Rate of deformation in quasi-static analysis

[avee]

Hello all!

Shouldn't the rate of deformation during an incremention be constant during a quasi-static non-linear analysis in ABAQUS?

I am approximating the rate of deformation with (DFGRD1-DFGRD0)/DTIME in UMAT and as I am printing out the values of this tensor for a given element at a given integration point, the components do not match during an incrementation.

I find it strange because I assumed that the perturbation was linear.

Does anyone have an explication?

Do I have to change the analysis type, I am using a STATIC, GENERAL step.

cheers

[cochiece]

If you're finding a rate of deformation from the deformation gradient then I don't think it will be constant if there are significant rotations in your model.
Usually the rate of deformation tensor is taken as the symmetric part of the velocity gradient.
Are there rotations in your model?

[avee]

You are completely right!! and there is indeed a little rotation...

However, calculating both the symmetric part of the velocity gradient D and the objective time rate of change of the right Cauchy-Green strain tensor Cp still gives me different values through the incrementation....

Fp=(DFGRD1-DFGRD0)/DTIME
L=Fp*INVERSE(DFGRD0) the spatial velocity gradient

D=0.5*(L + L') ; where ' means transposed, the symmetric part of L

Cp=Fp'*F0 + F0'Fp ; F0 is DFGRD0

Do you agree with me that an objective strain rate should be constant during an incrementation for a given integration point of a given element in a quasi-static analysis?

Thank you for your reply!

[avee]

Reviewing the non-linear solving procedure made me understand that the strain rate is most probably not constant during the analysis..

I solved the implementation anyway.

Thank you for your help, it has been helpfull!

sincerly