pk2isomatfic.for

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      SUBROUTINE pk2isomatfic(FIC,DISO,CBAR,CBARI1,UNIT2,NDI)
C>     ISOTROPIC MATRIX: 2PK 'FICTICIOUS' STRESS TENSOR
C      INPUT:
C       DISO - STRAIN-ENERGY DERIVATIVES
C       CBAR - DEVIATORIC LEFT CAUCHY-GREEN TENSOR
C       CBARI1,CBARI2 - CBAR INVARIANTS
C       UNIT2 - 2ND ORDER IDENTITY TENSOR
C      OUTPUT:
C       FIC - 2ND PIOLA KIRCHOOF 'FICTICIOUS' STRESS TENSOR
      IMPLICIT NONE
      include 'PARAM_UMAT.INC'
C
      INTEGER I1,J1,NDI
      DOUBLE PRECISION FIC(ndi,ndi),DISO(5),CBAR(ndi,ndi),UNIT2(ndi,ndi)
      DOUBLE PRECISION DUDI1,DUDI2,CBARI1
      DOUBLE PRECISION AUX1,AUX2    
C
      dudi1=diso(1)
      dudi2=diso(2)
C
      aux1=two*(dudi1+cbari1*dudi2)
      aux2=-two*dudi2
C
      DO i1=1,ndi
       DO j1=1,ndi
        fic(i1,j1)=aux1*unit2(i1,j1)+aux2*cbar(i1,j1)
       END DO
      END DO
C
      RETURN
      END SUBROUTINE pk2isomatfic