Automated Manufacture of Damage Detecting, Self-Healing Composite Cryogenic Pressure Vessels

During Phase I, Aurora Flight Sciences and the University of Massachusetts Lowell propose to demonstrate the feasibility of enhancing a commercially available out-of-autoclave (OOA) carbon prepreg material system (e.g. IM7/5320) via embedded structural health monitoring (SHM) and self-healing capabilities, which can be manufactured by an automated fiber placement (AFP) machine. This proposed "smart" material will ultimately enable the cost-effective manufacture of large, lightweight core-stiffened composite cryogenic pressure vessels. Carbon nanotubes (CNTs) will be transferred either directly onto the prepreg, or onto adhesive film plies that are subsequently laminated with the prepreg material. Electrical conductivity measurements via the CNTs will provide embedded SHM capabilities, while localized Joule heating will accelerate self-healing polymerization reactions. The CNT-enhanced prepreg will also serve as a carrier layer to embed well-dispersed self-healing micro-/nano-capsules within the polymer matrix and which will allow for self-healing of microcracks resulting from impact damage and thermal cycling. Self-healing efficiency will be characterized via mechanical testing. This smart material will ultimately be produced in spools of half-inch wide unidirectional prepreg slit tape, and laid down using Aurora's 7-axis, 16-spool automated fiber placement (AFP) machine. Trade studies will be performed on the AFP machine to determine the optimal processing parameters for laying down the smart material. The targeted demonstrator structure, a "smart" cryogenic pressure vessel, will detect microcracks caused by incident impact damage and rapidly repair the damage in situ.