In-situ analysis of cocured scarf patch repairs

To address the need for high-quality in-field repair of composite structures, a vacuum-bag-only (VBO) prepreg was designed, produced, and evaluated. The prepreg featured semi-preg formatting and a room-temperature-stable resin. The format provided a multitude of pathways with much shorter breathe-out distances relative to conventional, edge-breathing VBO prepregs, and thus enhanced through-thickness air permeability. A custom-built scarfed repair tool with an in-situ observation window was designed and employed to analyze the cure process during a repair. Microstructural quality, interlaminar shear strength, and glass transition temperature of semi-preg panels were compared to wet-laid epoxy panels processed with double vacuum debulking (DVD). The semi-preg formatting effectively reduced porosity for in-field scarf panels, and when used with the new material system, presents a viable alternative to DVD and wet layup.