Tribology Online
Online ISSN : 1881-2198
ISSN-L : 1881-218X
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Article
  • Wanjun Xu, Yongwei Tian, Ying Song, Mingjie Zhang, Jiangang Yang
    2021 Volume 16 Issue 2 Pages 81-88
    Published: April 15, 2021
    Released: April 15, 2021
    JOURNALS OPEN ACCESS

    This paper proposed a new approach to Reynolds boundary condition approximation in journal bearing CFD analysis. Dynamic mesh method was applied to approach the location where the rupture of oil film or cavitation started. A numerical model of half bearing geometry was constructed to obtain the Half-Sommerfeld solution. Using the solution, a pseudo-transient analysis was subsequently conducted. The boundary at the minimum film thickness was treated as the moving boundary. The Reynolds boundary condition was satisfied at a certain point when the pressure derivative of boundary nodes approached zero over the course of mesh growth. The analytical results were compared against the results of published works. It was discovered that the resulting cavitation angle and oil film pressure were consistent with those obtained by taking the Reynolds equation approach, with only slight differences observed from those obtained via the cavitation experiments and models. The proposed method is an extension of Reynolds boundary condition according to the CFD approach. It is considered an alternative to other cavitation models intended for journal bearings.

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  • Mamoru Tohyama, Takashi Izumi, Shuzo Sanda
    2021 Volume 16 Issue 2 Pages 89-98
    Published: April 15, 2021
    Released: April 15, 2021
    JOURNALS OPEN ACCESS

    The dominant factors and processes for the rapid progression of scuffing from a partial area to an entire surface under lubricated, plane contact, and pure sliding conditions were studied by performing an in situ observation of the surface, and in situ measurements of the oil-film thickness and temperature distributions during scuffing. Transitions of the oil-film thickness were measured using three-wavelength optical interferometry, and the temperature distributions of the sliding surface were measured using thermography. It was observed that oil-film breakdown progressed from a partial area to an entire surface within several tens of milliseconds under high sliding speed and high-load conditions. The proposed process of the rapid progression of oil-film breakdown on the surface was described using the "thermal-diffusion-induced spiral model." The processes in the model are as follows: (I) the frictional heat generated in a solid contact area diffused into the adjacent region of the surface; (II) the oil-film temperature in the adjacent region increased within a short time, as the films were very thin (several tens of nanometers); (III) the viscosities of the oil-films decreased; (IV) the solid contact area grew larger, and these phenomena repeated continuously until the oil-film breakdown reached the entire surface.

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  • RK Awasthi, Jagjit Singh Maan
    2021 Volume 16 Issue 2 Pages 99-112
    Published: April 15, 2021
    Released: April 15, 2021
    JOURNALS OPEN ACCESS

    Surface texturing may have significant role in tribo-element applications operating at high speed. This paper theoretically investigates the influence of depth and location of cylindrical shaped dimples on static as well as dynamic performance characteristics of partial textured hydrodynamic journal bearing vis-a-vis a smooth bearing working under turbulent regime. The non-dimensional Reynolds equation used for compressible flow is suitably modified for turbulent regime and Finite Element Method has been used to discretise the equation into linear algebraic equation. The governing equation satisfies mass-conservation throughout the solution domain. Eventually the results have been computed for three bearing configurations viz. smooth (untextured), partial textured with upstream and downstream zone respectively. The computed results reveal that the bearing surface if modified using texture at suitable location, enhances the performance of hydrodynamic bearing in terms of better load carrying capacity, low friction coefficient and enhanced stability. The study gives insight to the bearing designer.

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  • Shojiro Miyake, Masatoshi Miyake
    2021 Volume 16 Issue 2 Pages 113-124
    Published: April 15, 2021
    Released: April 15, 2021
    JOURNALS OPEN ACCESS

    We studied the tribological properties of extremely thin DLC films at high temperature. The films were deposited on nickel phosphorus (NiP) or Si substrates using filtered cathodic vacuum arc (FCVA) or plasma chemical vapor deposition (P-CVD). The nanoindentation hardness values and elastic moduli of the films were lower on NiP than on Si. The nanofriction force of the FCVA-DLC film on NiP was low at room temperature, but very high at high temperature. In this hard film, the lubricous adsorbate was removed by sliding at high temperature, making it easily damaged through the large deformation of NiP. In contrast, the friction force of the P-CVD-DLC films on both substrates was low at high temperatures. In this case, the lubricous tribochemical products from the P-CVD-DLC film reduced friction and wear. The friction map dependences on load and number of reciprocating cycles were evaluated using a friction test and statistical cluster analysis. The friction durability of both films depended more strongly on load on NiP than on Si, with the friction coefficients on Si being almost independent of load. At high temperatures and load, the durability of the FCVA-DLC film on NiP decreased and this film was easily damaged.

