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.
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.
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.
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.