material properties for butyl rubber

[daniel63]

Hello,

I work for a small consulting company and am trying to obtain material properties for buytl rubber at various strain rates. We are willing to pay for these properties. The loading condition is a drop test of an object that has butyl rubber as a component. The drop height varies.

Daniel

[Jorgen]

Hi Daniel,

You mentioned that the loading is a drop test. I assume that you therefore mainly interested in high strain rates (impact). I have a few questions:
:arrow: What material properties are you mostly interested in?
:arrow: What modeling technique and material model are you planing on using?
:arrow: What are the maximum strains that you are expecting in the real application?
:arrow: What temperatures are you interested in?

- Jorgen

[daniel63]

Hi Jorgen,

Yes, high strain rates. This object will eventually be subjected to blast forces. I can not quantify the exact range of strain rate since the customer has not quantified it. The butyl rubber component will be compressed by the impact and then released. We use LS-DYNA and the butyl rubber component will be solid elements.

The temperature will be normal room temperature.

I notice that our test results show that the rubber has a very high damping effect on the response we are monitoring from our load cell. The test results look as though the rubber is providing critical damping since we observe a very smooth decompression in the test data.

We have no material data and I want to try the various material models in LS DYNA to see if any of them will match the high level of damping we see in the test results. I see your web site has data for natural rubber. I am a neophyte. So I apologize for my simple questions. Are the parameters listed in the upper left corner of the graphs for each material model the parameters to enter into the fea code's material card? Is there a standard arrangement for how they are listed? What units are you using?

I also notice that LS-DYNA has a simplified rubber material model, MAT 181. This appears to have the advantage of supplying multiple load curves via a table. What is your opinion of this material model?

Do you know where to obtain butyl rubber material data?

Daniel

[Jorgen]

Hi Daniel,

You mentioned that the rubber has a very high damping effect of the reponse. How did you perform the experiments? Did you attempt to perform an impact experiment, or was it a dynamic vibration test?

As you noticed, this website contains predictions and data for a few different elastomers. The parameters listed in the upper left corners of the graphs are indeed the actual material parameters, but the order of the material parameters are not the same as what is used by LSDYNA, ABAQUS, ANSYS, or one of the other FE packages. If you are interested I can let you know what parameters the listed numbers correspond to.

LSDYNA Mat181 might be an option for you. I have not used that specific model and I cannot therefore say much about it. It certainly is an option that you can try out and see how well it works. I typically use models that are based on the Bergstrom-Boyce model. You can read about these models on this website.

The best way to obtain material parameters for the butyl rubber that you are interested in is to perform actual experiments. The best type of experiment will depend on the magnitude of the deformation that the final product is likely to see, and the nature of the actual loading.

Jorgen

[daniel63]

Hi Jorgen,

Our customer dropped the object from 38 inches and generated some loadcell data. We are using this test to work the kinks out of the FE model. The data shows the force recorded just above the rubber joint rising rapidly in compression and then slowly uncompressing and returning to equilibrium. The force in the loadcell looks very much like a critically damped system. There is no oscillation in the data after the initial impact.

I would very much like to try the natural rubber material parameters (am I correct in assuming that butyl rubber is very close to natural rubber?) for the models mooney-rivlin and ogden. I also am interested in learning about your material model and how it is patched into ls-dyna. Would you please list the material parameters for Natural Rubber in Ls-Dyna order

Mooney_Rivlin:

A=
B=

Ogden:

I assume N=0
NV=?
G=?
SIGF=?
MUi=?
ALPHAi=?
Gi=?
BETAi=?

I have to learn how to run external material models before I can try your model. I look forward to it.

We plan on doing some testing but are having some hiccups obtaining the material samples.

Thanks for your help and the website.

Daniel

[Jorgen]

Hi Daniel,

The Mooney-Rivlin material parameters for the filled natural rubber are as follows:
:arrow: mu=1.176 MPa
:arrow: kappa=3009 MPa
:arrow: s=0.088

The parameter s is the ratio W2/W1 where W1 is the partial derivative between strain energy density and the invariant I1, and W2 is the partial derivative between the strain energy density and the invariant I2. If s=0, then the model becomes the same as the neo-Hookean model.

These material parameters can be converted to the required LS-DYNA parameters by:

A = 0.5 * mu / (1+s)
B = s * A

In this case giving:
A = 0.5404
B = 0.0476

I will follow up with the parameters for the Ogen model at a later time.

- Jorgen

[daniel63]

I will be able to try it next week thanks for your help.

Daniel