Viscoelasticity in Abaqus
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 )
)
=G_0~J_s(t),%20j_k(t)=K_0~J_k(t))
where 
Is it c
orrect if I use my strain )
=\epsilon(t)/\sigma_0)
)
)
And then to get the shear and volumetric compliance, is it valid to use the following equations:
=2(1%20plus%20\nu)*1/E(t))
where 
=3(1-2\nu)*1/E(t))
where 
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
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Hi Andreas
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!
ABAQUS viscoelasticity
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.
Thanks
thanks for the link Aaron
Andreas