Mooney Rivilin

[rams]

Hi Sir,
I am using Mooney Rivilin Material for my analysis in Ansys. I have got a uniaxial tensile test data of NR. i got calculated the Mooney Rivilin Constants. My loading is rubber plate in between two metals. If i apply Tensile of compression load( Pressure) on the metallic plate i am getting results exactly as expected. But if i apply shear load on the metal plate, i am getting a result which is not corect. Please help me in this regard.

[Jorgen]

The Mooney-Rivlin model is a simple model that can be quite sensitive to the chosen material parameters. In your case the problem could be either that you don't happen to have representative material parameters, or simply that the Mooney-Rivlin model is not a good choice for your material.

Did you calibrate the Mooney-Rivlin model using the shear data? What material parameters did you end up using?

- Jorgen

[rams]

Sir,
Thank you for your reply.
I have calibrated my shear data for mooney rivilin i am getting some error. it is not exactly matching. Can you suggest me any other material model for my material (Natural Rubber). Is it sufficient to have only uniaxial tensile test data or is there to have multiaxial data.

[Jorgen]

When using the Mooney-Rivlin (MR) model it is generally recommended to use test data from a few different loading modes, such as uniaxial, shear, biaxial, plane strain.

There are other hyperelastic models that are often recommended over the MR model. For example, the 8-chain model of Arruda-Boyce, the Gent model, the Yeoh model, or a more recent model by Horgan et al.

Jorgen

[rams]

Thank you for ur reply sir,
I have got Uniaxial tension data and Shear test data for my material.
ANSYS is having a inbuild curve fitting module.
Can suggest me any references to calculate material constants from these two sets of experimental data.

[Jorgen]

Unfortunately, I don't think there are any good references for that. If you are up for it, you can write your own material parameter finder for the hyperelastic model. It is actually not too hard...

- Jorgen

[rams]

Thanks for ur reply
Can you sugget me any study material for writing my own hyperelastic material. I am trying to fit the stress strain behaviour of my rubber material from equbiaxial data. is it sufficient to model the material?

[Jorgen]

If you are writing your own hyperelastic model then I recommend that you use experimental data from at least two or three different loading modes. If you don't have a specific data set already, then you might want to use the classsical Treloar data.

You should be able to find references to the Treloar data through a web search. I will add that data set to this website when I get time... :(

- Jorgen

[rams]

Sir,
As per ur suggestion, i have got two different modes of data i.e. from uniaxial and shear test data..
i am trying to get biaxial test data. can u guide me how to write my own hyperelastic model.
i have taken the material data for NR from ur website. it contains uniaxial, biaxial test data. in biaxial test data only three columns are there. is the stress given there is same in both directions or it is equivalent principle stress. please clarify me.
and how have you done biaxial test and obtained this data.

[Jorgen]

The biaxial data for NR that you are referring to were obtained in equibiaxial tension, hence the stress was the same in the two loading directions. The tree columns contain: time, strain, and stress.

Typically, people don't write their own hyperelastic models any more. There are many different hyperelastic models that have been developed, and some of them are very general. Instead of creating your own model, I suggest that you select one model that you like and then simply calibrate that model your experimental data.

- Jorgen

[rams]

Hi sir
Thank you for ue reply...
i have modelled my material and calibrated too.
i am getting good results...
can you suggest me any text book reference or any journal papers for understanding polymer basics and their stress strain behaviour

[Jorgen]

There are supprisingly few good books out there. One classic book that most people use is the book by Ward (http://books.google.com/books?vid=ISBN047149626X&id=CjYxgGejjHAC&dq=intitle:an+intitle:introduction+intitle:to+inti tle:the+intitle:mechanical+intitle:properties+inti tle:of+intitle:solid+intitle:polymers): "An introduction to the mechanical behavior of solid polymers".

[rams]

Thank you sir,
Can i get the author name please sir.

[Jorgen]

That book is written by I. M. Ward and J. Sweeney.

- Jorgen

[rams]

Sir,
Do you have any testing procedure or standard for testing the rubber specimen for biaxial tensile test...
do you have any specimen and can i know in which machine you have done the biaxial test...
can it be done in normal instron machine....

[Jorgen]

There are different experimental test labs that perform biaxial tension. One lab is Axel Products (www.axelproducts.com).

Biaxial testing is typically performed using specialized test equipment.

Jorgen