About Material Assignment
Click > 
Material Assignment to open the Material Assignment dialog box. Use this dialog box to assign material to 2D and 3D models. For 3D models, you can assign material to the part and any volume in part mode, and to components and volumes in assembly mode. For 2D plain strain and axisymmetric models, you can assign material to surfaces. For 2D plain stress models, the Material Assignment command is not available. Instead you can assign materials to shell idealizations by using the Shell Definition dialog box.
Material Assignment to open the Material Assignment dialog box. Use this dialog box to assign material to 2D and 3D models. For 3D models, you can assign material to the part and any volume in part mode, and to components and volumes in assembly mode. For 2D plain strain and axisymmetric models, you can assign material to surfaces. For 2D plain stress models, the Material Assignment command is not available. Instead you can assign materials to shell idealizations by using the Shell Definition dialog box.In the part mode, you can assign material properties to the part and the volume regions of the part. If your model is an assembly, you can define material assignment for any component and volume region in the assembly.
To learn more about material assignment, see Guidelines for Material Assignment.
After you assign a material to your model, you can edit or delete it by right-clicking on Material Assignment—in the Model Tree and using the Edit Definition or Delete command, as appropriate. If you are deleting an existing material assignment, Creo Simulate asks for confirmation before deleting it.