**TBFT**, * Oper*,

`ID`

`Option1`

`Option2`

`Option3`

`Option4`

`Option5`

`Option6`

`Option7`

Compatible Products: – | Pro | Premium | Enterprise | Ent PP | Ent Solver | DYNA

Use material curve fitting to evaluate your experimental data
and correlate it to the program's built-in nonlinear material models.
You apply coefficients to your curve data, determine a fit with existing
model, and write the data according to the table configurations outlined
in the **TB** command. Curve fitting is available for
nonlinear models associated with the material behaviors listed below:

For hyperelastic material behavior, see "TBFT Specifications for Hyperelastic Models".

For creep material behavior, see "TBFT Specifications for Creep Models".

For viscoelastic material behavior, see "TBFT Specifications for Viscoelastic Models".

For Chaboche plasticity material behavior, see "TBFT Specifications for Chaboche Kinematic Hardening Plasticity Models".

**TBFT**, * Oper*,

`ID`

`Option1`

`Option2`

`Option3`

`Option4`

`Option5`

`Option6`

`Option7`

`Oper`

The specific curve-fitting operation:

**FADD --**Define a constitutive model.

**FDEL --**Delete a constitutive model.

**FSET --**Write data related to a constitutive model to the database (same as

**TB**command).**SET --**Initialize coefficients of a constitutive model for nonlinear curve-fitting procedure.

**CDEL --**Deletes coefficients at current reference temperature. Applicable only for temperature dependent coefficients.

**SOLVE --**Solve for coefficients.

**FIX --**Fix (hold constant) the coefficient you specify in

.`Option4`

**EADD --**Add experimental data.

**EDEL --**Delete experimental data.

**LIST --**List all data associated with the material model represented by the material

number.`ID`

`ID`

The material reference number (same as

argument used in the`MAT`

**TB**command). Valid entry is any number greater than zero (default = 1) but less than 100,000.`Option1`

For curve-fit function operations (

= FADD, FDEL, FSET, SET, CDEL, SOLVE or FIX) this field specifies the category (HYPER).`Oper`

For adding or deleting your experiment (

= EADD`Oper`

*or*EDEL), this field specifies the experimental data type.**Valid options:**UNIA, BIAX, SHEA, SSHE,and VOLU (default = UNIA).`Option2`

For curve-fit function operations (

= FADD, FDEL, FSET, SET, CDEL, SOLVE, or FIX), this field specifies constitutive model type. The valid entries are listed in Table 221: Hyperelastic Options below.`Oper`

When you need to specify a file name from which to get experimental data (

= EADD), place that string here. Valid entry is any file name string. You can enter the entire`Oper`

**path\filename.extension**string and leave the next two fields (and`Option3`

) blank, or you can specify the name here, the extension in the next field, and the path following.`Option4`

`Option3`

For

= FADD, FDEL, FSET, CDEL, SET, SOLVE or FIX, some of the cases specified in`Oper`

will require that the polynomial order be specified. The applicable values for the order specification are listed in Table 221: Hyperelastic Options.`Option2`

If a file name for experimental data is being specified in

(`Option2`

= EADD), this field will contain the file extension.`Oper`

`Option4`

When you are working on a specific coefficient (

= FIX), this field specifies the index of that coefficient. Valid entries vary from 1 to`Oper`

, where`n`

is the total number of coefficients (default = 1).`n`

For

= SET, see Table 220: Set Operations, below.`Oper`

If a file name for experimental data is being specified in

(`Option2`

= EADD), this field will contain the directory/path specification.`Oper`

If

= SOLVE, this value specifies the curve-fitting procedure. Valid entries are 0 for unnormalized least squares curve-fitting procedure, and 1 for normalized least squares curve-fitting procedure.`Oper`

`Option5`

When you are working on a specific coefficient (

= FIX), this field specifies the index of that coefficient. Valid entries vary from 1 to N, where N is the total number of coefficients (default = 1)`Oper`

For

= SET, see Table 220: Set Operations, below.`Oper`

**Table 220: Set Operations**Purpose Option4 Option5 Set the value of the coefficient. Index of coefficient Value of that coefficient Set temperature dependency ON/OFF* tdep 1 for ON and 0 for OFF Set reference temperature tref Temperature value * - Temperature data should be supplied in the same units as the TREF command.

