
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Influence of water on the tribological properties of zinc dialkyl-dithiophosphate and over-based calcium sulfonate additives in wet clutch contacts2015In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 87, p. 113-120Article in journal (Refereed)
    Abstract [en]

    Usually the wet clutch lubricant properties vary with different formulations of base oil types and additives. The aim of this paper was to evaluate the effect of water on the performance of additives in ATF. Simplified lubricants, ZDDP and over-based Ca-sulfonates detergent additives in an API Group I mineral base oil, were employed to compare with the commercial fully-formulated automatic transmission fluid (DEXRON®VI) during water-contamination. A full-scale wet clutch test rig was used to evaluate the frictional response due to water contamination of the lubricants. Fourier Transform Infrared Spectroscopy was utilized to evaluate the variation in the solubility of these polar organic additives in the water phase and Karl-Fischer titration was utilized to evaluate the post-test water content for different formulations.

  • 33.
    Fatima, Nowshir
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Minami, Ichiro
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Holmgren, Allan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Adsorption of ATF additives on wet clutch friction interfaces under water contaminated lubricant conditions2014Conference paper (Refereed)
    Abstract [en]

    Stable friction and positive slope of friction-speed is the typical criterion for a good clutch performance. Lubricated friction interfaces used for wet clutches produces different friction behavior depending on the lubricant conditions. Usually the lubricant conditions vary for different automatic transmission fluid (ATF) formulations implying e.g. water contamination and these conditions might influence the deterioration of the clutch plates. The aim of this paper is to verify additive adsorption on friction interfaces and ageing of the friction material in wet clutch system for a water contaminated commercial ATF (DEXRON® VI). Standard clutch plates are employed in an automated wet clutch test rig to evaluate the friction characteristics of the tested lubricant. For controlled test conditions (speed, contact pressure, oil temperature) and specific number of test cycles, the mean friction coefficient and the friction vs. speed relations are monitored during sliding test. The resultant tribofilms on the tested friction interface surfaces are characterized by means of Scanning Electron Microscopy-Energy Dispersive X-ray spectroscopy (SEM- EDS), Attenuated Total Reflectance -Fourier Transform Infrared Spectroscopy (ATR-FTIR) and X-ray Photoelectron Spectroscopy (XPS analysis). The spectroscopic techniques were used to analyse adsorbed additives on friction interfaces and made it possible to correlate measured data to the specific friction behavior obtained after water contamination of the ATF.

  • 34.
    Fatima, Nowshir
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Minami, Ichiro
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Holmgren, Allan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Adsorption of ATF additives on wet clutch friction interfaces under water contaminated lubricant conditions2014Conference paper (Refereed)
    Abstract [en]

    Stable friction and positive slope of friction-speed is the typical criterion for a good clutch performance. Lubricated friction interfaces used for wet clutches produces different friction behavior depending on the lubricant conditions. Usually the lubricant conditions vary for different automatic transmission fluid (ATF) formulations implying e.g. water contamination and these conditions might influence the deterioration of the clutch plates. The aim of this paper is to verify additive adsorption on friction interfaces and ageing of the friction material in wet clutch system for a water contaminated commercial ATF (DEXRON® VI). Standard clutch plates are employed in an automated wet clutch test rig to evaluate the friction characteristics of the tested lubricant. For controlled test conditions (speed, contact pressure, oil temperature) and specific number of test cycles, the mean friction coefficient and the friction vs. speed relations are monitored during sliding test. The resultant tribofilms on the tested friction interface surfaces are characterized by means of Scanning Electron Microscopy-Energy Dispersive X-ray spectroscopy (SEM- EDS), Attenuated Total Reflectance -Fourier Transform Infrared Spectroscopy (ATR-FTIR) and X-ray Photoelectron Spectroscopy (XPS analysis). The spectroscopic techniques were used to analyse adsorbed additives on friction interfaces and made it possible to correlate measured data to the specific friction behavior obtained after water contamination of the ATF.

  • 35. Fatima, Nowshir
    et al.
    Minami, Ichiro
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Holmgren, Allan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Surface chemistry of wet clutch influenced by water contamination in automatic transmission fluids2016In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 96, p. 395-401Article in journal (Refereed)
    Abstract [en]

    Lubricated friction interfaces used for wet clutches produces different friction behaviour depending on the lubricant conditions. Usually the lubricant conditions vary for water contamination in automatic transmission fluid (ATF). The presence of water retards the ATF performance by increasing the friction and can influence the deterioration of the clutch plates. Water as a polar contaminant can change the absorbability of the surface active additives, which might cause the characteristic friction behaviour. The aim of this paper is to verify the surface chemistry of tribotested standard friction interfaces lubricated with water contaminated commercial ATF (DEXRON® VI). The evidences of the influence of water on ATF performances were shown by surface analyses

  • 36.
    Gustafsson, Gustaf
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Häggblad, Hans-Åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Determination of bulk properties and fracture data for iron ore pellets using instrumented confined compression experiments2013In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 241, p. 19-27Article in journal (Refereed)
    Abstract [en]

    In this work, an experimental method for measuring the bulk properties and fracture loading relations for iron ore pellets is presented. Knowledge on the bulk behaviour and fracture data for iron ore pellets is of great importance for improving the material transportation systems and to increase the product quality. Trustworthy numerical simulations of iron ore pellets also demand reliable materials data for the models. Here, instrumented confined compression tests are carried out at different load levels. Measurement data of the axial and radial stresses and the axial displacement are recorded for each test. Measurements of fractured iron ore pellets are carried out at different loads giving rise to crushing up to 20% of the total material. From the measured data, the Poisson´s ratio, the bulk modulus and a plastic strain hardening function are determined. In addition, friction measurements of iron ore pellets are carried out at different loads and configurations. In conclusion, the test method developed here is usable for the determination of the bulk properties and fracture characteristics of iron ore pellets.

  • 37.
    Li, M.
    et al.
    Department of Mechanical and Industrial Engineering, Louisiana State University.
    Lingesten, Niklas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    McCarthy, D.M.C.
    Volvo CE.
    Lundin, Joakim
    Volvo Construction Equipment , Volvo CE.
    Model validation and uncertainty analysis in the wear prediction of a wet clutch2016In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 364-365, p. 112-121Article in journal (Refereed)
    Abstract [en]

    An uncertainty quantification analysis is performed to further investigate the nature of the “two-stage” wear process of the paper-based friction lining in a wet clutch. In this approach, the results of a computerized wear prediction model are examined through sensitivity analysis and a model validation that utilizes the Monte Carlo (MC) method. Extensive computational results that take into account the uncertainty and variability in the input data are presented to gain insight into the evolution of temperature and wear during the engagement process.

  • 38.
    Lingesten, Niklas
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Höglund, Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    On the significance of operating temperature to the durability of a wet clutch2013Conference paper (Refereed)
  • 39.
    Lingesten, Niklas
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Höglund, Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Studies on wear phenomena in wet clutches2012Conference paper (Other academic)
    Abstract [en]

    Wet clutches are critical components in many automatic transmissions in the automotive industry. These components handle large amounts of energy through sliding friction as they engage during machine operation, resulting in clutch disc wear. Wear experiments at high clutch engagement energies has revealed that a change in the friction material wear rate can occur at some point during the test, i.e. transitioning from a low to a high wear rate. This brings into question the conventional way of performing wear tests i.e. measuring a specimen before and after testing and the usual way of viewing wear i.e. as a constant wear rate after running in. The authors propose a two step wear model to describe the wear that can occur under some conditions exemplified in this paper.

