Difference meshing hex, hex-dominated, tet?

[blazzzzzz]

Hi,

I am just doing a simple compression test on a cylinder, with hyperelasticity (Mooney Rivlin coefficients), fixed on one edge and pressure applied on the other.
I get negative eigenvalues and excessive distortion and job's aborted. But if I change the element shape from hex to tet, then job's completed, no error, but the results show almost no deformation.
how do you know which mesh to use?
Most importantly actually, what did I do wrong with such a simple test?
Thank you

Ben

 

[gurmeet2003]

Ben,

The way you described your model you have adequate constraints. So the problem must be in your material defintion. The error message appears to be self explanatory.
Check that the material co-efficients and the load input by you are realistic.

Gurmeet.

 

[corus]

It depends on the tet elemnt you used. Linear tets are useless as they're too stiff. Maybe that's why you saw little deformation?

corus