Large Deformation in ANSYS

Hi,

I am developing a fea code for a glass compression molding process. (contact analysis, viscoelastic material, axisymmetric, quadrilateral element, small deformation model)

With a small deformation model, I get an exact match with ANSYS, but I lose volume. I want to conserve volume, and if I enable NLGEOM ON in ANSYS the volume is conserved.

I want to know what formulation is activated when the NLGEOM ON is flagged on in ANSYS, so that I could implement the same in my code. Can anyone please guide my in going about identifying what is going on when NLGEOM ON is flagged?

I am unable to make out if it uses the Hencky strain with large rotation (given in ANSYS manual for NLGEOM), large deformation small strain viscoelasticity or large deformation large strain viscoelasticity (given in the ANSYS manual for viscoelasticity).

Please help me out.

Thanks a lot

Shriram

First, I use Abaqus more often than Ansys, so these comments are just suggestions. Are you sure that NLGEOM ON causes an incompressible response? The incompressibility should be controlled by the material model not by activating large deformations.

Switchin on NLGEOM (likely) swithes Ansys to internally use large-deformation formulations. Most FE codes use Hencky (true) strain, and Cauchy stress for the calculations.

- Jorgen