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  • 1.
    Ghasemi, Rohollah
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting.
    Tribological and Mechanical Behaviour of Lamellar and Compacted Graphite Irons in Engine Applications2015Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    There has been much discussion about the beneficial uses of lamellar graphite iron in piston rings–cylinder liner systems, where a good combinations of both thermal and tribological properties are essential. The excellent tribological performance of lamellar iron under such sliding conditions is principally associated with lubrication behaviour of the graphite particles which are distributed as lamellas throughout the matrix. During sliding, graphite particles are extruded and smeared onto the counterfaces, act as solid lubricating agents and form a thin graphite film between the sliding surfaces. Although this process especially, during the running-in period significantly changes the sliding wear response of the components, the exact mechanism behind of this phenomenon has rarely been discussed in previous studies.

    It is tribologically beneficial to keep the graphite open, particularly in applications where the scuffing issues do matter. In this thesis, the main causes involved in closing the graphite lamellas are discussed, with a focus on matrix plastic deformation that occurs during sliding. In first step, the relationship between graphite lamellae orientation and plastic deformation was investigated. To do so, two piston rings, belonging to the same two-stroke marine engine operated for different periods of time, were selected and compared to the unworn sample. The worn piston rings displayed a substantial decrease in both frequency and area fraction of the graphite lamellas. Most of the lamellas were closed as a result of plastic deformation of matrix. This happening was caused mainly by the interaction between abrasive particles and metallic matrix. Additionally, it was found that graphite lamellas parallel or near-parallel to the sliding direction exhibited maximum closing tendency under sliding condition.

    In next step, to have a better understanding of the graphite film formation mechanism and matrix deformation role in closing the graphite lamellas, microindentation and microscratch testing were performed on typical lamellar iron. The qualitative results showed a similar mechanism involving in graphite contribution to lubricate the sliding surfaces. Moreover, microindentations made nearby the graphite lamellas demonstrated that the deformation of the matrix causes the formation of cracks in the centre of the graphite lamellas, compressing and then extruding the graphite from its natural position, irrespective of the lamellas′ size. Furthermore, it was found that subsurface graphite orientation had a large influence on the extrusion behaviour, in that, for graphite lamellas oriented towards the indenter, the effect was observed more pronounced.

    Furthermore, an improved fully ferritic solution strengthened compacted graphite iron was produced for future wear studies. The effects of different Si levels and section thicknesses on tensile properties and hardness were investigated as well. The influence of Si content and section thickness on mechanical properties was revealed by improving the materials strength and slightly enhancing the hardness through increasing Si content. Besides, Si addition up to 4.5 wt% significantly affected the strength and elongation to failure of cast samples.

  • 2.
    Ghasemi, Rohollah
    et al.
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting.
    Elmquist, Lennart
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting.
    A study on graphite extrusion phenomenon under the sliding wear response of cast iron using microindentation and microscratch techniques2014In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 320, no 1-2, p. 120-126Article in journal (Refereed)
    Abstract [en]

    This study focuses on the graphite flakes extrusion mechanism during microindenting and microscratching of cast iron. Observations on the graphite response under abrasive conditions revealed that the matrix deformation which is occurred during a sliding wear condition could have a significant influence on its lubricating performance. Simple microindentation and microscratch tests were conducted to explore the lamellar graphite contribution to tribofilm formation under abrasive wear conditions. The results obtained showed that induced plastic deformation which developed adjacent to the graphite compressed the lamellas and in turn resulting in extrusion of the graphite from its natural position. Further investigations on both indentation and scratch tests indicated that, surprisingly, the graphite began to be fractured and extruded from the centre of graphite lamellas, irrespective of the lamella size. Additionally, a mechanism was proposed to explain the self-lubricating and the extrusion behaviour of the lamellar graphite as a result of indentation.

  • 3.
    Ghasemi, Rohollah
    et al.
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting.
    Elmquist, Lennart
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting. Scania CV AB, Materials Technology, SE-151 87 Södertälje, Sweden.
    Cast iron and the self-lubricating behaviour of graphite under abrasive wear conditions2014Conference paper (Refereed)
    Abstract [en]

    Cast iron is assessed as a self-lubricating material under sliding conditions. This is due to the graphite particles distributed in the matrix, which come out from their pocket, and form a tribofilm between the mating surfaces, and by which improve the tribological characteristics. In this study, the directionality and the interaction between the graphite and matrix material was investigated by microindentation and microscratch techniques. The results showed that the graphite is fractured and pushed out from the middle of graphite lamellas as a result of indentation. It was also observed that the graphite orientation below the surface intensely influenced the pushing out behaviour. For the graphite oriented toward the indenter position, the effect was more pronounced. Moreover, it was found that a scratch test can be used to investigate and explain the graphite pushing out tendency. The result was used to explain the directionality and closing tendency of the graphite lamellas during sliding.

  • 4. Ghassemali, Ehsan
    et al.
    Tan, Ming-Jen
    Lim, Samuel C.V.
    Jarfors, Anders
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting.
    Friction Factor in a Progressive Microforming Process2012In: 7 th INTERNATIONAL CONFERENCE ON MICROMANUFACTURING, 2012Conference paper (Other academic)
    Abstract [en]

    In this work, the effect of global and localized friction factoron the material forming in the simulation is investigated. Tomatch the simulation and experimental results, a reverse engineeringmethod has been used to get the correct frictionfactor for the defined condition in the microforming process.The friction size effect in the progressive microformingprocess has also been addressed.

  • 5.
    Hsiung, Daniel
    Jönköping University, School of Engineering, JTH, Mechanical Engineering.
    REDESIGN OF A TRIBOLOGICAL TEST MACHINE2016Independent thesis Basic level (university diploma), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    The present work deals with developing a tribological test machine that had been built

    earlier but did not function properly. It was giving out abnormal noises and vibrations

    and was not corresponding to its desired functions. In this study, the root of these

    problems is analyzed and some solutions are suggested by developing a new

    construction concept for the machine.

  • 6.
    Manne, Akhil
    et al.
    Jönköping University, School of Engineering, JTH. Research area Product Development - Simulation and Optimization.
    Hiregoudra, Pramod S
    Jönköping University, School of Engineering, JTH. Research area Product Development - Simulation and Optimization.
    Modelling and Simulation of Mold filling in gravity casting of Aluminium and MMC alloys.2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
  • 7. Nilsson, Bertil
    et al.
    Hansbo, Peter
    Jönköping University, School of Engineering, JTH. Research area Product Development - Simulation and Optimization.
    A Stokes model with cavitation for the numerical simulation of hydrodynamic lubrication2011In: International Journal for Numerical Methods in Fluids, ISSN 0271-2091, E-ISSN 1097-0363, Vol. 67, no 12, p. 2015-2025Article in journal (Refereed)
    Abstract [en]

    We present a cavitation model based on the Stokes equation and formulate adaptive finite element methods for its numerical solution. A posteriori error estimates and adaptive algorithms are derived, and numerical examples illustrating the theory are supplied, in particular with comparison to the simplified Reynolds model of lubrication.

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