Thermal Expansion (for Constraints)
Add the Thermal Expansion subnode to a constraint (Fixed Constraint or Prescribed Displacement) to prescribe a deformation of the constrained boundary caused by changes in the surrounding temperature. This makes it possible to reduce the stresses caused by such boundary conditions.
Select an Input type to specify how the thermal strain is entered. The default is Secant coefficient of thermal expansion, in which case the thermal strain is given by
here, 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.
The Thermal Expansion subnode is only available with some COMSOL products (see https://www.comsol.com/products/specifications/).
Shell Properties

 
This section is only present in the Layered Shell interface, where it is described in the documentation for the Thermal Expansion (for Constraints) node.
Thermal Expansion Properties
Specify the thermal properties that define the thermal strain. This is a description of the thermal expansion of surroundings idealized by the constraints.
Select Inherit from domain to take the thermal expansion data from the domain being constrained. This should only be used when:
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The temperature and the thermal expansion coefficient do not have a spatial variation. For this reason, it is only possible to inherit from a Thermal Expansion node under a material model, not from the Thermal Expansion multiphysics coupling.
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The virtual surrounding material has the same thermal expansion as the domain itself.
The Inherit from domain check box is not available when the constraint in the parent node is applied to domains. In that case, the data is implicitly inherited from the domain.
When Inherit from domain is not selected, enter:
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A value or expression for the Volume reference temperature Tref that is the temperature at which there are no thermal displacements at the constraints.
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A value or expression for Temperature T, specifying the temperature distribution of the surrounding material. Any temperature variation must be an explicit function of the material frame coordinates. It is not possible to use a computed temperature distribution.
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Select the Input type — Secant coefficient of thermal expansion, Tangent coefficient of thermal expansion, or Thermal strain to specify how the thermal strain is entered. The default values From material are used. This requires that a material has been assigned to the boundaries, edges, or points where the constraint is active. When a nonisotropic coefficient of thermal expansion is used, the axis orientations are given by the coordinate system selected in the Coordinate System Selection section.
Enter the coordinates of the Reference point, the point where the displacement is zero. The choice of reference point only affects the rigid body motion. If there are several different constraints with a Thermal Expansion subnode, the same reference point should usually be selected in all of them.
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Constraints and Thermal Expansion in the Structural Mechanics Modeling chapter.
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Thermal Expansion of Constraints in the Structural Mechanics Theory chapter.
Location in User Interface
Context Menus
Solid Mechanics>Fixed Constraint>Thermal Expansion
Solid Mechanics>Prescribed Displacement>Thermal Expansion
Layered Shell>Fixed Constraint>Thermal Expansion
Layered Shell>Prescribed Displacement>Thermal Expansion
Membrane>Fixed Constraint>Thermal Expansion
Membrane>Prescribed Displacement>Thermal Expansion
Multibody Dynamics>Fixed Constraint>Thermal Expansion
Multibody Dynamics>Prescribed Displacement>Thermal Expansion
Ribbon
Physics tab with Fixed Constraint or Prescribed Displacement node selected in the model tree:
Attributes>Thermal Expansion