Problem with parameters in Mooney-Rivlin model - unknown units in stress-strain

[kilgore]

Hello,

I want to use Mooney-Rivlin parametrs from the paper publish in the internet - they received parameters :

C10: 2.7507e-2
C01: 1.3077e-1
C11: 6.8027e-2
D: 4.8694e-2
Objective: 3.0583e-3

My problem is :
1. Authors of these paper didn't mention what units of stress and strain they used to obtained the C10, C01, C11, D parameters. Is the units of input data of stress-strain important ? -> Will parameters Cij change if the units of input stress/strain data change ( for ex. Pa -> MPa -> PSI or mm -> inch). And therefore how they change?

2. Could you tell me what system of units is correct for these values of parameters which look like above. ( When C10=2.7507e-2, C02=... so we can suppose that the system of units looks like SI=MKS ? )

3. Is it enough to describe material model when I only put Cij parameters into Mooney-Rivlin material model. Do I have to put some more parameters to these model ?

Please, help me :)

[Jorgen]

- What FE software are you using?
- What material are you studying?

Yes, the parameters are dependent on the units of the input experimental data.

-Jorgen

[kilgore]

Hello,

- I use Ansys ver 11.0

- It is a rubber. I don't know the name of it. I have taken these parameters Cij from work which You can find on this site :

http://www.enginsoft.com/network/documentation/ch_rubber.pdf

This material is usefull for a element which connecting vibration machines (engines for ex.). From that reason, I want to use these parameters to discribe material model of my part -> You can see it here :
http://img258.imageshack.us/my.php?image=element.jpg

It is a part of suspension of car's engine. Here You can see an expamle of use :
http://img504.imageshack.us/my.php?image=zastosowanieelemntu.jpg

In my work I have to obtain plots, which look like these :
http://img529.imageshack.us/my.php?image=wykres.jpg

I asked about units, because I have problem with this model of material - when I put a small (1 or 2 [N]) force on 1 node I will receive error of large deformation (several meters), but when I put a large (50 - 70 MPa) pressure on small pice of it I will receive very small deformation (~0.3e-6 [mm]). I don't know the reason of that behavior :/ but I'm trying to find it out every day ;) Here you can see examples of it :
http://img246.imageshack.us/gal.php?g=test1q.jpg


I would be very greatfull from any Your help and pices of advice.

:)

[Jorgen]

First, since C01 > 0, C10 > 0, C11 > 0, the material model is stable. That is a good thing.

The magnitudes of the terms are small. I am not sure what units it might be. If it is MPa, then it must be a very soft rubber.

-Jorgen