Issue 30

F. Curà et alii, Frattura ed Integrità Strutturale, 30 (2014) 446-453; DOI: 10.3221/IGF-ESIS.30.54 449 Figure 3 : Initial crack position points. Figure 4 : Initial crack orientation in the tooth root fillet region. Totally 40 (20 for the full gear and 20 for the thin rim gear) numerical models have been created by means of Smacef v15 software. Firstly, gears have been meshed by traditional 3D finite element, then the region near the crack has been enriched with XFEM elements (Fig. 5); XFEM region has to be as big as the crack may be included during the propagation, but not too big in order to avoid long calculation time. The dimensions of the element in the XFEM region is 0.4mm. An elliptical crack has been inserted at one extremity of the tooth width. Gears have been loaded by a distributed force applied at the pitch diameter along the tooth width; the gear hub has been considered as clamped. Figure 5 : Mesh of the gear model with XFEM region. R ESULTS AND DISCUSSION esults show that the crack propagation path is generally influenced by both rim thickness and initial crack position, while initial crack orientation doesn’t seem to affect crack propagation. Tab. 3 resumes the main results concerning the effect of rim thickness and initial crack positions obtained from the simulations, where the letter S stands for the propagation direction along the tooth thickness (safe failure) and C stands for the propagation in radial direction (catastrophic failure). R