This project will evaluate highly aligned short fiber technology (TuFF) as a sustainable and environmentally friendly approach for structural repair of components on Department of Defense platforms. This project will demonstrate the feasibility of TuFF concepts for structural repair of complex airframe structures on a representative geometry, establish repair methodologies based on TuFF, demonstrate retention of structural performance in static load cases, and perform an environmental cost-benefit analysis to demonstrate sustainability. The effort is a collaboration between the University of Delaware Center for Composite Materials (UD-CCM) and the Naval Air Systems Command (4344 Polymers & Composites, technical point of contact: Stan Ng).

Under a recent Defense Advanced Research Projects Agency-funded program, a patent-pending short fiber alignment and preforming process called TuFF has been developed at UD-CCM. TuFF is a highly-aligned short fiber material form and composites have been manufactured with IM7 fiber and aerospace quality. Sustainable repair concepts based on TuFF will focus on thermoset and thermoplastic concepts with short IM7 in both prepreg and dry fiber forms, repair process design to improve consolidation quality with vacuum pressure only (field repair), and the use of recycled short carbon fiber (CF) for repair. Repair methods for thermoplastic vs thermoset repair to minimize use of hazardous materials, alternates to epoxy adhesives in the bondline, thin-ply vs thick-ply repair patch design, and sustainable strategies based on recycled CF are of particular interest. In parallel, a sustainability analysis will quantify hazardous material use in current repair procedures, including reactive materials use and storage, disposal costs for hazmat, current repair procedural impact on sustainability (e.g. consumables, hazmat scrap, volatile organics, NOx), and Depot to Operational use cases. Reductions in material scrap, and hazmat use based on the TuFF repair concepts will be quantified and compared, including the use of recycled fiber for repair patches and recycling/reuse of repair scrap.

Successful demonstration of TuFF based composite repair concepts has environmental and cost impact far beyond the military sector. A major advantage of the TuFF concept is the ability to form shapes from flat prepreg/dry material forms due to stretchability. This eliminates the need for splash molding of the scarf patch from a complex geometry part, and directly apply TuFF repair material to the structure. Repair concepts based on vacuum consolidation only with local heating can achieve high consolidation quality due to TuFF confirmability to the repair geometry. The synergy of TuFF material form advantages (in-plane stretch to conform to geometry, retention of performance, thin-ply effects, use of recycled CF) combined with reduced scrap, thermoplastic solutions and vacuum consolidation methods can significantly alleviate current challenges with expired shelf-life materials and process scrap. Use of recycled fiber provides a sustainable low-cost solution for repair, provided performance targets can be met.