Polymer Viscoplasticity

Use the subnode to define the viscoplastic properties of rubber, elastomer, and thermoplastic materials. This material model is available in the Solid Mechanics interface and can be used together with .

	See also Polymer Viscoplasticity in the Structural Mechanics Theory chapter.

Use this section to define the viscoplastic properties of the material.

Select a — , , , or . Then follow the instructions below.

The rheology of the Bergstrom–Boyce model adds a spring-dashpot network in parallel to the .

Enter the βv to describe the stiffness of the spring element in the network. The default value is 1.2, which means that at infinitesimal deformations the shear modulus of the network is 1.2 times the equivalent shear modulus of the .

Enter the settings for the nonlinear dashpot:

Select the hardening model from the list.

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Select if the material undergoes viscoplastic deformation without hardening.

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For enter a value or expression for the strain exponent c.

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For enter a value or expression for the hardening function. Write any expression in terms of the viscoplastic strain in the h(λvpe) field.

Select the — or . With the damper is assumed to be fully relaxed, whereas with the damper is assumed to be rigid.

The rheology of the Bergstrom–Bischoff model consists of two spring-dashpot networks added in parallel to a .

Enter the A.

Enter the settings for the nonlinear dashpot in the first network:

Enter the settings for the nonlinear dashpot in the second network:

Select the — or . With all dampers are assumed to be fully relaxed, whereas with all dampers are assumed to be rigid.

The rheology of the Parallel Network model consists of one or more spring-dashpot networks added in parallel to a .

Select a for the spring — , , , , , , or .

For , enter the βv to describe the stiffness of the spring element in the network. The default value is 1.2, which means that at infinitesimal deformations the shear modulus of the network is 1.2 times the equivalent shear modulus of the parent .

For the other options, enter the settings as described in Neo-Hookean, Mooney–Rivlin, Two Parameters, Yeoh, Ogden, Arruda–Boyce, or Gent.

Enter the settings for the nonlinear dashpot:

Select the hardening model from the list.

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Select if the material undergoes viscoplastic deformation without hardening.

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For (default) enter a value or expression for the strain exponent c.

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For enter a value or expression for the hardening function. Write any expression in terms of the viscoplastic strain in the h(λvpe) field.

Select the — or . With all dampers are assumed to be fully relaxed, whereas with all dampers are assumed to be rigid.

When the Parallel Network model is selected, it is possible to add subnodes to the node.

Enter the βv to describe the stiffness of the spring element in the additional network. The default value is 1.2, which means that at infinitesimal deformations the shear modulus of the network is 1.2 times the equivalent shear modulus of the parent Parallel Network.

The settings for the additional nonlinear dashpot are the same as described for the Parallel Network model.

The rheology of the User defined model consists of one spring-dashpot network added in parallel to a .

For enter a value or expression for the . Write any expression in terms of stress tensor components or its invariants in the λvp field.

Select the — or . With the damper is assumed to be fully relaxed, whereas with the damper is assumed to be rigid.

Select a thermal function g(T) — , , , or , which acts as a multiplier for the viscoplastic rate.

For , enter the following setting:

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Tref. The default value is 293.15 K.

For , enter the following setting:

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Tref. The default value is 293.15 K.

For , enter an expression for g(T) as a function of temperature T or other variables in the model.

Select a — , , or .

The method corresponds to the backward Euler method with predefined settings for the Newton loop used to solve the local equations.

For the method, enter the following settings:

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. To determine the maximum number of iteration in the Newton loop when solving the local viscoplasticity equations.

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. To check the convergence of the local viscoplasticity equations based on the step size in the Newton loop.

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. To check the convergence of the local viscoplasticity equations based on the step size in the Newton loop. The final tolerance is computed based on the current solution of the local variable and the entered value.

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. To check the convergence of the local viscoplasticity equations based on the residual of each equation.

If both a step size and residual convergence check is requested, it is sufficient that either of the conditions are fulfilled. Setting either the and or the to zero ignores the corresponding convergence check. An error is returned if all are set to zero.

No settings are needed for the method. However, this method adds degrees-of-freedom that are solved as part of the general solver sequence. The scaling of these fields can affect the convergence of the overall solution.

For a 2D geometry, enable to solve for all components of the viscoplastic strain tensor. By default, COMSOL assumes that the out-of-plane components are zero.

To display this section, click the button (

) and select in the dialog box.

	To compute the energy dissipation caused by viscoplasticity, enable the Calculate dissipated energy check box in the Energy Dissipation section of the parent Hyperelastic Material node.

Physics tab with node selected in the model tree: