User subroutine to define time-dependent, viscoplastic behavior (creep and swelling).

User subroutine CREEP will be called at all integration points of elements for which the material definition contains user-subroutine-defined metal creep, time-dependent volumetric swelling, Drucker-Prager creep, or cap creep behavior, during procedures that allow viscoplastic response of the above type to occur (such as the quasi-static procedure). This subroutine will also be called at all integration points of gasket elements for which the behavior definition contains user-subroutine-defined creep.

If user subroutine CREEP is used to define a material behavior, the subroutine:

  • is intended to provide the “uniaxial” creep laws that are to be included in a general time-dependent, viscoplastic material formulation;

  • can be used in the coupled-temperature displacement (Fully coupled thermal-stress analysis), coupled thermal-electrical-structural (Fully coupled thermal-electrical-structural analysis), soils (Coupled pore fluid diffusion and stress analysis), and quasi-static (Quasi-static analysis) procedures;

  • allows for the definition of creep laws for which the meaning and internal use depend on the material model with which they are being used;

  • allows creep and swelling to be combined with rate-independent plastic behavior in a coupled manner, or they may simply be the only inelastic behaviors of the material, in which case Mises behavior is assumed;

  • can use and update solution-dependent state variables; and

  • can be used in conjunction with user subroutine USDFLD to redefine any field variables before they are passed in.

If user subroutine CREEP is used to define rate-dependent behavior in the thickness direction for a gasket, the subroutine:

  • is intended to provide the creep laws that are used to prescribe the thickness-direction behavior for a gasket;

  • can be used only in a quasi-static (Quasi-static analysis) procedure;

  • is used in a coupled form with the elastic-plastic model used to define the rate-independent part of the thickness-direction behavior of the gasket; and

  • can use and update solution-dependent variables.

The following topics are discussed:

Related Topics
In Other Guides
Rate-dependent plasticity: creep and swelling
Extended Drucker-Prager models
Modified Drucker-Prager/Cap model
Defining the gasket behavior directly using a gasket behavior model
Verification of creep integration