SBIR-STTR Award

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

In modernizing its rotorcraft fleet, the US Army has identified the pressing need to increase the horsepower of existing rotorcraft transmissions without sacrificing component life, as well as the need for new transmission designs with higher power density capacity and improved durability. The concept of improving fatigue resistance without enlarging the design envelope or imposing changes that would require new part qualifications is attractive from both cost and time savings standpoints. Data and results from Phase I have provided new information concerning laser shock peening application and residual stress response in carburized Pyrowear 53 steel. Laser peening can improve fatigue life by achieving high levels of residual compression to significant depths in a given part. Promising modeling work associated with the Phase I physical testing has laid the foundation for a computer design tool, enabling laser peening residual stress prediction in combination with other manufacturing processes, such as prior heat treating. Phase II will characterize fatigue life improvement in carburized and hardened Pyrowear 53 steel by laser shock peening. Experimental results will be used to aid the development, validation and commercialization of a process modeling design tool for predicting the residual stresses which drive the fatigue life improvement.

Keywords:
Laser Shock Peening, Fatigue Life, Residual Stress, Steel, Gears, Design Tool, Finite Element Simulation