Use the Creep subnode to define the creep properties of the material. This material model is available in the Solid Mechanics, Shell, Layered Shell, and Membrane interfaces, and can be used together with Linear Elastic Material, Layered Linear Elastic Material, Nonlinear Elastic Material, and Hyperelastic Material.

The Nonlinear Structural Materials Module or the Geomechanics Module are required, the available options depend on the used products. For details, see https://www.comsol.com/products/specifications/.

Select the Formulation — Small strains or Large strains to apply either an additive or multiplicative decomposition between elastic and inelastic strains.

Select a Material model — Norton, Garofalo (hyperbolic sine), Nabarro-Herring, Coble, Weertman, or User defined.

For Norton, enter the following settings:

For Garofalo (hyperbolic sine), enter the following settings:

For Nabarro-Herring, enter the following settings:

For Coble enter the following settings:

For Weertman, enter the following settings:

For User defined, enter an expression for the creep rate f as a function of the equivalent stress σe. The default expression is <item>.sequ/1[Pa*s], where <item> is the name of the creep node.

For Norton, Garofalo (hyperbolic sine), Nabarro-Herring, Coble, Weertman, or User defined, select a Equivalent stress — von Mises (the default), Hill orthotropic, pressure, or User defined.

Select the isotropic hardening function h — None, Strain hardening, Time hardening, or User defined.

For Strain hardening, enter the following settings:

For Time hardening, enter the following settings:

For User defined, enter an expression for the hardening function h as a function of equivalent creep strain εce, time t or any other variable in the model.

Select a thermal creep function — None, Arrhenius, or User defined.

For User defined, enter an expression for the thermal creep function g as a function of temperature T or any other variable in the model.

Select a Method — Automatic, Backward Euler, Forward Euler, or Domain ODEs.

The Automatic method corresponds to the backward Euler method except for the Layered Shell interface or when the Layered Linear Elastic Material is used. Domain ODEs are solved in these cases.

For the Backward Euler method, enter the following settings:

If both a step size and residual convergence check is requested, it is sufficient that one of the conditions is fulfilled. Setting either the Absolute tolerance and Relative tolerance or the Residual tolerance to zero ignores the corresponding convergence check. An error is returned if all are set to zero.

For the Forward Euler method, enter the Maximum creep strain increment.

It is recommend to reset the solver settings to its default values when selecting the forward Euler method, since the method is only conditionally stable. This will add a Maximum step constraint to the Time-Dependent Solver based on an estimate of the stability limit used to update the creep equations. The value entered in the Maximum creep strain increment field is taken in to account, which can be used to improve the accuracy of the method. If the solver sequence cannot be reset, the stability limit can be entered manually in the Time-Dependent Solver settings by using the variable <item>.tmax, where <item> is the name of the creep node.

No settings are needed for the Domain ODEs method. However, this method adds degrees-of-freedom that are solved as part of the general solver sequence. The scaling of these fields can affect the convergence of the overall solution.

Physics tab with Linear Elastic Material, Layered Linear Elastic Material, or Nonlinear Elastic Material node selected in the model tree: