787 delamination [Archive]

Sunnyjohn

5th Feb 2012, 17:44

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

From Flight Global - link below

Boeing again faces a manufacturing quality issue, requiring inspections and repairs of its 787 fleet.

Structural stiffeners were found to be improperly joined to the composite skin in the aft sections of the aircraft, causing parts of the aircraft's carbon fibre structure to delaminate, confirms the airframer.

"Boeing has found that incorrect shimming was performed on support structure on the aft fuselage on certain airplanes in our facility in Everett, [Washington]," said the airframer.

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

NWSRG

5th Feb 2012, 18:37

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.

stuckgear

5th Feb 2012, 18:56

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.

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'.

Most importantly, this can be inspected for and addressed.

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.

glad rag

5th Feb 2012, 20:09

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

Denti

5th Feb 2012, 20:15

It's another example of poor programme execution from a subcontractor

The subcontractor in this case however is Boeing South Carolina.

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.

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 ;)

Intruder

5th Feb 2012, 20:33

Purely for the benefit of those who, like me, didn't actually know what "delaminating" looked like.
Doesn't look like the kind of thing you want to be happening in midair at any rate. From a naive perspective, is it not of some concern to see highlighted the obvious stress the fuselage is under already? Obviously it's all engineered to withstand it, just seems like it's a bit too reliant on everything being just so..
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.

NWSRG

5th Feb 2012, 21:12

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'.

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.

The subcontractor in this case however is Boeing South Carolina.

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

Denti

5th Feb 2012, 22:00

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.

ChristiaanJ

5th Feb 2012, 22:21

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

CJ

grounded27

6th Feb 2012, 02:22

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.

FullWings

6th Feb 2012, 07:54

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...

Intruder

6th Feb 2012, 16:59

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.

grounded27

6th Feb 2012, 17:10

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.

Turbine D

6th Feb 2012, 20:04

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/q609/DaveK72/536-611fb6971d.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.

Volume

6th Feb 2012, 21:57

If you read the detail on Flightblogger, it details how this is a manufacturing issue and not a design problem.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.

G&T ice n slice

9th Feb 2012, 12:05

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)

lomapaseo

9th Feb 2012, 14:15

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)

EEngr

9th Feb 2012, 15:43

If you read the detail on Flightblogger, it details how this is a manufacturing issue and not a design problem.Only if you accept that engineering is free to specify something that can't be built correctly. Or isn't responsible for specifying the applicable manufacturing processes. And then that there is no need for engineering to close the loop in with manufacturing to solve quality control problems.

The industry has been headed toward a philosophy of separating design from manufacturing in order to more easily outsource the latter. And then to lay off the design staff once the drawings are out the door. That comes back to bite them in the :mad: every time. But they keep doing it.

G&T ice n slice

9th Feb 2012, 15:53

But it would appear that the cracks in the wingy-bits are caused by a manufacturing process error? and there are several hundred of the little feet so lose 1 presumably you don;t lose them all at the same time?

but the fuselage issue being structural and pressurised menas that if it goes the whole lot goes in one go?

I'm just baffled by the lack of interest in the fuselage issue compared to the wing feet issue.

ChristiaanJ

9th Feb 2012, 16:28

Delamination is like a piece of plywood that evntually buckles and sags.
I like the comparison between carbon fibre composite and plywood.....
Plywood, in a way, is also a multi-layer carbon fibre composite, no?

Somehow, over the years, some design and material knowledge get lost.....

Just think of the DH Mosquito, or some of the late-WWII German aircraft, or maybe even the "Spruce Goose" ?

No, I'm not suggesting Boeing should have built the DreamyLiner from plywood.
But they could have learned from the experience from those days..... if it had been transmitted through the generations.....

CJ

stepwilk

9th Feb 2012, 17:21

It admittedly was some years ago, when Boeing first began using composite parts, but a Boeing engineer said to a friend of mine, "The more we learn about composites, the better aluminum looks."

boguing

9th Feb 2012, 20:00

Whether it's the Engineer or the person that pours the glue, there have been so many failures of composites in 'high end' racing yachts that are all due to being unable to properly inspect the finished product.

Pete Goss and 'Philips'. 600mm by several Metres of doubler on each hull - no bond.

Many carbon keels - not completely cured.

Can't remember which, but an Aus or Kiwi AC boat snapped in two.

De-lam from foam cores, so many.

None of which are the fault of the Carbon/Aramid fibre, but most certainly the fault of the manufacturing and inspection process. Which was designed by somebody.

R&D on those was very much limited by budget. Formula One is another big user, and we hear a lot less about their failures, perhaps because we expect the cars to break from time to time, and that a wheel falling off seems a lot less frightening than a keel. (To the spectator). Budget is less of a problem, but we just don't hear about the failures, of which there must be many.

Others please chip in - I don't go much further than the Beeb for F1, and am not aware of any pprune-type motor racing sites.

Carbon (or even Graphene) composites are quite obviously the future, but I'd really like to have more confidence than I do currently.

