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Calculation critical buckling stress for alu D tube skin, help needed

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Skyracer

Member
Joined
Sep 18, 2008
Messages
16
Hi all,




I need a little bit of help.


I would be very thankful if someone have any reference to calculating critical buckling stress (I am mainly interested in shear due to torsion) for aluminium skinned D-tube without stringers.


I say without stringers because I am familiar with methods for calculating buckling between stringers. Most books (Peery, Megson... ) give empirical calculations for this kind of examples, but I still didn't come over good example where simple D tube buckling is calculated - nose ribs, spar and skin, nothing more.


If stringers are present than you have mainly square piece of sheet metal connected at edges, flat or with some radius and you can calculate critical buckling stress. But if you have just D-tube what is the piece you consider for buckling? Do you look at it basically like cylinder (with part of airfoil as cross section) and calculate critical stress for local radius of curvature and treat those local segments like parts of cylinder (with circular cross section) with same radius as local one? Then you you could apply empirical equations for buckling of short cylinders between ribs.


I can make some assumptions from the theory (as explained in literature I found) and do FEM, but I would really like to see some more verified example/reference for this case. Practical experience would be the most welcome, because when it comes to buckling small irregularities make big difference and theoretic values quickly go down the drain.


Thanks in advance for the help!
 
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