# [Solved] MSC MARC Implementation of BB material model

Hello all,

Im far from a polymer simulation expert, my primary background is with steel/metallic structures, but occasionally I get pulled into projects that require more complicated materials. I have modeled a polymer component using MSC MARC, and preformed stress analysis (static) on this part based on Mooney-Rivlin curves supplied by the material manufacturer.

Now, we are looking to try to predict the dynamic response of this component, and for obvious reasons we need to change our material model. Its relatively easy to generate loading and unloading curves at 2 strain rates (data needed for BB mat model), so were planning on that. However, in MCalibration I see 9 material parameters are calculated. Where Im confused is that in MSC MARC, there are only 5 material parameters. What behaivior(s) are missing from MSCs material formulation. The material paremeters calculated by MSC from the test data are:

Nkt

Chain Length

and then under the title of Creep Rate Evolution Law

Multiplier

Exponent

Stretch Sensitivity

I dont need a dissertation on this, just a quick explanation for dummies 🙂

Thank You,

Mark

Hi, what i found out so far is the following:

Arruda-Boyce-Constants for Network B:

[B]MARC nkT[/B] is the same as [B]mu_B[/B] (initial shear modulus) found in the papers [URL= https://polymerfem.com/content.php?77-bergstrom-boyce-model ]here[/URL].

[B]MARC Chain Length[/B] is the same as sqrt(stretch_lock), where stretch_lock is the stretch where the chains begin to lock the stress strain behaviour.

For the parameters of the evolution law just read the papers in the link above: Multiplier = hat{C}, Exponent = c, Stretch sensitivity = m. There is barely any documentation inside Marc regarding Arruda-Boyce and Bergstroem-Boyce and especially their implementations, just a sample data set:

Multiplier: 1.75

Exponent: -1

Stretch Sens.: 4

Maybe you could post your experiences with this model, i would be really interested!

Good luck and best regargs,

Andreas

EDIT: I have to correct the definition of the Multiplier - it is hat{C}/(sqrt(2)^m). Found it somewhere in the Docs of Mentat 2015.

- Predicting Dynamic Moduli and Damping from B-B model4 years ago
- BB model Constants7 years ago

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