Phase-Field Damage (Multiphysics Coupling)
The Phase-Field Damage multiphysics coupling node () links the Solid Mechanics interface bidirectionally with the Phase Field in Solids interface to model the evolution of damage and cracks in deforming solids.
Settings
The Label is the default multiphysics coupling feature name.
The Name is used primarily as a scope prefix for variables defined by the coupling node. Refer to such variables in expressions using the pattern <name>.<variable_name>. In order to distinguish between variables belonging to different coupling nodes or physics interfaces, the name string must be unique. Only letters, numbers, and underscores (_) are permitted in the Name field. The first character must be a letter.
The default Name (for the first multiphysics coupling feature in the model) is pfdmg1.
Domain Selection
When the node is added from the context menu, you can select Manual (the default) from the Selection list to choose specific domains where the phase–field damage coupling is defined, or select All domains as needed.
When the Phase-Field Damage multiphysics interface is added from the Model Wizard or the Add Physics window, the domain selection of the coupling node is set to All domains by default.
Only domains that are active in the physics features selected in the Material Models section can be selected. The selection is only applicable when the participating Phase Field in Solids interface contains a single phase field variable.
Coupled Interfaces
This section defines the physics involved in this multiphysics coupling. The Solid mechanics and Phase field in solids lists include all applicable physics interfaces.
The default values depend on how the coupling node is created.
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If it is added from the Physics ribbon (Windows users), Physics contextual toolbar (macOS and Linux users), or context menu (all users), then the first physics interface of each type in the component is selected as the default.
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If it is added automatically when a multiphysics interface is selected in the Model Wizard or Add Physics window, then the two participating physics interfaces are selected.
You can also select None from either list to uncouple the Phase-Field Damage node from a physics interface. If the physics interface is removed from the Model Builder, for example if Phase Field in Solids is deleted, then the Phase field in solids list defaults to None as there is nothing to couple to.
If a physics interface is deleted and then added to the model again, then in order to reestablish the coupling, you need to choose the physics interface again from the Solid mechanics or Phase field in solids lists. This is applicable to all multiphysics coupling nodes that would normally default to the once present interface. See Multiphysics Modeling Workflow in the COMSOL Multiphysics Reference Manual.
Material Models
In the Parent material model list, choose the material model for which damage is applied. All Linear Elastic Material and Hyperelastic Material subnodes of the coupled Solid Mechanics interface are listed here. If the fallback option None is selected, the domain selection is not applicable.
Similarly, in the Parent phase field model list, select the Phase Field Model subnode of the coupled Phase Field in Solids interface that controls the phase field evolution equation. If the fallback option None is selected, the domain selection is not applicable.
Crack Driving Force
Select the Crack driving force — Elastic strain energy density, Total strain energy density, Rankine criterion, Principal stress criterion, or User defined. See Crack Driving Force for details.
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For Elastic strain energy density and Total strain energy density, enter the Critical energy release rate Gc. The default for the Critical energy release rate is to take its value From material. Choose User defined to enter another value or expression in the text field. If the Parent phase field model is of the AT2 type, it is also possible to enter a Strain energy threshold G0c.
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For the Rankine criterion, enter the Critical energy release rate Gc.
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For the Principal stress criterion, enter the Critical fracture stress σcr and the post-peak slope parameter ξ. Choose User defined to enter another value or expression in the text field. This criterion is only available when the Parent phase field model is of the AT2 type.
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For User defined, enter an expression for the crack driving force Dd (dimensionless).
In the Initial crack driving force list, select Automatic or Manual. The Automatic option computes the initial value for the dimensionless crack driving force as , which is required for admitting a homogeneous zero solution for the phase field based on the phase field potential Q(ϕ) and the damage evolution function d(ϕ) chosen. For example, for the AT2 phase field model the initial value is 0, while it becomes 3/16 for the AT1 model with a Quadratic damage evolution function. Choose Manual to enter another value or expression for the initial value (default 0).
In the Exclude compressive energy list, select a method for controlling which part of the strain energy density contributes to the crack driving force. This method also controls how the damaged stress tensor is constructed. See Strain Energy Split for details.
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If the Parent material model is a Linear Elastic Material, choose between Volumetric only; Spectral decomposition, stress; Spectral decomposition, strain; or No split. The option Spectral decomposition, strain is only available if the linear elastic material is isotropic.
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If the Parent material model is a Hyperelastic Material, choose between Volumetric only or No split. The option Volumetric only is only available if the hyperelastic material permits a clear split between the volumetric and isochoric strain energy density.
Damage Evolution
Select the Damage evolution function d(ϕ) — Quadratic; Cubic, Borden; Rational; Linear softening; Exponential softening; Cornelissen softening; or User defined. See Damage Evolution for Phase-Field Damage for details.
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For Quadratic, the damage evolution function (dimensionless) is defined as d(ϕ) = 1 − (1 − ϕ)2. If this option is used together with the PF–CZM phase field model, a constraint on the phase field might be required to ensure a unique solution.
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For Cubic, Borden, enter a value for the Model parameter s. This option is only available if the Crack driving force is Elastic strain energy density or Total strain energy density and the Parent phase field model is of the AT2 type.
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For Rational, enter values for the model parameters p, a1, a2, and a3. The damage evolution function is then defined as , with . The value for the exponent p should be greater than or equal to 2.
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The options Linear softening, Exponential softening, and Cornelissen softening are special cases of the Rational damage evolution function intended for modeling quasi-brittle fracture inspired by cohesive zone models. The parameter a1 is computed from the Critical stress σcr, while p, a2, and a3 are predetermined constants.
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For User defined, enter an expression for the damage evolution d(ϕ) as a function of the phase field variable (dimensionless).
Enter the Maximum damage, dmax, which controls the residual stiffness of the material when fully damaged. The default value for numerical stability is 1-1e-5.
See also
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Modeling Damage in the Structural Mechanics Modeling chapter.
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Theory for the Phase Field in Solids Interface and Phase-Field Damage Models in the Structural Mechanics Theory chapter.
The Multiphysics interface Phase-Field Damage, is only available with some COMSOL products. For a detailed overview of the functionality available in each product, visit www.comsol.com/products/specifications/
Phase-Field Modeling of Dynamic Crack Branching: Application Library path Nonlinear_Structural_Materials_Module/Damage/dynamic_crack_branching