TBFT

TBFT, Oper, MATID, Option1, Option2, Option3, Option4, Option5, Option6, Option7, –, –, Option10
Performs material curve-fitting operations.

PREP7: Materials

Use material curve-fitting to evaluate your experimental data and correlate it to the program's built-in nonlinear material models.

Curve-fitting occurs by applying coefficients to your curve data, determining a fit with an existing model, and writing the data according to the material data table configurations described in the TB command. Based on curve-fitting comparisons and error norms, you then select the model to use during the solution phase of the analysis according to the best fit.

Supported Material Models for Curve-Fitting

For more information, see Material Curve-Fitting in the Material Reference and the "Notes" section below.

TBFT Specifications

TBFT, Oper, MATID, Option1, Option2, Option3, Option4, Option5, Option6, Option7

Oper

The operation to perform:

Operation Set 1 (Curve-Fitting): - - - - - - - - - - - - - - - - - - - -
FADD --: Define a constitutive model for parameter-fitting and import all parameters (defined previously via TB and TBDATA).
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.
AINI --: Initialize coefficients automatically based on elastic properties and experimental data.
SOLVE --: Solve for coefficients.
FIX --: Fix (hold constant) the coefficient you specify in Option4.
Operation Set 2 (Experimental Data): - - - - - - - - - - - - - - - - - - - -
EADD --: Add experimental data.
EDEL --: Delete experimental data.
Other Operations: - - - - - - - - - - - - - - - - - - - -
LIST --: List all data associated with the material model represented by the material ID number (MATID)
PSCA: Activate parameter-scaling to improve optimization performance. Valid for the UserMat curve-fitting method only (TB,USER,,,,MXUP and TB,USER,,,,NONLINEAR [default]).

MATID

Material reference ID number (the same value as specified via MATID on the TB command). Valid value is any number n, where 0 < n < 100,000. Default = 1.

Option1

For curve-fitting function operations (Oper = FADD, FDEL, FSET, SET, CDEL, SOLVE or FIX) this value specifies the category (AML).

For adding or deleting your experiment (Oper = EADD or EDEL), this value specifies the experimental data type. Valid options: See Experimental Data Types in the Material Reference.

Option2

For curve-fitting function operations (Oper = FADD, FDEL, FSET, SET, CDEL, SOLVE, or FIX), set this value to GENR.

When you need to specify a file name from which to get experimental data (Oper = EADD), place that string here. Valid value is any file name string. You can enter the entire path\filename.extension string and leave the next two values (Option3 and Option4) blank, or you can specify the name here, the extension in the next value, and the path following.

Option3

For Oper = FADD, FDEL, FSET, CDEL, SET, SOLVE or FIX, set this value to a user-defined name (to be used consistently in the curve-fitting process).

If a file name for experimental data is being specified in Option2 (Oper = EADD), this value will contain the file extension.

Option4

When you are working on a specific coefficient (Oper = FIX), this value specifies the index of that coefficient. Valid values vary from 1 to n, where n is the total number of coefficients. Default = 1.

If Oper = SET, refer to this table:

Table 229: SET Operations

Purpose	Option4	Option5
Set the value of the coefficient	Index of a coefficient	Value of that coefficient
Set temperature dependency ON^[a]^[b]/OFF^[c]	TDEP	1 -- ON 0 -- OFF
Set reference temperature	TREF	Temperature value
Set optimization algorithm	ALGO	DEFA or GA
Set initial population size for generic algorithm	IPOP	Integer

^[a]Specify temperature data in the same units specified via TREF.

^[b]When TDEP is OFF, the Arrhenius term in the strain-hardening creep equation is calculated. Because TBTEMP is not included in the curve-fitting, the experimental data (in absolute temperature) must be provided via /TEMP.

^[c]When TDEP is ON, the Arrhenius term coefficient is set to 0 and the constants are calculated separately for each temperature. The curve-fitting process uses TBTEMP. You must provide the experimental data using the same units as specified via TREF.

If a file name for experimental data is specified in Option2 (Oper = EADD), this value specifies the directory/path specification.

If Oper = SOLVE, this value specifies the curve-fitting procedure. Valid values are 0 for non-normalized least squares curve-fitting procedure, and 1 for normalized least squares curve-fitting procedure.

Option5

When you are working on a specific coefficient (Oper = FIX), this value specifies the value of that coefficient as shown in Table 229: SET Operations.

If Oper = PSCA, use this value to specify the scaling option to be used in the parameter-fitting process. Options are LINE (default ), EXPO (exponential ), SQRD (squared) or LOG (logarithmic). Use with the UserMat curve-fitting method.

If Oper = SOLVE, use this value to specify the number of iterations to be used in the calculation of the coefficients. Valid value is any positive integer. Default = 1000.

Option6

If Oper = SOLVE, specifies the allowed tolerance in residual change to stop an iteration. Valid value is 0.0 to 1.0. Default = 0.0.

Option7

If Oper = SOLVE, specifies the allowed tolerance in coefficient change to stop an iteration. Valid value is 0 to 1. Default = 0.

Table 230: TBFT Command Summary

*`Oper`*	*`MATID`*	*`Option1`*	*`Option2`*	*`Option3`*	*`Option4`*	*`Option5`*	*`Option6`*	*`Option7`*
FADD	`MATID`	AML	GENR	`UserDefName`	-	-	-	-
FDEL	`MATID`	AML	GENR	`UserDefName`	-	-	-	-
FSET	`MATID`	AML	GENR	`UserDefName`	-	-	-	-
SET	`MATID`	AML	GENR	`UserDefName`	`Index`	`Value`	-	-
CDEL	`MATID`	`ExpType / Index`	-	`UserDefName`	-	-	-	-
AINI	`MATID`	AML	GENR	`UserDefName`	-	-	-	-
SOLVE	`MATID`	AML	GENR	`UserDefName`	`NormFlag`	`NumIter`	RTOL	CTOL
FIX	`MATID`	AML	GENR	`UserDefName`	`Index`	-	-	-
EADD	`MATID`	`ExpTyp`	`File`	`UserDefName`	`Directory`	-	-	-
EDEL	`MATID`	`ExpType / Index`	-	`UserDefName`	-	-	-	-

Notes

TBFT provides tools for comparing your experimental material data to program-provided calculated data for various nonlinear material options.

Your experimental parameters (defined prior to issuing TBFT) are imported directly from TB and TBDATA.

All TBFT command capabilities are accessible interactively via the standard material GUI.

To display material model data associated with the TB and the TBFT,FSET commands, issue TBLIST,ALL,ALL.

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

TBFT,AINI calls a Python script that predicts initial coefficient values for some material models. To ensure that the necessary Python libraries are installed, Mechanical APDL installation includes a Python version that has been tested and known to work with this feature. Therefore, you cannot use the feature with any other installed version of Python. Delete the PYTHONHOME environment variable if it exists.

TBFT does not support saving to, and resuming from, the database file (SAVE and RESUME, respectively). You must therefore rerun the curve-fitting analysis and then replot (TBFPLOT).

Menu Paths

Main Menu> Preprocessor> Material Props> Material Models