Use the Thermal Expansion, Layered Shell multiphysics coupling () to add an internal thermal strain caused by changes in temperature and account for the corresponding mechanical losses in the heat balance in layered materials represented by boundaries.

The Thermal Expansion, Layered Shell node is only available with some COMSOL products (see http://www.comsol.com/products/specifications/).

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 tel1.

This section defines the physics involved in the multiphysics coupling. The Heat transfer and Layered Shell lists include all applicable physics interfaces. The first physics interface of each type in the component is selected as the default.

Select the applicable layers (the default setting is All layered materials) defining the required material properties for the node.

If no layered materials have been included yet, there is a shorthand available for creating a Single Layer Material, a Layered Material Link, or a Layered Material Stack (the plus, next to the Layered Material list).

When a layered material stack or link is selected from the Layered Material list, deselect the check boxes corresponding to layers where the node should not be applied in the Selection table.

You can visualize the selected layered materials and layers in each layered material by clicking the Layer cross section preview and Layer 3D preview buttons.

The Volume reference temperature Tref is the temperature at which there are no thermal strains. As a default, the value is obtained from a Common model input. You can also select User defined to enter a value or expression for the temperature locally.

When using Common model input, you can see or modify the value of the volume reference temperature by clicking the Go To Source button (). This will move you to the Common Model Inputs node under Global Definitions in the Model Builder. The default value is room temperature, 293.15 K.

If you want to create a model input value which is local to your current selection, click the Create Model Input button . This will create a new Model Input node under Definitions in the current component, having the same selection as the current Thermal Expansion node.

Select an Input type to select how the thermal strain is specified. The default is Secant coefficient of thermal expansion, in which case the thermal strain is given by

where α is the secant coefficient of thermal expansion. α can be temperature dependent.

When Input type is Tangent coefficient of thermal expansion, the thermal strain is given by

where αt is the tangential coefficient of thermal expansion.

When Input type is Thermal strain, enter the thermal strain dL as function of temperature explicitly.

In all three cases, the default is to take values From material. When entering data as User defined, select Isotropic, Diagonal or Symmetric to enter one or more components for a general coefficient of the thermal expansion tensor or the thermal strain tensor. When a nonisotropic input is used, the axis orientations are given by the coordinate system selection in the parent node.

Select Thermoelastic damping to include the reverse coupling where the changes in stress act as a heat source in the heat transfer analysis. Thermoelastic damping is only used when Structural Transient Behavior is set to Include inertial terms.

Select Mechanical Losses to make any energy dissipation computed in the structural interface act as a heat source in the heat transfer interfaces. Examples of such contributions are work done by plastic deformation, and viscous damping.