High Strength, Affordable Helicopter Gears

The Army's Rotorcraft Force Modernization Fleet requires a substantial increase in main gear box power density, with minimal impact on the gearbox interface. Consequently the Army has specified the goal of achieving transmission gear tooth bending fatigue improvement of 25%. This project seeks to accommodate the higher power density requirements through enhanced and innovative material processing. The Phase I effort of this project has successfully demonstrated both the improvements in residual surface compressive stress and bending fatigue life possible for the gear steel Pyrowear 53 through an innovative heat treatment called "Intensive Quenching." Comparative evaluation of Pyrowear 53 notch bar specimens demonstrated a 2x increase in residual surface compression, and at least 20% improvement in bending fatigue performance with the use of intensive quench processing as opposed to standard oil quenching. Phase II will seek to expand the characterization of the innovative heat treatment, in conjunction with superfinishing, into full test gears. The Pryowear 53 gears will be fully processed, comparing the standard to the innovative heat treatment, with single tooth bending fatigue comparisons performed, along with full metallurgical, dimensional and residual stress characterization. With this assessment, technology transfer to the US Army OEM's will be facilitated.