Issue 30

F. Curà et alii, Frattura ed Integrità Strutturale, 30 (2014) 446-453; DOI: 10.3221/IGF-ESIS.30.54 452 Figure 10 : Crack paths for different initial crack positions for thin rim gear (m B = 0.3). C ONCLUSIONS n this work a numerical investigation about crack propagation path in thin rim gears has been done. In particular this work is focused on the analysis of the two different failure modes that a crack may cause on a gear: safe failure, if the crack growth through the tooth, and catastrophic, if the crack propagates in the radial direction. Numerical models have been meshed by using XFEM technique. The effect of rim thickness, initial crack position and initial crack orientation have been investigated. In order to better represent the value of the rim thickness respect to the gear geometry, according to the literature, the ratio between rim thickness and tooth height (backup ratio) has been adopted. Results shows that the crack propagation path depends on both backup ratio and initial crack position, while the initial crack orientation seems not to affect crack path. In particular if the full gear is considered crack paths seems not to be influenced by the initial crack position and cracks growth through the tooth; on the other hand, thin rim gears (gears with backup ratio ≤ 1) the initial crack position may change the crack path direction. If the rim thickness reduces and consequently the backup ratio decreases up to 0.4, again the crack path seems not to be influenced by the initial crack positions, but this time the growing path is in radial direction through the wheel. This work represents a first step of an ongoing research that will take into account other geometric parameters and others influencing factors such as rotational speed. So the main goal of this activity is to give to designers consistent information about gears geometry in order to avoid catastrophic failures possibilities. R EFERENCES [1] Lewicki. D. G., Crack Propagation Studies to Determine Benign or Catastrophic Failure Modes for Aerospace Thin- Rim Gears, NASA Tecnical Memorandum 107170. [2] Lewicki, D. G., Effect of Speed (Centrifugal Load) on Gear Crack Propagation Direction, U.S. Army Research Laboratory, Glenn Research Center, Cleveland, Ohio (2001). [3] Lewicki, D. G., Three-Dimensional Gear Crack Propagation Studies, U.S. Army Research Laboratory, Lewis Research Center, Cleveland, Ohio, NASA/TM-1998-208827. I