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F. Curà et alii, Frattura ed Integrità Strutturale, 34 (2015) 447-455; DOI: 10.3221/IGF-ESIS.34.50 450 Figure 3 : Geometric parameters of the wheel. Test Case Backup ratio m b Web ratio m w Load 1 Full gear Bending 2 2.16 0.125 Bending 3 1.08 0.012 Bending 4 0.87 0.125 Bending 5 Full gear Bending + speed 6 2.16 0.125 Bending + speed 7 1.08 0.012 Bending + speed 8 0.87 0.125 Bending + speed Table 2 : Test cases considered for the crack propagation study with XFEM. R ESULTS AND DISCUSSION Static analysis irstly, the interaction between bending force, centrifugal field and position of the maximum stressed point has been investigated. The model considered in this case is a solid gear without any thin rim or web. For doing that, a first analysis was carried on with the following parameters: 1. the centrifugal field has been set as constant (rotation speed = 10000 rpm), the value of the force has been increased and the crack direction investigated; 2. the force has been always applied at HPSTC and its magnitude has been changed in order to highlight the effect of the interaction between the two loads. In particular four models have been developed, starting from a value of the bending force F and then its magnitude has been increased at respectively 2F, 5F and 8F. Fig. 4 shows the results obtained from this study; it is possible to observe that, if the centrifugal load is dominant, the crack tends to propagate approximately on a radial direction, while, if the bending effect is higher then the centrifugal field, the crack tends to propagate through the tooth. The interaction between the bending force and the centrifugal field produced by the rotational speed on the position of the maximum equivalent stress (Von Mises) point has been also investigated. F