How are the composite materials when it comes to stress fracturing? Believe it or not, with aluminum, airline companies bolt a patch over the cracks until it can be sufficiently repaired, which may take months and in some cases years.
TJ, your points are well taken. The biggest problem of all in composite repair, though, compared to metal repair, is the lack of knowledge to identify damage in the first place, since it's much more difficult to detect. The next biggest problem is figuring out how to repair so many different materials with so many different uses and so many different possible procedures. And, by extension, lack of knowledge there, as well.
Bombardier may go for traditional repair techniques on the areas in danger of ground support damage, but if composites shrug off the damage that would ding aluminum, then composites would seem to be the better bet.
Follow-up from last night's comment: After I mentioned the American Airlines flight that crashed in 1979 after a design flaw left it vulnerable to maintenance damage, I tried to remember where I had once read about that accident. Here's the answer: Our distinguished columnist, Henry Petroski, wrote about it in his book, "To Engineer Is Human."
Thanks, Alex. The news just keeps coming out on this subject. Regarding standards, that's a really good question. One of the key critiques in the GAO report was the point that you can't base repair standards and best practices for composites on the same ones that were created for metal. There are too many differences across the board, and making the same assumptions or using the same templates would be ineffective and dangerous. That may be another reason why we're not hearing much yet about the details of repair whens and hows. I suspect it's a WIP.
@Charles: You're absolutely right; materials selection involves many considerations besides the material's response to stress and strain -- which can be complicated enough, since the material may respond very differently at different temperatures and strain rates, and its properties may be different in different directions. But how a given material will perform in your application also depends on its location in the galvanic series, among other things. Cost and manufacturability are always major concerns, too. Then there are externalities such as recyclability and end-of-life issues, sustainability and lifecycle emissions, etc. And -- although I may be somewhat biased in this regard! -- this is why having a good materials engineer is a necessity.
This is a classic example of the need to beware that what looks good on paper may not always be so. As design engineers, we are often trained to consider matters of stress and strain -- bending, shear, torsional capacity, etc. But here we have a situation where the composite is apparently appropriate in matters of material strength, but not in matters of maintenance. Obviously, maintenance is a huge consideration for aircraft. In 1979, an American Airlines flight leaving Chicago O'Hare crashed, killing 271 people, after a design flaw left the engine pylon vulnerable to maintenance damage.
I'm impressed by the breadth of your recent coverage on composites, Ann. I'm wondering if you see new standards emerging out of the FAA as regards composites repair, or will we see industry-standard practices come into play first, which will become de facto methodologies for both repair and recycling?
Rob, that's the $64,000 question. I think the answer here is also 'both." Composites are definitely moving forward in aerospace, as shown by all the aircraft makers using them in greater amounts. And detection of at least certain types of damage is difficult, but apparently not impossible.
I think the answer is a bit of both. Beth, the industry apparently has been working on solving this problem along with the FAA. At least, that's what they all tell us. But it's quite difficult to find out any details. And that's where ScotCan's point comes in. As the report delineates, industry has been extremely secretive regarding the details about their materials--the type of details which must be well known for determining when and how to repair--in the name of trade secrets.
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