Hi, I am trying to simulate the  observed spiral fractures in hardened metal shafts in one of our applications. I am using the Plastic, Damage Initiation and  Damage Evolution approach with the measured and estimated parameters.  I cannot see spiral like fractures that should correspond to the brittle material I have, instead I am just getting ductile like flat fractures. this is a picture of the simplistic model I am  using to test my material models.

Any suggestion......