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**bhattarai****Member**- Registered: 2014-01-31
- Posts: 134

Dear Developers and experts,

I needed the right Cauchy-Green strain tensor for the introduction of a new material model.

I found nmgeom.F90 calculates the deformation gradient. But when I make an output (AS CALL FLUSH) of

the deformation gradient [F] matrix and cauchy green strain tensor as C = transpose (F)*F, they are always an identity matrix at each time step with proper iteration. I was wondering why it is not updated with increased load and obvious deformation at the end of the simulation. Can anyone hint on this?

Also, I created a separate file to compute the matrix with following procedure:

! updated strain {E} in vector form

eps(1)=deps(1)+epsm(1)

eps(2)=deps(2)+epsm(2)

eps(3)=deps(3)+epsm(3)

eps(4)=deps(4)+epsm(4)

eps(5)=deps(5)+epsm(5)

eps(6)=deps(6)+epsm(6)

!modifying shear terms of the strain {E}

do i = 1, 3

epstot(i)=eps(i)

epstot(3+i)=eps(3+i)/sqrt(2.d0)

end do

! symmetric right cauchy green tensor {C} = 2{E} + {I} in vector form

c11 = 2.d0*epstot(1)+1.d0

c22 = 2.d0*epstot(2)+1.d0

c33 = 2.d0*epstot(3)+1.d0

c12 = 2.d0*epstot(4)

c13 = 2.d0*epstot(5)

c23 = 2.d0*epstot(6)

Here the components of the matrix is different and not unit matrix. can anyone provide

some light how to verify if the calculation of the {C} is correct or not?

Many thanks.

Bhattarai

*Last edited by bhattarai (2019-06-04 15:25:16)*

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**bhattarai****Member**- Registered: 2014-01-31
- Posts: 134

Part of the time increment is attached here.

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**bhattarai****Member**- Registered: 2014-01-31
- Posts: 134

Hello again,

I am wondering if my question does not fit to the Code_Aster development part of the forum. Can anyone put light on my question please?

Thank you again in advance.

Bests,

Bhattarai

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**AsterO'dactyle****Administrator**- Registered: 2007-11-29
- Posts: 248

Hello,

If you want to compute large strains (gradient F or Cauchy-Green tensor) you have to set "large" flag to .true. (parameter of nmgeom)

In code_aster, when you set DEFORMATION='GROT_GDEP' or 'SIMO_MIEHE', it's the case.

Where are you in the code ?

Code_Asterの開発者

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**bhattarai****Member**- Registered: 2014-01-31
- Posts: 134

Hi AsterO'dactyle,

My apologies for late reply. I set the parameter grand to .true. in geom.F90 and in my implementation file as,

call nmgeom(ndim, nno, axi, .true., geom,&

kpg, ipoids, ivf, idfde, depl,&

ldfdi, poids, dfdi, f, eps,&

r)

but got an error:

Error: Type mismatch in argument ‘grand’ at (1); passed LOGICAL(8) to LOGICAL(1)

Also, can one compute the Cauchy-Green strain (f^Txf) using this deformation gradient "f" from nmgeom? Theoretically, it should be correct, but confused with the aster behavior.

Bhattarai

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**AsterO'dactyle****Administrator**- Registered: 2007-11-29
- Posts: 248

Hello,

aster_logical is boolean(kind=1)

So, set .true._1 instead of .true.

Code_Asterの開発者

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