Validation Device for Cold Expanded Holes

ABSTRACT: Resodyn Corporation proposes to develop a portable, cost effective, near-surface residual stress measuring tools based on electromagnetic principles. Resodyn Corporation has patented technology developed for validating cold expanded button head rivet holes.The first application in Phase I is to apply this technology to countersunk cold expanded rivet holes in 7075 aluminum. In Phase II, probes will be developed for all of the common hole sizes of interest to the Air Force, and additional evaluation algorithms will be developed for other alloys such as 2024 aluminum and titanium. At the end of Phase II, field tools will be available for evaluation at Tinker AFB. The proposed work will include custom sensors, proprietary detection circuitry (patent pending), residual stress, strain and cold work studies, and correlating algorithms. Extending the technology to other surface stress processes such as peening on fan and compressor blades is also proposed for Phase II. BENEFIT: An operational need exists for a non-destructive method that can quantify the effectiveness of the cold expanded hole process. When the correct amount of residual stress is induced around a cold expanded rivet hole, fatigue life is enhanced up to 20,000 hours. However, because there is no method to guarantee, 100%, that the correct amount of residual compressive stress was created, the process cannot be given credit in design calculations. It is presently done to provide un-credited safety margin. The proposed validation device for cold expanded holes will provide 100% inspection and thus enable the design credit.