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#1 2019-06-04 11:32:53

bhattarai
Member
Registered: 2014-01-31
Posts: 133

Calculation of right Cauchy-Green strain

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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#2 2019-06-04 14:01:37

bhattarai
Member
Registered: 2014-01-31
Posts: 133

Re: Calculation of right Cauchy-Green strain

Part of the time increment is attached here.


Attachments:
Screenshot from 2019-06-04 14-58-37.png.tar.gz, Size: 96.04 KiB, Downloads: 19

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#3 2019-06-11 10:02:44

bhattarai
Member
Registered: 2014-01-31
Posts: 133

Re: Calculation of right Cauchy-Green strain

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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#4 2019-06-12 19:39:48

AsterO'dactyle
Administrator
Registered: 2007-11-29
Posts: 246

Re: Calculation of right Cauchy-Green strain

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 ?


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