Allowable basis for sandwich panels

[jokerbenj]

Dear engineers,

I trying to define guidelines for a stress engineer in aeronautic. We are making composite monuments for aircrafts/rotorcrafts. They are made with honeycomb panels (from Euro-Composite EC-PA-235G).
For the margin of safety calculation, what would you recommend to use: A-basis allowable strength values or B-basis?
By the way, does anyone have a clear datasheet of that panel?

Thanks for your coming answers!
Ben

 

[SWComposites]

A-basis values are typically only used for single load path structures. Interior monuments are most likely multiple load path (or if not they should be redesigned) thus you could use B-basis allowables. But you need to get agreement with your certifying agency (EASA, FAA, ?)

Have you contacted the manufacturer of the panels to see if they have any data? It is not likely that you will find publicly published allowables. You should plan a test program to obtain them.

 

[jokerbenj]

I already have the A and B basis allowable for the panels.
I do not have an agreement with the agency yet. I was more looking for a reference I could use for that (like MIL-HDBK-17).
But thanks for your answer.

 

[SWComposites]

Mil-Handbook-17 is going to state pretty much what I said above.

I think there is an AC for interior structures; don't have time to look for it now. Otherwise, there is not much clearly written down about what is single and multiple load path structure; though most of a commercial airplane is considered multiple load path and is sized with B-basis values.

 

[YoungTurk]

I believe SW is thinking of AC25-17, the "Crashworthiness handbook", but I don't see anything there to help answer your question.

GAMA Publication 13 may be of some help, though it doesn't appear to make an explicit statement on this issue.

In my opinion, SW is right in that most interior monuments are multiple load path - and as such B-Basis allowables should be acceptable.

However, in my experience, the certifying authorities require, or are much more comfortable with, the usage of A Basis allowables. In cases where I've needed to use B Basis, I've needed a seperate anlaysis or justification to demonstrate the multiple load paths. It is often easier to design to the A Basis values.