"Depending on the chemistry of the capsule wall, we intend to grade the wall structure so it fractures at different energy levels corresponding to different amounts of impact," Brown said. "Some coatings could be created for applications with damage that occurs at low energy levels of impact, and others could be developed for damage that occurs at higher energy levels of impact. Alternately, we could develop a single coating with different signatures that looks different depending on different energy levels of impact. For now, we are looking to develop one coating that displays one energy level of impact. Once you've proved the technology works for one energy level, there's no reason you couldn't dial up a different wall structure for a different energy level."
Both internal and external coating applications could be developed with this technology. For example, composites inside the aircraft are exposed to a less severe environment than those on the leading edge of a wing, so the types of energy events in these environments may be very different. "As we approach the end of the first 18 months, we may therefore have certain research strands that aim toward external coatings and others that aim toward internal coatings."
The research targets glass-fiber and carbon-fiber composites. Since GKN provides aerostructures, the coatings would be provided as added functionality to its current and future product portfolio.
Chuck, someone knows a lot about the subject, and I wish I did. I've already spent quite a lot of time surfing and snooping around on the Web, but it's quite difficult to find out anything aside from what's in that GAO report, and Boeing is less than forthcoming. I assume this is for security and/or market competition reasons. I'm checking the MRO schools' websites for course descriptions, e.g., but not much luck so far. The thing to remember, in general, is that repair techniques have existed as long as composites in aircraft have existed, but for some time it was all military. Then they entered the commercial aircraft sector, but not, I repeat not, in primary structures. Their use in primary structures has changed everything.
Alex, thanks for thinking industry-wide again. I agree, the technology is certainly in the early stages and it makes me wonder how many other coatings manufacturers or composite airstructure makers are conducting similar research under the radar, possibly even in partnership with each other. It might make more sense from an industry standpoint to develop and commercialize something that can be applied by all airstructure manufacturers and regulated by the FAA. But that also assumes that it can be applied in an aftermarket scenario and still work properly. I get the impression that GKN's coating needs to be "baked" in, either literally or figuratively, in order to do its job. But that could also be because they are not a coatings manufacturer.
TJ, that's funny, using whiteout to detect cracks and delams. I bet it worked great. But I doubt if that would work on CFR composites or even glass-reinforced composites. Damage on these, especially CFR, is invisible to the naked eye and techniques for detecting it different from those used for detecting same in traditional materials. You are right, I carefully did not reveal the wavelength since I honored the company's request in order to get this much published.
You say damage-detecting coatings have been around for awhile, but not using non-visible wavelengths. Do you mean that damage-detecting coatings *for these composites* have been around for awhile? Please inform us if you know!
Thanks for the info, Ann. So that means that the ability to utilize this detection technique will be proprietary, but I guess it also indicates that the state of the technology is at the point where other composite makers should be able to do this too, at least eventually. (That's unless there's only a very narrow class of coatings which are amenable to the detection process, and they're patented or trade secret.) Anyway, I guess the upshot is that this is not going to be anywhere near as industry-widee as I assume. At the same time, it opens up the idea that, with technology advancing, maybe the FAA can move towards some specificity in its composites directives.
I've seen simple things like White-Out used during materials testing to detect cracks and delaminations.
The damage-detecting coatings themselves I believe have been around for a while. The trick to which this article alludes is the non-visible wavelengths that would be used. THAT is a good idea. Damage-detecting coatings that the flying public can see are not confidence building.
The article carefully did not state which spectrums would be used, whether infrared or ultraviolet. I might consider watching the wing with my IR scanner in the future....
Alex brings up two important points. First, since this proposed coating or class of coatings will be available only as an inherent part of a composite airframe structure sold by one company, it won't be available for other composite airframe structures sold by other manufacturers. I've already heard of one other project targeting a similar purpose but using an entirely different chemical and behavioral model. That means competition among different types that work in different ways. So actually there may not be much in the way of industry-wide techniques.
Second, it does provide a great opportunity to gather MBTF data. Even if it's coming from airstructures using entirely different coating types, the data should be comparable about how composites break.
This is indeed a significant development because it holds the promise that there will be a cost-effective, easily implementable, repeatable, industry wide technique for inspect composites. This is going to be critical important not only to prevent in-flight failures, but also to gather life (MTBF) data on how different composite structures actually perform on commercial aircraft, particularly on primary structures like wings. (A primary structure in aerospace terms refers to a part where, if it fails, the plane will no longer be flyable. So for example you can survive a rip in the fuselage, but not the loss of a wing.)
I don't think the technology has been around for awhile, at least not for composites. The idea may have been. But there's a big difference between realizing one can use coatings to assist in detecting damage--the no-brainer aspect--on one hand, and on the other figuring out exactly what coatings, how they should work, how to apply them without causing other problems, etc. Since GKN is a supplier of composite airstructures and since their scientist describes redesigning a coating at the microsphere level, I would suspect that what's taken some time is the process of figuring out details of how to make and implement such a coating. Even at this point before the 18 months + another 18-24 months before commercialization, they gave a quite coherent description of the basic idea. Yet it will likely take 3+ years before a flight test is likely. So the R&D involved is not trivial.
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