Could carbon graphite structures be recycled? 2

[787tech]

Carbon graphite will sun be extensively used on the new generation of aircraft (787, A350). At least in the case of the 787, the whole fuselage will be made from such composites.
There are two issues that I would like you guys to help me out with.

Are carbon graphite composites recyclable?

In a potential crash, would it be possible to determine ( if the failure is structural rather than mechanical) the precise location or the leading cause of such failure.

 

[SWComposites]

Fractographic analysis has been done on composite parts to determine fracture paths and thereby deduce the failure initiation site. For instance NASA recently did a lot of work investigating the failure mechanisms in the AA587 A300 composite tail failure, which was caused by loads well above the design loads. The main difficulty with many structural failures is determining the loads on the structure at the time of failure.

 

[rb1957]

i guess you could recycle the graphite as pencils ...

as for reconstructing an accident, i guess it could be done, only there'd be a lot more pieces involved as graphite tends to shatter ...

 

[swall]

Not likely these composites could be recycled. The epoxy matrix is a thermoset material, i.e. you can't re-melt it.And once you chopped it up, the carbon fibers would be too small to be of much use, even if you could somehow separate them from the epoxy matrix.

 

[unclesyd]

I just talked with a friend that is senior engineering manager at a Carbon Composite Component manufacturer for airplanes, helicopters, and the likes about the above question.
His reply was an unequivocal no with the present state of the art with the materials and the manufacturing processes now employed.
He did mention that there is some work going on to actually allow an existing part to be modified to some small degree prior to being put into service.
All there parts that fail inspection in anyway are disposed of by being use as a test piece or in a pyrolysis furnace.

 

[aerodog]

787tech,

When Raytheon Aircraft (Beech) killed the Starship, they re-purchased the fleet (about 50 aircraft). A few of them went to museums the rest taken to the desert for incineration $$$. Contrast that with with scrapping a sheet metal aircraft...aircraft aluminum today brings about fifty cents a pound.

In the case of the 787, they will probably sink them in the oceans to replace the natural reefs that are dying off at an alarming rate.

Boeing is assuming a pretty big risk with out much gain to make the plastic 787. This issue is discussed in more detail in a post aerodog made on

http://www.yeald.com.

 

[CompositeGeek]

Are carbon graphite composites recyclable?

Not particularly, but then neither are automotive composites, printed circuit boards, or CRTs without some extraordinary efforts.
I have scrapped a number of parts in my past and the only good use I ever found was making dog houses out of radomes. Fun but not very fullfilling.

In a potential crash, would it be possible to determine ( if the failure is structural rather than mechanical) the precise location or the leading cause of such failure.

Depends on the crash, structural elements remaining, flight situation etc. Most aircraft crash investigations ultimately result in a number of likely causes with varying levels of probability of cause. It as very likely the cause can be identified if enough of the structure is recoverable.

I think it is a much more important consideration to evaluate the effects of repairs on structural performance over time in these large scale composite parts. There is a lot of incidental damage to composite structures on aircraft that frankly has little deep research to support repair effectiveness. The significant increase in "primary structure" components particularly on the 787, A380, A350, not to mention helicopter rotors, flaps, rudders, etc already in use should be a concern for everyone in the industry.

Composites and Airplanes - what was I thinking?

There are gremlins in the autoclave!

 

[aerodog]

787tech,

Your 06-04-05 post on

http://www.yeald.com

is interesting but not one that I agree with. I have certainly never heard that the 787 is being built like a snap together Lego set.

Am waiting for the rebuttal to the post as to whether the risk of using composites for the 787 is worth the 3 percent weight savings over an aluminum structure.

By the way, the yeald site is a European Financial site. It was first referred to me by a Boeing middle manager who was thrilled by one of the posts favoring the 787. The Boeing middle manager was not so thrilled with aerodog's two posts...but we are still friends

 

[ErikC]

One thing to remember is that when Raytheon was certifying the Starship, was that it was one of the first GA aircraft to go though the FAA ACO. As a result, the structure had to include much higher environmental and material variability load factors as well as scatter factors for fatigue testing. Today, ten years on and as a result of the AGATE program, the knowledge and acceptance of composites has grown and therefore the weight of composite structures has decreased as well.

As far as composite repairs are concerned. Both static and fatigue test articles include intentional defects in critical locations. These are used to substantiate BVID's, core delam's, disbonds, ply sand throughs, ply bridging, ect. Repairs are only made if the part can not be substantiated by either a comparison to the test articles, validated FEM's, and hand analysis. However, there are limits to what can be repaired. Certain structures like wing spar caps, which typically contain bundles of unidirectional tape, cannot be simply sanded off and spliced together with a new spar section.

 

[gwolf]

> Are carbon graphite composites recyclable?

No, and probably never will be.

Personally I don't like them for lots of other reasons which I won't go into on this thread.

 

[berkshire]

I would disagree with the last sentence in ErikC's remarks about spar caps.
It depends on the type of aircraft. Sailplane spars are routinely spliced using 50 to 1 splices. The manufacturers have schedules of where or where not on the wing you can do that. The splice is usually done with a router using a fixture to hold the scarf angle constant. Now I know that these systems are room temp cure, oven aged and is no match for a de-bulked autoclave cured system. Then again except at the root, the wing on that type of aircraft is not that highly loaded.
With regard to recycling carbon fiber it is common practice in some molding plants to run waste and trimmings through a hammermill then use the resultant powder as filler, where the resin systems are compatible.
B.E.

