The more primary a structure is, and the closer it operates to its design limits, the more difficult the repair. However, even heavily-loaded primary structural composites have been successfully repaired for many years. Heavily loaded, oriented-fiber, advanced composite structures require careful engineering design of major repairs—it is not simply a matter of slapping on a patch.
Given a good repair design, the skill and quality attitude of the repair technician becomes critical. Vacuum-bagging becomes virtually mandatory for advanced composite repairs, in order to achieve the required compaction and proper consolidation of the repair plies.
Prepreg can sometimes be repaired with either prepreg or wet materials in field conditions—autoclaves for repairs are rarely necessary.
Composite repairs can be quite time-consuming, and require careful attention to lots of picky details. Most of these repairs rely fundamentally on high-quality adhesive bonding. The strength of an adhesive bond cannot be measured without destroying it! Therefore, careful control of the repair process, especially regarding cleanliness, fit of the repair patch, and meticulous surface preparation of the bonding surfaces, becomes crucial. It all goes back to the skill, training, and integrity of the person doing the repair.
In spite of all these obstacles, successful repairs of complex composite structures are being done every day. There is no “black art” to composite repair—just a good attitude, training, and practice. Experimentation will always help to prove-out the best practices and clear-up uncertainties. Finally, quality assurance is an absolute must, requiring a thorough understanding and dedication to underlying principles and the testing required to ensure the repair will be successful long-term.
Published courtesy of Abaris Training Resources, Inc