  • 40.
    Lingesten, Niklas
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Höglund, Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    The influence of repeated high-energy engagements on the permeability of a paper-based wet clutch friction material2017In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 231, no 12, p. 1574-1582Article in journal (Refereed)
    Abstract [en]

    The behavior of a wet clutch during engagement is of great importance to the durability of the clutch and the drivability of a vehicle. While many different factors influence the engagement behavior, the focus of this paper is to investigate only one factor, the permeability of the wet clutch friction material. Two test cells for measuring the permeability of friction material mounted on clutch discs have been developed. The test cells were then used to examine the effect of clutch material ageing through clutch engagement on the permeability of the material. The tests were performed on full size friction discs including the steel core prior and subsequent to testing in a wet clutch engagement test rig. The ability of the friction material to allow for oil flow both through the sliding surface layer and the bulk of the material was measured. The results indicate that repeated clutch engagements will increase the bulk permeability. However, the repeated engagements will decrease the ability to pass fluid through the friction material sliding surface. This contradictory behavior could be explained by a combination of an increase in pore size through repeated compression and the surface glaze clogging of the friction interface surface pores.

  • 41.
    Lingesten, Niklas
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Höglund, Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Lund, Martin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Lundin, Joakim
    Volvo Construction Equipment.
    Mäki, Rikard
    Volvo Construction Equipment.
    Apparatus for continuous wear measurements during wet clutch durability tests2012In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 288, p. 54-61Article in journal (Refereed)
    Abstract [en]

    Wet clutches are used in many applications today such as automatic transmissions and limited slip differentials in cars as well as in heavy duty equipment such as wheel loaders. The present study is concerned with the wear and engagement behavior of wet clutches in the latter type of application. A test rig is developed in which the wet clutch engagement is monitored during an arbitrary number of test cycles.This rig has many similarities with the SAE #2 test rig in that they are both inertia type test rigs. However, the test rig presented here has several original parts from heavy duty equipment in production incorporated into it. The data collection includes a continuous measurement of the position of the piston used to apply force on the clutch pack in addition to the separator disc temperatures, hydraulic actuating pressure and torque transfer characteristics. The measurements of the piston position can then be related to the clutch wear during a long test series.

  • 42.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Optimized wet clutches: simulation and tribotesting2006Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Wet clutches are used in a variety of different machinery. Wet clutches and brakes are frequently used to distribute torque in vehicle drive-trains. The clutches can be located in e.g. automatic transmissions or limited slip differentials. Their frictional behavior is of great importance for the overall vehicle behavior and has to be thoroughly investigated when designing new wet clutch applications. Frictional behavior is normally investigated in test rigs where complete friction discs are tested under similar working conditions as for the clutches in the drive-train. However, it is today possible to simulate the clutch behavior and not limited ourselves to only use testings as a help in the design of the wet clutches. This is an advantage because it is possible to simulate behavior that is not possible to measure in test rigs. Another advantage is the faster and more cost efficient design process than when all tests are carried out in a laboratory.The torque transferred by the clutch during engagement can be roughly divided into full film torque and boundary lubrication torque. Full film torque originates from the part of the engagement where the friction discs are completely separated by a lubricant film and the friction surfaces are not in contact, whereas boundary lubrication torque occurs when the lubricant film is so thin that the surfaces of the friction discs are in direct contact. The distribution between these two types of torque is different for different types of wet clutches and engagements. When the clutch works in full film regime, it is possible to simulate the friction quite well, whereas the friction in the boundary regime is much more difficult to model and simulate, since it is very additive dependent.The most common use of wet clutches is in automatic transmissions for vehicles. Hence, most research in wet clutch testing and simulations are performed on wet clutches suitable for these applications. Here, the wet clutch is often used to brake a rotating shaft to standstill and the total engagement will have a duration of fractions of a second. During most of the engagement the clutch will be working in full film lubrication.In this investigation, the focus is on wet clutches working under limited slip conditions, i.e. the clutches will have a limited slip during a long duration without any lock-up. During this kind of engagement the clutch will work mainly in boundary lubrication and generate much heat. Such clutches can be found in, e.g. limited slip differentials.The optimum when designing a new wet clutch would be to simulate the clutch during the whole engagement without having to do any measurements in the laboratory. This, however, is not yet possible but an efficient way to design clutches can be obtained by combining fast friction measurements with efficient computer simulations. In this work, a simple friction measurement technique for wet clutches working in boundary lubrication is developed, based on pin on disc measurements. These friction measurements are combined with a temperature simulation of a wet clutch, where the lubricant cooling flow, dependent of the surface groove pattern, is simulated. This method makes it possible to allow a wet clutch working in boundary lubrication to be optimized for given working conditions regarding lubricant, friction material and surface groove pattern. The simulations are validated by measured data from a test rig in which whole friction discs are investigated with the same working conditions.