This a reply to a 787 thread, but, A380, alloy spar in the horizontal stab, with a Carbon skin? Alloy contracts with reducing temps, Carbon expands. Hmm.

TZ350

10th Feb 2012, 14:51

[quote]boguing
Whether it's the Engineer or the person that pours the glue, there have been so many failures of composites in 'high end' racing yachts that are all due to being unable to properly inspect the finished product. [quote]

Having had some composite experience in motorsport ( not at current F1 level ) boguing raises many valid points. When one sees the protocols and clean room conditions that are used for manufacturing of motorsport components ( which do not have the life cycle expectations of a commercial aircraft, nor the dimensional mass of 787 components ) the probability of issues related to non-compliance of the manufacturing protocols, tooling and material problems, human error and unforseen problems are high in a 787 sized project. Added to this are commercial pressures to delivery schedules and the requirement to be profitable.

No doubt there are very high levels of automation in the 787 manufacturing process, but it's unlikely there are no areas that do not require manual processes to completition. Which raises the question of the experience/training levels of the production staff, again dictated by keeping manufacturing costs to a minimum.

Prototyping is one thing, productionizing is a serious challenge.

Denti

10th Feb 2012, 15:20

And on the other hand much more aviation like, there are thousands of glider planes manufactured out of different fibre materials including aramid, polyamid and of course carbon. Very very few manufacturing related incidents or accidents, most stuff that happens is good old human factors stuff. Newer SEP planes like the Diamond Air series, or before that Grob trainers and more recently Cessna 300/400 and of course the Cirrus family. All of them built out of composite materials.

Composite is nothing new, in fact airplanes have been build in composite structure since the 1950iies. However it seems hard to transport the lessons learned onto newer commercial projects, including the 787.

grounded27

10th Feb 2012, 17:27

Tried and proven on light aircraft and certain structure on large aircraft, you can hardly relate this to a large fuscelage. You can make an RC aircraft out of foam and plastic, would it stand up full scale? I know, a bit draumatic but there is NO precedent for the 787 and using standard processes on what we know about this material may fail our expectations as we experience failures in design and manufacturing standards.

The in service test bed is a risky one.

boguing

10th Feb 2012, 17:41

Denti, I accept that.

If my Pa's Pik 17/19? hadn't had carbon in it he would not have survived the accident that he had.

I will be trusting an Extra 300's Carbon spar soon.

Good products.

It's the flipside - when the bits start to get bigger and more 'engineered' than simple spars and skins.

The current Volvo Race management have an independent surveyor using ultrasound on all of the boats in Sanya (China) at the moment.

One of the boats suffered some hull delamination early in the first leg, several others have had rig failures, again. The headline sponsor is trying to minimise the risk.

The shock loads put into these boats is way in excess of what the worst pilot could do to his aircraft (short of what Pa did to his anyway..) but the fact that an intrinsically weakened structure (through either misunderstanding of the load at a point, or poor manufacture, again at a point) is brutally punished by the completely unforgiving good structure surrounding it.

Yacht design R&D is heavily restrained by budget, and they have made major errors in the past. Would an Aero Engineer ever suggest a welded keel structure? Simon LeBon's boat Drum was the first casualty. There have been tens more of those, some fatal.

My main point is that Carbon is a fab material. Not necessarily the way it's stuck together though. It's the fact that it is so hard to inspect that gives me:-

Huge concern on a boat.

Not much concern on smaller structures - where the person with the glue/heat/vacuum knows what they are doing in a highly regulated industry.

It's the big composite stuff that I just don't know how to react to - in the same way that I believe fervently in nuclear power. But just how much do we really need to spend on testing?

lomapaseo

10th Feb 2012, 18:14

It's the big composite stuff that I just don't know how to react to

define "big"

is it volumetric, density per volumn or;

area (the size of a mack truck) or;

weight (something that can't be flown into the air on just one engine)

:confused:

boguing

10th Feb 2012, 18:29

Damn, picked up on a conveniently loose adjective.

By a trusted ppruner too.

I suppose 'big' as in:-

How much of this cylindrical fuselage can we do in one go?

Since you have the mould (mold) for rib 3 set up, can you knock out 50 by lunchtime?

Or, more technical.

The post cure shape is getting close to limits one way. The bit that it fits with is approaching limits 'tother way. Do we redesign both moulds or just glue them up anyway?

Industrial big.

TZ350

10th Feb 2012, 20:26

Big ; Some random thoughts . With prepregs, temperature and humidity are critical during the fabrication stage also. The larger the building, the harder it is to maintain control. Some materials are working time critical, if has been kept in cool storage, does it need x time in ambient temp before usage? Then there is the curing process(es).

Is the delamination area single skin, honeycomb or a secondary bond area ; we don't know ( yet ) whether manufacture or design is the cause, but size can present
challenges on large composite component. Protocols should be adhered to but commercial considerations would add pressure to continue in the event of an
" oops ". The $$$ involved are frightening..................

