The following figure shows how the list would look if an elastic-plastic
  material complete with stress-based failure limits were defined:
  

Using the selected behavior list, you can add, delete, or change materials
  as follows:
 - Adding material
behaviors
 
 - 
Select the behaviors needed to define your material from the menus just
  below the selected behavior list. When you select a behavior, its name appears
  in the list, and the parameters and data associated with the behavior appear in
  the data area in the bottom portion of the editor window. Suboptions appear
  beneath the corresponding primary behavior and are indented to indicate their
  subordinate position.
  
  - Deleting
material behaviors
 
 - 
Within the selected behavior list, click the behavior or suboption you want
  to delete; then click the 
  
 icon located near the lower right corner of the behavior list. This
  procedure removes the behavior from both the behaviors list and the material
  definition. If you delete a behavior that has suboptions shown beneath it in
  the list, the suboptions are also deleted.
  
  - Changing
material parameters or data
 
 - 
Within the selected behavior list, click the behavior whose data you want to
  change. When the parameters and data associated with the behavior appear in the
  data area in the bottom portion of the window, make the desired changes.