Automatic fitting allows you to automatically generate material parameters from experimental data using the TBFT command, without explicitly going through the curve fitting process. A single command enables this option, and the workflow is internally set up to work for a subcategory of problems. Automatic fitting is available for isotropic hyper-elastic material models that have no rate-dependency. Experimental data, defined using the TB,EXPE command, is converted to material parameters and saved in the TB database prior to solution with a single TBFT,AFIT command.

To generate and save material parameters with data provided from the TB,EXPE command:

TBFT,AFIT,MATID

where:

To print diagnostic information to help evaluate whether to accept the generated material model:

TBFT,AFPAR,PARAMNAME,FLAG

Experimental data for automatic fitting is provided using the TB,EXPE command option. Supported data types are Uniaxial Tension (TBOPT = UNIT), Uniaxial Compression (TBOPT = UNIC), Biaxial Tension (TBOPT = BIAX), Simple Shear (TBOPT = SSHE), Pure Shear (TBOPT = SHEA) and Volumetric Data (TBOPT = VOLU). Either you can provide lateral strain for the experimental data or you can provide Poisson's ratio using the TB,EXPE,MATID,,,POIS command followed by TBDATA. This is necessary when compressible hyperelastic materials are used for the automatic fitting process.

To define Poisson's ratio for compressible hyper elastic materials:

TB,EXPE,MATID,,,POIS
TBDATA,,VALUE

Diagnostics must be reviewed to decide whether the results are acceptable before moving on to the finite element solution step. In cases where automatic fitting does not provide acceptable results, you can continue the fitting process using the TBFT command by editing the parameters and generating a different solution. Use the TBFT,LIST,MATERIALID command to review the fitting model information.