deformation gradient in umat

[Schandra]

Dear all,

The deformation gradient for the case of finite deformation in programmer manual refers to F(3,3,4)(page number 23).
In dummy user materials provided in the feap package, it is mentioned as eps(3,3) for the case of finite deformation.
I need to calculate right cauchy green tensor and I have now used eps to do so.
Can you please let me know if it is how right cauchy green tensor is to be calculated using deformation gradient.

Warm Regards,
Chandra

[Prof. R.L. Taylor]

are you using a FEAP element or a user element?

All F
Feap elements pass F to umat you need a new array for C in the umat and must convert returned stress and tangent to Cauchy form

[Schandra]

I am not using a user element. For the case of finite deformation in umat, I am using deformation gradient as eps(3,3) to calculate C (right cauchy green tensor).

[Prof. S. Govindjee]

Comment:

Code: [Select]

      subroutine umatl1(eps,theta,td,d,ud,hn,h1,nh,ii,istrt, sig,dd,isw)
      real*8   eps(*), theta(*),d(*),ud(*),hn(nh),h1(nh), sig(*),dd(6,*)
Uncomment:

Code: [Select]

c     subroutine umatl1( f , detf,td,d,ud,hn,h1,nh,ii,istrt, sig,dd,isw)
c     real*8   f(3,3,*),detf(*),d(*),ud(*),hn(nh),h1(nh), sig(*),dd(6,*)

Then access f as a two-dimensional array, so that

Code: [Select]

do k=1:3
  c(i,j) = c(i,j) + f(k,i)*f(k,j)
end do

[Schandra]

Dear Prof. Govindjee,

Thanks for your suggestion. I hope my umat works as intended now.

Warm Regards,
Chandra