Define a User Material

Define the material response of the IM7_8552 composite in the bulk data file.

The MATUSR and MATUDS entries are used collectively to define a user material in a bulk data file.

Open the bulk data file and locate the GENUDS entry.
Enter the following lines below the GENUDS entry:
```
MATUSR, 9013, 1, 23
MATUDS, 9013, MATUSR, hpfa, UMAT
, REAL, 3, 1, 0, 0, 0, 0, 0,
,     , 0, 0, 0, 0, 0.1, 0.01
```
Note: The material identification number (9013) for the IM7_8552 material may vary from computer to computer. Please refer to the HPFAMatDB.xml file located in your materials directory to determine the appropriate material identification number to use.

The MATUSR entry above informs MSC Nastran that the stresses and strains from material 9013 are given in terms of the user-defined coordinate system. It also specifies that the deformation gradient, rotation, and stretch ratios should be passed to the material subroutine.

The MATUDS entry identifies the user material subroutine and determines the precise form of the multiscale constitutive relations to be used for material 9013.

User Material Constants

The user material constants (UMCs) immediately follow the REAL field in the MATUDS entry. Of particular importance to this tutorial are UMCs 1-3, and 8. For a detailed description of each UMC, refer to Appendix A of the User's Guide.

UMC#1 - The first constant specifies the use of the lb/in/R units system. Since our part has dimensions of inches and our material was defined in terms of pounds and inches, we set UMC#1 = 3.
UMC#2 - The second constant identifies 1 as the fiber direction.
UMC#3 - The third constant turns the progressive failure feature of Helius PFA on or off. Set UMC#3 = 0 to run the analysis without using progressive failure. With progressive failure deactivated, the stiffness of the elements remains unchanged throughout the analysis. In contrast, when Instantaneous or Energy-Based damage evolution routines are used, the stiffnesses of the elements are reduced after failure has been predicted by the failure criterion.
UMC#8 - The eighth constant specifies the failure criterion to use for the analysis. Set UMC#8 = 0 (default) to use the MCT criterion.