Design Tool for Fatigue Sensitive Steel Rotorcraft Components

In modernizing its rotorcraft fleet, the US Army has identified the need to increase the horsepower of existing rotorcraft transmissions without sacrificing component life, and also the need for new transmission designs with higher power density capacity and improved durability. The concept of improving durability without enlarging the current transmission envelop or imposing changes that would require new part qualifications is attractive from standpoints of cost and time savings. The Laser shock peening (LSP) process has this potential. A non-contact method, LSP can improve the fatigue life by achieving high levels of residual compression to significant depths in a part. While LSP is used commercially for other aerospace materials and parts for life improvement, it has not been used on carburized steels. In Phase I, carburized and quench hardened Pyrowearr 53 steel test bars will be treated using LSP to determine the effects of initial stress state of the part and process parameters on residual stress. A finite element process model will be developed and validated to provide the basis of a design tool that can be used to assess potential applications of LSP for transmission components and to predict the level of fatigue life improvement that may be anticipated.