Creep
Use the Creep subnode to define the creep properties of the material model. This material model is available in the Solid Mechanics, Membrane, and Layered Shell interfaces, and can be used together with Linear Elastic Material and Nonlinear Elastic Material.
The Nonlinear Structural Material Module or the Geomechanics Module are required for this material model, and the available options depend on the products used. For details, see http://www.comsol.com/products/specifications/.
See also Creep and Viscoplasticity in the Structural Mechanics Theory chapter.
Layer Selection
This section is only present in the in the Layered Shell interface, where it is described in the documentation for the Creep node.
Creep Data
Nonlinear Structural Materials Module
Select a Material model — Norton, Norton-Bailey, Garofalo (hyperbolic sine), Nabarro-Herring, Coble, Weertman, Potential, Volumetric, Deviatoric, or User defined. Then follow the instructions as below.
Geomechanics Module
Select a Material model — Potential, Volumetric, Deviatoric, or User defined. Then follow the instructions as below.
Norton
For Norton enter the following settings:
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Creep rate coefficient A.
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Reference creep stress σref. The default is 1 MPa.
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Stress exponent n.
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Select the Include temperature dependency check box to add an “Arrhenius-type” temperature dependence. Then enter a Creep activation energy Q.
Norton-Bailey
For Norton-Bailey enter the following settings:
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Creep rate coefficient A.
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Reference creep stress σref. The default is 1 MPa.
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Stress exponent n.
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Select a Hardening model — Time hardening or Strain hardening.
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For Time hardening, enter the hardening exponent m, the Time shift tshift and the Reference time tref.
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For Strain hardening, enter the hardening exponent m, the Effective creep strain shift εshift, and the Reference time tref.
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Select the Include temperature dependency check box to add an “Arrhenius-type” temperature dependence. Then enter a Creep activation energy Q.
Garofalo (hyperbolic sine)
For Garofalo (hyperbolic sine) enter the following settings:
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Creep rate coefficient A.
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Reference creep stress σref. The default is 1 MPa.
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Garofalo n parameter n.
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Select the Include temperature dependency check box as needed. Then enter a Creep activation energy Q.
Nabarro-Herring
For Nabarro-Herring enter the following settings:
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Volume diffusivity Dv.
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Burgers vector b.
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Grain diameter d.
Coble
For Coble enter the following settings:
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Ionic diffusivity Dgb.
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Burgers vector b.
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Grain diameter d.
Weertman
For Weertman enter the following settings:
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Diffusivity D0.
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Burgers vector b.
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Stress exponent n.
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Reference creep stress σref. The default is 1 MPa.
Potential
For Potential enter the following settings:
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Rate multiplier η.
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Creep potential Qcr.
Deviatoric
For Deviatoric enter the Effective creep strain rate ε cre.
Volumetric
For Volumetric enter the Volumetric creep strain rate εcr,vol.
User defined
For User defined enter each element for the symmetric Creep strain rate tensor εcr. The tensor components are interpreted in the coordinate system of the parent node.
To compute the energy dissipation caused by creep, enable the Calculate dissipated energy check box in the Energy Dissipation section of the parent material node (Linear Elastic Material or Nonlinear Elastic Material).
For an example of Norton and Norton-Baily material models, see Combining Creep Material Models: Application Library path Nonlinear_Structural_Materials_Module/Creep/combined_creep.
Location in User Interface
Context Menus
 Solid Mechanics>Linear Elastic Material>Creep
 Solid Mechanics>Nonlinear Elastic Material>Creep
 Layered Shell>Linear Elastic Material>Creep
 Membrane>Linear Elastic Material>Creep
 Membrane>Nonlinear Elastic Material>Creep
Ribbon
Physics tab with Linear Elastic Material or Nonlinear Elastic Material node selected in the model tree:
Attributes>Creep