ABAQUS VUMAT for the Neo-Hookean model

[Jorgen]

A single-precision Abaqus VUMAT subroutine for the Neo-Hookean (NH) model. The subroutine is an example of how to write a VUMAT. The subroutine only works for plane-strain, axisymmetric, and 3D-elements.

[doctorant59]

Hello Doctor;
I view the VUMAT, but when I have run Abaqus, it did not market, is that you can send me the file (.INP), for your example.
Thank you

[Jorgen]

You can get exemplar input files here (http://polymerfem.com/forums/showthread.php?t=43).

[doctorant59]

Hello Dr;
You below the condition that I applied to initialize the FE that correcpond in my simulation gradien elastic.
Abaqus compile when I got started in the calculation and stops immediately, and when I calculate this condition normally, but on this condition is necessary to get good results.
So is what you think is the right way to proceed?

IF (totTime.EQ.0.0) THEN
C setup FE (upper diagonal part)
FE(1,1) = 1.02
FE(2,2) = 1.039
FE(3,3) = 1.059
FE(1,2) = 1.079
if (nshr .eq. 1) then
FE(2,3) = 0.0
FE(3,1) = 0.0
FE(2,1) = 0.0
FE(3,2) = 0.0
FE(1,3) = 0.0
else
FE(2,3) = 1.0099
FE(3,1) = 1.029
FE(2,1) = 1.0049
FE(3,2) = 1.079
FE(1,3) = 1.809
end if
END IF

[Jorgen]

At time=0, should not FE = unit matrix ?
Why do you have non-zero values for FE?

[doctorant59]

Hello Dr;
Does it can introduce the Norton parameter (K and n) without Abaqus has gone through a routine for even the effect rate?
Strain-rate = (sig/K)**n
Thank you

[Jorgen]

The flow equation that you mention actually work rather well for many different types of polymers. Abaqus has two a model called "Two layer viscoplasticity" that I believe supports that flow rule. I have not had much luck with that model, however.

Another approach is to use the *Hysteresis model in Abaqus. That model is also based on that flow rule.

A third option is to write your own user-material.

- Jorgen

[doctorant59]

Dear Doctor
Can you tell me what the « Lemaître » model exists in Abaqus?
I introduced the viscosity parameters of in Abaqus, but I did not understand what "m and f?
Thank you

[Jorgen]

I don't recall a Lemaitre model in Abaqus. If there is such a model, can you provide a reference?

-Jorgen

[doctorant59]

Dear Dr ;
What I realize in order to Abaqus
To calculated of the damage parameter "D".
Is that there is a possibility to calculate this parameter "D", for me it’s the lemaitre model
In attached you find a page on the model.
Thank you

[Jorgen]

Thanks for the info. For some reason, the thumbnails are very small and and not easily readable.

I am not sure I understand what the "D" parameter is, so I don't know how to calculate it.

-Jorgen

[Ajaj]

Ok once again i posted too quickly by searching in the archives i found some interesting post i have to understand first.
My understanding is that anything rigid body is controlled by abaqus explicit if one wants by using U, and it is equivalent to F and V in this framework.

original message:
Dear Jorgen. I am trying to understand this vumat before wirting my own (TNM based). But i am struggling at one point.
By going backward in the code.
I am all ok for:
c Stress = mu/J * Dev(Bstar) + kappa*log(J)/J * Eye
and for
c Bstar = J^(-2/3) F Ft (upper diagonal part)

But my feeling by reading the code is that instead of calculating F Ft you take the square of the stretch tensor. I would have no problem with that if ABAQUS was proposing the left stretch tensor ( F = V*R => F * Ft = V* R * Rt * Vt = V² V being symmetric) but i read ABAQUS documentation and it says that VUMAT communicate the RIGHT STRETCH TENSOR F = R * U !

So i don't understand something. Can you explain ?

By the way the ABQ doc says that the user should use U instead of F to write hyperelastic law but i don't really see how.