November 28, 2022 at 11:33 amLovisa SvanborgSubscriber
I wonder about strain energy density plot for hyperelastic. How can a plot it to see material instabilities? Can I plot before simulation, because I want to see before if the material is instable?
I have done curve fit with mooney Rivlin 3 and 9. My simulation works for MR 3 and not for 9. But is MR 9 instable?I don't think it looks like that in the picture.
Plot MR 3
Plot MR 9
November 29, 2022 at 2:44 pmMike RifeAnsys Employee
Why not create a 1 element cube model and run the three typical stress conditions (uniaxial tension, shear etc) for a range of stretch ratios and post process? The MAPDL solver does this behind the scenes when a hyperelastic material is present but will only show the results if the material is unstable (shows as a list of conditions & ranges that were unstable in the output file).
November 29, 2022 at 3:05 pmLovisa SvanborgSubscriber
Ok, thanks. Can you please explain a litter more how I post process to plot strain energy density.
November 29, 2022 at 3:27 pmMike RifeAnsys Employee
Strain energy is a typical result available. If you want strain energy density then in the Details of the Analysis Settings; Output Controls make sure that Nonlinear Data is set to Yes. Solve. Then use a user defined result with the expression NLELWK (Non Linear ELastic WorK).
November 29, 2022 at 8:17 pmLovisa SvanborgSubscriber
Thanks, I will try.
December 3, 2022 at 10:47 amLovisa SvanborgSubscriber
It didn't work. I have turn on nonlinear data. It says I have error and also an invalid scopping method. I have choosen the body for hyperelastic material.
December 3, 2022 at 11:14 amLovisa SvanborgSubscriber
It works now to show strain energy density, but I would like to plot the contour plot of strain energy density. To se if the material is instable or not. How can I make contour plot of strain energy density?
December 5, 2022 at 3:15 pmMike RifeAnsys Employee
So if the plot worked, and it's a contour plot, then I don't get the question.
December 5, 2022 at 4:12 pmLovisa SvanborgSubscriber
I have read that to see if a material model is stable/unstable, you can plot the contour plot of strain energy density function. And it should looks like this in the rapport
If it is one local minimum it is stable (picture to the left) with more unstable (picture to the right).
The result I get in Ansys with that command you gave me
So is there another way to get the contour plot? Have I undetstand wrong?
December 5, 2022 at 6:31 pmMike RifeAnsys Employee
In traditional FEA parlance a contour plot is a color-coded plot of some field result plotting on the FEM. Which is what that strain energy density plot you posted is showing. If I understand the isoline plot you show, then the strain energy density can be calculated from the materials specific strain energy density function for differing values of lambda (principal stretch ratios). Stretch ratios are engineering strain plus 1.
December 5, 2022 at 6:43 pmLovisa SvanborgSubscriber
Thank you. Do you know how to plot the isoline plot?
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