• From: Gothenburg, Sweden
  • Registered: 08-09-2009
  • Posts: 1,419

Re: linear stability analysis with plane stress or plane strain elements

Hi.
I'm no expert on buckling analysis (only did it once, in a course 4 years ago), but I can tell you what the deal is with the implementation.
Right now, it seems only beams and springs implement "computeInitialStressMatrix" which is the basis for the linear stability analysis.

The other elements doesn't have this because of either
1. Laziness (noone has needed it before)
2. It doesn't make sense to use it for such an element
I can't tell if its 1 or 2 in this case.

  • giob
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  • Registered: 06-11-2011
  • Posts: 2

Re: linear stability analysis with plane stress or plane strain elements

The correct answer is in my opinion Mikael's number 2.
Buckling analysis is based on computation of geometric matrices, which represent the sensitivity of each element and of the system as a whole to second order eulerian effects, i.e. the effects under small displacements of the displacements themselves on equilibrium equations. In plane strain analyses (and plane stress ones as well), out of plane behavior is intrinsically excluded from start by the chosen approach itself, because of the fundamental hypothesis that out of plane strains (or stresses respectively) are zero. Such second eulerian effects are therefore, on those structures, simply not allowed to happen.
Buckling analysis should, on the other hand, work on structures made up of beam and shell elements.

Giorgio

3 Reply by bp

  • bp
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  • From: Prague, Czech Rep.
  • Registered: 02-03-2007
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Re: linear stability analysis with plane stress or plane strain elements

I think that in certain applications, the buckling analysis can make a sense, for example, one can use plane stress elements to model beams by discretizing the beam along its length and height.  And then it makes sense to perform buckling analysis, of course, only the in-plane buckling is  captured.
On the other hand, the initial stress matrix is not provided by plane strain (or stress) elements at the moments, as there was no interest in a such analysis before. If you will provide initial stress matrix for these elements (by implementing computeInitialStressMatrix) it will work.

Borek

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