Issue 21

D. Benasciutti et alii, Frattura ed Integrità Strutturale, 21 (2012) 37-45; DOI: 10.3221/IGF-ESIS.21.05 37 A numerical approach for the analysis of deformable journal bearings D. Benasciutti, M. Gallina, M. Gh. Munteanu Dip. di Ingegneria Elettrica Gestionale Meccanica (DIEGM), Università di Udine, via delle Scienze 208, 33100, Udine F. Flumian Centro Ricerche Danieli (CRD), Danieli Officine Meccaniche S.p.A., via G.B. Beltrame 30, 33042, Buttrio (UD) A BSTRACT . This paper presents a numerical approach for the analysis of hydrodynamic radial journal bearings. The effect of shaft and housing elastic deformation on pressure distribution within oil film is investigated. An iterative algorithm that couples Reynolds equation with a plane finite elements structural model is solved. Temperature and pressure effects on viscosity are also included with the Vogel-Barus model. The deformed lubrication gap and the overall stress state were calculated. Numerical results are presented with reference to a typical journal bearing configuration at two different inlet oil temperatures. Obtained results show the great influence of elastic deformation of bearing components on oil pressure distribution, compared with results for ideally rigid components obtained by Raimondi and Boyd solution. K EYWORDS . Journal bearing; Finite elements; Deformation; Lubrication. I NTRODUCTION ournal bearings are machine elements in which the applied force is entirely supported by an oil film pressure. They are used in many different engineering applications, for example as supports of rotating shafts. They are considered superior to roll bearings because of their higher load-bearing capacity, higher operating angular speed, lower cost and easier manufacturing. Furthermore, a proper design can assure very large service lives. The fluid-dynamic motion of oil film within the lubrication gap is described by the well-known Reynolds equation [1]. Explicit analytical solutions for the pressure distribution can be obtained only for asymptotic configurations (e.g. infinitely short and long journal bearings) [1, 2], while for other journal bearing configurations numerical solution of Reynolds equation is required. The early studies on journal bearing performance under different operating conditions, based on the numerical solution of Reynolds equation, date back to the fundamental work of Raimondi and Boyd (R&B) [3, 4]. They summarized their results in useful dimensionless charts ready for design, which are nowadays accepted also in code standards [5]. Raimondi and Boyd analysis is based on some simplified assumptions: constant viscosity of oil film, independency of viscosity on pressure and finally the postulation of perfectly rigid components (shaft and support). Such assumptions, however, can be somewhat oversimplified, considering for example that the deformation of journal bearing components under the imposed oil film pressure is expected to produce a change in the real lubrication gap and thus a modification in the resultant pressure distribution. Moreover, also the assumption of constant viscosity and its independence on pressure should be critically reviewed, as it is experimentally known that viscosity varies, other than with temperature, also with pressure, as summarized by many constitutive models [6]. It would be then of interest to investigate in a more detail the correlation existing between all the above-mentioned aspects and journal bearing performance and design. J