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  • 1.
    Hultqvist, Tobias
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Vrček, Aleks
    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.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements. Department of Mechanical Engineering, Tsinghua University, Beijing, China.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Transient analysis of surface roughness features in thermal elastohydrodynamic contacts2020In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 141, article id 105915Article in journal (Refereed)
    Abstract [en]

    Understanding the influence of surface roughness in elastohydrodynamically lubricated (EHL) contacts is essential to improve durability and friction performance of machine elements employing non-conformal contacting surfaces. In this work, the transient event of a surface feature passing through a thermal EHL line contact operating under different sliding conditions is investigated with the purpose of providing a deeper understanding of surface roughness influence. This is achieved by solving the EHL problem in space and time. It was seen that sliding influences the temperature rise in the contact significantly, especially in the vicinity of the asperity. However, due to the characteristic behaviour of EHL contacts, the local temperature rise mainly influence the film thickness during exiting of inlet perturbations and the asperity.

  • 2.
    Hultqvist, Tobias
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Vrček, Aleks
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Prakash, Braham
    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 lubricant pressure response on sub-surface stress in elastohydrodynamically lubricated finite line contacts2019In: Journal of tribology, ISSN 0742-4787, E-ISSN 1528-8897, Vol. 141, no 3, article id 031502Article in journal (Refereed)
    Abstract [en]

    In order to adapt to increasingly stringent CO2 regulations, the automotive industry must develop and evaluate low cost, low emission solutions in the powertrain technology. This often implies increased power density and the use of low viscosity oils, leading to additional challenges related to the durability of various machine elements. Therefore, an increased understanding of lubricated contacts becomes important where oil viscosity-pressure and compressibility-pressure behaviour have been shown to influence the film thickness and pressure distribution in EHL contacts, further influencing the durability. In this work, a finite line EHL contact is analysed with focus on the oil compressibility- and viscositypressure response, comparing two oils with relatively different behaviour and its influence on subsurface stress concentrations in the contacting bodies. Results indicate that increased pressure gradients and pressure spikes, and therefore increased localized stress concentrations, can be expected for stiffer, less compressible oils, which under transient loading conditions not only affect the outlet but also the edges of the roller

  • 3.
    Vrček, Aleks
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hultqvist, Tobias
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Baubet, Yannick
    SKF, Nieuwegein.
    Björling, Marcus
    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.
    Micro-pitting and wear assessment of engine oils operating under boundary lubrication conditions2019In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 129, p. 338-346Article in journal (Refereed)
    Abstract [en]

    Current state-of-the-art engine oils tend to enhance micro-pitting damage in rolling contacts under certain operating conditions. ZDDP anti-wear additive was shown to promote such behavior. However, in order to optimize an engine oil formulation for rolling contacts, further studies are needed to assess engine oils in terms of micro-pitting and wear damage. This investigation studies the micro-pitting and wear performance of a number of engine oils for rolling contacts in a ball-on-disc configuration under conditions prevalent in crankshaft roller bearing applications. Based on the results it was concluded that an engine oil containing higher blend of PAO base oil compared to the oil mixture of Group III and PAO has a lower tendency towards micro-pitting and wear.

  • 4.
    Vrček, Aleks
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hultqvist, Tobias
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Baubet, Yannick
    SKF Engineering & Research Centre, Nieuwegein, The Netherlands.
    Björling, Marcus
    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.
    Micro-Pitting and Wear Assessment of PAO vs Mineral-Based Engine Oil Operating under Mixed Lubrication Conditions: Effects of Lambda, Roughness Lay and Sliding Direction2019In: Lubricants, E-ISSN 2075-4442, Vol. 7, no 5, article id 42Article in journal (Refereed)
    Abstract [en]

    Under certain operating conditions, rolling contacts have been shown to experience some challenges when lubricated with engine oils containing zinc dialkyldithophosphate (ZDDP) anti-wear additive. In order to better understand the main damage mechanisms during various operating conditions, further studies are needed. This article studies micro-pitting and wear damages of bearing steel surfaces under mixed lubrication conditions in a ball-on-disc setup, lubricated with different engine oils. Based on the results, micro-pitting and wear damage is shown to be highly case-dependent. In general, PAO-based engine oil tends to eliminate micro-pitting damage compared to mineral-based engine oil at less severe lubricating conditions. Moreover, a critical lambda was found for both oils, where the highest micro-pitting damage was observed. 

