AGMA is happy to announce the publication of two new documents: AGMA 925-B22, Effect of Tribology and Lubrication on Gear Surface Distress, written by a subcommittee of the AGMA Helical Gear Rating Committee, and, AGMA 943-A22, Tolerances for Spur and Helical Racks, written by the AGMA Gear Accuracy Committee.
A common design goal for gears in helicopter or turboprop power transmission is reduced weight. To help meet this goal, some gear designs use thin rims. Rims that are too thin, however, may lead to bending fatigue problems and cracks. The most common methods of gear design and analysis are based on standards published by the American Gear Manufacturers Association. Included in the standards are rating formulas for gear tooth bending to prevent crack initiation (Ref. 1). These standards can include the effect of rim thickness on tooth bending fatigue (Ref 2.). The standards, however, do not indicate the crack propagation path or the remaining life once a crack has started. Fracture mechanics has developed into a useful discipline for predicting strength and life of cracked structures.
