XFEM

[Rose-Ama]

Hi, I want to ask a question about how the XFEM in Moose works. So generally, XFEM is a combination of an enrichment function and a level set function. I want to know if in Moose, these functions are inbuilt in the XFEM module or I need to predefine them. Also, I would like to know if when I use the XFEM module, and the maximum stress threshold is exceeded, Moose can say "the maximum stress threshold was exceeded in this element, so I will insert the crack here". Do you know if I need a custom code to help me with this ? I'm looking forward to receiving a response, thank you.

Rose

[GiudGiud]

Hello

Does this page answer your questions?
https://mooseframework.inl.gov/modules/xfem/theory/theory.html

[lynnmunday]

Ok, I see that. I would use the inputs in moose/modules/xfem/test/tests/mesh_cut_2D_fracture/ to make an example of what you want to do. It is easy to create a small 1D mesh element mesh to use as the initial dummy cutter mesh with something like this:

[Mesh]
  [gmg]
    type = GeneratedMeshGenerator
    dim = 1
    xmin =1.      # use xmin and xmax to put this outside your real simulation domain
    xmax = 2
    nx = 1
  []
[]

[Problem]
  solve = false
[]

[Executioner]
  type = Steady
[]

[Outputs]
  [in]
    type = Exodus
  []
[]

@bwspenc or @jiangwen84 Do all of the xfem cutting or nucleation objects require an initial crack.

[Rose-Ama]

Okay, thank you. Does that mean the XFEM in the Moose framework is not ideal for the initiation of cracks and propagation in realistic scenarios?

[Rose-Ama]

Is there a possibility of creating a custom code to this effect?

[lynnmunday]

Okay, thank you. Does that mean the XFEM in the Moose framework is not ideal for the initiation of cracks and propagation in realistic scenarios?

This is not the case. XFEM can easily nucleate and propagate cracks anywhere in a 2d domain. We have several tests showing this. You just need to make a small dummy cutter mesh outside the domain to initialize some data structures needed by the xfem and fracture integral objects. This is a simple 1D element mesh and I've given you the input file above to create it. Here is another example for thermal mechanical brittle fracture of a cylinder: https://github.com/lynnmunday/xfem_pellet
Work from this or one of the tests in xfem nucleation_uo directory.

Figure 4 in this osti report describes the xfem 2d mesh cutters: https://doi.org/10.2172/2000030
and shows the cutter mesh. It is a dummy mesh that we need for initialization, it can be anywhere outside the simulation volume.
Section 4 in this osti report describes other updates made to the 2d xfem mesh cutters: https://doi.org/10.2172/2403365

If creating a dummy 1D cutter mesh will not work for your purposes then you will need to write some custom code.

[Rose-Ama]

Alright, thank you. I will try it out and let you know.

[dschwen]

Crack propagation is handled by user objects and depend on stress integral measures. Crack nucleation is a bit more tricky. @bwspenc and @lynnmunday can probably comment on this.

[Rose-Ama]

Hi, I am currently working on incorporating the cohesive traction zone so that the laws can be used in the input file for crack initiation and propagation. However, I keep getting this error: *** ERROR ***
The following error occurred in the Problem 'MOOSE Problem' of type FEProblem.

Material property 'itz_czm_115.2', requested by 'itz_czm' is not defined on boundary itz_interface
Material property 'itz_czm_115.2', requested by 'itz_czm' is not defined on boundary itz_interface
Material property 'itz_czm_2.4e6', requested by 'itz_czm' is not defined on boundary itz_interface
Material property 'itz_czm_2.4e6', requested by 'itz_czm' is not defined on boundary itz_interface. 

I am unsure of the cause of the error, as I have tried everything I know. I would be grateful to receive some guidance. This is my current input file:

 [GlobalParams]
  displacements                    = 'disp_x disp_y'
  volumetric_locking_correction    = true
[]

[Mesh]
  type = FileMesh
  file = 'mesh8.msh2'
  dim  = 2
[]

[AuxVariables]
  [./p1_itz]
    family = MONOMIAL
    order  = CONSTANT
  [../]
  [stress_max_principal]
    order = CONSTANT
    family = MONOMIAL
  []
[]

[AuxKernels]
  [./itz_principal]
    type         = RankTwoScalarAux
    rank_two_tensor   = stress
    scalar_type  = MaxPrincipal
    variable     = p1_itz
    block        = 3
    execute_on   = TIMESTEP_END
  [../]
[]

[Physics/SolidMechanics/QuasiStatic]
  [./all]
    strain = FINITE
    planar_formulation = plane_strain
    add_variables = true ##this already defines the variables 
	incremental = true 
	block = '1 2 3'
  [../]
[]
[Physics/SolidMechanics/CohesiveZone]
  [CohesiveZone]
    type          = CohesiveZoneAction
    boundary      = 'itz_interface'
    base_name     = itz_czm
    displacements = 'disp_x disp_y'
    strain        = FINITE
    verbose       = true
  [../]
[]

