iMechanica - Viscoelasticity in Abaqus - Comments

Thanks

Andreas Burger — Sat, 26 Jul 2008 21:29:52 -0400

thanks for the link Aaron

Andreas

ABAQUS viscoelasticity

Aaron Goh — Wed, 23 Jul 2008 11:09:00 -0400

Andreas,

This has been discussed before:check out this thread:

http://imechanica.org/node/1784

ABAQUS does have a user-friendly way of modelling non-linear viscoelasticity.

Hi Andreas

Mike Graham — Tue, 15 Jul 2008 16:19:58 -0400

I've never used the built-in visco-elastic model in Abaqus, so I cannot be much of a help. I looked up that portion of the manual, but obviously I don't see anything you do not.

I think what you need to do really is to divide by the initial values. That gives you normalized values, but scaling them so that a certain value (in this case, the initial value) is 1. This sort of normalization is employed in many engineering problems.

Abaqus does not have built-in, nonlinear viscoelastic models (to the best of my knowledge). To perform a simulation with nonlinear viscoelasticity, you would need to use a UMAT user subroutine to define the material behaviour for Abaqus.

Good luck!

Viscoelasticity in Abaqus

Andreas Burger — Tue, 15 Jul 2008 14:25:59 -0400

Hi All,

I would like to use Abaqus to model the viscoelastic material behaviour of a polymer.

I have material data from a simple uniaxial creep experiment (nominal strain vs time). I tried to use the viscoelastic material model in Abaqus. I am a bit confused as to how I need to enter my data (what format).

The manual says I have to specify the normalized bulk and normalized shear compliance .

where is the shear compliance and the volumetric compliance

Is it correct if I use my strain to calculate the creep compliance, which is defined as:

where

then is the inverse of a "time-dependent elastic modulus":

And then to get the shear and volumetric compliance, is it valid to use the following equations:

where would be the shear compliance and

the Poisson's ratio

where would be the volumetric compliance .

Now according to the manual I have to calculate the normalized shear and bulk compliance by multiplying the values by G0 and K0, respectively. That part I'm not really understanding... I guess G0 and K0 are the initial shear and bulk modulus, respectively. To get them I need to again use the above equations (G=E/2(1+v) and K=E/3(1-2v)) and use the initial elastic modulus, which I can get from the initial elastic deformation.

What confuses me is that the shear and bulk compliance are supposed to be 1 at t=0.

All of the above of course assumes linear viscoelasticity... What if it is not linear??

Does anyone have any hints or comments about my approach?

Thanks,

Andreas