  • 43.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Permeability measurements of sintered and paper based friction materials for wet clutches and brakes2010In: SAE technical paper series, ISSN 0148-7191, no 2010-01-2229, p. 857-864Article in journal (Refereed)
    Abstract [en]

    Wet clutches are important components used in the transmission and drive trains of many modern vehicles. The clutches transfer torque via the friction between a number of friction discs and the friction characteristics is therefore of great importance for the overall behavior of the vehicles. The friction characteristics is governed by a number of parameters such as lubricant base oil and additives, type and permeability of the friction material and temperature and surface roughness of the interacting surfaces. The permeability is considered to influence time of engagement and supply the sliding interface with lubricant and additives during engagement. In this work, a permeability measurement method suitable for wet clutch friction materials is thus used to measure the permeability of friction materials of different types; sintered bronze and paper based materials. The investigated friction materials come from different vehicle applications such as Limited Slip Differentials and Automatic Transmissions. The investigation also includes measurements made with different types of lubricants such as mineral based lubricants, mineral based VHVI lubricants and ester based lubricants. As comparison similar permeability measurements are made with water since the permeability, according to Darcy's law, should not be influenced by the percolating fluid.

  • 44.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Permeability measurements of sintered and paper based friction materials for wet clutches and brakes2010In: SAE International Journal of Fuels and Lubricants, ISSN 1946-3952, E-ISSN 1946-3960, Vol. 3, no 2, p. 857-864Article in journal (Refereed)
    Abstract [en]

    Wet clutches are important components used in the transmission and drive trains of many modern vehicles. The clutches transfer torque via the friction between a number of friction discs and the friction characteristics is therefore of great importance for the overall behavior of the vehicles. The friction characteristics is governed by a number of parameters such as lubricant base oil and additives, type and permeability of the friction material and temperature and surface roughness of the interacting surfaces. The permeability is considered to influence time of engagement and supply the sliding interface with lubricant and additives during engagement. In this work, a permeability measurement method suitable for wet clutch friction materials is thus used to measure the permeability of friction materials of different types; sintered bronze and paper based materials. The investigated friction materials come from different vehicle applications such as Limited Slip Differentials and Automatic Transmissions. The investigation also includes measurements made with different types of lubricants such as mineral based lubricants, mineral based VHVI lubricants and ester based lubricants. As comparison similar permeability measurements are made with water since the permeability, according to Darcy's law, should not be influenced by the percolating fluid. It is found that even though permeability is considered to be a material parameter the measured permeability for a certain material will vary depending on which fluid that is used in the measurements. Therefore, if a detailed absolute value of the permeability is of interest, i.e. for use in simulations models, the permeability should be measured with the fluid that is going to be used in the clutch or brake application in order to obtain a detailed result. However the results show that if the permeability only is compared between different materials the test fluid is of less importance as long as the same fluid is used in all investigations

  • 45.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Permeability measurements of sintered and paper based friction materials for wet clutches and brakes2010In: SAE 2010 Powertrains, Fuels and Lubricants Meeting: October 25 - 27, 2010, San Diego, California, USA ; [papers], Society of Automotive Engineers, Incorporated , 2010Conference paper (Other academic)
    Abstract [en]

    Wet clutches are important components used in the transmission and drive trains of many modern vehicles. The clutches transfer torque via the friction between a number of friction discs and the friction characteristics is therefore of great importance for the overall behavior of the vehicles. The friction characteristics is governed by a number of parameters such as lubricant base oil and additives, type and permeability of the friction material and temperature and surface roughness of the interacting surfaces. The permeability is considered to influence time of engagement and supply the sliding interface with lubricant and additives during engagement. In this work, a permeability measurement method suitable for wet clutch friction materials is thus used to measure the permeability of friction materials of different types; sintered bronze and paper based materials. The investigated friction materials come from different vehicle applications such as Limited Slip Differentials and Automatic Transmissions. The investigation also includes measurements made with different types of lubricants such as mineral based lubricants, mineral based VHVI lubricants and ester based lubricants. As comparison similar permeability measurements are made with water since the permeability, according to Darcy's law, should not be influenced by the percolating fluid.It is found that even though permeability is considered to be a material parameter the measured permeability for a certain material will vary depending on which fluid that is used in the measurements. Therefore, if a detailed absolute value of the permeability is of interest, i.e. for use in simulations models, the permeability should be measured with the fluid that is going to be used in the clutch or brake application in order to obtain a detailed result. However the results show that if the permeability only is compared between different materials the test fluid is of less importance as long as the same fluid is used in all investigations.

  • 46.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Tribo-condition monitoring for optimized performance and longer service life2017Conference paper (Other academic)
  • 47.
    Marklund, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Wet clutch tribological performance optimization methods2008Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Wet clutches are used in a variety of machinery such as in vehicles where they are used to distribute torque in the drivetrains. Clutches can be located in automatic transmissions or in limited slip differentials. The frictional behavior of a clutch is of great importance for overall vehicle behavior and has to be thoroughly investigated when designing new wet clutch applications. Frictional behavior is normally studied in test rigs where whole friction discs or complete clutches are tested under similar working conditions to those pertaining to the clutches in the drivetrain of the vehicle. However, today clutch behavior may be simulated with regard to some clutch applications and design of the clutch system is not limited to testing. This is an advantage as it is possible to simulate behavior that may not be possible or suitable to study in a test rig. Another advantage is that the design process is faster and more cost efficient than that which is possible when all tests are carried out in a laboratory. The torque transferred by the clutch during engagement can roughly be divided into full film torque and boundary lubrication torque. Full film torque originates from the part of the engagement where the clutch discs are completely separated by a lubricant film and the friction surfaces are not in contact, whereas boundary lubrication torque occurs when the lubricant film is so thin that the surfaces of the clutch discs are in direct contact, only separated by a thin additive film. The distribution between full film torque transfer and boundary lubrication torque transfer differs for different types of wet clutch and for differing operating conditions. When the clutch works in full film regime it is possible to simulate the friction quite well. However, the friction in the boundary lubrication regime is much more difficult to model and simulate since it is very dependent on the additives. Wet clutches are most commonly used in automatic transmissions for vehicles. As a result, most research into wet clutch testing and most simulations concerns wet clutches suitable for such applications. In an automatic transmission the wet clutch is often used to brake a rotating shaft to stand still relative to another shaft and the total engagement has a duration of fractions of a second. During most of the engagement the clutch is working in full film lubrication. In this thesis the focus is on wet clutches working under limited slip conditions: in other words this thesis studies clutches that are working with a small amount of slip over a long period without reaching a state of lock-up. These clutch types can be found, for example, in limited slip differentials. During this type of engagement the clutch mainly works under boundary lubrication conditions and much heat can be generated. The optimum method of designing a new wet clutch would be to simulate the clutch performance without having to do any measurements in the laboratory. This, however, is not yet possible, but an efficient way to design clutches can be achieved by combining simple measurements with efficient computer simulations. In this thesis, simple measurement techniques for wet clutch materials are developed and combined with a temperature simulation of a wet clutch, where the lubricant cooling flow, which is dependent on the surface roughness and groove pattern, is simulated. This method makes it possible to optimize a wet clutch for given working conditions with regard to lubricant, friction material, surface roughness and groove pattern. The simulations are validated to measured data from a test rig in which torque behavior from whole friction discs are investigated. Good agreement between simulations and measurements is achieved.

  • 48.
    Marklund, Pär
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Almqvist, AndreasKassfeldt, Elisabet
    Nordtrib 2010: 14th Nordic Symposium on Tribology, Storforsen, Sweden2010Collection (editor) (Other academic)
  • 49.
    Marklund, Pär
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Berglund, Kim
    Kassfeldt, Elisabet
    Baldos II, Sweden's most fuel efficient car: approved for street use2010In: SAE 2010 Powertrains, Fuels and Lubricants Meeting: October 25 - 27, 2010, San Diego, California, USA ; [papers], Warrendale, Pa: Society of Automotive Engineers, Incorporated , 2010Conference paper (Other academic)
    Abstract [en]

    Baldos II originates as an entry for the 2009 Shell Eco-marathon competition. It is built in cooperation between students from different fields of study, such as Mechanical Engineering, Industrial Design Engineering and Computer Science from Luleå University of Technology, Sweden. The car has been designed to meet the requirements set by Swedish authorities for legal street use. This includes wind screen wiper, 3-point seat belt, proper lighting, reverse gear and twin electric engines. Baldos II is tested and found to be Sweden's most fuel efficient car approved for street use.The internal combustion engine in the serial hybrid drive train is modified from an ordinary gasoline engine to run on pure ethanol. The fuel consumption of the vehicle corresponds to 0.065 litres ordinary gasoline/10 km, which results in a CO2 emission of 12 g/km. The car is design for one person only, and has room for a luggage in the size of an ordinary cabin bag. With full tank the total weight is 220 kg, and the total length is 2650 mm. The light weight has been achieve thorough an advanced monocoque chassis manufactured of carbon fiber sandwich construction.According to safety regulations the car is equipped with dual circuit hydraulic disc brakes. Today, the Team Baldos aims for defining a higher standard for street vehicles in Sweden.

  • 50. Marklund, Pär
    et al.
    Berglund, Kim
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    The influence on boundary friction of the permeability of sintered bronze2008In: Tribology letters, ISSN 1023-8883, E-ISSN 1573-2711, Vol. 31, no 1, p. 1-8Article in journal (Refereed)
    Abstract [en]

    Components made of sintered bronze are often used in tribological systems. Examples of applications are self lubricated bearings, wet clutches and brakes and synchromesh components for manual gearboxes. The bronze material in these applications is often porous and permeable. However, the required level of permeability i.e., the ability for a fluid to flow inside the material varies widely for different applications. This implies the need to investigate if the permeability can influence the properties of a tribological system. Various studies have been performed in order to investigate the permeability of different materials but a possible relationship between permeability and boundary lubrication performance has not yet been thoroughly investigated. In this article this relationship has been investigated in a pin-on-disk apparatus for test specimens with a permeability that is well-defined. Materials with three different permeabilities were investigated together with non-permeable test specimens. The results indicate that permeability has a small influence on the friction coefficient when the tribological system is operating with good lubrication of the contact. The function of the tribological system when working under starved conditions is also investigated and a very clear relationship between permeability and the ability to cope up with starved running conditions is shown. This is explained in terms of the varying ability of the materials' to store lubricant in pores. Non-porous test specimens were also tested as a comparison with the permeable test specimens in the investigation with starved running conditions . The results show that a material with high permeability works much better under starved running conditions than that with low permeability.

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