*CREEP

Keyword type: model definition, material

This option is used to define the creep properties of a viscoplastic material. There is one optional parameter LAW. Default is LAW=NORTON, the only other value is LAW=USER for a user-defined creep law. The Norton law satisfies:

$$\dot{\epsilon} = A \sigma^n t^m$$ (165)

where $\epsilon$ is the equivalent creep strain, $\sigma$ is the true Von Mises stress an t is the total time. For LAW=USER the creep law must be defined in user subroutine creep.f.

All constants may be temperature dependent. The card should be preceded by a *ELASTIC card within the same material definition, defining the elastic properties of the material. If for LAW=NORTON the temperature data points under the *CREEP card are not the same as those under the *ELASTIC card, the creep data are interpolated at the *ELASTIC temperature data points. If a *PLASTIC card is defined within the same material definition, it should be placed after the *ELASTIC and before the *CREEP card. If no *PLASTIC card is found, a zero yield surface without any hardening is assumed.

If the elastic data is isotropic, the large strain viscoplastic theory treated in [64] and [65] is applied. If the elastic data is orthotropic, the infinitesimal strain model discussed in Section 6.7.9 is used. If a *PLASTIC card is used for an orthotropic material, the LAW=USER option is not available.

First line:

• *CREEP
• Enter the LAW parameter and its value, if needed

Following lines are only needed for LAW=NORTON (default): First line:

• A.
• n.
• m.
• Temperature.

Use as many lines as needed to define the complete temperature dependence.

Example:

*CREEP
1.E-10,5.,0.,100.
2.E-10,5.,0.,200.

defines a creep law with A=$10^{-10}$, n=5 and m=0 for T(temperature)=100. and A= $2 \cdot 10^{-10}$ and n=5 for T(temperature)=200.

Example files: beamcr.