787 delamination

Hopefully the ground crews will get additional training for the care of these carbon birds. There will be a lot more information generated over the years. New designs by necessity are based on theory instead of practice, in the long run watching these planes should benefit sailors as well.

 

http://seattletimes.nwsource.com/html/businesstechnology/2017449453_boeing08.htmlUpdate

 

what about the a380's , they are composite , have they had any problems.

 

Because it is usually the aluminum surface preperation that causes the epoxy to disbond resulting in an adhesion failure not a cohesion failure.

Disbonding of joint in adhesion led to further corrosion causing transfer of loads to rivets that set up the cumulative events.

As far as the 787 and Airbus 380 are concerned they are largely laminated structures that would fail by delamination not disbonding.

Dino

 

All A380s are crack tested extra now, as they showed problems.

 

Airlines have been ordered to inspect all A380's for cracks in the wings. Several different sets of cracks have been found. http://www.businessweek.com/news/20...eds-full-inspection-of-wings-amid-cracks.html

 

There is a lot at stake with the learning curve for composite aircraft construction. Not just in money but more importantly in terms of the lives they carry. While there is serious competition between these 2 rivals they both will benefit from the discoveries of the other in terms of safety. From wood and canvas to metal and rivets, glue bonding and now composite, progress marches on. Does first class get parachutes ? While you don't need a parachute to go skydiving you do need one to go skydiving twice Most product testers want to be around for the long haul so we'll hope every one keeps comparing notes.

 

The problems with epoxies debonding is that can happen at anytime for no apparent reason. I just hope they are checking every seam on a regular basis. Most HT epoxies can take higher temperatures like 300 degrees C with no problem, but they don't like quick temperature changes. It is the old dissimilar materials problem, as they cycle eventually they separate.

 

There haven't been epoxy debonding or delamination issues that weren't caused by something else in the cases sited, except the A380, of which I also have doubts, but am still (like everyone else) waiting on final disposition.

These issues aren't an epoxy issue, but a maintenance issue and is a matter of protocol, which has nothing to do with epoxy preformance, in a laminate or bonding situation. It's a people issue, not a product concern.

Maybe it's a translation thing here, but this statement is a huge assumption and is in direct contrast to what the NTSB has already found in the 737 incident and that Boeing is addressing in the 787. In regard (again) to the Aloha 737 flight MAINTENANCE (the lack of it) and procedural indifference to pressurization cycling, caused the multitude of failures, not surface prep with aluminum/epoxy bonds! No amount of surface prep could have prevented this failure. The 787's issue are also similar, in regard to maintenance and assembly crews screwing up and (again) has absolutely nothing to do with the laminate bond. Had they not forced the fit by wedging the assembly together, there wouldn't be an issue.

Yes, composites need to be carefully examined, but reasonable analyses need to be preformed, so reasonable actions and references can be established, instead of arbitrary and uninformed speculation about epoxy failures.

 

Ahem, yes, well Airbus was offering me a free flight to the next Golden Oldies Multihulls rendezvous accompanied by a stewardess of my choice if I asked hard questions about Boeing. Seriously, it is good for people to communicate about these things. The more noise people make the more official information is apt to be forthcoming and sometimes something comes to light that deserves more attention. I agree this is more of an human issue not epoxy but I'm also interested that there was delamination instead of the cracking the Airbus had, hence the epoxy and layup question. It is also fair to point out that maintenance issues are showing up faster than anticipated. If we didn't feel free to speculate I'd be really concerned.....for high performance craft there is much here to learn from.

 

Yes, there is an assumption that the disbond was an adhesion failure. The assumption is valid because this is the usual mode of aluminum-epoxy disbond. Boeing specifies BAC 5555 phosphoric acid etch to prep aluminum that would normally have produced a reliable, long term bond. In the Aloha 243 case it didn't.

That the assumption of epoxy failure was "arbitrary and uninformed"? No. It is founded on the NTSB findings http://www.ntsb.gov/investigations/summary/AAR8903.html "......probable cause of this accident was the failure of the Aloha Airlines maintenance program to detect the presence of significant disbonding and fatigue damage which ultimately led to failure of the lap joint a S-10L and the separation of the fuselage upper lobe."

As to semantics and "translation":

What would have happened if the bond remained intact is speculation. Maybe the lap joint would have retained its integrity until another area produced more detectable cracks. On the other hand adherance to maintenance protocol would with reasonable certainty have picked up the tell tale cracks that the disbond had set in motion. Awareness of pressurization cycles should have also raised a red flag.

It's a chicken and egg dilema and largely a matter of semantics. Disbond-corrosion-detectable cracks-lack of maintenance verses lack of maintenance/procedure-crack detection. Take your pick.

Dino

 

There wouldn't have been a debond, had an appropriate protocol been in place. Again, this isn't a debond issue, nor semantics. Either the design, assembly and/or epoxy were at fault or it was the protocol. The NTSB clear states the protocol was at fault and a new protocol is the solution. It's a bit like saying the screen door opening mechanism failed because the screws came out of the wooden door jam, when in fact the screen door oping mechanism was cycled 20% over it max opening rate, which caused the screws to pull. It's not the screws, nor the wood. Just as in the Aloha incident, the plane cycled well past it's limits and you can't ask any bond or material to tolerate this level of over human sight.

 

"Contributing to the accident were the failure of Aloha Airlines management to supervise properly its maintenance force"

"and the lack of a complete terminating action (neither generated by Boeing nor required by the FAA) after the discovery of early production difficulties in the B-737 cold bond lap joint which resulted in low bond durability, corrosion, and premature fatigue cracking"

 

Quote[This isn't a debond issue]Unquote

There was a debond issue. Quote from NTSB report conlcusions:

"8. The fatigue cracking initiated from the knife edge associated with the countersunk lap joint rivet holes; the knife edge concentrated stresses that were transferred through the rivets because of lap joint disbonding.

"9. The disbonding of lap joints and tear straps originated from manufacturing difficulties encountered with surface preperation and/or bond material processing during the construction of the airplane which resulted in lap joint bonds with low environmental durability or a lack of bonding"

The full report is definitive:

https://hfskyway.faa.gov/(A(9BCsBIA...s\Human Factor Maintenance\Aloha Airlines.pdf

The failure mechanism was improper assembly techniques by contaminating bond area, disbond, followed by fatigue cracking as a result of loads being transfered to the countersunk knife edge rivet hole area, non- implementation of service bulletins that had identified the problem before the accident.

Quote[Either the design, assembly and/or epoxy were at fault or it was the protocol]Unquote

As it turns out three faults of those mentioned were found ie. design,assembly and protocol.

Design deficiencies in the lap joint were identified by Boeing due to problems found in similar joints in other aircraft 747, 727 and 737. They addressed the issue by changing the design after 737 serial number 291 and by issuing a service bulletin.

There was also an assembly issue in that the epoxy saturated scrim cloth used for bonding was often prepared in advance then stored in dry ice until just before application. Moisture accumulation on the epoxy impregnated srim cloth while thawing was tranfered to the aluminum surface thus contaminating the bond area.

Quote[There wouldn't have been a debond, had an appropriate protocol been in place.]Unquote

This is speculation. In fact the disbond in some areas was present at production and progressed along the bond line further exposing the aluminum to corrosion.

No doubt the greater lesson to be learned is one of inadequate maintenance/protocol, but an equally valid conculsion is that of epoxy-aluminum bond failure due to inadequate aluminum surface preparation.

Please excuse for the slightly off topic drift.

Dino