Additional Creep
Use the Additional Creep subnode to define additional contributions to the creep model defined by the parent Creep node, such as primary or tertiary creep behavior. A Creep node can have any number of Additional Creep subnodes with different settings to model advanced creep mechanisms. Note that the time-integrated creep strain εcr is computed for the sum of all creep rate contributions only; the same applies for the equivalent creep strain εce.
The Nonlinear Structural Materials Module or the Geomechanics Module are required for this feature, and the available options depend on the used products. For details, see https://www.comsol.com/products/specifications/.
See also Creep and Viscoplasticity in the Structural Mechanics Theory chapter.
Shell Properties

This section is only present when parent Creep node is used as a subnode to:
Linear Elastic Material in the Layered Shell interface. See the documentation for the Additional Creep node in the Layered Shell chapter.
Linear Elastic Material, Layered in the Shell interface. See the documentation for the Additional Creep node in the Shell and Plate chapter.
Linear Elastic Material, Layered in the Membrane interface. See the documentation for the Additional Creep node in the Membrane chapter.
Creep Model
The available settings in this section are the same as for the Creep node. The Equivalent stress setting has an additional option — From parent, which is default. When selected, the Additional Creep subnode will use the same equivalent stress σe as in the parent Creep node.
Location in User Interface
Context Menus
Ribbon
Physics tab with Creep node selected in the model tree: