Extracting vonMises stress for all nodes of a surface structure

Hi All,

I am working on the structural analysis of a concrete plate and by using the "shell analysis" component of Karamba, I want to extract the vonMises stress levels of all of the nodes. I need these values to do a statistical analysis on them and then to verify the results with Ansys.

Currently, I have done the analysis in Karamba and can see the max/min values of vonMises. With the "result vectors on shells", I can see the first and second principal stresses. But I need the vonMises stress. can anyone help me with that? The plate image and the GH script are attached.

Thanks

Attachments:

Replies to This Discussion

Permalink Reply by Karamba3D on August 16, 2016 at 5:55am

Hi Nilou,

the Von Mises stress can be calculated from the principal stresses:
sig_v = sqrt(sig_1^2 + sig_2^2 - sig_1*sig_2)
See also https://en.wikipedia.org/wiki/Von_Mises_yield_criterion.

Best,
Clemens

Permalink Reply by Nilou on August 16, 2016 at 6:21pm

Thanks, Clemens. So by using the "Result Vectors on Shells" and then switching the type of result to the "princ-stress", I am getting V1 and V2. The V1 and V2 are represented as {x,y,z} which I assume are three vectors creating the sigma 1 and 2; therefore I need to first calculate sigma1 and 2 by using "sqr root of (x^2 + y^2 + z^2). Is my assumption and procedure for calculating sigma 1 and 2 correct?

Permalink Reply by Karamba3D on August 17, 2016 at 3:17am

Yes. You could try it on a simple example (e.g. rectangular plate with in-plane forces in one direction).

Permalink Reply by Nilou on August 20, 2016 at 11:21am

Thanks for your reply, Clemens. I'm trying the calculation on a simple plate with four supports at the corners and four in the middle. The calculated vonMises values are off in an amount of "10e4", compared to the results that Karamba automatically calculates for generating the view-shell legend. I appreciate if you take a look at the GH script and the python code that is calculating the vonMises. I was wondering if you can share the code that is being used in Karamba to calculate the vonMises in the legend.

Thanks again

Attachments:

plate_forum.3dm, 38 KB
plate_forum.gh, 35 KB

Permalink Reply by Karamba3D on August 22, 2016 at 11:31am

In Karamba 1.1.0 there was a bug in the 'ShellVecResults'-component: the output was in kN/m2 instead of kN/cm2. Karamba 1.2.1 gives correct results.
In Karamba 1.2.1 the vonMises stresses for the legend are generated in the method 'collectRenderedShellMesh' of class 'ModelDisp'. You can use e.g. the program 'ILSpy' (it's free) to decompile 'karamba.gh' and see the sourcecode.

Best,

Clemens

Permalink Reply by Nilou on August 29, 2016 at 6:48am

Ah ok. I upgraded my Karamba and the difference got resolved. Also thanks for introducing the ILSpy, I'll give it a try.

Best,

Nilou

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