D. B. L. Ferguson, Z. Li, A. Freborg, Deformation Control Technology, Inc., Cleveland, OH
It is well known that carburization of alloy steels promotes compressive residual surface stress upon hardening, and that residual compressive surface stress enhances fatigue life. Gear manufacturing process routings usually include steps such as shot peening to insure that critically loaded surfaces have residual compression. Gear design, however, typically ignores residual stress and the capability that it has for improving gear performance. Under US Army Sponsorship, SBIR projects are in-progress to improve the bending fatigue strength of helicopter gears through the achievement of deeper compressive surface stress. Two methods are being examined for the now standard helicopter transmission gear steel, Pyrowear 53. One method is based on an alternative quenching method, and the other is based on a high energy mechanical surface treatment, laser shockpeening. The coupling of these processes is also being investigated.
