Viscoelasticity
Use the Viscoelasticity subnode to add viscous stress contributions to an elastic material model. This material model is available in the Solid Mechanics, Shell, Layered Shell, and Membrane interfaces, and can be used together with Linear Elastic Material, Layered Linear Elastic Material, Nonlinear Elastic Material, and Hyperelastic Material.
See also Linear Viscoelastic Materials and Large Strain Viscoelasticity in the Structural Mechanics Theory chapter.
Shell Properties

This section is only present when Viscoelasticity is used as a subnode to:
Layered Linear Elastic Material in the Shell interface. See the documentation for the Viscoelasticity node in the Shell and Plate chapter.
Layered Linear Elastic Material in the Membrane interface. See the documentation for the Viscoelasticity node in the Membrane chapter.
Thermal Effects
Viscoelastic properties have a strong dependence on the temperature. For thermorheologically simple materials, a change in the temperature can be transformed directly into a change in the time scale. Thus, the relaxation time is modified to aT(Tm, where aT(T) is a shift function.
Select a Shift function None, Williams-Landel-Ferry, Arrhenius, or User defined.
When the default, None, is kept, the shift function aT(T) is set to unity and the relaxation time is not modified.
For Williams-Landel-Ferry enter values or expressions for these properties then the shift function aT(T) is computed from these parameters and the relaxations time is shifted according to it:
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Reference temperature TWLF The default is 293.15 K.
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WLF constant 1 C1WLF. The default is 17.44.
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WLF constant 2 C2WLF. The default is 51.6 K.
For Arrhenius enter values or expressions for these properties then the shift function aT(T) is computed from these parameters and the relaxations time is shifted according to it:
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Reference temperature T0. The default is 293.15 K.
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For User defined enter a value or expression for the shift function aT.
Viscoelasticity Model
Select a Material model Generalized Maxwell, Standard linear solid, Kelvin-Voigt, or Burgers. Then see the settings for each option that follows.
For any material model, you can select the shear modulus to use when solving a stationary problem. Choose the Static stiffness for the material model — Long-term or Instantaneous.
Generalized Maxwell
For Generalized Maxwell in the table enter the values for the parameters that describe the viscoelastic behavior as a series of spring-dashpot pairs.
For linear viscoelasticity, in each Branch row enter the stiffness of the spring Gm in the Shear modulus (Pa) column and the relaxation time constant τm in the Relaxation time (s) column for the spring-dashpot pair in branch m.
For large strain viscoelasticity, in each Branch row enter βm (the energy factor of the branch) in the Energy factor (1) column and the relaxation time constant τm in the Relaxation time (s) column for the spring-dashpot pair.
Use the Add button () to add a row to the table and the Delete button () to delete a row in the table.
Using the Load from file button () and the Save to file button () load and store data for the branches in a text file with three space-separated columns (from left to right): the branch number, the shear modulus or energy factor, and the relaxation time for that branch.
Standard Linear Solid
For Standard linear solid enter the values for the parameters that describe the viscoelastic behavior of the single spring-dashpot branch.
For linear viscoelasticity, select an option from the Relaxation data list and edit the default as needed:
Relaxation time τv. The default is 3000 s.
Viscosity ηv of the dashpot. The default is 6·1013 Pas.
In the Shear modulus field, enter the stiffness of the spring Gv. The default is 2·1010 Pa.
For large strain viscoelasticity, enter the Relaxation time τv, which default value is 3000 s, and the Energy factor βv of the dashpot. The default is 0.2.
Kelvin-Voigt

For Kelvin-Voigt enter the values for the parameter that describes the viscous behavior of the single dashpot.
For linear viscoelasticity, select an option from the Relaxation data list and edit the default as needed:
Relaxation time τv. The default is 3000 s.
Viscosity ηv of the dashpot. The default is 6·1013 Pas.
For large strain viscoelasticity, enter the Relaxation time τv. The default is 3000 s.
Burgers
For Burgers enter the values for the parameter that describes the viscous behavior of the spring dashpot in series with a second spring-dashpot pair.
For linear viscoelasticity, select an option from the Relaxation data list and edit the default as needed:
Relaxation time. The default is 3000 s for both dashpots τv1 and τv2.
Viscosity. Enter the viscosity of the dashpots. The default is 6·1013 Pas for both ηv1 and ηv2.
In the Shear modulus field, enter the stiffness of the second spring Gv2. The default is 2·1010 Pa.
Discretization
Select a Shape function type Discontinuous Lagrange (default) or Gauss point data for the components of the auxiliary viscoelastic tensor. When the discontinuous Lagrange discretization is used, the shape function order is selected as one order less than what is used for the displacements. This results in that fewer extra degrees of freedom are added to the model than when using Gauss point data. The accuracy does in general not differ much. If you want to enforce that the constitutive law is fulfilled at the integration points, select Gauss point data.
To compute the energy dissipation caused by viscoelasticity, enable the Calculate dissipated energy check box in the Energy Dissipation section of the parent material node.
Viscoelastic Structural Damper: Application Library path Structural_Mechanics_Module/Dynamics_and_Vibration/viscoelastic_damper_frequency
Viscoelastic Structural Damper — Transient Analysis: Application Library path Structural_Mechanics_Module/Dynamics_and_Vibration/viscoelastic_damper_transient
Location in User Interface
Context Menus
Ribbon
Physics tab with Linear Elastic Material, Layered Linear Elastic Material, Nonlinear Elastic Material, or Hyperelastic Material node selected in the model tree: