Create Material with Plastic Behavior

Elastic vs Plastic Behavior

Elastic behavior, or elastic strain, is the response of a material to loading and unloading such that the material returns to its original shape after the applied load is removed.

Plastic behavior, or plastic strain, begins when the material is stressed beyond its yield point, causing permanent deformation.

The yield point is the stress at which the material's strain transitions from elastic to plastic behavior. It is critical for simulations that simulate permanent deformation, such as in automotive crash tests, to properly account for the plastic strain.

Step 1: Input Raw Material Data

Prerequisite to import material data:

Launch AMM and select Elastoplastic.
Configure the file path for material data using Basic Settings.
Import raw material data, such as stress-strain curves, either from a local file system or AMDC database. Upload multiple material models data to define the material's plastic behavior.
Note: Ensure the raw material data includes both the elastic and plastic regions.
Specify the start position of the measurement data from the data file. Enter the initial column and row numbers as shown and then click OK.
Figure 1. Start Position of the Data

Step 2: Define Young's Modulus

To normalize the abscissa (x-axis) in a raw data file, select the file, set a scale value for the xvalues, and then hit Scale to multiply the axis values by that factor. For example, if the X values of the raw data are in percent [%], set the X value to 0.01 and then press Scale.

There are two ways to define Young’s modulus:

With YM Eval, the Modeler automatically starts fitting the elastic part and a new graph appears showing the Young’s modulus. The adapted value is displayed in the field below the Young’s Modulus (modulus of elasticity).
Figure 2. Define Young's Modulus Automatically
Move the slider to manually adjust the Young’s Modulus, after the initial identification. This is required for all imported files/curves.
Figure 3. Define Young's Modulus Manually
Select All Curves to set this value for all imported files/curves.
Smooth noisy or oscillating data using the Smooth button. For repetitive curves, one can use the Add Mean button to derive a mean curve and select the curves for averaging.

Step 3: Select Necking Point

It is necessary to define the necking point manually as it is useful for plastics and high-strength steel.

Select Necking Point and define this point for each selected curve.
Figure 4. Select Necking Point Manually
To complete the preprocessing of the data, click Workup > Select All from the list box. The curves are recalculated to True-Stress vs. True-Plastic-Strain.

Step 4: Select Curve Fitting

Each prepared curve is displayed in the Curve Fitting list.

Select the required functions of curve fitting. For example, one might pick Voce, Swift, Sherby, and Ghosh.
Figure 5. Curve Fitting and Extrapolation
Select further points to extrapolate to 100% (or beyond) from the list box. The extrapolation for each curve function with value is displayed in Extrapolation.
Select each extrapolation function in the Extrapolation box and verify the curve fitting
Use the Ratio slider to verify the curve fitting changes.
Click Combine and Save to save the combination of fitting functions. Now we have a CAE ready True Strain and Stress Curve.

Part 5: Create CAE Material Card

Select a material law for the CAE Card.
Figure 6. Create Material Card
Specify Solver and its metadata values.
Enter a Material ID number.
Enter a Material Name.
Click Create Card to create a simulation ready CAE Material File.
The material card is created and exported to solver-specific folder.

Step 6: Review the Exported CAE Card

Open the exported solver specific CAE Card using any code viewer.
Figure 7. Review CAE Card
Review the meta data of the CAE Card.
Import the exported CAE card in a Simulation software to test for plastic deformation and structural behavior.