Issue34

F. Curà et alii, Frattura ed Integrità Strutturale, 34 (2015) 447-455; DOI: 10.3221/IGF-ESIS.34.50 453 Figure 7 : Limit curve that highlights elements that reaches the yield condition before others. For doing that, a XFEM analysis has been carried on. Propagation analysis has been performed in four cases by varying rim and web thicknesses, as shown in Tab. 2. In all cases the crack initiation has been placed at the point where the maximum equivalent stress is reached by applying only the bending force, then the propagation simulations have been run for each test case without and with the centrifugal load, in order to evaluate how the speed affects the propagation direction. This is for highlighted the only effect of the rotational speed and geometrical features. Figs. 8 to 11 show the obtained results comparing the cracks propagated with and without centrifugal load (the bending force is always present). In particular in Fig. 8 is shown the case of full gear, in Fig. 9 a wheel with backup ratio m b = 2.16 and web ratio m w = 0.125, In Fig. 10 a gear with m b = 1.08 and m w = 0.012 and in Fig. 11 a gear with m b = 0.87 and m w = 0.125. Figure 8 : Propagation in full gear. Generally speaking, it is possible to observe that, in simulations with the centrifugal load, the crack path follows a direction that approaches the radial direction, independently by the geometrical features. As demonstrated in literature, the crack propagation related to the only bending action is ruled by the gear geometry; considering the effect of the centrifugal force, geometry gets less important and rotational speed always shifts the crack propagation towards a catastrophic failure.