# Compute Variable Eigenstrain

Computes an Eigenstrain and its derivatives that is a function of multiple variables, where the prefactor is defined in a derivative material

## Description

ComputeVariableEigenstrain calculates the eigenstrain as a function of a specified variable as well as the contributions of the eigenstrain to the first and second order derivatives of the elastic strain. This class is most often only used in phase field simulations where first and second derivatives are required and the limitation on elastic only strains is not overly restrictive.

The Rank-2 tensor eigenstrain is calculated as a function of a Rank-2 tensor base and a scalar material property. (1) where is the computed eigenstrain, is a scalar material property, and is the tensor selected by the user as the base of the eigenstrain. The material property is used to introduce dependence of the eigenstrain on the user-specified variable.

The contributions of the eigenstrain to the first and second elastic strain derivatives are calculated with use of the MOOSE DerivativeMaterialInterface applied to the prefactor variables. (2) where and are the first and second derivatives of the elastic strain contributions due to the eigenstrain.

warning:Use with Elastic Strain Only

This class assumes the presence of only elastic strain in the computation of the first and second derivatives.

## Example Input File

[./eigenstrain]
type = ComputeVariableEigenstrain
eigen_base = '1'
args = c
prefactor = prefactor
eigenstrain_name = eigenstrain
[../]

(modules/combined/test/tests/multiphase_mechanics/simpleeigenstrain.i)

where the argument for the args parameter in the eigenstrain matches the name of the coupled variable, here shown as an auxvariable

[./c]
order = FIRST
family = LAGRANGE
[./InitialCondition]
type = SmoothCircleIC
x1 = 125.0
y1 = 125.0
invalue = 1.0
outvalue = 0.1
int_width = 50.0
[../]
[../]

(modules/combined/test/tests/multiphase_mechanics/simpleeigenstrain.i)

and the argument for the prefactor parameter in the eigenstrain material matches the function name (f_name parameter) in the DerivativeParsedMaterial

[./prefactor]
type = DerivativeParsedMaterial
args = c
f_name = prefactor
constant_names = 'epsilon0 c0'
constant_expressions = '0.05     0'
function = '(c - c0) * epsilon0'
[../]

(modules/combined/test/tests/multiphase_mechanics/simpleeigenstrain.i)

Finally, the eigenstrain_name parameter value must also be set for the strain calculator, and an example parameter setting is shown below:

[./strain]
type = ComputeSmallStrain
eigenstrain_names = eigenstrain
[../]

(modules/combined/test/tests/multiphase_mechanics/simpleeigenstrain.i)

## Input Parameters

• eigen_baseVector of values defining the constant base tensor for the Eigenstrain

C++ Type:std::vector

Options:

Description:Vector of values defining the constant base tensor for the Eigenstrain

• argsvariable dependencies for the prefactor

C++ Type:std::vector

Options:

Description:variable dependencies for the prefactor

• eigenstrain_nameMaterial property name for the eigenstrain tensor computed by this model. IMPORTANT: The name of this property must also be provided to the strain calculator.

C++ Type:std::string

Options:

Description:Material property name for the eigenstrain tensor computed by this model. IMPORTANT: The name of this property must also be provided to the strain calculator.

### Required 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

• 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

• prefactor1Name of material defining the variable dependence

Default:1

C++ Type:MaterialPropertyName

Options:

Description:Name of material defining the variable dependence

### Optional Parameters

• 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

### Outputs Parameters

• enableTrueSet the enabled status of the MooseObject.

Default:True

C++ Type:bool

Options:

Description:Set the enabled status of the MooseObject.

• use_displaced_meshFalseWhether or not this object should use the displaced mesh for computation. Note that in the case this is true but no displacements are provided in the Mesh block the undisplaced mesh will still be used.

Default:False

C++ Type:bool

Options:

Description:Whether or not this object should use the displaced mesh for computation. Note that in the case this is true but no displacements are provided in the Mesh block the undisplaced mesh will still be used.

• 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.

• 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