PPRuNe Forums - View Single Post - Are Large Carbon Fibre structures Airworthy ?
Old 7th Aug 2008, 13:00
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SNS3Guppy
 
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I'm thinking of both, because carbon materials and glass are interchangable in construction and use in many cases. You seem to be under the impression that carbon fiber must be baked; this is not the case. Often it's used as a prepreg or lay up material in the same way that E or S glass or mat is used. It may be used in a number of different matrix compounds to make a finished part. Wound structures and heated, autoclaved, baked, and pressure formed parts are only some of the ways in which it may be utilized.

Testing processes that work on fiberglass don't necessarily work on wood, and that includes the tap test.

Delamination issues are particular to lay-ups, which are glass structures, or layups involving graphite and carbon fiber composites such as kevlar, etc. Sometimes the fix is as simple as injecting a filler such as certain types of epoxy, whereas other times it may involve cutting and grinding, and replacing the section with a patch, plug, core, or layup (or series thereof), or simply patching the outer or inner radius where the failure has occured.

You probably don't need to worry much about spent casings striking the wings of an airline aircraft.

Wood differs somewhat in that techniques useable for detecting problems in glass, layups, or other parts and structures don't necessarily reveal the problem in the wood. In fact, cutting a cross section may be the only way to see it. This isn't the case with glass necessarily, and I use the reference "glass" to be inclusive of all synthetic layups and parts/structures, not just glass fibers. That would include carbon fiber. I used the wood as an example of other materials that have long traditionally been used in aircraft which share similiar problems, but in the case of wood, an even greater drawback or limitation.

Wood, incidentally, also offers an advantage in that it has a nearly limitless fatigue life; it bends and bends, without fatiguing...one of it's better properties that made it suited for a long time to use in propellers, among other things. Glass enjoys similiar properties, with greater stiffness and strength.
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