Light Cavitation Peening of Carburized Gears

This Phase II project proposes to improve the fatigue life and power transmission capabilities of carburized gears by enhancing crack initiation resistance through cavitation peening. Cavitation peening is a low cost surface enhancement process that induces high magnitude residual stresses on a surface by sweeping an ultra-high pressure jet over the surface to be peened so that cavitation bubbles form and collapse on the workpiece. The shock of the collapsing bubbles causes the formation of beneficial residual compressive stresses. The process is further enhanced by combining it with shot peening. Phase I work showed that the combined process could generate 228,000 psi residual compressive stresses on the surface of carburized steels, even in simulated gear root radii. These beneficial stresses are at least 50% higher than can be achieved by conventional shot peening, and the induced stresses were shown to be stable, resisting exposure to stress cycling and high temperature. Phase II work will continue to optimize the combined process and demonstrate the benefits with coupon fatigue testing, single tooth bend tests and full gear testing. Target platforms include Sikorsky’s UH-60 and CH-53E/K, Boeing’s AH-64D and CH-47 and Bell’s OH-58D and the F-35 JSF.