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Author Topic: Beam Buckling  (Read 527 times)

ULBsha

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Beam Buckling
« on: October 07, 2016, 04:49:16 AM »
Dear all,


I have the structural model of an aircraft, including wing and fuselage. The wing is made of skin panels, as well as spars and ribs modelled by caps (beams) and webs (panels). The fuselage is composed of skin panels, longerons and ringframes beams.
I'm doing a SOL101 on this model with one set of mechanical and thermal loads simulating the cruise condition.

In "Help System>Failure Analysis>Buckling>Beam buckling", I noticed the following tip:
'Tip: If the beam is supported along its span (i.e. ringframe), beam buckling modes should be deactivated.'

I was wondering if this is also valid for my longerons, ribs and spars caps?
When I have the beam buckling activated, I get extremely high weights due to the huge (and sometimes unrealistic) size of the beams. But when I deactivate the beam buckling for longerons and spars/ribs cap beams, the result approaches what I was expecting.

I think that this Euler beam buckling is an over-conservative approach for these elements, but I would like to be sure that I'm not missing something important by deactivating this failure mode?

Thanks
Regards
« Last Edit: October 11, 2016, 02:52:17 PM by ULBsha »

Brent

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Re: Beam Buckling
« Reply #1 on: October 11, 2016, 11:05:06 AM »
When modeling the following structural components of an aircraft, our general approach in HyperSizer is not to activate beam buckling modes for rib, spar, or frame caps(cap meaning the flange fastened to the skin) because the flange is supported by either an orthogonal member and/or the skin. Therefore, Euler buckling would not apply for these cases. Typically the caps are sized by crippling, local buckling, and fastener requirements.

Longerons are not generally analyzed for beam buckling either since they are supported by the skin. Longerons are generally sized by stability methods such as crippling, local buckling, and flexural-torsional buckling. If your longerons are discretely modeled with bar elements, we suggest to use HyperSizer's DSM "Discrete Stiffener Modeling" technique to perform sizing and analysis of stiffened panel structures. HyperSizer DSM modeling technique builds segments loads assuming there is load sharing between the stiffener, left skin,and right skin. From our experience, this is how many major aerospace companies perform stiffened panel analysis. 

See Help Topic Detailing DSM:https://hypersizer.com/help_7.2/#BackdoorData/bd-16-dsm.php%3FTocPath%3DSoftware%2520Forms%7CBackdoor%2520Data%2520Form%7C_____13 

Hope this helps!   

-Brent 

ULBsha

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Re: Beam Buckling
« Reply #2 on: October 11, 2016, 02:51:27 PM »
Dear Brent,

This confirms exactly what I have done, and my results make sense.
Thanks a lot.

Regards