Learning Forum

[Kirstie]

Hello, I have been trying to use different material models in ANSYS by inputting experimentally obtained data for highly non-linear materials (e.g., silicone). However, when I use the curve fitting tool, the incompressibility parameter(s) are always 0 - why is this? I feel that something isn't being calculated correctly.

Any advice would be really appreciated, thanks!

[Ashish Khemka]

Hi,

You will need to define the incompressibility parameter. The incompressibility parameter, D, is nothing but 2/(initial bulk modulus). If you wish to add small amount of incompressibility (large but finite bulk modulus), then adding a small value for D will do it. Note that parameter D has the units of 1/stress. So, if the initial shear modulus of the material is, say 2.5 MPa, then a value of 1e-2 MPa^-1 would be a reasonable value for D.

Regards,

Ashish Khemka

[Kirstie]

Hi Ashish,

 

Thank you for your reply. If I have to add it in manually, how do I do this for 3 different D values, i.e., using Yeoh's 3rd order?

 

Thanks for your help!

Kirstie

[Ashish Khemka]

Hi Kirstie,

The 'd' parameters are inversely proportional to the bulk modulus, so if they are zero, the material is incompressible.

If the material is compressible, you can start with the initial value of d1 = 1/ K1 (initial bulk modulus) and likewise you will need to have data for K2 and K3.

Regards,

Ashish Khemka