linear vs. non - linear analysis
linear vs. non - linear analysis
(OP)
Are there any general guidelines as to when to use a non-linear analysis vs. a linear analysis?
I don't mean code specific or structure specific...for example if your out of plane deflection exceeds x percent of your part thickness, things of that nature.
Thanks
I don't mean code specific or structure specific...for example if your out of plane deflection exceeds x percent of your part thickness, things of that nature.
Thanks





RE: linear vs. non - linear analysis
Also standards and required levels of accuracy tend to vary depending on the industry in which you work.
You may find this link (and web site interesting):-
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RE: linear vs. non - linear analysis
Are there cases when running a non-linear analysis would actually take you further from the real result?
RE: linear vs. non - linear analysis
good57morning@netzero.com
RE: linear vs. non - linear analysis
The one exception to this is thin plates as feadude suggests. These structures frequently require nonlinear analysis when the plate deformation allows a redistribution of load from bending to membrane. Given that the linear bending stresses are usually higher than the nonlinear bending/membrane stresses, one does not tend to underestimate the resulting stresses.
RE: linear vs. non - linear analysis
Best regards,
Matthew Ian Loew
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: linear vs. non - linear analysis
Neuber correction can be used for fea nonlinear analysis of complicated structures?
good57morning@netzero.com
RE: linear vs. non - linear analysis
You use Neuber to estimate an elastic-plastic stress at a stress concentration feature starting from an elastic stress from a linear FE analysis.
RE: linear vs. non - linear analysis
It is widely accepted that the three main sources of non-linearity are:
- Plasticity of material (variation of the material Young's modulus will cause the stiffness of the structure to change)
- Large displacements (Stiffness varies as a result of large geometric difference between the initial and deformed shape)
- Contact: if two parts or bodies of the assembly come into contact, or lose contact, or the extent of their contact patch changes, then the stiffness of the assembly also varies.
RE: linear vs. non - linear analysis
Could you be a little clearer in "variation in stiffness"? One such variation is precisely what you are referring to when you talk about the variation in Young's modulus...varying the Young's modulus for plates or beams varies the stiffnes...I'm assuming you are referring to some other stiffness alteration?
I suspect the answer to your question is, "yes". If the material stiffness varies, you must input some type of curve properties. If you are simply referring to periodically stepping down to smaller beams under a plate, then you don't necessarily have to do this non-linearly.
Garland
Garland E. Borowski, PE
Borowski Engineering & Analytical Services, Inc.
www.borowskiengineering.com
RE: linear vs. non - linear analysis
The behaviour of the WHOLE STRUCTURE under the effect of loads can be non-linear (the stiffness of the structure varies) even if the stress in the material does not exceed the plastic limit anywhere (the stiffness of the material does not vary). Points 2 and 3 from my previous post are possible reasons of this effect
RE: linear vs. non - linear analysis
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: linear vs. non - linear analysis
But if overall deflections are beyond "rules-of-thumb" for deflections as a ratio of overall geometry then non-linear large deflection models might be needed.
David R. Dearth, P.E.
Applied Analysis & Technology