If

= SOLVE, use this field to specify the number of iterations to be used in the calculation of the coefficients. Valid entry is any positive integer (default = 1000)`Oper`

`Option6`

If

= SOLVE, specifies the allowed tolerance in residual change to stop an iteration. Valid entry is 0.0 to 1.0 (default = 0.0).`Oper`

`Option7`

If

= SOLVE, specifies the allowed tolerance in coefficient change to stop an iteration. Valid entry is 0 to 1 (default = 0).`Oper`

**Table 221: Hyperelastic Options**

Option1 | Option2 | Option3 |
---|---|---|

HYPER | MOON | 2, 3, 5, 9 |

HYPER | POLY | 1 to N |

HYPER | OGDEN | 1 to N |

HYPER | YEOH | 1 to N |

HYPER | BOYC | NA |

HYPER | GENT | NA |

HYPER | NEO | NA |

HYPER | BLAT | NA |

HYPER | FOAM | 1 to N |

Following table summarizes the format for hyperelastic operations
via the **TBFT** command:

Oper | ID | Option1 | Option2 | Option3 | Option4 | Option5 | Option6 | Option7 |
---|---|---|---|---|---|---|---|---|

FADD | ID | HYPER | Option | Order | ||||

FDEL | ID | HYPER | Option | Order | ||||

FSET | ID | HYPER | Option | Order | ||||

SET | ID | HYPER | Option | Order | Index | Value | ||

SOLVE | ID | HYPER | Option | Order | Norm Flag | Num Iter | RTOL | CTOL |

FIX | ID | HYPER | Option | Order | Index | Fix / Unfix Flag | ||

EADD | ID | Exp Type | File | Extension | Directory | |||

EDEL | ID | Exp Type / Index |

**TBFT**, * Oper*,

`ID`

`Option1`

`Option2`

`Option3`

`Option7`

`Oper`

The specific curve-fitting operation:

**FCASE --**Define a case/constitutive model for viscoelasticity (prony).

**FADD --**Define a constitutive model.

**FDEL --**Delete a constitutive model.

**FSET --**Write data related to a constitutive model to the database (same as

**TB**command).**SET --**Initialize coefficients of a constitutive model for nonlinear curve-fitting procedure.

**CDEL --**Deletes coefficients at current reference temperature. Applicable only for temperature dependent coefficients.

**SOLVE --**Solve for coefficients.

**FIX --**Fix (hold constant) the coefficient you specify in

.`Option4`

**EADD --**Add experimental data.

**EDEL --**Delete experimental data.

**LIST --**List all data associated with the material model represented by the material

number.`ID`

`ID`

The material reference number (same as

argument used in the`MAT`

**TB**command). Valid entry is any number greater than zero (default = 1) but less than 100,000.`Option1`

This option is set to VISCO for adding coefficients (

= FADD). The FADD operation is used to specify the shear order, the bulk order or the shift option.`Oper`

This option (

= CASE) is set to NEW or FINI. The FADD commands are always enclosed by`Oper`

**TBFT**,FCASE, ID, NEW and**TBFT**,FCASE, ID, FINI. See Material Curve Fitting in the*Structural Analysis Guide*for more information.For other curve-fit function operations (

= FDEL, FSET, SET, CDEL, SOLVE or FIX) this field is set to CASE.`Oper`

For adding or deleting your experiment (

= EADD`Oper`

*or*EDEL), this field specifies the experiment type.**Valid options:**SDEC (Shear Modulus vs. Time) or BDEC (Bulk Modulus vs. Time).`Option2`

For defining your viscoelastic case (

= FCASE), you specify PVHE.`Oper`

For curve-fit function operations (

= FDEL, FSET, SET, CDEL, SOLVE, or FIX), this field specifies the case name.`Oper`

To create a new case (

= FADD), the valid options are listed in Table 223: Viscoelastic Options below.`Oper`

When you need to specify a file name from which to get experimental data (

= EADD), place that string here. Valid entry is any file name string. You can enter the entire`Oper`

**path\filename.extension**string and leave the next two fields (and`Option3`

) blank, or you can specify the name here, the extension in the next field, and the path following.`Option4`

`Option3`

For

= FCASE, this field specifies the case name.`Oper`

For

= FADD, this field specifies the order`Oper`

If a file name for experimental data is being specified in

(`Option2`

= EADD), this field will contain the file extension.`Oper`

`Option4`

When you are working on a specific coefficient (

= FIX), this field specifies the index of that coefficient. Valid entries vary from 1 to`Oper`

, where`n`

is the total number of coefficients (default = 1).`n`

For

= SET, see Table 222: Set Operations, below.`Oper`

You can also specify TREF to indicate the reference temperature.

If a file name for experimental data is being specified in

(`Option2`

= EADD), this field will contain the directory/path specification.`Oper`

If

= SOLVE, this value specifies the curve-fitting procedure. Valid entries are 0 for unnormalized least squares curve-fitting procedure, and 1 for normalized least squares curve-fitting procedure.`Oper`

`Option5`

For

= SET, see Table 222: Set Operations, below.`Oper`

**Table 222: Set Operations**Purpose Option4 Option5 Set the value of the coefficient Index of coefficient Value of coefficient Set temperature dependency ON/OFF tdep 1 for ON and 0 for OFF Set reference temperature tref Temperature value Set current component to solve for comp pshea, pbulk, or pvhe If

= SOLVE, use this field to specify the number of iterations to be used in the calculation of the coefficients. Valid entry is any positive integer (default = 1000).`Oper`

If you are specifying a coefficient to be held constant (

= FIX), a 1 FIXES the specified coefficient, and a 0 allows it to vary (turns fixing OFF).`Oper`

`Option6`

If

= SOLVE, specifies the allowed tolerance in residual change to stop an iteration. Valid entry is 0.0 to 1.0 (default = 0.0).`Oper`

`Option7`

If

= SOLVE, specifies the allowed tolerance in coefficient change to stop an iteration. Valid entry is 0 to 1 (default = 0).`Oper`

**Table 223: Viscoelastic Options**

Category | Name | Option |
---|---|---|

VISCO | PSHEAR | 1 to N |

VISCO | PBULK | 1 to N |

VISCO | SHIFT | TN, WLF, NONE |

Following table summarizes the format for viscoelastic operations
via the **TBFT** command:

Oper | ID | Option1 | Option2 | Option3 | Option4 | Option5 | Option6 | Option7 |
---|---|---|---|---|---|---|---|---|

FCASE | ID | NEW | PVHE | Case Name | ||||

FCASE | ID | FINI | ||||||

FADD | ID | VISCO | Option | Order | ||||

FDEL | ID | CASE | Case Name | NA | ||||

FSET | ID | CASE | Case Name | NA | ||||

SET | ID | CASE | Case Name | NA | Index | Value | ||

SOLVE | ID | CASE | Case Name | NA | Norm Flag | Num Iter | RTOL | CTOL |

FIX | ID | CASE | Case Name | NA | Index | Fix / Unfix Flag | ||

EADD | ID | Exp Type | File | Extension | Directory | |||

EDEL | ID | Exp Type / Index |

**TBFT**, * Oper*,

`ID`

`Option1`

`Option2`

`Option3`

`Option7`

`Oper`

The specific curve-fitting operation:

**FCASE --**Define a case/constitutive model for plasticity.

**FADD --**Define a constitutive model.

**FDEL --**Delete a constitutive model.

**FSET --**Write data related to a constitutive model to the database (same as

**TB**command).**SET --**Initialize coefficients of a constitutive model for nonlinear curve-fitting procedure.

**CDEL --**Deletes coefficients at current reference temperature. Applicable only for temperature-dependent coefficients.

**SOLVE --**Solve for coefficients.

**FIX --**Fix (hold constant) the coefficient you specify in

.`Option4`

**EADD --**Add experimental data.

**EDEL --**Delete experimental data.

**LIST --**List all data associated with the material model represented by the material

number.`ID`

`ID`

The material reference number (same as

argument used in the`MAT`

**TB**command). Valid entry is any number greater than zero (default = 1) but less than 100,000.`Option1`

For

= FCASE, set to either NEW or FINI. The command`Oper`

**TBFT**,FCASE,,NEW initializes a new curve-fitting case. (The`ID`

**TBFT**,FADD commands described next are always issued between**TBFT**,FCASE,,NEW and`ID`

**TBFT**,FCASE,,FINI commands.) After issuing`ID`

**TBFT**,FCASE,,FINI, the Chaboche model is created and is ready to be used to perform other curve-fitting operations. For more information, see Material Curve Fitting in the`ID`

*Material Reference*.For

= FADD, set to PLAS to add options/parameters for the new case being created (via`Oper`

**TBFT**,FCASE,,NEW, which must be issued`ID`

*before*the**TBFT**,FADD command). This operation specifies the order of the Chaboche kinematic model.For other curve-fitting function operations (

= FDEL, FSET, SET, CDEL, SOLVE or FIX), set to CASE.`Oper`

For adding or deleting your experiment (

= EADD`Oper`

*or*EDEL), this option specifies the experiment type. The only valid option is UNIA (plastic strain vs. true stress).`Option2`

For

= FCASE (defining your Chaboche case), set to CPLA.`Oper`

For

= FDEL, FSET, SET, CDEL, SOLVE, or FIX (curve-fitting function operations), this value specifies the case name being operated on.`Oper`

For

= FADD (specifying options for the plasticity model), valid options are:`Oper`

CHAB -- Chaboche kinematic hardening (required for any defined curve-fitting case) BISO -- Bilinear isotropic hardening (optional) MISO -- Multilinear isotropic hardening (optional) VOCE -- Nonlinear isotropic hardening, Voce model (optional) The **TBFT**,FADD command can be issued twice, once to specify the order of the Chaboche model, and again to specify the isotropic hardening option. (Only*one*of the options BISO, MISO or VOCE can be used in a single curve-fitting case, and none of those options are required.)For

= EADD (specifying a file name from which to get experimental data), place that string here. A valid entry is any file name string. You can either:`Oper`

Enter the entire

**path\filename.extension**string and leave the next two fields (and`Option3`

) blank,`Option4`

*or*Specify the name here, the extension in the next field, and the path in the following field.

`Option3`

For

= FCASE, this field specifies the case name.`Oper`

For

= FADD, this field specifies either:`Oper`

The order of the Chaboche kinematic hardening model (

= CHAB),`Option2`

*or*The number of terms in the MISO model (

= MISO).`Option2`

If a file name for experimental data is being specified in

(`Option2`

= EADD), this field contains the file extension.`Oper`

`Option4`

When fixing a specific coefficient to a desired value (

= FIX), this field specifies the index of that coefficient. Valid entries vary from 1 to`Oper`

, where`n`

is the total number of coefficients (default = 1).`n`

For

= SET, see Table 222: Set Operations.`Oper`

You can also specify TREF to indicate the reference temperature, or COMP for a partial/complete solution (only for bulk, only for shear, or all coefficients).

If a file name for experimental data is being specified in

(`Option2`

= EADD), this field contains the directory/path specification.`Oper`

If

= SOLVE, this value specifies the normalized/non-normalized option. This option is not available for Chaboche curve fitting.`Oper`

`Option5`

For

= SET, refer to the following table.`Oper`

**Table 224: Set Operations**Purpose Option4 Option5 Set the value of the coefficient Index of coefficient Value of coefficient Set temperature dependency ON/OFF tdep 1 for ON and 0 for OFF Set reference temperature tref Temperature value If

= SOLVE, use this field to specify the number of iterations to be used in the calculation of the coefficients. Valid entry is any positive integer (default = 1000).`Oper`

If you are specifying a coefficient to be held constant (

= FIX): 1 fixes the specified coefficient, 0 allows it to vary (disables fixing).`Oper`

`Option6`

If

= SOLVE, specifies the allowed tolerance in residual change to stop an iteration. Valid entry is 0.0 to 1.0 (default = 0.0).`Oper`

`Option7`

If

= SOLVE, specifies the allowed tolerance in coefficient change to stop an iteration. Valid entry is 0 to 1 (default = 0).`Oper`

The following table summarizes the format for Chaboche curve-fitting
operations via the **TBFT** command:

Following table summarizes the format for viscoelastic operations
via the **TBFT** command:

Oper | ID | Option1 | Option2 | Option3 | Option4 | Option5 | Option6 | Option7 |
---|---|---|---|---|---|---|---|---|

FCASE | ID | NEW | CPLA | Case Name | ||||

FCASE | ID | FINI | ||||||

FADD | ID | PLAS | Option | Order | ||||

FDEL | ID | CASE | Case Name | NA | ||||

FSET | ID | CASE | Case Name | NA | ||||

SET | ID | CASE | Case Name | NA | Index | Value | ||

SOLVE | ID | CASE | Case Name | NA | Not used | Num Iter | RTOL | CTOL |

FIX | ID | CASE | Case Name | NA | Index | Fix / Unfix Flag | ||

EADD | ID | Exp Type | File | Extension | Directory | |||

EDEL | ID | Exp Type / Index |

**TBFT**, * Oper*,

`ID`

`Option1`

`Option2`

`Option3`

`Option7`

`Oper`

The specific curve-fitting operation:

**FADD --**Define a constitutive model.

**FDEL --**Delete a constitutive model.

**FSET --**Write data related to a constitutive model to the database (same as

**TB**command).**SET --**Initialize coefficients of a constitutive model for nonlinear curve-fitting procedure.

**CDEL --**Deletes coefficients at current reference temperature. Applicable only for temperature dependent coefficients.

**SOLVE --**Solve for coefficients.

**FIX --**Fix (hold constant) the coefficient you specify in

.`Option4`

**EADD --**Add experimental data.

**EDEL --**Delete experimental data.

**LIST --**List all data associated with the material model represented by the material

number.`ID`

`ID`

argument used in the`MAT`

**TB**command). Valid entry is any number greater than zero (default = 1) but less than 100,000.`Option1`

For curve-fit function operations (

= FADD, FDEL, FSET, SET, CDEL, SOLVE or FIX) this field specifies the category (CREEP).`Oper`

For adding or deleting your experiment (

= EADD`Oper`

*or*EDEL), this field specifies the experimental data type (CREEP).`Option2`

For curve-fit function operations (

= FADD, FDEL, FSET, SET, CDEL, SOLVE, or FIX), this field specifies constitutive model type. The valid entries are listed in Table 226: Creep Options below.`Oper`

When you need to specify a file name from which to get experimental data (

= EADD), place that string here. Valid entry is any file name string. You can enter the entire`Oper`

**path\filename.extension**string and leave the next two fields (and`Option3`

) blank, or you can specify the name here, the extension in the next field, and the path following.`Option4`

`Option3`

If a file name for experimental data is being specified in

(`Option2`

= EADD), this field will contain the file extension.`Oper`

`Option4`

When you are working on a specific coefficient (

= FIX), this field , specifies the index of that coefficient. Valid entries vary from 1 to`Oper`

, where`n`

is the total number of coefficients (default = 1).`n`

For

= SET, see Table 225: Set Operations, below.`Oper`

If a file name for experimental data is being specified in

(`Option2`

= EADD), this field will contain the directory/path specification.`Oper`

If

= SOLVE, this value specifies the curve-fitting procedure. Valid entries are 0 for unnormalized least squares curve-fitting procedure, and 1 for normalized least squares curve-fitting procedure.`Oper`

