Cavitation Peening of Aluminum Fastener Holes In-Situ

Aging aircraft experience fatigue cracking from stress concentrations around rivet holes. Current best practice is to pull an oversized mandrel through the hole to induce beneficial residual compressive stresses and this improves fatigue life significantly. However, the benefit is reduced for chamfered rivet holes, where the compressive stresses are lower. The goal of this proposal is to use cavitation peening to induce deep, high magnitude residual compressive stresses around the hole and in the chamfered area, thereby improving fatigue life. The cavitation peening process currently uses a high pressure jet to sweep over the surface of the part while it is submerged in a water tank. This project will modify the technology so the part does not have to be submerged in a water tank so large structures can be cavitation peened. The cavitation peening equipment would be mounted on a roll around cart and the peening nozzle clamped to the surface to be peened. The process will be very inexpensive and clean with no shot or risk of foreign object damage. The system would be extremely versatile and could be used for a wide variety of applications, not just rivet holes.