Comparison of the Crack-Growth Rates for Full-Encirclement and Patch Composite Repairs

Abstract In the United States, full-encirclement bonded composite repairs have been an allowable repair method for pressure vessels since 1991. These repairs are used to reinforce damaged pressure vessels by wrapping composite completely around the vessel wall. Installing a full-encirclement repair becomes expensive and cumbersome for larger diameter vessels. And so, a patch size repair becomes preferred for use on bigger vessels. This composite patch bonds over the desired area on the damaged wall instead of completely wrapping the circumference of the vessel. In this paper, we investigate the crack propagation behavior of two repair types used to repair through-wall defects on a pressure vessel. An optical method has been adopted which monitors the crack propagation by observing the out-of-plane deflection of the blister area. It was found that the two repair types have similar crack propagation behavior during fatigue testing.