  • 5.
    Vrček, Aleks
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Hultqvist, Tobias
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Baubet, Yannick
    SKF Research and Technology Development, Nieuwegein, Netherlands.
    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.
    Micro-pitting Damage of Bearing Steel Surfaces under Mixed Lubrication Conditions: Effects of Roughness, Hardness and ZDDP Additive2019In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 138, p. 239-249Article in journal (Refereed)
    Abstract [en]

    Micro-pitting presents a failure of the rolling/sliding contact metal asperities operating under boundary/mixed lubrication conditions. The studies have shown that micro-pitting failure competes with mild wear and that lubricant additives can have either detrimental or beneficial effects on micro-pitting evolution. This article describes a methodology to investigate micro-pitting damage on bearing steels using a twin-disc machine to better represent mechanical components, i.e. bearings, crankshafts, etc. In addition, effects of roughness, hardness and the ZDDP additive are presented and discussed. A sufficient hardness difference can completely eliminate micro-pitting damage mode. Furthermore, the presence of ZDDP anti-wear additive in fully formulated engine oil was shown to protect rougher surfaces and promote wear on smoother surfaces, thus completely eliminating the micro-pitting damage mode.

  • 6.
    Hultqvist, Tobias
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Shirzadegan, Mohammad
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Vrček, Aleks
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Baubet, Yannick
    SKF, Nieuwegein.
    Prakash, Braham
    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.
    Elastohydrodynamic lubrication for the finite line contact under transient loading conditions2018In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 127, p. 489-499Article in journal (Refereed)
    Abstract [en]

    Research related to elastohydrodynamic lubrication (EHL) has led to improved performance and durability of machine elements where non-conformal contact geometries interact. Only a relatively small portion of the EHL literature has, however, dealt with the lubricating performance of finite line contacts under non-steady conditions, commonly found in many practical applications. The purpose of this work has thus been to further understand the behaviour of finite line EHL contacts under transient conditions by studying a finite length roller subjected to a time varying load using a full-system finite element approach. The transient load was shown to initiate oscillations in the system, governed by waves of lubricant moving through the contact, affecting both pressure and film thickness throughout the contact.

  • 7.
    Vrček, Aleks
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Micro-pitting and wear characterization for crankshaft roller bearing application2018Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Efficiency of internal combustion engines (ICEs) is far from optimal. Due to the continuously increasing demands on CO2 regulations, automobile industries are forced to improve such efficiency. A crankshaft roller bearing (CSRB) can lead to significant improvements in engine efficiency. However, before this can be implemented into an actual engine, several challenges have to be addressed. One such challenge is the satisfactory performance of CSRB. The current crankshaft limits the service life since it must act as a roller bearing raceway. Therefore, better material properties are required for the use of CSRB in crankshaft applications.

    In order to select suitable material for the CSRB, development of several characterization methods is required. These methods are based on failure modes that are expected to occur in the actual application. Surface initiated fatigue was shown to be the main failure mode that could lead to complete failure of such a component. The following three characterizations needs are identified: material characterization, lubricant characterization and surface roughness characterization. Two of these methods are partially part of this thesis.

    Material characterization is required to select the optimal steel candidate for the CSRB component. A method was developed to assess the damage modes on a reference 100Cr6 steel pair under conditions prevalent to CSRB application. However, fully formulated oil was excluded from this investigation and only low-additive oil was employed. Micro-pitting and wear damage modes were identified and were later assessed. Different surface roughness combinations were tested, from where micro-pitting regions were identified. In addition, the effects of surface hardness and sliding on micro-pitting and wear were investigated. It was found that hard steel contacts are more prone to micro-pitting damage compared to soft ones, but less susceptible to mild wear. In addition, higher sliding increases the degree of micro-pitting and wear.

    Lubricant characterization was performed to optimize the engine oil formulation for rolling contacts. A method to assess different engine oils in terms of micro-pitting and wear damages of rolling contacts was employed. The effect of viscosity, additive chemistry and different mixtures of base oils on aforementioned performance were presented and discussed. In addition, lubricant characterization will provide in-depth knowledge for engine oils’ manufacturers to improve engine oil formulations for satisfactory performances of CSRB design.

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  • apa
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  • ieee
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