# Compute Linear Viscoelastic Stress

Divides total strain into elastic + creep + eigenstrains

## Description

This computes the stress of a linear viscoelastic material using a total small strain approximation. The stress is calculated from the mechanical strain and the creep strain as: (1)

## Example Input File Syntax


[./stress]
type = ComputeLinearViscoelasticStress
[../]
(modules/tensor_mechanics/test/tests/visco/visco_small_strain.i)

The mechanical strain must be computed with a ComputeSmallStrain material.


[./strain]
type = ComputeSmallStrain
displacements = 'disp_x disp_y disp_z'
[../]
(modules/tensor_mechanics/test/tests/visco/visco_small_strain.i)

The creep strain itself is computed by a linear viscoelastic material such as a GeneralizedKelvinVoigtModel or a GeneralizedMaxwellModel material. The elasticity tensor is also provided by the same linear viscoelastic material.

[./kelvin_voigt]
type = GeneralizedKelvinVoigtModel
creep_modulus = '10e9 10e9'
creep_viscosity = '1 10'
poisson_ratio = 0.2
young_modulus = 10e9
[../]
(modules/tensor_mechanics/test/tests/visco/visco_small_strain.i)

For the creep strains to be updated properly, the simulation must also include a LinearViscoelasticStressUpdate user object:


[UserObjects]
[./update]
type = LinearViscoelasticityManager
viscoelastic_model = kelvin_voigt
[../]
[]
(modules/tensor_mechanics/test/tests/visco/visco_small_strain.i)

## Input Parameters

• computeTrueWhen false, MOOSE will not call compute methods on this material. The user must call computeProperties() after retrieving the Material via MaterialPropertyInterface::getMaterial(). Non-computed Materials are not sorted for dependencies.

Default:True

C++ Type:bool

Options:

Description:When false, MOOSE will not call compute methods on this material. The user must call computeProperties() after retrieving the Material via MaterialPropertyInterface::getMaterial(). Non-computed Materials are not sorted for dependencies.

• base_nameOptional parameter that allows the user to define multiple mechanics material systems on the same block, i.e. for multiple phases

C++ Type:std::string

Options:

Description:Optional parameter that allows the user to define multiple mechanics material systems on the same block, i.e. for multiple phases

• store_stress_oldFalseParameter which indicates whether the old stress state, required for the HHT time integration scheme and Rayleigh damping, needs to be stored

Default:False

C++ Type:bool

Options:

Description:Parameter which indicates whether the old stress state, required for the HHT time integration scheme and Rayleigh damping, needs to be stored

• apparent_creep_strainapparent_creep_strainname of the apparent creep strain (defined by a LinearViscoelasticityBase material)

Default:apparent_creep_strain

C++ Type:std::string

Options:

Description:name of the apparent creep strain (defined by a LinearViscoelasticityBase material)

• elasticity_tensor_invelasticity_tensor_invname of the real compliance tensor (defined by a LinearViscoelasticityBase material)

Default:elasticity_tensor_inv

C++ Type:std::string

Options:

Description:name of the real compliance tensor (defined by a LinearViscoelasticityBase material)

• apparent_elasticity_tensorapparent_elasticity_tensorname of the apparent elasticity tensor (defined by a LinearViscoelasticityBase material)

Default:apparent_elasticity_tensor

C++ Type:std::string

Options:

Description:name of the apparent elasticity tensor (defined by a LinearViscoelasticityBase material)

• boundaryThe list of boundary IDs from the mesh where this boundary condition applies

C++ Type:std::vector

Options:

Description:The list of boundary IDs from the mesh where this boundary condition applies

• blockThe list of block ids (SubdomainID) that this object will be applied

C++ Type:std::vector

Options:

Description:The list of block ids (SubdomainID) that this object will be applied

### Optional Parameters

• control_tagsAdds user-defined labels for accessing object parameters via control logic.

C++ Type:std::vector

Options:

Description:Adds user-defined labels for accessing object parameters via control logic.

• enableTrueSet the enabled status of the MooseObject.

Default:True

C++ Type:bool

Options:

Description:Set the enabled status of the MooseObject.

• seed0The seed for the master random number generator

Default:0

C++ Type:unsigned int

Options:

Description:The seed for the master random number generator

• implicitTrueDetermines whether this object is calculated using an implicit or explicit form

Default:True

C++ Type:bool

Options:

Description:Determines whether this object is calculated using an implicit or explicit form

• constant_onNONEWhen ELEMENT, MOOSE will only call computeQpProperties() for the 0th quadrature point, and then copy that value to the other qps.When SUBDOMAIN, MOOSE will only call computeSubdomainProperties() for the 0th quadrature point, and then copy that value to the other qps. Evaluations on element qps will be skipped

Default:NONE

C++ Type:MooseEnum

Options:NONE ELEMENT SUBDOMAIN

Description:When ELEMENT, MOOSE will only call computeQpProperties() for the 0th quadrature point, and then copy that value to the other qps.When SUBDOMAIN, MOOSE will only call computeSubdomainProperties() for the 0th quadrature point, and then copy that value to the other qps. Evaluations on element qps will be skipped

• output_propertiesList of material properties, from this material, to output (outputs must also be defined to an output type)

C++ Type:std::vector

Options:

Description:List of material properties, from this material, to output (outputs must also be defined to an output type)

• outputsnone Vector of output names were you would like to restrict the output of variables(s) associated with this object

Default:none

C++ Type:std::vector

Options:

Description:Vector of output names were you would like to restrict the output of variables(s) associated with this object