This section describes how to set up a material law using an UMAT.

First, you have to open the Material Database and create a new material, according to the steps described under Setting up the internal material laws.

Under the General tab, check Mechanical Properties for the newly created material.

Under the newly appearing Mechanical tab, inside the Mechanical Properties Selection panel, enter Damage in the Add Material Law box, and click Add.

The parameters needed to define the mechanical properties of the new material appear under the panel grouped under the Law tab.

From the Type pull-down menu, select UMAT.

After selecting UMAT, a different panel opens below the Type pull-down menu, with the UMAT Parameters, Material Parameters, and State Variables tabs.

Under the UMAT Parameters tab, click Browse to find the UMATs for GeoDict 2026 in your user folder. Select the file IsotropicLinearElasticityDamage.f UMAT and click Open.

Alternatively, enter a path to the UMAT file relative to the user folder. For this example, this path would be UMAT/IsotropicLinearElasticityDamage.f. Relative paths have the advantage that they work independently from your username. Therefore, material database entries can be shared easily between different PCs, as long as the UMAT file is present in the UMAT folder.

For the material law (defined in the UMAT) to be applied to the Material_New, some material parameters must be entered under the Material Parameters tab.

These material parameters, that the particular UMAT requires, can be found by opening the UMAT source file, if available (*.f or *.f90). To do so, simply click Edit under the UMAT Parameters tab and open it with a text editor (for example, with NotePad++).

In the opened file, the text shows that applying the IsotropicLinearElasticityDamage.f UMAT to Material_New requires assigning the following material parameters or properties (PROPS):

• Young’s Modulus (E)
• Poisson’s Ratio (NU)
• Damage Hardening Modulus (DAMHARD)
• Initial Threshold for the equivalent strain (DAMAGE0).

Therefore, in the table under the Material Parameters tab, manually enter the needed parameters (Material Parameters), their values for Material_New (Value), and a brief parameter explanation (Description). For example, as follows:

The damage model defined in the IsotropicLinearElasticityDamage.f UMAT depends on the equivalent strain, which is calculated as

The degradation begins as soon as the minimal equivalent strain for damage is reached:

with : minimal equivalent strain for damage, : damage hardening modulus.

Next, go to the State Variables tab. State variables are internal variables of the UMAT, they store information which is used in the next iteration. When the State Variables are not properly defined, the UMAT does not work as intended, or it doesn’t work at all.

For the UMAT IsotropicLinearElasticityDamage.f, there is only one state variable which stores the damage value. It must be defined and initialized with 0, since there is no initial damage in the material. The number of state variables depends on the particular UMAT and is not always obvious. If you need more information about UMATs delivered with GeoDict, ask the Math2Market support team for help.

Finally, click Save Database at the bottom right of the Edit Material Data-Base dialog.

After saving, the newly defined material Material_New can be chosen as constituent material when using ElastoDict.

Make sure that the Damage material model is selected under Mechanical Properties tab.

Now, the material law assigned to Material_New is applied in the ElastoDict calculations.