External Strain

The subnode allows you to provide inelastic strain contributions to the material models Linear Elastic Material, Nonlinear Elastic Material, and Hyperelastic Material on a variety of formats, including using external coded functions.

The subnode is only available with some COMSOL products (see https://www.comsol.com/products/specifications/).

Shell Properties


	This section is only present when External Strain is used in the Layered Shell interface. See the documentation for the External Strain node in the Layered Shell chapter.

Coordinate System Selection

Select a . All inputs that you give below are interpreted in the given coordinate system. This also implies that external code should assume that strains are passed with its local orientations. Deformation gradients are rotated by the local system in both indices.

External Strain

Select the type of — , , , , or .

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The option is not available for a .

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The option is not available in the Layered Shell interface.

External Material

For , the computation of an additional inelastic strain contribution is delegated to external code that has been compiled into a shared library. External libraries must first be imported into an node under .

Select an from the list of compatible external materials added under .

For a material to be compatible with this subnode, its must be set to a type whose required input quantities are all defined in this node. Allowed required inputs include Green–Lagrange strains, the deformation gradient, second Piola–Kirchhoff stress as well as all standard model inputs. Select — or to define the type of quantity by which you want communicate with the external code.

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If the in the node is , then select .

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If the in the node is , then select . This is the only option for a hyperelastic material.

Strain Tensor

For , enter an inelastic strain contribution εext. From the list, you can choose or any strain tensor that is announced by another physics interface. If you select , enter values or expressions for the upper diagonal part of the symmetric strain tensor.

Deformation Gradient

For , enter an inelastic deformation gradient contribution Fext. From the list, you can choose or any deformation gradient tensor that is announced by another physics interface. If you select , enter values or expressions for the components of the deformation gradient tensor.

Deformation Gradient, Inverse

For , enter an inelastic inverse deformation gradient contribution

. From the list, you can choose or any inverse deformation gradient tensor that is announced by another physics interface. If you select , enter values or expressions for the components of the inverse deformation gradient tensor.

Stretches

For , enter values or expressions for the three principal stretches. Entering data on this form is convenient for some simple geometries and strain states, but in general it is difficult to provide suitable a coordinate system for the principal orientations.

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

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Selecting a tensor announced by the same physics interface as where the node is added, may result in an error (“Circular variable dependency detected”). This operation is usually meaningless.

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You can use a tensor from the same physics interface, but from a previous solution step. Select the input type and enter expressions where the withsol operator is used to point to the intended solution.

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If you select form the list, and the check box is selected in the parent material node during a geometrically nonlinear study step, the Green–Lagrange strain tensor is computed from

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If you select form the list when engineering strains are expected, the engineering strain tensor is computed from

This is the case if the study step is geometrically linear, or when the check box is selected in the parent material node.

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If you select from the list, and the parent material node operates with multiplicative strain decomposition, the external strain is converted into a deformation gradient using the infinitesimal strain assumption