Experiment types supported: uniaxial, biaxial, pure shear, simple shear, volumetric

Hyperelastic curve-fitting supports these primary behaviors:

Curve-fitting for fully- or nearly-incompressible hyperelastic material models use the incompressibility equation λ1 * λ2 * λ3 = 1 (where λ is the stretch) to evaluate deviatoric material parameters. The volumetric coefficients are not used during the evaluation of the coefficients that define the deviatoric terms for these models

J is the ratio of current volume to the original volume.

Euler angles are specified via /xcsys,euler,angle1,angle2,angle3 in the experiment header. See example.

Experiment types supported: uniaxial

/1,epto
/2,s
/temp,0
      0.0        0.0
 0.280000E-004  4.20000     
 0.560000E-004  8.40000     
 0.980000E-004  14.7000     
 0.144667E-003  21.7000     
 0.191333E-003  28.7000     

The header format to define a data attribute is /attr, value, where attr is the data-type abbreviation, and value is the value of the attribute.

Experiment types supported: creep test, uniaxial

Use /index,attributename to indicate what is defined in each column. Example: if column 1 is time, specify /1,time in the header before the experimental values are specified. See the examples.

The header format to define each column's data type is /n, abbr, where n is the index of the data column in the file, and abbr is the abbreviation for the type of data in the column, as described in Table 7.16: Creep Data Types and Abbreviations.

/1,seqv             ! indicates first column is stress 
/2,creq             ! indicates second column is creep strain 
/3,temp             ! indicates third column is temperature 
/4,dcreq            ! indicates fourth column is creep strain rate 
4000    0.00215869	100    0.000203055 
4000    0.00406109	100    0.000181314 
4000    0.00664691	100    0.000165303 
4000    0.0102068	100    0.000152217 
4000    0.0151416	100    0.000140946

When a given column is unchanged over the loading history, you can define it as an attribute. As shown in the example above, the stress and temperature are constant throughout the range. You define this data as an attribute.

The header format to define a data attribute is /attr, value, where attr is the data-type abbreviation, and value is the value of the attribute. The constant stress and temperature values above can be written into the file header:

/seqv,4000          ! indicate this creep has a constant stress of 4000 
/temp,100           ! indicate this creep data is at a constant temperature of 100 
/1,creq             ! indicate first column is creep strain 
/2,dcreq            ! indicate second column is creep strain rate 
0.00215869 0.000203055 
0.00406109 0.000181314 
0.00664691 0.000165303 
0.0102068 0.000152217 
0.0151416 0.000140946 
0.0220102 0.000130945 

Thirteen model types are available for creep curve-fitting. The model you select determines the experimental data required for the curve-fitting process. The following table describes the creep data required to perform curve-fitting for each model type:

For strain hardening and modified strain hardening, input both creep strain and creep strain rate in the experimental data.

Provide sufficient experimental data to fit the creep model selected for the fitting process. For example, the strain-hardening model is creep strain rate is a function of stress and creep. To use the model, data must be provided at multiple strain rates (whether in single or multiple files); otherwise, C2 and C3 in the strain-hardening creep equation can become zero in the fitting process and provide a perfect fit in this underconstrained problem. Similarly, experimental data having no multiple stress or creep strain values indicates that the data is independent of those variables.

Define the Prony series model (TB,ELAS and TB,PRONY). If needed, you can use the shift method (TB,SHIFT) to handle temperature experimental data.

For viscoelastic curve-fitting with multiple temperatures, you can evaluate coefficients at each discrete temperature point and write it as a temperature-dependent Prony data table, or you can use the Williams-Landau-Ferry (WLF) or Tool-Narayanaswamy (TN) shift functions to account for the temperature-dependency. (See Shift Functions in the Mechanical APDL Theory Reference.) A separate data file must be provided for each discrete temperature. The viscoelastic test data can be any of the following data types:

Experiment types supported: uniaxial