Hyperelasticity/ Viscoelasticity in LS-DYNA

[Willem]

Hello,

I am trying to model a three layer golf ball in LS-DYNA with a polybutadiene rubber core, a polybutadiene rubber middle layer, and a ionomer resin cover. Therefore, I am planning on using the *MAT_HYPERELASTIC_RUBBER model. This model has got an option for modelling linear viscoelastic properties, which I want to use for the two butadiene parts.The cover I will then just model using purely hyperelastic properties. My problem is that I don't have any experimental data for those particular materials to perform the often recommended curve fitting on the model. I have got a paper that provides me with material constants of the golf ball materials like Poisson's ratio, initial Young's modulus, initial shear modulus and also for the viscoelasticity the first two Prony series parameters (they were using ABAQUS in that paper). So my questions now are:

1. How do I get the parameters C01, C10 and C11 for the strain enegry density function from the material constants? Or what range of those parameter can I expect for the following materials considering compression loading. I don't even know what typical values look like:

Core: E0 = 50 MPa, Poisson's Ratio = 0.49, Rho = 1150 kg/m^3
Cover: E0 = 400 MPa, PR = 0.45, Rho = 950 kg/m^3

2. For those materials above, can I use experimental data posted on your webpage? And if so, do you know how to use the interactive material model driver in LS-DYNA? Is it right that I would get the parameters from testing the material with the material model driver?

3. For the viscoelasticity option, do I get a G_infinity in the relaxation function by assuming that the first parameter in the Prony series is zero?

Thanks you,

Willem

[Jorgen]

Here are a few comments:

(1) I am a bit confused: are not C01, C10, and C11, the material parameters?
You can convert Young's modulus and Poisson's ratio into the Cij parameters for some of the simple models. If I remember right, the LS-DYNA manuals describe that mapping.

(2) You are more than welcome to use any material data that is available on this website. I typically use my own software to find the material parameters from experimental data. Can you tell me more, or give a reference, to the LS-DYNA interactive material model driver? It sounds interesting.

(3) Yes, you get the G_infty term by setting one decay constant to be zero.

- Jorgen

[Willem]

Hi Jorgen,

Thanks for the quick reply.

I am sorry I confused you, and you are right. I just can't get the conversion done in a way that I can solve it. For small strain, the relation between Young's modulus, bulk modulus and Poisson's ratio will always give me a linear dependency of the Cij parameters or at least close to that which results in parameters like C10 = 9500 and C01= -9433.3. Those don't seem right and they didn't work either :)

Can you suggest any experimental data, that you have posted, for the materials that I mentioned? I am not sure which one to use for the ionomer cover of the the golf ball and if I can use your butadiene data for the rather stiff golf ball core. In terms of the interactive material model driver, I was hoping you had used it before and that you could tell me more about it, because it's mentioned in the LS-DYNA keyword manual under Appendix H. I also found a bit more information that I can email you, but i couldn't make it work with this little info.

Thanks so much,

Willem

[Jorgen]

Hmm, I am not sure I can recommend similar substitute materials since I don't have much experience testing golf balls :(

Also, I am not familiar with the LS-DYNA interactive material model driver. I will attempt to check it out.

- Jorgen