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Editorial
Article
  • Konstantinos Tsatsoulis, Anastasios Zavos, Pantelis G. Nikolakopoulos
    2021 Volume 16 Issue 2 Pages 125-137
    Published: June 15, 2021
    Released: June 15, 2021
    JOURNALS OPEN ACCESS

    The influence of operating conditions of the compression rings on the engine power losses affects confoundedly the design of the Internal Combustion Engines (ICEs). Normalized parameters such as Friction Mean Effective Pressure (FMEP) were used to regulate power losses. The purpose of this work was to create a primary control model of the friction mean effective pressure using an automatic control system. This study incorporates the creation of a mixed-hydrodynamic model for the top compression ring in MATLAB computing environment. The load of ring asperities was predicted using Greenwood-Tripp stochastic model. The pressure distribution along the ring face-width was determined using Reynolds equation through finite difference method with the half-Sommerfeld boundary condition for cavitation outlet zone. This was accomplished by finding the maximum ring pressure for a range of engine speeds and lubricant temperatures. Additionally, the computed results concerning the maximum pressure and the PID controlled characteristics are proposed and compared using a cavitation model. Regarding the automatic system, a PID controller was built using SIMULINK. The numerical results showed that FMEP could be the effective parameter in order to control the engine operation and to proof the tribotronics design in an Internal Combustion Engine.

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Review
  • Detlef Jannes, Lothar Hörl, Frank Bauer
    2021 Volume 16 Issue 2 Pages 138-145
    Published: June 15, 2021
    Released: June 15, 2021
    JOURNALS OPEN ACCESS

    This paper analyses the implications of swelling in perspective of sealing technology for redox flow batteries (RFB). Mechanical failure due to swell in static sealing can occur on the elastomeric seal or on sealing flanges. The mechanical failure is in this case a fractured or deformed RFB component because of the swelling pressure. Swelling of such an elastomeric seal is a coupling of different physics phenomena, namely diffusion and solid mechanics. In an assembled RFB, seal swelling increases the contact pressure with the sealing flange, while making the components softer. It shifts the mechanical material properties of the components and also the stress tolerances. Graphite-polymer bipolar plates or PTFE / PP flowframes are common RFB sealing flanges and can become softer due to diffusion of the electrolyte fluid, making the flanges more prone to creep. These are time dependent effects that can create sealing failure or mechanical break of the sealing flanges and must be taken into account in RFB design. The presented experimental and modelling results validate the swelling behaviour for an assembled RFB. The compatibility tables of sealing materials in catalogues do not often differentiate swelling compatibility from chemical compatibility of a fluid. In addition, this paper proposes a basic selection procedure for swelling compatibility based on group experiments on Hansen solubility parameters (HSP).

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Article
  • Kazumi Sakai, Yusuke Ayame, Yoshimu Iwanami, Nobuharu Kimura, Yoshihir ...
    2021 Volume 16 Issue 2 Pages 146-150
    Published: June 15, 2021
    Released: June 15, 2021
    JOURNALS OPEN ACCESS

    The grease fluidity and migration inside a ball bearing has been visualized non-destructively by using a neutron imaging technology. It has been clarified that a lithium (Li) complex grease with lower torque lubricates in the channeling state and that a single Li soap grease with higher torque lubricates in the churning state. Adhesion of the Li complex grease to bearing balls was quite limited, and most of the grease stayed on cage surfaces between the balls; adhesion of the single Li soap grease to bearing balls was remarkable. These observation results correlate to their grease performances for the bearing torque. The less adhesion of the Li complex grease to bearing balls contributes to reducing bearing torque due to easy rotations of bearing balls. In contrast, the remarkable adhesion of the single Li soap grease causes higher shear resistance for bearing ball rotations. The neutron imaging technology clarified the mechanism of the bearing torque difference depending on the grease types and could contribute to developments of energy-saving greases.

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