iMechanica - Large Deformation Viscoelasticity and ANSYS Validation - Comments

I am specifying elastic

shrimad — Tue, 12 Aug 2008 23:25:25 -0400

I am specifying elastic constants using the MP command. I am not using the TB, HYPER command to specify the elasticity. I am specifiying poisson's ratio of .49 to preserve volume, and there is relaxation only in shear. Till now I have implemented 4.8.1 (small strain viscoelasticity). ANSYS doesn't conserve volume with this and the results are in exact match with my code.

Specifying NLGEOM conserves the volume in ANSYS. I want to know what formulation ANSYS uses for viscoelasticity when NLGEOM is turned on. I am confused between the sections 4.8.6 (describes hypo type formulation) and section 3.2 - 3.3 which describes forumulation for NLGEOM. I have a feeling that section 4.8.6 is implemented, as 3.2 is for elastic-plastic elements.

Please let me know which one do you think is the one being used when the NLGEOM is flagged on?

Thanks,

Shriram

What underlying elasticity

Nimish — Tue, 12 Aug 2008 18:24:00 -0400

What underlying elasticity you are using for small strain viscoelasticity? I feel that for small strain viscoelasticity underlying elasticity is hypoelasticity & it may not conserve the volume. For large strain viscoelasticity the underlying elasticity is hyperelasticity and you might be using incompressible hyperelastic material model which is causing volume to be conserved.

Section 4.8 Viscoelasticity in the Theory of Reference discusses what stress/strain measures are used. You may find that useful.

~ Nimish.

I didn't know aabout

shrimad — Tue, 12 Aug 2008 16:34:30 -0400

I didn't know aabout Xansys. I joined it and it seems to be quite helpful. Thanks Nimish, for the reply.

Shriram

Shriram
Research Assistant
Structural and Multidisciplinary Optimization Lab.
University of Florida

As this is a question

Nimish — Tue, 12 Aug 2008 15:58:36 -0400

As this is a question specifically related to ANSYS, I would recommend you to post this to ANSYS forum at www.xansys.org. You will need to subscribe the forum before posting & also make sure to read the netiquettes before posting there.

~ Nimish.

Large Deformation Viscoelasticity and ANSYS Validation

shrimad — Sun, 10 Aug 2008 16:48:59 -0400

I am developing a fea code for a glass compression molding process. (involves contact analysis, viscoelastic material, axisymmetric analysis, quadrilateral element, small deformation model). With a small deformation model, I get an exact match with ANSYS, but the volume is not conserved after deformation. 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 (the latter two given in the ANSYS manual for viscoelasticity).