Determination of the Crack Propagation Life of a Planetary Gear Carrier

Fatigue cracks were discovered in two separate main transmission planetary gear carriers of U.S. Army helicopters. These cracks initiated in the blend between the gear post and the plate. An ultrasonic probe was developed by the aircraft manufacturer to inspect the planetary carrier without requiring its removal from the aircraft. This paper summarizes work performed to determine the crack propagation life of a planetary gear carrier, and thus a reliable inspection interval. The work included: finite element analysis, crack growth modeling, strain surveys of a planetary gear carrier, as well as metallurgical and fractographic analysis of the cracked parts. The integration of the components of this multi-disciplinary investigation will be discussed.