Pressure vessels overwrapped with graphite-fiber-based composite materials that become damaged would be salvaged by a proposed repair technique. The need for the technique arises as follows: High-performance graphite-fiber-based composites are very susceptible to damage from impact or cutting. Heretofore, when a composite-overwrapped vessel has been damaged, it has been necessary to replace the vessel in its entirety. However, some vessels of this type are so large and expensive that it is uneconomical to discard them in the event of damage.
The proposed repair technique would involve adhesive bonding of a composite doubler over each damaged area. The doubler would transfer structural loads around the damaged area.
The fiber reinforcement in a doubler could be made of graphite, polybenzoxazole, or aromatic polyamid, for example. The fiber and matrix materials and the dimensions of the doubler would be chosen by design to suit the specific damaged area. The doubler would be bonded in place by use of a room-temperature-curing adhesive. Use of additional fiber overwrapping of the doubler would be determined on a case-by-case basis.
This work was done by Joseph C. Lewis of Caltech for NASA's Jet Propulsion Laboratory. No further documentation is available. NPO-20456