Rubber and Ogden

[Valou]

Hello,

I'm working with the behavior law of Ogden. I have the terms (from tests...) which define the compressiblity of the material (ie béta_i). Unfortunately the code I'm using needs the Poisson's ratio. How can I define the Poisson's ratio with the béta_i of the law?
I know that there is a formula ( Nu=béta/(1+2*béta) ) in the documentation of ABAQUS...but I don't know where it comes from...
Can u help me?

Thank you.

 

[NickE]

I do believe that Poisson's ratio describes teh change in width resulting from changes in length. IE: Tensile forces cause the specimen to elongate and thin. Compressive forces case the specimen to shorten while getting thicker.

nick

 

[Valou]

OK I understand, but has anybody an idea about this kind of problem?
How can I get such a formula with the béta_i?
The fact is the material I'm using is a foam, that is to say compressible...