Spring Material

By adding the Predeformation subnode, you can prescribe that the spring force is zero at a nonzero spring extension.

The spring constants and loss factors are given with respect to the selected coordinate system.

Select the and its associated spring constant or force using Table 4-8 as a guide.

Use the built-in variables for the thin layer extension for the options , , or . The names are <item>.uelt1, <item>.uelt2, and <item>.ueln, where <item> is the name of the Thin Layer node (for example, solid.tl1), and t1, t2, and n are the coordinate names of the local boundary system.

The spring constants can be entered as , , or . For the same spring constant is used in all the diagonal elements of the spring matrix.

Table 4-8: Spring Types for the Spring Material Feature.
Spring Type	variable	SI units	Space Dimension
Spring constant per unit area	kA	N/(m⋅m2)	3D, 2D, and 2D axisymmetric
Spring constant per unit length	kL	N/(m⋅m)	2D
Total spring constant	ktot	N/m	3D, 2D, and 2D axisymmetric
Force per area as function of extension	FA	N/m2	3D, 2D, and 2D axisymmetric
Force per length as function of extension	FL	N/m	2D
Total force as function of extension	Ftot	N	3D, 2D, and 2D axisymmetric

Enter the of the thin elastic layer — , , or . For thin layers on 2D geometries, it is also possible to enter the ρL.

Geometric Nonlinearity

The settings in this section control the overall kinematics, the definition of the strain decomposition, and the behavior of inelastic contributions, for the material.

Select a — (default), , or to set the kinematics of the deformation and the definition of strain. When is selected, the study step controls the kinematics and the strain definition.

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With the default , a total Lagrangian formulation for large strains is used when the check box is selected in the study step. If the check box is not selected, the formulation is geometrically linear, with a small strain formulation.

To have full control of the formulation, select either , or . When is selected, the physics will force the check box in all study steps.

When inelastic deformations are present, such as for plasticity, the elastic deformation can be obtained in two different ways: using additive decomposition of strains or using multiplicative decomposition of deformation gradients.

Select a — (default), , or to decide how the inelastic deformations are treated. This option is not available when the formulation is set to .

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When is selected, a multiplicative or additive decomposition is used with a total Lagrangian formulation, depending on the check box status in the study step.

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Select to force an additive decomposition of strains.

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Select to force a multiplicative decomposition of deformation gradients. This option is only visible if is set to .

The input is only visible for material models that support both additive and multiplicative decomposition of deformation gradients.

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There are some cases when a small strain formulation could be useful for a certain domain, even though the study step is geometrically nonlinear. One such case is contact analysis, where the study step is always geometrically nonlinear, but where a geometrically linear formulation is sufficient for the material.

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When a multiplicative decomposition is used, the order of the subnodes matters. The inelastic deformations are assumed to occur in the same order as the subnodes appear in the model tree.


	See Lagrangian Formulation, Deformation Measures, and Inelastic Strain Contributions in the Structural Mechanics Theory chapter. See Modeling Geometric Nonlinearity in the Structural Mechanics Modeling chapter. See Study Settings in the COMSOL Multiphysics Reference Manual.