Damage-tolerant polymeric composite overwraps have been proposed for lightweight pressure vessels that are made of composites of graphite fibers in polymeric matrices. Graphite-fiber/polymer composites are vulnerable to impact damage; overwraps on the pressure vessels help to protect against such damage.
In current practice, an overwrap is made of a composite of glass fibers in a polymeric matrix. The glass fibers are too weak to contribute significantly to the structural strength of the underlying pressure vessel, and the glass-fiber-based overwrap adds significantly to the weight of the vessel.
According to the proposal, the outer layers of a graphite-fiber/polymer pressure vessel would be made of polybenzoxazole (PBO) fibers in a polymeric matrix. The PBO fibers would protect the underlying graphite/polymer composite layers against impact damage, but unlike glass fibers, the PBO fibers would be almost as structurally efficient as the graphite fibers. Layers of PBO fibers could even be used as substitutes for some of the layers of graphite fibers, in which case the overwrap would contribute very little additional weight to the vessel.
This work was done by Joseph Lewis of Caltech for NASA's Jet Propulsion Laboratory. No further documentation is available. NPO-20442