Power Law Creep Stress Update

This class uses the stress update material in a radial return isotropic power law creep model. This class can be used in conjunction with other creep and plasticity materials for more complex simulations.

Description

In this numerical approach, a trial stress is calculated at the start of each simulation time increment; the trial stress calculation assumed all of the new strain increment is elastic strain: (1)

The algorithms checks to see if the trial stress state is outside of the yield surface, as shown in the figure to the right. If the stress state is outside of the yield surface, the algorithm recomputes the scalar effective inelastic strain required to return the stress state to the yield surface. This approach is given the name Radial Return because the yield surface used is the von Mises yield surface: in the devitoric stress space , this yield surface has the shape of a circle, and the scalar inelastic strain is assumed to always be directed at the circle center.

Recompute Iterations on the Effective Plastic Strain Increment

The recompute radial return materials each individually calculate, using the Newton Method, the amount of effective inelastic strain required to return the stress state to the yield surface. (2) where the change in the iterative effective inelastic strain is defined as the yield surface over the derivative of the yield surface with respect to the inelastic strain increment.

The increment of inelastic strain is computed from the creep rate in this class. (3) where is the scalar von Mises trial stress, is the isotropic shear modulus, is the activation energy, is the universal gas constant, is the temperature, and are the current and initial times, respectively, and and are exponent values.

This class calculates an effective trial stress, an effective creep strain rate increment and the derivative of the creep strain rate, and an effective scalar inelastic strain increment; these values are passed to the RadialReturnStressUpdate to compute the radial return stress increment. This isotropic plasticity class also computes the plastic strain as a stateful material property.

This class is based on the implicit integration algorithm in Dunne and Petrinic (2005) pg. 146 - 149.

Example Input File


[./powerlawcrp]
  type = PowerLawCreepStressUpdate
  block = 1
  coefficient = 3.125e-14
  n_exponent = 5.0
  m_exponent = 0.0
  activation_energy = 0.0
  max_inelastic_increment = 0.01
[../]
(modules/tensor_mechanics/test/tests/material_limit_time_step/creep/nafems_test5a_lim.i)

PowerLawCreepStressUpdate must be run in conjunction with the inelastic strain return mapping stress calculator as shown below:


[./radial_return_stress]
  type = ComputeMultipleInelasticStress
  block = 1
  inelastic_models = 'powerlawcrp'
[../]
(modules/tensor_mechanics/test/tests/material_limit_time_step/creep/nafems_test5a_lim.i)

Input Parameters

  • coefficientLeading coefficent in power-law equation

    C++ Type:double

    Options:

    Description:Leading coefficent in power-law equation

  • n_exponentExponent on effective stress in power-law equation

    C++ Type:double

    Options:

    Description:Exponent on effective stress in power-law equation

  • activation_energyActivation energy

    C++ Type:double

    Options:

    Description:Activation energy

Required Parameters

  • max_inelastic_increment0.0001The maximum inelastic strain increment allowed in a time step

    Default:0.0001

    C++ Type:double

    Options:

    Description:The maximum inelastic strain increment allowed in a time step

  • gas_constant8.3143Universal gas constant

    Default:8.3143

    C++ Type:double

    Options:

    Description:Universal gas constant

  • base_nameOptional parameter that defines a prefix for all material properties related to this stress update model. This allows for multiple models of the same type to be used without naming conflicts.

    C++ Type:std::string

    Options:

    Description:Optional parameter that defines a prefix for all material properties related to this stress update model. This allows for multiple models of the same type to be used without naming conflicts.

  • relative_tolerance1e-08Relative convergence tolerance for Newton iteration

    Default:1e-08

    C++ Type:double

    Options:

    Description:Relative convergence tolerance for Newton iteration

  • acceptable_multiplier10Factor applied to relative and absolute tolerance for acceptable convergence if iterations are no longer making progress

    Default:10

    C++ Type:double

    Options:

    Description:Factor applied to relative and absolute tolerance for acceptable convergence if iterations are no longer making progress

  • absolute_tolerance1e-11Absolute convergence tolerance for Newton iteration

    Default:1e-11

    C++ Type:double

    Options:

    Description:Absolute convergence tolerance for Newton iteration

  • 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

  • m_exponent0Exponent on time in power-law equation

    Default:0

    C++ Type:double

    Options:

    Description:Exponent on time in power-law equation

  • start_time0Start time (if not zero)

    Default:0

    C++ Type:double

    Options:

    Description:Start time (if not zero)

  • 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

  • temperatureCoupled temperature

    C++ Type:std::vector

    Options:

    Description:Coupled temperature

Optional Parameters

  • effective_inelastic_strain_nameeffective_creep_strainName of the material property that stores the effective inelastic strain

    Default:effective_creep_strain

    C++ Type:std::string

    Options:

    Description:Name of the material property that stores the effective inelastic strain

  • 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

  • internal_solve_output_onon_errorWhen to output internal Newton solve information

    Default:on_error

    C++ Type:MooseEnum

    Options:never on_error always

    Description:When to output internal Newton solve information

  • internal_solve_full_iteration_historyFalseSet true to output full internal Newton iteration history at times determined by `internal_solve_output_on`. If false, only a summary is output.

    Default:False

    C++ Type:bool

    Options:

    Description:Set true to output full internal Newton iteration history at times determined by `internal_solve_output_on`. If false, only a summary is output.

Debug 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

Input Files

References

  1. Fionn Dunne and Nik Petrinic. Introduction to Computational Plasticity. Oxford University Press on Demand, 2005.[BibTeX]