EPDM and ls-dyna

[austenite]

Hi All,

This is my first post, I am trying to model the strain rate dependent material properties of EPDM rubber. I have the quasi-static and high strain rate experimental stress strain data. I am using ls-dyna for this purpose and also trying to use the *MAT_SIMPLIFIED_RUBBER model to model the strain rate dependency.

When I check the input deck, I have seen that there are couple of material parameters that I have no idea, for example, linear bulk modulus, damping coefficient, shear modulus for frequency independent damping and limit stress for frequency independent, frictional damping. Does anyone have any idea about these parameters especially the last two?

Or any other material model that I can use for this purpose.

P.S. I am succefully simulating the constitutive behavior of EPDM by using Ogden material model at a definite high strain rate value.

Many thanks for your help.

[Jorgen]

Hello Austenite,

I have not worked with *Mat_Simplified_Rubber before, and when I read the ls-dyna manuals it is not clear to me how that model works.

If you are interested in modeling strain-rate effects then I recommend the Bergstrom-Boyce model (BB-model). The BB-model is well tested and has been shown to capture the experimental data for different classes of elastomers. The BB-model, however, is not a built-in model in ls-dyna. I have implemented it as a user-subroutine. Check out the user-materials section (http://www.polymerfem.com/modules.php?name=User_Subroutines) if you are interested.

Best of luck,
Jorgen

[austenite]

Hi Jorgen,

Many thanks for your reply, Is it possible to give the experimental stress strain data at different strain rates as an input in your model ? How about the avaliability of this model in ls-dyna ?

Best Regards

[Jorgen]

The BB-model can be calibrated to experimental data at different strain rates. Once the model has been calibrated, it can be used to accurately predict the non-linear response, including strain-rates. Note, the BB-model is not available as a built-in model in ls-dyna. It can be made available through an external subroutine that I have developed, and that can be licensed for a fee.

The most appropriate material model in your case will depend on what you are trying to simulate and how accurate you need your simulation results to be.

Jorgen

[eddy]

Hi All;
I will perform fem analysis of EPDM Sponge rubber by using Ansys. I need Uniaxial,Biaxial,Shear and Volumetric tests in order to find the coefficients of the constitutive model to be used. Do u know a paper,report and another source that ı can get these data? Especially volumetric test is requred because i intend to use models such as Blatz-Ko and Hyperfoam which are suitable to compressible materials.
Thank you for your attention.

[Jorgen]

Hi Eddy:

I don't have any data for EPDM foams :(
Unfortunately, since the behavior of foams is strongly dependent on the reduced density (i.e. amount of porosity) it will probably be difficult to find good data for the material you are interested in.

Best of luck!
Jorgen