Issue 21

D. Benasciutti et alii, Frattura ed Integrità Strutturale, 21 (2012) 37-45; DOI: 10.3221/IGF-ESIS.21.05 44 compared to the result for rigid components (R&B solution), seems to support the idea of using the average specific pressure p m as a structural design parameter, as suggested in some design codes [5]. The elastic deformation also induces an increase in eccentricity, from e =0.2392 mm (rigid components) to e =0.2953 (elastic components). Fig. 6(b) compares the geometry of lubrication meatus for the case of deformable and rigid components (angles are referred to the position of minimum oil gap θ h0 ). In particular, it is observed that for deformable components the meatus is not symmetric and that eccentricity can assume values greater than the nominal clearance c , as the elastic deformation can increase the gap between shaft and support. -200 -100 0 100 200 -50 -40 -30 -20 -10 0 10 20 30 Angle [deg] Stress [MPa] radial hoop axial von Mises (a) (b) (c) Figure 7 : (a) Radial and (b) von Mises stresses in the support (MPa units); (c) stress components on inner surface of support. For what concerns the calculated mechanical stresses, Fig. 7(a)-(b) show the overall distribution of radial and von Mises stresses within the housing, while Fig. 7(c) plots the values of stress components (radial σ r , hoop σ θ , axial σ z ) and von Mises stress on the hole surface of the housing, as a function of angle θ (the vertical symmetry axis is at angle θ =0). All stress values are compressive and show a similar trend with θ . The maximum absolute radial stress is 43 MPa, exactly equal to the maximum oil pressure ( p max =43 MPa) applied on the inner hole. Hoop and axial stress components have approximately similar values, with the axial stress under plane strain condition calculated as σ z =ν(σ θ +σ r ), where ν is the Poisson ratio. Since the stress distribution of Fig. 7(c) is partly hydrostatic, the maximum von Mises stress (σ vm =21 MPa) is shown to be significantly lower than the maximum absolute radial stress σ r =43 MPa. In particular, the elastic deformation of journal bearing elements gives a maximum von Mises stress on the hole surface that is smaller than the maximum oil pressure p max and that is comparable with the static strength of materials usually employed (for instance, white metal generally used as internal coating has a yield stress of about 50 MPa [8]). Instead, in the region underneath the hole surface the overall stress state becomes “less hydrostatic” and a larger von Mises stress (σ vm =35 MPa) then develops. C ONCLUSIONS n this paper, a numerical procedure for the static analysis of hydrodynamic radial journal bearings has been developed. Influence of temperature and pressure on viscosity and thus on resultant pressure distribution were studied. A mechanical plane finite element model, coupled with solution of Reynolds equation, was also developed to study journal bearing structural behavior and its influence on pressure distribution. The main findings of the work can be summarized as follows:  a temperature increase was shown to give a decrease of attitude angle β and an increase in pressure peak;  an increase of viscosity-to-pressure sensitivity (α value) gives a general increase of peak pressure, especially for pressure peaks greater than about 100 MPa;  the temperature effect was shown to be generally larger than pressure effect on pressure distribution;  the elastic deformation of journal bearing elements gives a more uniform pressure distribution, with a reduced maximum pressure peak compared to the case of perfectly rigid components. In addition, the overall stress state on the surface hole in the support is partly hydrostatic, so that the maximum von Mises stress is lower than the maximum radial stress modulus (i.e. the maximum peak pressure). I