In addition to repairing composites in aircraft structures, figuring out whether they have been damaged in the first place was a top priority in a GAO report that critiqued the growing use of composites.
We have reported before on this site on self-monitoring adhesives that could predict aircraft structural failures. Now GKN Aerospace, one of Boeing's composite aerostructure suppliers, is researching a class of coatings that may make fractures and other damage visible under certain nonvisible wavelengths.
GKN Aerospace has partnered with a UK university in an 18-month collaborative research venture that's in its first quarter, Max Brown, head of engineering at GKN Aerospace's Filton engineering center, told us.
"Our collaborative coating research is aimed at supplying inspection techniques for the future maintenance and repairability of composites," said Brown. "Today, it may not be immediately obvious to an inspector of composite material as to what level of damage has been experienced, if any. What we envisage is a more intelligent inspection capability. For example, when inspectors are looking at a wing structure, they could look in the right wavelength range, and any areas that have damage above a certain preset threshold will clearly display that damage."
By the end of the program, GKN expects the coating to reach TRL (technology readiness level) 2 or 3. That would indicate that the research team has proven the basic chemistry and would then be able to move to detailed conversations within the engineering community about development for specific applications. "In an additional 18 to 24 months or so, we would probably be approaching TRL 5 or 6." When a technology reaches TRL 6, it's ready for a demonstration -- in this case, a flight trial.
GKN's goal is to design specific microspheres held within a coating. On impact, if damage has occurred, the microsphere capsule wall fractures, and the chemical reactions produce a signature within the coating that is visible at specific wavelengths.