Complete Guideline for an Integrally Stiffened Panel Analysis (ie, wing ribs - metallic structure) 2

[aerostress82]

Hi everyone, (Happy New Year!!)
I have performed Static Stress Analysis, Freebody Load extractions and finally Hand Calculation analysis on "wing-ribs with integrally stiffened panels" on a commercial transport category aircraft (FAR Part 25) previously. (STATIC STRESS HAND CALCULATION ANALYSIS)

What I've seen in most calculations is that there were so many additional "rotational restraint, diagonal tension redistribution, edge member flexibility, stiffener stiffness factor for pure shear and pure compression, panel edge fixity, buckling enhancement factor, panel post-buckling load redistribution, edge member flexibility effect on permanent panel buckling, stiffener flexural/local instability & similar coefficients" used to perform those analysis for the most light-weight design.

My question is, do you know of any references/approaches that guidelines "ALL analyses to be performed for panels and stiffeners" on an integrally stiffened panel design (like wing-ribs) at an intermediate level without using all these additional coefficients compiled by aircraft companies?

I'm aware of most common references used for aircraft industry like Bruhn, Niu, Roark, MIL Handbook as well as Boeing, Airbus, Bombardier, MTS004/Aerospatiale manuals. But couldn't find a solution from beginning to end for only this integrally stiffened panel type of structure. Yes, the formulas to be used are mostly in main textbooks already. But without going into any "commercial manual coefficient or graph data" constants, is there a whole guideline of how to analyze these structures at ALL aspects?

What I'm trying to do is to be able to understand the conservative / unconservative approaches already used in some Mathcad/Excel VBA combined stress hand calculation analysis in the future. It looks like a lot of companies are using these readily compiled packages (some call them black boxes - I don't) and my concern is merely safety as I am and will be in the commercial aerospace industry in the next 20-30 years ahead.

Just for the note, I'm very enthusiastic about aerospace stress analysis and have checked all above documents I mentioned before on the job as this is my hobby rather than a job.
I'm just looking to see if you-senior stress guys- have any approaches or guidelines to make sure if anything is conservative/unconservative in such a structure..

Spaceship!!


Aerospace Engineer, M.Sc. / Aircraft Stress Engineer with 7 years of experience
(United States)

 

[SWComposites]

without going into any "commercial manual coefficient or graph data" constants, is there a whole guideline of how to analyze these structures at ALL aspects? > doubt you will find anything outside of OEM manuals. No one else has the $ to run the tests required to develop all of the factors and to validate the part specific methods.

any approaches or guidelines to make sure if anything is conservative/unconservative in such a structure > yes, it involves conducting tests of representative structure and comparing to predictions.

 

[aerostress82]

Actually, a proper combination of Bruhn, Niu, Wagner, MIL Handbook and some other references seem to be able to guideline what I'm asking for.

I'm just looking for what other reference there is available "without any test" but only with pure theory and moderate-level hand calculation methodologies.

I understand the value of tests and what kind of data is extracted from those tests and how they correlate with the analysis process, but what I'm asking for could actually be guidelined thoroughly by someone had worked on these structures for around 15-20 years (or less) and had finally compiled a whole outline of these analyses "just for the sake of the safety for the analysis methodologies used and for cross-check of these results".

Spaceship!!


Aerospace Engineer, M.Sc. / Aircraft Stress Engineer with 7 years of experience
(United States)

 

[SWComposites]

Well, this site is eng-TIPs, not eng-DESIGN_MANUAL, so dont get your hopes up too high.

And please stop the shouting with bold text; its really annoying.

 

[aerostress82]

I'm not familiar with shouting text online. Sorry if I meant any disturbance, but I think I made my point. If someone is out there who is knowledgeable enough, please help with this dillemma that I'm stuck with. I don't care about knowing more, I sincerely only care about safety.

Spaceship!!


Aerospace Engineer, M.Sc. / Aircraft Stress Engineer with 7 years of experience
(United States)

 

[Burner2k]

Why don't you create a detailed design summary of integrally stiffened panel from the various reference sources you have mentioned and provide a copy here for the experts to review & suggest changes if required?

I don't think you would get such a document on open source. Although I haven't worked with OEMs, the guidelines provided by Niu seems quite comprehensive, at least for initial sizing purposes.

 

[rb1957]

find NACA 2661 and 2662 online (somewhere).

there should be lots of references online for diagonal tension.

someone with 7 years experience should know this ...

another day in paradise, or is paradise one day closer ?

 

[aerostress82]

Thanks for the documents rb1957. Both were related with web + stringer/frame assemblies rather than integrally stiffened panels, but they are nice documents that I didn't have a chance to look at as of yet.

