Influence of frame on fuselage skin stress 3

[jetmaker]

Does anyone have some information on how the hoop stress(or strain) distribution varies between frame stations along a fuselage.

Textbook data will be ok, but I am primarily looking for source data.

Thanks to all.

jetmaker

 

[crackman]

One of the most accepted methods is that for stiffened cylinders by Flugge. It gives a pretty accurate stress at the frame location (have seen test correlation data to it). However, it does not accurately predict stress in the middle of the skin panel due to bulging effects. The stress in the mid panel region is more like PR/t.

James Burd

 

[joekm]

I think the approach crackman refers to is here:

http://naca.larc.nasa.gov/reports/1949/naca-tn-1981/

crackman - please confirm, and thanks for the lead...I'll add it to my "spellbook".

My favorite reference (Bruhn) does not seem to refer to it, Although fuselage analyisis is addressed in Chapters A20, C9.9 on, and - for the hardcore - A8.

--
Joseph K. Mooney
Director, Airframe Structures - FAA DER
Delta Engineering Corporation

 

[crackman]

Joseph

Here is the reference I was speaking of:

Pressurized Cabin Stress Analysis
NACA TN 2612 Stress Problems in Pressurized Cabins
W.Flügge, Stanford University

Here is the link to the NACA site for it:

http://naca.larc.nasa.gov/reports/1952/naca-tn-2612/naca-tn-2612.pdf

I have a simple java script which runs it, its pretty straightforward. You could also just code it up in Matchcad. Very useful method.
Good luck

James Burd
FAA DER - Structures/Damage Tolerance

 

[joekm]

Thanks crackman, Octave is actually my "weapon of choice" for number crunching (used MatLab 4.0 while I was going for my Master's - Octave is pretty darned similar). I've also grown rather fond of Python as of late.

Presently, I'm trying to code an arbitrary doubler analysis program loosely akin to RAPID (mainly for the challenge). This looks like it could be useful.

If nothing else though, It'll go in my "library of useful things to know"

Looking forward to going over it.

Regards,

--
Joseph K. Mooney
Director, Airframe Structures - FAA DER
Delta Engineering Corporation

 

[Sparweb]

crackman:

Thanks for the NACA Report.

joekm:

I've started a similar process using MathCAD, and Swift's paper (AIR-90-01). I'm having some success, how about you?



Steven Fahey, CET
"Simplicate, and add more lightness" - Bill Stout

 

[joekm]

Some time ago, I wrote a generic fatigue program in Python (eventually - early prototypes were in SciLab and other stuff). I kept adding stuff to it and sort of doing the GUI as an afterthought. I've also got a "quick and dirty" python script for implementing Swift's rivet load analysis on doublers.

With this new program, I've decided to write the GUI first in the hopes that it will be a little more efficient (read: easier to troubleshoot). Been on it for about a couple of weeks and have just started what will be my, admittedly primitive, drawing engine. Still kicking around what I will exactly do when I get my "collection of nodes". I'm hoping that by coming up with a hybrid of (semi)empirical methods and simple FEA, I can manage my computational overhead.

...but we'll see. If it works, maybe I'll GPL it. If not, I'll have learned something nonetheless.

--
Joseph K. Mooney
Director, Airframe Structures - FAA DER
Delta Engineering Corporation

 

[crackman]

Hey guys

Just as a side note, while I was on the ARAC committe to assist the FAA in developing the new WFD rules (should be out this year), we investigated lardge damage capability with the presence of MSD. Several people developed various methods of accounting for the stiffened panel stresses. The best code I witnessed (NASA and Lockheed cofunded) was STAGS. The bulging response of the skin is fairly complex and Swifts/Kuhn's methods is fairly rough (take care to re-center his equation to the center of the panel) and not very useful for large cracks. Several papers were published and correlation to testing was performed. I will try to dig up the references but I beleive they were presented in the NASA/DOD Aging Aircraft Conference as well as in the ICAF proceedings I believe, will verify.

Cheers

James Burd
FAA DER - Structures/Damage Tolerance

 

[joekm]

crackman,

Please do, I'd love to see it. I wonder if starting a fatigue and damage tolerance spin off of this group would be worth it?



--
Joseph K. Mooney
Director, Airframe Structures - FAA DER
Delta Engineering Corporation

 

[Sparweb]

I'll ask Dave Murray about that idea, joekm.

Just knowing where to find all the proceedings of these conferences would be helpful, Crackman. I've located a few on the web - but not all, yet. They don't seem to be collected in a central location.


Steven Fahey, CET
"Simplicate, and add more lightness" - Bill Stout