"Hyper-elastic material may become unstable" message for Mooney-Rivlin model

[farhan3d]

Hi All,

I am trying to use my experimental data for vulcanized natural rubber for some finite element simulation in ANSYS, and noticed that the closest fit is given by Mooney-Rivlin. But unfortunately, this material model gives the warning mentioned in the subject prior to solving, and the process terminates with "error in element formulation".

Other material models like Neo-Hookean and Ogden don't seem to be providing a good fit with the experimental stress-strain curve, but there's no such warning or element formulation error for those.

I'm simply using a rectangular area with Plane Stress w/Thk element real constant specified, plus the aforementioned curve fitting of my experimental curve.

Please advise.

Farhan

[Jorgen]

Can you show figures with the experimental stress-strain curve(s) that you have?

-Jorgen

[farhan3d]

Hi Jorgen,

I was able to curve-fit by unchecking the "Use Normalized Error" checkbox in the curve-ftting dialog in ANSYS. I'm not exactly sure what purpose it serves, but the fits are good now.

Currently I don't have access to the images. I will share as soon as availble.

Many thanks!