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Non-Linear Buckling analysis for hyperelastic material

Hi,

I am trying to solve a non-linear buckling analysis using Altair Hyperworks with Optistruct as a solver. I am unable to find the load step for it. Both non-linear static and linear buckling work. linear buckling won't accept NL static as input or as a STATSUB Preload. Is this option for non-linear buckling even available in this solver? or do I have to use any other solver. please advise. If there is any example available for this kind of analysis, that would be a lot of help. I couldn't find anything in the ebook 'Non linear FEA using Optistruct'.

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Rahul Rajan_21763

STATSUB(BUCKLING) can refer to NLSTAT -SMDISP (N2S/S2S contact) but is not allowed to refer a LGDISP subcase.

However, linear buckling solution can reference LGDISP-preloaded linear static subcase.

charlesfm

Yeah, but would it accurately predict non linear buckling behavior? what is your recommendation?

or Is there any way I can get a buckling or any other type of load step to reference non-linear quasi static ?

Simon Križnik

Hi,

my suggestion is to use Radioss solver due to nonlinear geometry (buckling) and material (hyperelasticity) and possibly contact. Radioss also supports implicit method which can be used for preloading and quasistatic analysis.

charlesfm

The only reason I was using Optistuct was because of material. I am using Yeoh model for Hyperelastic material. RADIOSS only has Ogden and Mooney Rivlin. and out of all Yeoh model best fits the stress strain curve. Also, I don't have any contact associated with my geometry.

I thought Optistruct was capable of doing Non Linear buckling, I also wanted to see post buckling behavior.

Is there any example problem referencing NL Buckling using Radioss, that would help a lot..

Simon Križnik

Actually, Radioss also supports Yeoh material (law 94). Check the attached tutorial RD-E: 5600 Hyperelastic Material with Curve Input.

Postbuckling behavior is difficult to converge for implicit solvers like Optistruct.

There are two tutorials and one example on NL buckling:

RD-T: 3030 Buckling of a Tube Using Half Tube Mesh (Hypercrash)
RD-T: 3530 Buckling of a Tube Using Half Tube Mesh (Hypermesh)
RD-E: 0300 S-Beam Crash

Unable to find an attachment - read this blog

charlesfm

Hi,

Thanks for the reference material. I'm still having some trouble with the analysis. Getting the Error ID 120 reference function.

Also, How do I get the different modes for buckling and Buckling load factor. Any suggestions on that?

Unable to find an attachment - read this blog

Simon Križnik

The model you shared had several issues:

no card image and material parameters were assigned to the 'rubber' material
rigid elements should be placed in a separate component
the pressure load collector did not have pressure versus time function referenced (The cause of error id 120)
only one linear (first order) tetrahedral element through thickness is not recommended (too stiff in bending). In order to calculate the bending stresses accurately in thin-walled structures, a minimum of 3 solid elements through the thickness should be used.

You can take advantage of geometry and boundary condition symmetry by modeling only a quarter of the model.

Use Quality> ModelChecker in HyperCrash or Tools>model checker>radiossblock in Hypermesh

https://insider.altairhyperworks.com/wp-content/uploads/2017/09/T-T-1248-HyperMesh-Model-Checker.pdf

<a href="https://community.altair.com/home/leaving?allowTrusted=1&target=https%3A%2F%2Fwww.youtube.com%2Fembed%2F0Lawq0Z1lek%3Fstart%3D1484%26feature%3Doembed">https://www.youtube.com/embed/0Lawq0Z1lek?start=1484&feature=oembed</a>

In order to get different buckling modes and Buckling load factor a geometric imperfection should be introduced. Either use a /RANDOM nodal noise or the procedure described in thread:

https://community.altair.com/community?id=community_question&sys_id=2876043a1b2bd0908017dc61ec4bcba4