Light Cavitation Peening of Carburized Gears

Cavitation peening (CP) is a novel method of inducing residual compressive stresses in components to enhance fatigue life and improve damage tolerance. The process involves sweeping ultra high-pressure waterjets over the surface to be peened so that cavitation bubbles form and collapse on the workpiece. The intensity of the peening is controlled by varying the speed at which the jet traverses the workpiece so that light peening can be accomplished inexpensively. Recent work has demonstrated the ability to induce high magnitude compressive stresses in carburized gear material, resulting in significant improvements in coupon fatigue life. An additional feature of the process is that it has little or no effect on the surface finish, which may be important to gears that are subjected to Superfinishing. Also, unlike conventional shot peening, CP does not substantially cold work the material which has lead to speculation that the residual stresses might not be relieved through exposure to high localized temperatures or to repeated stress cycles, allowing designers to “take credit” for the residual stresses. The proposed work would explore this issue by peening carburized coupons, measuring residual stresses and fatigue testing the coupons to determine if the residual stresses remain effective through time/temperature/stress cycles.