Chapter 7: Material Curve-Fitting

Material curve-fitting (TBFT) enables you to derive coefficients from experimental data that you provide for your material. Curve-fitting involves comparing your experimental data to existing nonlinear material models. Mechanical APDL compares your experimental data to program-calculated data for various nonlinear models; based on the comparisons, you can then determine the best material model and parameters to use in a finite element simulation.

Curve-fitting is based on the material model parameters imported from the material data table definitions (TB and TBDATA / TBPT).

The curve-fitting process begins by defining an initial set of parameters (TBDATA / TBPT). You can also set initial parameters automatically (TBFT,AINI) for supported material models. Data manipulation and parameter-fitting occur on these imported models and parameters (TBFT).

Material curve-fitting uses the Ansys Materials Lab (AML), a material modeling component used by Mechanical APDL encompassing material calculations such as stress, material state, and material tangent. The elements use these quantities to assemble the finite element analysis matrices. Standard experiments such as the uniaxial state or the biaxial state are available; the program implements the experiments by enforcing the necessary conditions that define them. Parameter-fitting via AML is available for many material models and combinations of models.

Curve-fitting involves this general process:

Step 1. Prepare the Experimental Data

Step 2. Input the Experimental Data

Step 3. Select a Material Model

Step 4. Initialize the Coefficients

Step 5. Specify Solution-Control Parameters and Solve

Step 6. Plot Your Experimental Data and Analyze

Step 7. Write the Curve-Fitting Data to the Database

Also see Example Curve-Fitting Problems.

Limitation:

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