Airbus Composite Design Allowables

[USACompositeGuy]

Does anyone know what airbus uses for composite design allowables? Do they have a spec like Boeing, MD, etc…, or do they use vendor test data? Can anyone provide any information on this?

 

[RPstress]

Airbus have extensive qualification programmes producing allowables for a number of different composite materials to Airbus specs.

I'm not aware of any aerospace prime (or sub-prime, etc.) using vendor data for structural composites.

With metals we're all quite happy to use test data from qualification work done by the vendor (e.g., Carpenter have recently completed their program for their new Custom 465 stainless, which is now in MIL-HDBK-5J with A and B-basis allowables).

However, composites vendors just don't seem set up to provide data customers need for hot/wet allowables with damage present. I think this is partly historical: most users of composites have had their own qual programmes, because the materials are relatively new and a high level of control has been needed, plus different users have had different needs (temperature, damage, etc.). Perhaps this will begin to change now more standardisation is coming into how allowables are arrived at.

 

[USACompositeGuy]

RP,

I am not sure if you work with AIB airplanes, but the reason I ask the question is because the SRM(Standard Repair Manual) will sometimes call out an AIB part number and other times it will call for a specific product by the vendors identification. This led me to believe that Airbus was using the vendor's data to design the part.

As a composite engineer on the repair side of the industry, it is invaluable to have access to the design allowables. With metals this not an issue because, as you stated, the data is readily available through sources such as the mil hbdk. However with composites the companies, like Boeing, AIB, etc keep this data secret.

So in summery, my hopes were to find that AIB designed using the vendors data, and to obtain the data straight from the vendors.

Do you know of any source to find these allowables or any further information on them?

 

[RPstress]

I think you're mostly out of luck! Whenever I've worked for Airbus (or Boeing) the allowables have, as you say, been in in-house documents. (It's important here to note that the acceptance test values in material procurement specs are often quite different from the design allowables.)

Because it costs a lot of money to do a qual programme they tend to jealously guard their intellectual property.

Your best bet is to find a contract stress analyst who's (naughtily) copied the allowables documents...

I can tell you now that using 30 ksi as a ply-based allowable for woven carbon epoxy 175 C autoclave cure with damage at up to 70 C wet (compression or tension) will, as far as I'm aware, always be conservative (by a fair bit, especially in tension for secondary structure). I hesitate to go further; I'm not exactly anonymous here.

However, the allowables for repair materials cured using a vac bag and heater mat are going to be different (especially for nominal RT cure resin). For that you need someone who's specifically worked in in-service support, which I can't help with at all. I did work in support in Filton 10 years ago, but retain not even a memory of the values we used.

I would have thought that, if you're genuinely working on supporting Airbuses in the field, then they would consider a request for data seriously (I can't speak for parts other than the wings, here). Keith Armstrong, who's written a book on repair*, worked for British Airways on repair for many years and has strong connections with Filton. Getting in touch with him (he's now a UK based consultant) might give further contacts, etc. If you like, I will ask a friend of mine, who's just left the in-service support group, who he'd suggest you contact in Airbus UK for this sort of thing. (I probably won't be able to follow this up for a week.)

I think for now that's the best we can do...sorry not to be more help.

* "Care and Repair of Advanced Composite Structures" by Richard T. Barrett and Keith B. Armstrong is available from

http://www.amazon.co.uk

;

http://www.amazon.com

lists it as out of stock.

 

[RPstress]

USACompositeGuy: I have a contact at Airbus whom you could try approaching professionally. If you post an e-mail address for yourself I can send you the details.
-R.

 

[USACompositeGuy]

RPstess,

Sorry, I have not checked this forum in a while. I would appreciate any contact info that you could give me.

Thanks,

USACompositeGuy

 

[RPstress]

USACompositeGuy: no probs. However, I don't want to splash this guy's name around publicly, hence my desire for an e-mail address. (Can be anonymous, e.g., USACompositeGuy@yahoo.com . I'm not trying to get any personal info on you!)

 

[USACompositeGuy]

Sorry, I actually just forgot to add my address: james_honeycutt@usairways.com

Talk to you soon.

Thanks,

USACompositeGuy