# ComputeEigenstrainFromInitialStress

Computes an eigenstrain from an initial stress

## Description

Computes an eigenstrain, , defined by , where is the elasticity tensor and is the initial stress entered by the user. The initial stress is entered as a vector of 9 Functions.

This allows a user to enter an insitu stress in rock-mechanics problems, for instance, by specifying the component to be a function of depth into the ground, and the , , and components of the initial stress to be related to the maximum and minimum principal horizontal tectonic stresses. A general anisotropic initial stress is allowed.

The eigenstrain thus computed is added to the mechanical strain on the first time step, and is unchanged in subsequent timesteps. The eigenstrain thus computed is given a name that is specified by the user, and that name must be included in the eigenstrain_names input parameter of the strain calculator (eg, in ComputeSmallStrain), otherwise MOOSE will not add the eigenstrain to the mechanical strain!

warning:Time-dependent elasticity tensors

The eigenstrain is computed on the first time step, using the elasticity tensor; hence, the elasticity tensor should not be time-varying in the first timestep.

## Example Input File Syntax


[Materials]
[./elasticity_tensor]
type = ComputeIsotropicElasticityTensor
youngs_modulus = 1
poissons_ratio = 0.25
[../]
[./strain]
type = ComputeSmallStrain
eigenstrain_names = ini_stress
[../]
[./strain_from_initial_stress]
type = ComputeEigenstrainFromInitialStress
initial_stress = 'kxx 0 0  0 kxx 0  0 0 weight'
eigenstrain_name = ini_stress
[../]
[./stress]
type = ComputeLinearElasticStress
[../]
[]
(modules/tensor_mechanics/test/tests/initial_stress/gravity.i)

In this example the eigenstrain is given the name ini_stress. This name is passed to the ComputeSmallStrain strain calculator using the eigenstrain_names parameter. The initial stress is defined by the functions defined in


[Functions]
[./weight]
type = ParsedFunction
value = '0.5*z' # initial stress that should result from the weight force
[../]
[./kxx]
type = ParsedFunction
value = '0.4*z' # some arbitrary xx and yy stress that should not affect the result
[../]
[]
(modules/tensor_mechanics/test/tests/initial_stress/gravity.i)

## Input Parameters

• initial_stressA list of functions describing the initial stress. If provided, there must be 9 of these, corresponding to the xx, yx, zx, xy, yy, zy, xz, yz, zz components respectively. To compute the eigenstrain correctly, your elasticity tensor should not be time-varying in the first timestep

C++ Type:std::vector

Options:

Description:A list of functions describing the initial stress. If provided, there must be 9 of these, corresponding to the xx, yx, zx, xy, yy, zy, xz, yz, zz components respectively. To compute the eigenstrain correctly, your elasticity tensor should not be time-varying in the first timestep

• 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

• 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

• 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.

• 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

• base_nameThe base_name for the elasticity tensor that will be used to compute strain from stress. Do not provide any base_name if your elasticity tensor does not use one.

C++ Type:std::string

Options:

Description:The base_name for the elasticity tensor that will be used to compute strain from stress. Do not provide any base_name if your elasticity tensor does not use one.

### Optional 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

### Advanced 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