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# Viscoelastic (generalized maxwell) model in MSC.Marc or ABAQUS

Greetings all,

I am trying to use gerenalized maxwell viscoelastic model for polyimide polymer films (Kapton) in MSC Marc (or ABAQUS). I have never used the prony series representation of the maxwell model (hereditary integral approach). Has anyone ever used MSC Marc to incorporate the prony series relaxation to the material? or ABAQUS? Here is my game plan for doing this:

1. I have the uniaxial relaxation curve for the polymer film, I obtain elastic modulus as a function of time for this model by curvefitting the relaxation curve and then obtain the prony series coefficients.

2. By assuming a constant bulk mudulus (time-independent dilatational response) I calculate the bulk modulus using equation K=E(0)/(3*(1-2n)).

3. I obtain prony series representation of shear modulus by using the equation G(t)=E(t)/(2*(1+n)).

4. I input K and G(t) to the VISELPROP command.

My questions are:

- Does this procedure make sense?

- Can I still use the elastic-plastic scheme for an isotropic material using ISOTROPIC command or it has to be just elastic?

- Is there any easy way to get the prony series coefficient from uniaxial tensile test (Instron)?

Thanks a lot.

Roham.

## Abaqus - Linear Viscoelasticity

Hi Roham,

Your approach appears reasonable for Abaqus. I am not aware of the required format for MSC.Marc.

Abaqus has another useful capability in that you can input the relaxation curve (test data) and the software internally calculates the Prony coefficients (limited to 13 coefficients, which I think is sufficient in most cases). However, in that case you have to provide shear or volumetric test data. You could check recent Abaqus version for more details.

If you are using visco-elasticity model (again Abaqus) you have to use *Elastic and *Viscoelastic. I don't think Abaqus allows *Plastic with *Viscoelastic option (but I need to double-check). On the other hand, if you want to include (rate-dependent) plasticity you may have to resort to a visco-plastic option. Essentially, you will then model an elastic/visco-plastic material.

I shall be glad to hear back from you.

All the best.

Thanks,

~Shailendra

## calibration method

In ABAQUS, the Prony series can be input as ratios, i.e. Ei/sum Ei. Sample calibration methods for the viscoelastic model can be found at

dx.doi.org/10.1023/B:MTDM.0000046750.65395.fe

and for viscoplastic model at

dx.doi.org/10.1016/j.actamat.2007.02.035

## Sample determination

Sample determination methods for the viscoelastic model can be found at

http://www.viscodata.de/