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## Creep for anisotropic materials (ucreep.f)

The user subroutine ``ucreep.f'' is made available to allow the user to incorporate his own creep law in subroutine umat_aniso_creep. This is a viscoplastic material routine for elastically anisotropic materials. The viscoplasticity, however, is isotropic. The creep routine must return the Von Mises stress for a given equivalent creep strain rate. The header and a description of the input and output variables is as follows:

          subroutine ucreep(amat,iel,iint,t1l,epini,ep,dtime,svm,dsvm)

    !
    !     INPUT:
    !
    !     amat:  material name
    !     iel:   element number
    !     iint:  integration point number
    !     t1l:   temperature
    !     epini: equivalent creep strain at the start
    !            of the increment
    !     ep:    present equivalent creep strain
    !     dtime: time increment
    !
    !     OUTPUT:
    !
    !     svm:   present Von Mises stress
    !     dsvm:  derivative of the Von Mises true stress with respect
    !            to the present equivalent creep strain.
    !            Numerically: change the present equivalent
    !            strain with a small amount, calculate the amount
    !            of change this causes in the present Von Mises
    !            true stress, and divide the latter amount through the
    !            former amount.