> For the complete documentation index, see [llms.txt](https://dante-solutions-inc.gitbook.io/dante-6.3-help-documentation/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://dante-solutions-inc.gitbook.io/dante-6.3-help-documentation/readme/material-models-for-steels/stress-relaxation-and-creep-model.md).

# Stress Relaxation and Creep Model

Creep model (primary creep, dependent on creep strain) and stress relaxation (secondary creep, independent on creep strain) can be used along with DANTE mechanical models to simulate time and temperature dependent stress changes. In version 6.3 or later, both ***stress relaxation model*** and ***creep model*** can be be activated simultaneously.

The primary creep model equation is described using the equation below.

$$\dot{\epsilon} = c\_1 \cdot \sigma^{c\_2} \cdot ((1+c\_3)\*CreepStrain)^{c\_3} \cdot \exp\left(\frac{-c\_4}{T + 273.5}\right)$$

Where *ė* is strain rate, σ is current stress, a<sub>0</sub>, b<sub>0</sub>, and c<sub>0</sub> are constants, and *T* is temperature. The creep model covers a wide range of temperature. The model parameters are defined by keyword **\*STEEL\_CREEP** in the **\*.MEC** file as shown in the example below.

```
  ** ---Primary Creep Model: (Dependent on creep Strain)
  *STEEL_CREEP
  ** Primary creep rate: (C1*(Sig)^C2*((1+C3)*creep_strain)^C3)*(1/(1+C3)*EXP(-C4/(T+273.5))
  ** 1st data line: C1, C2, C3, C4
   1.5305E-18,  12.50,  0.0, 29840.0
```

To activate DANTE’s creep model, add the keyword ***\*IFLG\_CREEP*** value needs in **DCTRLA.CTL** file to be set to "1", as shown below. A value of “1” activates the model specified by the keyword and “0” deactivates the creep model.

```
	** Creep IFLG_CREEP (1: Activated; 0: Inactivated/Default)
	*IFLG_CREEP
	 1
```

The stress relaxation model is defined as temperature

$$\dot{\epsilon} = a\_0 \cdot \left(\frac{\sigma}{\sigma\_0}\right)^{b\_0}$$

Where *ė* is strain rate, σ is current stress, a<sub>0</sub>, b<sub>0</sub> are constants, and σ<sub>0</sub> is stress constant.

The stress relaxation model parameters are defined for multiple temperature points, and interpolation is used to calculate the stress relaxation rate of any temperature between. The stress relaxation model parameters are defined by keyword **\*STEEL\_STRSRLX** in the **\*.MEC** file as shown in the example below.

```
	** ---Stress Relaxation---------------------------------------------
	*STEEL_STRSRLX
	**  Temperature, A0, B0, sig0 
	**  A0 * (Sig/sig0)^B0 == (Relaxation strain rate)
	 200.0, 5.2823D-14, 12.5D0,   700.0
	 300.0, 5.2823D-13, 12.5D0,   600.0
	 500.0, 5.2823D-12, 12.5D0,   125.0
	 700.0, 5.2823D-11, 12.5D0,   10.0
	 900.0, 5.2823D-10, 12.5D0,   1.0
```

To activate DANTE’s stress relaxation model, add the keyword ***\*IFLG\_STSRLX*** value needs in **DCTRLA.CTL** file to be set to "1", as shown below. A value of “1” activates the model specified by the keyword and “0” deactivates the stress relaxation model.

```
	** Stress Relaxation:  (1: Activated; 0: Inactivated/Default)
	** If IFLG_CREEP==1, IFLG_STSRLX will be set to 0 
	*IFLG_STSRLX
	 1
```

Note: In DANTE version 6.3 or later, ***both creep and stress relaxation model can be activated simultaneously.***

Control keywords can be defined in multiple places: working directory, installation directory, and material data directory. For the control keyword priority list, please reference [**Material Model Control File (DCTRLA)**](/dante-6.3-help-documentation/readme/material-database/material-model-control-file-dctrla.md).