D. B. L. Ferguson, Z. Li, A. M. Freborg, Deformation Control Technology, Inc., Cleveland, OH
To meet a goal of at least a 25% improvement in helicopter gear tooth bending fatigue life, a project was initiated at DCT under Army Aviation Technology Directorate sponsorship to improve the compressive residual surface stress state by applying intensive quenching in place of conventional oil quenching. The feasibility was demonstrated and reported upon using a carburized and quench hardened notched bar sample subjected to three point bend testing. This paper reports on single tooth bending of carburized and quench hardened Pyrowear 53 steel gears that were subjected to single tooth bend tests. The fatigue test data show the intensively quenched gears were superior to conventionally heat treated gears. The surface residual stress state had a higher magnitude of surface compression for the intensively quenched gear than for the oil quenched gear. Computer simulations of the heat treat processes provides a sound understanding of why these quenching methods produced different bending fatigue strength for the same essentially the same martensitic microstructures and hardness levels.
Summary: To meet a goal of at least a 25% improvement in helicopter gear tooth bending fatigue life, a project was initiated at DCT under Army Aviation Technology Directorate sponsorship to improve the compressive residual surface stress state by applying intensive quenching in place of conventional oil quenching. The feasibility was demonstrated and reported upon using a carburized and quench hardened notched bar sample subjected to three point bend testing. This paper reports on single tooth bending of carburized and quench hardened Pyrowear 53 steel gears that were subjected to single tooth bend tests. The fatigue test data show the intensively quenched gears were superior to conventionally heat treated gears. The surface residual stress state had a higher magnitude of surface compression for the intensively quenched gear than for the oil quenched gear. Computer simulations of the heat treat processes provides a sound understanding of why these quenching methods produced different bending fatigue strength for the same essentially the same martensitic microstructures and hardness levels.
