panel post buckled capacity
panel post buckled capacity
(OP)
Hi all,
I'm looking for some sort of confirmation regarding whether a panel web can support shear loads after it has buckled under a uniaxial compressive load..
Cheers in advance.
I'm looking for some sort of confirmation regarding whether a panel web can support shear loads after it has buckled under a uniaxial compressive load..
Cheers in advance.





RE: panel post buckled capacity
if the loads are applied concurrently (more typical), then this sounds much more like a diagonal tension problem, so the panel would have quite some shear ability.
RE: panel post buckled capacity
RE: panel post buckled capacity
RE: panel post buckled capacity
if the loads are applied concurrently, i don't think your question arises ... at some ratio of loads the combined shear and compression loads buckle the panel and it may continue as a diagonal tension panel. uniaxial compression and shear is textbook diagonal tension, bi-axial compression and shear isn't ... drag out the FEA !
i suspect that in your case the panel is basically buckling in compression (rather than shear) and probably won't have much post-buckling strength ... it'll depend on redistribution.
RE: panel post buckled capacity
Post-compression buckling the elastic forces in the panel do not drop, and continue to increase for additional applied compression; however the compression stiffness becomes so low that small additional forces over the buckling load cause very large deflections which rapidly lead to material failure. However, a lack of compression stiffness does not markedly decrease shear stiffness. (Though any applied shear will hasten collapse in compression.)
I'm not aware of any classical references which address post-buckling under combined loads. (I'm pretty sure that Timoshenko and Southwell both present elastic behavior post-buckling only under uniaxial compression.) So, the only way to assess post-compression buckling capacity for shear is by large-deflection non-linear FEA (unless someone knows better). Because stiffness never goes negative the usual Newton methods can be used for NL convergence.
* The additional structure can be quite low stiffness and low strength.
RE: panel post buckled capacity
Just my 2 cents.
TOP
CSWP, BSSE
www.engtran.com www.niswug.org
"Node news is good news."
RE: panel post buckled capacity
The mix of shear and uniaxial compression will change the angle of the diagonal tension buckles compared with straight shear.
The solution resides in classic diagonal tension buckling per NACA TN 2661 (about May 1952) available from the NASA web-site. It deals with both elastic and plastic behaviour.
FEA may produce pretty pictures but for accuracy the old way is still more accurate. Takes a while though.
RE: panel post buckled capacity
Although my panel is part of a larger structure and is bounded by stiffeners (that may or may not offer simple support) that will have any redistributed load once it has become unstable, i'm still trying to determine the reduction in shear stiffness of the plain panel due to being buckled. My initial feeling is that the change in the shear stiffness of the panel will be related to its buckling ratio.
I have a simple piece of paper in front of me (and a glass of vino), and badly re-creating the DT tension field by hand movement. However, if i form the paper to a curved shape then apply the same movement, the paper forms a completely different shape. Not very accurate or even probably applicable, but it does make me think that the shear stiffness post compressive buckle is the key to the amount of shear it can support subsequently.
RE: panel post buckled capacity
RE: panel post buckled capacity
Very carefully! Often the repair doublers cover the entire bay (depends on the size, specific configuration). Can be much more difficult for composite structure. Tests of post-buckled panels with specific repairs should be conducted to validate the repair designs.
RE: panel post buckled capacity
RE: panel post buckled capacity
Also, there will the option of bonded composite repairs.
And, hopefully, the composite primary structure is more damage resistant.
RE: panel post buckled capacity
TOP
CSWP, BSSE
www.engtran.com www.niswug.org
"Node news is good news."