Issue 30

F. Curà et alii, Frattura ed Integrità Strutturale, 30 (2014) 446-453; DOI: 10.3221/IGF-ESIS.30.54 450 Initial crack position point Backup ratio A B C D E Full Gear S S S S S 1 S S S C C 0.5 S C C C C 0.4 C C C C C 0.3 C C C C C Table 3 : Crack propagation direction for different backup ratios and initial crack position ( S = propagation along tooth thickness, C = propagation in radial direction). Considering the full gear, results show that the crack path brings always, independently form the initial crack position, to the tooth removal (fail safe), as shown in Fig. 6. On the other hand in thin rim gears the initial crack position seems to affect the crack path and, in particular, if the crack nucleates near the bottom of the tooth fillet (points D and E, Fig. 3), then it follows a path in radial direction bringing to a catastrophic failure. Figure 6 : Crack paths for different initial crack positions for the full gear. As an example Fig. 7 and 8 show the crack paths for backup ratio m B respectively 1 and 0.5. Figure 7 : Crack paths for different initial crack positions for thin rim gear (m B = 1).