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.

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(T)τm, where aT(T) is a shift function.

Select a Shift function — None, Williams-Landel-Ferry, Arrhenius, or User defined.

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.

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.

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:

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.

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:

For large strain viscoelasticity, enter the Relaxation time τv. The default is 3000 s.

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:

In the Shear modulus field, enter the stiffness of the second spring Gv2. The default is 2·1010 Pa.

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.

Physics tab with Linear Elastic Material, Layered Linear Elastic Material, Nonlinear Elastic Material, or Hyperelastic Material node selected in the model tree: