ANSYS V12 Bergstrom

Dear Dr. Bergstrom,

I found the answer in your PhD thesis so please ignore my previous question.

But I have another problem so I would appreciate your help. I am trying to compare the experimentally gathered hysteresis from rubber specimens with the one obtained by ANSYS V12.

My problem is in material definition, and I have full set of experimental data. I used three models (two cannot catch the hysteresis curve but I troubleshoot the convergence issue).

1. Model Yeoh, third order

After the curve fitting the only material property required by ANSYS is density

Problem converges very well

2. Model Ogden third order

After the curve fitting again the density is required from ANSYS to run the analysis. Convergence is poor but this is a problem of implementation of Ogden model in ANSYS (poor curve fitting)

3. Bergstrom Boyce model

Setup 1

I entered model parameters, but to run the analysis I need to enter density and Isotropic Elasticity (Poisson and Young modulus). I used values of 0,3 and 2 MPa from your PhD. I used other model properties from yours PhD. The only thing I dont know is the bulk modulus so I experimented with various values (I entered values of 1/K as D1 which I obtained from Yeoh model).

I have a catastrophic convergence.

Setup 2

I modified the ANSYS model and tried to expand the ANSYS model by using the D2 and D3 values like this:

TB, BB, 1, , , ISO !Activate Bergstrom-Boyce ISO data table

TBDATA, 1, 2 !Define material constant μ,A

TBDATA, 2, 1.45 !Define N0=(λ,Alock)2

TBDATA, 3, 8 !Define material constant μ,B

TBDATA, 4, 1.45 !Define N1=(λ,Block)2

TBDATA, 5, 0.01 !Define material constant

TBDATA, 6, -1 !Define material constant c

TBDATA, 7, 4 !Define material constant m

!

TB, BB, 1, , , PVOL !Activate Bergstrom-Boyce PVOL data table

TBDATA, 1, 4.55938486420696E-06 ! as 1/K, K is the bulk modulus

[COLOR=Red]TBDATA, 2, 1.49167943507736E-06 ! as 1/K, K is the bulk modulus

TBDATA, 3, -2.81403546179751E-06 ! as 1/K, K is the bulk modulus[/COLOR]

ANSYS doesnt accept highlighted text but the Isotropic Elasticity is not required anymore.

Convergence is very bad, but slightly better than at setup 1.

Where is my mistake in defining yours model. Or the implementation of the model is ANSYS is an issue?

.