[Materials]
  [./cement_matrix]
    type           = ComputeIsotropicElasticityTensor
    youngs_modulus = 2.5e10    # 25 GPa :contentReference[oaicite:19]{index=19}
    poissons_ratio = 0.2       # :contentReference[oaicite:20]{index=20}
    block          = 1
  [../]
  [./aggregate]
    type           = ComputeIsotropicElasticityTensor
    youngs_modulus = 5.0e10    # 50 GPa :contentReference[oaicite:21]{index=21}
    poissons_ratio = 0.16      # :contentReference[oaicite:22]{index=22}
    block          = 2
  [../]
  [./itz_mat]
    type           = ComputeIsotropicElasticityTensor
    youngs_modulus = 2.1e10    # 21 GPa :contentReference[oaicite:23]{index=23}
    poissons_ratio = 0.2       # :contentReference[oaicite:24]{index=24}
    block          = 3
  [../]
  [./elastic_stress]
    type  = ComputeLinearElasticStress
    block = '1 2 3'
  [../]
  [./small_strain]
    type  = ComputeSmallStrain
    block = '1 2 3'
  [../]
  [./itz_czm]
  type               = BiLinearMixedModeTraction
  base_name          = itz_czm
  boundary           = 'itz_interface'           # your ITZ interface
  normal_strength    = 2.4e6           # 2.4 MPa from Table 1 :contentReference[oaicite:8]{index=8}
  shear_strength     = 2.4e6           # assume equal to normal
  GI_c               = 115.2           # Mode I fracture energy (N/m) :contentReference[oaicite:9]{index=9}
  GII_c              = 115.2           # Mode II fracture energy (N/m) :contentReference[oaicite:10]{index=10}
  eta                = 1.0             # power‐law exponent
  penalty_stiffness  = 1e10            # stiff penalty to enforce continuity
  displacements = 'disp_x disp_y'
  [../]
  [./itz_disp_jump]
    type      = CZMComputeDisplacementJumpSmallStrain
    base_name = itz_czm
    boundary  = 'itz_interface'
  [../]
  [./itz_global_trac]
    type      = CZMComputeGlobalTractionSmallStrain
    base_name = itz_czm
    boundary  = 'itz_interface'
   [../]
[]

[UserObjects]
  [./itz_marker]
    type         = XFEMRankTwoTensorMarkerUserObject
    tensor       = stress
	average 	 = true
    scalar_type  = MaxPrincipal
    threshold    = 2.4e6         # same as CZM initiation :contentReference[oaicite:28]{index=28}
    block        = 3
    execute_on   = TIMESTEP_END
  [../]
[]

[XFEM]
  block      = '3'
  geometric_cut_userobjects   = 'itz_marker'
  qrule                  = volfrac
  output_cut_plane       = true
[]

[BCs]
  [./fixed_left_x]
    type     = DirichletBC
    variable = disp_x
    boundary = left
    value    = 0
  [../]
  [./fixed_left_y]
    type     = DirichletBC
    variable = disp_y
    boundary = left
    value    = 0
  [../]
  [./top_loading]
    type     = FunctionDirichletBC
    variable = disp_y
    boundary = top
    function = '0.01*t'
  [../]
[]

[Executioner]
  type                   = Transient
  solve_type             = NEWTON
  petsc_options_iname    = '-pc_type -pc_factor_mat_solver_package'
  petsc_options_value    = 'lu superlu_dist'
  nl_max_its             = 50
  nl_rel_tol             = 1e-6
  nl_abs_tol             = 1e-8
  start_time             = 0.0
  end_time               = 0.5
  dt                     = 0.01
[]

[Outputs]
  file_base   = cracktest
  exodus      = true
  execute_on  = 'TIMESTEP_END'
  [./console]
    type          = Console
    output_linear = true
  [../]
[]

[Postprocessors]
  [./p1_itz_max]
    type         = ElementExtremeValue
    variable     = p1_itz
    value_type   = max
    execute_on   = TIMESTEP_END
  [../]
  [./top_disp_y]
    type         = SideAverageValue
    variable     = disp_y
    boundary     = top
    execute_on   = TIMESTEP_END
  [../]
[]

[Debug]
  show_var_residual_norms = true
[]

[Rose-Ama]

It has been solved, thanks. But I have a question. If they are considered as generic constant materials, are they still considered in the calculations?

[GiudGiud]

In the calculations, whenever the properties are retrieved at a quadrature point with for example _property[_qp], they are constants.

If you look at this page
https://mooseframework.inl.gov/source/materials/GenericConstantMaterial.html
you ll see the properties are defined as constant on a per-subdomain basis. So for all elements within a subdomain, they are not re-computed

[Rose-Ama]

Okay, thank you very much. One more question. Have you ever tried creating a crack in material at a microstructural level? I have been trying to limit the crack to only one block/boundary in the interface; however, it does not seem to work. Do you have any knowledge on this?

[GiudGiud]

sorry not my field. If you make a new targetted post on this we can tag XFEM developers

[Rose-Ama]

okay, thank you for your help.

[lynnmunday]

@Rose-Ama Are you getting a crack to propagate? You can change the k critical in every block. If you set it high enough, a fracture won't be able to propagate in it. Something like this would work:

[VectorPostprocessors]
  [CrackFrontNonlocalScalarVpp]
    type = CrackFrontNonlocalScalarMaterial
    property_name = k_crit_mat
    crack_front_definition = crackFrontDefinition
    box_length = 0.05
    box_height = 0.1
    execute_on = NONLINEAR
  []
[]
[UserObjects]
  [cut_mesh2]
    type = MeshCut2DFractureUserObject
    mesh_file = make_edge_crack_in.e
    growth_increment = 0.05
    ki_vectorpostprocessor = "II_KI_1"
    kii_vectorpostprocessor = "II_KII_1"
    k_critical_vectorpostprocessor=CrackFrontNonlocalScalarVpp
    k_critical_vector_name = "crack_tip_k_crit_mat"
  []
[]
[Materials]
  [k_critical]
    type = ParsedMaterial
    property_name = k_crit_mat
    extra_symbols = 'x'
    expression = 'if(x < -0.5,500,if(x<0.3,40,500))'
  []
[]