Buckling of thin shells/membranes

[cspkumar]

Hello all,

Is it right to assume that buckling in thin hells/membranes occurs if the minimum principal stress is negative? If so, then, is the min. principal stress the intermediate principal stress or the through-the-thickness principal stress? Could anyone explain this to my confused mind? Btw, I am using Algor nonlinear analysis software.

Thanks,
Surya

 

[corus]

You need compressive stresses for buckling to occur. In a general section that can either be the mean (through thickness) stress or the bending stress. If Algor can do it, run a buckling analysis or do a large displacement analysis on the structure with an increasing load and a small perturbation in the geometry or load.

corus

http://www.corusresearch.com

 

[freebody]

Corus makes a good statement. Thin shell/membrane buckling is highly dependent on thickness, geometry, and boundary conditions. It also occurs usually due to compression and/or shear loading. I like to first run an eigenvalue buckling solution (based on the differential stiffness matrix) to get a feel for when the structure might buckle. Then, I will run non-linear with large displacement effects and tailor my load stepping for smaller increments around the first buckling mode. If additional problems or snap-through occurs, you might need to go with a non-linear line-search or Rik's type solution.
-George

 

[glenn11897]

just to add, a negative principal stress does not necessarily mean the membrane will buckle. it is ,as pointed out by corus & freebody, dependent on geometry and boundary conditions. bending, compressive (in x or y directions), and shear stresses or two or more combination of theses stresses will affect the stability of your plate.

Bruhn & Niu books have good references for buckling of thin plates.

hope this helps...