Nonlinear Elastic Material

The feature is used to model stress-strain relationships which are nonlinear even at infinitesimal strains. It is available in the Solid Mechanics and Membrane interfaces. This material model requires either the Nonlinear Structural Materials Module or the Geomechanics Module.

By adding the following subnodes to the node you can incorporate many other effects:

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Thermal Expansion (for materials)

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Hygroscopic Swelling

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Initial Stress and Strain

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Note: Some options are only available with certain COMSOL products (see http://www.comsol.com/products/specifications/)

Coordinate System Selection

The is selected by default. The list contains any additional coordinate systems that the model includes (except boundary coordinate systems). The coordinate system is used when stresses or strains are presented in a local system. The coordinate system must have orthonormal coordinate axes, and be defined in the material frame. Many of the possible subnodes inherit the coordinate system settings.

Nonlinear Elastic Material

To use a mixed formulation by adding the pressure as an extra dependent variable to solve for, select the check box. For a material with a very low compressibility, using only displacements as degrees of freedom may lead to a numerically ill-posed problem.

The available material models depend on the COMSOL products you are using.

Nonlinear Structural Materials Module: Select a : , , , , or .

Geomechanics Module: Select a : , , , , , or .

Density

All nonlinear elastic material models have density as an input. The default ρ uses values . For enter another value or expression.


	The density is needed for dynamic analysis or when the elastic data is given in terms of wave speed. It is also used when computing mass forces for gravitational or rotating frame loads, and when computing mass properties (Computing Mass Properties).

Ramberg-Osgood, Power law, Hyperbolic law, Hardin-Drnevich, Duncan-Chang, or Duncan-Selig

Select from the applicable list to use the value or enter a value or expression.

From the list select a pair of elastic properties for an isotropic material — (the default for Ramberg-Osgood, Power law, Duncan-Chang, and Duncan-Selig) or (the default for Hyperbolic law and Hardin-Drnevich).

Then depending on the selections, define the applicable parameters:

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ν.

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For :

σref .

εref.

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For and :

γref.

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For , define the γref.

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For , define the qult.

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For :

qult.

εult.

Uniaxial Data

For enter a value or expression for the σax as a function of the uniaxial strain. The default expression is the linear function (210[GPa])*solid.eax N/m2, which corresponds to a linear elastic material with Young’s modulus 210 GPa.

From the list select how to specify the second elastic property for the material — or . Then depending on the selection, enter a value or select from the applicable list to use the value or enter a value or expression:

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ν.

When you select , the Young’s modulus is computed from the tensile part of the σax. When you select , you can either use the tensile part (default), or use the full tensile-compressive function by selecting the check box .

Bilinear Elastic

For enter a value or select from the applicable list to use the value or enter a value or expression.

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Kt.

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Kc.

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User Defined

In the material model, you specify the bulk modulus implicitly by entering the relation between pressure and volumetric elastic strain. Enter a value or select from the applicable list to use the value (the default) or enter a value or expression.

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p. The default expression is (-160[GPa])*solid.eelvol N/m2, which corresponds to a linear elastic material with bulk modulus 160 GPa.

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Geometric Nonlinearity

The settings in this section affect the behavior of the selected domains in a geometrically nonlinear analysis.

If a study step is geometrically nonlinear, the default behavior is to use a large strain formulation in all domains. Select the check box to always use a small strain formulation, irrespective of the setting in the study step.

When a geometrically nonlinear formulation is used, the elastic deformations used for computing the stresses can be obtained in two different ways if inelastic deformations are present: additive decomposition and multiplicative decomposition. The default is to use multiplicative decomposition. Select to change to an assumption of additivity.

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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 in contact analysis, where the study is always geometrically nonlinear, but it is possible that a geometrically linear formulation is sufficient in the material.

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

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In versions prior to 5.3, only the additive strain decomposition method was available. If you want to revert to the previous behavior, select . If the results then differ significantly, probably the assumption of additivity is questionable, however.

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Modeling Geometric Nonlinearity

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Inelastic Strain Contributions

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Studies and Solvers in the COMSOL Multiphysics Reference Manual

Energy Dissipation

To display this section, click the button (

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Select the check box as needed to compute the energy dissipated by , , , or .

Location in User Interface

Context Menus

Ribbon

Physics tab with selected: