Material

User defined material model

This subroutine is used to extend numgeo with user-defined constitutive material models, characterized by *Mechanical = user command in the input file. The header and variable description is given in the following. Notice, that numgeo searches for the file user_material.so (Linux) or user_material.dll (Windows) in the current working directory.

Linux

subroutine user_material(material_name, nchar, ielem ,igp ,istep ,iinc ,ntens ,nprops ,nstatev , &
                         strain ,dstrain ,coords ,time ,dtime ,props ,statev ,stress ,dds_dde) bind(c,name='user_material')
  use, intrinsic :: iso_c_binding
  implicit none
  character(c_char), intent(in) :: material_name (*)
  integer(c_int), intent(in) :: nchar
  integer(c_int), intent(in) :: ielem
  integer(c_int), intent(in) :: igp
  integer(c_int), intent(in) :: istep
  integer(c_int), intent(in) :: iinc
  integer(c_int), intent(in) :: ntens
  integer(c_int), intent(in) :: nprops
  integer(c_int), intent(in) :: nstatev
  real(c_double), dimension(ntens), intent(in) :: strain
  real(c_double), dimension(ntens), intent(in) :: dstrain
  real(c_double), dimension (3), intent(in) :: coords
  real(c_double), intent(in) :: time
  real(c_double), intent(in) :: dtime
  real(c_double), dimension(nprops), intent(in) :: props
  real(c_double), dimension(nstatev), intent(inout) :: statev 
  real(c_double), dimension(ntens), intent(inout) :: stress
  real(c_double), dimension(ntens ,ntens), intent(inout) :: dds_dde
  character(len=nchar) :: material_str

  real(c_double) :: E, nu, k1, k2, k3

  ! required to make the material name usable in select case of if-clauses
  material_str = transfer(material_name(1:nchar), material_str)

  E = props(1)
  nu = props(2)

  dds_dde = 0.0d0

  k1 = nu * E / (1.0d0+nu) / (1.0d0-2.0d0*nu)
  k2 = E / 2.0d0 / (1.0d0+nu)
  k3 = k1 + 2.0d0 * k2

  dds_dde(1:3,1:3) = k1
  dds_dde(1,1) = k3
  dds_dde(2,2) = k3
  dds_dde(3,3) = k3
  dds_dde(4,4) = k2

  if (ntens == 6) then
    ! 3D case
    dds_dde(5,5) = k2
    dds_dde(6,6) = k2
  end if

  stress = stress + matmul(dds_dde,dstrain)

end subroutine user_material

Windows

subroutine user_material(material_name, nchar, ielem ,igp ,istep ,iinc ,ntens ,nprops ,nstatev , &
                         strain ,dstrain ,coords ,time ,dtime ,props ,statev ,stress ,dds_dde) 
  implicit none
  !DEC$ ATTRIBUTES DLLEXPORT, STDCALL, REFERENCE :: user_material
  character, intent(in) :: material_name (*)
  integer, intent(in) :: ielem
  integer, intent(in) :: nchar
  integer, intent(in) :: igp
  integer, intent(in) :: istep
  integer, intent(in) :: iinc
  integer, intent(in) :: ntens
  integer, intent(in) :: nprops
  integer, intent(in) :: nstatev
  real(8), dimension(ntens), intent(in) :: strain
  real(8), dimension(ntens), intent(in) :: dstrain
  real(8), dimension (3), intent(in) :: coords
  real(8), intent(in) :: time
  real(8), intent(in) :: dtime
  real(8), dimension(nprops), intent(in) :: props
  real(8), dimension(nstatev), intent(inout) :: statev 
  real(8), dimension(ntens), intent(inout) :: stress
  real(8), dimension(ntens ,ntens), intent(inout) :: dds_dde

  character(len=nchar) :: material_str

  real(8) :: E, nu, k1, k2, k3

  ! required to make the material name usable in select case of if-clauses
  material_str = transfer(material_name(1:nchar), material_str)

  E = props(1)
  nu = props(2)

  dds_dde = 0.0d0

  k1 = nu * E / (1.0d0+nu) / (1.0d0-2.0d0*nu)
  k2 = E / 2.0d0 / (1.0d0+nu)
  k3 = k1 + 2.0d0 * k2

  dds_dde(1:3,1:3) = k1
  dds_dde(1,1) = k3
  dds_dde(2,2) = k3
  dds_dde(3,3) = k3
  dds_dde(4,4) = k2

  if (ntens == 6) then
    ! 3D case
    dds_dde(5,5) = k2
    dds_dde(6,6) = k2
  end if

  stress = stress + matmul(dds_dde,dstrain)

end subroutine user_material

• material_name: material name

• ielem: Element label (id)

• igp: Integration point number

• istep: Step number

• iinc: Increment number

• ntens: Total number of components of the stress/strain tensor

• nprops: User-defined number of material constants associated with this user material.

• nstatev: Number of solution-dependent state variables that are associated with this material type

• strain: Total strains at the beginning of the increment (in Voight notation \(\varepsilon_i\) )

• dstrain: Strain increment (in Voight notation \(\Delta\varepsilon_i\) )

• coords: An array containing the coordinates of this integration point \(x_i = \{x_1,x_2,x_3\}\). These are the current coordinates if geometric nonlinearity is accounted for during the step. Otherwise, the array contains the original coordinates of the point.

• time: Value of step time at the beginning of the current increment

• dtime: Time increment \(\Delta t\)

• props: User-specified array of material constants associated with this user material.

• statev: Solution-dependent state variables that are associated with this material type

• stress: Stress tensor passed in as \(\sigma_{ij}^{t}\) at the beginning of the increment and must be updated to \(\sigma_{i}^t + \Delta \sigma_{j}\)

• dds_dde: Jacobian matrix of the constitutive model \(\partial \Delta \sigma_{i} / \partial \Delta \varepsilon_{j}\)