Date: Jan 01, 2012 Source: ARMY SBIR Success Story (
click here to go to the source)
The Army is continuously modernizing its rotorcraft fleet and has identified the need for new transmission designs with higher power density and improved durability. The performance, reliability and safety of fatigue sensitive steel components in military and commercial rotorcraft can be significantly improved with the creation of deep compressive residual stresses in critical surface regions. The objective of this SBIR project was to develop a design tool to estimate and optimize the residual stress profiles and fatigue life improvement resulting from laser shock peening (LSP) of fatigue sensitive steel rotorcraft components. In the past, creation of post heat treatment compressive residual stresses has been limited to only shallow depths of 0.005 inches or less.
Deeper compressive residual stresses are possible but result in excessive roughness of the surface, which is undesirable in precision dynamic components with lubricated contacts. The use of a laser to create a high-energy pressure pulse on the surface of titanium and aluminum has shown the capability to achieve significant surface residual stresses 1020 times greater in depth than conventional peening and with minimal increase in surface roughness. The process results in large increases in the fatigue strength of components fabricated from these materials.
Deformation Control Technology, Inc. (DCT) developed a LSP process design tool, consisting of a validated computer model capable of predicting residual stress response in prior heat treated, carburized gear steels in support of efforts to develop LSP technology for helicopter drive-train gears. Helicopter gears must transmit high powers at the lowest possible weights (i.e., high power densities). Consequently improving gear fatigue strength in the flank and root areas with the associated inhibition of crack initiation and growth in the gear root is projected to have high payoffs, including meeting new and more demanding mission needs as well as improved component lifetime and reliability and lower maintenance costs.
Technology Transition:
DCT's objective transition was to develop, validate, and verify a software release for use by commercial industries in an effort to broaden the number of materials and geometries in the software database and validate the software on arbitrary LSP components. The resulting residual stress and fatigue life optimization tool will be highly beneficial to both military and commercial rotorcraft components. Boeing and Metals Improvement Company are currently using the product to develop a LSP method for gears on the Ah-64 helicopter. $200K in additional funds to further develop the modeling tool has been provided by Metals Improvement Company who has the capability to provide LSP services to the Original Equipment Manufacturers.
