Brittle material in FEA analysis

[MechJr]

Hello,
I have read many posting regarding analyzing parts made of brittle material. I would like to get some extra help, if possible
What are the best engineering practices when analyzing a part made of brittle material? Instinctively, I would compare my max principal stress to my ultimate tensile stress (also known as the maximum stress criterion).
I could also use the Mohr Theory of Failure which takes into account the uniaxial tensile strength and uniaxial compression strength. The Mohr Theory is more conservative. The thing is these apply to plane stress. Since it will be a 3d model, should I use the Mohr–Coulomb failure criterion in three dimensions? If not, what do you recommend? And when would someone use the 3d Mohr-Coulomb failure criterion?

Thank you

PS: by brittle, I mean cast iron. I know glass or ciment gets more complicated.
It will be a static solution. No dynamic loads or anything that can produce fatigue

 

[flash3780]

I would go with a maximum principal stress failure criteria for cast iron. Mohr-Coulomb failure criterion is more for concrete and soil modeling.

http://www.roymech.co.uk/Useful_Tables/Mechanics/stress.html

http://en.wikipedia.org/wiki/Mohr–Coulomb_theory