`Option5`

If

= SOLVE, use this field to specify the number of iterations to be used in the calculation of the coefficients. Valid entry is any positive integer (default = 1000)`Oper`

If you specify a coefficient to be held constant (

= FIX), enter a 1 to FIX the coefficient, and a 0 to allow it to vary (turn fixing OFF).`Oper`

For

= SET, see Table 225: Set Operations, below.`Oper`

**Table 225: Set Operations**Purpose Option4 Option5 Set the value of the coefficient Index of coefficient Value of coefficient Set temperature dependency ON/OFF* tdep 1 for ON and 0 for OFF Set reference temperature tref Temperature value * - When tdep is OFF, the Arrhenius term (e.g. C4) in the strain hardening creep equation is calculated. Because TBTEMP is not included in the curve-fitting regimen, the experimental data (in absolute temperature) must be supplied using the /TEMP command.

* - When tdep is set ON, the Arrhenius term is set to 0 and the constants are separately computed for each temperature. The curve-fitting regimen uses

**TBTEMP**. You must provide the experimental data using the same units as the**TREF**command.`Option6`

= SOLVE, specifies the allowed tolerance in residual change to stop an iteration. Valid entry is 0.0 to 1.0 (default = 0.0).`Oper`

`Option7`

= SOLVE, specifies the allowed tolerance in coefficient change to stop an iteration. Valid entry is 0 to 1 (default = 0).`Oper`

**Table 226: Creep Options**

Category | Name | Option |
---|---|---|

CREEP | SHAR | NA |

CREEP | THAR | NA |

CREEP | GEXP | NA |

CREEP | GGRA | NA |

CREEP | GBLA | NA |

CREEP | MTHA | NA |

CREEP | MSHA | NA |

CREEP | GGAR | NA |

CREEP | EXPO | NA |

CREEP | NORT | NA |

CREEP | PSTH | NA |

CREEP | PSRP | NA |

CREEP | GTHA | NA |

Following table summarizes the format for creep operations via
the **TBFT** command:

Oper | ID | Option1 | Option2 | Option3 | Option4 | Option5 | Option6 | Option7 |
---|---|---|---|---|---|---|---|---|

FADD | ID | CREEP | Option | NA | ||||

FDEL | ID | CREEP | Option | NA | ||||

FSET | ID | CREEP | Option | NA | ||||

SET | ID | CREEP | Option | NA | Index | Value | ||

SOLVE | ID | CREEP | Option | NA | Norm Flag | Num Iter | RTOL | CTOL |

FIX | ID | CREEP | Option | NA | Index | Fix / Unfix Flag | ||

EADD | ID | Exp Type | File | Extension | Directory | |||

EDEL | ID | Exp Type / Index |

The **TBFT** command provides tools for comparing
experimental material data to the program-provided calculated data
for various nonlinear material options. Based on curve-fitting comparisons
and error norms, choose the model to use during the solution phase
of the analysis according to the best fit. All of the capabilities
of the **TBFT** command are accessible interactively
via the standard material GUI. See Material Curve Fitting in the *Structural Analysis Guide* for more information.

Display material model data associated with both the **TB** command and the **TBFT**,FSET command
via **TBLIST**,ALL,ALL.

Material model data associated with the *most recent * **TB** or **TBFT**,FSET command overwrites previous data.

Display material model data associated with both the **TB** command and the **TBFT**,FSET command
via **TBLIST**,ALL,ALL.

The capability to fix coefficients (* Option4* = FIX) applies only to nonlinear curve fits (as listed in Table 7.3: Hyperelastic Curve-Fitting Model Types.

The uniaxial, biaxial, and shear experimental data use *engineering* stress. The volumetric data uses *true* stress. See the *Material Reference* for details
about experimental data for creep and viscoelasticity.