sovietjet
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Joined: Sat Mar 15, 2003 12:32 am

Boeing 787 Composite Materials Questions

Tue Dec 04, 2007 5:27 am

So I've been wondering about this recently...the 787 is supposed to have a fairly large amount of composite materials in its structure. So I have a few questions:

1) What exactly will be made from composites?

2) How are these sections going to be put together? If the fuselage is composite, will it be one big piece(tube) or is it going to be several pieces joined together?

3) If several pieces, how will they be connected? Rivets dont seem like a good idea, and I know that today adhesives are used during final assembly. Will these work on a composite? What about aligning the fibers within the matrices of the composite pieces? Wouldn't misaligned fibers weaken the strucure where the bonds are, especially once the fuselage is pressurized?

4) Whether one piece or not, how would something be fixed if it becomes damaged? Say a truck hits the fuselage and dents/damages it, how can just that part be replaced if it is all composite? Again, how can a new piece of composite be integrated into the matrix/fiber orientation of the original piece? How big will this new piece have to be?

I guess overall, I'm just confused on how everything will be done with composites involved....
 
tdscanuck
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RE: Boeing 787 Composite Materials Questions

Tue Dec 04, 2007 7:23 am



Quoting Sovietjet (Thread starter):
So I've been wondering about this recently...the 787 is supposed to have a fairly large amount of composite materials in its structure. So I have a few questions:

1) What exactly will be made from composites?

Roughly: wings (skins, spars, stringers, ribs, fixed and movable trailing edge), fuselage (stringers, skins, most frames, floor, and floor beams), horizontal and vertical stab (everything but the leading edge), fan case (at least on the GE), fan blades, gear doors, nacelles (I think), wing/body fairing, and most of the interior partitions and stow bins.

Quoting Sovietjet (Thread starter):
2) How are these sections going to be put together? If the fuselage is composite, will it be one big piece(tube) or is it going to be several pieces joined together?

The fuselage comes in four big sections. The nose, the center, the aft pressurized fuselage, and the tail. Join, in each case, is a butt splice between sections.

The wing comes in three major sections (center, left, and right). The join is a very complicated splice. Vertical stab bolts on to the fuselage. The horizontal stab might be all one piece, but I can't remember for sure.

Quoting Sovietjet (Thread starter):
3) If several pieces, how will they be connected? Rivets dont seem like a good idea, and I know that today adhesives are used during final assembly. Will these work on a composite? What about aligning the fibers within the matrices of the composite pieces? Wouldn't misaligned fibers weaken the strucure where the bonds are, especially once the fuselage is pressurized?

Bonded + fasteners, I think, although I'm not positive about the bonding..not sure if the fasteners are rivets or bolts. Alignment of the fibers is easy to achieve (if you need it) because the fibers are all layed down by CNC tape layers...the fibers are always in the alignment that the program says they should be. Pressurization loads are primarily hoop stress, so the fuselage joints don't see that. They do see longitudinal stress, but that comes more from bending than from pressurization.

Quoting Sovietjet (Thread starter):
4) Whether one piece or not, how would something be fixed if it becomes damaged? Say a truck hits the fuselage and dents/damages it, how can just that part be replaced if it is all composite? Again, how can a new piece of composite be integrated into the matrix/fiber orientation of the original piece? How big will this new piece have to be?

Depends on the degree of damage. Based on known repairs today, I would expect:
For minor damage, temporarily seal with speed tape and go about your day.
For more major damage, apply a fastened patch or seal the exposed fibers until you get a chance for permanent repair.
For permanent repair: cut out the damaged area, taper the edges of the existing hole, layup repair plies with the same orientation and ply count as before + some extra on the inside. Generous overlap between layers to ensure good bond.

The repair part is pretty well known in the industry already...applies to most fairings and doors, a lot of nacelles and T/R's, the vertical stab on a lot of Airbii, and the whole empennage on the 777.

Tom.
 
brendows
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Joined: Thu Apr 27, 2006 4:55 pm

RE: Boeing 787 Composite Materials Questions

Tue Dec 04, 2007 12:50 pm



Quoting Tdscanuck (Reply 1):
fan blades

The fan blades on the Trent 1000 are made out of titanium IIRC (but the fan blades on the GEnX are made out of composite materials.)
 
soon7x7
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Joined: Thu May 04, 2006 10:51 am

RE: Boeing 787 Composite Materials Questions

Tue Dec 04, 2007 4:01 pm



Quoting Sovietjet (Thread starter):

Read thread on "AOG Composite Repairman"...might find some info there...we are bringing up similar issues...or at least I am....My argument against compostes in primary structure is that composite internal failure, like delamination,expansion of frozen moisture, etc...go undetected and when composites fail, usually it is catastrophic whereas metal construction is more foregiving and usually indicates problems before failure.If you have ever seen phoyos of burned up airliners, you'll notice what appears to be towels of bed sheets dangling in the wind...that is all the composite materials (carbon and glass fibres) hanging after the resins have been burned out of them.It's sort of bizarre looking. No more bizar than molten metal...but just reminds you you're flying around in a bolt of fabric at 550MPH....! It will be interesting to follow this technology being used on such a large scale...j
 
sovietjet
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Joined: Sat Mar 15, 2003 12:32 am

RE: Boeing 787 Composite Materials Questions

Wed Dec 05, 2007 8:21 pm

Thanks guys for the quick informative answers!
 
tdscanuck
Posts: 8572
Joined: Wed Jan 11, 2006 7:25 am

RE: Boeing 787 Composite Materials Questions

Thu Dec 06, 2007 2:19 am



Quoting Soon7x7 (Reply 3):
My argument against compostes in primary structure is that composite internal failure, like delamination,expansion of frozen moisture, etc...go undetected

They only go undetected if you don't look for them. Metals have the same problem, in several configurations.

Quoting Soon7x7 (Reply 3):
when composites fail, usually it is catastrophic

Although true, to first order, it's because composites have a much wider elastic range. When they fail catastrophically, it's because you totally overloaded them. Metals will yield long before then, which is "less catastrophic" but not really any more useful because you still have to fix it.

Tom.
 
soon7x7
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Joined: Thu May 04, 2006 10:51 am

RE: Boeing 787 Composite Materials Questions

Fri Dec 07, 2007 8:25 pm



Quoting Tdscanuck (Reply 5):

With metals...thats my point as you get an opportunity to repair the offending components but as we learned with AA flight 587, the opportunity usually doesn't present itself until it's too late, at least internal failures.Also, I don't know if uneaven temperature distribution is still an issue with composites...I have heard that different color topcoats adjacent to each other will cause uneaven expansion and contraction and ultimetely failure as in sublevel delamination. New science/new issues...j

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