Use the Thermal Expansion, Thin Layer multiphysics coupling () to add an internal thermal strain caused by changes in temperature and to account for the corresponding mechanical losses in the heat balance in thin layers represented by boundaries.

The Thermal Expansion, Thin Layer node is only available with some COMSOL products (see https://www.comsol.com/products/specifications/).

The Label is the multiphysics coupling feature name. The default Label (for the first multiphysics coupling feature in the model) is Thermal Expansion, Thin Layer 1.

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 tetl1.

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

You can also select None from either list to uncouple the Thermal Expansion, Thin Layer node from a physics interface. If the physics interface is removed from the Model Builder, for example Heat Transfer in Solids is deleted, then the Heat transfer list defaults to None as there is nothing to couple to.

Select a Thin layer type — Nonlayered or Layered.

For Layered boundaries, select the applicable layers (the default setting is Use all layers) 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 symbol next to the Layer list). See Shell Properties for details.

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.

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 which 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 Mechanical losses to make any energy dissipation computed in the thin layer act as a heat source in the heat transfer interface. Examples of such contributions are work done by plastic deformation or viscous damping.

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.