 

[btrueblood]

Well, it's not perhaps recycling in the PC sense....

but if you burn the carbon composite, it will go into the atmosphere as CO2, and eventually be recycled into plant matter somewhere.

 

[ErikC]

Sorry, I should not have made such a blanket statement. I was thinking of a more heavily loaded wing with many more plies of tape in the cap. The amount of time/money spent on scarfing and repairing would be very high and would require additional analysis/testing to substantiate.
One thing to also consider is that you are now relying on the interlaminar strength. Some of our DER's have expressed concern with fatigue failures of repaired areas without sufficient test data to substantiate. So if you are doing a large spliced spar repair on an certified aircraft, you may end up having to redo the fatigue testing on that particular component. This could also lead into redoing GVT testing if the EI of the structure changed.

 

[WKTaylor]

787tech…

I am sure that the auto industry will show us how to recycle fiber-reinforced plastics (glass, carbon, boron, aramid, etc) simply because of the potential applications in the vast world of auto manufacturing that has to mesh with world-wide regulations for environmental protection. However... it is still obvious why metals are favored over FRP and FRE [fiber reinforced plastics and elastomers]: metals are so easy to recycle. HOWEVER... there is a distinct problem with aerospace materials in that they are so heavily alloyed for high strength/stiffness, that they cannot be recycled with industrial/automotive grades of steel, aluminum, magnesium, etc. For instance: The alloying elements favored for aerospace aluminums are considered tramp/trash elements that contaminate commercial grades of aluminum.

As for what to expect in a crash... Hmmm. I can only speak from my experiences with Carbon fiber-epoxy & Boron-fiber epoxy residues in military mishaps.

FRP that doesn’t burn exposes sharp “needle-fragments” at the fracture surfaces. Typically these dangerous fragment ends are confined to sharply defined areas within the matrix… so they are confined along the fracture zones.

If burned… I suspect that the carbon-reinforced epoxy will burn-off the epoxy leaving the carbon-fibers to decompose under heat [if sustained]. Depending on fire-exposure, the carbon fibers could decompose completely… or remain as relatively soft/sharp fragments to deal with. I have a funny story about F-18 mid-air wing debris [CFRP] recovered from the water… but not now…

My experience with Boron-epoxy in a mishap was [excuse the expression]… a BITCH. In my case the epoxy matrix burned-off [to a point] releasing the boron-fibers which splayed-out in loose broom-straw-like bundles. Boron fibers are individually very fine/brittle/stiff/strong and heat/fire-resistant. These fibers were inevitably fragmented and were far worse than porcupines and/or cactus needles to get stuck with. They were incredibly sharp and stiff right-up to the point where they pierced, then sheared-off and imbedded in skin/bones. I think I still carry a few fine boron-needle fragments in my hands, which have worked-in too deep to notice any more. Since the material is inert, and time has long-since passed, I haven’t had any appreciable problems… so far. I hate the idea of dealing with this material.

Now, as for evaluating composite failures… You need to get a copy of an Air Force Wright-Labs document for “composites failure analysis”. Unfortunately, after assisting in an accident investigation course, I appear to have lost my copy of this document (was on display)… which is just killing me (ticking me off). It was very helpful assessing damage “causes” for various F-15 composite part failures.


Regards, Wil Taylor

 

[gwolf]

> The alloying elements favored for aerospace aluminums are considered tramp/trash elements that contaminate commercial grades of aluminum.

In the aero industry these materials are high value scrap, go into separate bins, and are carefully re-cycled. Much modern CNC machining generates 90% scrap - you don't think that they just throw all that stuff away do you?

> As for what to expect in a crash... Hmmm

Fibre/resin components are stunningly good at absorbing kinetic energy in crashes compared to metals. They are capable of huge strains (you get a big spring), and they absorb huge amounts of energy by creating multiple fracture surfaces as they break.

I still hate them though - mostly.

 

[WKTaylor]

gwolf...

Of course, aerospace grades of aluminum are valuable for scrap... but usually when segreggated and disposed of as discrete alloy groups [IE: 2XXX with 2XXX, 6XXX with 6XXX, 7XXX with 7XXX, etc...]. Mixing alloy types in a scrap bin degrades the mix which then requires EXPENSIVE reprocessing due to the hodge-podge of alloying elements, that CANNOT be allowed to co-exist, except in precisely defined quantities. Like-alloys are easilly melted together & reprocessed... but just contaminate 7XXX series with silicon, or copper, etc... and see what happens.
------------------------

Also... in crashes, there is a high probability of fire and explosion with accompanying combustion by-products. The fire will consume the matrix and MOST organic based fibers [carbon amide & aramid] in the combustion mix... wheras glass and boron fibers tend to remain after burn-out.

Perhaps composite fuselages/wings will reduce tendency break-open and to "flash-fire-ball"... present with metallic structures when integral-tank structure is torn asunder and the fuel-coud passes thru the electrical-arcing and metallic-friction-sparking. Also [maybe], composite materials combined with an effective coating system(s), could effectively retard effects of fire long-enough to allow evacuation, in a survivable crash.

As Larson [farside] might put-it... Fud-4-thot.



Regards, Wil Taylor