Issue34

F. Curà et alii, Frattura ed Integrità Strutturale, 34 (2015) 447-455; DOI: 10.3221/IGF-ESIS.34.50 447 Focussed on Crack Paths Effect of centrifugal load on crack path in thin-rimmed and webbed gears F. Curà, A. Mura, C. Rosso Politecnico di Torino, Italy francesca.cura@polito.it , andrea.mura@polito.it , carlo.rosso@polito.it A BSTRACT . Thin rimmed and webbed gears are used in particular applications to reduce systems weight. This kind of gears need an accurate and fail safe design. As a matter of fact, a possible failure, due to bending fatigue, consists in crack nucleation and consequent growth, in particular in the tooth root zone. These cracks may propagate through the tooth or through the rim. Crack propagation direction is basically influenced by the wheel geometry parameters, above all the rim thickness. Studies available in literature emphasize three ranges for the backup ratio values, involving different behaviors. These ranges are related to the crack propagation paths; respectively through the tooth, through the rim and in an unforeseeable way. This last uncertainty zone depends on other parameters, related to both geometry and loading conditions. In this work the effect of wheel speed related to the bending load has been investigated. The investigation has been carried out by means of numerical models involving both 2D finite element and extended finite element models (XFEM). Results shows that both crack initiation point and crack propagation path are strongly influenced by centrifugal load; this effect is mainly evident in the uncertainty zone of the backup ratio. K EYWORDS . Fracture mechanics; Crack path; Crack propagation; Gears; XFEM I NTRODUCTION hin rim gears are used in those applications where weight reduction is needed, such as aerospace environment; in this field an accurate and fail safe design is required [1]. Fail safe design means that, if a failure occurs, serious consequences must be avoided. Considering thin rimmed gears, a possible failure, due to bending fatigue, consists in crack nucleation and consequent growth, in particular in the tooth root zone [2, 3]. These cracks may propagate through the tooth (causing a safe failure) or through the rim (causing a catastrophic failure). Crack propagation direction is basically influenced by the wheel geometry parameters, above all the rim thickness (ruled by the so called backup ratio). Studies available in literature emphasize three ranges for the backup ratio values, involving different behaviours [4, 5]. These ranges are related to the crack propagation paths, respectively through the tooth, through the rim and in an unforeseeable way. This last uncertainty zone depends on other parameters, related to both geometry and loading conditions, in particular considering as loading condition the centrifugal load (generated by the wheel rotation) that may significantly influence the crack growth path [6]. Concerning the effect of load conditions on crack propagation it is possible to find in literature some interesting works: Glodez et al. [7] experimentally investigated the effects of different load distributions along the tooth width. Pehan et al. [8] evaluated the effect of not uniform load distributions and the not uniformly crack growth along the tooth width, by T