Issue 21

D. Benasciutti et alii, Frattura ed Integrità Strutturale, 21 (2012) 37-45 ; DOI: 10.3221/IGF-ESIS.21.05 43 The plane FE models of both shaft and housing used in the analysis are shown in Fig. 5. The shaft is modeled by a mapped mesh with 4-nodes isoparametric linear elements, while the housing is free meshed using 3-nodes CST triangular elements. Shaft and support are loaded by the same oil pressure distribution p ( θ ) applied on the outer and inner surfaces, respectively. The analysis assumes small displacements and a plane strain condition. Material has linear elastic behavior, with properties typical of a structural steel. (a) (b) Figure 5 : Finite element model of (a) shaft and (b) housing It is worth noting that the use of a plane FE model for the structural analysis of a journal bearing requires a special attention in modeling mechanical constraints. In fact, in a real journal bearing the applied load F and the resulting pressure distribution are actually applied along different longitudinal locations along the shaft axis. Instead, in the plane FE model here adopted the external load F that balances the oil pressure is replaced by an appropriate constrain on shaft geometry. For this purpose, the shaft has been modeled with a central hole and all nodes on the inner circumference have imposed zero radial displacements; the support, instead, has all the external edges constrained. This modeling strategy, however, affects the shaft structural stiffness: a large inner radius determines an anomalous increment of shaft stiffness, while a very small inner hole gives rise to very large deformations and abnormally high reaction forces at constrained nodes. A proper sensitivity analysis has been preliminary carried out, in order to find the optimal radius of inner hole. (a) (b) Figure 6 : (a) Pressure distribution for JB1 configuration (α=0, T in =40°C – T out =80 °C) with deformable components; (b) lubrication meatus for rigid and deformable components. As an example, the coupled fluid-structural numerical approach that includes journal bearing elastic deformation was applied for the analysis of JB1 configuration for the case of α=0 and linear temperature variation in the range T in =40°C− T out =80°C. Fig. 6(a) shows the calculated pressure distribution, which has to be compared to that of perfectly rigid components shown in Fig. 3(a). The comparison emphasizes that elastic deformation contributes to a reduction of about 48% (from 83 MPa to 43 MPa) of the maximum peak pressure and, accordingly, an increase in the attitude angle β (since the resultant of pressure distribution is always the same applied force F ). The pressure profile, more uniform