Components of defgradNew

[ashu28]

Hello all!
I am writing a VUMAT using defgradNew, but ABAQUS always gives me only F11, F22 and F33 non zero defgradNew values. My solution diverges at long times due to this. In all the user subroutines I have written before, I used to get all non zero components in defgradNew or DFGRD1, but something is screwing up my input here. As I dont control defgradNew values, I am stuck with this problem.

Can anyone help me out ?

Ashu

[Jorgen]

Are you saying that the defgradNew tensor given by ABAQUS is always diagonal?

What element type are you using? Note, some elements don't supply a deformation gradient.

- Jorgen

[ashu28]

Hi!
Thanx for the reply Jorgen. I figured out that F was diagonal as I had only uniaxial loading. But there is one more problem. I am using the same approach for VUMAT as I did for writing UMAT for Mulliken's model

If (time=0)
Fp=I,Fpdot=0,st=s0
else
read the state variables
end

Fp=Fp+Fpdot*dt,Fe=F*inv(Fp),Fe=Ve*Re, calculate stress, tau, gammapdot,st-->Np-->Dp-->Fpdot
Update Stress
Update Statev: Fp, Fpdot, st
Return

Are there any obvious errors in the approach ? Does my input file (https://netfiles.uiuc.edu/dikshit2/shared/velocityBC1.inp) look okay ?

Also, I came to know that till the material is elastic, I should have ALLKE very less than ALLIE. It doesnt happen in my case. What exactly does this point to ?


Regards,
Ashu