787 delamination checks
 

Boeing inspects 787 Dreamliner for possible repairs to carbon fiber skin

ttp://bottomline.msnbc.msn.com/_news/2012/02/05/10321423-boeing-inspects-787-dreamliner-for-possible-repairs-to-carbon-fiber-skin

who has more on this?

Isn't this old news?

Only if they used the same vendor as Airbus to manufacture the wing

787 delamination
 

(Sorry, Mods - I see this has already appeared in another thread!)

From Flight Global - link below

I believe that large structural use of carbon fibre in civil aviation is new. Let's hope the Dreamliner doesn't fall to earth.

If you read the detail on Flightblogger, it details how this is a manufacturing issue and not a design problem. And it will only potentially lead to a reduced fatigue life, not the risk of dramatic or catastrophic failure. It's another example of poor programme execution from a subcontractor, not of a fundamental flaw in the design. Most importantly, this can be inspected for and addressed.

well, technically speaking it is. A reduced life results in the asset having to be amortised over a shorter period with a reduced value at the end of that period, which makes the aircraft more expensive to operate. That makes it a fundamental flaw in the design as potentially it affects the operational cost to the user, which is the result of the actual 'design'.


it can yes, but the reality as anyone who has dealt with de-lam on flight control surfaces, its often cheaper to bin the part and buy again than to repair a de-lam composite structure.

Intriguing post Loma, do you have some insider info you would care to pass on?:hmm:

The subcontractor in this case however is Boeing South Carolina.

True for flight control surfaces. Not so true for the fuselage itself. Besides, even flight control surfaces can be repaired, done that quite a few times myself, however on gliders ;)

To me, that looks more like compression and/or buckling failure due to significant overstress, not simple delamination. While strength of a delaminated material will be reduced, it is not a foregone conclusion that such a failure will result from simple delamination, especially if the part is in tension, not compression.

Don't agree. A technical design issue that results in a changed operational cost is one thing, but this is a manufacturing problem. Correctly manufactured models will perform to specification (excluding other issues), so this is purely a programme issue.

...and Boeing South Carolina was previously Vought, a subcontractor, that Boeing decided to buy out, because of...programme issues...

True enough, back then it was other program issues, iirc too much traveled work. And as a thank you they got the second 787 line, hope they dont work as diligent in that as in their work up til now, that would be truly bad for the program.

When it says 7X7 on my next airline ticket...; I will have a damn more close look at what rhe X stands for.....

CJ

Jambone
 

This is not a representation of practical delam. Time, temperature, water and by your most important example stress will result in delimitation. Time will tell if there is a high stress area in the fuselage that will allow the elements to penetrate and degrade a composite fuselage.

Having owned and operated composite aircraft for the last three decades, I was interested to see the wide scale adoption of these materials by Boeing. I am more concerned about the maintenance / repair schedules, as by all accounts they seem rather simplistic, given the 'battle damage' that commercial aircraft suffer during normal operation.

From experience, I know that stress and/or impact damage to load bearing composite structures is nothing like that suffered by bonded metals. The most severe problems can be a long way from the site of the initial 'injury' and be quite hard to detect and even harder to repair. Often the only realistic thing to do is construct a whole new part...

Since they put the stiffeners in there, it is most likely because they are required for stiffness. It doesn't ALLUDE to anything other than that there is stress in the area that must be mitigated. It does NOT allude to any excess stress, nor does it indicate the type of stress (tension, compression, shear) the stiffeners mitigate.

Fact is we are all 'wet behind the ears' in this regard. The 787 is an unprecedented leap of faith into a composite fuselage. Actually reading the OP's link for the first time it sounds like Boeing are seeing problems already after a short term of fatigue.

I think the illustration below gives some insight into what I believe the problem is that Boeing uncovered and is dealing with. The cartoon that is inside the rectangular box depicts what happens when the shim between the stiffener and the composite shell doesn't close the gap and the fastener is tightened. Initially, there would be no noticeable problem, but over time, the stresses set up by this condition and the fact it is at a hole (a natural stress riser) in the composite material eventually could lead to delamination at the hole location. I am sure the detected flaw/flaws can be repaired.

http://i1166.photobucket.com/albums/...611fb6971d.jpg

The particular composite Boeing is using in the 787 fuselage application is very strong, more comparable to high strength steel than to aluminum. The composite behavior is different from aluminum. Impacting aluminum causes a dent, taken to extreme, it causes a dent and fracture. Impacting this particular composite result in no dent up until the point the tensile strength of the composite is exceeded. Then it will begin to delaminate meaning separation of the built up layers.

I hope this helps the understanding.

I disagree. Tolerances are something which happens during manufacturing just like rain will happen during operation. When building from composites, more tolerances will happen. Not properly taking this into account is a design deficiency. There is always a way to design structural details in a way, that tolerances can be compensated. Shimming typically is the least favourable way to deal with it, as it adds weight and is prone to yet another tolerance issue (especially if tapered shims, individually produced to close tolerances are required). Designers with experience in manufacturing and repair will find a way to handle the issue, designers knowing just their computers will have to rely on the manufacturing people to correct for their shortcomings. If things like this happen, the design is as much responsible as the manufacturing.

Just out of curiosity, and from a non-pilot, non-engineer (also NOT a bean-counter)

why is this delamination issue which appears to a complete idiot layman to be very, very, very worrying as it is in the actual fuselage so much less important than the fact that some in-wing fastener points in 'another aircraft' have developed some cracks?

working on "page count" as a measure of "issue seriousness"
the page-count for what appears to be a complete structural failure = 2 (Boeing 787)
the page-count for what appears to be a fixable minor issue = 6 (another aircraft manufacturers product)

Delamination is like a piece of plywood that evntually buckles and sags.

Cracks through a solid beam spontaneously snap and the beam collapses.

What level of load, across a supporting structure, is carried (basic everyday stress) plays a part. Only the designer knows what level of basic stress is present. Thus I don't sense a conclusion between a fuselage and wing part without knowing this stress (its not just a load issue)