Maybe I'm wrong, but I remember reading that integrally stiffened panels have been started to be used after 2000s, so there may not be much related information regarding this kind of structure before 2000s.

I have 7 years of various aircraft "stress & interface/internal load extraction/interpolation" experience from interior to fuselage and wing ribs, and I came across the integrally stiffened panels in those wing ribs project very recently. And I wasn't getting paid to set methods for advanced structures like integrally stiffened panel - but rather to apply the previously decided methodologies (decided by OEMs) in the fastest way via Excel VBA & Mathcad. I'm also very diverse with software and programming (I use around 18 softwares for FEA only), so I would always be given something to work on at all times to speed up the team at its best..

I actually know about diagonal tension. My question was more on the stiffener side of such a structure. I guess there is no "public" guideline for such a new type of structure - I understand..
To be more specific, I want to rephrase my question to:
"What would be the hand calculation analysis steps to be performed on an integrally stiffened panel structure under combined in-plane bending, shear & compression loadings?" (I'll write some down)
Panel:
Panel onset of buckling,
Panel diagonal tension,
Panel post-buckling,
Stiffener:
Stiffener inertia check for simple-support of the panel,
Maximum fiber stress check,
Local Buckling,
Flexural Instability,
Torsional Instability,
Stiffener Landing:
Local instability.


What else do you think should be covered in addition to these analyses? (Burner2k, you had also asked for this outline, so here it is)
I don't think there is any guideline for integrally stiffened panel analysis with all above mentioned, so I'll leave that for the future - maybe I'll compile it someday when I can find enough time to go through every detail.

Spaceship!!


Aerospace Engineer, M.Sc. / Aircraft Stress Engineer with 7 years of experience
(United States)

 

[SWComposites]

Integrally stiffened panels have been around for a long time. For instance isogrid panels used on rockets back in the '60's.

Analysis of an integrally stiffened panel is really not much different from a panel with separate fastened stiffeners. Static checks are essentially the same. Fatigue and DT is a bit different as a crack can propagate from the skin to the stiffeners, and vis versa.

 

[RPstress]

SOR 51 (a Hawker Siddeley document from 1968) is worth finding. This covers post-buckling of metallic panels in shear and is fairly comprehensive. ESDU 77014 covers similar ground.

 

[rb1957]

if anyone has pdfs of SORs ...

another day in paradise, or is paradise one day closer ?

 

[aerostress82]

I tried to find SORs, couldn't find it online ever.. Could also seldomly find ESDU documents online. (only 4-5 pages - maybe 2-3 sections - checked again, they are not coming up from the search this time, I guess I had used different keywords)

In my previous company, they had all ESDU and SOR 51 documents. Planing to pay more attention to SOR 51 next time when I can get my hands on it..

Spaceship!!


Aerospace Engineer, M.Sc. / Aircraft Stress Engineer with 7 years of experience
(United States)

 

[rb1957]

you were working at British Aerospace ?

another day in paradise, or is paradise one day closer ?

 

[aerostress82]

I was working with an OEM of Airbus



Spaceship!!


Aerospace Engineer, M.Sc. / Aircraft Stress Engineer with 7 years of experience
(United States)

 

[santoshaero]

If you can get APA115v3 manual then that covers all the topics that you have mentioned. APA115 is an Airbus collection program and v3 manual is a total description of it. This program is specifically mentioned for shear panel analysis. It is basically a implementation of SOR51. If anyone needs it and if its not an issue then i can upload both the SOR51 and APA115 document. The SOR51 is a typed copy quite old, from 60s i guess, so would be tough to read though.

Regards,
Santosh

 

[Burner2k]

Hi Santoshaero,
I am interested in having copies of both APA115v3 & SOR51 documents. Please do upload them if it ain't an issue for you.

Thanks...

 

[santoshaero]

Hi Burner2k,

Please find the link to SOR51.

Now a question for all the gurus, there is a graph on pdf page number 28. This is used to calculate permanent deformation at limit load and panel failure at ultimate load (This in turn is combined with stiffener stresses, by a equation similar to von-mises). Both of these are RFs, while the panel buckling ratio is not. These are the three RFs calculated for panel analysis. Now in other companies (other than Airbus) have you guys come across this calc of permanent deformation and panel failure? How is this addressed there, is it similar to this graph or some method. I have had a chat with lot of guys but never understood, how these two RFs based on these graphs are generated. Any help would be great.

Thanks.

 

[santoshaero]

Hi all,

Please find the link for APA115v3 document.

 

[Burner2k]

Santoshaero man,
Thanks for sharing those documents. Would appreciate if you could share similar Airbus documents about other important topics...

 

[santoshaero]

Burner2k, is there any particular topic you have in mind? Post it here, and if i have the document then i will share it here.