Using Ogden, Mooney-Rivlin material model

RIZA BAYOGLU_21565

Hi,

I am developing an FE model of the human spine where I use the Ogden, Mooney-Rivlin material model (MATX42) for the intervertebral discs. I am getting some errors, and I would like to make sure I am using the right analysis settings. I defined an explicit analysis with the subcase option of NLEXPL, I am running the simulation in OptiStruct. The error I am getting is:

A fatal error has been detected during input processing:

*** ERROR # 5920 ***
Only the following solid elements are supported in explicit analysis:
eight nodes HEXA, ten nodes TETRA, and six nodes PENTA.

I understand that some of my elements are not supported by this analysis. As for solid elements, I have CPYRA (5-noded, unsupported), CHEXA (8-noded, supported), CTETRA (4-noded, unsupported). My questions are:

1) Is using explicit analysis my only option? To accurately represent discs, I will need to use the Ogden, Mooney-Rivlin material model. Is it possible to use a different analysis type where I can use this material model?

2) If using explicit analysis is my only option, how to fix the error I am getting? I have a very complex geometry and re-meshing unsupported elements are likely to be difficult.

Looking forward to seeing some help.

Best,

Riza Bayoglu.

 

Adriano Koga_20259

Hi,

 

you can do it in Implicit mode.

Just a clarification, this cards ending with an X were the old way of calling an explicit model in OptiStruct, which turned out converting the model to RADIOSS (expliciti).

 

In newer versions, you have both Implicit and Explicit all inside OptiStruct.

 

For your ase, you might want to use MATHE cards for hyperelastic models, such as MR.

Take a look at OptiStruct tutorials working with HE materials, and help documentation for MATHE, PLSOLID.

 

RIZA BAYOGLU_21565

Thanks so much, Adriano! I was able to run my simulation in implicit mode using MATHE cards. The model did not converge eventually, but I will investigate that further later.