Can I change the material properties of a zone
during an analysis?
It is possible to change the material properties in a Child analysis. You should therefore make a child analysis and, using stop / restart, start it from the increment block in the parent where you want the material properties to change.
Parent / Child and Stop restart are both advanced options in the program and should be fully understood before use.
What value of phi do I chose for metals obeying
Metals have zero value for angle of internal friction. It is best to use a von-Mises material model for which you only need the following in the material properties box:
Cohesion (=Yield stress/2)
The remaining fields are irrelavent and may be left blank.
Suitable values for the above may be obtained from engineering data or furmulae books (eg An Engineering Data Book by Munday and Farrar, University of Southampton)
For the Cohesion field, choose a suitable value for the metal's yield stress and devide by two to obtain the equivalent cohesion.
The procedure above is also applicable to Tresca Yield criterion.