AGMA 07FTM11 PDF

Gear tooth wear is a very difficult phenomenon to predict analytically. The failure mode of wear is closely correlated to the lambda ratio. Wear can be the limiting design parameter for long-term durability. Also, the failure mode of wear can manifest into more sever failure modes such as bending. Presented is a failure analysis in which this occurred.

A legacy aerospace gear mesh experienced nine failures within a two year time period. The failures occurred after more than eight years in service and within tight range of cycles to one another. Each failure resulted in the loss of all gear teethwith origins consistent with classic bending fatigue. None of the failureswere detected prior to tooth loss.

Non-failed gears, with slightly lower time than the failed gears, were removed from service and inspected. Gear metrology measurements quantified a significant amount of wear. The flank form of these worn gears was measured and the measured data used to analytically predict the new dynamic load distribution and bending stress. To predict if the failure mode of wear was expected for this gear mesh, an empirical relationship of wear to lambda ratio was created using Rolls-Royce field data from multiple gear meshes in multiple applications.

The empirical understanding of wear coupled with the analysis was used in an analytical design of experiments (ADOE). The results of the ADOE were then used to guide design changes. Presented are the metallurgical failure analysis findings, dynamic gear mesh analysis, the empirical wear rate curve developed, results of the ADOE, and design changes.