[quote] boguing

Not much concern on smaller structures - where the person with the glue/heat/vacuum knows what they are doing in a highly regulated industry.
[quote]

Very good summation.

ChristiaanJ

10th Feb 2012, 20:59

I'm following this with interest.
I can write 'aeronautical engineer' behind my name, so I've got some knowledge about structural engineering, even if I sailed off into the flight control world.

As I mentioned earlier..... laminated structures date back to WWII (and before).... the stuff was called plywood. Just remember the Mosquito.

And glue in aviation goes back quite some time too.... may I remind you of Redux, and the Fokker F-27 ?
(And no, the F-27 isn't all glued.... I still remember being taught riveting on F-27 wing panels.)

My point being.... design engineering is one thing, production engineering is another.... and indeed, if the two are not talking to each other enough.... things come apart.

CJ

stuckgear

10th Feb 2012, 21:02

i'm also interested in how a composite structure is going to be dealt with following 'ramp rash'.

lomapaseo

10th Feb 2012, 21:13

boguing

Damn, picked up on a conveniently loose adjective.

Well your latest post certainly nailed it and have now provided some damn good explanations on this techical forum :ok:

TZ350

10th Feb 2012, 22:39

These may be interesting ; Construction of composite fuselage section of a Boeing 787 - YouTube

http://www.youtube.com/watch?v=f07HpUAuWgk&feature=related

Boeing 787 Dreamliner - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Boeing_787)

File:787fuselage.jpg - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/File:787fuselage.jpg)

Boeing 787 Update : Composites World (http://www.compositesworld.com/articles/boeing-787-update)

Landroger

10th Feb 2012, 23:25

Boquing

None of which are the fault of the Carbon/Aramid fibre, but most certainly the fault of the manufacturing and inspection process. Which was designed by somebody.

My main point is that Carbon is a fab material. Not necessarily the way it's stuck together though. It's the fact that it is so hard to inspect that gives me:-

Huge concern on a boat.

ChristiaanJ

My point being.... design engineering is one thing, production engineering is another.... and indeed, if the two are not talking to each other enough.... things come apart.

A good few years ago now, we had a CT Scanner in the research labs of an oil exploration company. They never used it for people, it was for scanning rock samples. It was actually fascinating stuff for my peers and myself looking after it.

The rock was often repressurised to that which it had been under when drilled from the bottom of a well and, in order to do that, it was encased in a variety of (usually) aluminium or even steel pressure vessels. I remember the really scary one was the size of a dustbin, pressurised to 800psi (I'm sorry, I'm a Chain/Hundredwieght/Fortnight man :uhoh:) with GAS :eek: and 'flooded' with live crude oil at about 150C!!

At one time they ran an experiment that used fibre tubes - probably early carbon fibre, this was late eighties - to repressurise 5 inch core samples. These vessels were a (carbon) fibre tube about two feet long with truly massive stainless steel flanges on each end and in use were pressurised to 22 or 23 thousand psi, some even more than that.

The thing being, it wasn't until they got these things - live - onto the CT scanner and scanned down the length of the tube, that they saw for the first time there were huge voids, about a layer thick, sometimes over a third of the circumference and a big chunk of the length! :eek:

They had been manufactured to the highest standards - believe me, this company were class in that respect - and designed for astronomic pressures, but they didn't know there was anything wrong until a new technique (CT imaging) was used for some other purpose.

Just my few penn'orth. :)

Roger.

TURIN

11th Feb 2012, 00:01

G&T ice n slice

11th Feb 2012, 14:05

Ah well, so that's alright then?

But presumeably is subject to a whole bunch of stresses in a whole bunch of different directions, and if it were to delaminate in flight?

And if it delaminates somewhere unpressurised does this mean that it could do the same somewhere pressurised?

Volume

11th Feb 2012, 22:36

but the fuselage issue being structural and pressurised menas that if it goes the whole lot goes in one go?
...
And if it delaminates somewhere unpressurised does this mean that it could do the same somewhere pressurised?I do not understand your osession with the pressurized part of the aircraft. Delamination is failure of the laminate perpendiular to the fiber layers. If loaded in tension, the effect is minimal as the fibres will keep straight and be able to carry a signifiicant part of their ultimate load. Only in compression the fibres will buckle and the strength of the part is significantly reduced, most probably below limit load capability.
As a pressurized fuselage creates tension in the skin, delamination in the pressurized area is not critical. You will probably first have a problem to maintain the fuselage pressurized due to the air leak before you reach any critical strength condition. I would be more worried about delaminations in the upper wing skin where it under extreme compression. And so did Boeing when they found issues there.

G&T ice n slice

12th Feb 2012, 14:14

Ah... ok

It's not that I'm obsessed, I have a zero level of mechanical understanding or ability (anything I approach with a screwdriver falls apart - permanently & of its own volition)

So what you're saying is that if the thing delaminates in flight, it wouldn't actually disintegrate, but would actually be held together by the pressure inside the fuselage holding the different layers together, but there might be an air leak?

I'm not sure I'm exactly comforted by this thought...