Cavitation Peening of Dynamic Components to Improve Fatigue Resistance

Cavitation peening is a novel method of inducing deep residual compressive stresses in metal 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 shock of the collapsing bubbles causes the formation of beneficial residual compressive stresses. Measurements have indicated no weight loss or change in surface finish of the workpiece. Because no heat is used there are no detrimental thermal effects. The process has the promise of achieving the similar beneficial effects as laser shock peening but without the negative side effects and at less than 10% the cost. In addition, the nozzles can be miniaturized so as to access tight spaces such as the root of gear teeth, small IBRs and bearing races. The induced stresses can be deeper than detectable flaw size, thereby enabling the detection of flaws before they become critical. An alternative version of the process is to peen at high speed to induce residual stresses that are deeper than are possible with conventional peening but at very low cost.BENEFITS: Fatigue is a common problem for dynamically loaded parts in all industries and is frequently the life limiting consideration. Surface enhancement through shot peening has been shown shown to improve fatigue life but more recently new processes have been developed that induce much deeper stresses than are possible with conventional shot peening. Cavitation peening is the least expensive of these processes and holds out the promise of widespread application to transmission gears, high performance springs, aircraft engine components, even nuclear power plant tubing. The fact that just pure water is used means that there is no waste stream from the process. Most of the equipment required to accomplish cavitation peening is available in job shops and manufacturing facilities throughout the country, making widespread adoption of the technology more likely. The proposed research would expend it's application from specialty materials to common high strength steels.